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Accepted: 7 October 2010 / Published online: 28 October 2010 ... Division of Pharmaceutical Chemistry, Faculty of Pharmacy,. University of Helsinki, P.O. ..... SIMS is usually divided into two classes depending ... surface material than laser desorption-ionization tech- ..... movable stage in aid of proper sample positioning.
Histochem Cell Biol (2010) 134:423–443 DOI 10.1007/s00418-010-0753-3

REVIEW

Molecular mass spectrometry imaging in biomedical and life science research Jaroslav Po´l • Martin Strohalm • Vladimı´r Havlı´cˇek Michael Volny´



Accepted: 7 October 2010 / Published online: 28 October 2010 Ó Springer-Verlag 2010

Abstract This review describes the current state of mass spectrometry imaging (MSI) in life sciences. A brief overview of mass spectrometry principles is presented followed by a thorough introduction to the MSI workflows, principles and areas of application. Three major desorptionionization techniques used in MSI, namely, secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption ionization (MALDI), and desorption electrospray ionization (DESI) are described, and biomedical and life science imaging applications of each ionization technique are reviewed. A separate section is devoted to data handling and current challenges and future perspectives are briefly discussed at the end. Keywords Mass spectrometry  Chemical imaging  Molecular imaging  Biological surfaces  DESI  MALDI  SIMS

J. Po´l and M. Strohalm contributed equally. J. Po´l  M. Strohalm  V. Havlı´cˇek  M. Volny´ (&) Laboratory of Molecular Structure Characterization, Institute of Microbiology of the Academy of the ASCR, v.v.i., Vı´denˇska´ 1083, 142 20 Prague, Czech Republic e-mail: [email protected] V. Havlı´cˇek e-mail: [email protected] J. Po´l Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, P.O. Box 56, FI-00014 Helsinki, Finland V. Havlı´cˇek Department of Analytical Chemistry, Faculty of Science, Palacky´ University, Trˇ. Svobody 8, 771 46 Olomouc, Czech Republic

Introduction Mass spectrometry imaging (MSI) is a technique for visualization of molecules on surfaces. Originally it was referred to as imaging mass spectrometry but the abbreviation IMS is easily mistaken for ion mobility spectrometry (IMS). Given that mass spectrometry imaging and ion mobility spectrometry are now being combined, some of the new reviews (Chughtai and Heeren 2010; Svatos 2010) prefer to avoid the confusion and use the term, mass spectrometry imaging, instead. This has been also adopted in this text. The very basis of the technique is a surface desorptionionization phenomenon. Any molecular species that can be desorbed from a surface and converted into a gas-phase ion can be theoretically analyzed and visualized by MSI. The technique has its origin mostly in inorganic surface analysis and in material science, where it is sometimes called surface mass spectrometry. A swift development during the past 15 years brought it to biomedical and life sciences where it is used for analysis of biological surfaces, mainly different histological sections. This review briefly summarizes principles of mass spectrometry, covers three main techniques used in MSI and describes recent developments in MSI applications and data handling. An interested reader can find more information in other reviews of MSI that have been recently published (Amstalden van Hove et al. 2010; Chughtai and Heeren 2010; Heeren et al. 2009; MacAleese et al. 2009; McDonnell and Heeren 2007; Setou 2010; Setou et al. 2007; Stoeckli et al. 2001; Svatos 2010; Walch et al. 2008).

Mass spectrometry Mass spectrometry (MS), one of the major analytical techniques of our time, has as its basis the measurement of

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Fig. 1 Schematic description of basic ionization techniques. a Spray ionization (SI). b Desorption ionization (DI). c Chemical ionization (CI). d Electron ionization (EI). In EI the impacting particle is either electron (electron impact) or photon (photoionization). All direct surface imaging techniques in mass spectrometry are based on desorption ionization (b). Details in Cooks 2010

mass-to-charge ratios (m/z) of ions (De Hoffmann et al. 2007; Gross 2004). Any atomic or molecular species that can be ionized and transported into a gas phase can be, in principle, analyzed by mass spectrometry, which makes it a universal analytical method. Its implementation requires suitable methods of ion generation (ionization), ion analysis (mass separation) and ion detection. There are always

multiple ways how to achieve the three basic steps of any mass spectrometry experiment. We will briefly consider each of them and describe the necessary basic concepts. The first step is to convert molecules into gas-phase ions. From the physical-chemistry point of view there are four basic groups of ionization techniques for molecular species: (a) electron ionization (EI), (b) spray ionization (SI), (c) desorption ionization (DI) and (d) chemical ionization (CI) (Cooks 2010). The principles of all four ionization approaches are schematically described in Fig. 1 and their characteristics are summarized in Table 1. In the current biological mass spectrometry the most important ionization techniques are electrospray ionization [ESI, belongs to the group (b)] and matrix-assisted laser desorption ionization [MALDI, belongs to the group (c)]. Both of them are able to ionize polar compounds and large macromolecules, which makes them suitable for solving life science problems. For mass spectrometry to be usable as imaging technique the ionization must be done from a solid surface. Thus, the DI techniques category is the one of interest for mass spectrometry imaging (MSI) applications. Technically, any surface DI technique could be used for 2D imaging because scanning the surface in x and y directions is a mechanical engineering problem that can be solved relatively easily. However, due to several practical considerations (sufficient spatial resolution, sensitivity, integration into the instrument interface) mass spectrometry

Table 1 Overview of the ionization techniques used in molecular mass spectrometry (adapted from Cooks 2010) Method

Abbreviation Examples

Analyte state

Characteristics of the ion

Other decription

Electron ionization

EI

Gas phase (vapor state)

Odd electron ions (ion radicals)

Highly reproducible

Chemical ionization

Spray ionization

CI

SI

Electron impact

Hard ionization (fragmentation in the ion source due to high internal energy)

Chemical ionization, Gas phase APCI (vapor state)

Even electron ions (ion adducts)

Thermospray, electrospray, nanospray

Even electrons (ion adducts)

Liquid (solution)

SIMS, MALDI, LDI, DESI

Odd electron ions can be generated electrochemically Solid (surface)

Good control of internal energy Useful for non-polar molecules

Soft ionization

Soft ionization Desorption ionization DI

Useful for small organic molecules often in connection with gas chromatography

Even electron ions (ion adducts) Rarely odd electron ion radicals Soft ionization

The softest ionization available Multiply charged ions Often used in connection with liquid chromatography ESI capable of ionizing large biomolecules (e.g., proteins) Compatible with surface sampling Applicable in surface analysis and mass spectrometry imaging MALDI capable of ionizing large biomoleculeas (e.g., proteins) Complex matrix effects. Matrix can be used to protect the analyte and enhance the ionization

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Fig. 2 Schematic description of six mass analyzers used in mass spectrometers that are currently available on the market. a Quadrupole (Q). b Time-of-flight (TOF). c Magnetic sector (B). d Ion trap (IT). e Orbitrap (OT). f Ion cyclotron resonance (ICR)

imaging is currently commercially available only for secondary ion mass spectrometry (SIMS), MALDI (and for other compatible laser desorption-ionization techniques) and for the desorption electrospray ionization (DESI). These three molecular ionization techniques are supplemented by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), which is an atomic ionization technique designed for elemental analysis by MS that can be used in imaging mode as well. Although LA-ICP-MS has been used for imaging of metal-containing biological

samples (Becker et al. 2007, 2008), it is still primarily an elemental technique and it is not going to be discussed here. Once the ions are generated, they need to be separated so the mass spectrum can be recorded. One of the unique features of mass spectrometry is that mass analysis, the process of separation of ions according to their different m/ z (mass-to-charge) ratios, can be done by different physical principles. The basic types of mass analyzers are summarized in Fig. 2 (De Hoffmann et al. 2007; Gross 2004). All

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Table 2 Overview of the mass analyzers used in mass spectrometry Quadrupole

Ion trap

Linear TOF (rTOF)

Magnetic sector

FT-ICR

FTOrbitrap

Upper mass limit (m/z)

4,000

6,000

1,000,000 (10,000)

20,000

30,000

50,000

Mass resolution

2,000

4,000

5,000 (20,000)

\100,000

500,000

100,000

Mass accuracy (ppm)

100

100

200 (10)

10

\5

\5

Ion sampling

Continuous

Pulsed

Pulsed

Continuous

Pulsed

Pulsed

Tandem MS experiment

Yes, low energy collision

Yes, multiple low energy collision

Yes, low or high energy collision

Yes, high energy collision

Yes, multiple low energy collision

No

The mass resolution and accuracy depend on many factors. The values in this table were taken from De Hoffmann et al. 2007 and are for illustration of common setup of each analyzer

of them can be found in new mass spectrometers used in analytical and bioanalytical chemistry (although some of them are more common than others). Interestingly, all six mass analyzers can be utilized for mass spectrometry imaging, but time-of-flight (TOF) is by far the most frequent analyzer currently used in imaging mass spectrometers (Colliver et al. 1997; Stoeckli et al. 1999; Walch et al. 2008). The overview of the performance of all mass analyzers is listed in Table 2. Finally, the ions must be detected. There are in principle two types of ion detection in mass spectrometry. One is destructive and it is based on collision of the ion with the surface of the detector. The photographic plate was the first destructive ion detector and nowadays there are several types of ion detectors with different surfaces used for efficient collection and detection of the ions. The other type of ion detection in mass spectrometry is non-destructive but it can only be used for mass analyzers in which the ions undergo a periodic motion with different frequencies that depend on their m/z values. External electrodes measure an image current induced by the periodic motion of the ions and so called free induction decay is recorded and converted from time domain to frequency domain [by a mathematical process of Fourier transformation (FT)]. The individual frequencies are then recalculated to m/z values, while amplitudes of the signals represent abundances of the ions. Thus, mass spectrum can be constructed. This type of detection is only used in Fourier transform ion cyclotron resonance (FT-ICR) instruments (Comisarow and Marshall 1996) and in FT-Orbitrap (Hu et al. 2005), although radio frequency ion traps, which are normally equipped with destructive ion detectors, could in principle use it as well (Badman et al. 1999).

Mass spectrometry imaging The ability to visualize surfaces of biological samples has always played a crucial role in life sciences and many

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surface analysis techniques were modified to be usable in 2D imaging mode. MSI combines molecular analysis of surfaces with spatial information in a way that each pixel in a mass spectrometry image is represented by a regular mass spectrum. The obtained image is thus multidimensional and suitable software tools allow generating 2D distribution of each peak in the mass spectrum and one can thus obtain molecular images of single species as well as their combined distributions (McDonnell and Heeren 2007; Setou 2010; Setou et al. 2007). SIMS was the first technique used for MSI in the early 1960s (Castaing and Slodzian 1962), but it was used chiefly for inorganic materials. Approximately 10 years after the first papers about soft laser desorption-ionization (Tanaka et al. 1988) and MALDI ionization (Karas and Hillenkamp 1988), the first MALDI imaging paper (Caprioli et al. 1997) has been published, followed by a first application of protein MSI in histochemistry of cancer (Stoeckli et al. 2001). DESI imaging was introduced in 2006 and it is thus the youngest of the three major MSI techniques (Wiseman et al. 2006). Figure 3 shows principles of all three desorption-ionization techniques used for MSI. There are two different modes of operation in mass spectrometry imaging, which differ significantly in a way how the spatial information is obtained. The first one is called microprobe or scanning probe and the second is called microscope. The difference is schematically described in Fig. 4. Microprobe (scanning probe) This approach is technically easier and most imaging mass spectrometers operate in this mode. In principle, microprobe mass spectrometry imaging is the same as any other position-correlated spectrometry. The ionization beam strikes a small localized region of the surface and the ionized species are separated according to their m/z and detected. The measured mass spectrum is stored and the

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that it is easy to perform, it is compatible with all six mass analyzers and any desorption-ionization technique can be utilized in scanning mode. The disadvantage is that any spatial information from within the localized region of ionization is lost. The 2D resolution is thus defined and limited by the profile of the primary ionization beam. Microscope In microscope mode the original surface position of an ion in x and y coordinates (z coordinate being the surface normal and the ion flight direction) is maintained after the ionization. If suitable ion optics, analyzer and position sensitive ion detector are used, then it is possible to determine the original position of an ion on the surface even after its detection. The detector must be able to record not only intensity and information necessary for the determination of m/z (usually time-of-flight) but also x, y position of the ion impacting the detector surface. One can visualize the microscope mode of operation as a set of flying images, each of them consist of the ions with the same m/z (Fig. 4). The advantage is obvious—superior spatial resolution, which is not limited by the focusing of the primary beam. The disadvantages are that the spatially sensitive ion optics and detector are more expensive and the microscope mode is only compatible with TOF analyzer or dispersing magnetic sector analyzer. In addition, ambient desorption-ionization techniques (such as DESI or atmospheric pressure MALDI) cannot be performed in microscope mode. In ambient ionization (Cooks et al. 2006) the ions must first go through the ‘so called’ atmospheric pressure inlet (API) where they get mixed and thus the original position cannot be maintained. Resolution

Fig. 3 Desorption-ionization techniques used in mass spectrometry imaging. a Desorption electrospray ionization (DESI). b Secondary ion mass spectrometry (SIMS). c Matrix-assisted laser desorption ionization (MALDI)

surface stage with sample moves so the next localized region can be exposed to the ionization impulse and its spectrum obtained and stored. This process is repeated until the whole region of interest (ROI) or the whole sample is measured in set raster pattern. The mass spectrometry image is then reconstructed from all measured spectra; each of them represents a single pixel of the image, by a software tool. The advantage of the microprobe approach is

When the term resolution is used in the context of MSI, it can refer to three phenomena (Chandra et al. 2000; Fletcher et al. 2007; Jun et al. 2010). First is the resolution of two peaks in mass spectrum, which is defined by the performance of the mass analyzer. The mass resolution is the measure of the ability to distinguish species with close m/z ratios and it is especially important when complex samples are examined by MSI. Second resolution refers to the size of the pixel and defines the 2D surface resolution of the final image. SIMS is the only MSI technique, which is normally capable of pixel sizes way below 1 lm. Especially high 2D resolution can be achieved in microscope mode. The MALDI 2D resolution is given by the laser focusing and typically is in the range of 1–100 lm. The DESI surface resolution, which is usually on the order of hundreds of micrometers, is discussed below in details in the specialized section of this article. Third usage of the

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Fig. 4 Two basic concepts used in mass spectrometry imaging

term resolution is the least common and refers to the image resolution in third dimension. Because MSI cannot be normally done directly in 3D (the exceptions are some of the imaging studies with dynamic SIMS (Fletcher and Vickerman 2010)) the procedure for obtaining 3D images is based on reconstruction of consecutive slices of objects that were cut and the individually imaged in 2D mode. Then the resolution in 3D is defined by the thickness of the slice. Areas of application Traditionally, the MSI was based on SIMS ionization and it was used to investigate inorganic surfaces in areas of research and industry that are beyond the scope of this review (Vickerman 1997). The situation changed after MALDI-based MSI of biological samples was introduced, which made the whole area of life science imaging accessible for MSI technology (Caprioli et al. 1997). The major industrial applications of biological MSI are in pharmaceutical industry (Solon et al. 2010), where it can provide faster and simpler option for performing ADME (absorption, distribution, metabolism, excretion) (Kool et al. 2010; Tang and Prueksaritanont 2010) studies on model organisms than techniques based on isotopic labeling. While there are not yet any established clinical applications of MSI, its importance in basic life science research

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is growing rapidly. Unlike other imaging techniques, MSI does not require labeling. This is especially useful for metabolome-mapping, where many molecules can be mapped simultaneously using only a single sample. In addition, lipids and low-molecular weight compounds in tissue sections cannot be imaged with usual microscopic or labeling-based imaging techniques. Thus, MSI is the first technique that provides distribution maps of small molecules in tissues (Debois et al. 2009). In the area of protein imaging, MSI has to compete with established techniques based on traditional imaging such as conventional or fluorescence microscopy. But protein MSI still has advantages in situations, where sample is especially precious or where extraction of proteins into solution cannot be done. Biopsies of human patients are a good example of such precious samples. It is difficult to treat 1 mm3 of a biopsy by traditional proteomics techniques based on sample dissolution in a small volume followed by subsequent separation steps (Setou 2010). MSI requires no sample treatment; the tissue obtained by biopsy only needs to be flash-frozen, sliced and mounted on surface compatible with the given mass spectrometer. This represents an advantage and some authors (Setou 2010) argue that MSI will finally become established technique for analysis of biopsies. Biomedical MSI is an emerging technology that is just starting to be applied outside the basic research. Besides

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Table 3 Comparison of commercially available methods used for mass spectrometry imaging Abbreviation

Full name

Ionization impulse

Lateral resolution

Upper mass limit

SIMS

Secondary ion mass spectrometry

Beam of focused high energy primary ions

Below 1 lm (only method with subcellular resolution)

500–1,000 Da

(MA)LDI-MS

(Matrix-assisted) Laser desorption-ionization mass spectroscopy

Laser light; energy can be transferred: a) directly or via surface, b) through matrix (MALDI)

10–150 lm

Without matrix: 2 kDa

Desorption electrospray ionization mass spectrometry

Extraction by electrospray droplets

100–500 lm

DESI-MS

vendor-specific documents, new application notes can be found on the web page of the MALDI-MSI interest group ( http://www.maldi-msi.org/) and on the webpage of the COMPUTIS consortium (http://www.computis.org/). We will now provide more detailed description of the three main desorption-ionization techniques used for molecular MSI. Their summary in Table 3) presents an overview of some interesting applications relevant for biomedical and life sciences research. MALDI is the most important MSI technique in life sciences and thus the center of gravity of this report was placed in the MALDI section.

SIMS SIMS has a long history and has been widely applied to surface analysis in many areas of science and technology (Chandra 2004; Delcorte et al. 2006; Dickinson et al. 2006; Gillen et al. 2006; Hoshi and Kudo 2003; Layne and Sim 2000; Pachuta and Cooks 1987; Spoto 2000; Ullrich et al. 2005; Van Vaeck et al. 1999; Winograd 2005). In SIMS, projectile (primary) ions strike the surface at well defined energies in range 1–30 keV and eject secondary ions from the surface (Fig. 3b) that are subsequently analyzed by the mass analyzer (Vickerman 1997). The mechanism of SIMS has been debated for many years and comprehensive fundamental review is available (Pachuta and Cooks 1987). SIMS is usually divided into two classes depending upon the primary ion intensity. Static SIMS uses low intensity projectile primary beams (\1013 ions/cm2), which minimizes sample damage and makes the method mostly non-destructive. Dynamic SIMS on the other hand employs intense primary beams ([1013 ions/cm2), which results to surface sputtering, damages the sample but also allows depth profiling from few nanometers to several hundreds of micrometers (Harton et al. 2006). Both, static and dynamic SIMS can be used for imaging but static configuration provides better spatial resolution (Hoshi and Kudo 2003). As was already mentioned, SIMS imaging has been used for almost half a century and it has been broadly applied for

50 lm commonly used

30–60 kDa

40 lm reported

visualization of inorganic surfaces in material science. Due to the upper mass limit (the practical mass range is limited to approximately m/z = 1,000) of the classic SIMS, it has not previously made a major impact on life sciences, but the situation is changing (Clerc et al. 1997). The use of Matrix-Enhanced SIMS (ME-SIMS) and Metal-assisted SIMS (Met-SIMS) can overcome this limit and improves detection of higher mass species (Chughtai and Heeren 2010). The advantage of ME-SIMS is that it consumes less surface material than laser desorption-ionization techniques (e.g., MALDI). That is why the same tissue can be re-imaged by MALDI after ME-SIMS. The subsequent imaging of the same tissue sample by different SIMS and MALDI techniques is the principle of the Multi-Modal Mass Spectrometry Imaging protocol that was developed in the AMOLF Institute (Amstalden van Hove et al. 2010). This approach is relatively costly and time consuming, but it allows obtaining unprecedented amount of information about the molecular composition of the analyzed surface. Although the low-mass range limits SIMS applications in biomedical research, there are still many important small molecules that are reporters of pathological states and can be imaged by SIMS (Altelaar et al. 2006; Chandra et al. 2000; Colliver et al. 1997). Visualization of lipids and small molecules is a well established application of SIMS imaging (Debois et al. 2009; Eijkel et al. 2009; Fletcher et al. 2007). Lipids in the brain tissue sections are often imaged by SIMS (example in Fig. 5) (Touboul et al. 2005). SIMS was also used to visualize the distribution of small molecules in steatotic liver (Le Naour et al. 2009). Lipids that contain no sugar modification are impossible to visualize by immunochemistry techniques but they are small enough to be below SIMS ionization limit (Debois et al. 2009; Malmberg et al. 2007). SIMS imaging was used to monitor changes of membrane lipid composition of mating Tetrahymena (Ostrowski et al. 2004) Matrix-enhanced SIMS with 2,5dihydroxybenzoic acid electrosprayed on neuroblastoma cells allowed intact molecular ion imaging of phosphatidylcholine and sphingomyelin at the cellular level (Altelaar

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Fig. 5 Example of SIMS tissue imaging. Negative secondary ion images obtained from a rat brain section under the irradiation of Bi3? primary ions. Reprinted from Touboul et al. (2005) Copyright, with permission from Elsevier

et al. 2006). Another example of subcellular imaging was visualization of the mitotic spindle from T98G human glioblastoma tumor cells (Chandra 2004). SIMS imaging was also used to obtain ion images in ischemic retinal tissues (Kim et al. 2008), of lipids in healthy rat aorta and human atherosclerotic plaque (Nygren et al. 2007). Atherosclerotic lesions were analyzed by cluster SIMS to obtain micrometer surface resolutions (Mas et al. 2007). SIMS is also very well suited for detection of inorganic ions. For instance, high-resolution images of cations in ischemic retinal tissues were obtained. The changes in Ca2?, Mg2?, K? and Na? were described during progression of ischemia (Kim et al. 2008). Inorganic ions were also imaged by 3D SIMS in single cells (Nygren et al. 2007). In some cases, characteristic secondary fragment ions of larger molecules can provide biomedically relevant information too. For instance, imaging of secondary ions from fragmented proteins was used to monitor the state of medical devices that suffer from protein adsorption (Aoyagi et al. 2004a, b).

MALDI Together with electrospray ionization, matrix-assisted laser desorption ionization has become soft ionization technique of choice for the analysis of large biomolecules. In a traditional MALDI a laser beam is aimed at a surface (in vacuum) with deposited sample mixed with a matrix (a carefully chosen compound that serves as a primary acceptor of the laser energy). In a subsequent chain of events the analyte is desorbed and ionized by a combination of different mechanisms, which are still largely

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debated. Soft Laser Desorption Ionization (LDI) has been introduced in 1980s and for its first successful application in the area of protein mass spectrometry Koichi Tanaka received a quarter of the 2002 Chemistry Nobel Prize. His breakthrough experimental approach was based on usage of an inorganic metal-based matrix (Tanaka et al. 1988). However, current MALDI users usually take advantage of an alternative type of matrices (organic compounds that cocrystallize with the analyte) developed mostly by Karas and Hillenkamp (Karas and Hillenkamp 1988). The analyzed compound is mixed with a matrix, usually an aromatic acid, which absorbs the energy of primary UV laser pulses and ionizes the analyte (De Hoffmann et al. 2007). The simplified scheme of MALDI is documented in Fig. 3c. Molecules desorbed from the sample are typically singly protonated even electron ions or adducts with alkali metals. In 2003, several tutorial papers were published in a special issue of Chemical Reviews Journal that fundamentally discussed MALDI mechanism in full details (Dreisewerd 2003; Karas and Kru¨ger 2003; Knochenmuss and Zenobi 2003; Zhigilei et al. 2003). There is also a new variant of the standard MALDI, an atmospheric pressure MALDI (AP-MALDI) (Laiko et al. 2000). The analysis of proteins/peptides by atmospheric pressure and standard vacuum MALDI has been reviewed (Grasso et al. 2007; Konn et al. 2005; Mayrhofer et al. 2006; Pittenauer et al. 2006; Schneider et al. 2005). The main difference is in speeds of collisional cooling (AP-MALDI is softer and ions generated by AP-MALDI generally undergo less fragmentation) (Karas et al. 2000; Konn et al. 2005). Sample preparation for MALDI imaging Sample preparation is a crucial step in MALDI-MSI experiment and all steps must be carefully considered in order to preserve the tissue integrity (thus the spatial localization of compounds) and compounds’ stability. The sample preparation protocol consists of a set of several consequential steps—tissue collection, storage, sectioning, transfer onto a MALDI plate, and MALDI matrix deposition—and it has been described in detail elsewhere (Chughtai and Heeren 2010; Schwartz et al. 2003; Walch et al. 2008). The following paragraphs briefly summarize the procedure and discuss recent progress. The sample is usually collected by resection (laboratory animals) or as a biopsy (human patients). After the collection, the sample is immediately loosely wrapped in an aluminum foil and shock-frozen by dipping into in liquid nitrogen for 30–60 s. It is important to minimize direct contact of the tissue with liquid nitrogen, which prevents the tissue from cracking and also from possible dissolution and loss of molecules of interest. After freezing in liquid nitrogen the tissue is stored in a freezer under -80°C. It has been reported that after

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1 year of storage of the sample its peptide/protein content starts to undergo degradation (Schwartz et al. 2003). Medical samples that have been fixed in formaldehyde solution (formalin) can be used for MSI analysis of proteome and protocols recovering peptides from its crosslinked form has been established (Chaurand et al. 2008a; Djidja et al. 2009b; Groseclose et al. 2008). However, it is not possible to recover spatial distribution of lipids because after formalin fixation the tissue is incubated in increasing concentrations of alcohol and in xylene. RCL2-CS100 is a new tissue fixative, which contrary to formaldehyde, is non-toxic and non-volatile and allows easy proteomics analysis and MSI (Mange et al. 2009). MSI only allows analysis of flat samples. The tissue is sectioned in a cryomicrotome into slices 10–20 lm thin, which assures that average mammalian cells are cut open and thus exposing their intracellular content. Besides the thickness, which can control the stability of the tissue slice, temperature of the cryomicrotome is another key parameter for successful slicing of the tissues and obtaining intact non-torn slices. A general rule is that fatty tissues require lower temperatures than tissues with higher water content, but each tissue is unique and may require specific approach. Optimum cutting temperature (OCT) polymer was used for stabilizing the tissue during slicing, but the used material suppressed the ionization process and is not thus generally recommended in MSI (Crecelius et al. 2005; Schwartz et al. 2003). The transfer of the tissue slice onto a MALDI plate can be done in different ways. The traditional approach uses thaw-mounting of the tissue slice on a conductive microscope glass coated with indium-tin oxide (ITO) to assure the conductivity. Another approach uses glass bead embed in parafilm to stretch the landed tissue slice, in order to increase the spatial resolution (Zimmerman et al. 2008). Samples may require further treatment such as selective washing and enzymatic digestion, and must undergo deposition of MALDI matrix for MS analysis. Analysis of proteins and peptides involve washing off lipids and salts using cold 70–80% ethanol (Todd et al. 2001) or more nonpolar solvents (Lemaire et al. 2006), which may otherwise cause low signal intensity by ion suppression. Lipids are analyzed directly from the tissue without any pre-treatment. Enzymatic digestion of proteins is performed directly on the tissue and aims at accessing wider range of proteins for the MS analysis. During the digestion a diffusion of the analytes in the tissue must be considered since it may compromise their spatial localization (Djidja et al. 2009a). MALDI matrix for MSI is an organic acid dissolved in mixture of organic solvent, water and trifluoroacetic acid, which is uniformly deposited on the tissue surface. There are several deposition methods. Some of them are laboratory know-how and some of them are commercially

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available. They have been reviewed elsewhere (Amstalden van Hove et al. 2010). The matrix mixture must be able to extract the analytes from the tissue surface and successfully co-crystallize with them without comprising the spatial distribution. The matrix is usually applied in cycles with repetitive wetting and drying steps and it is important to assure that the tissue is not over wetted. The deposition must be uniform and reproducible across the whole tissue. Several matrices are used in MALDI-MSI; the most often used are alpha-cyano-4-hydroxycinnamic acid (CHCA), 2,6-dihydroxyacetophenone (DHA), 2,5-dihydroxybenzoic acid (DHB) and sinapic acid (SA). The selection of matrix depends on the analyte and usually SA and DHB are used for high molecular range compounds such as proteins and CHCA for low-molecular range species like lipids. The size of the matrix crystals influences the spatial distribution and it is important to optimize this parameter during deposition. Usually, the matrix deposition step requires intensive practice (including many successes and fails) before the operator gains sufficient handiness. MALDI-MSI data are often complemented with histopathological information of the tissue attached on ITO glass, and those can be obtained before or after the MSI experiment. Histology image acquired before the MSI analysis has the advantage that the MSI acquisition, which is more time and instrumental demanding, can be targeted to a certain region of the tissue. In this case the staining must not interfere with the ionization technique. Several media, such as methylene blue, cresyl violet, and Terry’s polychrome have been proposed for MSI of proteins and peptides (Chaurand et al. 2004). Recent alternative procedure employs surface of silicon nanowires (commonly used as nano-assisted laser desorption ionization, NALDI), which allows chemical transfer from the attached tissue onto the nanosurface (Vidova´ et al. 2010a). The chemical imprint on the silicon nanosurface maintains the spatial distribution and after thorough removal of the tissue with pure water the absorbed nonpolar compounds are analyzed directly from the silicon surface without addition of MALDI matrix. This approach allows immediate matrix-free laser desorption ionization (LDI). Comparison of standard MALDI-MSI with matrixfree approach can be seen in Fig. 6. Proteins MALDI-MSI of peptides and proteins, which has been pioneered by Caprioli et al. in (1997), triggered the instrumental and method development of MSI. Nowadays, established procedures for bottom-up (Groseclose et al. 2007) and top–down MSI proteomics are available (Caprioli et al. 1997; Chaurand et al. 1999). While bottom-up approach uses enzymatic on-tissue digestion of proteins to

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Fig. 6 Comparison of standard MALDI imaging with the matrix-free NALDI approach using two different 2D resolutions (150 and 50 lm). MALDI and NALDI imaging found the same distribution of the lipid species within the two consecutive mouse kidney sections. The overlay images (last row) show the different lipid composition of pelvis (orange) and adrenal gland (yellow) from the rest of the kidney. The exact m/z of imaged ions are: 760.5851, 772.5851, 792.5901, and 810.6008. Reprinted from Vidova´ et al. (2010a) Copyright, with permission from ACS

smaller peptides, which can be easier analyzed within the limited mass range of an MS analyzer, the top–down method analysis intact proteins directly from the tissue, which creates demands for upper mass limit and the detection of proteins above MW of 30 kDa may be problematic. Besides the use of enzymatic digestion, the sensitivity can be improved by contact blotting of the tissue on a surface (C18 beads, conductive polymer, PTFE with antibodies), which allows transfer of the proteins. This clean-up procedure reduces sample complexity that could cause ion suppression effects. The early MALDI-MSI work has demonstrated the capabilities of the technology and has been used for instance for visualization of insulin and hormone peptides in rat pancreas and pituitary (Caprioli et al. 1997). Later MALDI-MSI has been used to study several diseases related to local changes of proteome or peptidome in affected tissues and thus has created an alternative screening approach to histopathological analysis. MALDIMSI has been used to study Alzheimer’s disease (Rohner

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et al. 2005; Stoeckli et al. 2002; Touboul et al. 2007), Parkinson’s disease (Pierson et al. 2004; Skold et al. 2006; Stauber et al. 2008), Fabry’s disease (Roy et al. 2005, 2006; Touboul et al. 2007), eye lens cataract (Borchman and Yappert 2010; Fliesler 2010; Grey and Schey 2008; Jacob et al. 2005; Rujoi et al. 2004), kidney diseases and functions (Herring et al. 2007; Meistermann et al. 2006), biologically active compounds in mouse spinal cord (Monroe et al. 2008), and many types of cancer (Cazares et al. 2009; Chaurand et al. 2008b; Cornett et al. 2006; Djidja et al. 2009a, b, 2010; Kang et al. 2010; Lemaire et al. 2007; Minerva et al. 2008; Patel et al. 2009; Sanders et al. 2008; Schwamborn et al. 2007; Schwartz et al. 2004, 2005; Yanagisawa et al. 2003) [reviewed also in McDonnell et al. (2010a)]. An example of MALDI imaging of cancer tissue is shown in Fig. 7. The increasing interest in MALDI-MSI in biomedical field resulted in automated MALDI setup allowing for high-throughput (McDonnell et al. 2010b). Several reviews have discussed the importance of MALDI-MSI in disease-related research

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Fig. 7 MALDI ion images of differentially expressed proteins in ovarian tissues. a Optical H&E stained images. b Images of the differentially expressed proteins in ovarian cancer by MALDI-IMS. N normal, T tumor. Reprinted from Kang et al. (2010) Copyright, with permission from ACS

proteomics (Rohner et al. 2005; McDonnell et al. 2010a; Burnum et al. 2008; Caprioli 2008; Fournier et al. 2008; Wisztorski et al. 2007, 2008). Lipids Lipids are important molecules in the cell, which have several functions—they act as building units of the cell membrane, second messengers, and storage of energy (Wenk 2005). Recent MALDI-MSI experiments have been focused on studying how lipid functions in biochemical pathways correlates with the tissue histology. The sample preparation is easier than in protein MSI and no washing steps are required. The tissue is usually coated with a MALDI matrix and analyzed by imaging MALDI (Kim et al. 2010). Lipids can be ionized in both positive and negative ion mode. Phosphatidylcholines (PCs), sphingomyelins (SMs), and sterols can be ionized in positive ion mode. Phosphatidylinositols, phosphatidylserines, and sulfatides ionize in negative ion mode. Phosphatidylethanolamines (PEs) can be detected in both, positive and negative ion modes. The lipid mass spectra are quite complex, usually showing protonated ions accompanied with potassium and sodium adducts (in the positive ion mode). A protocol for proper selection of MALDI matrix, which would favor particular class of lipids in positive ion mode, has been published (Sugiura and Setou 2009). To reduce the number of ion peaks for one lipid species to a single one and thus to increase the sensitivity and reduce possible mass peak overlaps, potassium acetate (Sugiura

and Setou 2009) or lithium chloride (Jackson et al. 2005) have been added to the matrix solution. Several MALDI-MSI works have been used to visualize PCs (Garrett et al. 2007; Jackson et al. 2005; Mikawa et al. 2009; Sugiura et al. 2009), gangliosides (Chan et al. 2009; Sugiura et al. 2008), sulfatide (Ageta et al. 2009), cerebrosides (Jackson et al. 2007) in mouse or rat brain. Glycosphingolipids and glucosylceramide were analyzed in type 1 Gaucher disease knock out mouse spleen (Snel and Fuller 2010), phospholipids in mouse brain model of TaySachs and Sandhoff disease (Chen et al. 2008). Also, other organs were investigated and visualization has been performed for PCs in mouse retina (Hayasaka et al. 2008), sphingolipids in porcine (Vidova´ et al. 2010b) and human (Deeley et al. 2010) ocular lens, phospholipids in primate macula (Garrett and Dawson 2010), PCs in dystrophic muscle (Touboul et al. 2004), phospholipids in mouse embryo (Burnum et al. 2009), several lipid classes in a liver (Astigarraga et al. 2008), phospholipids in colon cancer liver metastasis (Shimma et al. 2007). Progress in MALDIMSI and lipidomics led to establishing unsupervised and supervised multivariant statistical analysis which was demonstrated on analysis of lipids in mouse brain (Trim et al. 2008a). Review on MALDI-MSI of lipids (Murphy et al. 2009) and a protocol (Sugiura and Setou 2010b) are available. MALDI-MSI has been also used for studying spatial distribution of lipid in plants and insects (Vrkoslav et al. 2010). The efficient identification of lipids in mass spectrometry imaging usually requires high mass resolution and

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accuracy. It is based on the determination of molecular formula from the measured exact mass. The molecular formula is then searched for in a database (for example Lipidmaps at http://www.lipidmaps.org). The database search provides a list of all lipid isomers with the same formula. Usually, the isomers are from the same lipid class and differ by different combinations of fatty acids or different positions of double bonds in unsaturated carbon chains. When tracking actual lipid species, this information might be already sufficient for designing the molecular map of interest. If more structural information is needed then the ion must be fragmented (by tandem mass spectrometry). The first fragmentation reveals important diagnostic ions for major structural components—head group (e.g., phosphocholin) and fatty acid chains. If the product ion intensity from the first fragmentation is sufficient, further fragmentation can be performed. (This can for instance reveal the position of the double bond, if any.) However, the fragmentation experiment is time consuming and is not usually performed on-line during imaging, but it can be done separately. Another option is to microdissect regions of interest from a consecutive slice of the tissue, dissolve them and perform regular analysis by a standard LC–MS. The results of LC–MS analysis are than compared with the results from MSI experiment (an example of such approach can be found in Hankin and Murphy 2010). Metabolites and pharmaceuticals Metabolomics studies qualitative and quantitative changes of low-molecular weight compounds in the organism (cells, tissues, body fluids) that correspond to its physiological functions and changes (Nicholson and Lindon 2008). The concentration of different metabolites in an organism varies significantly, which calls for analytical techniques with high dynamic range. The origin of metabolites can be endogenous (their synthesis occurs in the organism) and exogenous (drugs or food). Monitoring of concentration levels and spatial localization of both groups of metabolites in tissues is important for instance in pharmacological and toxicological studies. MSI can visualize endogenous metabolites and visualize their response to an administered drug (Sugiura and Setou 2010a) and assist in ADME studies. The general problem is that MALDI of low-molecular mass compounds suffer from interferences with MALDI matrix. Target compound can be isolated using tandem MS or high-resolution MS, which efficiently separate biologically relevant compounds from the MALDI matrix can be used (Cornett et al. 2008). Recent studies have also introduced MSI using surfaces that assisted LDI without the use of interfering MALDI matrix (Vidova´ et al. 2010a; Liu et al. 2009). MALDI-MSI has been used to visualize pharmaceutically active compound and its metabolites in the whole rat

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body (Hopfgartner et al. 2009; Stoeckli et al. 2007). The MSI data have been in agreement with autoradiograph image showing high concentration of the drug in trachea and lung. MALDI-MSI has also been used for visualizing olanzapine and its metabolites (Khatib-Shahidi et al. 2006) and anticancer drug vinblastine (Trim et al. 2008b) in the whole rat body. In other experiment, olanzapine has been localized in kidney and liver and imatinib in glioma (Cornett et al. 2008). Other applications have used MALDI-MSI to localize antipsychotic drug clozapine (Hsieh et al. 2006), anti-tumor drug SCH 226374 (Reyzer et al. 2003) and chlorisondamine (Wang et al. 2005) in rat brain slices. Further, ketoconazole applied in medicated shampoo has been analyzed on a porcine skin (Bunch et al. 2004). Distribution of the bioreductive drug AQ4N and its active metabolite AQ4 has been visualized in human tumors (Atkinson et al. 2007). Platinum anticancer drug oxaliplatin was imaged in rat kidney (Bouslimani et al. 2010). The role of MSI in drug discovery has been reviewed (Rubakhin et al. 2005). Primary metabolites, such as AMP, ADP, ATP, UDPGlcNAc, etc. have been analyzed and localized in rat brain sections (Benabdellah et al. 2009). Mono Mac 6 cells cultured with the HIV protease inhibitors saquinavir and nelfinavir were analyzed with MALDI-MSI (Dekker et al. 2009). A hybrid ionization approach matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS) was used for localization of low-molecular mass metabolites (Liu et al. 2009). This approach has significantly reduced matrix background and improved survival yields of low-molecular mass ions. A short review that describes MSI of drugs and metabolites has been recently published (Sugiura and Setou 2010a).

DESI DESI, introduced in 2004, is the youngest of the commercially available imaging MS techniques (Takats et al. 2004). It is also the technique that ignited the interest in ambient DI-MS techniques, which allow for the direct analysis of surfaces in the open atmosphere of the laboratory or even in the natural environment. In DESI, a pneumatically assisted electrospray source aims at the surface to be analyzed (Fig. 3a), which is usually mounted on a movable stage in aid of proper sample positioning. A high voltage (2–5 kV) is applied to the emitter same as in standard electrospray and together with solvent and nebulizing gas flow create an electroaerosol that consists of high-velocity charged microdroplets (Takats et al. 2005; Venter et al. 2006). The spray is directed at the surface, where it desorbs the analyte and transports it into the mass spectrometer inlet. DESI has been reviewed thoroughly in

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several tutorial papers (Van Berkel et al. 2008; Venter et al. 2008) and its mechanism has been investigated by computer simulation (Costa and Cooks 2007, 2008) as well as by experiments (Benassi et al. 2009; Van Berkel et al. 2008; Venter et al. 2006; Volny´ et al. 2008). DESI can be coupled to all mass spectrometers with an open atmospheric pressure inlet. The instruments most utilized for DESI are probably ion traps but less common mass spectrometers can be used as well. Powerful coupling of DESI with high-resolution Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR-MS) was reported (Bereman et al. 2006; Pol et al. 2009). DESI can be used to analyze solids and liquids and it can analyze small and larger biomolecules. It produces very similar spectra to electrospray and multiply charged ions can be obtained by DESI. Imaging of surface distribution of molecules of interest with DESI is a particularly interesting application. It was used mainly to profile phospholipids in different tissue sections (Bereman et al. 2006; Ifa et al. 2007b; Wiseman et al. 2006) but other uses, e.g., analyte bands in TLC (Pasilis et al. 2008; Van Berkel and Kertesz 2006) or inked lettering and imaging on paper (Ifa et al. 2007a) were reported too. A recent review (Dill et al. 2009b) describes utilization of DESI in imaging of a variety of tissue samples such as rat brain, human breast tissue (Dill et al. 2009b) and canine tumor tissue (Dill et al. 2009a). High spatial resolution DESI imaging was used to image rat spinal cord cross-section (Girod et al. 2010) (Fig. 8). High mass resolution DESI imaging of mouse brain tissue demonstrated usefulness of DESI ionization for imaging of sphingolipids and ceramides (Pol et al. 2009). An interesting application of DESI imaging was presented by Kertesz and van Berkel who have shown the ability to quickly visualize the localization of propranolol in regions of whole body thin tissue sections from mice dosed at pharmacologically relevant levels (Kertesz et al. 2008). Poor 2D resolution (roughly 100–250 lm) is often listed as a disadvantage of DESI imaging compare to SIMS and MALDI. However, resolution much below 100 lm could be achieved (Kertesz and Van Berkel 2008). Commercial DESI stage can be modified and used also for other compatible ambient DI techniques, but their principles and applications are beyond the scope of this article. Efficiency of the ion transport through the atmospheric pressure inlet, a bottleneck in both DESI and conventional ESI, is currently debated in the literature (Clowers et al. 2008; Kelly et al. 2008; Page et al. 2008; Volny´ and Turecek 2006).

Data handling In addition to hardware setup and sample preparation, data handling poses additional challenge of any MSI

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experiment. Depending on the resolution (both, surface and mass), each MSI experiment produces several gigabytes of data. Any further processing, such as image reconstruction or statistical analysis, or even archiving, requires powerful computers and adequate memory capacity. While proprietary raw data formats, developed by original instrument vendors, are typically memory efficient, its tight software–instrument relationship poses a significant problem in data exchange and sharing. To overcome this limitation, an MSI-specific imzML data format was developed by the COMPUTIS consortium (http://www. computis.org). Every imaging experiment stored in the imzML format consists of two separate files. All the experiment metadata are described within an XML based file (*.imzML), using controlled vocabulary. The XML model used, is the same as for the recently developed mzML format (version 1.1.0), which is rapidly becoming a standard in mass spectrometry (Deutsch 2008). Its controlled vocabulary was extended by all the necessary parameters related to MSI experiments. In order to store large amount of acquired data in a more efficient way than could be achieved using XML structure, respective mass spectra are stored in a separate binary file (*.ibd). In a typical MSI experiment, unprocessed continuous spectra share a single m/z array. This is effectively utilized to decrease overall data size—a single copy of particular m/z array is stored, followed by the intensity arrays of all acquired spectra. But any processed data (which typically do not share a single m/z array) can be stored in a regular way as well. Both files are tightly connected using universally unique identifier (UUID) to ensure corresponding files are handled together. One of the most widely used software for MSI data processing today is BioMap (http://www.maldi-msi.org). While it was originally developed for evaluation of magnetic resonance imaging (MRI) data in biomedical research, many more imaging data formats are now supported after the multiple modifications, including MSI. Beside its powerful visualization capabilities, such as overlaying of two separate data sets, it provides couple of additional tools for spectra processing and can be further extended by modules of specific needs. DataCube Explorer (http://www.maldi-msi.org) developed at the FOM Institute AMOLF, is a lightweight visualization tool providing a nice alternative to share and explore MSI data sets, especially in connection with the imzML format. Several useful features are available to dynamically scroll through the data, analyze selected regions and process and classify the image. Several instrument vendors have developed their own software platform for MSI experiment to acquire and process the data. Raw data from Bruker Daltonics instruments can be analyzed by their FlexImaging software,

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Fig. 8 Selected molecular ion images of specific lipids and fatty acids from analysis of a 3.8 9 3.5 mm area of rat spinal cord cross-section in the negative ion mode. Ion images of a plasm-PE(38:4). b PS(36:1). c PE(40:4). d PG(40:6). e PI(38:4). f ST(24:1). g (18:1). h (20:4). i (22:6). j Optical image of the rat spinal cord cross-section. Reprinted from Girod et al. (2010) Copyright, with permission from Elsevier

which provides tools for color-coded image reconstructions of spatial distribution for any ion measured. Together with ClinProTools package, statistical tools such as principal component analysis (PCA) or hierarchical clustering can be utilized, mainly in biomarker discovery. Similar software packages are available for Shimadzu and Thermo Fisher Scientific instruments. Some other general software tools used for various tasks in mass spectrometry can be utilized to analyze MSI data as well. As a typical example, Mascot tools (http://www. matrixscience.com) are often used for identifications of unknown proteins or mMass (Strohalm et al. 2010) software for identification of lipids in high-resolution data sets.

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Conclusion MSI is a very rapidly developing branch of mass spectrometry and one of the new concepts in biological imaging that are under a swift development in the twenty first century. It is a quickly booming field, as can be demonstrated by an increasing number of publications (Heeren et al. 2009). While MALDI and SIMS are already well established, DESI is still an emerging technique. However, its development is currently very swift and it is reasonable to expect that DESI will provide a practical alternative to MALDI and SIMS. DESI is relatively simple and unlike traditional DI techniques offers an ‘‘ESI like’’ ionization mechanism.

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One of the challenges in biological MSI is the ion suppression effect that is caused by the complex chemical environment of the tissue (Heeren et al. 2009). Several protocols for salt removal prior the analysis and lipid washing procedures prior the imaging of peptides and proteins have been developed to simplify the chemical environment and this effort still continues (Lemaire et al. 2006; Murphy et al. 2009). Like in other molecular imaging techniques, results obtained by MSI can be correlated with histomorphology. Examples can be cited for cancer tissues (e.g., Stoeckli et al. 2001; Dill et al. 2009b) as well as for healthy tissues (Amstalden van Hove et al. 2010; Dill et al. 2009b; Girod et al. 2010; Vidova´ et al. 2010a, b). However, the described ion suppression effects can hinder any such correlation and care must be always taken in this respect, especially when using SIMS, which is very sensitive to different matrix effects. The imaging of proteins by MSI is seriously hindered by a poor limit of detection (combined with lower abundance of important proteins). As was reviewed above in the MALDI section, this can be overcome by using on-tissue digestion that converts the task of protein imaging to much easier imaging of proteolytic peptides (Stauber et al. 2010) and we expect that this approach will become more common in MSI—not just for proteins but also for other biomacromolecules. Nevertheless, the real potential of biological MSI is in imaging of molecules that can be only hardly visualized by other imaging techniques (e.g., in metabolomic studies). Although the biological MSI was originally introduced for peptides and proteins we think that imaging of small molecules will be the driving force of the visualization applications of MSI in the life sciences in the near future. The necessary key tool for small-molecule MSI experiments, which is still missing, is a fast and user friendly software platform that would be able to work with MSI data that were acquired with ultra high mass resolution. New protocols for matrix-free laser desorption-ionization-based MSI are being developed for small molecules imaging (Svatos 2010). As an example of matrix-free approach, Fig. 9 compares workflow of a standard MALDI-MSI with recently developed matrix-free imaging of tissue lipid imprints (Vidova´ et al. 2010a). An interesting new approach in MSI is utilization of ion mobility spectrometry (IMS) as an additional ion-separation step during imaging (Stauber et al. 2010; Trim et al. 2008a). This allows imaging of different conformations of the same molecules and distinguishing isobaric overlaps that exist in standard MSI, especially if low resolution mass analyzers are used. It’s hard to make predictions, especially about the future is hoary aphorism that is variously attributed to different authors. Nevertheless, we would still like to take the risk of

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Fig. 9 Examples of workflow in two different MSI methodologies that both used laser desorption ionization. Left side standard MALDIMSI, Right side matrix-free NALDI-MSI

making our own prediction. In our opinion, MSI has a potential to be used as a routine tool for imaging of histological samples, in tissue banks or even during some types of surgeries. We hope that it will help to understand

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the localization of molecules and its importance during disease or treatment states. That will have a direct impact on development of more efficient therapies for many types of diseases. MSI is an addition to classical techniques and it should be able to support current histological techniques and to broaden the diagnostic/therapeutic relevant information obtained from the sample. Acknowledgments The work was supported by the Ministry of Education, Youth, and Sports of the Czech Republic (LC545, ME10013) and by an Institutional research concept of the Institute of Microbiology, Academy of Sciences of the Czech Republic (AV0Z50200510) and by Czech Science Foundation (Project P206/ 10/P018). MV’s research was supported by a Marie Curie International Reintegration Grant within the 7th European Community Framework Program. JP thanks the Academy of Finland for financial support (1122354).

References Ageta H, Asai S, Sugiura Y, Goto-Inoue N, Zaima N, Setou M (2009) Layer-specific sulfatide localization in rat hippocampus middle molecular layer is revealed by nanoparticle-assisted laser desorption/ionization imaging mass spectrometry. Med Mol Morphol 42:16–23 Altelaar AFM, Klinkert I, Jalink K, de Lange RPJ, Adan RAH, Heeren RMA, Piersma SR (2006) Gold-enhanced biomolecular surface imaging of cells and tissue by SIMS and MALDI mass spectrometry. Anal Chem 78:734–742 Amstalden van Hove ER, Smith DF, Heeren RM (2010) A concise review of mass spectrometry imaging. J Chromatogr A 1217:3946–3954 Aoyagi S, Hayama M, Hasegawa U, Sakai K, Hoshi T, Kudo M (2004a) TOF-SIMS imaging of protein adsorption on dialysis membrane. Appl Surf Sci 231:411–415 Aoyagi S, Hayama M, Hasegawa U, Sakai K, Tozu M, Hoshi T, Kudo M (2004b) Estimation of protein adsorption on dialysis membrane by means of TOF-SIMS imaging. J Membr Sci 236:91–99 Astigarraga E, Barreda-Gomez G, Lombardero L, Fresnedo O, Castano F, Giralt MT, Ochoa B, Rodriguez-Puertas R, Fernandez JA (2008) Profiling and imaging of lipids on brain and liver tissue by matrix-assisted laser desorption/ionization mass spectrometry using 2-mercaptobenzothiazole as a matrix. Anal Chem 80:9105–9114 Atkinson SJ, Loadman PM, Sutton C, Patterson LH, Clench MR (2007) Examination of the distribution of the bioreductive drug AQ4N and its active metabolite AQ4 in solid tumours by imaging matrix-assisted laser desorption/ionisation mass spectrometry. Rapid Commun Mass Spectrom 21:1271–1276 Badman ER, Patterson GE, Wells JM, Santini RE, Cooks RG (1999) Differential non-destructive image current detection in a Fourier transform quadrupole ion trap. J Mass Spectrom 34:889–894 Becker JS, Zoriy M, Dobrowolska J, Matusch A (2007) Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in elemental imaging of biological tissues and in proteomics. J Anal At Spectrom 22:736–744 Becker JS, Dobrowolska J, Zoriy M, Matusch A (2008) Imaging of uranium on rat brain sections using laser ablation inductively coupled plasma mass spectrometry: A new tool for the study of critical substructures affined to heavy metals in tissues. Rapid Commun Mass Spectrom 22:2768–2772

123

Histochem Cell Biol (2010) 134:423–443 Benabdellah F, Touboul D, Brunelle A, Lapre´vote O (2009) In situ primary metabolites localization on a rat brain section by chemical mass spectrometry imaging. Anal Chem 81:5557–5560 Benassi M, Wu CP, Nefliu M, Ifa DR, Volny M, Cooks RG (2009) Redox transformations in desorption electrospray ionization. Int J Mass Spectrom 280:235–240 Bereman MS, Nyadong L, Fernandez FM, Muddiman DC (2006) Direct high-resolution peptide and protein analysis by desorption electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Rapid Commun Mass Spectrom 20:3409–3411 Borchman D, Yappert MC (2010) Lipids and the ocular lens. J Lipid Res jlr.R004119 Bouslimani A, Bec N, Glueckmann M, Hirtz C, Larroque C (2010) Matrix-assisted laser desorption/ionization imaging mass spectrometry of oxaliplatin derivatives in heated intraoperative chemotherapy (HIPEC)-like treated rat kidney. Rapid Commun Mass Spectrom 24:415–421 Bunch J, Clench MR, Richards DS (2004) Determination of pharmaceutical compounds in skin by imaging matrix-assisted laser desorption/ionisation mass spectrometry. Rapid Commun Mass Spectrom 18:3051–3060 Burnum KE, Frappier SL, Caprioli RM (2008) Matrix-assisted laser desorption/ionization imaging mass spectrometry for the investigation of proteins and peptides. Annu Rev Anal Chem 1:689–705 Burnum KE, Cornett DS, Puolitaival SM, Milne SB, Myers DS, Tranguch S, Brown HA, Dey SK, Caprioli RM (2009) Spatial and temporal alterations of phospholipids determined by mass spectrometry during mouse embryo implantation. J Lipid Res 50:2290–2298 Caprioli RM (2008) Perspectives on imaging mass spectrometry in biology and medicine. Proteomics 8:3679–3680 Caprioli RM, Farmer TB, Gile J (1997) Molecular imaging of biological samples: Localization of peptides and proteins using MALDI-TOF MS. Anal Chem 69:4751–4760 Castaing R, Slodzian G (1962) Optique corpusculaire—premiers essais de microanalyse par emission ionique secondaire. Microscopie 1:395–399 Cazares LH, Troyer D, Mendrinos S, Lance RA, Nyalwidhe JO, Beydoun HA, Clements MA, Drake RR, Semmes OJ (2009) Imaging mass spectrometry of a specific fragment of mitogenactivated protein kinase/extracellular signal-regulated kinase kinase kinase 2 discriminates cancer from uninvolved prostate tissue. Clin Cancer Res 15:5541–5551 Chan K, Lanthier P, Liu X, Sandhu JK, Stanimirovic D, Li JJ (2009) MALDI mass spectrometry imaging of gangliosides in mouse brain using ionic liquid matrix. Anal Chim Acta 639:57–61 Chandra S (2004) 3D subcellular SIMS imaging in cryogenically prepared single cells. Appl Surf Sci 231–232:467–469 Chandra S, Smith DR, Morrison GH (2000) Subcellular imaging by dynamic SIMS ion microscopy. Anal Chem 72:104A–114A Chaurand P, Stoeckli M, Caprioli RM (1999) Direct profiling of proteins in biological tissue sections by MALDI mass spectrometry. Anal Chem 71:5263–5270 Chaurand P, Schwartz SA, Billheimer D, Xu BJ, Crecelius A, Caprioli RM (2004) Integrating histology and imaging mass spectrometry. Anal Chem 76:1145–1155 Chaurand P, Latham JC, Lane KB, Mobley JA, Polosukhin VV, Wirth PS, Nanney LB, Caprioli RM (2008a) Imaging mass spectrometry of intact proteins from alcohol-preserved tissue specimens: bypassing formalin fixation. J Proteome Res 7:3543–3555 Chaurand P, Rahman MA, Hunt T, Mobley JA, Gu G, Latham JC, Caprioli RM, Kasper S (2008b) Monitoring mouse prostate development by profiling and imaging mass spectrometry. Mol Cell Proteomics 7:411–423

Histochem Cell Biol (2010) 134:423–443 Chen YF, Allegood J, Liu Y, Wang E, Cachon-Gonzalez B, Cox TM, Merrill AH, Sullards MC (2008) Imaging MALDI mass spectrometry using an oscillating capillary nebulizer matrix coating system and its application to analysis of lipids in brain from a mouse model of Tay-Sachs/Sandhoff disease. Anal Chem 80:2780–2788 Chughtai K, Heeren RMA (2010) Mass spectrometric imaging for biomedical tissue analysis. Chem Rev 110:3237–3277 Clerc J, Fourre C, Fragu P (1997) Sims microscopy: Methodology, problems and perspectives in mapping drugs and nuclear medicine compounds. Cell Biol Int 21:619–633 Clowers BH, Ibrahim YM, Prior DC, Danielson WF, Belov ME, Smith RD (2008) Enhanced ion utilization efficiency using an electrodynamic ion funnel trap as an injection mechanism for ion mobility spectrometry. Anal Chem 80:612–623 Colliver TL, Brummel CL, Pacholski ML, Swanek FD, Ewing AG, Winograd N (1997) Atomic and molecular imaging at the singlecell level with TOF-SIMS. Anal Chem 69:2225–2231 Comisarow MB, Marshall AG (1996) The early development of Fourier transform ion cyclotron resonance (PT-ICR) spectroscopy. J Mass Spectrom 31:581–585 Cooks RG (2010) Foreword: desorption ionization and spray ionization: connections and progress. In: Cole RB (ed) Electrospray and MALDI mass spectrometry: fundamentals, instrumentation, practicalities, and biological applications. Wiley, Hoboken Cooks RG, Ouyang Z, Takats Z, Wiseman JM (2006) Ambient mass spectrometry. Science 311:1566–1570 Cornett DS, Mobley JA, Dias EC, Andersson M, Arteaga CL, Sanders ME, Caprioli RM (2006) A novel histology-directed strategy for MALDI-MS tissue profiling that improves throughput and cellular specificity in human breast cancer. Mol Cell Proteomics 5:1975–1983 Cornett DS, Frappier SL, Caprioli RM (2008) MALDI-FTICR imaging mass spectrometry of drugs and metabolites in tissue. Anal Chem 80:5648–5653 Costa AB, Cooks RG (2007) Simulation of atmospheric transport and droplet-thin film collisions in desorption electrospray ionization. Chem Commun 38:3915–3917 Costa AB, Cooks RG (2008) Simulated splashes: elucidating the mechanism of desorption electrospray ionization mass spectrometry. Chem Phys Lett 464:1–8 Crecelius AC, Cornett DS, Caprioli RM, Williams B, Dawant BM, Bodenheimer B (2005) Three-dimensional visualization of protein expression in mouse brain structures using imaging mass spectrometry. J Am Soc Mass Spectrom 16:1093–1099 De Hoffmann E, Charette J, Stroobant V (2007) Mass spectrometry: principles and applications. Wiley, Chichester Debois D, Bralet MP, Le Naour F, Brunelle A, Laprevote O (2009) In situ lipidomic analysis of nonalcoholic fatty liver by cluster TOF-SIMS imaging. Anal Chem 81:2823–2831 Deeley JM, Hankin JA, Friedrich MG, Murphy RC, Truscott RJ, Mitchell TW, Blanksby SJ (2010) Sphingolipid distribution changes with age in the human lens. J Lipid Res 51:2753–2760 Dekker LJ, van Kampen JJ, Reedijk ML, Burgers PC, Gruters RA, Osterhaus AD, Luider TM (2009) A mass spectrometry based imaging method developed for the intracellular detection of HIV protease inhibitors. Rapid Commun Mass Spectrom 23:1183–1188 Delcorte A, Poleunis C, Bertrand P (2006) Stretching the limits of static SIMS with C60. Appl Surf Sci 252:6494–6497 Deutsch E (2008) mzML: A single, unifying data format for mass spectrometer output. Proteomics 8:2776–2777 Dickinson M, Heard PJ, Barker JHA, Lewis AC, Mallard D, Allen GC (2006) Dynamic SIMS analysis of cryo-prepared biological and geological specimens. Appl Surf Sci 252:6793–6796 Dill AL, Ifa DR, Manicke NE, Costa AB, Ramos-Vara JA, Knapp DW, Cooks RG (2009a) Lipid profiles of canine invasive

439 transitional cell carcinoma of the urinary bladder and adjacent normal tissue by desorption electrospray ionization imaging mass spectrometry. Anal Chem 81:8758–8764 Dill AL, Ifa DR, Manicke NE, Ouyang Z, Cooks RG (2009b) Mass spectrometric imaging of lipids using desorption electrospray ionization. J Chromatogr B Anal Technol Biomed Life Sci 877:2883–2889 Djidja MC, Claude E, Snel MF, Scriven P, Francese S, Carolan V, Clench MR (2009a) MALDI-ion mobility separation-mass spectrometry imaging of glucose-regulated protein 78 kDa (Grp78) in human formalin-fixed, paraffin-embedded pancreatic adenocarcinoma tissue sections. J Proteome Res 8:4876–4884 Djidja MC, Francese S, Loadman PM, Sutton CW, Scriven P, Claude E, Snel MF, Franck J, Salzet M, Clench MR (2009b) Detergent addition to tryptic digests and ion mobility separation prior to MS/MS improves peptide yield and protein identification for in situ proteomic investigation of frozen and formalin-fixed paraffin-embedded adenocarcinoma tissue sections. Proteomics 9:2750–2763 Djidja MC, Claude E, Snel MF, Francese S, Scriven P, Carolan V, Clench MR (2010) Novel molecular tumour classification using MALDI-mass spectrometry imaging of tissue micro-array. Anal Bioanal Chem 397:587–601 Dreisewerd K (2003) The desorption process in MALDI. Chem Rev 103:395–425 Eijkel GB, Kaletas BK, van der Wiel IM, Kros JM, Luider TM, Heeren RMA (2009) Correlating MALDI and SIMS imaging mass spectrometric datasets of biological tissue surfaces. Surf Interface Anal 41:675–685 Fletcher JS, Vickerman JC (2010) A new SIMS paradigm for 2D and 3D molecular imaging of bio-systems. Anal Bioanal Chem 396:85–104 Fletcher JS, Lockyer NP, Vaidyanathan S, Vickerman JC (2007) TOF-SIMS 3D biomolecular imaging of Xenopus laevis oocytes using buckminsterfullerene (C-60) primary ions. Anal Chem 79:2199–2206 Fliesler SJ (2010) Lipids and lipid metabolism in the eye. J Lipid Res 51:1–3 Fournier I, Wisztorski M, Salzet M (2008) Tissue imaging using MALDI-MS: a new frontier of histopathology proteomics. Expert Rev Proteomics 5:413–424 Garrett TJ, Dawson WW (2010) Lipid geographical analysis of the primate macula by imaging mass spectrometry, pp 247–260 Garrett TJ, Prieto-Conaway MC, Kovtoun V, Bui H, Izgarian N, Stafford G, Yost RA (2007) Imaging of small molecules in tissue sections with a new intermediate-pressure MALDI linear ion trap mass spectrometer. Int J Mass Spectrom 260:166–176 Gillen G, Fahey A, Wagner M, Mahoney C (2006) 3D molecular imaging SIMS. Appl Surf Sci 252:6537–6541 Girod M, Shi YZ, Cheng JX, Cooks RG (2010) Desorption electrospray ionization imaging mass spectrometry of lipids in rat spinal cord. J Am Soc Mass Spectrom 21:1177–1189 Grasso G, Rizzarelli E, Spoto G (2007) AP/MALDI-MS complete characterization of the proteolytic fragments produced by the interaction of insulin degrading enzyme with bovine insulin. J Mass Spectrom 42:1590–1598 Grey AC, Schey KL (2008) Distribution of bovine and rabbit lens alpha-crystallin products by MALDI imaging mass spectrometry. Mol Vis 14:171–179 Groseclose MR, Andersson M, Hardesty WM, Caprioli RM (2007) Identification of proteins directly from tissue: in situ tryptic digestions coupled with imaging mass spectrometry. J Mass Spectrom 42:254–262 Groseclose MR, Massion PP, Chaurand P, Caprioli RM (2008) Highthroughput proteomic analysis of formalin-fixed paraffin-embedded tissue microarrays using MALDI imaging mass spectrometry. Proteomics 8:3715–3724

123

440 Gross JH (2004) Mass spectrometry. Springer, Berlin Hankin JA, Murphy RC (2010) Relationship between MALDI IMS intensity and measured quantity of selected phospholipids in rat brain sections. Anal Chem 82:8476–8484 Harton SE, Stevie FA, Ade H (2006) Carbon-13 labeling for improved tracer depth profiling of organic materials using secondary ion mass spectrometry. J Am Soc Mass Spectrom 17:1142–1145 Hayasaka T, Goto-Inoue N, Sugiura Y, Zaima N, Nakanish H, Ohishi K, Nakanish S, Naito T, Taguchi R, Setou M (2008) Matrixassisted laser desorption/ionization quadrupole ion trap time-offlight (MALDI-QIT-TOF)-based imaging mass spectrometry reveals a layered distribution of phospholipid molecular species in the mouse retina. Rapid Commun Mass Spectrom 22:3415– 3426 Heeren RMA, Smith DF, Stauber J, Kukrer-Kaletas B, MacAleese L (2009) Imaging mass spectrometry: hype or hope? J Am Soc Mass Spectrom 20:1006–1014 Herring KD, Oppenheimer SR, Caprioli RM (2007) Direct tissue analysis by matrix-assisted laser desorption ionization mass spectrometry: application to kidney biology. Semin Nephrol 27:597–608 Hopfgartner G, Varesio E, Stoeckli M (2009) Matrix-assisted laser desorption/ionization mass spectrometric imaging of complete rat sections using a triple quadrupole linear ion trap. Rapid Commun Mass Spectrom 23:733–736 Hoshi T, Kudo M (2003) High resolution static SIMS imaging by time of flight SIMS. Appl Surf Sci 203–204:818–824 Hsieh Y, Casale R, Fukuda E, Chen JW, Knemeyer I, Wingate J, Morrison R, Korfmacher W (2006) Matrix-assisted laser desorption/ionization imaging mass spectrometry for direct measurement of clozapine in rat brain tissue. Rapid Commun Mass Spectrom 20:965–972 Hu QZ, Noll RJ, Li HY, Makarov A, Hardman M, Cooks RG (2005) The Orbitrap: a new mass spectrometer. J Mass Spectrom 40:430–443 Ifa DR, Gumaelius LM, Eberlin LS, Manicke NE, Cooks RG (2007a) Forensic analysis of inks by imaging desorption electrospray ionization (DESI) mass spectrometry. Analyst 132:461–467 Ifa DR, Wiseman JM, Song Q, Cooks RG (2007b) Development of capabilities for imaging mass spectrometry under ambient conditions with desorption electrospray ionization (DESI). Int J Mass Spectrom 259:8–15 Jackson SN, Wang H-YJ, Woods AS (2005) In situ structural characterization of phosphatidylcholines in brain tissue using MALDI-MS/MS. J Am Soc Mass Spectrom 16:2052–2056 Jackson SN, Ugarov M, Egan T, Post JD, Langlais D, Schultz JA, Woods AS (2007) MALDI-ion mobility-TOFMS imaging of lipids in rat brain tissue. J Mass Spectrom 42:1093–1098 Jacob JT, Ham BM, Keese MM, Cole RB (2005) Identification and comparison of phosphorylated lipids in normal and dry eye rabbit tears by MALDI-TOF MS. Invest Ophthalmol Vis Sci 47:3330–3338 Jun JH, Song ZH, Liu ZJ, Nikolau BJ, Yeung ES, Lee YJ (2010) High-spatial and high-mass resolution imaging of surface metabolites of arabidopsis thaliana by laser desorption-ionization mass spectrometry using colloidal silver. Anal Chem 82:3255–3265 Kang S, Shim HS, Lee JS, Kim DS, Kim HY, Hong SH, Kim PS, Yoon JH, Cho NH (2010) Molecular proteomics imaging of tumor interfaces by mass spectrometry. J Proteome Res 9:1157–1164 Karas M, Hillenkamp F (1988) Laser desorption ionization of proteins with molecular masses exceeding 10,000 daltons. Anal Chem 60:2299–2301 Karas M, Kru¨ger R (2003) Ion formation in MALDI: the cluster ionization mechanism. Chem Rev 103:427–439

123

Histochem Cell Biol (2010) 134:423–443 Karas M, Glu¨ckmann M, Scha¨fer J (2000) Ionization in matrixassisted laser desorption/ionization: singly charged molecular ions are the lucky survivors. J Mass Spectrom 35:1–12 Kelly RT, Page JS, Marginean I, Tang KQ, Smith RD (2008) Nanoelectrospray emitter arrays providing interemitter electric field uniformity. Anal Chem 80:5660–5665 Kertesz V, Van Berkel GJ (2008) Improved desorption electrospray ionization mass spectrometry performance using edge sampling and a rotational sample stage. Rapid Commun Mass Spectrom 22:3846–3850 Kertesz V, Van Berkel GJ, Vavrek M, Koeplinger KA, Schneider BB, Covey TR (2008) Comparison of drug distribution images from whole-body thin tissue sections obtained using desorption electrospray ionization tandem mass spectrometry and autoradiography. Anal Chem 80:5168–5177 Khatib-Shahidi S, Andersson M, Herman JL, Gillespie TA, Caprioli RM (2006) Direct molecular analysis of whole-body animal tissue sections by imaging MALDI mass spectrometry. Anal Chem 78:6448–6456 Kim JH, Ahn BJ, Park JH, Shon HK, Yu YS, Moon DW, Lee TG, Kim KW (2008) Label-free calcium imaging in ischemic retinal tissue by TOF-SIMS. Biophys J 94:4095–4102 Kim Y, Shanta SR, Zhou L-H, Kim KP (2010) Mass spectrometry based cellular phosphoinositides profiling and phospholipid analysis: a brief review. Exp Mol Med 42:1–11 Knochenmuss R, Zenobi R (2003) MALDI ionization: the role of inplume processes. Chem Rev 103:441–452 Konn DO, Murrell J, Despeyroux D, Gaskell SJ (2005) Comparison of the effects of ionization mechanism, analyte concentration, and ion ‘‘cool-times’’ on the internal energies of peptide ions produced by electrospray and atmospheric pressure matrixassisted laser desorption ionization. J Am Soc Mass Spectrom 16:743–751 Kool J, Lingeman H, Niessen W, Irth H (2010) High throughput screening methodologies classified for major drug target classes according to target signaling pathways. Comb Chem High Throughput Screen 13:548–561 Laiko VV, Moyer SC, Cotter RJ (2000) Atmospheric pressure MALDI/ion trap mass spectrometry. Anal Chem 72:5239–5243 Layne GD, Sim KW (2000) Secondary ion mass spectrometry for the measurement of 232Th/230Th in volcanic rocks. Int J Mass Spectrom 203:187–198 Le Naour F, Bralet MP, Debois D, Sandt C, Guettier C, Dumas P, Brunelle A, Lapre´vote O (2009) Chemical imaging on liver steatosis using synchrotron infrared and ToF-SIMS microspectroscopies. PLoS One 4:e7408 Lemaire R, Wisztorski M, Desmons A, Tabet JC, Day R, Salzet M, Fournier I (2006) MALDI-MS direct tissue analysis of proteins: improving signal sensitivity using organic treatments. Anal Chem 78:7145–7153 Lemaire R, Ait Menguellet S, Stauber J, Marchaudon V, Lucot J-P, Collinet P, Farine M-O, Vinatier D, Day R, Ducoroy P, Salzet M, Fournier I (2007) Specific MALDI imaging and profiling for biomarker hunting and validation: fragment of the 11S proteasome activator complex, reg alpha fragment, is a new potential ovary cancer biomarker. J Proteome Res 6:4127–4134 Liu Q, Xiao Y, Pagan-Miranda C, Chiu YM, He L (2009) Metabolite imaging using matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS). J Am Soc Mass Spectrom 20:80–88 MacAleese L, Stauber J, Heeren RMA (2009) Perspectives for imaging mass spectrometry in the proteomics landscape. Proteomics 9:819–834 Malmberg P, Nygren H, Richter K, Chen Y, Dangardt F, Friberg P, Magnusson Y (2007) Imaging of lipids in human adipose tissue by cluster ion TOF-SIMS. Microsc Res Tech 70:828–835

Histochem Cell Biol (2010) 134:423–443 Mange A, Chaurand P, Perrochia H, Roger P, Caprioli RM, Solassol J (2009) Liquid chromatography-tandem and MALDI imaging mass spectrometry analyses of RCL2/CS100-fixed, paraffinembedded tissues: proteomics evaluation of an alternate fixative for biomarker discovery. J Proteome Res 8:5619–5628 Mas S, Touboul D, Brunelle A, Aragoncillo P, Egido J, Laprevote O, Vivanco F (2007) Lipid cartography of atherosclerotic plaque by cluster-TOF-SIMS imaging. Analyst 132:24–26 Mayrhofer C, Krieger S, Raptakis E, Allmaier G (2006) Comparison of vacuum matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI (AP-MALDI) tandem mass spectrometry of 2-dimensional separated and trypsin-digested glomerular proteins for database search derived identification. J Proteome Res 5:1967–1978 McDonnell LA, Heeren RMA (2007) Imaging mass spectrometry. Mass Spectrom Rev 26:606–643 McDonnell LA, Corthals GL, Willems SM, van Remoortere A, van Zeijl RJ, Deelder AM (2010a) Peptide and protein imaging mass spectrometry in cancer research. J Proteomics 73:1921–1944 McDonnell LA, van Remoortere A, van Zeijl RJ, Dalebout H, Bladergroen MR, Deelder AM (2010b) Automated imaging MS: toward high throughput imaging mass spectrometry. J Proteomics 73:1279–1282 Meistermann H, Norris JL, Aerni HR, Cornett DS, Friedlein A, Erskine AR, Augustin A, De Vera Mudry MC, Ruepp S, Suter L, Langen H, Caprioli RM, Ducret A (2006) Biomarker discovery by imaging mass spectrometry: transthyretin is a biomarker for gentamicin-induced nephrotoxicity in rat. Mol Cell Proteomics 5:1876–1886 Mikawa S, Suzuki M, Fujimoto C, Sato K (2009) Imaging of phosphatidylcholines in the adult rat brain using MALDI-TOF MS. Neurosci Lett 451:45–49 Minerva L, Clerens S, Baggerman G, Arckens L (2008) Direct profiling and identification of peptide expression differences in the pancreas of control and ob/ob mice by imaging mass spectrometry. Proteomics 8:3763–3774 Monroe EB, Annangudi SR, Hatcher NG, Gutstein HB, Rubakhin SS, Sweedler JV (2008) SIMS and MALDI MS imaging of the spinal cord. Proteomics 8:3746–3754 Murphy RC, Hankin JA, Barkley RM (2009) Imaging of lipid species by MALDI mass spectrometry. J Lipid Res 50:S317–S322 Nicholson JK, Lindon JC (2008) Systems biology: Metabonomics. Nature 455:1054–1056 Nygren H, Hagenhoff B, Malmberg P, Nilsson M, Richter K (2007) Bioimaging TOF-SIMS: high resolution 3D imaging of single cells. Microsc Res Tech 70:969–974 Ostrowski SG, Van Bell CT, Winograd N, Ewing AG (2004) Mass spectrometric imaging of highly curved membranes during Tetrahymena mating. Science 305:71–73 Pachuta SJ, Cooks RG (1987) Mechanisms in molecular SIMS. Chem Rev (Washington, DC) 87:647–669 Page JS, Tang K, Kelly RT, Smith RD (2008) Subambient pressure ionization with nanoelectrospray source and interface for improved sensitivity in mass spectrometry. Anal Chem 80:1800–1805 Pasilis SP, Kertesz V, Van Berkel GJ, Schulz M, Schorcht S (2008) HPTLC/DESI-MS imaging of tryptic protein digests separated in two dimensions. J Mass Spectrom 43:1627–1635 Patel SA, Barnes A, Loftus N, Martin R, Sloan P, Thakker N, Goodacre R (2009) Imaging mass spectrometry using chemical inkjet printing reveals differential protein expression in human oral squamous cell carcinoma. Analyst 134:301–307 Pierson J, Norris JL, Aerni HR, Svenningsson P, Caprioli RM, Andren PE (2004) Molecular profiling of experimental Parkinson’s disease: direct analysis of peptides and proteins on brain tissue sections by MALDI mass spectrometry. J Proteome Res 3:289–295

441 Pittenauer E, Zehl M, Belgacem O, Raptakis E, Mistrik R, Allmaier G (2006) Comparison of CID spectra of singly charged polypeptide antibiotic precursor ions obtained by positive-ion vacuum MALDI IT/RTOF and TOF/RTOF, AP-MALDI-IT and ESI-IT mass spectrometry. J Mass Spectrom 41:421–447 Pol J, Vidova V, Kruppa G, Kobliha V, Novak P, Lemr K, Kotiaho T, Kostiainen R, Havlicek V, Volny M (2009) Automated ambient desorption-ionization platform for surface imaging integrated with a commercial Fourier transform ion cyclotron resonance mass spectrometer. Anal Chem 81:8479–8487 Reyzer ML, Hsieh YS, Ng K, Korfmacher WA, Caprioli RM (2003) Direct analysis of drug candidates in tissue by matrix-assisted laser desorption/ionization mass spectrometry. J Mass Spectrom 38:1081–1092 Rohner TC, Staab D, Stoeckli M (2005) MALDI mass spectrometric imaging of biological tissue sections. Mech Ageing Dev 126:177–185 Roy S, Touboul D, Brunelle A, Germain DP, Laprevote O, Chaminade P (2005) Imaging mass spectrometry and direct analysis of globotriaosylceramide and galabiosylceramide in tissue. Med Sci 21:55–56 Roy S, Touboul D, Brunelle A, Germain DP, Prognon P, Laprevote O, Chaminade P (2006) Imaging mass spectrometry: a new tool for the analysis of skin biopsy. Application in Fabry’s disease. Ann Pharm Fr 64:328–334 Rubakhin SS, Jurchen JC, Monroe EB, Sweedler JV (2005) Imaging mass spectrometry: fundamentals and applications to drug discovery. Drug Discov Today 10:823–837 Rujoi M, Estrada R, Yappert MC (2004) In situ MALDI-TOF MS regional analysis of neutral phospholipids in lens tissue. Anal Chem 76:1657–1663 Sanders ME, Dias EC, Xu BJ, Mobley JA, Billheimer D, Roder H, Grigorieva J, Dowsett M, Arteaga CL, Caprioli RM (2008) Differentiating proteomic biomarkers in breast cancer by laser capture microdissection and MALDI MS. J Proteome Res 7:1500–1507 Schneider BB, Lock C, Covey TR (2005) AP and vacuum MALDI on a QqLIT instrument. J Am Soc Mass Spectrom 16:176–182 Schwamborn K, Krieg RC, Reska M, Jakse G, Knuechel R, Wellmann A (2007) Identifying prostate carcinoma by MALDI-imaging. Int J Mol Med 20:155–159 Schwartz SA, Reyzer ML, Caprioli RM (2003) Direct tissue analysis using matrix-assisted laser desorption/ionization mass spectrometry: practical aspects of sample preparation. J Mass Spectrom 38:699–708 Schwartz SA, Weil RJ, Johnson MD, Toms SA, Caprioli RM (2004) Protein profiling in brain tumors using mass spectrometry: feasibility of a new technique for the analysis of protein expression. Clin Cancer Res 10:981–987 Schwartz SA, Weil RJ, Thompson RC, Shyr Y, Moore JH, Toms SA, Johnson MD, Caprioli RM (2005) Proteomic-based prognosis of brain tumor patients using direct-tissue matrix-assisted laser desorption ionization mass spectrometry. Cancer Res 65:7674– 7681 Setou M (2010) Imaging mass spectrometry. Springer, Berlin Setou M, Heeren RMA, Stoeckli M, Simma S, Matsumoto M (2007) Mass microscopy. Seikagaku (J Jpn Biochem Soc) 79:874–879 Shimma S, Sugiura Y, Hayasaka T, Hoshikawa Y, Noda T, Setou M (2007) MALDI-based imaging mass spectrometry revealed abnormal distribution of phospholipids in colon cancer liver metastasis. J Chromatogr B Anal Technol Biomed Life Sci 855:98–103 Skold K, Svensson M, Nilsson A, Zhang XQ, Nydahl K, Caprioli RM, Svenningsson P, Andren PE (2006) Decreased striatal levels of PEP-19 following MPTP lesion in the mouse. J Proteome Res 5:262–269

123

442 Snel MF, Fuller M (2010) High-spatial resolution matrix-assisted laser desorption ionization imaging analysis of glucosylceramide in spleen sections from a mouse model of Gaucher disease. Anal Chem 82:3664–3670 Solon EG, Schweitzer A, Stoeckli M, Prideaux B (2010) Autoradiography, MALDI-MS, and SIMS-MS imaging in pharmaceutical discovery and development. AAPS J 12:11–26 Spoto G (2000) Secondary ion mass spectrometry in art and archaeology. Thermochim Acta 365:157–166 Stauber J, Lemaire R, Franck J, Bonnel D, Croix D, Day R, Wisztorski M, Fournier I, Salzet M (2008) MALDI Imaging of formalin-fixed paraffin-embedded tissues: application to model animals of Parkinson disease for biomarker hunting. J Proteome Res 7:969–978 Stauber J, MacAleese L, Franck J, Claude E, Snel M, Kaletas BK, Wiel I, Wisztorski M, Fournier I, Heeren RMA (2010) On-tissue protein identification and imaging by MALDI-ion mobility mass spectrometry. J Am Soc Mass Spectrom 21:338–347 Stoeckli M, Farmer TB, Caprioli RM (1999) Automated mass spectrometry imaging with a matrix-assisted laser desorption ionization time-of-flight instrument. J Am Soc Mass Spectrom 10:67–71 Stoeckli M, Chaurand P, Hallahan DE, Caprioli RM (2001) Imaging mass spectrometry: a new technology for the analysis of protein expression in mammalian tissues. Nat Med 7:493–496 Stoeckli M, Staab D, Staufenbiel M, Wiederhold KH, Signor L (2002) Molecular imaging of amyloid beta peptides in mouse brain sections using mass spectrometry. Anal Biochem 311:33–39 Stoeckli M, Staab D, Schweitzer A (2007) Compound and metabolite distribution measured by MALDI mass spectrometric imaging in whole-body tissue sections. Int J Mass Spectrom 260:195–202 Strohalm M, Kavan D, Novak P, Volny M, Havlicek V (2010) mMass 3: a cross-platform software environment for precise analysis of mass spectrometric data. Anal Chem 82:4648–4651 Sugiura Y, Setou M (2009) Selective imaging of positively charged polar and nonpolar lipids by optimizing matrix solution composition. Rapid Commun Mass Spectrom 23:3269–3278 Sugiura Y, Setou M (2010a) Imaging mass spectrometry for visualization of drug and endogenous metabolite distribution: toward in situ pharmacometabolomes. J Neuroimmune Pharmacol 5:31–43 Sugiura Y, Setou M (2010b) Matrix-assisted laser desorption/ ionization and nanoparticle-based imaging mass spectrometry for small metabolites: a practical protocol. Methods Mol Biol 656:173–195 Sugiura Y, Shimma S, Konishi Y, Yamada MK, Setou M (2008) Imaging mass spectrometry technology and application on ganglioside study; visualization of age-dependent accumulation of C20-ganglioside molecular species in the mouse hippocampus. PLoS One 3:e3232 Sugiura Y, Konishi Y, Zaima N, Kajihara S, Nakanishi H, Taguchi R, Setou M (2009) Visualization of the cell-selective distribution of PUFA-containing phosphatidylcholines in mouse brain by imaging mass spectrometry. J Lipid Res 50:1776–1788 Svatos A (2010) Mass spectrometric imaging of small molecules. Trends Biotechnol 28:425–434 Takats Z, Wiseman JM, Gologan B, Cooks RG (2004) Mass spectrometry sampling under ambient conditions with desorption electrospray ionization. Science 306:471–473 Takats Z, Wiseman JM, Cooks RG (2005) Ambient mass spectrometry using desorption electrospray ionization (DESI): Instrumentation, mechanisms and applications in forensics, chemistry, and biology. J Mass Spectrom 40:1261–1275 Tanaka K, Waki H, Ido Y, Akita S, Yoshida Y, Yoshida T (1988) Protein and polymer analyses up to m/z 100,000 by laser

123

Histochem Cell Biol (2010) 134:423–443 ionization time-of-flight mass spectrometry. Rapid Commun Mass Spectrom 2:151–153 Tang CY, Prueksaritanont T (2010) Use of in vivo animal models to assess pharmacokinetic drug–drug interactions. Pharm Res 27:1772–1787 Todd PJ, Schaaff TG, Chaurand P, Caprioli RM (2001) Organic ion imaging of biological tissue with secondary ion mass spectrometry and matrix-assisted laser desorption/ionization. J Mass Spectrom 36:355–369 Touboul D, Piednoel H, Voisin V, De La Porte S, Brunelle A, Halgand F, Laprevote O (2004) Changes of phospholipid composition within the dystrophic muscle by matrix-assisted laser desorption/ionization mass spectrometry and mass spectrometry imaging. Eur J Mass Spectrom (Chichester, Eng) 10:657–664 Touboul D, Kollmer F, Niehuis E, Brunelle A, Laprevote O (2005) Improvement of biological time-of-flight-secondary ion mass spectrometry imaging with a bismuth cluster ion source. J Am Soc Mass Spectrom 16:1608–1618 Touboul D, Roy S, Germain DP, Chaminade P, Brunelle A, Lapre´vote O (2007) MALDI-TOF and cluster-TOF-SIMS imaging of Fabry disease biomarkers. Int J Mass Spectrom 260:158–165 Trim PJ, Atkinson SJ, Princivalle AP, Marshall PS, West A, Clench MR (2008a) Matrix-assisted laser desorption/ionisation mass spectrometry imaging of lipids in rat brain tissue with integrated unsupervised and supervised multivariant statistical analysis. Rapid Commun Mass Spectrom 22:1503–1509 Trim PJ, Henson CM, Avery JL, McEwen A, Snel MF, Claude E, Marshall PS, West A, Princivalle AP, Clench MR (2008b) Matrix-assisted laser desorption/ionization-ion mobility separation-mass spectrometry imaging of vinblastine in whole body tissue sections. Anal Chem 80:8628–8634 Ullrich M, Burenkov A, Ryssel H (2005) Ion sputtering at grazing incidence for SIMS-analysis. Nucl Instrum Methods Phys Res B Beam Interact Mater Atoms 228:373–377 Van Berkel GJ, Kertesz V (2006) Automated sampling and imaging of analytes separated on thin-layer chromatography plates using desorption electrospray ionization mass spectrometry. Anal Chem 78:4938–4944 Van Berkel GJ, Pasilis SP, Ovchinnikova O (2008) Established and emerging atmospheric pressure surface sampling/ionization techniques for mass spectrometry. J Mass Spectrom 43:1161–1180 Van Vaeck L, Adriaens A, Gijbels R (1999) Static secondary ion mass spectrometry: (S-SIMS) part 1. Methodology and structural interpretation. Mass Spectrom Rev 18:1–47 Venter A, Sojka PE, Cooks RG (2006) Droplet dynamics and ionization mechanisms in desorption electrospray ionization mass spectrometry. Anal Chem 78:8549–8555 Venter A, Nefliu M, Graham Cooks R (2008) Ambient desorption ionization mass spectrometry. Trends Anal Chem 27:284–290 Vickerman JC (1997) Secondary ion mass spectrometry—the surface mass spectrometry. In: Vickerman JC (ed) Surface analysis—the principal techniques. Wiley, Chichester Vidova´ V, Novak P, Strohalm M, Pol J, Havlicek V, Volny M (2010a) Laser desorption-ionization of lipid transfers: tissue mass spectrometry imaging without MALDI matrix. Anal Chem 82:4994–4997 Vidova´ V, Pol J, Volny M, Novak P, Havlicek V, Wiedmer SK, Holopainen JM (2010b) Visualizing spatial lipid distribution in porcine lens by MALDI imaging high-resolution mass spectrometry. J Lipid Res 51:2295–2302 Volny´ M, Turecˇek F (2006) High efficiency in soft landing of biomolecular ions on a plasma-treated metal surface: are doubledigit yields possible? J Mass Spectrom 41:124–126

Histochem Cell Biol (2010) 134:423–443 Volny´ M, Venter A, Smith SA, Pazzi M, Cooks RG (2008) Surface effects and electrochemical cell capacitance in desorption electrospray ionization. Analyst 133:525–531 Vrkoslav V, Muck A, Cvacka J, Svatos A (2010) MALDI imaging of neutral cuticular lipids in insects and plants. J Am Soc Mass Spectrom 21:220–231 Walch A, Rauser S, Deininger S, Ho¨fler H (2008) MALDI imaging mass spectrometry for direct tissue analysis: a new Frontier for molecular histology. Histochem Cell Biol 130:421–434 Wang HYJ, Jackson SN, McEuen J, Woods AS (2005) Localization and analyses of small drug molecules in rat brain tissue sections. Anal Chem 77:6682–6686 Wenk MR (2005) The emerging field of lipidomics. Nat Rev Drug Discovery 4:594–610 Winograd N (2005) The magic of cluster SIMS. Anal Chem 77:142A–149A Wiseman JM, Ifa DR, Song Q, Cooks RG (2006) Tissue imaging at atmospheric pressure using desorption electrospray ionization

443 (DESI) mass spectrometry. Angewandte Chem Int Edn 45:7188–7192 Wisztorski M, Lemaire R, Stauber J, Menguelet SA, Croix D, Mathe OJ, Day R, Salzet M, Fournier I (2007) New developments in MALDI imaging for pathology proteomic studies. Curr Pharm Des 13:3317–3324 Wisztorski M, Croix D, Macagno E, Fournier I, Salzet M (2008) Molecular MALDI imaging: an emerging technology for neuroscience studies. Dev Neurobiol 68:845–858 Yanagisawa K, Shyr Y, Xu BJ, Massion PP, Larsen PH, White BC, Roberts JR, Edgerton M, Gonzalez A, Nadaf S, Moore JH, Caprioli RM, Carbone DP (2003) Proteomic patterns of tumour subsets in non-small-cell lung cancer. Lancet 362:433–439 Zhigilei LV, Leveugle E, Garrison BJ, Yingling YG, Zeifman MI (2003) Computer simulations of laser ablation of molecular substrates. Chem Rev 103:321–347 Zimmerman TA, Monroe EB, Sweedler JV (2008) Adapting the stretched sample method from tissue profiling to imaging. Proteomics 8:3809–3815

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