Nov 17, 2016 - Dan Zhao, Selective recognition of cis-trans-isomers of platinum drugs and the detection of triplex DNA based on fluorescence reversible ...
Accepted Manuscript Title: Selective recognition of cis-trans-isomers of platinum drugs and the detection of triplex DNA based on fluorescence reversible model of quantum dots Author: Xiaoling Xu Fang Gao Xincai Xiao Yan Hu Chaozhen Zhu Dan Zhao PII: DOI: Reference:
S0731-7085(16)31191-8 http://dx.doi.org/doi:10.1016/j.jpba.2016.11.033 PBA 10942
To appear in:
Journal of Pharmaceutical and Biomedical Analysis
Received date: Revised date: Accepted date:
13-8-2016 17-11-2016 19-11-2016
Please cite this article as: Xiaoling Xu, Fang Gao, Xincai Xiao, Yan Hu, Chaozhen Zhu, Dan Zhao, Selective recognition of cis-trans-isomers of platinum drugs and the detection of triplex DNA based on fluorescence reversible model of quantum dots, Journal of Pharmaceutical and Biomedical Analysis http://dx.doi.org/10.1016/j.jpba.2016.11.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Selective recognition of cis-trans-isomers of platinum drugs and the detection of triplex DNA based on fluorescence reversible model of quantum dots Xiaoling Xu, Fang Gao, Xincai Xiao, Yan Hu, Chaozhen Zhu, Dan Zhao*
College of Pharmacy, School of Pharmaceutical Sciences South-Central University for Nationalities, Wuhan, P. R. China, 430074
Graphical Abstract
Highlights
A rapid and simple method for distinguishing cis and trans platinum is proposed. Interactions between polymorphic DNA and cisplatin is studied The selective recognition and sensitive detection of triplex DNA is realized.
Abstract: The identification of spatial structures of drugs and the researches on their interaction mechanism with DNA are always attractive to the researchers. However, their realization is lack of simple and fast method. This paper reports the establishment of multiple-functional detection platform based on the “turn off-on” model of ZnCdSe quantum dots. In this system, ZnCdSe quantum dots work as the fluorescent probe, platinum anti-cancer drugs as the quencher and triplex DNA as the trapping agent. The seemingly similar cisplatin and transplatin exhibited different fluorescent recovery behaviors due to their difference in structure, and thus realized the selective detection of cisplatin and transplatin with the reaction time set at 10min as well as the quantitation of cisplatin over the range of 2.5×10-8-100×10-8M. Based on this, the interactions between platinum anti-cancer drugs and ctDNA as well as polymorphic DNA were further studied, and realized the recognition of triplex DNA. The multiple-functional detection platform integrates the functions of the filtration of high-efficient platinum anti-cancer drugs, the researches on interaction mechanism of drugs, and the recognition of polymorphic DNA, meaningful to the future treatment of viral and cancers based on antisense gene strategy.
Keywords: quantum dots; fluorescence; cis-trans-isomers; triplex DNA
1. Introduction As an excellent type of nano-material, quantum dots （QDs） have become the hotspot of various research fields thanks to their small particle size, excellent fluorescent properties and stabilities [1]. The fluorescent “turn off-on” mode of QDs exhibits strong anti-interference ability, wide application possibility, high selectivity and sensitivity in detections of metal ions, anions, small biochemical molecules [2], proteins and DNA [3-5], and thus attracts strong research interests. Researchers have further applied this mode into the detection of many types of anti-cancer drugs and DNA, as well as the researches on their interaction mechanisms. Diversity of DNAs configuration and the differences in the stereo structures of drugs offer more challenge and opportunities for the application of this fluorescence mode into the detection of drugs and researches in pharmacological mechanism. The recognition and separation of the spatial isomers of drugs, and their interaction mechanism have always been an important research field in pharmacy. The spatial isomers mainly include optical isomers, cis-trans-isomers and enantiomer. As one of the important types of spatial isomers, cis-trans-isomers, though constituted by same elements, exhibit different physicochemical properties, biology activities and pharmacokinetic properties. For instance, the trans-isomer of clopenthioxol can be used as antimicrobial drug while its cis-isomer is effective in sedation and tranquilization [6]. Some teams discovered that the gene-toxicity of cisethylhexylmethoxycinnamate is greater than that of its trans-isomer [7]. Similarly, the
cis-trans-isomers of platinum drugs showed different clinical behaviors. Cisplatin is an important anti-cancer drug, while transplatin was recognized to be inactive in vivo. These properties have been explained by the following reasons: weaker inhibition of DNA replication and transcription by transplatin than by cisplatin adducts; short lifetime of the platinumized-DNA resulted from more rapid repair of transplatin adducts, consistent with the inability of high-mobility group protein HMG1 to recognize transplatin adducts; inability of transplatin to produce 1,2-intrastrand cross-links, which are the most frequent adducts formed by cisplatin[8]. The distinction of cisplatin from transplatin and other platinum complexes is the precondition of precision medicine. The commonly-used detection methods, such as atomic absorption spectrophotometry [9], extraction spectrophotometry [10], UV-vis absorption spectrophotometry [11], are based on the
detection of platinum elements, lacking of the ability of distinguishing the cis-trans-isomers and other platinum complexes. Chromatography [12-14], and electrochemical method based on carbon nanotubes [15, 16], though possessing such ability, require expensive equipment. However, due to its merits, the fluorescence method has also been used to realize the fast and simple detection of platinum drugs [17, 18], but not for the distinction of cis-trans-isomers. Transplatin is the putative impurity in commercial preparations of cisplatin[19] and the existing detection methods often take this into consideration [20,21]. The traditional method for distinguishing between the cis and trans isomers is make them react with thiourea. Cisplatin produces a deep yellow solution of [Pt(Th)4]2+(Th=thiourea), whereas transplatin produces white insoluble trans-[Pt(NH3)2(Th)2]Cl2, thus providing a visual confirmation of the geometry of the complex.[22] Therefore, the development of a fast and simple detection method to cis-trans-isomers of drugs, and the establishment of a multiple-functional platform that integrates detection, mechanism study and drug filtration are of great significance to the pharmacy and cancer treatment. DNA is an important target for anticancer drugs. However, the nucleic acids exhibit rich spatial structures, such as hairpin, pseudoknot, bulge, T-junction, G-quadruplex and triple helical structures. Some research group used tetrahedral hairpin DNA structure and fluorescence “turn off-on” mode to realize the detection of Intracellular telomerase [23]. A team realized the selective detection of telomerase and spot release of anticancer drugs based on fluorescence resonance energy transfer (FRET), and finally established the multi-functional system of cancer detection and target treatment [24]. However, the fluorescence dyes employed in these systems possess obvious drawbacks, including weak fluorescence and instability. Another fluorescent nano-material QDs, by contrast, exhibit obvious merits. The fluorescence of QDs could be quenched by many drug molecules, and be recovered by double-stranded DNA [25-28]. Some researchers have already established the fluorescence “turn off-on” mode based on this fluorescence quenching and recovery phenomenon to study the interaction between double-stranded DNA and drugs, and finally realized the detection of DNA [25-27]. Our group also studied the interactions among QDs, ruthenium complex and DNA based on this fluorescence “turn off-on” mode, and realized the detection of double-stranded DNA [28] and the researches on the interaction mechanism between platinum drugs and single-stranded DNA with different lengths and base sequences [17]. This mode has been further employed to study the interactions
between tetrakis (N-methyl-4-pyridinio) porphyrin and G-quadruplex [29]. Triplex DNA is the combination of a DNA or RNA oligonucleotide fragment with double-stranded DNA through hydrogen bond. It has been widely used in the antisense gene technology, that is, using proper oligonucleotide to form triplex DNA with DNA of virus or virulence gene fragments to interrupt their transcription level, so as to cure the diseases from root [30,32]. Therefore, the studies on the interaction between drugs and three-stranded DNA have become an important research field in antisense gene technology in curing virus infectious diseases and cancers. This paper reports the establishment of a multi-functional platform with ZnCdSe QDs as the fluorescence probe, where based on fluorescence “turn off-on” mode, QDs fluorescence could be quenched by platinum anticancer drugs, and recovered by triplex DNA. The platform integrates the functions of selective recognition of spatial isomer of platinum drugs and the mechanism study on the interaction between drug and triplex DNA. By setting one gene locus in HBV nucleocapsid promote as target sequence and combing it with triplex-forming oligonucleotides (TFO) to form triplex DNA [33], the platform realized the recognition of polymorphic DNA, meaningful to the future treatment of viral and cancers based on antisense gene strategy.
2. Experimental 2.1 Chemicals and Instruments Deionized distilled water was prepared from a Milli-Q-RO4 water purification system (Millipore, USA). Fluorescence spectra were recorded on a LS55 spectrofluorometer (PerkinElmer Company, USA). Unless stated, all the chemicals were of analytical reagent grade or better. Se, NaBH4, CdCl2, KH2PO4, Na2HPO4•12H2O, KCl, NaCl, MgSO4, CaCl2, ZnCl2 were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China), N- acetyl -L cysteine (NAC) from Aladdin Chemistry Co., Ltd. (Shanghai, China). Bovine serum albumin (BSA) and Human serum albumin (HSA) were purchased from Sigma Aldrich (USA). Cisplatin, transplatin and Platinum chloride were purchased from the National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). Calfthymus DNA (ctDNA) was obtained from Solarbio. Cisplatin for injection was obtained from Qilu Pharmaceutical Co., Ltd. Oligonucleotide products came from Sangon Biotech Co., Ltd (Shanghai, China).
Oligonucleotide sequences：1.CCCTCCTCAACCCCCTCCTCT 2.GGGAGGAGTTGGGGGAGGAGA 3.GGGTGGTGTTGGGGGTGGTGT（TFO）
2.2 Methods The same amount of three oligonucleotides were dissolved in the triplex-DNA -formation-buffer (Tris-HCl pH=7.0, 10% sucrose solution, 20 mM Mg2+). After ten times dilution, it was heated at 95 ℃ for 10 min and then maintained at -20℃ for 5 min. The triplex DNA was put into freezer at 4 ℃ overnight to achieve a stable state. The stock solutions containing the platinum drugs (0.1 mM) and AgNO3 (0.15 mM) were preserved in darkness for 12 h. The platinum drugs were precipitated through centrifugation at 10000 rpm for 10 min. Then it was diluted 5 times after filtration. The same amount of Platinum chloride was operated with the same method while adding twice amount of AgNO3. ZnCdSe QDs were synthesized by our laboratory [34]. Samples containing ZnCdSe QDs, buffer solution (PBS, 50 mM, pH=7.8) and different amounts of platinum drugs were made up to 1mL. The emission spectrum of the solution was then measured 10 min later. All optical measurements were performed at room temperature under ambient conditions, and the excitation wavelength (λex) was 310 nm. The diluted platinum drugs interacted with ctDNA or triplex DNA for 2 h at the temperature of 37 ℃. Samples containing ZnCdSe QDs, buffer solution (PBS, 50 mM, pH=7.8), platinum drugs and ctDNA or different amounts of triplex DNA solution were made up to 1 mL. The emission spectrum of the solution was then measured 10 min later.
3. Results and discussion 3.1 Detection of stereo isomer of platinum anticancer drugs 3.1.1 QDs fluorescence quenching by platinum drugs At the initial stage of research, it is discovered that platinum drugs exhibited better quenching ability to QDs fluorescence after their hydroxylation. The hydroxylation process, in common operation, usually takes three days. To enhance the hydroxylation efficiency and the repeatability
of the experiments, silver nitrate was used to speed up the hydroxylation process of platinum drugs. Fig. S1 to S3 indicate that the QDs are stable in an extensive range of pH values, ionic intension and standing time. The interaction time between cisplatin and QDs, and its quenching ability to QDs fluorescence were firstly examined. As shown in Fig. S4, cisplatin (1.0×10-6 M） exhibits good quenching ability to the fluorescence of QDs（1.14×10-6 M）. The fluorescence was quenched to 62% of the original intensity after ten minutes, and then stayed stable. The reaction time of afterward experiments was thus set as 10 min. The quenching abilities of different platinum drugs were then investigated. As shown in Fig. 1, cisplatin and transplatin possess similar quenching ability (38% of the original intensity), while the quenching ability of platinum chloride is much stronger (0.5% of the original intensity). The difference in quenching ability originates in the structural difference of these three platinum drugs (Scheme.1). The hydroxylation process deprives the two chlorine atoms away from cisplatin and transplatin, while platinum chloride lost four chlorine atoms in this process, which brings more positive charges and vacant electron tracts, beneficial to the acceptance of electrons from QDs and electrostatic combination with negatively-charged ZnCdSe QDs. Therefore, platinum chloride, thanks to its more chlorine atoms on the surface, exhibits stronger quenching ability to QDs fluorescence. Since the quenching behavior of both cisplatin and transplatin is the result of photo-induced electron transfer effect, the quenching abilities of drugs greatly depend on their charges rather than on their stereo structures. This one-directional quenching mode, shows its ability in distinguishing platinum chloride from cisplatin and transplatin because of their great structural difference, while for cisplatin and transplatin, the cis-trans-isomers with same element compositions, this mode loses its effectiveness.
3.1.2 The stereo structure recognition of cisplatin and transplatin To further realize the effective distinction of cisplatin and transplatin, the two-directional fluorescence “turn off-on” mode was used to examine the recovery behavior of ctDNA to the quenching system. As shown in Fig. 2a, the addition of ctDNA could recover the fluorescence of QDs quenched by cisplatin, but could not recover the fluorescence quenched by transplatin (Fig.
2b). This difference in recovery behavior shows the possibility in distinguishing cisplatin and transplatin by fluorescence “turn off-on” mode. To exclude the possible interference from ctDNA to the fluorescence, ctDNA was added into pure solution of QDs. As shown in Fig. S5, the fluorescence of QDs stays stable when the concentration of ctDNA is in the range of 5.0×10-6-2.0×10-4 M, which means the fluorescence recovery is the result of the interaction between cisplatin and ctDNA, and the difference in recovery behavior originates in the structural difference of cisplatin and transplatin. The structures of cisplatin and transplatin are greatly alike, and their mere difference is the positions of two chlorine atoms on the surface. The chlorine atoms in cisplatin are in opposite position while the chlorine atoms in transplatin are in adjacent position. Therefore there must be a high degree of selectivity for binding sites on DNA by these two molecules. The cis-isomer requires two groups about 3.3 Å apart on the same side of the molecule whereas the tram isomers can only bind two groups about 5.0 Å apart approaching from opposite sides of the molecule. Transplatin cannot lead to an inter-strand cross-link without the deformation of a short section of the DNA helix because the N-7 groups of guanosine residues on opposite strands are over 8 Å apart with bulky groups between [8,35] . When it comes to cisplatin, it often forms 1,2-intrastrand cross-link with the N(7) positions of two adjacent guanosines which can be recognized by HMG domain proteins while transplatin cannot bring this kind of binding [35,36]. The geometry of the cisplatinated d(GpG) fragment could be retained in double helical DNA [31], so the well-matched combination renders the formed platinumized-DNA more stable attributed to that retained helical structure. By contrast, since the distance between the chlorine atoms in transplatin is shorter than that between the nitrogen atoms of DNA sequence [35], it leads to the obvious deformation of double helical structure during the formation of inter-strand-cross-link thus harm its stability (Scheme. 2). Because of this difference, the addition of ctDNA could only recovery the fluorescence quenched by cisplatin, and ensures the selectivity of the two-directional fluorescence “turn off-on” mode. Additionally, we have done some other experiments to reveal the disparity of recovery at different concentrations (Fig. S6-S8). It can be concluded that the increasing concentration of drug is conducive to distinguish cis and trans platinum drugs and there is no obvious difference when the concentration is less than 2.0×10-7 M. This mode could be further used to filtrate and identify DNA-targeted anticancer drugs in effective concentration range, even
though the drug and other interfering compounds all possess the quenching ability to QDs fluorescence.
3.1.3 The quantitative detection of cisplatin The quantitative relationship between the concentration of cisplatin and fluorescence quenching ability has been examined to realize further quantitative detection of cisplatin. The relationship follows “Stern-Volmer” equation: F0/F=1 + KSV[M] where F and F0 are the fluorescence intensities in the absence and presence of cisplatin, [M] is the concentration of cisplatin and KSV is the quenching constant. As shown in Fig. 3, with the increase of cisplatin concentration, the fluorescence intensity gradually quenches within 10 min. Three parallel experiments show that the concentration of cisplatin and the fluorescence intensity follow excellent linear relationship in the range of 2.5×10-8-100×10-8 M with the best R square at 0.99824.
3.2 The recognition and detection of polymorphic DNAs In the fluorescence “turn off-on” mode, the selection of the quencher and the scavenger is important for the system. Based on the above-mentioned experiments, this mode has successfully realized the recognition and detection of spatial isomer of the platinum anti-cancer drugs. As a common scavenger, DNA also plays an important role in the detection. The charges on the DNA and its spatial size would greatly determine the form and ability of its combination with the quencher, and the studies on polymorphic DNAs’interaction with cisplatin-QDs system is of significance to the understanding of the pharmacological mechanism and the application of anti-genetic technology. By setting one gene locus in HBV nucleocapsid promote as target sequence, and combing it with triplex-forming oligonucleotides (TFO) to form triplex DNA, the reaction of the fluorescence “turn off-on” mode to different morphic DNAs (single-stranded, double stranded and triplex DNAs) has been investigated. As shown in Fig. 4, after the QDs fluorescence intensity was quenched to 35.8% of its original intensity by 1.2×10-6 M cisplatin, the addition of 1.25 nM DNA would recover the fluorescence intensity with the reaction time was also
set at 10 min, regardless of DNA type. However, the recovery abilities of DNAs are different. The single-stranded DNA (sequence 2) recovers the intensity to 43.4% of its original intensity, double stranded DNA 55.2% (sequence 1-2) and triplex DNA 64.7%. It is worth noting that when the concentration of double stranded DNA increases to 2.5 nM，the recovery level no longer ascends. The recovery ability of triplex DNA surpasses that of the single-stranded and double stranded ones. The interaction mechanisms of single-stranded (sequence 2) and triplex DNA are illustrated in Scheme 3.The fluorescence of QDs is quenched by cisplatin through electron transfer effect. Since DNA is negatively-charged, the addition of DNA could combined with positively-charged hydrolysate of cisplatin, draw it away from the surface of QDs, and thus recover the fluorescence. The similar mechanism have been proposed by some groups.[37,38] However, compared with single and double-stranded DNA, triplex DNA possesses more negative charges and larger spatial structure, which is beneficial to the interaction between cisplatin and DNA and the break-up of the electron transfer, and consequently exhibit better recovery abilities. The impact of DNA concentration to the fluorescence intensity was then investigated. As shown in Fig. 5, with the increase of concentration of triplex DNA, the fluorescence intensity gradually recovers. The fluorescence recovers 70% when the concentration of DNA increases from 0.0625 nM to 1.95 nM, and three parallel experiments show that the relative recovery rate F2/F0 stays in excellent linearity with concentration. The calculated linear range is 0.0625 -1.95 nM with the best R at 0.998. The fluorescence “turn off-on” mode has been proven to possess the function of multi-target recognition and detection. The operation is simple and highly sensitive. The realization of the detection to three-stranded DNA formed by DNA fragments of HBV virus is meaningful to the anti-genetic treatment of hepatitis B virus, and the direct illustration of three-stranded DNA numbers through fluorescence enhancement could quantify the treatment, and offers new route for the detection of other disease-related triplex DNA. To examine the selectivity of the fluorescence “turn off-on” mode in its detection of triplex DNA, several common interferents have been chosen in the interference tests. The serum of mice was diluted 5 times for the further detection. As shown in Fig. 6, three parallel experiments show the addition of Na+, K+, Ca2+, Zn2+, (1.0×10-5 M） 、HAS (1.0 μg mL-1）、serum of mice (0.5%) and the commonly-used excipient mannitol (2×10-4 M) could not produce obvious fluorescence recovery phenomena even at high concentration. The common interferents, such as HAS, mannitol
and other ions, lacking of helical structural of DNA, do not have the ability to combine with the quencher. The fluorescence “turn off-on” mode exhibits excellent anti-interference ability with satisfactory detection limit, which provides promising outlook in its application in the detection of practical samples. In addition, we have also done some other relevant interference experiments. Similarly, we investigated the effects of the above substances on the quenching system. As shown in Fig. S9, three parallel experiments show the common distractors did not bring out the quenching behavior. Besides, we chose Na+, K+, Ca2+, Zn2+ (1.0×10-5 M） 、mannitol (2×10-4 M) and serum to configure two kinds of mixed samples, (Fig. S10) the first one contains the distractors, cisplatin (1.0×10-6 M) and QDs (black bars). The second one were made up by distractors above, cisplatin (1.0×10-6 M), ctDNA (3.0×10-6 M) and QDs (blue bars). In order to study the effect of serum on the detection more clearly, we investigated the interference of serum which was diluted 5 times (Sample 1) and the pure one (Sample 2). As shown in Fig. S10, sample 1 indicates that both the quenching experiment and the recovery process are not affected by the existing interfering substances. However, the fluorescence intensities were enhanced by 24.6% and 32.7% during the quenching and recovery process when the pure serum (2.5%) was used (Sample 2).
3.3 Determination of cisplatin in real samples To assess the applicability of the nano-sensor to real samples, cisplatin for injection was prepared by dilution. The solution was added with appropriate amounts of cisplatin and the final measured cisplatin contents in all samples were derived from the standard curves and regression equations (F0/F1=1.0.182+0.00151 [c], R=0.9993). The results are summarized in Table 1. Significantly, the recovery of the supplemented cisplatin was above 90% and the RSD were generally satisfactory. These results demonstrate that the proposed assay strategy could be acceptable in real samples, indicating that it has potential application in the sensing field and analytical detections.
4. Conclusion Based on the interaction between ZnCdSe QDs, platinum drugs and polymorphic DNA, a multifunctional platform has been established. With ZnCdSe QDs as the fluorescence probe, the platform has been used to identify cisplatin from transplatin. Cisplatin and transplatin could quench the fluorescence and exhibit same quenching ability, while the difference in their interaction with ctDNA caused by their structural difference makes a simple distinction of cisplatin from transplatin. The platform realized qualitative and quantitative detection of cisplatin, and further proved the anticancer mechanism of cisplatin in its interaction with DNA. Furthermore, the platform also proved its ability in detection of triplex DNA based on the different recovery ability of single/double-stranded DNA and triplex DNA. The platform, integrating the functions of identification of drug stereo isomers, qualitative and quantitative detection of both drugs and three-stranded DNA, and mechanism study of the interaction between anticancer platinum drugs and DNA, offers experiment basis and new route for the simple and fast recognition of spatial isomers of drugs, and treatment of viral diseases and cancers. The detection of polymorphic DNA is also meaningful to the combination of traditional medication and burgeoning gene therapy, opening up a way of integration of multiple therapies.
Acknowledgements This research was supported by Natural Science Foundation of Hubei Province (2016CFB615), the Fundamental Research Funds for the “Central Universities”, South Central University for Nationalities (CZY15020, CZW15017) and the National Science Foundation of China (21105130).
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Sheet of figure captions
Fig. 1 Emission spectroscopy of QDs upon addition of the same amount of cisplatin, transplatin and platinum chloride ( 9.0×10-7 M ).
Fig. 2 Influence of (a) cisplatin/ (b) transplatin (9.0×10-7 M) and ctDNA ( 4.0×10-6 M ) on the emission behavior of ZnCdSe QDs. (The reaction time was set at 10 min.)
Fig. 3 Emission spectra of QDs upon addition of increasing amount of cisplatin with excitation at 310 nm. Inset: Stern–Volmer plot of QDs quenched by cisplatin. ([cisplatin] = 0, 2.5, 5.0, 10.0, 20.0, 40.0, 60.0, 85.0, 100.0×10-8 M.).
Fig. 4 Fluorescence spectra represent the comparison of restoration of QDs–cisplatin system in the presence of different ssDNA and triplex DNA.（Ccisplatin =1.2×10-6 M, CDNA=1.25 nM）
Fig. 5 The fluorescence recovery by different amounts of triplex DNA. (From bottom to top, Ctriplex DNA= 0, 0.0625, 0.125, 0.25, 0.5, 1.0, 1.25, 1.6, 1.95 nM, CCisplatin=1.0×10-6 M)
Fig. 6 Effects of different metal ions (1.0×10-5 M), HSA (1.0 μg mL-1) and triplex DNA (1.95 nM) on the relative fluorescence intensity (F1/F0) of ZnCdSe QDs-cisplatin system. ( [cisplatin]=7.0× 10-7 M)
Scheme. 1 Structure of cisplatin, transplatin and platinum chloride.
Scheme. 2 Schematic illustration of the possible combination of ctDNA and cisplatin (left)/ transplatin (right).
Scheme. 3 Schematic illustration of QDs-cisplatin-DNA system.
Table 1 Determination of cisplatin in real samples (cisplatin for injection) Samples 1 2 3
Cisplatin supplemented -7
4.13×10 M 6.66×10-7 M 9.0×10-8 M
Cisplatin measured -7
3.96×10 M 6.14×10-7 M 9..66×10-8 M
Recovery (%)
RSD（n=3）
95.6% 92.1% 107.3%
1.4% 2.5% 1.9%
