CURRENT TOPICS IN NUTRACEUTICAL RESEARCH Vol. 13, No. 4, pp. 259-266, 2015 ISSN 1540-7535 print, Copyright © 2015 by New Century Health Publishers, LLC www.newcenturyhealthpublishers.com All rights of reproduction in any form reserved
GREEN SYNTHESIS AND STABILIZATION OF GOLD NANOPARTICLES VIA CARBOXYMETHYLATED CURDLAN Jing-Kun Yan, 2Yao-Yao Wang and 2Hai-Le Ma
1,2
The Key Laboratory of Carbohydrate Chemistry & Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, Jiangsu, China; and 2School of Food & Biological Engineering, Jiangsu University, Zhenjiang, 212013, China 1
[Received June 15, 2015; Accepted August 23, 2015] [Communicated by Guest Editor Prof. Zhao-Jun Wei]
ABSTRACT: In this work, a novel and simple method is developed for the green synthesis of gold nanoparticles (AuNPs) by carboxymethylated curdlan (CMC), which served as both reducing and stabilizing agent in an aqueous medium. The synthesized AuNPs were characterized by UV-Vis spectroscopy, HR-TEM, DLS, XRD and FT-IR measurements. Results indicate that the particle size decreases with increase in reaction time and CMC concentration. The as-synthesized AuNPs were spherical and monodispersed with a mean particle size of ~16 nm. FT-IR spectra indicated that the as-synthesized AuNPs could readily bind covalently with the carboxylate groups of CMC molecules in the reaction medium. During the synthesis process, the heat treatment of the CMC and HAuCl4 suspension could induce the conformation transition from the triple helix to single flexible chains. In addition, the as-prepared AuNPs exhibit almost negligible cytotoxicity against the MCF-7 cell lines. KEY WORDS: Carboxymethylated curdlan, Characterization, Cytotoxicity, Gold nanoparticles, Green Synthesis Corresponding Author: Dr. Jing-Kun Yan, The Key Laboratory of Carbohydrate Chemistry & Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, Jiangsu, China; and School of Food & Biological Engineering, Jiangsu University, Zhenjiang, 212013, China; Tel: +08615952819661; E-mail:
[email protected]; jkyan27@ ujs.edu.cn INTRODUCTION In recent years, biomolecules and bio-organisms are gaining considerable attention in developing “green” approaches for the feasible synthesis of gold nanoparticles (AuNPs). The biomolecules-assisted green synthesis of nanomaterials has emerged as a simple and viable alternative for conventional synthesis methodologies. In general, the toxic reducing agents,
such as hydrazine, sodium borohydride (NaBH4), and N, N-Dimethylformamide frequently used in conventional synthesis (Das et al., 2011; Esumi et al., 2003; Mucic et al., 1998; Singaravelu et al., 2007). Of the different biomolecules, polysaccharides isolated from plants, animals, and microorganisms are regarded nontoxic, biocompatible, biodegradable, and stable molecules, which could potentially develop for the “green” synthesis of nanoparticles. Especially, polysaccharides are considered as promising candidates for the preparation of AuNPs due to the presence of abundant hydroxyl groups and other functional groups, including carboxyl (COO−) and amino (NH2+) groups. In 2003, Raveendran et al. firstly demonstrated a facile “green” method for synthesis of metal nanoparticles using glucose as the reducing agent and starch as the stabilizing agent (Raveendran et al., 2003). Up to now, there are many polysaccharides and their derivatives have been developed for the “green” synthesis of AuNPs, such as cyclodextrin (Huang et al., 2009), chitosan (Huang et al., 2007), cellulose (Tan et al., 2010), pullulan (Choudhury et al., 2014), dextran (Wang et al., 2010), glucan (Jia et al., 2013; Sen et al., 2013), and alginate (Saha et al., 2009). However, further developments are still warranted for the effective utilization of polysaccharides as both reducing and stabilizing agents for the “green” synthesis of AuNPs in an aqueous medium. Curdlan, which is a bacterial polysaccharide produced by Alcaligenes faecalis, has a linear structure composed entirely of β- (1, 3)-D-glucan (Harada et al., 1966; 1968). It is widely used in foods, pharmaceutical, and cosmetic applications due to its strong bioactivity and its ability to form physical hydrogels (Cui et al., 2011; Lehtovaara and Gu, 2011; Nishinari et al., 2009; Zhan et al., 2012; Zhang and Edgar, 2014). However, curdlan is insoluble in water, which limits its biological applications, particularly in the food industry and biomedicine. Carboxymethylation has been considered as one of the most effective approaches to improving the water-
260 Green synthesis of gold nanoparticles solubility and bioactivities of curdlan (Jin et al., 2006; Ohya et al., 1994). More specifically, carboxymethylated curdlan (CMC) is being widely used in the preparation of nanoparticles for biomedical applications. For instance, Lee et al. demonstrated the synthesis of superparamagnetic iron oxide nanoparticles (SPIN) capped with CMC for use in cellular and in vivo imaging applications. Accordingly to that study, the stability and dispersibility of SPIN in water were greatly improved with the introduction of the CMC moiety (Lee et al., 2009). More recently, CMC has been used as both reducing and stabilizing agent for the green synthesis of silver nanoparticles (AgNPs) in aqueous solutions by various methods (Jin et al., 2006; Ohya et al., 1994). However, to the best of our knowledge, there are no studies reported so far on the green synthesis of AuNPs in CMC solution. Therefore, in the present work, a facile and simple approach is employed for the “green” synthesis of polysaccharide-capped AuNPs by using CMC as both reducing and stabilizing agent in an aqueous medium. The as-prepared AuNPs in CMC solution were investigated by UV-Vis absorption spectroscopy, high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and Fouriertransform infrared (FT-IR) spectroscopy analyzes. Based on the results obtained, the possible mechanism underlying the formation of AuNPs in CMC solution is proposed. Furthermore, the in vitro cytotoxicity of the prepared CMCAuNPs is also evaluated. MATERIALS AND METHODS Materials and chemicals Commercial curdlan (Mw: 1.1×106 g/mol) purchased from Wako Pure Chemical Co., Japan. Hydrogen tetrachloro aurate (III) tetrahydrate (HAuCl4·4H2O, 99%), 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) was obtained from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). Synthesis of carboxymethylated curdlan (CMC) Carboxymethylated curdlan (CMC) was prepared according to the method reported in the literature (Jin et al., 2006). The degree of substitution (DS) of CMC was 0.75 units of carboxymethyl group per glucose unit in curdlan, as estimated according to electric conductimetric titration (Saito, and Isogai, 2004). The weight-average molecular weight (Mw) and molecular weight distribution (MWD) of CMC were determined by the size-exclusion chromatography with multiangle laser-light scattering (SEC-MALLS) analysis described in our previous study (Yan et al., 2014). The results showed that the Mw and MWD of CMC were estimated to be 6.3 × 105 g/mol and 1.57, respectively. Preparation of CMC-stabilized gold nanoparticles (CMCAuNPs) For the synthesis of AuNPs, a stock solution of CMC, with
concentrations ranging from 0.5 to 2.0 mg/mL, was prepared under continuous stirring at room temperature. Subsequently, 2.0 mL of the stock solution of CMC was added to an equal volume of HAuCl4 solution at different concentrations of 0.5, 1.0, 1.5, and 2.0 mM, respectively. The resulting suspensions were stirred gently at the desired temperature (100 °C) for different reaction times (15-120 min) to yield AuNPs. Characterization of CMC-AuNPs UV-Vis absorption spectra of the AuNPs in CMC solutions recorded on a Perkin-Elmer Lambda 35 spectrophotometer in the wavelength range of 300-600 nm at an interval of 1.0 nm. A digital camera was used to observe the changes in the color of the solutions. The size and morphology of the as-synthesized CMC-AuNPs were determined with HR-TEM (Tecnai 12, Philips, 120 kV). The particle size and the size distribution of as-prepared AuNPs were measured by using DLS on a Malvern Zetasizer Nano (3000 SHA Malvern Instruments Ltd., UK) at 632.8 nm and scattering angle of 90°. The crystal structure of the nanoparticles was analyzed by using wide-angle X-ray diffraction (XRD, D8-Advance, Bruker, Co., Germany) with Cu Kα radiation (λ = 0.15406 nm) at 40 kV and 40 mA. The scattering angle (2θ) was in the range of 30°-80° with a step speed of 4°/min. The elemental composition of the nanoparticles was analyzed by using EDX (Inca Energy-350, Oxford Co., UK) attached to the SEM (JSM-7001F, JEOL Ltd., Japan, 5kV). The CMC and freeze-dried CMC-AuNPs were used for Fourier-transform infrared (FT-IR) analysis. The FT-IR analysis was performed on a Nexus 670 FT-IR spectrometer (Thermo Nicolet Co., USA) in the wavenumber range of 500–4000 cm−1 with KBr pellets and referenced against air. In vitro cytotoxicity assay The in vitro cytotoxicity of the as-prepared CMC-AuNPs was evaluated by using the MTT method. The MCF-7 (human breast carcinoma cell line) was maintained in RPMI 1640 medium (10% FBS, 1% penicillin-streptomycin; 5% CO2 at 37 ºC). The cells were seeded in a 96-well plate (104 cells/well) and incubated for 24 h. Subsequently, different concentrations (0-0.5 mg/mL) of CMC-AuNPs solutions were added to the designated wells and further incubated for 72 h. After that, the cell viability was determined by measuring the absorbance at 492 nm. The mean absorbance value of three experiments expressed as the percentage of cell viability as compared to the control. RESULTS AND DISCUSSION Effect of reaction time on the synthesis of AuNPs According to recent studies (Leung et al., 2010; Wu et al., 2012), carboxymethylated curdlan (CMC) is a negatively charged curdlan derivative that can use as both reducing and stabilizing agent for the preparation of AgNPs. Motivated by this concept, in this work, we have developed a facile and green
Green synthesis of gold nanoparticles 261 method for the preparation of AuNPs using CMC as both reducing agent and stabilizing agent in an aqueous medium. Figure 1 shows the UV-Vis absorption spectra of AuNPs prepared by using 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 °C for different time intervals. After an incubation period of 15 min, the UV-Vis spectra exhibited a broad absorption band at around 550 nm, which is a typical surface plasmon resonance (SPR) band of AuNPs. This indicates the formation of AuNPs (Szunerits and Boukherroub, 2006). As the reaction time increased to 60 min, we could observe a gradual increase in the absorption intensity. Furthermore, the absorption peak slightly blue-shifted from about 550 nm to 530 nm, and the bands became much narrower with the increase in reaction time from 15 min to 60 min. It may associate to the change in refractive index of the reaction medium due to chemical changes occur during reaction (Castillo-López and Pal, 2014). However, the intensity of the peak at around 530 nm remains unchanged with an increase in reaction time for up to 90 min or even 120 min, suggesting the complete formation of AuNPs. As can be seen from the inset image shown in Figure 1, the suspension of HAuCl4 and CMC is initially colorless. After incubation at 100 °C, the color of the solution changes from blue or black to wine red with an increase in reaction time from 15 min to 60 min. As is well known, nanoparticles with different shapes appear in different colors, which can use as a visual evidence for estimating the shape of the as-prepared nanoparticles. In general, golden yellow, wine red, blue or black color of the solution can be associated with the formation of metallic gold, spherical AuNPs, and gold nanorods, respectively (Burda et al., 2005; Thakor et al., 2011). In this study, during the reaction period of 15-30 min, the color of the solution changed to blue or black, suggesting the formation of gold nanorods. With the increase in reaction time to 60 min, the
color of the solution changed to wine red color, indicating the formation of spherical AuNPs. These results indicate that the shape of the AuNPs formed by the reaction of CMC and HAuCl4 in the aqueous medium can tune by the adept control of the reaction time.
FIGURE 1. UV-vis absorption spectra of CMC-AuNPs prepared with 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 ºC for different reaction times (inset images: solution color at different reaction times).
FIGURE 2. UV-vis absorption spectra of CMC-AuNPs prepared by 2.0 mM HAuCl4 and different concentration of CMC at 100 ºC for 60 min (inset images: solution color at different concentration of CMC).
0
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Effect of CMC concentration on the synthesis of AuNPs According to previous studies (Wu et al., 2012), the concentration of CMC has a significant influence on the formation of AgNPs. Therefore, in the present study, we analyzed the effects of CMC concentration on the synthesis of the as-prepared AuNPs. Figure 2 shows the UV-Vis absorption spectra of CMC-AuNPs prepared by adding 2.0 mM HAuCl4 and CMC of concentrations ranging from 0.5 mg/mL to 2.0 mg/mL at 100 °C for 60 min. Irrespective of the concentration of CMC, the absorption spectra showed the characteristic SPR band of AuNPs in the wavelength range of 500-600 nm. With the increase in the concentration of CMC from 0.5 mg/mL to 2.0 mg/mL, the intensity of the absorption peak gradually increased and became much narrower. This may be indicative of the formation of more number of AuNPs with narrow size distribution. In addition, the Maxima of the SPR band gently blue-shifted from 550 nm to 530 nm, indicating the decrease in particle size with the increase in CMC concentration from 0.5 mg/mL to 2.0 mg/mL. The effect of CMC concentration on the formation of AuNPs was also evaluated by visually observing the color changes in the solution. As can be seen from the inset image shown in Figure 2, the color of the solution changes from light blue to blue or black color and subsequently to wine red color with an increase in the concentration of CMC from 0.5 mg/mL to 2.0 mg/mL. This may indicate that the shape of the as-prepared particles can be also tuned by controlling the concentration of CMC.
0.4 0.3 0.2
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262 Green synthesis of gold nanoparticles mM, the intensity of the maximum absorption peak ranging from 500 to 600 nm increased gradually and blue-shifted from 550 nm to 530 nm. These results demonstrate that the concentration of HAuCl4 has an influence on the amount and particle size of the as-synthesized AuNPs. More interestingly, the width of the characteristic SPR band remained almost FIGURE 3. UV-vis absorption spectra of CMC-AuNPs unchanged with the increase in the concentration of HAuCl4. prepared with 2.0 mg/mL CMC and different concentration This may indicate that the as-prepared AuNPs showed spherical of HAuCl4 at 100 ºC and 60 min. shape and uniform size, irrespective of the concentration of 0.6 0.6 HAuCl4. According 0to mMthe theory proposed by Mie (Mie, 0 mM 0.5 mM 1908), small spherical nanocrystals show single SPR band, 0.50.5 mM 1.0 mMshow two or three bands, depending while anisotropic particles 0.5 1.0 mM 1.5 mM on their shape. In this study, the AuNPs prepared by using 1.5 mM 2.0 mM 2.0 mg/mL CMC and different concentrations of HAuCl4 0.42.0 mM exhibited a single SPR band in the wavelength range of 5000.4 600 nm. This result indicates that the as-prepared AuNPs are 0.3 small, well-dispersed, and spherical in shape. 0.3 Characterization of CMC-AuNPs Figure 4(A) shows the typical TEM image of the as-prepared 0.2 AuNPs with 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 0.2 °C for 60 min. It can be clearly seen that the as-synthesized AuNPs are isotropic and well-dispersed spherical particles 0.1 400 450 500 550an average 600 size650 with of ~16 700 nm. The size-dependent SPR and 0.1 the wine color of the as-synthesized AuNPs suggested that a 400 450 500 550 600 650 700 Wavelength (nm) mean of ~16 nm was reliable. The histogram showing the Wavelength (nm) absorption spectra of CMC-AuNPs prepared with 2.0 mg/mL was FIGURE 3. UV-vis CMC and particle size distribution of the as-prepared AuNPs (Figure
Absorbance
Absorbance
Effect of HAuCl4 concentration on the synthesis of AuNPs Figure 3 shows the UV-Vis absorption spectra of CMCAuNPs prepared by using 2.0 mg/mL CMC and different concentrations of HAuCl4 at 100 °C for 60 min. With an increase in the concentration of HAuCl4 from 0.5 mM to 2.0
different concentration of HAuCl4 at 100 ºC and 60 min.
FIGURE 4. (A) Typical TEM image, (B) Particle size distribution histogram, (C) XRD patterns, and (D) EDX of CMC-AuNPs obtained by 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 ºC for 60 min.
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FIGURE 4. (A) Typical TEM image, (B) Particle size distribution histogram, (C) XRD patterns, and (D) EDX of CMC-AuNPs obtained by 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 ºC for
Green synthesis of gold nanoparticles 263 4B), as determined by using DLS, indicates a mean particle size of around 20 nm. Intriguingly, the particle size of the assynthesized AuNPs investigated by DLS was larger than that observed by HR-TEM. This may explain on the basis of the sample preparation process. The particle size determined by TEM is the actual diameter (dry state) of the nanoparticles. On the other hand, the particle size determined by DLS is indicative of the hydrodynamic diameter (hydrated state). Figure 4C shows the XRD patterns of AuNPs prepared by using 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 °C for 60 min. The diffraction peaks observed at 2θ values of 38.2°, 44.4°, 64.7°, and 77.7° correspond to (111), (200), (220), and (311) planes, respectively, of the face-centered cubic (fcc) gold. The XRD patterns clearly illustrate the crystalline nature of the AuNPs formed in the present study. Figure 4D shows the EDX spectra of the nanoparticles. The strong and typical optical emission peak in the EDX spectrum at approximately 200 eV can reveal the presence of the Au in the sample. FT-IR analysis In this work, FT-IR analysis was employed to explore the possible interaction of AuNPs with CMC. The FT-IR spectra of CMC and CMC-AuNPs prepared by 2.0 mg/mL CMC and 2.0 mM HAuCl4 at 100 °C for 60 min showed in Figure 5. The CMC spectrum showed that the absorption bands at 1602 and 1430 cm-1 attributed to the asymmetrical and symmetrical COO- stretching vibrations, respectively (Jin et al., 2006). In the FT-IR spectrum of CMC-AuNPs, the peak at 1602 cm-1, which is ascribed to the COO- stretching vibration in CMC molecule, is slightly shifted towards 1625 cm-1. The result indicates that the Au nanoparticles are combined with the CMC molecules through affinity or electrostatic interaction with carboxylate (COO-) groups, leading to no traces of blank AuNPs in the suspension. More specifically, a new peak appeared at around 1730 cm-1, which can be ascribed FIGURE 5. FT-IR spectra of CMC and CMC-stabilized AuNPs.
CMC-AuNPs Transmittance
2890
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1422 1625
CMC
1065
3383 2936 3425
1430 1602
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3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)
to the stretching vibration of free -COOH group (Shi and Sun, 1988). This may be indicative of the reduction of Au3+ to Au0 by the polysaccharide in the solution. As reported in the literature (Sun et al., 2008), a number of glycosidic linkages in the polysaccharide chain get destroyed to shorter segments in an acidic HAuCl4 solution. Besides, some -CHO groups would exist in the opened structure. In the presence of Au3+ ions, these -CHO groups may be oxidized to -COOH groups along with a reduction of Au3+ to Au0. Possible formation mechanism of CMC-AuNPs As previously reported in literature (Jin et al., 2006), carboxymethylated curdlan essentially exists in the form of triple helices in the aqueous medium, which are maintained by hydrogen bonds. The -CH2COO− groups are mainly in the C-6 position. This may destroy the formation of micelles of curdlan molecules, but exert little effect on the hydrogen bonds at C-2, C-4 positions. Consequently, the derivative maintains its original triple-stranded helical structure. It believes that the major driving force for the helix structure of polysaccharides in water is due to the intramolecular hydrogen bonding, whereas that for triple-strand formation is a result of intermolecular hydrogen bonding. Some studies have indicated that the intra- and intermolecular hydrogen bonds, which sustain the triple-helical structure of polysaccharides, have been disrupted at higher treatment temperature. This will lead to the conformation transition of polysaccharides from triple helix to single the flexible chain and even random coil chain (Nakanishi, and Norisuye, 2003; Wang et al., 2008). Therefore, the heat treatment at 100 °C might destroy the solution behavior and chain conformation of CMC, resulting in the conformation transition from triple helix to flexible chain. Based on the above analysis, we proposed the possible mechanism underlying the formation of AuNPs in CMC solution (Figure 6). During the first 30 min of reaction, the CMC molecules mainly exist in the form of rigid triple helices in aqueous solution. The Au3+ ions attached to the –CH2COO− groups of CMC chains through electrostatic interaction or physical affinity. Subsequently, the hydroxyl groups in CMC reduced the absorbed Au3+ ions to Au0, resulting in the formation of nanorod-shaped AuNPs. This could be visually confirmed by the change in the color of the solution to blue color. In addition, some aggregates of AuNPs were also observed at the short reaction time of 30 min. With continuous stirring at 100 °C for 60 min, the triple helical structure of CMC transformed to the flexible randomly coiled structure as a result of the destruction of the intra-molecular hydrogen bonds. This may result in the formation of a greater number of hydroxyl groups on the CMC chains, which could further promote the stabilization of the as-prepared AuNPs. Consequently, the aggregates were well dispersed to form individually separated spherical nanoparticles. More specifically, the flexible chains of CMC capped the reduced Au to yield well-dispersed spherical AuNPs in an aqueous medium. This was accompanied by the
264 Green synthesis of gold nanoparticles change in the color of the solution to wine red color. These results indicate that the CMC acted as both reducing and stabilizing agent can facilitate the formation of AuNPs with
breast cancer cell line (MCF-7) under different concentrations (125, 250, and 500 μg/mL) (Figure 7). The cell viability percentage exhibited a slightly decreasing trend from 87.5%
FIGURE 6. Scheme of the process mechanism of AuNPs by the use of CMC in an aqueous medium.
-
OOCH2C
HAuCl4 (100°C, 30 min) Au3+
Au3+
Au3+
CMC
:
HAuCl4 (100°C,60 min)
Au3+
Nanorod-like AuNPs
RO RO
CMC:
O O OR
n
R = H or CH2COONa Spherical AuNPs
different shapes in the aqueous system. In vitro cytotoxicity assay One of the major drawbacks of AuNPs in the biomedical application is their potential cytotoxicity. To test whether or not as-prepared CMC-AuNPs are safe candidates for drug delivery. In this study, MTT method was used to evaluate the in vitro cytotoxicity of the as-prepared CMC-AuNPs tested on human FIGURE 7. Effect of CMC-AuNPs on the MCF-7 cell viability at different concentration after incubation for 72 h. The results represent the means ± SD (n =6). 100
Cell Viability (%)
80 60 40 20 0
0.125
0.25 Concentration (mg/mL)
0.50
to 73.2% with an increase in the concentration of CMCAuNPs from 125 to 500 μg/mL. This suggests that the growth of MCF-7 cells is not significantly affected even at higher CMC-AuNPs concentration of 500 μg/mL after incubation for 72 h. The result implies that the CMC-capped AuNPs have no or almost negligible cytotoxicity against MCF-7 cell lines in vitro. Lately, highly stable non-toxic polysaccharides with biocompatible and biodegradable properties have received increased attention in the field of drug delivery (Liu et al., 2008; Zhang et al., 2013). The CMC-AuNPs prepared in this study have non-toxic functional groups, such as carboxylic groups, on their surface. Hence, they hold great promise as a potential drug carrier for cancer therapeutics. CONCLUSION In summary, this study demonstrates a facile and simple method for the green synthesis of AuNPs by the reaction of HAuCl4 with CMC, where CMC acts as both reducing and stabilizing agent in the aqueous medium. Systematic characterization of the as-prepared CMC-AuNPs indicates that the shape, particle size, and size distribution of the particles depend on the reaction time and the concentrations of CMC and HAuCl4 used in the reaction. When 2.0 mg/ mL CMC and 2.0 mM HAuCl4 were complexed at 100 °C for 60 min, the well dispersed AuNPs were synthesized. The spherical AuNPs are well dispersed with a mean particle size
Green synthesis of gold nanoparticles 265 of ~16 nm by TEM, DLS, XRD and EDX measurements. The FT-IR spectra indicated that the COO- groups in the CMC molecules tend to adsorb and stabilize the surface of AuNPs. More specifically, the rigid triple helices of CMC were denatured to a flexible randomly coiled structure during the heat treatment. This transformation in the structure of CMC facilitated the capping and stabilization of the reduced Au to yield well-dispersed spherical AuNPs in an aqueous medium. The in vitro cytotoxicity assay using MCF-7 cell lines indicated that the as-prepared AuNPs have no or almost negligible effect in inhibiting the cell growth. The CMCcapped AuNPs synthesized in this study could potentially be used in biotechnology and biomedical applications. Further investigations are currently underway.
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ACKNOWLEDGEMENTS This work was supported financially by the Natural Science Foundation of Jiangsu Province (BK20140542) and the Open Foundation of Key Laboratory of Carbohydrate Chemistry & Biotechnology Ministry of Education (KLCCB-KF201202).
Jia, X., Xu, X. and Zhang, L. (2013). Synthesis and stabilization of gold nanoparticles induced by denaturation and renaturation of triple helical β-glucan in water. Biomacromolecules 14: 17871794.
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