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Adsorption behavior of l -cysteine on Ag nanoparticles under water environment studied by S K-edge NEXAFS
Applied Surface Science 262 (2012) 231–233
Contents lists available at SciVerse ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Adsorption behavior of l-cysteine on Ag nanoparticles under water environment studied by S K-edge NEXAFS C. Tsukada a , S. Yagi a,b,∗ , T. Nomoto c , T. Mizutani a , S. Ogawa a , H. Nameki c , Y. Nakanishi c , G. Kutluk b , H. Namatame b , M. Taniguchi b a
Department of Quantum Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Synchrotron Radiation Center, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-0046, Japan c Aichi Industrial Technology Institute, Onda, Kariya 448-0013, Japan b
a r t i c l e
i n f o
Article history: Available online 25 July 2012 Keywords: Ag nanoparticle l-Cysteine Solution plasma method He-path NEXAFS
a b s t r a c t We have focused on the biocompatibility of the Ag nanoparticles. In this paper, we have fabricated the Ag nanoparticles by means of the solution plasma method. Since this method does not need to use the surfactant molecule, such as the water soluble polymer, the fabricated nanoparticle might possess the clean surface. The average diameter of the Ag nanoparticles is estimated to be 5.0 ± 1.1 nm. NEXAFS spectra show l-cysteine thiolate adsorbs on the Ag nanoparticle surface and l-cystine is synthesized. Though this reaction behavior is similar to the result of Rh(PVP, polyvinylpyrrolidone) system, in our previous study, the reaction speed for the Ag nanoparticle is much faster than that for the Rh(PVP) nanoparticle. © 2012 Elsevier B.V. All rights reserved.
1. Introduction In our previous studies, we have investigated l-cysteine adsorption on metal surfaces under atmospheric or water environment [1,2]. Yagi et al. reported that the l-cysteine molecules adsorb as an adsorbate of l-cysteine thiolate and/or atomic S by a dissociative reaction on the transition metal surfaces. Tsukada et al. described that the l-cysteine and l-cysteine thiolate species adsorb on the Pd thin layer surface and react with some water molecules under water environment. On the other hand, Gohda et al. have reported that the l-cysteine molecules adsorb on Rh nanoparticle surface as the thiolate species under water environment [3]. There is no atomic S adsorbate on the Rh nanoparticle. Those results suggest that water molecules make some influences to the adsorption behavior of the l-cysteine. Although we have used PVP (polyvinylpyrrolidone) as a surfactant to prevent from an aggregation of the nanoparticles about the fabrication of Rh nanoparticles by means of chemical reduction method, there is a possibility to poison the surface of the nanoparticle. Therefore we have tried to fabricate the nanoparticle by the method without the surfactant. One solution is a plasma discharge method in water solution, so called solution plasma method [4,5]. Though the detailed
∗ Corresponding author at: Department of Quantum Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. Tel.: +81 52 789 3789; fax: +81 52 789 5155. E-mail address: [email protected] (S. Yagi). 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.06.107
reaction structure of the solution plasma method is unclear, this method does not use the surfactant, such as water soluble polymer molecules, in case of the nanoparticle fabrication. Therefore the method possesses many advantages for application field. One is the surface of the fabricated nanoparticle is clean, because of without the surfactant use. In this study, we have tried to fabricate the metal nanoparticles by means of the solution plasma method. Meanwhile, some materials including an Ag nanoparticle are using antimicrobial system, biosensor and toxicity in those years [6–8]. When Ag nanoparticles are used for the antimicrobial material, do the nanoparticles show a biocompatibility? We strongly think that it is important to investigate the adsorption structure, the kinds of adsorbates and the chemical changing of the nanoparticle surface to judge the biocompatibility. In this study, we have studied the adsorption behavior between the l-cysteine amino acid molecule and the Ag nanoparticle surface under water environment by S K-edge near edge X-ray absorption fine structure (NEXAFS) technique. 2. Experimental A nanocolloidal solution, including the synthesized Ag nanoparticles, has been prepared by means of the solution plasma method [4,5]. The starting materials were AgNO3 and NH3 , purchased from Wako Pure Chemical Industries, Ltd., and distilled water. The tungsten electrodes with Ø1.0 mm were placed in a glass vessel filled with the solution at 0.1–0.2 mm gap. A pulsed DC power supply (Kurita Co. Ltd.) was used to generate the pulsed plasma. Fig. 1
232
C. Tsukada et al. / Applied Surface Science 262 (2012) 231–233
fore the X-ray in the soft X-ray region can transmit to the colloidal solution. 3. Results and discussion 3.1. AFM observation Observed typical AFM image and distribution of the nanoparticle diameter are shown in Fig. 2(a) and (b), respectively. Some bright spots can be seen in Fig. 2(a). Those spots mean the Ag nanoparticles on Si wafer. There are no aggregated nanoparticles. Thus, it is clear that the fabricated Ag nanoparticles show a highly dispersed phase. The height value of the AFM analysis has a good resolution in comparison with the horizontal one. Therefore the diameter of nanoparticle is evaluated by the height value of AFM image. Fig. 2(b) shows the distributions of the Ag nanoparticles. The statistic was obtained by measuring 100 dots of the nanoparticles. The average diameter of the Ag nanoparticle is estimated to be 5.0 nm with standard deviations of ±1.1 nm. Fig. 1. Photographic view of the solution plasma system for the Ag nanoparticle fabrication. An inset shows a part of the plasma production with the needle-toneedle electrodes.
shows a photographic view of the solution plasma system. After about 30 min, the fabrication of the Ag nanoparticles is finished and the colloidal solution possesses yellow color. An average diameter of the Ag nanoparticles was estimated by means of atomic force microscopy (AFM) observations using NanoScope III-a by Veeco Inst. with tapping mode. The l-cysteine powder, purchased from Sigma–Aldrich, of 0.5 mmol was dissolved into the Ag nanocolloidal solution of 5 ml in the plastic vessel. We have left the mixed sample for the appropriate time at room temperature to stimulate the reaction between l-cysteine and Ag nanoparticle. The S K-edges NEXAFS measurements for the liquid samples were carried out by yielding fluorescence X-ray using the atmospheric pressure system with He gas at the beamline BL-3 on Hiroshima Synchrotron Radiation Center (HSRC) [9,10]. The photon energy was calibrated on the assumption that the first peak of K2 SO4 appears at 2481.70 eV. The fluorescence yield detection was employed using a UHVcompatible gas-flow type proportional counter with P-10 gas (10% CH4 in Ar). The measurement samples were inserted into a special measurement cell for the liquid specimens using a syringe. The cell is made of a polyethylene thin film with 12 m thickness. There-
3.2. Sulfur K-edge NEXAFS spectra Fig. 3 shows sulfur K-edge NEXAFS spectra for the mixed samples that have left for arbitrary time (1 h, 4 h and 2 weeks). Both l-cysteine aqueous solution and l-cystine powder spectra also shown in Fig. 3 as standard spectra. All spectra are normalized by the edge-jump. The spectra after 1 and 4 h have two peaks around 2472.5 eV and 2481.8 eV. Those peaks are assigned to the transition peak for the chemisorbed l-cysteine adsorbate on the Ag nanoparticle and SO4 2− species, respectively. Moreover, there are peak and shoulder structures in the spectrum after 2 weeks around 2471.8 eV and 2473.7 eV. These peak positions are the same as those of lcystine spectrum. Therefore, this means l-cystine molecules are synthesized in the mixed colloidal solution after 2 weeks. This result is almost the same as the mixed sample condition of Rh nanoparticle colloidal solution. However, the peak intensity for the Ag nanoparticle (our study) assigned to the l-cystine is quite larger than that for previous study about Rh(PVP) nanoparticle [3], which size is 3.2 ± 0.7 nm. Two spectra for the adsorption reaction with Rh(PVP) and Ag nanoparticles are summarized in Fig. 4. While the element kinds for the nanoparticles are different, that results mean that the synthesized reaction of l-cystine started from the adsorption reaction of l-cysteine on the Ag nanoparticle surface is significantly fast in comparison with the Rh one. Since the reaction of the molecular adsorption on metal surface strongly correlate
Fig. 2. (a) AFM image of the Ag nanopacrticles on Si wafer. (b) A distribution for the Ag nanoparticles.
C. Tsukada et al. / Applied Surface Science 262 (2012) 231–233
S K-edge NEXAFS
Fluorescence Yield (arb. units)
L-Cystine powder L-Cysteine aq.
2 weeks 4 hours
233
it would be thought that the adsorbed PVP reduce the electron density at the nanoparticle surface. Since there is no use of the polymer molecules as the PVP about the Ag nanoparticle, in other words, the surface is maintaining the cleanness. Furthermore, it can be observed a shoulder structures around 2477–2479 eV in the spectrum after 2 weeks. Judging from the studies of SO2 or SO3 adsorption on the transition metal surface and sulfur compounds with the transition metal [11–13], this shoulder structures mean the presence of the SO2 or SO3 adsorbate on the substrate surface. As described by earlier research, the peak located around 2482 eV is assigned to SO4 2− species [13]. Though it might exist two sulfur oxidized adsorbates or coordination bonding species between sulfur of cysteine and oxygen of water on the Ag nanoparticle surface, the details are not cleared. To elucidate the details, we have a future plan to investigate the oxygen and silver K- and L3 -edges NEXAFS with use the He-path system. If we will obtain those edges NEXAFS spectra, we can discuss about the chemical states of both the adsorbates and the silver atoms on the nanoparticle surface. 4. Conclusion
1 hour
2460 2465 2470 2475 2480 2485 2490 2495
Photon Energy (eV) Fig. 3. S K-edge NEXAFS spectra for the mixed samples for the appropriate time at room temperature to stimulate the reaction between l-cysteine and Ag nanoparticle. Two standard spectra of l-cysteine and l-cystine are also shown in figure. All spectra are normalized by the edge-jump.
Fluorescence Yield (arb. units)
S K-edge NEXAFS
Rh(PVP) nanoparticles 30 days [3]
2 weeks
2460
2465
2470
2475
2480
2485
2490
2495
Photon Energy (eV) Fig. 4. S K-edge NEXAFS spectrum for the mixed sample after 2 weeks and the reference spectrum for the Rh(PVP) nanoparticles after 30 days [3].
with an electron transfer phenomenon between the adsorbate and the surface, that synthesized reaction would depend upon the electron density of state for the nanoparticle surface. Considering the adsorption of the PVP polymer molecules on the Rh nanoparticle,
We have investigated the adsorption behavior of l-cysteine on the Ag nanoparticle surface under colloidal solution. The Ag nanoparticles were fabricated by means of the solution plasma method. The average diameter of the Ag nanoparticles is estimated to be 5.0 nm. It is found that l-cysteine thiolate adsorbs on the Ag nanoparticle surface and l-cystine is synthesized. This synthesis reaction for the Ag nanoparticle is much faster than that for the Rh(PVP) nanoparticle as previous study. Acknowledgements This work was supported by a Knowledge-Cluster II at Aichi/Chubu area and JST Innovation Plaza Hiroshima/Tokai. This work was performed under the approval of HSRC Program Advisory Committee (Nos. 10-A-17 and 11-A-19) and of Ritsumeikan SR Center (Nos. S20-02 and S21-05). Especially part of NEXAFS measurements is supported by the nanotechnology network project of the Ministry Education, Culture, Sports, Science and Technology, Japan (MEXT). References [1] S. Yagi, Y. Matsumura, K. Soda, E. Hashimoto, M. Taniguchi, Surface and Interface Analysis 36 (2004) 1064–1067. [2] C. Tsukada, S. Ogawa, H. Niwa, S. Yagi, T. Nomoto, G. Kutluk, H. Namatame, M. Taniguchi, e-Journal of Surface Science and Nanotechnology 9 (2011) 289–292. [3] S. Gohda, T. Ashida, S. Yagi, K. Matsuo, H. Namatame, M. Taniguchi, e-Journal of Surface Science and Nanotechnology 7 (2009) 314–318. [4] N. Saito, J. Hieda, O. Takai, Thin Solid Films 518 (2009) 912–917. ˇ Potocky, ´ N. Saito, O. Takai, Thin Solid Films 518 (2009) 918–923. [5] S. [6] K.D. Secinti, H. Özalp, A. Attar, M.F. Sargon, Journal of Clinical Neuroscience 18 (2011) 391–395. [7] M. Ahamed, M.S. Alsalhi, M.K.J. Siddiqui, Clinica Chimica Acta 411 (2010) 1841–1848. [8] B.P. Ting, J. Zhang, Z. Gao, J.Y. Ying, Biosensors & Bioelectronics 25 (2009) 282–287. [9] S. Yagi, G. Kutluk, T. Matsui, A. Matano, A. Hiraya, E. Hashimoto, M. Taniguchi, Nuclear Instruments & Methods 467–468 (2001) 723–726. [10] S. Yagi, T. Nomoto, T. Ashida, K. Miura, K. Soda, K. Yamagishi, N. Hosoya, G. Kutluk, H. Namatame, M. Taniguchi, AIP Conference Proceedings 879 (2007) 1638–1641. [11] T. Yokoyama, S. Terada, S. Yagi, A. Imanishi, S. Takenaka, Y. Kitajima, T. Ohta, Surface Science 324 (1995) 25–34. [12] G.J. Jackson, S.M. Driver, D.P. Woodruff, N. Abrams, R.G. Jones, M.T. Butterfield, M.D. Crapper, B.C.C. Cowie, V. Formoso, Surface Science 459 (2000) 231–244. [13] R.P.W.J. Struis, T.J. Schildhauer, I. Czekaj, M. Janousch, S.M.A. Biollaz, C. Ludwig, Applied Catalysis A-General 362 (2009) 121–128.
Contents lists available at SciVerse ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Adsorption behavior of l-cysteine on Ag nanoparticles under water environment studied by S K-edge NEXAFS C. Tsukada a , S. Yagi a,b,∗ , T. Nomoto c , T. Mizutani a , S. Ogawa a , H. Nameki c , Y. Nakanishi c , G. Kutluk b , H. Namatame b , M. Taniguchi b a
Department of Quantum Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Synchrotron Radiation Center, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-0046, Japan c Aichi Industrial Technology Institute, Onda, Kariya 448-0013, Japan b
a r t i c l e
i n f o
Article history: Available online 25 July 2012 Keywords: Ag nanoparticle l-Cysteine Solution plasma method He-path NEXAFS
a b s t r a c t We have focused on the biocompatibility of the Ag nanoparticles. In this paper, we have fabricated the Ag nanoparticles by means of the solution plasma method. Since this method does not need to use the surfactant molecule, such as the water soluble polymer, the fabricated nanoparticle might possess the clean surface. The average diameter of the Ag nanoparticles is estimated to be 5.0 ± 1.1 nm. NEXAFS spectra show l-cysteine thiolate adsorbs on the Ag nanoparticle surface and l-cystine is synthesized. Though this reaction behavior is similar to the result of Rh(PVP, polyvinylpyrrolidone) system, in our previous study, the reaction speed for the Ag nanoparticle is much faster than that for the Rh(PVP) nanoparticle. © 2012 Elsevier B.V. All rights reserved.
1. Introduction In our previous studies, we have investigated l-cysteine adsorption on metal surfaces under atmospheric or water environment [1,2]. Yagi et al. reported that the l-cysteine molecules adsorb as an adsorbate of l-cysteine thiolate and/or atomic S by a dissociative reaction on the transition metal surfaces. Tsukada et al. described that the l-cysteine and l-cysteine thiolate species adsorb on the Pd thin layer surface and react with some water molecules under water environment. On the other hand, Gohda et al. have reported that the l-cysteine molecules adsorb on Rh nanoparticle surface as the thiolate species under water environment [3]. There is no atomic S adsorbate on the Rh nanoparticle. Those results suggest that water molecules make some influences to the adsorption behavior of the l-cysteine. Although we have used PVP (polyvinylpyrrolidone) as a surfactant to prevent from an aggregation of the nanoparticles about the fabrication of Rh nanoparticles by means of chemical reduction method, there is a possibility to poison the surface of the nanoparticle. Therefore we have tried to fabricate the nanoparticle by the method without the surfactant. One solution is a plasma discharge method in water solution, so called solution plasma method [4,5]. Though the detailed
∗ Corresponding author at: Department of Quantum Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. Tel.: +81 52 789 3789; fax: +81 52 789 5155. E-mail address: [email protected] (S. Yagi). 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.06.107
reaction structure of the solution plasma method is unclear, this method does not use the surfactant, such as water soluble polymer molecules, in case of the nanoparticle fabrication. Therefore the method possesses many advantages for application field. One is the surface of the fabricated nanoparticle is clean, because of without the surfactant use. In this study, we have tried to fabricate the metal nanoparticles by means of the solution plasma method. Meanwhile, some materials including an Ag nanoparticle are using antimicrobial system, biosensor and toxicity in those years [6–8]. When Ag nanoparticles are used for the antimicrobial material, do the nanoparticles show a biocompatibility? We strongly think that it is important to investigate the adsorption structure, the kinds of adsorbates and the chemical changing of the nanoparticle surface to judge the biocompatibility. In this study, we have studied the adsorption behavior between the l-cysteine amino acid molecule and the Ag nanoparticle surface under water environment by S K-edge near edge X-ray absorption fine structure (NEXAFS) technique. 2. Experimental A nanocolloidal solution, including the synthesized Ag nanoparticles, has been prepared by means of the solution plasma method [4,5]. The starting materials were AgNO3 and NH3 , purchased from Wako Pure Chemical Industries, Ltd., and distilled water. The tungsten electrodes with Ø1.0 mm were placed in a glass vessel filled with the solution at 0.1–0.2 mm gap. A pulsed DC power supply (Kurita Co. Ltd.) was used to generate the pulsed plasma. Fig. 1
232
C. Tsukada et al. / Applied Surface Science 262 (2012) 231–233
fore the X-ray in the soft X-ray region can transmit to the colloidal solution. 3. Results and discussion 3.1. AFM observation Observed typical AFM image and distribution of the nanoparticle diameter are shown in Fig. 2(a) and (b), respectively. Some bright spots can be seen in Fig. 2(a). Those spots mean the Ag nanoparticles on Si wafer. There are no aggregated nanoparticles. Thus, it is clear that the fabricated Ag nanoparticles show a highly dispersed phase. The height value of the AFM analysis has a good resolution in comparison with the horizontal one. Therefore the diameter of nanoparticle is evaluated by the height value of AFM image. Fig. 2(b) shows the distributions of the Ag nanoparticles. The statistic was obtained by measuring 100 dots of the nanoparticles. The average diameter of the Ag nanoparticle is estimated to be 5.0 nm with standard deviations of ±1.1 nm. Fig. 1. Photographic view of the solution plasma system for the Ag nanoparticle fabrication. An inset shows a part of the plasma production with the needle-toneedle electrodes.
shows a photographic view of the solution plasma system. After about 30 min, the fabrication of the Ag nanoparticles is finished and the colloidal solution possesses yellow color. An average diameter of the Ag nanoparticles was estimated by means of atomic force microscopy (AFM) observations using NanoScope III-a by Veeco Inst. with tapping mode. The l-cysteine powder, purchased from Sigma–Aldrich, of 0.5 mmol was dissolved into the Ag nanocolloidal solution of 5 ml in the plastic vessel. We have left the mixed sample for the appropriate time at room temperature to stimulate the reaction between l-cysteine and Ag nanoparticle. The S K-edges NEXAFS measurements for the liquid samples were carried out by yielding fluorescence X-ray using the atmospheric pressure system with He gas at the beamline BL-3 on Hiroshima Synchrotron Radiation Center (HSRC) [9,10]. The photon energy was calibrated on the assumption that the first peak of K2 SO4 appears at 2481.70 eV. The fluorescence yield detection was employed using a UHVcompatible gas-flow type proportional counter with P-10 gas (10% CH4 in Ar). The measurement samples were inserted into a special measurement cell for the liquid specimens using a syringe. The cell is made of a polyethylene thin film with 12 m thickness. There-
3.2. Sulfur K-edge NEXAFS spectra Fig. 3 shows sulfur K-edge NEXAFS spectra for the mixed samples that have left for arbitrary time (1 h, 4 h and 2 weeks). Both l-cysteine aqueous solution and l-cystine powder spectra also shown in Fig. 3 as standard spectra. All spectra are normalized by the edge-jump. The spectra after 1 and 4 h have two peaks around 2472.5 eV and 2481.8 eV. Those peaks are assigned to the transition peak for the chemisorbed l-cysteine adsorbate on the Ag nanoparticle and SO4 2− species, respectively. Moreover, there are peak and shoulder structures in the spectrum after 2 weeks around 2471.8 eV and 2473.7 eV. These peak positions are the same as those of lcystine spectrum. Therefore, this means l-cystine molecules are synthesized in the mixed colloidal solution after 2 weeks. This result is almost the same as the mixed sample condition of Rh nanoparticle colloidal solution. However, the peak intensity for the Ag nanoparticle (our study) assigned to the l-cystine is quite larger than that for previous study about Rh(PVP) nanoparticle [3], which size is 3.2 ± 0.7 nm. Two spectra for the adsorption reaction with Rh(PVP) and Ag nanoparticles are summarized in Fig. 4. While the element kinds for the nanoparticles are different, that results mean that the synthesized reaction of l-cystine started from the adsorption reaction of l-cysteine on the Ag nanoparticle surface is significantly fast in comparison with the Rh one. Since the reaction of the molecular adsorption on metal surface strongly correlate
Fig. 2. (a) AFM image of the Ag nanopacrticles on Si wafer. (b) A distribution for the Ag nanoparticles.
C. Tsukada et al. / Applied Surface Science 262 (2012) 231–233
S K-edge NEXAFS
Fluorescence Yield (arb. units)
L-Cystine powder L-Cysteine aq.
2 weeks 4 hours
233
it would be thought that the adsorbed PVP reduce the electron density at the nanoparticle surface. Since there is no use of the polymer molecules as the PVP about the Ag nanoparticle, in other words, the surface is maintaining the cleanness. Furthermore, it can be observed a shoulder structures around 2477–2479 eV in the spectrum after 2 weeks. Judging from the studies of SO2 or SO3 adsorption on the transition metal surface and sulfur compounds with the transition metal [11–13], this shoulder structures mean the presence of the SO2 or SO3 adsorbate on the substrate surface. As described by earlier research, the peak located around 2482 eV is assigned to SO4 2− species [13]. Though it might exist two sulfur oxidized adsorbates or coordination bonding species between sulfur of cysteine and oxygen of water on the Ag nanoparticle surface, the details are not cleared. To elucidate the details, we have a future plan to investigate the oxygen and silver K- and L3 -edges NEXAFS with use the He-path system. If we will obtain those edges NEXAFS spectra, we can discuss about the chemical states of both the adsorbates and the silver atoms on the nanoparticle surface. 4. Conclusion
1 hour
2460 2465 2470 2475 2480 2485 2490 2495
Photon Energy (eV) Fig. 3. S K-edge NEXAFS spectra for the mixed samples for the appropriate time at room temperature to stimulate the reaction between l-cysteine and Ag nanoparticle. Two standard spectra of l-cysteine and l-cystine are also shown in figure. All spectra are normalized by the edge-jump.
Fluorescence Yield (arb. units)
S K-edge NEXAFS
Rh(PVP) nanoparticles 30 days [3]
2 weeks
2460
2465
2470
2475
2480
2485
2490
2495
Photon Energy (eV) Fig. 4. S K-edge NEXAFS spectrum for the mixed sample after 2 weeks and the reference spectrum for the Rh(PVP) nanoparticles after 30 days [3].
with an electron transfer phenomenon between the adsorbate and the surface, that synthesized reaction would depend upon the electron density of state for the nanoparticle surface. Considering the adsorption of the PVP polymer molecules on the Rh nanoparticle,
We have investigated the adsorption behavior of l-cysteine on the Ag nanoparticle surface under colloidal solution. The Ag nanoparticles were fabricated by means of the solution plasma method. The average diameter of the Ag nanoparticles is estimated to be 5.0 nm. It is found that l-cysteine thiolate adsorbs on the Ag nanoparticle surface and l-cystine is synthesized. This synthesis reaction for the Ag nanoparticle is much faster than that for the Rh(PVP) nanoparticle as previous study. Acknowledgements This work was supported by a Knowledge-Cluster II at Aichi/Chubu area and JST Innovation Plaza Hiroshima/Tokai. This work was performed under the approval of HSRC Program Advisory Committee (Nos. 10-A-17 and 11-A-19) and of Ritsumeikan SR Center (Nos. S20-02 and S21-05). Especially part of NEXAFS measurements is supported by the nanotechnology network project of the Ministry Education, Culture, Sports, Science and Technology, Japan (MEXT). References [1] S. Yagi, Y. Matsumura, K. Soda, E. Hashimoto, M. Taniguchi, Surface and Interface Analysis 36 (2004) 1064–1067. [2] C. Tsukada, S. Ogawa, H. Niwa, S. Yagi, T. Nomoto, G. Kutluk, H. Namatame, M. Taniguchi, e-Journal of Surface Science and Nanotechnology 9 (2011) 289–292. [3] S. Gohda, T. Ashida, S. Yagi, K. Matsuo, H. Namatame, M. Taniguchi, e-Journal of Surface Science and Nanotechnology 7 (2009) 314–318. [4] N. Saito, J. Hieda, O. Takai, Thin Solid Films 518 (2009) 912–917. ˇ Potocky, ´ N. Saito, O. Takai, Thin Solid Films 518 (2009) 918–923. [5] S. [6] K.D. Secinti, H. Özalp, A. Attar, M.F. Sargon, Journal of Clinical Neuroscience 18 (2011) 391–395. [7] M. Ahamed, M.S. Alsalhi, M.K.J. Siddiqui, Clinica Chimica Acta 411 (2010) 1841–1848. [8] B.P. Ting, J. Zhang, Z. Gao, J.Y. Ying, Biosensors & Bioelectronics 25 (2009) 282–287. [9] S. Yagi, G. Kutluk, T. Matsui, A. Matano, A. Hiraya, E. Hashimoto, M. Taniguchi, Nuclear Instruments & Methods 467–468 (2001) 723–726. [10] S. Yagi, T. Nomoto, T. Ashida, K. Miura, K. Soda, K. Yamagishi, N. Hosoya, G. Kutluk, H. Namatame, M. Taniguchi, AIP Conference Proceedings 879 (2007) 1638–1641. [11] T. Yokoyama, S. Terada, S. Yagi, A. Imanishi, S. Takenaka, Y. Kitajima, T. Ohta, Surface Science 324 (1995) 25–34. [12] G.J. Jackson, S.M. Driver, D.P. Woodruff, N. Abrams, R.G. Jones, M.T. Butterfield, M.D. Crapper, B.C.C. Cowie, V. Formoso, Surface Science 459 (2000) 231–244. [13] R.P.W.J. Struis, T.J. Schildhauer, I. Czekaj, M. Janousch, S.M.A. Biollaz, C. Ludwig, Applied Catalysis A-General 362 (2009) 121–128.