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Synthesis and characterization of CdS nanoparticles using C-phycoerythrin from the marine cyanobacteria
Materials Letters 74 (2012) 8–11
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of CdS nanoparticles using C-phycoerythrin from the marine cyanobacteria D. MubarakAli a, V. Gopinath b, N. Rameshbabu c, N. Thajuddin a,⁎ a b c
Department of Microbiology, School of Life Sciences, Bharathidasan University, Tiruchirappalli-620 024, Tamil Nadu, India Department of Biotechnology, School of Bioengineering, SRM University, Chennai, Tamil Nadu, India Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 16 September 2011 Accepted 6 January 2012 Available online 18 January 2012 Keywords: Biosynthesis CdS nanoparticles C-phycoerythrin Biolabeling
a b s t r a c t In the background that the marine cyanobacteria offer great potentials as source of fine chemicals, pharmaceuticals, biofuels, etc., in the present study the pigment, C-phycoerythrin (C-PE) extracted from the marine cyanobacterium, Phormidium tenue NTDM05 was used to synthesize CdS nanoparticles. The CdS nanoparticles thus synthesized were characterized adopting UV–Visible spectrum, Fourier transform infra-red spectrum, EDAX and transmission electron microscopy. The size of the CdS nanoparticles was found to be about 5 nm. Essentially, it was found that the pigment stabilized the CdS nanoparticles. The pigments labeled CdS nanoparticles could be applied as a biolabel. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Recently, there is great emphasis on nanomaterials. The nanomaterials are synthesized adopting physical and chemical and biological approaches. The products of synthesis adopting the physical and chemical methods contribute to contaminations to the environment, and it is believed that the nanoparticle synthesis adopting biological methods is simple, safe and environmentally friendly. Cadmium sulfide nanoparticles (CdS NP's) are among the widely studied in semiconductor nanoparticles that possess unique, photochemical and photophysical properties. The semiconductor nanoparticles are often referred to as Quantum Dots (QDs). These particles, when embedded within an appropriate matrix, act as potential wells that confine and stabilize electrons in discrete energy levels. The technologically useful properties of CdS QDs are due in part to the fact that the band-gap is tunable over a range of 1.5 to 3.5 eV [1]. CdS NPs have been successfully synthesized using a wide range of organisms, like algae [2, 3], fungi [4], yeast [5, 6] and bacteria [6, 7]. Apart from the synthesis of such CdS NPs, the stabilization of synthesized particles is also important. Several stabilizing agents such as enzymes [4], starch [8-10], chitosan [11], 3-mercaptopropionic acid (MPA), mercaptosuccinic acid (MSA), and glutathione (GSH) have also been used to synthesize CdS NPs. These stabilizing agents provide the thiol group that would bind Cd through the S\H group [12]. R-phycoerythrin also has this property [13]. Phormidium tenue, a marine cyanobacterium is a rich source of phycoerythrin, the C-phycoerythrin.
⁎ Corresponding author. E-mail address: [email protected] (N. Thajuddin). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.01.026
Fig. 1. Biosynthesis of CdS nanoparticles.
D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
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The major advantages of C-phycoerythrin are that its content in the cyanobacterium is about 70% of the total protein, and it can be easily extracted from the cell. 2. Materials and method The C-phycoerythrin pigment used in this study was extracted from the marine cyanobacterium, Phormidium tenue NTDM05 adopting a procedure recently modified from the one already in practice [14]. CdS nanoparticles were synthesized by reacting Cd 2 + with the extracted C-phycoerythrin. Simply, the extract was mixed with aqueous CdCl2 and Na2S in the concentration 0.25 mM and 1 mM, respectively. The reaction mixture was closely monitored for color change; the temperature and pH of the solution were also measured periodically over a period of 5 days. The appearance of nanoparticles was gauzed in a UV–vis spectrophotometer, in the wavelength range 200 to 900 nm, periodically. Once the nanoparticles were formed, the preparation was lyophilized and analyzed adopting FTIR and EDAX, with Li drift Si detector (Thermo elution corporation, USA). A drop of the sample was placed onto a carbon coated copper grid, and air-dried and then analyzed in a transmission electron microscope (TEM). 3. Results and discussion In the earlier study, cytotoxicity of C-PE was evaluated in human cell lines by assessment of cell proliferation and neutral red uptake; it was found that the C-PE is not cytotoxic [15]. Among various concentrations of CdCl2 and Na2S, CaCl2 at 0.25 mM and Na2S at 1 mM proved to be most optimum concentration for the synthesis of CdS nanoparticles. The first step in this reaction sequence in the nanoparticles synthesis was formation of C-PE–Cd 2 + complex, then this complex reacted with Na2S to produce CdS nanoparticles, when the color reaction mixture changed to yellow to orange (Fig. 1). CdS nanoparticles thus synthesized measured about 5 nm and, this size remains unchanged well over 8 months of storage. In an earlier investigation using R-PE, the solution contains only coarse CdS nanoparticles. It also found that R-PE prevents the growth and aggregation of nanoparticles [13]. A similar experiment in higher pH the charged capping agent was found to be very high, which might be the basis of the colloidal stability of QDs. Also, the size of the Cd–R-PE complex was primarily depending on the concentration of salts, pH of the reaction mix and the concentration of the pigments. [12]. Soluble starch has also been used as a capping agent in the synthesis of CdS and CdSe nanoparticles, ranging from 8 to 15 nm [8, 16]. The hydroxyl group of the starch polymer acts as passivation contacts
Fig. 3. FTIR spectrum recorded for CdS nanoparticles stabilized by C-PE. (A) Spectrum of C-PE (B) the bands seen at 1364 and 1034 cm− 1 were assigned to the C\N stretching vibrations of the aromatic amino amines.
for the stabilization of the CdS nanoparticles in aqueous solution [10]. The synthesis of CdS nanoparticles occurs due to pH sensitive membrane-bound oxido-reductase and carbon source-dependent rH2
Fig. 2. UV–vis spectrum of CdS nanoparticles, the peak corresponds to the formation of CdS nanoparticles capped with C-PE at 470 nm (a) and absorption peak of C-PE at 550 nm (b).
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D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
in the culture solution [6]. This work also emphasizes that the fluorescent protein in the pigment is mainly due to tyrosine, phenylalanine and tryptophan moieties, which would be the basis of the very efficient formation of CdS nanoparticles and stabilizing it to prevent agglomeration. The presence of CdS nanoparticles was confirmed by the absorption peak at 470 nm. The maximum absorption peak position of hollow nanoparticle chains is at 487 nm with the band gap at 2.56 eV [17]. Compared with that of bulk material (515 nm, 2.42 eV), the absorption peak was a blue shift at 28 nm and its band gap enlarged about 0.14 eV. This is an indication of quantum size effect [18]. It was reported that the band gap value 2.57 eV is shifted compared with the bulk value and this could be a consequence of a size quantization effect in the sample [19] and the absorption peak of C-PE was 550 nm (Fig. 2). The FTIR spectrum of the C-phycoerythrin is shown in Fig. 3a. The characteristic bands due to S\H stretching, appearing at 3398, 2074, 1637, 1365 cm − 1 for pure C-PE were not seen in capped CdS, which is due to the interaction of thiol group of the capping agent with CdS. The characteristic band such as S\H stretching was found in the entire capping agent that was not found in all capped CdS. It could be formed due to bonding with CdS NPs [12]. In the interaction between
carboxymethyl chitosan (CMCH) and CdS NPs, there were two kinds of bonding; carboxymethyl group was strongly bonded by coordination with Cd ions on to the particle surface and the unsubstituted other groups were linked to the particle surface via hydrogen bonding [20]. From this observation, it was suggested that the biological molecules can possibly perform the function for formation as well as stabilization of the CdS nanoparticles in aqueous medium [7]. The peak at 1543, 1364, 1223 cm − 1 appeared only in CdS–CPE complex (Fig. 3b). This new band was not observed in unbound CdS, which indicates a new vibration from the CPE due to C\S band at another possible scheme of bonding between CPE and CdS and the bands seen at 1364 and 1034 cm –1 were assigned to the C–N stretching vibrations of the aromatic amino amines. The interaction mechanism is mainly due to hydrogen bonding. Generally CdS QDs grow well in a solution that may has a large amount of hydroxyl groups and in water-bound surface, which are active sites for the formation of hydrogen bonding with the surrounding molecules [21]. The morphology and size of the CdS nanoparticles were observed adopting TEM. It was found that the nanoparticles were of uniform size, at about 5 nm. The EDAX revealed the presence of both Cd and S in the nanoparticles synthesized (Fig. 4). The lifetime of capped CdS QDs was higher than that of uncapped CdS QDs. The results also
Fig. 4. CdS nanoparticle. (a) TEM image, spherical shaped CdS nanoparticles in the range of 5 nm in size and (b) EDAX of the CdS nanoparticles confirming the presence of CdS signals in higher percentage.
D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
indicated that the lifetime of the particles increased with increase in size, which may be due to the uniform passivation caused by MSA on the surface of CdS particles [12]. In the present study the particle size was 5.1 ± 0.2 nm. This size range may possibly be due to the formation of nanoparticles over a time period. In support of this inference, an earlier report also found difference in size of the particles over the incubation time [6]. Since CdS nanoparticles, synthesized in aqueous phase, could be a novel fluorescence probe for ultrasensitive detection of DNA as a biolabel [22], the enhanced syntheses of CdS nanoparticles using C-PE, are the unique properties of the particles that might prove to be of great advantage. 4. Conclusion CdS nanoparticles were synthesized using C-phycoerythrin as the capping agent. A bright fluorescent protein was extracted from the genetically characterized marine cyanobacterium, Phormidium tenue NTDM05 (GU585847). This protein was used for the biosynthesis of CdS nanoparticles, which was characterized adopting UV–vis and FTIR. CdS elemental signals were confirmed by EDAX. The TEM result confirmed the spherical shape of nanoparticles at the size of about 5 nm. The simplicity of the procedure in this study can be useful in commercial scale production of stable CdS nanoparticles of fairly uniform size. Note: The 16S rDNA nucleotide sequences of the Phormidium tenue NTDM05 have been submitted to the GenBank (NCBI) with accession number GU585847. Acknowledgment The first and corresponding authors are grateful to Prof. M.A. Akbersha, Director, Mahatma Gandhi Dorencamp Centre (MGDC) for his critical evaluation of the manuscript and thankful to the
11
Department of Biotechnology (Government of India), New Delhi (BT/PR11316/PBD/26/164/2008) for their financial assistance. References [1] Flenniken M, Allen M, Drouglas T. Chemistry & Biology 2004;11:1480. [2] Hosea M, Greene B, McPherson R, Henzl M, Alexander MD, Darnall DW. Inorg Chim Acta Bioinorg Chem 1986;123:161. [3] Scarano G, Morelli E. Plant Sci 2003;165:803. [4] Ahmed A, Mukherjee P, Mandal D, Senapati S, Khan MI, Kumar R, Sastry M. J Am Chem Soc 2002;124:12108. [5] Dameron CT, Reese RN, Mehra RK, Kortan AR, Carroll PJ, Steigerwald ML, Brus LE, Winge DR. Nature 1989;338:596. [6] Prasad K, Jha Anal K. J Col Inter Sci 2010;342:68–72. [7] Bai HJ, Zhang ZM, Guo Y, Yang GE. Colloids Surf B 2009;1:142–6. [8] Wei Q, Kang S-Z, Mu J. Physiochem Eng A 2004;247:125–7. [9] Rodriguez P, Munoz-Aguirre N, S-M E, Martinez G, Gonzalez O Zelaya, Mendoza J. App Surf Sci 2008;225:740–2. [10] Rodriguez P, Munoz-Aguirre N, S-M E, Martinez GG, Cruz SA, Tomas, Angel OZ. J Cryst Growth 2008;310:160–4. [11] Li YF, Huang CZ, Li M. Anal Chem Acta 2002;452:285. [12] Liji Shobhana SS, Vimala Devi M, Sastry TP, Mandal AS. J Nanopart Res 2011;13: 1747–57. [13] Brekhovskikh AA, Bekasova OD. Inorg Mater 2005;41:331–7. [14] Mishra SK, Shrivastav A, Mishra S. Proc Biochem 2008;43:339–45. [15] Soni B, Visavadiya NP, Dalwadi N, Madamwar D, Winder C, Khalil C. J App Toxicol 2010;30:542–50. [16] Li JH, Ren CL, Liu XY, Hu ZD, Xue DS. Mater Sci Eng A 2007;458:319. [17] Liu JK, Luo CX, Yang XH, Zhang XY. Mat Lett 2009;63:124–6. [18] Gao F, Lu QY, Xie SH, Zhao DY. Adv Mater 2002;14:1537. [19] Castanon GAM, Loredo MGS, Mendoza JRM, Ruiz F. Adv Tech Mat Mat Proc 2005;7:171–4. [20] Li Z, Mat YDu. Lett 2003;57:2480–4. [21] Ladizhansky V, Hodes G, Vega S. J Phy Chem B 1998;102:8505–9. [22] Wang L, Fie J, Chen H, Liang A, Qian B, Ling B, Zhou C. J Lumines 2010;130:845–50.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of CdS nanoparticles using C-phycoerythrin from the marine cyanobacteria D. MubarakAli a, V. Gopinath b, N. Rameshbabu c, N. Thajuddin a,⁎ a b c
Department of Microbiology, School of Life Sciences, Bharathidasan University, Tiruchirappalli-620 024, Tamil Nadu, India Department of Biotechnology, School of Bioengineering, SRM University, Chennai, Tamil Nadu, India Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India
a r t i c l e
i n f o
Article history: Received 16 September 2011 Accepted 6 January 2012 Available online 18 January 2012 Keywords: Biosynthesis CdS nanoparticles C-phycoerythrin Biolabeling
a b s t r a c t In the background that the marine cyanobacteria offer great potentials as source of fine chemicals, pharmaceuticals, biofuels, etc., in the present study the pigment, C-phycoerythrin (C-PE) extracted from the marine cyanobacterium, Phormidium tenue NTDM05 was used to synthesize CdS nanoparticles. The CdS nanoparticles thus synthesized were characterized adopting UV–Visible spectrum, Fourier transform infra-red spectrum, EDAX and transmission electron microscopy. The size of the CdS nanoparticles was found to be about 5 nm. Essentially, it was found that the pigment stabilized the CdS nanoparticles. The pigments labeled CdS nanoparticles could be applied as a biolabel. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Recently, there is great emphasis on nanomaterials. The nanomaterials are synthesized adopting physical and chemical and biological approaches. The products of synthesis adopting the physical and chemical methods contribute to contaminations to the environment, and it is believed that the nanoparticle synthesis adopting biological methods is simple, safe and environmentally friendly. Cadmium sulfide nanoparticles (CdS NP's) are among the widely studied in semiconductor nanoparticles that possess unique, photochemical and photophysical properties. The semiconductor nanoparticles are often referred to as Quantum Dots (QDs). These particles, when embedded within an appropriate matrix, act as potential wells that confine and stabilize electrons in discrete energy levels. The technologically useful properties of CdS QDs are due in part to the fact that the band-gap is tunable over a range of 1.5 to 3.5 eV [1]. CdS NPs have been successfully synthesized using a wide range of organisms, like algae [2, 3], fungi [4], yeast [5, 6] and bacteria [6, 7]. Apart from the synthesis of such CdS NPs, the stabilization of synthesized particles is also important. Several stabilizing agents such as enzymes [4], starch [8-10], chitosan [11], 3-mercaptopropionic acid (MPA), mercaptosuccinic acid (MSA), and glutathione (GSH) have also been used to synthesize CdS NPs. These stabilizing agents provide the thiol group that would bind Cd through the S\H group [12]. R-phycoerythrin also has this property [13]. Phormidium tenue, a marine cyanobacterium is a rich source of phycoerythrin, the C-phycoerythrin.
⁎ Corresponding author. E-mail address: [email protected] (N. Thajuddin). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.01.026
Fig. 1. Biosynthesis of CdS nanoparticles.
D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
9
The major advantages of C-phycoerythrin are that its content in the cyanobacterium is about 70% of the total protein, and it can be easily extracted from the cell. 2. Materials and method The C-phycoerythrin pigment used in this study was extracted from the marine cyanobacterium, Phormidium tenue NTDM05 adopting a procedure recently modified from the one already in practice [14]. CdS nanoparticles were synthesized by reacting Cd 2 + with the extracted C-phycoerythrin. Simply, the extract was mixed with aqueous CdCl2 and Na2S in the concentration 0.25 mM and 1 mM, respectively. The reaction mixture was closely monitored for color change; the temperature and pH of the solution were also measured periodically over a period of 5 days. The appearance of nanoparticles was gauzed in a UV–vis spectrophotometer, in the wavelength range 200 to 900 nm, periodically. Once the nanoparticles were formed, the preparation was lyophilized and analyzed adopting FTIR and EDAX, with Li drift Si detector (Thermo elution corporation, USA). A drop of the sample was placed onto a carbon coated copper grid, and air-dried and then analyzed in a transmission electron microscope (TEM). 3. Results and discussion In the earlier study, cytotoxicity of C-PE was evaluated in human cell lines by assessment of cell proliferation and neutral red uptake; it was found that the C-PE is not cytotoxic [15]. Among various concentrations of CdCl2 and Na2S, CaCl2 at 0.25 mM and Na2S at 1 mM proved to be most optimum concentration for the synthesis of CdS nanoparticles. The first step in this reaction sequence in the nanoparticles synthesis was formation of C-PE–Cd 2 + complex, then this complex reacted with Na2S to produce CdS nanoparticles, when the color reaction mixture changed to yellow to orange (Fig. 1). CdS nanoparticles thus synthesized measured about 5 nm and, this size remains unchanged well over 8 months of storage. In an earlier investigation using R-PE, the solution contains only coarse CdS nanoparticles. It also found that R-PE prevents the growth and aggregation of nanoparticles [13]. A similar experiment in higher pH the charged capping agent was found to be very high, which might be the basis of the colloidal stability of QDs. Also, the size of the Cd–R-PE complex was primarily depending on the concentration of salts, pH of the reaction mix and the concentration of the pigments. [12]. Soluble starch has also been used as a capping agent in the synthesis of CdS and CdSe nanoparticles, ranging from 8 to 15 nm [8, 16]. The hydroxyl group of the starch polymer acts as passivation contacts
Fig. 3. FTIR spectrum recorded for CdS nanoparticles stabilized by C-PE. (A) Spectrum of C-PE (B) the bands seen at 1364 and 1034 cm− 1 were assigned to the C\N stretching vibrations of the aromatic amino amines.
for the stabilization of the CdS nanoparticles in aqueous solution [10]. The synthesis of CdS nanoparticles occurs due to pH sensitive membrane-bound oxido-reductase and carbon source-dependent rH2
Fig. 2. UV–vis spectrum of CdS nanoparticles, the peak corresponds to the formation of CdS nanoparticles capped with C-PE at 470 nm (a) and absorption peak of C-PE at 550 nm (b).
10
D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
in the culture solution [6]. This work also emphasizes that the fluorescent protein in the pigment is mainly due to tyrosine, phenylalanine and tryptophan moieties, which would be the basis of the very efficient formation of CdS nanoparticles and stabilizing it to prevent agglomeration. The presence of CdS nanoparticles was confirmed by the absorption peak at 470 nm. The maximum absorption peak position of hollow nanoparticle chains is at 487 nm with the band gap at 2.56 eV [17]. Compared with that of bulk material (515 nm, 2.42 eV), the absorption peak was a blue shift at 28 nm and its band gap enlarged about 0.14 eV. This is an indication of quantum size effect [18]. It was reported that the band gap value 2.57 eV is shifted compared with the bulk value and this could be a consequence of a size quantization effect in the sample [19] and the absorption peak of C-PE was 550 nm (Fig. 2). The FTIR spectrum of the C-phycoerythrin is shown in Fig. 3a. The characteristic bands due to S\H stretching, appearing at 3398, 2074, 1637, 1365 cm − 1 for pure C-PE were not seen in capped CdS, which is due to the interaction of thiol group of the capping agent with CdS. The characteristic band such as S\H stretching was found in the entire capping agent that was not found in all capped CdS. It could be formed due to bonding with CdS NPs [12]. In the interaction between
carboxymethyl chitosan (CMCH) and CdS NPs, there were two kinds of bonding; carboxymethyl group was strongly bonded by coordination with Cd ions on to the particle surface and the unsubstituted other groups were linked to the particle surface via hydrogen bonding [20]. From this observation, it was suggested that the biological molecules can possibly perform the function for formation as well as stabilization of the CdS nanoparticles in aqueous medium [7]. The peak at 1543, 1364, 1223 cm − 1 appeared only in CdS–CPE complex (Fig. 3b). This new band was not observed in unbound CdS, which indicates a new vibration from the CPE due to C\S band at another possible scheme of bonding between CPE and CdS and the bands seen at 1364 and 1034 cm –1 were assigned to the C–N stretching vibrations of the aromatic amino amines. The interaction mechanism is mainly due to hydrogen bonding. Generally CdS QDs grow well in a solution that may has a large amount of hydroxyl groups and in water-bound surface, which are active sites for the formation of hydrogen bonding with the surrounding molecules [21]. The morphology and size of the CdS nanoparticles were observed adopting TEM. It was found that the nanoparticles were of uniform size, at about 5 nm. The EDAX revealed the presence of both Cd and S in the nanoparticles synthesized (Fig. 4). The lifetime of capped CdS QDs was higher than that of uncapped CdS QDs. The results also
Fig. 4. CdS nanoparticle. (a) TEM image, spherical shaped CdS nanoparticles in the range of 5 nm in size and (b) EDAX of the CdS nanoparticles confirming the presence of CdS signals in higher percentage.
D. MubarakAli et al. / Materials Letters 74 (2012) 8–11
indicated that the lifetime of the particles increased with increase in size, which may be due to the uniform passivation caused by MSA on the surface of CdS particles [12]. In the present study the particle size was 5.1 ± 0.2 nm. This size range may possibly be due to the formation of nanoparticles over a time period. In support of this inference, an earlier report also found difference in size of the particles over the incubation time [6]. Since CdS nanoparticles, synthesized in aqueous phase, could be a novel fluorescence probe for ultrasensitive detection of DNA as a biolabel [22], the enhanced syntheses of CdS nanoparticles using C-PE, are the unique properties of the particles that might prove to be of great advantage. 4. Conclusion CdS nanoparticles were synthesized using C-phycoerythrin as the capping agent. A bright fluorescent protein was extracted from the genetically characterized marine cyanobacterium, Phormidium tenue NTDM05 (GU585847). This protein was used for the biosynthesis of CdS nanoparticles, which was characterized adopting UV–vis and FTIR. CdS elemental signals were confirmed by EDAX. The TEM result confirmed the spherical shape of nanoparticles at the size of about 5 nm. The simplicity of the procedure in this study can be useful in commercial scale production of stable CdS nanoparticles of fairly uniform size. Note: The 16S rDNA nucleotide sequences of the Phormidium tenue NTDM05 have been submitted to the GenBank (NCBI) with accession number GU585847. Acknowledgment The first and corresponding authors are grateful to Prof. M.A. Akbersha, Director, Mahatma Gandhi Dorencamp Centre (MGDC) for his critical evaluation of the manuscript and thankful to the
11
Department of Biotechnology (Government of India), New Delhi (BT/PR11316/PBD/26/164/2008) for their financial assistance. References [1] Flenniken M, Allen M, Drouglas T. Chemistry & Biology 2004;11:1480. [2] Hosea M, Greene B, McPherson R, Henzl M, Alexander MD, Darnall DW. Inorg Chim Acta Bioinorg Chem 1986;123:161. [3] Scarano G, Morelli E. Plant Sci 2003;165:803. [4] Ahmed A, Mukherjee P, Mandal D, Senapati S, Khan MI, Kumar R, Sastry M. J Am Chem Soc 2002;124:12108. [5] Dameron CT, Reese RN, Mehra RK, Kortan AR, Carroll PJ, Steigerwald ML, Brus LE, Winge DR. Nature 1989;338:596. [6] Prasad K, Jha Anal K. J Col Inter Sci 2010;342:68–72. [7] Bai HJ, Zhang ZM, Guo Y, Yang GE. Colloids Surf B 2009;1:142–6. [8] Wei Q, Kang S-Z, Mu J. Physiochem Eng A 2004;247:125–7. [9] Rodriguez P, Munoz-Aguirre N, S-M E, Martinez G, Gonzalez O Zelaya, Mendoza J. App Surf Sci 2008;225:740–2. [10] Rodriguez P, Munoz-Aguirre N, S-M E, Martinez GG, Cruz SA, Tomas, Angel OZ. J Cryst Growth 2008;310:160–4. [11] Li YF, Huang CZ, Li M. Anal Chem Acta 2002;452:285. [12] Liji Shobhana SS, Vimala Devi M, Sastry TP, Mandal AS. J Nanopart Res 2011;13: 1747–57. [13] Brekhovskikh AA, Bekasova OD. Inorg Mater 2005;41:331–7. [14] Mishra SK, Shrivastav A, Mishra S. Proc Biochem 2008;43:339–45. [15] Soni B, Visavadiya NP, Dalwadi N, Madamwar D, Winder C, Khalil C. J App Toxicol 2010;30:542–50. [16] Li JH, Ren CL, Liu XY, Hu ZD, Xue DS. Mater Sci Eng A 2007;458:319. [17] Liu JK, Luo CX, Yang XH, Zhang XY. Mat Lett 2009;63:124–6. [18] Gao F, Lu QY, Xie SH, Zhao DY. Adv Mater 2002;14:1537. [19] Castanon GAM, Loredo MGS, Mendoza JRM, Ruiz F. Adv Tech Mat Mat Proc 2005;7:171–4. [20] Li Z, Mat YDu. Lett 2003;57:2480–4. [21] Ladizhansky V, Hodes G, Vega S. J Phy Chem B 1998;102:8505–9. [22] Wang L, Fie J, Chen H, Liang A, Qian B, Ling B, Zhou C. J Lumines 2010;130:845–50.