Synthesis of Aqueous Au Core−Ag Shell Nanoparticles Using Tyrosine as a pH-Dependent Reducing Agent and Assembling Phase-Transferred Silver Nanoparticles at the Air−Water Interface

Abstract

We demonstrate that the amino acid tyrosine is an excellent reducing agent under alkaline conditions and may be used to reduce Ag+ ions to synthesize stable silver nanoparticles in water. The tyrosine-reduced silver nanoparticles may be separated out as a powder that is readily redispersible in water. The silver ion reduction at high pH occurs due to ionization of the phenolic group in tyrosine that is then capable of reducing Ag+ ions and is in turn converted to a semi-quinone structure. These silver nanoparticles can easily be transferred to chloroform containing the cationic surfactant octadecylamine by an electrostatic complexation process. The now hydrophobic silver nanoparticles may be spread on the surface of water and assembled into highly ordered, linear superstructures that could be transferred as multilayers onto suitable supports by the versatile Langmuir-Blodgett technique. Further, tyrosine molecules bound to the surface of Au nanoparticles through amine groups in the amino acid may be used to selectively reduce silver ions at high pH on the surface of the Au nanoparticles, thus leading to a simple strategy for realizing phase-pure Au core-Ag shell nanostructures.

Evaluation of Silver Nanoparticles as a Comparative Study and Determination of Its Effect on Vigna Radiata

“…The color indicating the formation of silver nanoparticles is in accordance with the result of Srivastava et al 15 . This result is also in line with that of previous study 9 in which they have said that the reducing ability of tyrosine will occur only in alkaline pH.…”

“…For chemical synthesis, the maximum peak of absorbance obtained was 436.5 nm which is in contrast with that of the result of author, 9 the maximum wavelength obtained was 415 nm.…”

“…It is less time consuming when compared to the other methods. This method involves the use of biomolecules especially amino acids as reducing agents 9 .…”

Nanosilver: new ageless and versatile biomedical therapeutic scaffold

“…The electron-donating property of the phenolic hydroxyl group of Tyr could directly reduce silver ion to AgNP. 202 Thus, it is possible to synthesize AgNPs through the reduction of Ag + by silk fibroin in situ to prepare the antibacterial silk film. Biopolymer film such as AgNPs silk is limited in its packaging application due to its poor mechanical property.…”

Biosynthesis of Au, Ag and Au&ndash;Ag bimetallic nanoparticles using protein extracts of <em>Deinococcus radiodurans</em> and evaluation of their cytotoxicity

“…The different roles of the Dps2 in reducing Au(III) and Ag(I) might be due to the following: first, the Dps2, which functions as a sequester of intracellular Fe 2+ ion and stores iron ions in the form of Fe 3+ , 53 could not adsorb or interact with the trivalent Au ions; however, it did reduce the monovalent Ag ions; second, Dps2 only contains three tryptophan and six tyrosine molecules that have the ability of donating electrons from their NH or OH groups (Table S2) 54,55 and thus could not have enough potential to synthesize the AuNPs, considering the relative higher reduction potential of gold (E =0.799 V). 56,57 Thus, the metal NP's biosynthetic ability with different proteins might be determined by their composition or reducing capability. Biogenerated noble metal NPs of different organisms might have different properties due to the distinct composition of biomolecules between species.…”