Studies on Differential Behavior of Silver Nanoparticles Towards Thiol Containing Amino Acids

Silver nanoparticles offer a broad range of applications in biomedical and bioanalytical areas. In lieu of inadequate prior reports the present study aims to investigate the differential interaction of silver nanoparticles with cysteine and glutathione. Cysteine and glutathione were chosen as the model biomolecules owing to its strong affinity towards silver nanoparticles and potential applications in the field of biomedicine. Cysteine induced aggregation of particles but under similar experimental conditions glutathione failed to cause aggregation. The interaction of silver nanoparticles with cysteine resulted in a shift in the plasmon bands to higher wavelengths, which was further confirmed by microscopic studies which showed randomly arranged aggregates of the particles. The disappearance of the - SH band in the FT-IR spectra and the shift in the peaks of COO- and NH3 + groups indicated the S-Ag interaction and the aggregation of the particles. Further DLS and zeta potential measurements showed relatively high degree of polydispersity confirming the aggregation of the particles. The positive amine group of cysteine formed salt bridges with carboxylate groups which result in the aggregation of the particles. Unlike in the cysteine treated samples the FT-IR spectra of glutathione treated samples did not show any shift in the peaks of COO- and NH3 + stretching, confirming that these groups have not taken part in the interaction in order to cause the aggregation of the particles. We anticipate that further improvements on this approach will enable the exploitation of the nanoparticles functionalized with amino acids containing thiol group towards bio-sensing applications.