Lysine-functionalized silver nanoparticles for visual detection and separation of histidine and histidine-tagged proteins.

A new chromogenic chemosensor based on lysine-functionalized silver nanoparticles a was prepared and characterized by transmission electron microscopy (TEM), Fourier transform Raman, and ultraviolet-visible (UV-vis) spectroscopy. The color changes of nanoparticles I in the absence and the presence of metal ion were observed upon addition of various amino acids and proteins in aqueous Solution. Among the various amino acids, the sensor I in the absence of metal ion shows it novel colorimetric sensor with capability to probe histidine and histidine-tagged proteins. On the other hand, the color changes of I in the presence of metal ions such as KCl or NiCl2 did not occur with ally aminoacids. Therefore, the sensor I in the absence of metal ion responds selectively to histidine, it response which can be attributed to its aggregation induced by histidine with high numbers of electrostatic interactions. This highly selective sensor I allows a rapid quantitative assay of histidine to concentrations as low as 5.0 mu M. providing it new tool for the direct measurement of histidine and histidine-tagged proteins in vitro system. Furthermore, we examined lie effect of pH oil absorbance (A(520)) Of I ill the Presence of histidine (pH 4-12). The absorbance under basic conditions was higher than that Under acidic or neutral Conditions, in accord with the stronger aggregation of I with histidine by electrostatic interaction between the carboxylate anion of I and ammonium protons of histidine under basic conditions.