Gold nanoparticles crosslinking by peptides and amino acids: A tool for the colorimetric identification of amino acids.

Gold nanoparticles are known to aggregate in the presence of proper multifunctional compounds. For those larger than 3 nm, the process can be followed with the naked eye because the surface plasmon absorption band of the particles shifts to longer wavelengths and the solution color changes from red to blue. To exploit this property, we have used amino acids and peptides as crosslinking agents in ethanol at low µM concentrations. In the case of amino acids, we report a straightforward protocol for their colorimetric identification. We also report that the presence of precise secondary structure and conformational constraints in oligopeptides, directly influence their crosslinking ability. A discussion on the nature of the interactions that induce these phenomena is also reported.