Method for detection of thiol-containing amino acids using gold-polystyrene composites

This paper reports the preparation of PS-PEI-Au composite colloids via the utilization of a facile method involving poly(ethylenimine) (PEI). The PEI used in the reaction scheme served as a linker between gold (Au) and polystyrene (PS) and additionally as a reducing agent in the conversion of Au ions to gold nanoparticles (Au NPs). The PS-PEI-Au colloids thus prepared were characterized by scanning electron microscopy, ultraviolet-visible and infrared spectroscopy, and cyclic voltammetry. The PS-PEI-Au composites were further used for the detection of the thiol-containing amino acids, cysteine and homocysteine, via attenuated total reflection spectroscopy. Experimental results revealed interfacial binding of the amino acids to the composites and correlated with successive additions of the respective amino acids.