Determination of Cysteine by Diffuse Reflectance Spectroscopy by Its Influence on the Formation of Gold Nanocomposites Based on Polyurethane Foam

A method is proposed for the determination of cysteine in an aqueous solution by its effect on the formation of gold nanoparticles on the surface of polyurethane foams. The method is based on the interaction of in situ formed gold nanoparticles with cysteine, which results in their stabilization in solution and in a decrease in the color intensity of the nanocomposite detected by diffuse reflectance spectroscopy. The effect of the concentration of the precursor, aurichlorohydric acid, contact time of phases, and the pH of the solution on the sensitivity of cysteine determination is studied. Under the selected conditions, the limit of detection for cysteine was 0.36 μg/mL. A possibility of using the proposed method for the determination of cysteine in brewer’s yeast is demonstrated.