Specific detection of cysteine and homocysteine in biological fluids by tuning the pH values of fluorosurfactant-stabilized gold colloidal solution

This study describes the use of 14 nm nonionic fluorosurfactant-capped gold nanoparticles (FSN-capped AuNPs) for the simultaneous detection of cysteine (Cys) and homocysteine (Hcy) using colorimetric method, requiring no use of separation techniques. It was found that the kinetics of Cys/Hcy-induced aggregation of the 14 nm FSN-capped AuNPs strongly depends on the pH value of gold colloidal solution. At a pH of 6.5, the Cys-induced aggregation kinetics of the FSN-capped AuNPs was almost identical to that induced by Hcy, facilitating simultaneous detection of total Cys and Hcy up to a concentration as low as 0.15 mu M; while at pH 12.0, the kinetics of Cys-induced aggregation was much faster than that inducted by Hcy, leading to selective detection of Cys at concentration as low as 1.0 mu M in the presence of Hcy. The applicability of the method was validated by spiking known amount of Cys and Hcy in human urine and plasma samples, obtaining a recovery of 95.4-105.5%. The present approach is simple, high selective and provides high reproducibility, and has a great potentiality in disease diagnosis. (C) 2011 Elsevier B.V. All rights reserved.