Surface plasmon resonance additivity of gold nanoparticles for colorimetric identification of cysteine and homocysteine in biological fluids.

In this work, with the assistance of the additivity of surface plasmon resonance band of nonionic fluorosurfactant-stabilized gold nanoparticles, we developed a new colorimetric assay approach of cysteine (Cys) and homocysteine (Hcy) in biological fluids, requiring no use of separation techniques. The detection limits of Cys and Hcy can be as low as 0.4 μM. The applicability of the method was validated by spiking known amount of Cys and Hcy in human urine and plasma samples. Recoveries were in the range of 97.2-106.7%. The present approach is simple, high selective and reproducible. In addition, the universality of the additivity of surface plasmon resonance band was demonstrated by virtue of silver nanoparticles. Therefore, the proposed method has a great potentiality in disease diagnosis associated with Cys and Hcy.