Citrate capped silver nanoparticles as naked-eye colorimetric sensor for sensitive and rapid detection of cysteine in biological and environmental samples

Abstract

The use of citrate capped silver nanoparticles (Cit/Ag NPs) as a highly selective and fast colorimetric sensor for the determination of cysteine by UV–Vis spectrophotometric detection was described in the present work. The colorimetric recognition strategy was based on the significant change in the surface plasmon resonance (SPR) band of Cit/Ag NPs from 403 to 550 nm with cysteine. By adding cysteine to the Cit/Ag NPs solution, the color of the solution rapidly changed from yellow to red in a short time of 1 min. This is attributed to the aggregation of citrate-capped Ag NPs induced by cysteine due to the formation of the strong covalent Ag–S bond and electrostatic binding. With this strategy, a linear relationship between the A550/A403 extinction ratio and Cys concentrations was obtained in the range of 0.01–100 μM with a coefficient of determination of 0.9931 and a limit of detection of 5.1 nM. The proposed method was successfully applied for detection of cysteine in biological and environmental samples with significant recovery rates in the range of 95.5–105.1% and the relative standard deviation (RSD) lower than 5.5%.Therefore, the Cit/Ag NPs as a chemical sensor in colorimetry assay is simple, very fast, easy synthesis, highly selective and sensitive, a single-step process, and mainly cost-effective, providing a possibility to develop an analysis in real-time and an effective rapid detection way for monitoring and visualizing Cys.