Gold Nanoparticle-Based Optical Probe for Quick Colorimetric Visualization of Cysteine

In this work, a highly sensitive and selective optical probe for cysteine was developed using unmodified gold nanoparticles. Quick visual detection depended on the distance‐dependent optical properties of gold nanoparticles, the self‐assembly of cysteine on the surface of gold nanoparticles, and the chelation in the presence of lead ions. The form of complex could rapidly induced the aggregation of gold nanoparticles, thereby resulting in red‐to‐blue (or purple) color change. The concentration of cysteine was determined with a limit of detection (LOD) lower than 1 × 10−7 M by the naked eye and could further be monitored by a UV‐vis spectrometer easily. The highest selectivity was proved in comparison with other seventeen amino acids and the relative mechanism was detailedly investigated by the addition of ethylenediaminetetraacetate (EDTA). Compared with other amino acids, only cysteine can rapidly induce the aggregation of gold nanoparticles in the presence of Pb2+, thereby resulting in red to blue color change. The concentration of cysteine was determined with a LOD lower than 1×10‐7 M by the naked eye and could further be monitored by a UV‐vis spectrometer.