Non-Aggregation Gold Nanorods Colorimetric Sensor for Detection of Cysteine

The strong coordination of hydrosulfide groups (–SH) in cysteine (Cys) with Hg²⁺ results in a stable Hg(Cys)₂ complex, which inhibits vitamine C (Vc) to reduce Hg²⁺ to form Hg0 and further inhibits the reaction between Hg0 and Au at the tips of gold nanorods (AuNRs) to form gold amalgamation (AuHg₂(L)). As a result, the longitudinal surface plasmon resonance (LSPR) peak of Au NRs red shifts and the corresponding absorbance (A) increass along with a rapid color change from red to blue. Simultaneously, A was gradually enlarges with the increase of Cys content. Bearing this in mind, a quick, sensitive and simple non-aggregation AuNRs colorimetric sensor for the determination of Cys has been established. Under optimized experimental conditions, the developed colorimetric sensor gave a linear range of 0.050~3.0 μmol/L with a limit of quantization (LOQ) of 0.030 μmol/L. The proposed colorimetric sensor has been successfully applied to the determination of Cys in human urine samples, the results agreed well with those obtained by inductively coupled plasma-mass spectroscopy (ICP-MS). Furthermore, the sensing mechanism for the determination of Cys is also discussed.