Design of highly sensitive non-aggregation colorimetric sensor and its application based on inhibiting vitamin C reducing Hg2+

Hg0, the product of vitamin C (Vc) reducing Hg2+, could react with Au along on the longitudinal axis of gold nanorods (AuNRs) to form gold amalgamation (AuHg2(L)), which caused the longitudinal surface plasmon resonance (LSPR) absorption peak of AuNRs to blue shift (Δλ) and the absorbance (A) to decrease. However, the strong coordination between hydrosulfide group (SH) in cysteine (Cys) and Hg2+ can effectively inhibit the formation of AuHg2(L), resulting in that the LSPR absorption peak of AuNRs red shift (Δλ), the corresponding absorbance enhances as well as the color of solution obviously changes. Thus, a responsive, sensitive and simple non-aggregation AuNRs colorimetric sensor for the determination of Cys has been developed based on the inhibiting effect of Cys on Vc reducing Hg2+. The limit of quantitation (LOQ) of this sensor is 0.030 μM, which is much lower than that of aggregation colorimetric sensor and gold nanocluster fluorometry, showing its great sensitivity. What is more, the sensor has been applied to the detecting of Cys in human urine samples with the results agreeing well with inductively coupled plasma-mass spectroscopy (ICP-MS), showing its great practicality. Furthermore, the morphological changes of AuNRs were characterized by high resolution transmission electron microscope (HRTEM) and the sensing mechanism for the determination of Cys was also discussed.