Colorimetric Sensor for Thiocyanate Based on Anti-aggregation of Gold Nanoparticles in the Presence of 2-Aminopyridine

Based on the anti-aggregation mechanism of citrate stabilized gold nanoparticle (AuNPs), a new specific and sensitive colorimetric sensor for thiocyanate (SCN^-) was developed. In this scheme, the AuNPs were aggregated in the presence of the aggregating agent 2-aminopyridine (2-AP) due to electrostatic attraction. The solution color changed from red to blue. When SCN^- was present, SCN^- formed a sulfur-gold bond with the AuNPs to protect the AuNPs from aggregation. Thiocyanate can be detected by the color change of the solution from blue to red. The results showed that the absorbance ratio A675/A520 was linear with the concentration of SCN^- in the range of 0.4 - 1.2 pmol L^-1 by UV-Vis spectroscopy. The limit of detection (LOD) of this assay was 0.37 pmol L^-1. The system also had excellent selectivity and anti-interference ability. In addition, this method was successfully used for the detection of SCN^- in actual water samples and achieved good results.