Highly sensitive and selective colorimetric sensor for thiocyanate based on electrochemical oxidation-assisted complexation reaction with Gold nanostars etching

In this work, we developed an electrochemical oxidation-assisted complexation strategy for highly sensitive and selective detection of thiocyanate (SCN⁻). Gold nanostars (AuNSs) with uniform and sharp tips were first prepared, and we found they can be quickly etched to gold nanoparticles (AuNPs) under electrochemical oxidation with the existence of halide and halogen-like ions. Through introducing SCN⁻-selective molecule: zinc phthalocyanine (ZnPc), the fabricated ZnPc-AuNSs/ITO electrode can rapidly and selectively response to SCN⁻ under electrochemical oxidation, manifesting as a noticeable change in color from navy blue to red. Thus SCN⁻ concentration can be easily reflected. The wide wavelength tuning range of AuNSs to AuNPs make the ZnPc-AuNSs/ITO sensor obtain a much wider detection range for SCN⁻ (10 nM to 80 mM) than most other reported studies. In addition, the detection limit is as low as 3 nM. It renders the sensor to be easily used in much diluted matrixes, which can further lower the interference. We further applied the colorimetric sensor to SCN⁻ detection in wastewater and milk, excellent performance was obtained. The proposed electrochemical oxidation-assisted complexation strategy will have good promise in developing colorimetric sensors with high selectivity and wide detection range, and will display more useful application in environmental monitoring.