A simple fluorescent assay for thiocyanate based on Cu2+-triggered oxidation of o-phenylenediamine

Thiocyanate (SCN − ) is an anionic contaminant and is a biomarker of environmental cyanide exposure. Therefore, it is particularly necessary to develop a simple, fast and sensitive method for SCN − assay. Herein, a fluorescent assay method was developed to determine SCN − based on Cu 2+ -triggered oxidation of o-phenylenediamine (OPD). Without SCN − , OPD was oxidized by Cu 2+ and the resultant product (i.e., OPD oxide) exhibited a high fluorescence. However, in the presence of SCN − , Cu 2+ reacted with SCN − ; and thus, the oxidation ability of Cu 2+ toward OPD was reduced, resulting in a weak fluorescence. Several important parameters such as the concentrations of Cu 2+ and OPD, pH and the reaction time were optimized. Under the optimized conditions, the linear range was 5–80 μM and the limit of detection was 5 μM for SCN − assay. In addition, the high selectivity and the satisfactory recoveries in tap water and artificial saliva were achieved for SCN − detection due to the strong chelation between SCN − and Cu 2+ . The whole detection process was simple and fast without using complex nanoparticles. More importantly, the developed assay method will have promising applications in monitoring of SCN − for the assessment of water safety and human health. Graphical abstract