Fluorescence turn-on detection of iodide, iodate and total iodine using fluorescein-5-isothiocyanate-modified gold nanoparticles

Selective turn-on fluorescence detection of I- was accomplished using fluorescein isothiocyanate-decorated gold nanoparticles (FITC-AuNPs). FITC molecules, which fluoresce strongly in an alkaline solution, were severely quenched when they were attached to the surface of AuNPs through their isothiocyanate group. Upon the addition of I-, FITC molecules were detached because of I- adsorption on the surface of AuNPs. As a result, released FITC molecules were restored to their original fluorescence intensity. Because I- has a higher binding affinity to the surface of Au than do Br-, Cl-, or F-, the FITC-AuNPs obviously have a higher selectivity toward I- than toward these other anions. Meanwhile, after IO3- was reduced to I- with ascorbic acid, the detection of IO3- was successfully achieved using the FITC-AuNPs. Under an optimum pH and AuNP concentration, the lowest detectable concentrations of I- and IO3- using this probe were 10.0 and 50.0 nM, respectively. The FITC-AuNPs provide a number of advantages, including easy preparation, selectivity, sensitivity, and low cost. This unique probe was applied to an analysis of the total iodine in edible salt and seawater.