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

Abstract

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.