Detection and determination of iodide in dual-mode through thiosulfate sensitized silver nanoparticles: UV–visible and SERS approach

Abstract We herein present the citrate capped silver nanoparticles (AgNPs) as colorimetric and Surface-Enhanced Raman Spectroscopic (SERS) probe for real time detection and determination of iodide (Iˉ). The yellow colored AgNPs exhibited local surface plasmon resonance (LSPR) band at 418±3 nm. Addition of 20 µL of sodium thiosulfate (1.0×10-3 M) to AgNPs (2.0 mL) caused their etching and a blue-shift in UV–Vis spectrum accompanied by suppression in major SERS signals. However, exclusive addition of Iˉ (20 µL) resulted into visual color change in its appearance (from yellow to burnt orange) and bifurcation of LSPR band (425 nm and 515 nm) along with the re-appearance of strong SERS peak (1363 and 1570 cm-1). Excellent naked-eye selectivity of AgNPs for Iˉ was observed among diverse analytes with correlation coefficient (R2) of 0.983. The intensity of SERS signals was found to be linearly related to Iˉ (R2=0.981). The limit of detection (LOD) and limit of quantification (LOQ) was estimated 1.95 µM and 6.5 µM respectively (colorimetric) and 60 nM and 200 nM respectively (SERS). The quantification of Iˉ through UV–Vis spectroscopy in its few real samples such as kelp, L-thyroxine tablets and blood serum with their percentage recovery 97-102% was successfully performed. The sensing action of AgNPs demonstrated AND logic gate involving S2O32ˉ and Iˉ as the first and second inputs.