Calix[4]arene functionalized gold nanoparticles for colorimetric and bare-eye detection of iodide in aqueous media and periodate aided enhancement in sensitivity

AbstractA water- soluble p-sulphonatocalix[4]arene was synthesized and anchored onto the surface of gold nanoparticles (AuNPs) in aqueous medium. The conjugate was characterized by IR, UV–Vis and TEM analysis. This material responds to iodide in giving a color change from pink to blue which is easily detectable with bare eyes. While periodate itself does not cause any spectral changes, a substantial spectral change can be seen in the presence of traces of iodide. The lower detection limit for iodide in the absence of periodate is 2.5 μM, which is further lowered to 80 nM in presence of periodate. A mechanistic study revealed that the chemisorption of the ions I− and I3−, formed by the reaction I− and periodate on the surface of AuNPs resulted in spontaneous oxidation of the anions. The electron transfer changes the size and morphology of the nanoparticles and results in the color change. The method is specific for iodide. It was successfully applied to the determination of I− in (spiked) waters and in solutions of iodized edible salt. Graphical abstractWater-soluble calixarene functionalized gold nanoparticle, which selectively detects iodide in aqueous media with colour change, detectable by bare-eyes is reported. The detection limit is greately enhanced with the aid of periodate in presence of iodide, mechanistic study was also carried out by spectroscopic and microscopic techniques.