Carbon Dot-Gold Nanoparticles Ensemble for Specific Visual Iodide Recognition

Iodide has long been recognized as an effective shape-directing agent for facilitating the growth of anisotropic noble metal nanostructures. However, little attention has been paid to the specific interaction between iodide and metal nanoparticles. In this study, we demonstrate the selective recognition of iodide in solution by the carbon-dot-gold nanoparticles (Cdot-AuNPs) ensemble. Irregularly-shaped AuNPs were generated through the reduction of HAuCl4 by citrate ions and stabilized by Cdot at ambient temperature. Upon the addition of iodide, the color of the solution changed from blue to red with the growth of AuNPs to semi-spherical nanoparticles, as confirmed by transmission electron microscopy. The selectivity test validated that only iodide could induce this specific visual response, highlighting a novel interaction mechanism between iodide and AuNPs. The recognition of iodide by this Cdot-AuNPs ensemble showed good resistance toward many environmentally relevant metal ions, particularly Ca2+, providing potential for the identification of iodide ions in real samples. Mixing tetrachloroauric acid, sodium citrate, and bee pollen-derived carbon dots (Cdot) at ambient temperature leads to the preparation of Cdot-AuNPs ensemble for the specific colorimetric recognition of iodide by reshaping the dimensions of the AuNPs.