Gold Nanostars as a Novel and Sensitive Indicator of Iodometry for Colorimetric Sensing

Iodometry (iodometric method) is one of the simplest, fastest, and most accurate oxidation-reduction titrations for colorimetric detection. Starch is a key indicator for determining the reaction end point. However, the low solubility and instability of starch limit the sensitivity and application of the iodometry. Plasmonic nanomaterials have emerged as innovative tools to inject modern vitality into traditional methods. In this study, we report gold nanostars as a novel and sensitive indicator of iodometry for colorimetric sensing. Branched gold nanostars possess localized surface plasmon resonance (LSPR) properties, and their protruding tips can be specifically reshaped by iodide to tune the optical readout. As a color indicator, gold nanostars can be gradually etched with increasing iodide concentration, displaying a variety of color changes from blue to purple and finally to red. This colorimetric sensing strategy enables highly sensitive detection of iodine standards with a linear range from 0.125 μM to 20 μM and a limit of detection of 0.0375 ± 0.0013 μM. Proof-concept experiments demonstrate the colorimetric performance of gold nanostar indicators in direct iodometry, remnant iodometry, and displacement iodometry by detecting chlorine, sulfide, and copper ions in hospital wastewater. Gold nanostars have advantages such as good stability, easy handling, low cost, and high sensitivity, which provide great prospects for the widespread application of iodometry.