Highly sensitive and selective assay method for iodide ion determination based on gold nanoparticles conjugated with glycol chitosan

Abstract

ABSTRACTA sensitive colorimetric method for the determination of iodide ions was developed using gold nanoparticles (AuNPs) functionalised with glycol chitosan (GCS). The iodide ions were at the centre of the O–I––O coordination structure, formed with the GCS-AuNPs, reducing their interparticle distance and inducing aggregation. Time-of-flight secondary ion mass spectrometry analyses showed that the bound iodide ions were coordinated to the oxygen atoms of the ethylene glycol in GCS, with this aggregation leading to a considerable variation in colour from light red to dark violet. Using this GCS-AuNP probe, the iodide ion concentration in environmental, biological and pharmaceutical samples could be determined by both the naked eye and UV-Vis spectroscopy. Additionally, the sensitivity of the detection was found to be markedly enhanced at pH 6, where a more pronounced colour change was observed. The absorption ratio A700/A521 of the functionalised AuNP solution correlated linearly with the iodide ion concentration within the range 0.0–10.0 mg/L, and the limits of detection in tap water, pond water, and bovine serum solution were 3.5, 3.6, and 3.4 μg/L, respectively. The present assay method can thus be utilised to rapidly measure the concentration of iodide ions in aqueous samples.