Robust colorimetric detection based on the anti-aggregation of gold nanoparticles for bromide in rice samples

Inorganic bromide (Br(−)) is an important contaminant ion as it can originate from the overuse of illegal methyl bromide as a fumigant in stored rice samples. Herein, we developed a simple and highly sensitive colorimetric sensor for bromide ion detection in rice samples. The sensor is based on the anti-aggregation of gold nanoparticles (AuNPs) by Br(−) in the presence of Cr(3+), which made the method more selective than other typical aggregations of nanoparticles. The AuNPs underwent an aggregation process as a result of the coordination of Cr(3+) and the carboxylate group of a citrate ion stabilized the AuNPs, resulting in a red-to-blue color change. When Br(−) was pre-mixed with the AuNPs and Cr(3+) was added, the solution color changed from blue to red with an increase in the Br(−) concentration. The anti-aggregation process can be detected with the naked eye and monitored using UV-vis spectrophotometry. The linear calibration curve ranged between 0.31 and 3.75 μM Br(−) with a low LOD and LOQ of 0.04 and 0.13 μM. The recovery was excellent, ranging from 79.9–92.2% with an RSD of less than 4.0%. The good inter-day and intra-day precisions were 2.9–6.4% and 3.1–7.1%, respectively. The developed sensor has proved to provide a robust method for Br(−) detection in rice samples.