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, 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 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 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.