Anti-aggregation of Gold Nanoparticles for Inorganic Bromide Detection in Rice Sample

Abstract

A simple and highly sensitive colorimetric sensor for inorganic bromide (Br) detection in rice samples was developed. The sensor is based on anti- aggregation of gold nanoparticle (AuNPs) via the adsorbed Br on AuNPs surface, leading to interruption of an AuNPs aggregation process based on coordination of chromium ion (Cr3) and citrate capped AuNPs. Consequently, the solution color of aggregation state changed from blue to red color of anti-aggregation state with increasing the Br concentration. Under the optimum condition of 1.83 nM AuNPs with 4.81 μM Cr3+ in 10 mM phosphate buffer (pH 6.5) and 10 min of reaction time, a linear calibration curve based on the color transition observed by naked eye was 0.31 - 3.75 μM Br (y = 3.4803x - 0.6065, R2 = 0.9970). The limit of detection (LOD) and limit of quantification (LOQ) were 0.04 and 0.13 μM, respectively. The recoveries were 79.9 - 92.2% and intra- and inter-day precisions as % relative standard deviation were better than 7.12 %. However, due to matrix effect, a standard addition curve was applied for accurate determination of Br in rice samples. The preparation of rice samples before colorimetric detection was carried out by alkaline digestion and dry ashing at 600 °C for 4 h that can remove organic compounds and the minor elements. The X-ray fluorescence spectrometry (XRF) results confirmed that Bri did not evaporate after ashing at high temperature (600 °C). The developed sensor is very selective to Br compared to other ions which is found in rice samples. Moreover, it was successfully applied for determination of Br1 in five brands of white rice samples. The Br` residues were detected ranging from 3.12-5.21 mg kg1 in all samples which was corresponded to the Br detected by ion chromatography with no significant difference and no over the maximum residue limit of 50 mg kg1 set by CODEX.