Highly sensitive, selective and naked-eye detection of bromide and bromate using distance–based paper analytical device

Abstract

Bromine (Br) can usually be found as a bromide (Br‾) form contained in drinking water. Bromate (BrO3‾) formation often occurred during the ozonation process in the presence of Br‾. BrO3‾ is classified as a potential human carcinogen, so both the Br‾ and BrO3‾ concentrations must be strictly controlled before and after an ozone-based treatment procedure, respectively. This work reports on distance-based paper analytical devices (dPADs) that have been modified with silver hexagonal nanoprisms (AgNPrs) for highly sensitive and selective determination of both Br‾ and BrO3‾. The measurement of BrO3‾ is based upon its conversion to bromine vapor (Br2) when gauged with a paper-based headspace extractor (PAD-HS) that is coupled with dPADs (PAD-HS-dPADs). For Br‾ analysis, O2 plays an important role in the change from Br‾ to Br2 within an acid media. Br2 changes rapidly in water to give us HBrO which is a strong oxidizing agent of AgNPrs. Then, the oxidative reaction of the AgNPrs (pink color) within the presence of Br‾ and BrO3‾ establishes both silver bromide (AgBr) and the silver nanosphere (AgNPs, yellow color), which can then be easily observed as a change of a pink color band to a yellow color band by the naked eye. Quantification of Br‾ and BrO3‾ is then achieved by measuring the length of the yellow color band. Under the optimal conditions, the calibration curve will be linear in the range of 25 μg L−1 to 2 mg L−1, and from 0.5 to 50 μg L−1 for Br‾ and BrO3‾, respectively. The naked-eye detection limits were found to be 10 and 0.5 μg L−1 for Br‾ and BrO3‾, respectively. The proposed dPADs for the Br‾ and BrO3‾ detection exhibited an exceptional sensor performance combined with a low detection limit. They also have the benefits of ease of use, an instrument-free convenience, coupled with portability and a low-cost efficiency. Consequently, our sensing device should be applied to the low-level detection of Br‾ and BrO3‾ in real samples, including drinking water, rice, and flour.