In situ generation of polydopamine as photothermal reporter for on-site testing of azodicarbonamide in flour using an...

The detection of the illegal additive azodicarbonamide (ADA) in flour and related products is crucially important due to the harmful effects of excessive consumption on human health. However, the requirement for expensive instruments and trained operators poses a major challenge for on-site testing of ADA, particularly in field enforcement and consumer self-monitoring. Herein, an economical and portable 3D-printed photothermal (PT) device constructed by a 3D-printed sample bracket, a separable 96-well plate, an 808 nm laser, and a thermometer was rationally designed for quantitative on-site testing of ADA in flour. Since the target ADA could convert reducing glutathione (GSH) into non-reducing glutathione disulfide (GSSG), manganese dioxide nanosheets (MnO₂ NSs) in this sensing system remain intact to catalyze the conversion of dopamine (DA) into polydopamine nanoparticles (PDA NPs). During the detection process, the PT signal changes induced in the sample driven by the 808 nm laser could be easily recorded with a digital thermometer. The proposed PT method demonstrates an excellent linear response for ADA in the range of 30-1000 μM, with a detection limit as low as 10 μM, which was significantly lower than the maximum allowable ADA level in flour extracts (388 μM). This portable and cost-effective PT sensing system shows great potential for quantitative on-site testing, enabling immediate food safety identification in resource-limited regions.