Heavy atom-induced quenching of fluorescent organosilicon nanoparticles for iodide sensing and total antioxidant capacity assessment.

We present a novel approach for iodide sensing based on the heavy-atom effect to quench the green fluorescent emission of organosilicon nanoparticles (OSiNPs). The fluorescence of OSiNPs was significantly quenched (up to 97.4% quenching efficiency) in the presence of iodide ions (I^-) through oxidation by hydrogen peroxide. Therefore, OSiNPs can serve as a fluorescent probe to detect I^- with high selectivity and sensitivity. The highly selective response is attributed to the hydrophilic surface enabling good dispersion in aqueous solutions and the lipophilic core allowing the generated liposoluble I₂ to approach and quench the fluorescence of OSiNPs. The linear working range for I^- was from 0 to 50 μM, with a detection limit of 0.1 μM. We successfully applied this nanosensor to determine iodine content in edible salt. Furthermore, the fluorescent OSiNPs can be utilized for the determination of total antioxidant capacity (TAC). Antioxidants reduce I₂ to I^-, and the extent of quenching by the remaining I₂ on the OSiNPs indicates the TAC level. The responses to ascorbic acid, pyrogallic acid, and glutathione were investigated, and the detection limit for ascorbic acid was as low as 0.03 μM. It was applied to the determination of TAC in ascorbic acid tablets and fruit juices, indicating the potential application of the OSiNP-based I₂ sensing technique in the field of food analysis.