Analyte-triggered cascade signal amplification strategy for highly sensitive detection of iodate in table salt with...

A novel and highly sensitive upconversion fluorescence and colorimetric dual readout iodate (IO₃^-) nanosensor system was constructed by using both the outstanding optical performance of NaYF₄:Yb, Tm upconversion nanoparticles (UCNPs) and the analyte-triggered cascade signal amplification (CSA) technique. The construction of the sensing system consisted of three processes. First, IO₃^- oxidized o-phenylenediamine (OPD) to diaminophenazine (OPDox), while IO₃^- was reduced to I₂. Second, the generated I₂ can further oxidize OPD to OPDox. This mechanism has been verified by ¹H NMR spectra titration analysis and HRMS measurement, which effectively improves the selectivity and sensitivity of the measurement of IO₃^-. Third, the generated OPDox can effectively quench the fluorescence of UCNPs via the inner filter effect (IFE), realize analyte-triggered CSA, and allow quantitative determination of IO₃^-. Under the optimized conditions, the fluorescence quenching efficiency showed a good linear relationship to IO₃^- concentration in the range of 0.06-100 μM, and the detection limit reached 0.026 μM (3RSD/slope). Moreover, this method was applied to detect IO₃^- in table salt samples, yielding satisfactory determination results with excellent recoveries (95.5-105%) and high precision (RSD <5.5%). These results suggest that the dual-readout sensing strategy with well-defined response mechanisms has promising application prospects in physiological and pathological studies.