A ratiometric optical strategy for bromide and iodide ion sensing based on target-induced competitive coordination of a metal–organic nanosystem

Abstract

A ratiometric sensor through the built-in correction gains stronger anti-interference ability and more accurate analysis results compared with a single-signal sensor. Herein, a novel ratiometric assay platform coupled with fluorescence (FL) and scattering has been constructed for the selective and accurate quantization of Br⁻/I⁻. The ratiometric sensor is based on a metal–organic nanosystem, which is constructed via coordination bonding-induced self-assembly between non-conjugated polymer nanoparticles (NC-PNPs) and Hg(II), consequently displaying fluorescence and strong second-order scattering (SOS) signals. In the response system, the NC-PNPs function as a signal unit, and the Hg(II) ion serves as a recognition element. Upon the introduction of Br⁻/I⁻, the high affinity with Hg(II) makes Br⁻/I⁻ snatch Hg(II) from the NC-PNP–Hg(II) nanosystem, causing the nanocomplex to disassemble. The target-triggered disaggregation results in a decrease in the SOS intensity, and meanwhile the Hg–Br⁻ or Hg–I⁻ compounds produced in situ reduce the FL intensity of the NC-PNPs via static quenching, suggesting the feasibility of ratiometric Br⁻/I⁻ detection. Finally, the FL–SOS dual-signal strategy towards Br⁻/I⁻ is successfully applied to real water/food samples. The ratiometric analytical platform coupled with FL and SOS offers a new perspective for applications based on target-induced aggregation and disaggregation behavior.