A robust dual-readout ratiometric assay for dopamine based on NiMn 2 O 4 -catalyzed DHNP fluorophore conversion

nanoflowers. The nanozyme simultaneously exhibits peroxidase- and oxidase-like activities, catalyzing a highly selective cyclization reaction between DA and 1, 3-dihydroxynaphthalene (DHNP). As the DA concentration increased, the intrinsic fluorescence of DHNP at 440 nm was progressively quenched, accompanied by the formation of a new optically active fluorophore with emission at 485 nm and a corresponding absorbance at 455 nm. This dual-mode ratiometric fluorescence-colorimetric sensing strategy enabled self-calibrated detection, effectively minimizing signal fluctuation and matrix interference. The platform displayed excellent linearity over the range of 0-250 µM for fluorescence and absorbance responses, allowing accurate, sensitive, and selective DA determination. Owing to its robustness and reliability, the proposed method is well suited for high-throughput dopamine analysis in diverse biological sample matrices.