Dual mode fluorescence-colorimetric sensing of trace nitrite using amino functionalized carbonized polymer dots

Herein, we report a dual-mode sensor based on green-emission carbonized polymer dots (g-CPDs, amino density 9.64 %), synthesized by optimizing the molar ratio of m-PD (functional precursor) to EDTA (cross-linking agent) and using a cross-linking polymerization strategy. It enables highly selective and accurate detection of NO₂^- by leveraging the directional enrichment of amino groups within the cross-linked polymer network and the stabilizing effect of the π-π conjugated structure of the carbon core. The sensor achieved low detection limits of 0.109 μM (fluorescence, 513 nm) and 0.129 μM (colorimetric, 450 nm). It showed excellent resistance to interference and high accuracy in analyzing real samples (food and environmental water samples), with recoveries from 97.13 % to 106.90 % and RSDs below 4.88 %. Through systematic structural characterization, quantum chemical calculations, and Stern-Volmer analysis, the structure-activity relationship of the g-CPDs was clarified, revealing the synergistic mechanism of static fluorescence quenching and amino-positive-potential-driven diazotization color development.