Abstract: One Au NCs/blue carbon dots-based ratiometric fluorescent probe, which was synthesized by a simple and low-cost method, was developed to detect NO-2rapidly and visually. The red fluorescence of Au NCs can be quenched by NO-2sensitively and selectively, while the fluorescence of BCDs acting as background reference, remained blue. The probe showed colour changes from red to blue under ultraviolet in response to NO-2. By studying the response time of the ratiometric fluorescence probe, the reaction system could complete the reaction within 2 minutes. The fluorescence intensity ratio of the ratiometric fluorescent probe had a good linear relationship with NO-2concentration in the range of 75-200 μmol/L with a detection limit (LOD) as low as 0.8 μmol/L. NO-3was reduced to NO-2with vanadium ion as reducing agent, and the reduction rate can reach more than 90%. Therefore, NO-3concentration was detected by ratiometric fluorescent probe indirectly, with a detection limit of 0.6 μmol/L. The method was applied to the determination of NO-3in water and soil samples, and the spiked recovery rate was between 94.7%-104.51%. The measured results were basically consistent with the spectrophotometric method, which realized the rapid, sensitive and accurate detection of NO-3. Based on this, a fluorescent test paper has been constructed and it showed high selectivity and sensitivity to NO-2. The fluorescent test paper not only extraordinarily improved the detection efficiency, but also cut down its cost. The feasibility of rapid semi-quantitative detection of NO-3in real samples by fluorescent test paper was proved by experiments.

Key words: AuNCs, ratiometric fluorescent probe, nitrate, fluorescent test paper, visual detection