Novel and portable cotton swab–based fluorometry was constructed for the first time for 3-aminosalicylic acid (3-ASA) and 5-aminosalicylic acid (5-ASA) detection. It was carried out by fluorescence enhancement on silver (Ag)–doped black phosphorus quantum dots (Ag@BPQD). Ag@BPQD were prepared from AgNO₃ and bulk black phosphorus in N, N-dimethylformamide (DMF) solution by solvothermal decomposition after mechanical exfoliation. Ag@BPQD show blue fluorescence with a quantum yield (QY) of 2.43%. In the presence of Ag@BPQD, 3-ASA exhibited bright blue fluorescence (λ_ex = 328 nm, λ_em = 448 nm). The fluorescence of 5-ASA was also enhanced significantly and exhibited bright green emission (λ_ex = 328 nm, λ_em = 484 nm). The linear range of 3-ASA is 0–90 μM with a detection limit (LOD) of 0.10 μM, relative standard deviation (RSD) ≤ 2.04%, and a recovery range of 98.0–104.3%. The linear range of 5-ASA is 0–120 μM with a LOD of 0.12 μM, RSD ≤ 1.34%, and a recovery range of 98.0–101.3%. When 3-ASA and 5-ASA were mixed in different ratios, the fluorescence showed different colors. The possible mechanism of the interaction between 3-ASA (or 5-ASA) and Ag@BPQD may be ascribed to the generation of excited-state intramolecular proton transfer. To realize convenient detection of 3-ASA and 5-ASA, a Ag@BPQD portable sensing method using cotton swabs were built. The proposed approach provides the detection of 3-ASA and 5-ASA in environmental and biological samples with high efficiency, accuracy and portability.

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