Soybean straw/histidine carbon dots-based ratiometric fluorescent probe for the visual inspection of epinephrine

Blue fluorescent carbon dots (Soy-His CDs) with high fluorescence quantum yield were synthesized via a hydrothermal method using biowaste soybean straw and L-histidine as precursors. A ratiometric fluorescence probe (Soy-His CDs@PEp-PEI) was subsequently constructed for the visual detection of epinephrine (Ep). Upon the continuous formation of the PEp-PEI copolymer, the green fluorescence of the Soy-His CDs@PEp-PEI probe at 515 nm gradually intensified, while the blue fluorescence at 420 nm was progressively quenched. This allows for the rapid and sensitive detection of Ep by monitoring the variation in the I₅₁₅/I₄₂₀ ratio. The limit of detection (LOD) was determined to be 0.025 µmol/L in the linear range 0.1-20 µmol/L. The response mechanism is attributed to the inner filter effect (IFE) between the Soy-His CDs and the polyepinephrine-polyethyleneimine (PEp-PEI) copolymer. The proposed method was successfully applied to detect Ep in human urine samples, yielding recoveries ranging from 95.82% to 102.01%. Furthermore, portable visual and intelligent detection of Ep was achieved using a smartphone equipped with RGB analysis software based on the Soy-His CDs@PEp-PEI probe system, with recoveries ranging from 94.65% to 108.33%. A good linear relationship was obtained in the range 0-10 µmol/L, with a limit of detection (LOD) of 0.14 µmol/L.