Fluorescent iron-doped polymer dot nanozyme-based cascade reaction for α-glucosidase activity and inhibitor detection

The accurate quantification of α-glucosidase (α-Glu) activity and its inhibitor is of vital for diabetes diagnosis and drug screening. Enzyme activity could be detected by developing a sensing method based on nanozyme-involved cascade reaction. However, such a cascade reaction typically produces only one signal, whereas the fabrication of multifunctional nanozymes toward this end remains a formidable challenge. Herein, iron-doped fluorescent polymer dots (Fe-PDs) were one-pot synthesized under mild conditions. Iron doping accelerates PDs formation and imparts prominent peroxidase (POD)-like activity to the material. The as-prepared Fe-PDs could catalyze the oxidation of colorless TMB by H₂O₂ to form chromogenic oxTMB, which quenched the intrinsic fluorescence of Fe-PDs via the inner filter effect (IFE). Relying on three-catalyst cascade catalysis of α-Glu, glucose oxidase (GOx) and POD, this work constructed a highly sensitive colorimetric-fluorescent sensing platform. By introducing p-nitrophenyl-α-D-glucopyranoside (PNPG) as the substrate, the system enables quantitative analysis of H₂O₂, glucose, α-Glu activity as well as α-Glu inhibitors. Benefiting from cascade-induced signal amplification, the dual-modal assay enables quantitative analysis of α-Glu activity with linear ranges of 0.2-20 mU/mL (colorimetry) and 0.2-25 mU/mL (fluorometry), and detection limits of 0.10 and 0.094 mU/mL, respectively. Furthermore, this assay enables the screening of α-Glu inhibitors (AGIs) and determination of AGIs in real samples, which shows satisfactory consistency compared with the traditional PNPG assay, demonstrating the great application prospects for clinical diagnosis and anti-diabetic drug discovery.