Facilely fabricating fluorescent iron-doped polymer dots nanozyme with oxidase-like activity for dual-mode analysis of glutathione S-transferase and its inhibitor.

Glutathione S-transferase (GST) is a key enzyme involved in detoxification, antioxidation, and signal transduction, and its abnormal activity is closely associated with tumor drug resistance, liver damage, and inflammatory diseases. In this study, a bifunctional nanozyme based on novel iron-doped polymer dots (Fe-PDs) was constructed, which exhibits both yellow-green fluorescence and excellent oxidase-like activity. The Fe-PDs can oxidize N,N-diethyl-p-phenylenediamine (DPD) to generate a red oxidized product oxDPD (with an absorption peak at 551 nm), while simultaneously quenching their own fluorescence at 522 nm through fluorescence resonance energy transfer. Upon the addition of reduced glutathione (GSH), oxDPD is reduced, leading to a decrease in absorbance and restoration of fluorescence. Catalyzed by GST, GSH conjugates with 1-chloro-2,4-dinitrobenzene, consuming GSH in the reaction system and thereby re-triggering the oxidation of DPD, which enables dual-mode fluorescence and colorimetric detection. The fluorescence method shows a linear range of 0.001-5 U/L with a detection limit of 0.25 mU/L, while the colorimetric method achieves a linear range of 0.05-20 U/L with a detection limit of 13 mU/L. This platform shows promising potential for GST detection in human serum and for inhibitor screening. Furthermore, a portable hydrogel-based visual sensing platform was constructed, demonstrating good application performance in the analysis of GST in biological samples.