Bi₂Fe₄O₉/reduced graphene oxide nanocomposites with enhanced peroxidase activity for sensitive glutathione detection

Bi₂Fe₄O₉/reduced graphene oxide nanocomposites (Bi₂Fe₄O₉/rGO NCs) were hydrothermally synthesized to address analytical challenges in glutathione (GSH) detection in complex biological matrices. The incorporation of rGO not only disperses aggregated Bi₂Fe₄O₉ nanoparticles (Bi₂Fe₄O₉ NPs) into nanosheets to expose more active Fe³⁺ sites, but also acts as an efficient electron sink that accelerates interfacial charge transfer and the Fe³⁺/Fe²⁺ redox cycling essential for H₂O₂ activation, thereby substantially boosting the peroxidase-like activity. Density functional theory calculations further reveal that the heterojunction interface markedly strengthens substrate adsorption. The adsorption energies for 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂ decrease from - 2.18 to - 1.49 eV on Bi₂Fe₄O₉ NPs to -5.67 and - 3.44 eV on Bi₂Fe₄O₉/rGO NCs, respectively. Steady-state kinetics confirm enhanced substrate affinity and faster catalytic rate relative to Bi₂Fe₄O₉ NPs. The competitive inhibitory effect of GSH toward the Bi₂Fe₄O₉/rGO NCs-catalyzed TMB-H₂O₂ reaction was exploited to construct a colorimetric sensor with a linear range of 10-250 nM and a detection limit of 3.1 nM. Its reliable performance in fetal bovine serum, human serum, and plasma underscores the practical applicability of this mechanistically elucidated platform for complex biological matrices.