High peroxidase-like activity realized by facile synthesis of FeS₂ nanoparticles for sensitive colorimetric detection of H₂O₂ and glutathione

In the last decades, enzyme mimics have been regarded as strong substitutes to natural enzymes. The construction of biosensors based on these enzyme mimics with competitive catalytic activity and substrate specificity has attracted a lot of research interest. Herein, for the first time, we investigated the capability of nanoscale FeS₂ to serve as enzyme mimics. Then, a facile and effective biosensor is fabricated based on its intrinsic peroxidase-like catalytic activity. In the presence of H₂O₂, FeS₂ nanoparticles (NPs) possess high peroxidase-like activity to 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, which can be ascribed to the generation of hydroxyl radicals (·OH) from the H₂O₂ decomposition catalyzed by FeS₂ NPs. As for TMB, the resulting Michaelis−Menten constant (K_m) value of FeS₂ NPs is found to be about 12 times lower than that of natural horseradish peroxidase (HRP), highlighting the superiority of FeS₂ NPs. Based on these intriguing observations, a reliable colorimetric method is then developed for detection of H₂O₂ and glutathione (GSH) by a simple mix-and-detect strategy. The detection limits of H₂O₂ and GSH are as low as 0.91 μM and 0.15 μM (3σ/slope), respectively. Moreover, FeS₂ NPs can also catalyse the photoluminescence (PL) substrate terephthalic acid (TA) under the assistance of H₂O₂. This work remarkably extends the utilization of FeS₂ NPs in the construction of colorimetric and PL biosensors in the fields of biosensing, environmental monitoring, and medical diagnosis.