FeS_x-graphene heterostructures: Nanofabrication-compatible catalysts for ultra-sensitive electrochemical detection of hydrogen peroxide

Hydrogen peroxide (H₂O₂) is one of the most important redox-active metabolites in biological processes, from cell signaling to oxidative stress. Incorporation of catalytic nano-phase heterostructures can significantly improve the detection limit of H₂O₂ electrochemical sensors. Here, we report an iron sulfide (FeS_x)/graphene heterostructure for detection of H₂O₂ down to ∼500 picoMolar pM, with a dynamic range over six orders of magnitude. By relying on the Fenton reaction, the developed catalyst enables selective detection of H₂O₂ vs. common redox-active metabolites in physiological condition. Electrochemical analysis reveals a strong substrate-dependent performance, where the type and doping of the graphene layer dramatically impact sensitivity. Specifically, for the first time, the electrochemical performance of chemical vapor deposited versus epitaxial graphene (EG) layers is examined and compared in a systematic way. The results demonstrate that a heterostructure of FeS_x with chemical vapor deposited graphene (CVD-G) exhibits the highest reduction in charge transfer resistance (more than 16×), leading to a significantly higher sensitivity compared to n-doped and p-doped EG. Furthermore, the excellent sensitivity and material stability of the developed heterostructures enable in situ detection of redox changes due to heat shock-induced oxidative stress on E. coli cells. Since the developed heterostructures are directly-grown, they can be patterned with nanometer-scale resolution. Hence, this work can open up new possibilities for developing ultracompact devices for monitoring redox changes in situ, with high spatial resolution.