Boosted Sensitivity of Single-Atom Sites for Dopamine and Hydrogen Peroxide Detection

Single-atom (SA) sites have garnered significant attention in electrochemical applications due to their ability to leverage the unique electronic properties of isolated metal atoms, thereby enhancing interfacial charge transfer and detection sensitivity. Despite the limited exploration of electrochemical sensors utilizing SA, their integration into sensing electrodes holds great promise for improving the sensitivity and selectivity of bioactive molecule detection. In this study, SA modified electrodes were developed by anchoring transition metal atoms (Fe, Co, or Cu) onto nitrogen-doped graphene (N–C) via M–N–C coordination, synthesized through a ball milling–pyrolysis method. Electrochemical impedance spectroscopy measurements demonstrated a significant reduction in electrochemical impedance for Fe, Co, and Cu SA electrodes, indicating an enhanced electron transfer rate at the sensor interface. To evaluate the electrochemical sensing performance of SA-modified electrodes, dopamine (DA) and hydrogen peroxide (H₂O₂)—two biologically important molecules—were selected as representative analytes. Chronoamperometry revealed that Fe SA exhibited an enhanced sensitivity toward DA, reaching 0.02 A/µM, attributed to the unique electronic structure and catalytic properties of Fe sites, whereas Co SA and Cu SA did not show a notable improvement in DA detection sensitivity compared to the N–C electrode (0.01 A/µM). In contrast, Fe, Co, and Cu SA electrodes demonstrated improved sensitivity for H₂O₂ detection, achieving 0.35, 0.28, and 0.35 A/mM, respectively, surpassing the performance of the N–C electrode (0.076 A/mM). Density functional theory calculations of DA oxidation kinetics demonstrated that Fe–N site facilitated the adsorption and conversion of OH, thereby improving electrochemical response. These findings highlight the potential of SA as an effective electrode modification strategy for advancing electrochemical sensing technologies and enabling highly sensitive biomolecular detection.