Fe-N₅ single-atom sites on C₃N₄ enable ultrasensitive electrochemical sensing of hydrogen sulfide in bone metastatic...

The limited electrocatalytic activity of graphitic carbon nitride (C₃N₄) constrains its application in electrochemical sensing. Herein, Fe-doped C₃N₄ (Fe-C₃N₄) featuring atomically dispersed Fe-N₅ sites was synthesized via a one-step solid-state thermal polycondensation approach. Comprehensive structural characterization, including transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and aberration-corrected electron microscopy, confirms both the structural integrity of C₃N₄ and the atomic dispersion of Fe species. Additionally, synchrotron radiation-based X-ray absorption spectroscopy verifies the Fe-N₅ coordination environment. Density functional theory calculations demonstrate that the Fe-N₅ sites modulate the local electronic structure, enhance sulfide adsorption, and decrease the limiting free-energy step for hydrogen sulfide (H₂S) oxidation. As a result, the Fe-C₃N₄ electrode exhibits a significantly enhanced anodic response toward H₂S, along with excellent selectivity against common biological interferents. Furthermore, reliable electrochemical signals are obtained in bone metastasis tissue homogenates, enabling effective discrimination between tumor and normal tissues. This work presents a scalable strategy for the design of Fe-N₅ single-atom catalysts for electrochemical sensing in complex biological environments.