Engineering Atomically Precise Cobalt Charge-Transfer Bridges for Cascade Amplification-Enhanced Photoelectrochemical Sensing

Single-atom materials (SAMs), which are characterized by unique electronic structures and unsaturated coordination environments, exhibit maximum atomic utilization efficiency and exceptional reactivity, thus offering an advanced atomic-level strategy to mitigate sluggish charge transfer kinetics that severely affect photoelectrochemical (PEC) responses. Herein, a cobalt single atom is employed to construct N─Co─O charge transfer bridges (termed Co-ACTB) to facilitate charge separation in ZnIn₂S₄ and MIL-125-NH₂ (ZIS/MIL) Z-scheme heterojunctions. Synchrotron radiation X-ray absorption spectroscopy suggests the successful construction of Co-ACTB by elucidating the atomic configuration and local coordination characteristics of Co species. Theoretical calculations reveal coexisting regions of charge depletion and accumulation enveloping N─Co─O configuration, confirming their function as effective charge-transfer channels. Co-ACTB obviously strengthen charge transfer and enhance photoelectric properties. Consequently, ZIS/Co/MIL achieves a peak photocurrent of −349.85 µA cm⁻², representing 9.6-fold and 162.7-fold enhancements over those of ZIS/MIL and ZIS, respectively. Furthermore, a template reconstruction-mediated bidirectional cascade rolling circle amplification strategy is integrated with a Co-ACTB-based photoelectrode to afford a sensitive PEC sensing platform, exhibiting a linear response ranging from 0.1 fM to 10 nm with a detection limit of 0.34 fM. This work provides novel insights into utilization of SAMs to enhance carrier separation within heterojunctions, thereby enhancing PEC sensing performance.