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

Abstract 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 ZnIn 2 S 4 and MIL‐125‐NH 2 (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 n m 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.