Deciphering target-binding selectivity of waste printed circuit board-derived carbon nanozymes for pyrophosphate sensing

Developing nanozyme-based sensors enables the upcycling of waste printed circuit boards (WPCBs) into functional sensing materials, offering both environmental sustainability and practical analytical capabilities. However, unlike natural enzymes with inherent target recognition, nanozymes often lack molecular selectivity, limiting their broader sensing applications. Moreover, developing waste-derived nanozymes with target recognition abilities presents considerable obstacles due to their uncontrolled and underexplored surface functionalities. In this study, we developed pyrophosphate (PPi)-responsive carbon nanozymes (CNZs) derived from WPCBs and investigated their intrinsic target-binding behavior. The peroxidase-mimicking CNZs were synthesized via simple carbonization of non-metallic fractions of WPCBs, followed by refluxing in alkaline solutions. Notably, the peroxidase-mimicking activity of CNZs was significantly suppressed by PPi, an important anionic biomarker in physiological processes and disease monitoring. Kinetic studies and comparative assays revealed the inhibition mechanism underlying the unique interaction between PPi and WPCB-derived CNZs. Upon the H₂O₂-CNZ complex formation, PPi subsequently interacts with the active carbonyl sites (C = O) on the CNZ surface, resulting in target-responsive inhibition. Built upon this unique binding behavior, the CNZ-based system achieved highly sensitive and selective colorimetric PPi sensing with a detection limit of 8.7 nM, with negligible interference even from structurally similar phosphate analogs. This work not only demonstrates the feasibility of converting waste into functional enzyme mimics, but also highlights a strategy for achieving intrinsic molecular selectivity in nanozyme-based sensors without relying on external recognition elements.