Single-Atom-Enhanced Fully Inkjet-Printed Electrochemical Sensor for Dopamine Detection.

Single-atom (SA) engineering offers atomic-level control over interfacial reactivity, yet the lack of printable SA-based inks hinders its practical translation into electrochemical sensing. Here, a fully water-based inkjet-printable ink is introduced based on nitrogen-doped graphene acid (NGA) hosting atomically dispersed Cu centers (NGA-Cu-ink). The ink enables digitally controlled, spatially defined deposition and fabrication of low-cost ($0.04 per sensor), fully inkjet-printed sustainable electrodes on paper. A comparison of NGA functionalized with different SA dopants (Cu, Mn, Fe, Ce) identifies a strong dopant-dependent electrochemical response, with Cu uniquely enhancing the analyte signal while other dopants suppress it, demonstrating that SA identity is a decisive design parameter in printed sensing interfaces profiling sensitivity and selectivity. The functional role of the NGA support is to provide dense anchoring sites (nitrogen and carboxylate groups) that stabilize atomically dispersed metal centers and create adsorption- and electron-transfer-active microenvironments. The NGA-Cu-ink yields enhanced dopamine oxidation, enabling quantitative detection on fully printed devices (limit of detection 9.7 µM; linear range 50-400 µM) and printed-on-electrode platforms (10.6 µM), while maintaining <10% signal variation over 11 weeks. The approach establishes a general route to single-atom graphene-based inks for scalable, reproducible, and low-material-consumption manufacturing of advanced electrochemical sensors.