Fe Single-Atom and Fe Cluster-Coupled N, S Co-doped\nCarbon Nanomaterial-Based Flexible Electrochemical Sweat Biosensor\nfor the Real-Time Analysis of Uric Acid and Tyrosine

Fe\nsingle-atom and Fe cluster-coupled N, S co-doped carbon nanomaterials\n(Fe<sub>SA</sub>–FeO<sub>NC</sub>-NSC) were prepared through\na two-step high-temperature pyrolysis process using Gelidium corneum\nenriched with C, Fe, O, N, and S as precursors. The analysis by aberration-corrected\nscanning transmission electron microscopy and X-ray absorption spectroscopy\nrevealed the presence of single-atom Fe in Fe–N<sub>4</sub> coordination structures, along with small clusters as Fe–O-coordinated\nFe<sub>2</sub>O<sub>3</sub>. Single-atom Fe in the form of Fe<sup>2+</sup>/Fe<sup>3+</sup> provides more electrocatalytic active sites,\nwhich synergistically accelerates the charge migration process in\nthe assembly of Fe<sub>SA</sub>–FeO<sub>NC</sub>-NSC with Fe<sub>2</sub>O<sub>3</sub> clusters. The flexible nonenzymatic sensor,\nbased on Fe<sub>SA</sub>–FeO<sub>NC</sub>-NSC and fabricated\nusing a polydimethylsiloxane substrate, exhibited excellent catalytic\nactivity for both uric acid (UA) and tyrosine (Tyr). Low detection\nlimits for UA (0.14 μmol L<sup>–1</sup>) and Tyr (0.03\nμmol L<sup>–1</sup>) were observed by using chronoamperometry\nin artificial sweat. The in situ detection of sweat was performed\nin combination with an integrated circuit board affixed to human skin,\nand the results were generally consistent with those of the high-performance\nliquid chromatography method. Therefore, Fe<sub>SA</sub>–FeO<sub>NC</sub>-NSC serves as a good modifier for wearable electrochemical\nsweat sensor applications.