Electrochemical tyrosine-click bioconjugation enables multiplexed cytokine sensing and immunoprofiling in native serum.

Electrochemical biosensors require robust, well-controlled biointerfaces, but existing protein immobilization chemistries are slow and poorly defined. Here we report an interfacial electrochemical tyrosine-click (i-eY-Click) strategy that enables rapid (<3 min), chemoselective covalent attachment of native proteins under physiological conditions. At mild potentials (+0.36 V vs Ag/AgCl), electrode-grafted 4-phenylurazole is oxidized in situ to phenyltriazolinedione intermediates that react specifically with tyrosine residues, without genetic modification or soluble catalysts. i-eY-Click displays ~20-fold faster kinetics than conventional amide coupling while preserving protein activity. Implemented on carbon microelectrode arrays, it yields well-controlled antibody monolayers and supports multiplexed cytokine sensing in native serum with markedly improved sensitivity, detection limits and reproducibility. We further use this platform for in vivo serum immunoprofiling in a nanoplastic exposure model, revealing charge-dependent cytokine signatures and delayed inflammatory responses to polylactic acid particles. i-eY-Click thus provides a general, chemistry-driven route to high-performance biointerfaces for multiplexed immunosensing and biomarker profiling.