Ultrasensitive electrochemiluminescence biosensor for catechol based on tyrosinase immobilized on N-acetyl-L-cysteine-functionalized upconversion nanoparticles/reduced graphene oxide

We present the first electrochemiluminescence (ECL) biosensor integrating N-Acetyl-L-cysteine (NALC)-functionalized upconversion nanoparticles (UCNPs) with reduced graphene oxide (COOH-rGO) for the covalently immobilization of tyrosinase (TYR), and ultrasensitive detection of catechol, a highly toxic and recalcitrant aquatic pollutant. The NALC layer establishes a dense array of enzyme-anchoring sites on the COOH-rGO electrode while preserving TYR activity and extending its operational lifetime. The ECL signal originates from TYR-mediated redox cycling between catechol and o-quinone, generating electrons that amplify UCNPs luminescence. Under optimized conditions, the limit of detection of this biosensor for catechol was 2.7 × 10 −9  M (S/N = 3), detection range of 0.1 × 10 −6 –100 × 10 −6  M. The platform demonstrates high sensitivity, stability, and selectivity, and has been validated in water samples, offering a robust strategy for enzymatic ECL-based environmental monitoring.