Copper-carbidopa nanoparticles as highly active laccase-mimics for colorimetric detection and oxidative catalysis of o-phenylenediamine

Abstract Copper-carbidopa nanoparticles (PCD-Cu NPs) have emerged as efficient laccase-mimicking nanozymes with strong potential for biosensing and oxidative catalysis. Their catalytic performance was investigated using o -phenylenediamine (OPD) as a model substrate which undergoes a colorimetric transformation into an oxidized chromophore detectable at 422.0 nm. The reaction followed typical Michaelis-Menten kinetics exhibiting a low apparent K m of 30.0 µM indicating a high binding affinity between the nanozyme and OPD while the V max was determined to be 7.0 µM/min reflecting moderate catalytic turnover. The colorimetric response was linear in the OPD concentration range of 3.0-100.0 µM with a calculated limit of detection (LOD) of 2.46 µM confirming the material’s applicability in sensitive and quantitative biosensing. Optimal catalytic activity was observed at pH 6.0 and 40 °C conditions that closely mimic physiological environments thus supporting the nanozyme’s suitability for biological and clinical sample analysis. Kinetic studies under various pH and temperature conditions further affirmed the robustness of PCD-Cu NPs with negligible activity loss across a pH range of 5.0 to 7.5. Reusability assessments showed that the nanoparticles retained over 80% of their initial activity after five catalytic cycles indicating excellent operational stability. The oxidation of OPD not only provides a straightforward visual signal for detection but also serves as a model for monitoring oxidative transformations relevant in biomedical assays. Collectively, the high substrate affinity, broad detection range, thermal endurance, and biological compatibility of PCD-Cu NPs establish them as promising candidates for applications in biosensor platforms, diagnostic devices, and green oxidation processes.