PEG-directed structural modulation of short hexagonal Co-nanozyme: enhanced aqueous stability, high peroxidase activity and colorimetric detection of H2O2 and dopamine.

Nanozyme offers promising alternatives to natural enzymes, but has poor aqueous stability and aggregation, which limit their practical applications. In this work, a polyethylene glycol (PEG)-modulated short hexagonal-Co-nanozyme was synthesized via co-precipitation methods to address these limitations. Different PEG molecular weights (2000-8000) were evaluated, and scanning electron microscope (SEM) imaging and dynamic light scattering (DLS) results confirmed that PEG 6000 at 10% w/w produced uniform hexagonal particles, non-aggregates, well-dispersed with an excellent particle size distribution (PSD), and aqueous stability. The morphological, crystallographic, and phase structure analysis supported by SEM, PSD, transmission electron microscopy (TEM), seleced area electron diffraction (SAED), and XRD. Surface area, porosity, and chemical composition by AFM, BET, and FTIR. Additionally, the surface state, surface charge and colloidal stability by X-ray photoelectron spectroscopy (XPS) and zetapotential by DLS. The optimized nanozyme exhibited strong peroxidase activity with a low Km = 20.77 µM (Vmax = 0.046 µM/s). Under the optimized conditions of TMB, nanozyme (pH 4.0, 55 °C) and 10 min reaction time, the system enabled sensitive colorimetric detection of H2O2 (limit of detection [LOD] = 0.79 µM, limit of quantification [LOQ] = 2.4 µM, linear range 1-20 µM) and dopamine (LOD = 0.86 µM, LOQ = 2.63 µM, linear range 2.5-25 µM). The interference studies confirmed high selectivity, while spiked assays achieved recoveries between 105 to 116% with RSD % below 5%. These findings establish PEG-modulated Co-MOF as a stable, sensitive, and versatile platform for next-generation sensing.