Chromogenic nanozyme sensing: CuO nanoparticles and other of its related kind as versatile colorimetric platforms for environmental and biological analyte detection

Chromogenic nanozyme sensing has emerged as a transformative strategy for colorimetric detection, offering a robust alternative to natural enzyme based assays that are often constrained by instability, high cost, and limited operating conditions. This review is founded on the hypothesis that CuO nanoparticles exhibiting nanozyme activity, together with related metal-oxide nanozymes, can be effectively coupled with chromogenic reagents to form versatile, highly sensitive, and tunable platforms for reliable environmental and biological analyte detection. To assess this, the review systematically evaluates reported experimental designs, catalytic mechanisms, and structure–activity relationships of CuO-based nanozymes, particularly those demonstrating peroxidase- and oxidase-like activities.Emphasis is placed on synthesis strategies, surface functionalization, and interactions with classical chromogenic substrates, alongside applications in detecting diverse analytes such as environmental pollutants, biological biomarkers, and laboratory reagents. The evidence collectively shows that CuO nanozymes possess strong catalytic efficiency, rapid response times, and distinct visible color changes, enabling ultra-sensitive, naked-eye detection with minimal instrumentation. Compared to natural enzymes, they exhibit superior chemical and thermal stability, broader pH tolerance, and enhanced adaptability through surface engineering, leading to improved selectivity and signal amplification.Characterization techniques play a central role in understanding these properties. XRD confirms crystalline phase and purity; SEM and TEM reveal nanoscale morphology and structural features; FTIR identifies surface functional groups; UV–Vis spectroscopy monitors optical and catalytic behavior; XPS provides insights into elemental composition and oxidation states; while DLS and zeta potential assess particle size distribution and colloidal stability. Together, these techniques elucidate structure–function relationships governing catalytic performance.Overall, this review highlights CuO and related nanozyme-based chromogenic systems as cost-effective, high-performance tools for next-generation sensing, while offering mechanistic insights and methodological guidance for advancing environmental, biomedical, and analytical applications.