Nanozymatic platform for dual colorimetric and fluorimetric sensing of H₂O₂ and glucose using Ni-CoWO₄ nanoparticles.

Hydrogen peroxide (H₂O₂) plays a crucial role in both biological and industrial systems. Excessive H₂O₂ can lead to oxidative stress, cellular damage, and process-related issues in manufacturing. For this reason, fast and sensitive detection methods are needed. In this study, Ni-CoWO₄ nanoparticles, belonging to the bimetallic nanozymes family, were used as catalysts to promote the oxidation of ortho-phenylenediamine (OPD) by H₂O₂. Polyoxometalates are renowned for their structural diversity, large surface area, and robust redox activity, making them exceptional candidates for catalytic applications. Ni-CoWO₄ was prepared using a hydrothermal method and characterized using SEM-EDX, XRD, and FT-IR techniques. The nanoparticles exhibited an even distribution of nickel and cobalt within a multi-metallic framework, resulting in numerous active sites and a high surface-to-volume ratio. Compared to the system without the catalyst, Ni-CoWO₄ significantly improved the reaction rate, produced a stronger yellow color, and reduced the oxidation time. The reaction was monitored by visible spectrophotometry, spectrofluorimetry, and smartphone-based colorimetry. A linear range of 0.5-150 µM and a limit of detection of 485 nM for H2O2, and a linear range of 1-125 µM for glucose were obtained by the spectrophotometry. In spectrofluorimetry, it showed a linear range of 0.1-50 µM, and LOD was 64 nM. In the smartphone-based method, RGB (Red, Green, Blue) and CMYK (Cyan, Magenta, Yellow, Key (Black)) were used for colorimetric and fluorimetric determination. Overall, the results demonstrate that Ni-CoWO₄ is a low-cost and effective nanocatalyst for H₂O₂ and glucose sensing, with significant potential for both biological and industrial applications.