Nanofibras cerâmicas eletrofiadas como nanozymes: síntese, caracterização e aplicação em sensores colorimétricos

Abstract

The increasing demand for food safety and access to potable water has spurred the development of simple, rapid, and low-cost analytical methods for determining chemical species of interest. However, although highly sensitive, conventional analytical techniques often require expensive instrumentation, extensive laboratory infrastructure, and long analysis times. In this context, nanozyme-based colorimetric sensing has emerged as a promising alternative. Nanozymes are nanomaterials that mimic the catalytic activity of natural enzymes, promoting the oxidation of chromogenic substrates and producing color changes that enable the detection and quantification of analytes. Among the materials investigated for this purpose, metal oxides have attracted significant attention due to their high chemical stability and catalytic activity. However, the use of ceramic nanofibers in nanozyme-based platforms remains limited, despite their structural advantages, such as high surface area and one-dimensional morphology, which can enhance catalytic performance. In this work, precursor nanofiber membranes containing zinc and manganese salts were produced by electrospinning and subsequently calcined to yield ceramic nanofibers (NFII, NFIII, NFIV, and NFV) with compositions controlled by the metal salt ratio. The physicochemical properties of the materials were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectrometry, and nitrogen physisorption, enabling correlations between morphology, composition, crystalline structure, and surface area. The oxidase-like activity of the nanofibers was evaluated using the chromogenic substrates tetramethylbenzidine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and o-phenylenediamine (OPD), yielding kinetic parameters (Km and Vmax) comparable to or higher than those reported in the literature. Based on this catalytic activity, colorimetric sensors were developed for the determination of nitrite and ascorbic acid. The NFII/TMB system was applied to nitrite detection using ratiometric, spectrophotometric, and smartphone-assisted approaches, with limits of detection (LOD) of 4.0 and 4.8 µmol L-1, respectively. For ascorbic acid determination, the NFIII/ABTS and NFIII/OPD systems showed LODs of 0.7 and 1.5 µmol L-1, respectively. The developed sensors showed good sensitivity, selectivity, and stability, and were successfully applied to the determination of the analytes in drinking water and fruit juice samples, with recoveries ranging from 92.0 to 104.9%. These results demonstrate the potential of electrospun ceramic nanofibers as nanozymes for developing simple, accessible colorimetric platforms for food and water quality monitoring.