Development of a colorimetric sensing assay for ascorbic acid and sarcosine utilizing the dual-class enzyme activity of Fe3O4@SiO2@NiCo2S4

In this paper, Fe3O4@SiO2@NiCo2S4 nanocomposite catalytic materials were prepared using a low eutectic solvent and hydrothermal method. Characterization was performed using scanning electron microscopy, transmission electron micrographs, X-ray photoelectron spectra, X-ray diffraction, Zeta potential and Fourier transform infrared spectrometry, and Vibrating sample magnetometry. The catalytic mechanism was verified by Electron Paramagnetic Resonance experiments. Several assay platforms were established based on their different enzyme activities. Based on the oxidase-like activity, a colorimetric sensing assay for ascorbic acid was developed with a linear range and detection limit of 1–200 µM and 0.36 µM, respectively. Sarcosine can be effectively quantified by utilizing its peroxidase-like activity. The linear range of sarcosine assay was 1.25–350 µM with a detection limit of 0.42 µM. Notably, Fe3O4@SiO2@NiCo2S4 exhibited reusability and high precision in quantifying sarcosine in human urine samples. The nanomaterials could be easily and quickly separated from the reaction system using a magnet for future use due to their superior magnetic properties. Therefore, the colorimetric sensing analytical method established in this study provided a new strategy for the detection of ascorbic acid in food matrices and serum samples as well as sarcosine in urine samples. The developed method also provided a potential application of composite and bimetallic materials in the fields of food detection, bioanalysis, and clinical disease diagnosis.