Silver–zinc oxide-doped hydroxyapatite nanocomposite: an efficient peroxidase nanozyme for the colorimetric detection of ascorbic acid

Ascorbic acid is an important player in the food and pharmaceutical industries and plays a key role in the human body. Its abnormal concentration is linked to pathological conditions and monitoring the quality of food and pharmaceutical products. Therefore, it is necessary to monitor its concentration through reliable platforms that are easy to use and affordable. The current work reports a new silver and zinc oxide-doped hydroxyapatite (Ag-ZnO@HAp) nanocomposite based colorimetric sensor prepared using a waste valorization approach through a salt-melting method. The synthesis of the nanocomposite was validated through multiple spectroscopic and morphological techniques, which confirmed the desired synthesis. The synthesized nanozyme was able to act as a peroxidase mimic in the presence of hydrogen peroxide. This activity of the nanozyme resulted in the oxidation of tetramethylbenzidine (TMB) to a blue-green oxTMB. Introduction of the analyte to the system transformed the blue-green color of oxTMB to a colorless form. Various variables affecting the efficiency of the proposed sensor were optimized, and the optimized conditions were reported to be 5 mg of the nanozyme, 4 mM TMB, 18 mM H₂O₂, a pH of 7, and a time of 100 seconds. The proposed sensor showed a significant selectivity towards the specific analyte in the presence of various interfering species. The analytical parameters of the fabricated sensor, such as linear range, limit of detection, and limit of quantification, were reported to be 5-85 μM, 0.5 μM, and 1.6 μM, respectively. The synthesized platform was successfully used for the detection of ascorbic acid in the fruit juices. The synthesized nanozyme has the potential to be used in the food, pharmaceutical, and diagnostic industries.