Design and fabrication of a new sol-gel based sensor for the visual detection of oxalate and investigation of the effect of boiling on the oxalate content of some foods

Abstract

Sol–gel chemistry is a unique method for constructing high-performance flexible sensors. Sol-gel silica matrices doped with a controlled amount of sensing agent (dopant) lead to the fabrication of suitable sensors. According to this knowledge, we decided to describe the development and performance characteristics of the sol-gel glasses with a nanoporous structure as the novel naked eye sensor for fast detection of oxalate based on the incorporation of indole inside pores of the silica matrix obtained by sol–gel technology. Several sols were made with different water: alkoxide ratios and pHs to design a highly sensitive and selective thin film without dopant leaching. The Field emission scanning electron microscopy (FE-SEM) technique was employed to evaluate the surface morphology and porosity growth. Also, the sol–gel films were characterized by Fourier-transform infrared (FTIR) spectroscopy. The optimum performance in terms of sensitivity, leaching, and response time was achieved using water: alkoxide ratio of 4:1, water acidity (HCl concentration) of 0.01 M, and ethanolic solution of Indole 0.01 mol L-1. The calibration plot was obtained within 0.01–6.00 μg mL−1 of oxalate with a detection limit value of 0.005 μg mL−1. Meanwhile, the prepared sensor exhibited excellent and acceptable RSDs for both inter-day and intra-day precision. The present sensor was used to measure oxalate in various samples and investigate the effects of the celeryʼs cooking time and the brewing duration of tea on oxalate content.