Low-Temperature Base-Catalyzed\nSi-Capped ZnO Quantum\nDots for pH-Switchable Dual Sensing of Amoxicillin and Cr<sup>3+</sup>

Amoxicillin (AMX), one of the most commonly used antibiotic\ndrugs,\ncan cause overwhelming hazards if abused, particularly when it contaminates\nthe environment and affects individuals. As a result, devising an\neasy and accurate method for estimating AMX content is vital. In this\nwork, we describe a turn off/on detection method for Cr<sup>3+</sup> and AMX using a smart pH-switchable ZnO quantum dot (QD) nanoprobe.\nThe ZnO QDs were synthesized using tetraethyl orthosilicate (TEOS)\nas a capping agent through a simple low-temperature base-hydrolysis\nreaction. The TEOS-capped ZnO QDs exhibited strong fluorescence with\na peak at 520 nm under excitation at 330 nm. Numerous methods, such\nas energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR),\nX-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution\ntransmission electron microscopy (HRTEM), UV–vis absorption,\nand UV–vis reflectance, have been used to demonstrate the successful\nsynthesis of TEOS-capped ZnO QDs. The lowest excited state exhibits\nselective fluorescence quenching and enhancement upon the addition\nof Cr<sup>3+</sup> and AMX, respectively, in the presence of other\ninterferences at pH 7 and pH 1 respectively (both in liquid and solid-state\nPL). The estimated LOD of 15.94 nM (in case of Cr<sup>3+</sup>) and\n77.86 nM (in case of AMX) was achieved. The recovery of various concentrations\nof AMX in real samples ranged from 95% to 101.1%, with a relative\nstandard deviation of 0.05–1% (<i>n</i> = 3). This\nwork harnesses the specific and excellent performance of TEOS-capped\nZnO QDs, contributing to further progress in the analytical and materials\nresearch fields. There is ample scope for using this nanoprobe in\nthe fabrication of both pH sensors (owing to its pH-switching ability)\nand capacitive sensors (owing to the semiconducting nature of ZnO).