A Label-Free DNAzyme Biosensor Using a SiO2/Si Interferometer for Multianalyte Detection of Pb2+, Cd2+, and Hg2+

Heavy metal (HM) contamination poses a significant threat to the environment and public health, creating a growing demand for rapid, sensitive, and field-deployable analytical practices. Herein, a label-free multianalyte DNAzyme biosensor based on a SiO2/Si Fabry-Pérot interferometer was constructed for sensitive and selective detection of Pb2+, Cd2+, and Hg2+. The sensing concept relies on metal-induced DNAzyme-catalyzed substrate cleavage, which alters the optical thickness of the sensing interface and produces measurable spectral shifts monitored by reflective interferometric Fourier transform spectroscopy. Systematic optimization of the interferometer architecture, surface chemistry, DNA probe density, and catalytic reaction conditions resulted in an effective sensing platform. The SiO2/Si biosensor exhibited high sensitivity with detection limits of 1.27, 1.67, and 1.76 ppb for Pb2+, Cd2+, and Hg2+, respectively; sufficient selectivity with negligible interference from As3+, Zn2+, Cu2+, and Co2+; efficient regeneration over three sensing cycles; storage stability for 6 weeks; and excellent analytical performance against ICP–MS analysis, yielding recoveries of 86.4–106.8%. Collectively, these features highlight the cost-effectiveness, practical utility of the biosensing platform with potential future field-deployable monitoring of HM in environmental waters, agricultural water assessment, and regulatory screening applications.