Label-free DNAzyme Biosensor based on Si-SiO2 Interferometry for Multiplexed Heavy Metal Detection

Santhosh Mallesh, Institute of Agricultural and Biosystems Engineering, ARO, Volcani Institute, Rishon LeZion, Israel (santu.bt@gmail.com)
Giorgi Shtenberg, Institute Of Agricultural And Biosystems Engineering, Aro, Volcani Institute, Rishon Lezion, Israel

In recent years, heavy metal pollution has escalated, posing significant threats to the environment and human health. Highly toxic heavy metal ions (HMs) like Pb²⁺, Hg²⁺, and Cd²⁺ are major public health concerns, capable of causing multi-organ damage even at low exposure levels. Monitoring HMs in environmental and biological samples like water, soil, and bodily fluids is essential for safety and regulatory compliance. Existing detection methods often fail to support on-site monitoring needs. To overcome these limitations, a new label-free DNAzyme-based biosensor using Si-SiO₂ interferometry was proposed for simple, sensitive, and selective detection of prevalent HMs. Specific DNAzyme triggers a catalytic cleavage reaction in the presence of particular HMs. The binding of HMs and the subsequent cleavage of the DNA substrate changes the arrangement and conformation of the DNA molecules on the sensor surface and causes a detectable shift in the wavelength (Δλ) of the reflected light, which can be correlated to HMs concentration. In this research, we incorporated multiple DNAzymes, each specifically tailored to recognize distinct HMs, onto a Si-SiO₂ interferometric platform, which can detect and differentiate Pb²⁺, Cd²⁺, and Hg²⁺ ions. Studies were conducted to optimize surface chemistry, the concentrations of DNAzymes and their corresponding substrates, the reaction temperature, and the duration of the catalytic cleavage process to maximize the sensor performance. The developed Si-SiO₂ interferometric biosensor system achieved detection limits of 0.92, 0.97 and 1.31 ppb for Pb²⁺, Cd²⁺ and Hg²⁺, respectively. The limit of detection values fall below the U.S. Environmental Protection Agency (EPA) acceptable level for drinking water, suggesting that the developed sensor platform can be implemented for testing environmental water samples.

Keywords: Heavy metal ions, DNAzyme, Interferometric biosensor