Research Of Impedimetric Method For Lead Ions Detection Based On GR-5 DNAzyme

With the rapid development of modern industry, lead pollution got worse. Due to its non-biodegradability, even a small amount of Pb²⁺ can accumulate into a fatal level and cause server impact on human health and the eco-system. Available methods for the lead detection can offer high sensitivity. However they are expensive and complex, only suitable for laboratory analysis, therefore, developing low-cost, simple, fast and efficient methods for detecting Pb²⁺ is of particularly important. Compared with traditional ways, the electrochemistry impedance spectroscopy（EIS） has the advantage of simplicity, label-free and facility to miniaturize; it has shown promising potentials for analysis and detection field, and is suit to developing biosensors for lead ions detection.The thesis focuses on developing impedimetric biosensors for lead ions detection combining the specific cleavage of GR-5 DNAzyme, the property of gold interdigitated electrodes（GIE） for amplifying the impedance signal without extra amplification strategies. The specific contents are as follows:（1） A new impedimetric biosensor based on the property of GIE for impedance signal amplification and the specific cleavage of GR-5 DNAzyme was presented to determine Pb²⁺ in water. The catalytic strand of GR-5 DNAzyme modified with thiol was easily immobilized onto the GIE surface through Au-S bounding, In the presence of lead, the substrate strand was cleaved into two parts at the RNA site（rA） and changed the interfacial properties of the GIE, resulting in diminishing the charge transfer resistance accordingly. The changes were recorded by using Nyquist plot and analyzed with choosing the appropriate equivalent circuit for lead ion detection. The results revealed that the proposed impedimetric biosensor was highly sensitive to lead ions with a detection limit of 1 nM and the linear range from 1 nmol/L to 100 nmol/L. We completed the experiment on the custom-made GIE made on ceramic material, and it showed the feasibility to lead ions detection combing GR-5 DNAzyme and GIE.（2） To cut the cost, the GIE made on printed circuit board（PCB） was introduced into the study which is simplicity, cost-effective and easy mass production because of the mature production technology. A novel impedimetric biosensor was developed by immobilizing GR-5 DNAzymes onto the GIE surface through Au-S bonding. In the presence of lead, the substrate strand was cleaved and changed the interfacial properties of GIE, causing a corresponding decrease in the impedance magnitude. Using Bode plot to record the change and calculating the decrease, the concentration of lead ion can be determined. Our proposed lead biosensor exhibited a high sensitivity with a detection limit of 6.61 nmol/L which is much lower than the 72 nM defined as the maximum contamination level（MCL） of lead ions in drinking water by The United States Environmental Protection Agency（EPA）, at the same time, with a linear range from 10 nmol/L to 100 nmol/L and a prominent selectivity against other heavy metal ions. What’s more, different from the traditional way, the GIE are made on PCB, this makes the biosensor has the superiority of simplicity, low-cost and easy mass production, and it can easily be widely used.（3）Based on the superparamagnetism of MNPs, the magnetic susceptibility increased with the external field, at the time the corresponding permeability increased, resulting in the inductive impedance changed. Here, we provide extra magnetic field by the AC voltage from CHI604 E, and explored the effect of introducing MNPs to the GIE. Further work will investigate the influence conditions to develop an impedimetric lead biosensor with high sensitivity and selectivity based on MNPs.