Electrochemical DNA Sensor Based On MWCNTs/GNPs For Pb²⁺ Detection

Electrochemical DNA sensors is a relatively new technology for detecting DNA (gene), compared with the traditional detection method, it is fast, responsive, and easy to operate, low cost, and has a certain molecular recognition function, it has been played an increasingly important role in the health and epidemic prevention, medical diagnosis, drug research, environmental monitoring and biological engineering, and other fields. Many new biotechnology developments have injected new vitality for the study of high sensitivity and specificity of detection method, the use of specific complementary matching rule between DNA molecules and developed all sorts of electrochemical DNA sensing technology has caused the widely attention and has become a frontier topic.A sensitive electrochemical lead ion (Pb2+) sensor based on the carboxylic acid group functionalized multi-walled carbon nanotubes (MWNTs-COOH) and the direct electro-deposited gold nanoparticles (GNPs) was developed for Pb2+detection. The DNA capture probe was self-assembled onto the surface of the modified electrode for hybridizing with the guanine-rich (G-rich) aptamer probe and forming DNA double helix structure. When Pb2+added in, the DNA duplex unwind and forming a stabilizing G-quadruplex (G4) due to Pb2+-induced G-rich DNA conformation. And methylene blue (MB) was selected as the G4-binding indicator, and the current decreased with adding Pb2+. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for discussing the electrochemical performance of the sensor. Compared with bare glassy carbon electrode, MWCNTs modified electrodes and MWCNTs/GNPs modified electrodes, the modified electrode which we assembled had a larger specific surface area and better electronic conductivity, which could largely improve the limit of detection with Pb2+. We also optimized all experimental parameters affecting the performance of the electrode reaction time (including MB reaction time, the reaction time of S2and Pb2+, electrode-position time, and pH value, etc.). Under the optimum experimental conditions, the sensor could detect Pb2+in a range from5.0×1-11to1.0×10-14M with a detection of4.3×10-15M. In addition, this sensor showed good stability and anti-interference ability, also feasible to testing water samples. The preparation method is easy, sensing performance is good, and the limit of detection is low. That provides a new method for Pb2+detection.