Construction And Application Of DNA-Based Electrochemical Sensors

DNA-based electrochemical sensor is a brand new research method for life science, which combines electroanalytical chemistry and molecular biology, and arouses extensive concern in the field of life sciences. DNA-based electrochemical sensor has the characteristic of electroanalytical chemistry, but also has special affinity between biomolecule and specific recognition with target, which realized highly selective detection of target. In recent years, due to its simplicity, rapidity, sensitivity, and low cost, DNA-based electrochemical sensor has wide application prospect in food safety, environmental monitoring, drug studies, clinical medicine and other fields, which is of very important research and application’value. In this paper, several DNA-based electrochemical sensors for detection of specific-sequence DNA, pH, and silver(I) have been developed by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The main contains of this research are as follows:1. A sensitive and label-free impedimetric biosensor based on an adjunct probeA highly sensitive and label-free impedimetric sensing was fabricated based on an adjunct probe immobilized nearby the capture probe. In this assay, along with the capture probe, the adjunct probe was self-assembled on the gold electrode surface, and then6-mercapto-l-hexanol was used to block the nonspecific binding sites. Consequently reporter probe hybridized to the capture probe. After addition of target DNA, the adjunct probe was used to immobilize the section of reporter probe supplanted by target DNA and induced the reporter probe to come near the electrode surface, resulting in effective blocking of charge transfer. The enhancement in charge transfer resistance is quantitative relation to the concentration of target DNA in a broad range. The linear range for specific-sequence target DNA was from0.1nM to0.5μM with a good linearity (R=0.9988). The proposed sensor is simple, rapid, economic, highly sensitive, and selective without any label tags.2. A label-free and reversible electrochemical pH sensor based on crystal violet as a selective electrochemical probe for i-motif structureA simple electrochemical pH sensor based on i-motif structure is developed by using crystal violet as a selective electrochemical probe for i-motif structure. Thiol modified cytosine-rich single-strand oligonucleotide (C-rich ssDNA) can be self-assembled on the gold electrode surface via gold-sulfur interaction. Crystal violet is employed as an electrochemical probe for i-motif structure because of its capability of binding with i-motif structure through end-stacking mode. In acidic aqueous solution, crystal violet may approach to the electrode surface owing to the formation of the i-motif structure, resulting in an obvious signal. Whereas in neutral or basic aqueous solution, the i-motif structure unfolds to dissociative single strand, which makes crystal violet leave from the electrode surface, and a weak signal is obtained. In the range of pH4.6-7.3, the increase in current has a good linear relationship (R=0.989) with pH value in the testing solutions. This pH sensor has advantages of simplicity, sensitivity, high selectivity, and good reversibility. Furthermore, it provides a possible platform for pH measurement.3. A simple and label-free electrochemical sensor for selective detection of silver(I) ions and cysteineA label-free and simple electrochemical sensor for detection of silver(I) ions and cysteine (Cys) was designed based on cytosine (C)-Ag+-cytosine (C) base pairs and strong interaction between Ag+and Cys. In the experiment, C-rich ssDNA was used as capture probe. In the absence of Ag+, the dissociative C-rich ssDNA was random-coil, and charge transfer between electrode and electrolyte was inhibited by the repelling between DNA and redox probe. Ag+may specifically bind with C-C mismatched pair to form C-Ag+-C base pairs. In the presence of Ag+, random coil C-rich ssDNA bended to form hairpin structure, which would greatly increase steric hindrance on the electrode surface, effectively decrease the charge transfer and obviously increase resistance. The increase in resistance is related to the quantity of Ag+in a wide range. Due to its strong interaction with Ag+, Cys was able to seize Ag+from the C-Ag+-C base pairs. In the presence of Cys, the C-Ag+-C base pairs were broken, and hairpin structure unfolded to dissociative C-rich ssDNA. At this moment, steric hindrance decreased, charge transfer increased and resistance decreased. In a certain range, decrement in resistance was related to the quantity of Cys. Based on these results a simple and high sensitive electrochemical sensor for selective determination of Ag+ions and Cys was developed.