A Sensitive Electrochemical Method Based On Label-free DNA For Detection Of Hydroxyl Radical, ATP, And Silver Ions

Electrochemical biosensor based on biologic reactive materials has the ability of selective recognition for the target. In recent years, many label-free biosensors attracted attentions and research interest, and DNA electrochemical biosensor is one of them. The electrochemical biosensors have been reported in many fields, such as disease diagnosis, gene sequencing, food safety, environmental protection, forensic and metal ions detection, and have good sensitivity and selectivity. In this paper, several DNA-based electrochemical sensors for detection of hydroxyl radical, adenosine triphosphate and silver(I) have been developed by electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV). The main contains of this research are as follows:1. A sensitive electrochemical method based on Fenton-induced DNA oxidization for detection of hydroxyl radical. The linear DNA and6-mercaptohexanol (MCH) were firstly self-assembled onto a planar Au electrode, successively. When the modified electrode was immersed in the Fenton solution containing Fe2+and H2O2, DNA on the electrode surface was oxidatively damaged and cloven into pieces by?OH. This phenomenon could be monitored by the electrochemical probe [Ru(NH3)6]3+, and used to sensitively detect hydroxyl radical. Square wave voltammetry was employed to characterize the electrochemistry of [Ru(NH3)6]3+absorbed on the DNA/MCH monolayer of the gold electrode surfaces. The oligonucleotide with negative charge would adsorb [Ru(NH3)6]3+with positive charge and self-assembled on the gold electrode. Therefore the more the oligonucleotide sequences were fixed on the gold electrode, the more the [Ru(NH3)6]3+would approach upon the electrode surface by the DNA phosphoric acid skeleton with negative charge. However, because of the hydroxyl radical, the monolayer was slit into pieces and unfixed on the surface of electrode. Consequently, a substantial decrease in the signal of [Ru(NH3)6]3+is monitored by SWV. The resulted electrochemical biosensor showed a wide linear range from125pM to625nM with a detection limit of80pM, and satisfactory selectivity.2. A label-free electrochemical sensor for sensitive detection of adenosine triphosphate. Through Au-S bond the ATP aptamer is self-assembled on the gold electrode surface. With the presence of target, the DNA configuration changes and forms a new duplex DNA. The new duplex DNA contains the recognition site of nicking enzyme. With the existence of the nicking enzyme, the duplex DNA is splitted into two pieces and the shorter one remains on the surface of the gold electrode. Due to less DNA on the surface of the electrode, the rate of electron transfer is improved and the impedence is decreased. Electrochemical Impedance Spectroscopy(EIS) and Differential Pulse Voltammetry(DPV) performed in [Fe(CN)6]3"/4-solution. The resulted electrochemical biosensor showed a wide linear range from1nM to10μM with a detection limit of156pM, and satisfactory selectivity.3. A simple and label-free electrochemical sensor for selective detection of silver(I) ions. Considering that Ag+can selectively combine with C-C mismatch bases, we build an electrochemical sensor for Ag+. Through Au-S bond the hairpin DNA is self-assembled on the gold electrode surface. Due to the specificity of Ag+and the C-C mismatch bases, the incomplete complementary DNA chain and hairpin can form a stable C-Ag+-C double chain which containing enzyme recognition sites. The resulted electrochemical biosensor showed a wide linear range from100pM to1μM with a detection limit of75pM. This method has advantages of simple, sensitive and good selectivity.