Piezoelectric Electrochemical Studies On Adsorption And Electrooxidation Behaviors Of Purine Bases

Nucleic acids are genetic material, and their variations cause a series of abnormal reactions. Many cancers and chronic lymphocytic leukemia are also related to the change of genetic material, so the sensitive detection of DNA and RNA is very important. The detection of nucleic acid mainly includes the detection of content, hybridization, mutation of a base or spatial conformation of nucleic acid. There are a variety of methods to detect the content of nucleic acid, such as fluorescence spectrometry, chemiluminescence, optical fiber sensing method, and colorimetry. The electrochemical methods for the analysis of nucleic acid involve polarography, voltammetry, impedance method, potentiometry, and electrochemiluminescence, to study nucleic acids and the electrical activity of nucleic acids (such as the electrooxidation of guanine (G), guanine (A), and cytosine (C)). The research of the electrochemical activity of nucleic acid is an important part of electrochemical detection of nucleic acid, and the analysis and detection of the purine bases with high electrical activity becomes extremely important. Electrochemical quartz crystal microbalance (EQCM), as a sensitive qualitative detection technique, is rarely used in the study of the purines. In this thesis, the conventional research methods of nucleic acid, electrochemical detection of nucleic acid and bases, piezoelectric sensor research for nucleic acid and bases are briefly reviewed. Moreover, we explore here the adsorption and electrooxidation behaviors of adenine (A) and guanine (G) on carboxylated multiwalled carbon nanotubes (MWCNTs) or purified single-walled carbon nanotubes (SWCNTs) modified EQCM Au electrode, and the electroanalysis of purine bases on SWCNTs or graphene modified glassy carbon electrode (GCE) are conducted. The main centents are as follows:1. The electrochemical quartz crystal microbalance (EQCM) technique was used to study the adsorption and electrooxidation behavior of adenine (A) and guanine (G) on bare and multiwalled carbon nanotubes (MWCNTs) modified gold electrodes. The results showed that the adsorption amount and oxidation current of A is larger than those of G on the Au electrode. Both A and G can be similarly adsorbed on the surface of MWCNTs/Au electrode, but the oxidation peak potentials for both A and G shift negatively, and their oxidation peak currents increase. The numbers of electrons transferred for oxidation of A and G on the Au electrode are5.4(RSD=±2.3%) and1.9(RSD=±1.3%), and those for oxidation of A and G on the MWCNTs/Au electrode are5.1(RSD=±1.8%) and1.5(RSD=±1.6%), respectively, as calculated from the EQCM data.2. A glassy carbon electrode (GCE) modified with single-walled carbon nanotubes (SWCNTs) can enhance the oxidation peak current of adenine (A) and guanine (G) by62.7%and356%in pH7.4phosphate buffer solution, respectively. The experimental parameters were optimized, and the linear concentration range and limit of detection (LOD) on SWCNTs/GCE are0-50μmol L-1and10nmol L-1for A as well as 0-100μamol L-1and20nmol L-1G, respectively. An electrochemical quartz crystal microbalance study reveals that the adsorbed amount of A is larger than G on bare Au and SWCNTs/Au electrodes. The numbers of electrons transferred for the oxidation of A and G are estimated to be6.4±0.2and2.6±0.1on both electrodes, respectively. This method was used for assay of A and G in a siRNA sample. The found contents of A and G agree well with its chemical structure, and the recovery of A and G were96.2%(RSD=3.2%) and96.0%(RSD=2.9%), respectively.3. A glassy carbon electrode (GCE) was modified with graphene oxide (GO), after the electrochemical reduction (ER) of GO, the ER-GO/GCE was prepared. The oxidation peak current of adenine (A) and guanine (G) significantly increased on ER-GO/GCE in pH7.4phosphate buffer solution, and the oxidation potential for both A and G also negatively shifted. The experimental parameters were optimized, and the linear concentration range and limit of detection (LOD) on ER-GO/GCE are0-40μmol L-1and7.2nmol L-1for A as well as0-30μmol L-1and7.4nmol L-1G, respectively. This method was used for assay of A and G in a siRNA sample. The found contents of A and G agree well with its chemical structure, and the recovery of A and G were97.8%(RSD=2.8%) and99.4%(RSD=2.8%), respectively.