Studies On Electrochemical Biosensor Based On Conducting Polymer And Aptamer

In this paper, three biosensors were fabricated based on conducting polymer and aptamers. An electrochemical method to lable-free detect DNA hybridization was developed on the basis of a new conductive polymer, indole-5-carboxylic acid(ICA); two electrochemical sensing strategies for highly sensitive detection of small molecules were developed based on switching structures of aptamers from DNA/DNA duplex to DNA/target complex. This paper contained five chapters.In the first chapter, the principle and classification of DNA biosensor was introduced. Research status of DNA biosensor and research progress of aptamer sensor were reviewed. This article described mainly the research status of DNA electrochemical biosensor and aptamer-based biosensor.In the second chapter, an electrochemical method to directly detect DNA hybridizationwas developed on the basis of a new conductive polymer, which was polymerized on the glassy carbon electrode with an indole monomer having a carboxyl group, indole-5-carboxylic acid (ICA). Hybridization with complementary, non-complementary and one-base mismatched DNA targets was studied by cyclic voltammetry (CV). Results showed a significant decrease in the current upon addition of complementary target. The change in peak current that was used as an index of sensor response was found to be linear with target concentration in the range of 3.34×10?9 to 1.06×10?8 mol·L-1. The detection limit was 1.0 nmol·L-1. The lable-free sensor have good selectivity.In the third chapter, an electrochemical sensing strategy for highly sensitive detection of small molecules was developed based on switching structures of aptamers from DNA/DNA duplex to DNA/target complex. A gold electrode was first modified with gold nanoparticles (AuNPs), and thiolated capture probe was immobilized onto the electrode via sulfur-gold affinity. Then, a"sandwich-type"strategy was employed, which involved a linker DNA containing anti-adenosine aptamer sequence and reporter DNA loaded on AuNPs. In the presence of adenosine, the aptamer part bound with adenosine and folded to the complex structure. As a result, the reporter probes together with AuNPs were released into solution and reduced a decrease in peak current. [Ru(NH3)6]3+ was used as signal molecule, with the enhancement effect of AuNPs, adenosine could be quantified over the ranges from 5.0×10-10 to 4.0×10-9 mol·L-1 with a linear correlation of R2 = 0.9982 and a detection limit of 1.8×10-10 mol·L-1. The sensor exhibited excellent selectivity against other nucleosides.In the fourth chapter, an electrochemical sensing strategy for simultaneous detection of adenosine and thrombin was developed based on switching structures of aptamers. A Au electrode as the sensing surface was modified with two kinds of thiolated capture probes, complementary to the linker DNA containing either adenosine aptamer or thrombin aptamer. Then the captures hybridized with their corresponding linker DNA, which has prehybridized with the reporter DNA loaded on the AuNPs. The AuNP contained two kinds of bio-bar-code DNA, one was complementary to the linker DNA (reporter), while the other was not (signal), tagged with different metal sulfide nanoparticles. Thus, a"sandwich-type"sensing interface was fabricated for adenosine and thrombin. With the introduction of adenosine and thrombin, the aptamer parts bound with their targets and folded to the complex structures. As a result, the bio-bar-coded gold nanoparticles (AuNPs) were released into solution. The metal sulfide nanoparticles were measured by anodic stripping voltammetry (ASV), and the concentrations of adenosine and thrombin were proportional to the signal of either metal ion. With the dual-amplification of bio-bar-coded AuNP and preconcentration of metal ions through ASV technology, adenosine could be quantified over the ranges from 2.0×10-11 to 2.0×10-9 mol·L-1 with a linear correlation of R2 = 0.9999 and a detection limit of 6.6×10-12 mol·L-1; thrombin could be quantified over the ranges from 2.0×10-12 to 2.0×10-10 mol·L-1 with a linear correlation of R2 = 0.9998 and a detection limit of 1.0×10-12 mol·L-1. The sensor exhibited excellent selectivity and detectability in biological samples.In the last chapter, it was summarized for the whole thesis.