Study On Electrochemical Biosensors Based On Carbon Nanotubes And Aptamers

Carbon nanotubes (CNTs) have attracted great interests since they were discovered in1991by Iijima. Due to their novel physiochemical properties and one-dimensional nanosize characteristics, carbon nanotubes have been widely used in electrochemical biosensors; Meanwhile, combination of metals or metal oxides with CNTs will lead to new composite materials possessing the properties of each component, or even with a synergistic effect, which would be more useful in the fields of electroanalysis and biochemistry. On the other hand, aptamers are artificial oligonucleic acids that can bind many specific target moleculars. As alternatives to antibodies, aptamers become molecular recognition elements in the biochemical analysis and would be used widely in various fields. Based on the advantages of aptamers and doped/undoped CNTs, electrochemical biosensors based on aptamer and CNTs(MnO2-WCNTs) have been developed. The main points of this thesis are summarized as follows:(1) Manganese dioxide-carbon (MnO2-WCNTs) nanocomposite as a novel nanomaterial has been synthesized by a direct redox reaction between carbon nanotubes (CNTs) and permanganate ions. On basis of this, a nonenzymatic H2O2sensor was fabricated successfully. Cyclic voltammetry (CV) and Amperometric i-t Curve were applied to investigate the electrochemical properties of the nonenzymatic sensor. Compared with the bare glassy carbon (GC) electrode and the WCNTs/GC electrode, the MnO2-WCNTs nanocompo-site modified electrode displayed higher catalytic activity towards the oxidation of H2O2. It may be due to the excellent properties of the MnO2-WCNTs nanocomposite, which combined the advantages of MnO2particles and WCNTs, leading to the increase of electrocatalytic active sites and the promotion of electron transfer rates. Influence of various experimental parameters on H2O2sensing, including the solution pH and applied potential were also investigated. Under the optimum conditions, the sensor exhibited a linear dependence (r=0.9987) on the concentration of H2O2from5×10-7mol L-1to0.2mol L-1, a high sensitivity of21.26μA mM-1cm-2and a low detection limit of1.4×10-7mol L-1(signal/noise=3). Additionally, the MnO2-WCNTs/GC electrode showed good stability and excellent anti-interferent ability. These results demonstrated that the MnO2-WCNTs nanocomposite offers great promise for the development of nonenzymatic H2O2sensors. (2) A label-free electrochemical sensing strategy for highly sensitive detection of adenosine was constructed. The design relied on the structrue-switching properities of aptamers upon binding to their target molecules and signal enhancement of nanotechnology. The change of the interfacial feature of the electrode was characterized by electrochemical impedance analysis with [Fe(CN)6]3-/4-as the redox probe. Influence of various experimental parameters on adenosine sensing, including the ionic strength、 solution pH and incubation time, were also investigated. Using [Ru(NH3)6]3+as the signaling moiety, as low as0.027nM denosine can be detected and dicrimin-ated from its analogues, indicating high sensitivity and high selectivity. Additionally, the time of adenosine determination was low and the fabrication approach was simple. Compared with other procedures that require specific label, the proposed technique demonstrated lowered cost and simplified need in oligonucleotide probes. Because there were no special requirements on the aptamer part, the design was not only applied to adenosine as a model system but also possessing the potential of wider application for other targets.