Electrochemical Aptamer Sensor

The aptamer has a number of advantages such as high specificity, affinity, easier modification and functionalization, low cost and so on, it would be widely reached and used in chemistry, biomedical and material science, and becomes one of the research hotspots. The electrochemical methods have many advantages compared with the traditional optical method, such as rapid response, high sensitivity, simple design, miniaturization of the instruments, portable, low cost and so on. So the electrochemical technology has great attractiveness for researching the biosensor. Recently, the electrochemical methods have been receiving much attention. In this thesis, the interaction betweent the aptamer and the thrombin was investigated, the CdS hollow nanospheres and the water-soluble CdSe quantum dots were synthesized, the morphology and stucture of CdS and CdSe nanoparticles were characterized. The methylene blue (MB) was used as an electrochemical marker, the aptamer biosensor and a nonenzymatic cholesterol sensor by using porous tubular silver nanoparticles were constructed, the main results are as follows:1. A simple method to amplify the electrochemical signal by an aptamer with 22 bases modified with CdS hollow nanospheres (CdSHNs) was described. Using the thrombin as a model, the interaction between the aptamer and CdSHNs was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and circular dichroism spectroscopy. CdSHNs promoted the electron transfer between the gold electrode and K3[Fe(CN)6] and facilitated the conformation conversion of the aptamer from hairpin to G-quadruplex after the aptamer interacted with thrombin. Under optimal conditions, the modified electrode could be used for the determination of thrombin from 0 to 33μgmL-1 and the sensitivity was 1.34μA·mLμg-1cm-2, while the linear range of the modified electrode without the immobilization of CdSHNs was from 2.75 to 27.5μgmL-1 and the sensitivity was 0.062μA·mLμg-1cm-2. This constructed biosensor also had a good stability, specificity, reproducibility and accuracy which could provide a promising platform for fabrication of aptamer based biosensors.2. An easy and sensitive aptamer biosensor was developed by immobilizing the aptamer on water soluble CdSe quantum dots (QDs) modified on top of the glassy carbon electrode (GCE). Methylene blue (MB) was intercalated into the aptamer sequence and used as an electrochemical marker. CdSe QDs improved the electrochemical signal because of their larger surface area and ion centers of CdSe QDs may also had a major role on amplifying the signal. The higher ion concentration caused more combination of aptamer which caused larger signal. The thrombin was detected by differential pulse voltammetry (DPV) quantitatively. Under optimal conditions, the two linear ranges were obtained from 3 to 13μg·mL-1 and from 14 to 31μg·mL-1, respectively. The detection limit was 0.08μg·mL-1 at 3a. The constructed biosensor had better responses compared with that in the absence of the CdSe QDs immobilization. The control experiment was also carried out by using BSA, casein and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by fluorescence method which could provide a promising platform for fabrication of aptamer based biosensors.3. Porous tubular silver (Ag) nanoparticles were successfully synthesized by electrodeposition of Ag into cadmium sulfide (CdS) modified porous anodic alumina (PAA) template and removal of CdS subsequently. Only the solid nanorods were obtained without CdS. The strong affinity between S2- and Ag (I) caused preferential deposition of Ag on the pore walls to form tubular Ag. After removal of CdS, porous tubular Ag nanoparticles were obtained. This novel nanostructure was characterized by XRD, TEM, FESEM, EDS and nitrogen adsorption-desorption isotherms. Using porous tubularAgnanoparticlesmodifiedglassy carbon electrode (GCE) as a working electrode, a good nonenzymatic cholesterol sensor was constructed, which showed markedly improved electrocatalytic activity toward cholesterol oxidation compared to that of solid Ag nanorods. Under optimal detection conditions, the constructed sensor had a linear response range of 2.8×10-4 M to 3.3×10-2 M and the detection limit was 1.8×10-4 M at a signal-to-noise ratio of 3. The biosensor showed an acceptable reproducibility, good stability and low interferences. To the best of our knowledge, it is the first example of a nonenzymatic cholesterol biosensor based on Ag nanoparticles. The experimental results demonstrated that porous tubular Ag nanoparticles provided a promising platform for rational design and fabrication of nonenzymatic cholesterol sensors.