Study On Novel Electrochemical Biosensor Based On Functionalized Nanomaterials

Biosensors, as an interdisciplinary frontier involved chemistry, biology, physics, electronics and medical science, have broad application prospects in clinical medicine, industry, agriculture, environmental protection and many other fields. Biosensing technology is also becoming the new growth point during the development of intelligent economy in 21st century. Electrochemical biosensor is extensively investigated and becomes one of the most prospective devices among all kinds of biosensors. And the emergence of nanotechnology has opened up new horizons for the development and applications of nanomaterials in analytical chemistry. Many nanomaterials with unique characteristics promoted the growing of rapid chemical and biological sensors. Moreover, the integration of nanomaterials and bio-molecular recognition has significantly improved the performance of biosensors. Therefore, developing new features of nanomaterials and expanding its applications in biosensors may have huge impact on analytical chemistry.In this thesis, we try to develop novel electrochemical biosensors for sensitive and selective analytical applications both in aqueous and nonaqueous systems based on functionalized nanomaterials.The dissertation includes five chapters as follows:In chapter 1, we provided the background on the development and applications of nanomaterials. And then we summarize the recent progress on nanomaterials based electrochemical biosensors, including fabrication techniques and analytical applications for different targets. Finally, we outline the experimental ideas and the research purposes of this thesis.In chapter 2, the electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by adsorption of cyt c, primarily via electrostatic interactions, onto the modified ITO electrodes. The heme protein displayed a quasi-reversible response in aqueous solution with a redox potential of +324 mV (vs NHE), the surface coverage (Γ) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm2-. On immersion of the modified electrodes in 95%(v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On re-immersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites have potential as stable supports for redox proteins and enzymes.In chapter 3, characterization and application of graphene sheets modified glassy carbon electrodes (graphene/GC) have been proposed for the electrochemical bio-sensing. A probe molecule, potassium ferricyanide is employed to study the electrochemical response at the graphene/GC electrode, which shows better electron transfer than graphite modified (graphite/GC) and bare glassy carbon (GC) electrodes. Based on the highly enhanced electrochemical activity of NADH, alcohol dehydrogenase (ADH) is immobilized on the graphene modified electrode and displays a more desirable analytical performance in the detection of ethanol, compared with graphite/GC or GC based bio-electrodes. It also exhibits excellent performance of ethanol determination in the real samples. From the results of electrochemical investigation, graphene sheets with a favorable electrochemical activity could be an advanced carbon electrode materials for the future design of electrochemical sensors and biosensors.In chapter 4, an aptamer-SWNT based electrochemical biosensor is developed for sensitive detection of thrombin via mediated signal transduction. To realize this purpose, a dense monolayer of 16-mercaptohexadecanoic acid was modified on the gold electrode. In the presence of thrombin, SWNTs were controllably assembled on this insulating monolayer, which could mediate efficient electron transfer between the electrode and eletroactive species to generate a larger redox current. Through detecting the redox signal mediated by SWNTs, this strategy could present significant signal amplification and a detection limit of 50 pM thrombin was achieved. Such an aptamer-SWNT based biosensor opens a rapid, selective and sensitive route for thrombin detection and offers a promising strategy for specific protein detection.Finally, we summarized and pointed out the shortcomings in this dissertation. And then, we proposed the objects and schemes of further research.