Novel Nano-biomaterials Applied For Preparation Of Biosensors

Recently, there has been rapid development in the research and application of biosensors, which can detect analytes selectively using the specific reaction of bioactive materials such as the enzyme-substrate, enzyme-coenzyme, antigen-antibody, incretion-acceptor and so on. Biosensors could be applied directly in the detection of complex samples using the specific bio-recognition of bioactive materials. Meanwhile, due to their high sensitivity, good selectivity, no sample pretreatment and integration of the sample separation and detection steps, biosensors have been applied to a wide rage of analytical tasks, including clinical diagnosis, control of industrial process, environmental monitoring, safety evaluation of chemicals and analyses in food and pharmacy industries.This work focuses on developing new kind of nano-biomaterials and their immobilization methods to improve the performance and long-term stability of biosensors. Therefore, magnetic nanoparticles (Chapter 2), nano-sized flower-like ZnO (Chapter 3, 4) and ZnO nanorods (Chapter 5) were synthesized by a simple hydrothermal method, which is convenient, environment friendly, inexpensive and efficient. The AIV-H1 biosensor based on the magnetic nanoparticles,H₂O₂ and glucose biosensors based on the ZnO showed excellent performance. In addition, N-acetylaniline was selected and electropolymerized on the glassy carbon electrode to enhance the electron transfer between HRP and electrode surface. The details are summarized as follows:1. In chapter 2, magnetic nanoparticles were synthesized by hydrothermal method, and then coated with dextran to fabricate AIV biosensors. An AIV detection method was reported as follows: the nucleic acid hybridization was realized by the mixture of oligonucleotides Probe a immobilized on magnetic nanoparticles, oligonucleotides Probe b modified with biotion, and sample DNA in the hybridization buffer. Then streptavidin-modified Au nanoparticles could be linked to the magnetic nanoparticles through the special binding of streptavidin-biotion. Silver deposition facilitated by Au nanoparticles bridged the electrode gap and led to readily measurable conductivity changes. The detection of the target-DNA could be realized by the measurement of the current changes.2. In chapter 3, the nanoscaled flower-like ZnO synthesized by a simply hydrothermal method were dispersed in chitosan and used as HRP immobilization matrix to fabricate H₂O₂ biosensors. The parameters affecting the performance of biosensors were optimized. The experiment results showed that HRP was firmly immobilized on the surface of electrode, and the current response was 40 times larger than that without ZnO nanoparticles. The linear range was from 1.0×10^-6 to 5.0×10^-3 M H₂O₂ with a correlation coefficient of 0.9977, and the detection limit of the biosensor was 1.0×10^-7 M based on a signal-to-noise ratio of 3.3. In our previous work, we found that nano-ZnO was a good matrix to immobilize HRP. In chapter 4, a glucose biosensor based on GOx immobilized in Pt_nano-ZnO/CHIT composite film was fabricated. As ZnO has a higher isoelectric point than GOx, it is suitable for the adsorption of GOx. In a phosphate buffer solution with a pH value of 7.4, positively charged ZnO provided a friendly microenvironment for the immobilization of negatively charged GOx. The Pt_nano-ZnO/CHIT material brought new capabilities for biosensors by using the synergistic action of Pt nanaoparticles and ZnO. Cyclic voltammetry measurements showed a mixed controlled electrode reaction. The bioactivity of GOx immobilized in the composite was maintained well and the as-prepared biosensor demonstrated high sensitivity and good stability.4. In chapter 5, a H₂O₂ biosensor was fabricated based on HRP immobilized in polyaniline/ZnO-CHIT film. N-acetylaniline was electropolymerized on the glassy carbon electrode to enhance the electron transfer between HRP and electrode surface. Experiment showed that the response of the modified electrode toward interferences like ascorbic acid was greatly diminished while still maintaining relatively large response to hydrogen peroxide.