상세정보

Redox enzymes can be used as biorecognition molecules in various biosensors because electrons are generated during their selective chemical conversion processes. Enzyme-based biosensors offer high specificity and they can be used extensively in various applications, such as disease diagnosis, drug discovery, and contaminants detection. However, most enzymes are non-conductive in nature, seriously interfering with effective electron transfer in enzyme bioelectrodes. Enzymes can be combined with conductive polymers to enhance electrons transfer, but some enzymes naturally contain oligosaccharides on their surfaces, often resulting in the poor contact between enzymes and conductive polymers. Herein, I report the engineering of glucose oxidase (GOx) from Aspergillus niger by surface-wired conductive polymer nanolayer via a two-step process of (1) diffusion-controlled GOx surface modification and (2) in-situ polymerization of aniline in the presence of surface-modified GOx (PAN-GOx). Dynamic light scattering and zeta potential analyses represented that amine groups on GOx surface were successfully modified with phenylamine groups by the diffusion-controlled surface modification with no formation of enzyme aggregates. Conductive polyaniline layers with ~2.7 nm thickness was grown on the surface of phenylamine-displayed GOx molecules via following in-situ polymerization. Activity, stability, and kinetic analysis showed that significant amount of biocatalytic performance was retained after the formation of PAN-GOx. Glucose biosensors were prepared by using PAN-GOx and their electrochemical performances were characterized. Importantly, PAN-GOx-based glucose biosensor showed 16-fold higher sensitivity compared to that obtained from biosensors prepared by using free GOx. It is believed that surface-wired conductive polymer can be applied to other redox-active enzymes because the protocol introduced in this thesis employs surface amine groups, which are ubiquitous for enzymes. In other words, engineered redox enzymes with surface-wired conductive polymer can potentially improve sensitivities for various biosensor applications.

CONTENTS
1. Introduction	1
1.1. Glucose oxidase-based glucose sensor	1
1.2. Objective	4
2. Experimental Methods	6
2.1. Reagents and materials	6
2.2. Surface modification of GOx	7
2.3. Synthesis of polyaniline (PAN) on GOx surface	7
2.4. Zeta potential (ZP) and dynamic light scattering (DLS)	8
2.5. Activity and stability of PAN-GOx	8
2.6. Enzyme kinetics	9
2.7. Enzyme electrode fabrication	9
2.8. Electrochemical analysis	10
3. Results and Discussion	12
3.1. Surface modification of GOx	12
3.1.1 Synthesis mechanism of surface-wired polyaniline nanolayer on GOx	12
3.1.2 Particle size of GOx	13
3.1.3 Zeta potential and Conductivity of GOx	13
3.1.4 Activity of GOx	15
3.2. Fabrication of nanoscale PAN wired on GOx surface	22
3.2.1 Particle size of PAN-GOx	22
3.2.2 Zeta potential and Conductivity of PAN-GOx	22
3.2.3 Activity and Stability of PAN-GOx	23
3.3. Biosensor performance of PAN-GOx	31
3.3.1 Electrochemical Impedance Spectroscopy	31
3.3.2 Cyclic voltammetry and Stability	32
3.3.3 Chronoamperometry	34
4. Conclusions	45
REFERENCES	46