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Title Page

Contents

ABSTRACT 14

CHAPTER I. INTRODUCTION 16

1.1. Motivation 16

1.2. Research Backgrounds 19

1.2.1. Miniaturized biochemical detection systems based on microelectromechanical system (MEMS) techniques 19

1.2.2. Microfluidics and Lab-on-a-chip techniques 23

1.3. Research Objective 27

1.4. Outline 29

CHAPTER II. THERMOELECTRIC BIOCHEMICAL SENSOR 30

2.1. Theory of Thermoelectric Biosensor 30

2.2. Conventional Thermoelectric Biochemical Sensor 35

2.3. Micro Thermoelectric Biochemical Sensor 37

CHAPTER III. ELECTRODYNAMIC PRECONCENTRATION DEVICE 41

3.1. Theory of Electrodynamic Preconcentration 41

3.2. Design and Fabrication 43

3.2.1. Design of a electrodynamic preconcentrator 43

3.2.2. Fabrication of a electrodynamic preconcentrator 50

3.3. Experimental Details 52

3.4. Result and Discussion 54

3.5. Summary and Conclusion 61

CHAPTER IV. ELECTRODYNAMIC PRECONCENTRATOR INTEGRATED THERMOELECTRIC BIOSENSOR 62

4.1. Design and Fabrication 62

4.1.1. Design of an Integrated Biosensor 62

4.1.2. The Fabrication of an Integrated Biosensor 66

4.2. Experimental Details 69

4.3. Result and Discussion 71

4.3.1. Self-compensation of thermal noise by using split-flow microchannel 71

4.3.2. Streptavidin detection with the antigen-antibody immunoassay 74

4.4. Summary and Conclusion 79

CHAPTER V. SUMMARY AND CONCLUSION 81

REFERENCES 83

Table 1.1. Characteristics of various miniaturized biochemical detection systems 22

Table 2.1. Seebeck coefficients of materials relative to platinum 33

Table 3.1. Distributions of 10μm-diameter PS particles near the end of the... 57

Table 3.2. Relative concentration efficiencies at varying flow rates and at applied voltage. 59

Table 4.1. Detailed design description and the value of the continuous split-flow microchannel 65

Figure 1.1. Overview of research motivation 18

Figure 1.2. Sensing principles of miniaturized biochemical detection systems 19

Figure 1.3. Miniaturized biochemical detection systems 21

Figure 1.4. Photographs of microfluidics and lab-on-a-chip (LOC) 24

Figure 1.5. (a) Conceptual view and (b) principle of sequential in situ electrodynamic... 28

Figure 2.1. The Seebeck effect. A temperature gradient along a conductor gives rise to... 31

Figure 2.2. (a) A commercial isothermal titration calorimeter and its (b) principle. 36

Figure 2.3. Categorization of micro thermoelectric biochemical sensor. 37

Figure 2.4. Open chamber type micro calorimeter (thermoelectric biosensor): (a) bulk... 39

Figure 2.5. Closed chamber type micro calorimeter (thermoelectric biosensor): (a) the... 39

Figure 3.1. Schematics and principles of a symmetric interdigitated microelectrode... 44

Figure 3.2. Numerical simulation result of the electric field gradient in the... 45

Figure 3.3. Numerical simulation result of high-density electric field gradient... 47

Figure 3.4. (a) Numerical simulation results of the particle trajectories at the cross-... 49

Figure 3.5. Simplified fabrication sequences of the (a) preconcentrator and thermopiles,... 51

Figure 3.6. (a) Experiments setup and (b) focusing area determination 53

Figure 3.7. Photographs of the preconcentration device showing focusing of... 55

Figure 3.8. Focusing region and x-y plane. Distributions of 10μm-diameter PS... 57

Figure 3.9. Measured relative concentration efficiencies at varying flow rates and at... 60

Figure 4.1. Schematic view and principles of the split-flow microchannel: (a) reaction... 63

Figure 4.2. Design description of the split-flow microchannel for manipulation of... 65

Figure 4.3. Simplified fabrication sequences of the (a) thermopiles, (b) PDMS replica,... 68

Figure 4.4. (a) Schematic view of the experiments setup and (b) photographs of... 70

Figure 4.5. Two sequential pictures showing particle movement in 5 seconds under... 72

Figure 4.6. Performance of the split-flow microchannel: thermal noises due to the... 73

Figure 4.7. Schematic of the fluorescent magnetic particle (FMP) with the sandwich... 74

Figure 4.8. Output voltages that resulted from biotin-streptavidin reactions according... 76

Figure 4.9. Effect of flow rates on output voltage of thermoelectric biosensor:... 78

초록보기

Based on the increased demand for continuous monitoring of biochemical process, thermoelectric biosensors have been widely researched due to its advantages such as being label-free and immobilization-free. At the same time, for accurate analysis in continuous monitoring scheme, a pretreatment process of raw sample is required, since their concentration might fall below the detection limits of certain biosensors. In this respect, several pretreatment processes have been studied, but most of them, which are ex-situ pretreatment processes, suffer from contamination problem, as well as limitations relating to complex labeling steps and low-throughput. Therefore, there is great demand for a completely label-free and in situ concentration-detection process on a single microchip for continuous monitoring of biochemical processes.

This thesis proposes an integrated thermoelectric biosensor chip for continuous monitoring of biochemical process. The integrated microfluidic chip is composed of a preconcentrator and a thermoelectric biosensor. In the preconcentrator, the concentration of the biochemical sample is electrodynamically condensed, which results in enhancement of the downstream biosensor sensitivity. Then, in the sensor, the reaction heat between preconcentrated sample and injected reagent is detected by thermoelectric effect, and the use of an integrated split-flow microchannel enables excellent self-compensation of thermal noise.

The performance of the proposed biochip was evaluated at various flow rates and varied applied voltages. First, in order to verify characteristics of the electrodynamic preconcentrator, 10µm polystyrene particles in PBS were used. The particles were concentrated under an applied AC voltage from 0 to 16Vpp at 3MHz. In the experimental results, approximately 95.8% of preconcentration efficiency was achieved at a voltage over 16Vpp and at a flow rate below 50111/h. The performance of the downstream thermoelectric biosensor was characterized by measuring reaction heat of the biotin-streptavidin interaction. The measured output voltage of the biosensor was 288.2μV at a flow rate of 100μl/h without any pretreatment. However, when a voltage of 16Vpp is applied for upstream preconcentration, output voltage of 812.3μV was achieved in the same given sample.

According to these results, the proposed sequential biomolecular preconcentration-detection technique can be applied in various continuous and high-throughput biochemical applications. Moreover, it is expected that the proposed completely label-free micro total analysis technique could potentially be used in the development of preventive care and point-of-care testing (POCT).

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