Title Page
Contents
Abstract 16
Chapter 1. Introduction 17
1.1. Flexible device 17
1.2. Biosensor 18
1.3. Flexible biosensor system 20
1.3.1. Active layer 21
1.3.2. Conductive electrode 23
1.3.3. Flexible substrate 24
1.4. Dissertation objectives 25
1.5. Structure of the dissertation 26
References 28
Chapter 2. Electrochemical performance of the spinel NiCo₂O₄ based nanostructure synthesized by chemical bath method for glucose detection 31
2.1. Introduction 31
2.2. Experimental procedure 32
2.2.1. Materials and chemicals 32
2.2.2. Synthesis of spinel-type NiCo₂O₄ (NCO) 32
2.2.3. Material characterizations 33
2.2.4. Electrochemical Characterization 34
2.3. Results and Discussion 34
2.3.1. Characterizations of NCO 34
2.3.2. Electrochemical test of NCO 43
2.3.3. Electrochemical performance of NCO for glucose detection 45
2.4. Conclusion 51
References 52
Chapter 3. Self-assembly of morphology controlled NiCo₂O₄ nanostructure via additive-assisted hydrothermal synthesis for electrochemical glucose detection 55
3.1. Introduction 55
3.2. Experimental procedure 56
3.2.1. Materials and reagents 56
3.2.2. Synthesis of the morphology-controlled NCO (NCOs) 57
3.2.3. Material characterizations 58
3.2.4. Electrochemical measurements 59
3.3. Results and Discussion 59
3.3.1. Characterizations of the NCOs 59
3.3.2. Electrochemical test of the NCOs 74
3.3.3. Electrochemical performance of the NCOs for glucose detection 77
3.4. Conclusion 84
References 85
Chapter 4. Surface Activated bonding of Copper/PDMS composite for flexible electrode 91
4.1. Introduction 91
4.2. Experimental procedure 93
4.2.1. Surface activated bonding of Copper/PDMS composite 93
4.2.2. Material characterizations 93
4.3. Results and Discussion 96
4.3.1. Effect of the plasma treatment on copper and PDMS 96
4.3.2. Adhesion strength of Cu/PDMS composite as a function of plasma conditions 100
4.3.3. Electrical properties of Cu/PDMS during bending test 105
4.4. Conclusion 106
References 107
Chapter 5. Fabrication of the flexible biosensor system. 109
5.1. Introduction 109
5.2. Experimental procedure 110
5.2.1. Fabrication process of the flexible biosensor system 110
5.2.2. Measurement and characterization of the flexible biosensor system 111
5.2.3. Integration of the flexible biosensor system with the soft, skin-interfaced component 111
5.3. Results and Discussion 113
5.4. Conclusion 117
References 118
Chapter 6. Summary 119
Table 1.1. Comparison of optical and electrochemical biosensor 19
Table 1.2. Conductivity and costs of candidate materials for conductive electrode 24
Table 2.1. Electrochemical performance of NCO in our work to that of nonenzymatic glucose sensors in other works. 48
Table 3.1. Synthetic details of NCO with controlled morphology via additive assisted hydrothermal synthesis. For controlling the morphology of NCO,... 57
Table 3.2. Summary of the BET results of the NCOs. 73
Table 3.3. Electrochemical performance of NCO in our work to that of nonenzymatic glucose sensors in other works. 80
Figure 1.1. Applications of flexible device in human life. 17
Figure 1.2. The development direction of the flexible device. 18
Figure 1.3. Components of a biosensor. 19
Figure 1.4. Representative examples of the flexible electrochemical biosensor 20
Figure 1.5. Typical configuration of a flexible biosensor key components. 21
Figure 1.6. Schematic representation of the redox reaction of the active layer. 22
Figure 1.7. Requirement characteristic for active layer sensing 22
Figure 1.8. Conducting electrode material electrical and mechanical characteristics. 24
Figure 2.1. (a) XRD patterns of as-prepared NCH and NCO, (b) FT-IR spectra of as-prepared NCH and NCO, (c) XRD patterns of NCO by different post-heat... 37
Figure 2.2. XRD patterns of crystallographic differences depend on the pH conditions of NCH and NCO; (a) as-prepared samples (before post-heat... 38
Figure 2.3. FE-SEM image of (a) as-synthesized NCH, and (b) NCO. The morphologies of NCH and NCO were investigated by scanning electron... 39
Figure 2.4. HRTEM images and the corresponding HAADF elemental mapping images of Ni, Co and O; (a) as-prepared NCH, and (b) NCO. 40
Figure 2.5. FE-SEM image of microstructural differences in NCO depending on the pH conditions during chemical bath synthesis. (a) as-prepared samples... 41
Figure 2.6. The XPS spectrum of NCH and NCO (a) Ni 2p, (b) Co 2p, and (c) O 1s. 42
Figure 2.7. CV curves of (a) NCH and (b) NCO electrodes at different scan rates. (c) Their respective Randles-Sevick plots. 44
Figure 2.8. Chronoamperometry response of (a) NCH, and (b) NCO electrodes with the addition of glucose to 0.1 M NaOH solution at 0.50 V. (c) their... 47
Figure 2.9. chronoamperometry response of NCH and NCO for the stepwise addition of 1 mM glucose and 0.1 mM interfering species (LA, DA, AA, and UA). 49
Figure 2.10. Chronoamperometry response of (a) NCH, and (b) NCO electrodes for long-term stability in 0.1 M NaOH. Long-term stability of the NCH and... 50
Figure 3.1. Schematic illustration of the formation process of morphology controlled NiCo₂O₄ nanostructures. The schematic and SEM images of the... 61
Figure 3.2. FE-SEM image and EDS mapping image of the NCOs. (a) the different nanostructures are also shown, and (b) Ni, Co and O in the NCOs 62
Figure 3.3. Morphological and structural characterizations of the NCOs: (a) TEM images, (b) TEM images along with the SAED patterns, (c) lattice-resolved... 63
Figure 3.4. (a) XRD patterns of as-prepared NCH and NCO, (b) FT-IR spectra of as-prepared NCH and NCO, (c) XRD patterns of NCO by different post-heat... 67
Figure 3.5. The XPS spectra of Ni2p and Co2p; (a) PNCO, (b) TNCO, and (c) FNCO 68
Figure 3.6. XPS spectra of O1s; (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO 69
Figure 3.7. FE-SEM image of the as-prepared NCOs. 70
Figure 3.8. XRD patterns of the as-prepared NCOs; (a) as-prepared UNCO, (b) as-prepared PNCO, (c) as-prepared TNCO, and (d) as-prepared FNCO. 71
Figure 3.9. (a) Raman spectra, (b) FT-IR spectra of the as-prepared NCOs. 72
Figure 3.10. BET results of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO. The insets show the corresponding pore size distributions. 73
Figure 3.11. CV curves of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO electrodes in the absence of glucose and with the addition of 5 mM glucose at a... 75
Figure 3.12. Cyclic Voltammetry curves of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO electrodes at different scan rates in 0.1M NaOH solution. 76
Figure 3.13. CA responses of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO electrodes with the addition of glucose (0.01-6 mM) to 0.1 M NaOH solution at 0.50 V. 79
Figure 3.14. CA responses of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO with the stepwise addition of 1 mM glucose and 0.1 mM interfering species (LA, DA, AA, and UA). 81
Figure 3.15. CA response of (a) UNCO, (b) PNCO, (c) TNCO, and (d) FNCO electrodes for long-term stability in 0.1 M NaOH. Long-term stability of the... 82
Figure 3.16. Schematic illustration of electro paths on the morphology controlledNiCo₂O₄ nanostructures. 83
Figure 4.1. Schematic illustration of preparation of the Cu/PDMS composite 95
Figure 4.2. The image of the customized multiple deformation machine. 95
Figure 4.3. Contact angle of Cu and PDMS before and after plasma treatment with different plasma treatment conditions; (a) Cu, and (b) PDMS. 98
Figure 4.4. The XPS spectra of Cu and PDMS before and after plasma treatment; (a) Cu (Cu2p and O1s), and (b) PDMS (Si2p and O1s) 99
Figure 4.5. The adhesion strength of Cu/PDMS composite as a function of plasma conditions; (a) Schematic illustration of 90° peel test for Cu/PDMS... 101
Figure 4.6. Profile of the adhesion strength according to energy area. 101
Figure 4.7. The FE-SEM images of cross-sectional plane and SEM in EDAX line profile of copper, silicon, carbon and oxygen element for Cu/PDMS; (a) FE-SEM... 103
Figure 4.8. The XPS spectra of the peel-off surfaces of Cu/PDMS; (a) Cu2p, and (b) Si2p. 104
Figure 4.9. Bending cycle measurement of Cu/PDMS over 3000 times. 105
Figure 5.1. Fabrication procedures of the flexible biosensor system; (a) illustration of the flexible biosensor system, (b) fabrication sequences of the... 112
Figure 5.2. Integration of the flexible biosensor system with the porous PDMS foam. 113
Figure 5.3. The electrochemical properties of the flexible biosensor system; (a) CV profile in 0.01 M NaOH at scan rate 50 mVs¯¹, and (b) CA response in 0.01 M... 115
Figure 5.4. The CA response of the interference species on the flexible biosensor system upon the addition of 1 mM glucose, then 0.1 mM of LA, DA, AA, and UA... 116
Figure 5.5. Demonstration of integration of flexible biosensor system with the porous PDMS foam on-body. The diluted artificial sweat solution injection into... 116