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Liquid Crystal Biosensors Final Liquid Crystal Biosensors A thesis submitted to the University of Manchester for the degree of Doctor of Engineering in the faculty of Engineering and Physical Sciences 2011 Thomas Cronin School of Physics and Astronomy 1 Contents Chapter 1 Introduction (31) 1.1 Biosensors and liquid crystals (31) 1.2 Sharp Laboratories of Europe (34) 1.3 Sociological drivers for the research project (35) 1.4 Commercial drivers for the research project (36) 1.5 Position of the project within SLE's corporate strategy (37) 1.6 Progression of the project (38) 1.7 Commercial value of the current state of the project and further development needed for commercialisation (40) 1.8 Potential markets for the project (41) 1.9 Structure of the thesis (41) Chapter 2 Existing Work in the Field of Liquid Crystal Biosensors, a Literature Review (43) 2.1 Surface bound analytes (44) 2.1.1 Oblique gold (44) 2.1.2 Detection of gaseous analytes (46) 2.1.3 Detection of DNA (46) 2.1.4 Substrates without a gold layer (46) 2.1.5 Investigations into the system parameters important for analyte detection (47) 2.1.6 Quantification of analyte binding (51) 2.1.7 Modelling the effects of surface bound analytes on LC alignment (52) 2.2 LC-aqueous interfaces (54) 2.2.1 LC films supported by copper and gold grids (54) 2.2.2 DNA detection at LC-aqueous interfaces (57) 2.2.3 Modelling of the effect of analytes bound at the LC- aqueous interface on LC alignment (57) 2.3 Detection of analytes in the liquid crystal bulk (57) 2.4 Non-optical detection (58) 2 2.5 Wearable sensors (59) 2.6 Summary (59) Chapter 3 Liquid Crystal Theory (63) 3.1 Introduction to liquid crystals (63) 3.2 Liquid crystal phases (65) 3.3 Chirality (67) 3.4 The nematic order parameter (69) 3.5 The birefringence of liquid crystals (71) 3.6 Dielectric anisotropy (73) 3.7 Liquid crystal alignment (75) 3.8 Liquid crystal textures (77) 3.9 Elastic Constants (81) 3.10 Measuring the elastic constants of nematic liquid crystals (82) 3.11 Anchoring energy (87) 3.11.1 Surface chemistry (87) 3.11.2 Surface topography: grooved surfaces (89) 3.12 Particles in liquid crystals (93) 3.13 Summary (95) Chapter 4 Modelling a Biological Analyte with Latex Beads (98) 4.1 Introduction (98) 4.2 Materials used (99) 4.2.1 Biotin coated beads and streptavidin coated surfaces (99) 4.2.2 Liquid crystals (101) 4.3 Cell construction (101) 4.3.1 Measurements of cell thickness (103) 4.4 Optical polarized microscopy (104) 4.4.1 Conoscopy (106) 4.5 Results (107) 4.5.1 Testing alignment layers (108) 4.5.2 Imaging beads with 5CB (109) 4.5.3 Sensitivity of 5CB to UV illumination (111) 3 4.5.4 Imaging beads with ZLI 1695 (112) 4.6 Investigation into bead-surface binding patterns (115) 4.7 Summary (116) Chapter 5 Modelling a Biological Analyte Using Gold Microdots (119) 5.1 Introduction (119) 5.2 Introduction to liquid crystals used (121) 5.3 Refractive index measurements (123) 5.4 Capacitance measurements using commercial cells (125) 5.4.1 Elastic constants calculated from capacitance measurements (126) 5.5 Substrate construction (130) 5.6 SAM construction (132) 5.7 Cell fabrication (134) 5.8 Optical polarising microscopy (135) 5.9 Summary (139) Chapter 6 Ancillary Results – Physical Properties of Liquid Crystals (140) 6.1 Refractive index measurements (140) 6.2 Elastic constants measurements (149) 6.3 Summary (157) Chapter 7 The Effect of Controlling Surface Chemistry Using Thiols (159) 7.1 Images of the behaviour of the 5CB on the surfaces (160) 7.1.1 Plain Au (161) 7.1.2 Alcohol thiol: 3-mercapto-1-propanol (165) 7.1.3 Acid thiol: 3-mercaptopropionic acid (166) 7.2 Reflection of monochromatic light as a function of temperature (168) 7.2.1 Plain Au (166) 4 7.2.2 Alcohol thiol: 3-mercapto-1-propanol (173) 7.2.3 Acid thiol: 3-mercaptopropionic acid (175) 7.3 Discussion (178) 7.4 Summary (179) Chapter 8 The Effect of Cell Thickness (181) 8.1 Nominal 7.5 µm thickness (183) 8.2 Nominal 10.0 µm thickness (187) 8.3 Nominal 12.7 µm thickness (191) 8.4 Nominal 40.0 µm thickness (194) 8.6 Discussion (197) 8.6.1 Intensity vs. thickness (198) 8.7 Summary (201) Chapter 9 The Effects of Different Liquid Crystals (203) 9.1 5CB (204) 9.2 E7 (208) 9.3 ZLI 1695 (214) 9.4 ZLI 1132 (219) 9.5 MDA 01-2012 (225) 9.6 Discussion (231) 9.6.1 Optical textures in the nematic phase (232) 9.6.2 Optical textures on heating and cooling (234) 9.6.3 The relationship between peak height and birefringence (235) 9.6.4 The relationship between peak height and elasticity (237) 9.7 Summary (241) Chapter 10 The Effects of Spot Size and Separation, Array Properties (243) 10.1 2µm spot diameter, 5 µm array pitch (244) 10.2 4µm spot diameter, 7 µm array pitch (246) 10.3 4µm spot diameter, 10 µm array pitch (248) 5 10.4 4µm spot diameter, 20 µm array pitch (250) 10.5 4µm spot diameter, 40 µm array pitch (252) 10.6 8µm spot diameter, 20 µm array pitch (254) 10.7 16 µm spot diameter, 40 µ array pitch (256) 10.8 Reflected intensities (258) 10.8.1 2µm spot diameter, 5µm array pitch (258) 10.8.2 4µm spot diameter, 7µm array pitch (259) 10.8.3 4µm spot diameter, 10µm array pitch (259) 10.8.4 4µm spot diameter, 20µm array pitch (261) 10.8.5 4µm spot diameter, 40µm array pitch (262) 10.8.6 8µm spot diameter, 20µm array pitch (262) 10.8.7 16µm spot diameter, 40µm array pitch (263) 10.9 Discussion (264) 10.9.1 The effect of spot size (264) 10.9.2 The effect of spot separation (268) 10.10 Summary (271) Chapter 11 Conclusions (272) 11.1 Measurements taken and effects observed (274) 11.2 Summary of results (273) 11.3 Implications for biosensor design (274) 11.4 Future work (274) Appendix A Calculating the Elastic Constants (277) A.1 Modelling the permittivity curve (277) A.2 Permittivity calculations and the elastic constants (279) Appendix B Fitting Using MATLAB (292) B.1 Fredhybridpre (293) B.2 Fredhybridpreepsfit (296) 6 List of Figures Figure 3.1 A model of the chemical structure of the liquid crystal 5CB as a rigid rod. The length of the rod in the z axis is longer than in the x and y axes. The dotted line represents the prolate spheroid shape of a usual mesogen model. (65) Figure 3.2 Orientation of calamitic mesogens in a nematic liquid crystal. (66) Figure 3.3 (a) Schematic of the layered structure of the Smectic A phase. (b) Schematic of the layered structure of the smectic C phase. (67) Figure 3.4 The helical orientation of mesogens in a cholesteric liquid crystal. Note, this does not indicate a layered structure, as in the case of smectic phases. (68) Figure 3.5 Azimuthal rotation of mesogen tilt between the layers of the SmC* phase. (69) Figure 3.6 Orientational order parameter, S, as a function of T/TNI for a typical nematic. [Redrawn from reference 10, pg 133]. (71) Figure 3.7 Indicatrix of optically positive and optically negative uniaxial mediums. [Figure redrawn from reference 11, pg 36.] (72) Figure 3.8 Diagram showing how the indicatrix interacts with light propagating in direction k, to give ne. [Figure redrawn from reference 13, pg 87.] (73) 7 Figure 3.9 Different alignments of liquid crystal mesogens on glass substrates in the x, y plane. (a) Random planar orientation of mesogens lying in the plane of the substrate. (b) Aligned, homogeneous planar orientation. (c) Homeotropic orientation with mesogens orientated at 90° to the x, y plane. [Figure redrawn from reference 11, pg 22.] (75) Figure 3.10 Surfactant induced homeotropic alignment. (a) Sufficient concentration of amphiphiles allows steric interdigitation with LC mesogens. (b) Too high a concentration of amphiphiles prevents alignment. [Figure redrawn from reference 21, pg 8.] (76) Figure 3.11 Strength, molecular alignment and Schlieren brushes of the four defect types seen in nematic liquid crystals. [Figure redrawn from references1, pg 138] (79) Figure 3.12 (a) Vertical cross-section of a pair of Dupin cyclides. (b) Smectic A focal-conic domain. [Figures from reference 1, pg 184 and reference 24, pg 322 respectively] (80) Figure 3.13 Arrangement of tangential focal conics building up polygonal domains. [From reference 14, pg 468.] (80) Figure 3.14 Schematics of the three fundamental elastic deformations of nematic liquid crystals 9 showing the change in n with respect to ∂x, ∂y and ∂x for each deformation. 26 [Figure redrawn from reference 9, pg 60, and reference 26, pg 21.] (81) Figure 3.15 A planar aligned nematic liquid crystal cell. (a) With no electric field. (b) With an electric field perpendicular to the plane of the substrates with V>V0. [Figure redrawn from reference 1, pg 209.] (83) Figure 3.16 The behaviour of the permittivity of a planar nematic liquid aligned cell in response to a potential difference across the cell. (84) 8 Figure 3.17 Schematic of a pure twist cell. [Figure redrawn from reference 21, pg 14.] (88) Figure 3.18 The director of a nematic liquid crystal on a grooved glass substrate. (a) With the director aligned perpendicular to the grooved direction.
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