以光電法與電容法發展液晶生物檢測的定量分析

Abstract

在液晶生物檢測技術這塊領域中，利用光學紋理去做生物檢測是目前的核心技術，但利用光學紋理僅能以樣品在正交偏光板下的亮暗態判斷生物分子的存在與否，並無法對不同濃度下的液晶生物檢測樣品做出精準的量化。有鑑於此，吾人以液晶材料之電控雙折射與介電特性，針對液晶生物感測技術，在本碩論中分別提出以光電法與電容法，發展可定量分析生物分子濃度的液晶生物感測技術。實驗中所使用的生物分子為牛血清蛋白，偵測平台則為具高雙折射率的正型液晶HDN。 實驗結果顯示，光電法與電容法對於生物分子濃度的偵測極限分別為106 g/ml與109 g/ml，其差別取決於將蛋白質附著於基板上的方式。針對光電量測法，吾人以旋轉塗佈的方式使蛋白質附著於含DMOAP的導電玻璃基板上，避免因光散射造成相位計算上的誤差。透過量測待測樣品在正交偏光板下之電壓相依的穿透率曲線並藉此計算各樣品的相位變化，本研究計算樣品的有效折射率與液晶材料的雙折射率比值，定義出一個N值，評估液晶分子排列受蛋白質濃度影響的程度。 另一方面，電容法所使用的樣品將使用傳統的液滴法將蛋白質附著於基板上。經由量測樣品電容值隨電壓的變化，可得到電容在高電壓時的最大值（Cmax）以及計算電容值變化量（ΔC）。實驗結果指出，吾人可經由在交流電場驅動下，電容值變化量與電容最大值的比值（ΔC/ Cmax），分析液晶傾角變化與蛋白質濃度的關係，判斷附著在垂直配向基板上的牛血清蛋白的濃度，達到量化分析。

The texture observation has long been the core technique in liquid crystal (LC)-based biosensing. However, quantitative analysis of this method for determining the biomolecular concentration can hardly be realized since the existence of biomolecules immobilized on the substrate is examined in accordance with the brightness of optical textures. In considering with the electrical response of birefringence and dielectric anisotropy of LC materials, in this study, two approaches―electro-optical and capacitive measurements, are proposed specifically for quantitative analysis of LC-based biosensing. Here, the biomolecule used is bovine serum albumin (BSA), a protein standard commonly used in the assay of protein concentration, and the LC material used as the sensing platform is highly birefringent HDN with positive dielectric anisotropy. Experimental results indicate that the detection limit of the BSA concentration is 106 g/ml for the electro-optical measurement and is 109 g/ml for the electric capacittance measurement. The difference between the detection limit of the two measurements stems from the method used for the immobilization of BSA on the DMOAP-coated substrates. For the electro-optical measurement, the BSA biomolecules were spin-coated on the substrate to reduce percentage error on the calculation of phase retardation, attributable to the light scattering. By measuring voltage-dependent transmission (VT) curves and calculating phase retardations of experimental samples, we propose an N value, defined as the ratio of the effective refractive index of the sample to the birefringence of the LC material, to quantitatively estimate the influence of the BSA concentration on the orientation of LC molecules. On the other hand, samples used for the capacitive measurement were prepared using droplets to attach protein on the substrates. Experimental results based on the voltage-dependent capacitive (VC) curves render information on the maximum capacitance Cmax and the capacitance difference ΔC. Furthermore, a quantitative value defined as the ratio of Cmax to ΔC of a sample driven by external AC voltages is calculated to analyze the relationship between the LC tilted angle and the BSA concentration.