Study Of DNA-Liquid Crystal Biosensing Method For Small Molecular Substances

Liquid crystals ?LCs? are materials that present a special state intermediate between solid phase and liquid phase. LCs are particular materials possessing the mobility of liquids and the anisotropy of solid crystals, which exhibit the intrinsic properties of long-range orientational order and optical anisotropy. Since the LCs act as a special kind of photoelectric-sensitive material, they have been widely used in high-tech fields. LCs plays a very important role in social development and daily life. A key to making LCs well-suited as sensing element is that LCs can respond rapidly to chemical and biomolecular binding events, and can transform them into amplified and visible optical appearances. These properties make LCs of great potential for providing a visual and label-free biosensor that well suited the primary screening assay of analytes without the requirement of complex instruments. Thermotropic liquid crystals are materials that the liquid crystal phase is formed at certain temperatures, and thermotropic liquid crystals are the most widely used material. Typical liquid crystal biosensors mainly depend on the special birefringence phenomenon and the orientation of liquid crystal molecules which are extremely sensitive to the changes of surface morphology. Combined the advantages of functional nucleic acids with the sensitivity of the LC molecules responding to the interface reaction, a novel LC-based biosensors have been developed for the determination of Ag⁺and cysteine; In addition, a DNA logic gate is built for intelligent analysis of Ag⁺and cysteine.In chapter 2:In view of sensing mechanism of LC-aqueous interface is still not very clear, we investigated the appropriate buffer environment ?including ion concentration, pH and so on? to build a reasonable LC biosensor; The negative charge of nucleic acid can act as a special kind of polyanion electrolyte. The conformational changes of nucleic acid molecular lead to the change of negative charge density. The electric double layer of interface can trigger the orientation transition of the LCs from planar orientation to homeotropic orientation, resulting in an optical image change. In this chapter, a simple, fast, cost-effective LC-based biosensor was constructed,and it opens a new way to other small molecule detection.In chapter 3:We have constructed a LC-based biosensor for cysteine ?Cys? detection combining the functional nucleic acids and small molecules, and developed a logic gates system for analysis of multiple target analytes. The electric filed at liquid-aqueous interface varied with the conformational change of DNA aptamer, which will induce the orientation transition of LC. According to this principle, we constructed an LC biosensor for Cys detection. In addition a novel logic gate was designed for intelligent identification and detection of heavy ions Ag⁺and Cys by using the conformation change of rich C bases dsDNA as logical switch, Ag⁺and Cys as the input signal and the optical response of LCs as the output signal. The proposed method was simple, convenient, quick, and high throughput for multiple target analytes. On this basis, we also constructed a platform for H₂O₂ detection by using that the oxidized Cyscan not bond to Ag⁺.