| Liquid crystal is a kind of special material state which is different from solid,liquid and gas state in a certain temperature range.Liquid crystal has the birefringence of the crystal and the fluidity of the liquid,which is based on the combination of molecular long-range orientation and liquid fluidity.With the rapid development as a new type of biosensor technology from 1960s,liquid crystal biosensors have much research findings from different scientists and researchers.Liquid crystal biosensors with different type of substrates are divided into three parts:solid phase liquid crystal biosensors,liquid crystal-liquid phase biosensors and liquid crystal droplet biosensors,and each type has its own advantages and disadvantages.The interaction between the substance and liquid crystal molecules induced the birefringence change of liquid crystal from black to light depending on the orientation changes of the liquid crystal molecules from vertical to planar.Many materials can be tested using liquid crystal biosensors by simple and accurate microscopic images observed in polarizing microscope.During these years,liquid crystal biosensors have played an important role in many fields such as,medicine,agriculture,food safety,homeland security,bioprocessing,environmental and industrial monitoring.As a simple and convenient,highly sensitive detection technology and a more powerful detection tool in our life,however,the application of liquid crystal biosensor needs to be further explored.In this thesis,we designed liquid crystal-liquid phase biosensor to detect small molecules such as cocaine and ATP combing the liquid crystal researches and the characteristics of nucleic acid aptamer.(1)On the basis of mechanism researches on the liquid crystal-liquid phase interface in our group,a new liquid crystal biosensor is constructed for cocaine,in which there is no any surfactant doped in 5CB liquid crystal.The orientation of 5CB liquid crystal molecules mainly depends on the interaction between nucleic acid aptamer and liquid crystal molecules,that is,these changes of the nucleic acid aptamer spatial structure of and the interfacial double-layer density have influenced in liquid crystal molecules arrangement.With the double-layer structure stable/broken,the liquid crystal molecules are arranged vertically/horizontally.The cocaine nucleic acid aptamer has a hairpin structure,which form a stable double electric layer structure in the liquid crystal-liquid interface in the absence of cocaine,so the liquid crystal molecules are vertical arrangement with black image.In the appearance of the cocaine molecules,the nucleic acid aptamer with a special "triangle" structure breaks the stability of the electric double layer and makes liquid crystal molecules disordered with the bright and colorful birefringence color texture pattern that can be seen obviously under the polarized light microscope.Developing a more convenient and fast signal amplification method than the previous method,this method achieve a more sensitive detection of cocaine molecules even the concentrations of cocaine is 1 nM.(2)This part used the specific advantages of slip aptamer chips of ATP to design label-free liquid crystal biosensor with the similar detection design theory of cocaine molecules.Similarly,with the addition of the ATP molecules,nucleic acid aptamers conformation changed from simple chains to "sandwich" structure result in the orientation alignment change from planar to vertical.In the liquid crystal-liquid phase interface,the electrostatic interaction between nucleic acid aptamers and liquid crystal molecules changed from weak to strong.We also can observe the image changes from light to black in polarized light microscope when the concentration of ATP is 10 nM.This method amplify the signal of nucleic acid aptamer,improve the detection sensitivity and use low energy,establishing a label-free and high throughput rapid liquid crystal-liquid interface detection method. |
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