Construction Of Liquid Crystals Sensing Platform Based On Weak Interaction For Detecting Biomolecules

Recently,liquid crystals(LCs)sensing platform could open up a significant approach for detection of biomolecules due to its advantages such as simple construction,low cost,high specificity and sensitivity.LCs sensing platform can achieve monitoring analytes via the variation in orientational alignment of LC molecules triggered by slight changes in physical and chemical properties when adding analytes.It can transform such changes into amplified and visible optical signals.In view of this,we chose a thermotropic LC,namely 4-cyano-4'-pentylbiphenyl(5CB),as sensing substrate in this dissertation.Some biomolecules including lithocholic acid,a-amylase,and thrombin were detected by the LCs sensing platform designed based on the intermolecular weak interactions(e.g.host-guest interaction and electrostatic interaction).Polarized optical microscope(POM)was employed to observe the optical response signal of sensing platform.We also explained the responsive mechanism,aided by isothermal titration calorimetry(ITC)and surface tensiometer.There are four main parts in this dissertation as follows:Chapter 1 is an introduction of the relevant background knowledge of LCs,LCs sensing platforms and weak intermolecular interactions,as well as the recent research status of LCs sensing platform in detection at home and abroad,and the research ideas for this dissertation.In chapter 2,we constructed a LCs sensing platform based on host-guest interaction and detected lithocholic acid(LCA)by competitive host-guest inclusion.When sodium dodecyl sulfate(SDS)/?-cyclodextrin(?-CD)complex was added to the aqueous/LCs interface,a bright image was observed under POM,because almost all of SDS molecules were into the cavities of p-CD.In this case,no free SDS existed in the bulk of solution and adsorbed at the fluid interface to induce the homeotropic ordering of LCs.When injecting LCA into the aqueous/LCs interface,POM captured a bright-to-dark transformation of optical response.The as-prepared LCs sensing platform could detect LCA as low as?2 ?M,without interference from other components such as inorganic salt,glucose,ascorbic acid,urea and uric acid.According to the experimental results of ITC,the possible LCA detection mechanism was speculated.The host-guest interaction between ?-CD and LCA is much stronger than that of ?-CD with SDS.Therefore,upon addition of LCA,SDS molecules which were excluded from the cavity of ?-CD on account of competitive host-guest inclusion adsorbed at the aqueous/LCs interface and resulted in the orientational transition of LCs from tilted to homeotropic state.Moreover,the practicability of such approach was validated by monitoring the amount of LCA in human urine.The research work in this chapter can provide a basis for the early clinical diagnosis of hepatic disease.In chapter 3,we detected a-amylase by disruption of host-guest interaction between SDS and ?-CD on the basis of chapter 2.Only in the presence of SDS/?-CD solution,a bright optical image was observed.While a black optical appearance was captured when the pre-incubated mixture containing SDS/?-CD complex and a-amylase was transferred onto the fluid interface.According to the data of surface tension,we inferred that a-amylase could hydrolyze ?-CD and subsequently destroy the host-guest interaction between SDS and P-CD.SDS molecules escaping from the cavity of ?-CDs adsorbed at the aqueous/LCs interface and evoked the homeotropic state of LCs.The POM images of LCs always kept bright within a wide range of pH(3.0?11.0)and ionic strength(0?1.0 mM),indicating high stability of the LCs sensing platform.Based on these,detection of ?-amylase could be achieved and its detection limit was about 15 U/L.This sensing platform shew no response to other enzymes such as trypsin,pepsin and lysozyme.Moreover,it was successfully utilized to monitor ?-amylase in dilute urine and saliva.This approach has a great potentiality in sensitive and label-free detection of a-amylase.In chapter 4,we designed a LCs sensing platform based on electrostatic interaction to analyze thrombin.LCs doped with octadecyl-trimethylammonium bromide(OTAB)adopted homeotropic alignment under the induction of OTAB.When thrombin aptamer was added,it was attached to aqueous/LCs interface because of the electrostatic interaction between aptamer and OTAB,and then the hydrophobic nucleobases of thrombin aptamer associate directly with the LCs,effectively competing with OTAB molecules for interfacial sites,which caused the orientational transition of LCs from homeotropic to tilted state corresponding to variation in the optical morphology of LCs from dark to bright.When thrombin was present,the aptamer was preferred to bind to it.After that,OTAB induced the vertical arrangement of LCs corresponding to a dark image under POM.Therefore,thrombin could be detected by observing the bright and dark change in the optical appearance of LCs.The detection limit of thrombin was about 136 nM.The LCs sensing platform constructed based on electrostatic interaction can detect biomolecules by the specific combination of target molecule and corresponding aptamer,which reveals a new way to relevant clinical application in the future.