Fabrication And Application Of Functional Nucleic Acid And SECs Material Based Liquid Crystal Sensing Platform

Liquid crystals(LC)-based sensors are well constructed due to the unique features of LCs such as extraordinary sensitivity,long-range orientational order,and optical anisotropy.Chemical and biological events at the aqueous/LC interface can be readily transduced and amplified into the optical outputs that are visible by the naked eye.Hence,as a promising analytical tool,they show advantages of easy construction,low cost,high portability,and independent on complex instrumentation.LC-based sensors have shown potential in detection of volatile organic compounds,heavy metal ions and biomarkers.However,they always suffer from poor sensitivity,matrix interference,and low throughput.Hence,in order to solve these problems,we combine LCs with functional nucleic acids and nanomaterials to construct new types of LC-based sensors and study their applications and sensing mechanisms.There are five sections in this dissertation:Chapter 1 introduces the basic knowledge and recent advances of LC-based sensors,functional nucleic acids,and surfactant-encapsulated clusters materials in biological and analytical areas.Based on these advances,the subject topics basis and ideas are proposed.Chapter 2 demonstrates construction of LC-based sensing platforms for sensitive and fast detection of H2O2 and blood glucose with high accuracy.Single-stranded DNA(ssDNA)adsorbed onto the surface of nanoceria is released to the aqueous solution in the presence of H2O2,which disrupts arrangement of the self-assembled cationic surfactant monolayer decorated at the aqueous/LC interface.Thus,the orientation of LCs changes from homeotropic to planar state,leading to change in the optical response from dark to bright appearance.As H2O2 can be produced during oxidation of glucose by glucose oxidase(GOx),detection of glucose is also fulfilled by employing the H2O2 sensing platform.Our system can detect H2O2 and glucose with a concentration as low as 28.9 nM and 0.52 ?M,respectively.It shows high promise of using LC-based sensors for the detection of H2O2 and its relevant biomarkers in practical applications.Chapter 3 proposes use of LCs to detect biomarkers in blood with high sensitivity and specificity by employing in situ rolling circle amplification(RCA)on magnetic beads(MBs).Specific recognition of cancer biomarkers(e.g.platelet derived growth factor BB(PDGF-BB)and adenosine)by aptamers leads to formation of a nucleic acid circle on MBs pre-assembled with ligation DNA,linear padlock DNA,and aptamers,thereby triggering in situ RCA.LCs changes from dark to bright appearance after the in situ RCA products being transferred onto the LC interface decorated with octadecy trimethyl ammonium bromide(OTAB),which is particularly sensitive to the amplified DNA on MBs.However,when RCA does not take place without targets,the optical response of LCs is dark after pre-assembled MBs are introduced onto the OTAB-laden interface.Thus,the changes of LC appearance can been employed as signals to detect the targets.Overall,this label-free approach takes advantages of high specificity of aptamer-based assay,efficient enrichment of signaling molecules on MBs,remarkable DNA elongation performance of the RCA reaction,and high sensitivity of LC-based assay.It successfully eliminates the matrix interference on the LC-based sensors and improves the sensitivity.In addition,performance of the developed sensor is comparable to that of the commercial ones.Chapter 4 proposes a strategy called substrate-assisted aqueous/LC sensing assay coupled with stimulus-responsive surfactant-encapsulated clusters(SECs)for detection of enzyme and environmental pollution.This strategy can decrease the matrix effect.It displays dark appearance when the aqueous solution is in contact with LCs supported on the octadecyltrichlorosilane-treated glass deposited with the supramolecular spheres,suggesting perpendicular orientation of LCs at the aqueous/LC interface.In contrast,LCs show bright appearance when the surface-deposited supramolecular spheres are disassembled,corresponding to planar orientation of LCs at the aqueous/LC interface.We fabricated pH-responsive SECs to achieve highly sensitive and specific detection of urease and heavy metal ions(Cu2+ is taken as an example)by using this strategy.The detection limits are 0.03 mU/mL and 1 nM,respectively.We also demonstrate use of acetylcholinesterase(AChE)-responsive SECs to build a LC-based sensing platform for detection of organophosphorus pesticides(OPs).The detection limit of the sensing platform reaches 0.9 ng/mL for dimethoate that is an organophosphate.This method can avoid disturbance of external interference with excellent specificity and sensitivity,which makes it very promising in detection of enzyme and environmental pollution.Chapter 5 demonstrates a strategy for simultaneous detection of multiple tumor markers in blood by functional LC sensors assisted with target-induced dissociation(TID)of aptamer.MBs coated with an aptamer(apt 1)are employed to specifically capture target proteins in blood.After adding duplexes of another aptamer(apt2)and signal DNA,sandwich complexes of aptl-protein-apt2 are formed due to specific recognition of target proteins by apt2,which induces release of signal DNA into the aqueous solution.Subsequently,signal DNA is added into a 3D printed optical cell(each channels have been decorated by probe DNA that is complementary to signal DNA).Multiplex detection of different proteins can be achieved by detection of corresponding signal DNA,due to specifically recognized by highly sensitive DNA-laden LC sensors.This strategy is employed to enable simultaneous detection of multiple tumor markers such as carcinoembryonic antigen(CEA),alpha-fetoprotein(AFP),and prostate specific antigen(PSA)with high specificity and high sensitivity.Plus,it offers performance that is competitive to that of commercial ELISA kits without potential interference from hemolysis which makes it very promising in clinical detection of tumor markers and diagnosis of cancer.