Study Of Liquid Crystal Biosensing Method For Organphosphorus And L-histidine Assay

Liquid crystals (LCs) are special materials which present with a special stateintermediate between solid phase and liquid phase. Due to the special opticalanisotropy and mobility properties of liquid crystals, the liquid crystals materials havebeen widely used in the LCD screen. Thermotropic liquid crystals are referring thatthe liquid crystal phase is formed by changing the temperature of the material. Typicalliquid crystal biosensor mainly depends on the special birefringence phenomenon andthe orientation of liquid crystal molecules which are extremely sensitive to thechanges of surface modification. These LCs materials based sensors can be used toamplify and transduce the surface binding events into optical outputs which can beeasily observed with polarizing microscope. The liquid crystal biosensor permitlabel-free detection with high sensitivity and without the requirement of complexinstruments and even the need of electrical power, making them sufficiently simpleand well suitable for the primary screening assay of analytes performed away fromcentral laboratories. Given the sensitivity of the LC molecules orientation to theproperty of a bounding interface and the characteristic of visible, novel liquid crystalbiosensors have been developed for the identification of organphosphorus anddetecting L-histidine.In chaper2: An improved liquid crystal biosensor has been developed foramplified identification of AChE inhibitors. The introduction of the enzymatic growthof AuNPs can greatly change the surface topology of LC sensing interface and causean enhanced disruption of the LC orientation, resulting in the obvious birefringentappearances for AChE LC biosensing system. After the immobilized AChE isinhibited by organphosphorus (OPs), lower yields of AuNPs are produced withdifferent AChE inhibitors, which can offer a low optical background with only a fewbright spots in the optical images for the identification of AChE inhibitors. Thepralidoxime reactivator can reactivate the catalytic activity of inhibited AChE in adifferent degree, and the optical images of birefringent textures have obvious decreasefrom methamidophos, trichlorfon to paraoxon. The AChE LC biosensors do not needcomplicated analytical instruments, and have visual optical images which can even beobserved with the naked eyes. This new constructing LC biosensor may extend tooffer a promising tool for the identification of other AChE inhibitors, and can be potential to be used in medicine for judging the sort of organophosphorus poisoningand using suitable cholinesterase reactivators with suitable concentration for rapiddetoxification.In chaper3: A novel label-free liquid crystal biosensor has been developed forthe detection of L-histidine with high sensitivity and high selectivity. This principlemainly relies on the DNA conformational change in the substrate which can inducethe changes of the alignment of liquid crystals materials and results in the differentoptical singal captured by optical instrument. L-histidine dependent DNAzymes arethe catalytic nucleotide sequences which are selected in vitro. In the presence ofL-histidine, the self-cleaving will occur which can release a single-stranded DNA.The single-stranded DNA can be fixed in the substrate by the hybridization reactionwith the designed capture probe and then the double-stranded DNA generate in thesubstrate. With the rigid structure of double-stranded DNA, the alignment of liquidcrystals has been induced to change and the different optical signal will be obtainedwith different concentrate L-histidine. In absence of the L-histidine, no changes of theDNA conformational will occur in the substrate and no different optical signals willbe obtained. The results show that the mentioned liquid crystal biosensor is sensitiveto the L-histidine and the detection limit of the sensor is50nM.In chaper4: A novel liquid crystal/aqueous biosensor has been developed for thedetection of L-histidine which mainly based on the DNA conformational change. Thestrategy of the proposed liquid crystal biosensor mainly depends on adding thesurfactant (SDS) in the interface of liquid crystal and the aqueous. The differentalignment of liquid crystals can be induced by the electrostatic interaction andhydrophobic interaction between the surfactant and DNA, which can result indifferent optical signals. In the absence of the L-histidine, the DNAzymes will appearin dsDNA, the electrostatic interaction between the surfactant and dsDNA will disturbthe vertical LC orientation; In the presence of the L-histidine, the self-cleaving willoccur which can release different ssDNA, the different ssDNA can generateLC-SDS-ssDNA complexes which can induce tilted/planar LC orientation. Theproposed liquid crystal biosensors have exhibited advantages of high sensitivity, highselectivity, label-free and easy in operation for the detection of L-histidine, with thedetection limit of100nM.