Enzyme-responsive Cleavable Surfactants Participate In The Construction Of A Liquid Crystal Sensor Platform To Detect Enzymes And Their Inhibitors

Liquid crystals(LCs)sensing platform,as a simple and low cost detection platform,was utilized to achieve sensitivity and specificity of target detection.This is based on the interaction of surfactant and target will induce the changes of alignment of the LC molecules.Therefore,first of all,we designed and synthesized enzyme-responsive cleavable surfactants based on the intermolecular interaction.Then the LCs sensing platform was constructed by decorating the cleavable surfactant at aqueous/LC interface.The enzyme and its inhibitor were detected by this fluid interface based on hydrolysis mechanism and inhibition mechanism of enzyme.The signals of the sensing platform was characterized mainly by polarized optical microscopy(POM),and the interpretation of response mechanism by using fourier transform infrared spectroscopy(FT-IR),isothermal titration calorimetry(ITC),enzyme-linked immune detector.More importantly,the detection of biological molecules was applied to the practical situations.There are four main parts in this paper as follows.Chapter 1 is a brief introduces of the relevant background knowledge of LCs,surfactant as well as LCs sensing platform,and the research ideas for this dissertation.In chapter 2,the amide surfactant-dodecyl N-ethanamide N,N,N-trimethylammonium bromide(DAA)was designed and used to modify the aqueous/LC interface.A sensing platform based on LCs in the presence of ?-Glutamyl transpeptidase(?-GT)was constructed for the detection of glutathione(GSH).The homeotropic-to-planar orientational transition of LCs after transferring ?-GT to the interface because DAA could be enzymatically hydrolyzed by ?-GT.The alignments of LCs were still homeotropic orientations because the inhibition of ?-GT by GSH when the DAA-decorated LC interface was incubated with ?-GT and GSH.Specitivity and sensitivity detection of GSH was due to the optical response of LCs caused by the alignment of LC molecules.The detection mechanism of GSH was verified by ITC and FT-IR.The detection limit of GSH reached 1 pg/mL,which realized the detection of GSH in blood samples.In chapter 3,a sensing platform based on alkaline phosphatase(ALP)was developed for the detection of organophosphorus pesticides(DDVP)and L-phenylalanine(L-Phe).We devised a strategy to construct the sodium monododecyl phosphate(SMP)-decorated LCs sensing platform.(1)We studied response signals of organophosphorus pesticides on the LCs droplet patterns sensing platform.It was found that LCs turned to bright fan-shaped optical appearance after adding the mixture of ALP and SMP.LCs remained dark crossed optical images in contact with the pre-incubated mixture of DDVP,SMP,and ALP.The detection mechanism of DDVP was verified by ITC and humam ALP ELISA kit,and the detection limit of DDVP was 0.1 ng/mL.This strategy was also used to the detection of pesticide residues in tomatoes.(2)On the basis of the above research,we developed a LCs sensing substrate based on copper grids,and LCs sensing platform constructed by using SMP as modifier.A dark-to-bright optical images alteration of LCs was observed after transferring ALP to the interface,owing to the cleavage of SMP induced by ALP.LCs remained dark images due to the inhibition of ALP after in contact with the pre-incubated ALP and L-Phe.The detection mechanism of L-Phe was verified by ITC,and the detection limit was 6.06 pM.In chaper 4,carboxylate surfactants,N-octadecyloxycarbonylmethyl-N,N,N-trimethylammonium bromide(OTB),was designed and synthesized to detect carboxylesterase(CES).A sensing substrate was constructed by doping OTB with LCs.When CES was added to the sensing platform,the change of optical morphology of LCs from dark to bright would be caused by enzymatic hydrolysis.The sensing substrate has the long-term stability for ~20 days,and the detection limit of CES reaches 18 U/L,which realizes the detection of CES in urine samples.