Construction Of Biosensor At Aqueous Solution/Liquid Crystal Interfaces Participated By Surfactants And Their Applications

Recently,liquid crystals(LCs)have been generally used as a promising and sensitive sensing platform for real-time monitoring biomolecules.The novel optical sensors possess some advantages such as simplicity,low cost,label-free analysis and portability.The orientational alignment of LC molecules at the fluid interface could be changed due to the interactions between the decorating surfactants and analytes,and subsequently the sensors based on aqueous-LC interfaces could achieve to detect the targets.Moreover,they are convenient for operating and monitoring the dynamic processes of biochemical reactions.Based on above,in this dissertation,we investigated the construction of LC-based biosensors at aqueous-LC interfaces participated by surfactants and their applications.And we comprehensively characterized the signals of the sensors by polarized optical microscopy(POM),and explained the responsive mechanism by fluorescence microscope,circular dichroism(CD)spectrometer and fluorescence spectrometer.There are four main parts in this dissertation as follows.Chapter 1 is a brief introduction of the relevant background knowledge,recent research status closely related to the construction of LC-based biosensors and their applications,and the research ideas for this dissertation.In chapter 2,construction of the LC-based sensing platform for simple and sensitive detection of acetylcholinesterase(AChE)and pesticides using a cationic surfactant-decorated LC interface was demonstrated.(1)We developed a LC-based sensor by preparing the sensing substrate with grids and decorating the aqueous-LC interface using myristoylcholine chloride(Myr).A dark-to-bright transition of the optical appearance was then observed when AChE was transferred onto the Myr-decorated LC interface.The sensitivity of the LC-based sensor is 0.001 mg/mL in the buffer solution.Particularly interesting,although bovine serum albumin(BSA)could not induce the response,the detection sensitivity for AChE in the presence of BSA is 3 orders of magnitude higher than that without BSA.And this LC sensor also shows a very high sensitivity for the detection of the enzyme inhibitor,namely neostigmine bromide,which is around 1 fM.(2)On the basis of above,we observed the signal of pesticides on the LC droplet patterns.On one hand,AChE leads to the bright fan-shaped images of LC droplet patterns when in contact with the pre-incubated mixture of AChE and Myr.On the other hand,the hydrolysis of Myr is inhibited in the presence of AChE-inhibiting pesticides such as baycarb and dimethoate.As a result,the LC droplet patterns present the dark cross appearances.Noteworthy is that the senor could detect trace pesticides.The LC droplet patterns were sensitive to baycarb and dimethoate with a detection limit of about 0.1 pg and 0.01 pg,respectively.The constructed LC-based sensing platform could provide a technical support for sensitively detecting pesticides.In chaptr 3,LC-based sensor for highly selective and sensitive detection of lysozyme,concanavalin A(Con A),and BSA was constructed by utilizing the LC interface decorated with a nonionic surfactant,dodecyl ?-D-glucopyranoside.For this sensor,the LC remained dark appearances with a high stability within a wider range of pH(3-11)and salt concentration(0-1 M).The three proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl ?-D-glucopyranoside,viz.enzymatic hydrolysis,specific saccharide binding,and physical absorption.The limit of detection(LOD)for lysozyme,Con A and BSA reaches around 0.1 ?g/mL,0.01 ?g/mL and 0.001 ?g/mL,respectively.These results might provide new insights into sensitive,selective and lable-free sensors for the detection of proteins.In chapter 4,we still chose the dodecyl ?-D-glucopyranoside as the decorator to build the LC sensor,which is capable of detecting cellulase and cysteine(Cys).The sensor displays a bright transition in the optical appearance for cellulase.Furthermore,the LC functionalized with dodecyl ?-D-glucopyranoside maintained dark by adding cellulase and Cu2+.What's interesting is that our surfactant-LCs system performs an ability to detect Cys,through the addition of Cys into solution including cellulase and Cu2+,leading to the transition of LCs from dark to bright.The detection limit of the LC sensor was about 0.01 ?g/mL and 82.5 ?M for cellulase and Cys,respectively.The method has a favorable prospect in constructing LC sensor,which is based on the enzymatic hydrolysis and inhibition between the targets and decorators.