Photonic-crystal And Liquid-crystal Biosensosrs For Visual Detection Of Environmental Pollutants

The environmental pollution has become a major contemporary problem.The excessive emission of pollutants has created extremely serious threat to the human health.Currently,some common approaches have been reported for the determination of environmental pollutants,including liquid chromatography-mass spectrometry(LC-MS),gas chromatography-mass spectrometry(GC-MS),inductively coupled plasma-mass spectrometry(ICP-MS),atomic absorption spectroscopy,electrochemical,and fluorometric methods.Although various approaches have achieved good results,they often need expensive equipment,trained personnel,and complex signal label,which limit their application in a certain degree,particularly when the assay has to be performed at sites far away from central laboratories.Therefore,there is still of great significance to develop simple,label-free,and visual platforms for environmental pollution prevention,ecosystems improvement and human health protection.In recent years,many new materials with excellent properties have been applied to the field of analysis and detection due to the development of materials science.Among them,photonic crystals and liquid crystals exhibit unique advantages in the field of visual detection because of their excellent optical properties,which provide a new way for the development of simple and portable detection techniques.In this paper,the photonic crystals and liquid crystals were employed as signal converters to develop several sensors for rapid and sensitive detection of penicillin,uranyl ion and organophosphorus pesticide.The details are as follows:In chapter 2:A simple,label-free,and visual three-dimensional photonic crystal-based ?-lactamase biosensor is developed for ?-lactam antibiotic and?-lactamase inhibitor detection in which the penicillinase(a ?-lactamase)is immobilized on the pH-sensitive photonic crystal hydrogel film to form penicillinase photonic crystal hydrogel biosensing film.The hydrolysis of penicillin G(a ?-lactam antibiotic)can be catalyzed by penicillinase to produce penicilloic acid,leading to a pH decrease in the microenvironment of PCCH film,which causes the shrink of pH-sensitive CCH film and triggers a blue-shift of the diffraction wavelength.Upon the addition of ?-lactamase inhibitor,the hydrolysis reaction is suppressed and no clear blue-shift is observed.The concentrations of ?-lactam antibiotic and ?-lactamase inhibitor can be sensitively evaluated by measuring the diffraction shifts.The minimum detectable concentrations for penicillin G and clavulanate potassium(a?-lactamase inhibitor)can reach 1 and 0.1 ?M,respectively.Furthermore,the proposed method is highly renewable and selective,and allows determination of penicillin G in fish pond water samples.In chapter 3:Uranyl ion(UO2 2+)pollution is a serious environmental problem,and developing novel adsorption materials is essential for UO22+ monitoring and removal.Although some progress is achieved,it is still a challenging task to develop an adsorption material with indicating signal for real-time evaluation of the adsorption degree and the UO22+ concentration.This chapter describes a smart three-dimensional photonic crystal hydrogel(PCH)material which not only can be used for real-time monitoring function but also can be utilized for UO22+ removal based on the chelation of UO22+ with ligand groups in PCH material.The working principle is based on the binding of a uranyl ion to multiple ligand groups which results in the shrinkage of PCH material and triggers a blue-shift of diffraction wavelength.Consequently,the adsorption degree and the UO22+ concentration can be sensitively evaluated by measuring the diffraction shift or observing the color change with naked eye.With our PCH material,the lowest detectable concentration for UO22+is 10 nM,and the maximum adsorption capacity at 25 ? is 169.67 mmol kg-1.In addition,this material also holds good selectivity and regeneration feature,and shows desirable performance for UO22+ analysis in real water samples.In chapter 4:A two-dimensional photonic crystal biosensor for the visual detection of penicillin and penicillinase inhibitor is developed by embedding the monolayer polystyrene photonic crystal array in a pH-sensitive hydrogel film.The reaction between penicillinase and penicillin would decrease the microenvironmental pH value of the hydrogel which would result in the shrinking of the hydrogel with increased Debye diffraction ring diameter.The volume change of the hydrogel then leads to the diffraction color change of the two-dimensional photonic crystal.The concentrations of penicillin and penicillinase inhibitor can be sensitively evaluated by measuring the diffraction shifts.This two-dimensional photonic crystal biosensor is superior to the previously reported three-dimensional photonic crystal sensors due to its fast preparation and simple operation.This biosensor exhibits high sensitivity,high selectivity and can be applied for the sensing of penicillin in real samples.In chapter 5:A novel liquid crystal-based acetylcholinesterase(AChE)biosensor has been designed for sensitive detection of organophosphorus pesticide based on the hydrolysis of myristoylcholine chloride(Myr)triggering the liquid crystal(LC)reorientation at the interface between LC and aqueous phase.Myr is a kind of water-soluble amphiphile with long hydrocarbon chain that can induce liquid crystal molecules into homeotropic orientation and provide a uniform dark image.AChE facilitates the hydrolysis of Myr to form choline chloride and tetradecanoic acid(TA),causing a dark-to-bright shift in the optical appearance.Upon the addition of organophosphorus pesticide,the activity of AChE is inhibited,and the Myr still dominates the homeotropic alignment of LC molecules appearing dark images.On the basis of this,a simple,visual and label-free strategy for the detection of organophosphorus pesticide was established.The lowest detectable concentration for organophosphorus pesticide(paraoxon)was 0.1 ng mL-1.