Study On The Biomimetic Capillary Electrophoresis And Its Application

As a kind of highly efficient separation methods,capillary electrophoresis(CE)has potential applications in separation science,especially the separation and detection of the trace components in biological samples as well as the study on the molecular interactions.However,CE is not as universal as high performance liquid chromatography(HPLC)in practical analysis and the breakthrough of encountered bottlenecks of the CE methodology is urgently required.In addition,all kinds of organisms in nature produce a lot of natural structures and materials with excellent performances after long-term evolution.Consequently,various biomimetic design principles inspired by nature are proposed,which plays a vital role in the development of material science and other fields.In recent decades,with the progress of modern analytical technologies,especially the microscopic characterization techniques,the biomimetic design and preparation of functional materials have achieved rapid development.Likewise,the biomimetic principles have great potentials in analytical chemistry.Hence,in this thesis,we aim to introduce the novel biomimetic materials and principles(including molecular crowding,polydopamine coating,and bacteria adhesive coating)into CE for the development of the novel CE methodology.For this purpose,the thesis consists of four parts as follows:(1)Based on the biomimetic principles,the concept of molecular crowding,which is an important feature of the molecular environments in biological cells,was first utilized to enhance the enantioselectivity of hydroxypropyl-beta-cyclodextrin(HP-?-CD)in chiral CE.Additionally,in order to further explore the mechanism underlying the improved enantioselectivity,both fluorescence spectroscopy and affinity CE(ACE)technique were used to evaluate the association constants between the model analytes(salbutamol enantiomers)and cyclodextrins with and without crowding-inducing agents.The experimental parameters of the enantioseparation of salbutamol enantiomers,including the variety and concentration of crowding-inducing agents,the concentration and pH of running buffer as well as the concentration of cyclodextrins,were first investigated and optimized.It was found that dextran and dextrin as the crowding-inducing agents could significantly enhance the enantioselectivity of HP-?-CD to salbutamol enantiomers,verifying that molecular crowding could be used to enhance the enantioselectivity of cyclodextrin in chiral CE.Furthermore,the association constants between salbutamol enantiomers and cyclodextrins were determined through the fluorescence spectroscopy and ACE technique.The results revealed that the presence of crowding-inducing agents could promote the association of enantiomers with cyclodextrins and magnify the interacting differences of two enantiomers with cyclodextrins,which leaded to the enhanced enantioselectivity of HP-?-CD.Considering that this biomimetic principle has strong extensibility,molecular crowding could be a potential and effective strategy to improve the enantioselectivity of chiral CE.(2)Based on the co-deposition of mussel-inspired polydopamine(PDA)and branched polyethyleneimine(PEI)on the capillary inner surface as the hybrid functional coating,a facile and versatile approach was first developed for achieving diverse and controllable electroosmotic flow(EOF)in CE.It was found that PDA and PEI can be self-polymerized onto the inner surface of columns in situ to form the PDA/PEI co-deposited capillaries.The co-deposition strategy can render the hybrid coatings with various surface charge properties.Accordingly,various magnitude and direction of EOF could be easily controlled by tailoring the preparation parameters,including the mass ratio of PDA/PEI and the molecular weight of PEI(including PEI-600,PEI-1800,PEI-10000 and PEI-70000).After reinforced by the post-incubation of FeCl3,the stability and repeatability of the PDA/PEI co-deposited capillaries were significantly improved,which could satisfy the requirements for the CE separation of practical samples.By using the PDA/PEI co-deposited columns with controllable EOF,the high separation efficiency and controllable elution order of aromatic acids and aniline compounds were successfully achieved,which verified the good stability and practicability of the proposed biomimetic columns.(3)Based on the above study on the biomimetic PDA coating,a novel open-tubular capillary electrochromatography(OT-CEC)column with a high phase ratio coated with polydopamine/gold nanoparticle/thiols(PDA/Au NPs/thiol)was firstly developed.This method utilized the technique of layer-by-layer(LBL)self-assembly and multiple physicochemical properties of PDA(such as its strong adhesive property,porosity property,metal ion chelating and reducing properties,and latent reactivity toward amine or thiol groups).The morphology and surface properties of the PDA/Au NPs/thiol coatings were characterized by scanning electron microscopy(SEM),energy dispersive spectrometry(EDS)and atomic force microscopy(AFM).This PDA/Au NPs/thiol coated columns not only made full use of the application potential of PDA surface chemistry but also combined the advantages of LBL self-assembly and nanoparticles.Accordingly,the phase ratio and column capacity of PDA/Au NPs/thiol coated columns could be improved significantly.The results of CE experiments showed that the separation efficiency of PDA/Au NPs/thiol coated columns was gradually enhanced with increasing the number of self-assembly PDA/Au NPs/thiol layers.Under optimum conditions,the effective baseline separation of alkylbenzenes could be easily achieved by PDA/Au NPs/thiol coated column.Moreover,this columns showed good stability and repeatability.(4)Taking advantages of the interfacial adhesion tendency and stereoselective properties of bacteria,a novel biomimetic OT-CEC column by introducing bacteria as chiral stationary phases was firstly constructed for chiral separation of ofloxacin enantiomers and some other fluoroquinolone antibiotics.As a proof-of-concept demonstration,non-pathogenic Escherichia coli(E.coli)strain DH5? was used as the model bacteria to fabricate bacteria coated columns.After pre-modification of the inner surface of columns with positively charged PEI,the bacteria were attached on the capillary through electrostatic interaction and their interfacial adhesion tendency.The morphology and thickness of the bacteria adhesive coatings in the capillary were characterized by FESEM and AFM.The results showed that the coating time and concentration of E.coli suspension could affect the amounts of E.coli adhered on the capillary inner-surface.Under optimum conditions,the column inner surface became rough with lots of E.coli cells.By using the fabricated E.coli coated columns,the effective baseline separation of ofloxacin and simultaneous separation of six fluoroquinolones could be achieved.Besides the enantioseparation efficiency,bacterial stationary phases may be used to evaluate the interaction between bacteria and chiral antimicrobial compounds under different conditions as well as reveal the possible difference in antibacterial activities of potentially chiral antimicrobial compounds simultaneously.