PMOXA/PAA Brushes Toward On-line Preconcentration Of Bovine Serum Albumin In Capillary Electrophoresis

The separation and analysis of proteins have always been challenging,and capillary electrophoresis(CE)has broad application prospects in the field of protein separation and analysis because of its advantages such as less sample amount,high separation efficiency,and high separation speed.In commercial CE instrument,ultraviolet detector(CE-UV)is the most commonly used one,however,it often suffers from the poor detection sensitivity owing to its short optical path length and small injection volume.In order to conquer these shortcomings,some approaches have been developed,and the most effective method at present is on-line preconcentration.Common methods of on-line preconcentration include capillary isotachophoresis(CITP),stacking,sweeping,and so on.Stacking is most commonly used during the analysis of proteins by using CE,for example,conventional stacking,large volume sample stacking(LASS),field-amplified sample stacking(FASS),and so on.Although the stacking method can effectively improve the detection sensitivity of the CE-UV,it is impossible to eff-ectively detect very dilute solutions because the injection volume is limited by the capillary volume.On-line sample preconcentration using the coated capillary has been used to overcome the drawbacks mentioned above.In this work,the capillaries coated with poly(2-methyl-2-oxazoline)(PMOXA)and responsive poly(acrylic acid)(PAA)mixed coating(PMOXA/PAA)were prepared and used to on-line preconcentrate the bovine serum albumin(BSA)in CE,and the sensitivity of this method was analyzed.Firstly,amine-terminated PMOXA(PMOXA-NH2)and thiol-terminated PAA(PAA-SH)were synthesized by cationic ring-opening polymerization(CROP)and reversible addition fragmentation chain transfer(RAFT)polymerization,respectively.Then,the polymer coated capillaries based on PMOXA and PAA were prepared by sequentially grafting of PMOXA-NH2 and PAA-SH onto fused-silica capillary inner surface through poly(dopamine)(PDA)as an anchor.The obtained PMOXA/PAA mixed brushes coated capillary or capillary raw material were characterized in terms of the thickness,surface chemical composition by using scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS).The switchable protein adsorption/desorption performance of the mixed polymer coated capillary was investigated by using fluorescence microscope under different pH and ionic strength(I).The results showed that a large amounts of bovine serum albumin(BSA)could be adsorbed on PMOXA/PAA mixed brushes coated capillary at pH 5.0(I=10-5 M),and then the adsorbed BSA could be released at pH 9.0(1=10-1M).This mixed polymer coated capillary was then used to preconcentrate BSA on line in CE.Under the optimal conditions,a sensitivity enhancement factor(SEF)of BSA exceeds 5000,which greatly improves the detection sensitivity of CE-UV.