| Capillary electrophoresis(CE),as a powerful analytical technique,offers rapid separation time,high separation efficiency,therefore it is suitable for the separation of proteins.However,commercial CE usually equipped with UV-detector bears low concentration sensitivity due to a consequence of the limited sample volume and short path length for absorbance-related detection.Therefore,it was a challenge to determine trace protein with commercial CE.Some methods have been established to solve this problem:(i)alternative capillary geometry to increase the optical path length,(ii)concentration of the sample solution before CE performance,and(iii)on-line sample preconcentration.The first approach frequently suffers from limited improvement because of limited design.The second approach is usually called off-line sample preconcentration.The sample must be concentrated before detection by using filtration,centrifugation,distillation,and so forth.However,this approach has to bear massive organic solvent consumption,operations,environmental pollution,etc.The third approach includes sample stacking,sweeping,transient isotachophoresis(t-ITP),and dynamic pH junction,which is particularly worthy of investigation since it can improve the detection sensitivity of analytes,however,it has limited application prospects.In this work,mixed brushes PDA/PMOXA/PAA coated capillary based on poly(2-methyl-2-oxazoline)(PMOXA)and poly(acrylic acid)(PAA)with switchable absorption/desorption of protein was used to on-line preconcentration lysozyme on CE.Firstly,amine-terminated PMOXA(PMOXA-NH2)and thiol-terminated PAA(PAA-SH)were synthesized successfully.Then,mixed brushes based on PMOXA and PAA coated capillary were prepared by poly(dopamine)(PDA)as an anchor.This study of electroosmotic flow(EOF)and fluorescence microscope showed that the inner surface charge of PMOXA/PAA mixed brush coated capillary displayed the switchable behavior toward the change of pH value and ionic strength(I),and PMOXA/PAA mixed brushes coated capillary could adsorb high amounts of lysozyme at pH 7.0(I=10-5 M),and the most of adsorbed lysozyme could then be desorbed at pH 3.0(I= 10-1 M).Subsequently,this coated capillary with switchable protein adsorption/desorption ability was applied for on-line extraction and preconcentration of lysozyme during capillary electrophoresis performance.Under the process of on-line preconcentration,the detection signal(peak area)of lysozyme obtained in PDA/PMOXA/PAA coated capillary was 26 times that obtained in bare capillary under normal CE while the contour chain length of PAA was 1.56 times that of PMOXA.Moreover,the value of low detection limit(LOD)of lysozyme using above coated capillary under on-line preconcentration method reached to 4.5×10-9 mg/mL,and 1×105-fold sensitivity enhancement was realized for lysozyme as compared with the bare capillary under normal CE. |
