One-step immobilization of cationic polymer onto a poly(methyl methacrylate) microchip for high-performance electrophoretic analysis of proteins

Abstract

One-step covalent immobilization of poly(ethyleneimine) (PEI) onto poly(methyl methacrylate) (PMMA) substrates was investigated to achieve an efficient separation of basic proteins in microchip electrophoresis (MCE). The PEI-treated PMMA chip showed the anodic electroosmotic flow and its rate was almost kept stable during 32 days with over 50 runs. This longer stability of the prepared microchip indicated that the loss of PEI was successfully suppressed by the immobilization through the covalent bond. Furthermore, the PEI modification onto the PMMA chip could apparently reduce the surface adsorption of cationic proteins. In the MCE analysis on the PEI-modified microchip, two proteins were successfully separated within 30 s only utilizing a separation length of 5 mm. While the migration time of the protein gradually increased during only four consecutive runs on an untreated PMMA chip, reproducible analyses were attained by using the PEI immobilized microchip. These results demonstrated that Coulombic repulsion force generated between cationic PEI and basic proteins could avoid the irreversible adsorption of the analytes onto the PMMA surface, which provided a high-performance analysis medium for biogenic compounds.