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 PEImodified 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 highperformance analysis medium for biogenic compounds. r

Studies of electroosmotic flow and the effects of protein adsorption in plasma‐polymerized microchannel surfaces

“…Despite the simplicity of the physical adsorption methods, it is well known that this type of coating has limited stability with coating detachment only after 420 EOF runs [49]. We observed the coatings of these physically adsorbed polymers deteriorated after the second to third day of runs ($30 runs each day).…”

“…It is also not practical for applications requiring mass spectrometry, as analysis may be disrupted and samples contaminated by the polymer released from the microchannel walls. In previous studies, covalent immobilization techniques have been shown to improve the coating stability [49].…”

Fabrication, modification, and application of poly(methyl methacrylate) microfluidic chips

“…The EOFs in the modified channels were nearly an order of magnitude smaller than native PMMA. Kitagawa et al [54] have developed a one-step covalent immobilization of poly(ethyleneimine) (PEI) onto PMMA substrates to achieve an efficient separation of basic proteins in microchip electrophoresis. The PEI-treated PMMA chip showed the anodic EOF and apparently reduced the surface adsorption of cationic proteins.…”

Poly(ethylene glycol)‐coated microfluidic devices for chip electrophoresis

“…In this context, several approaches for coating glass and in part also polymer chips with materials based on hydrophilic polymers such as poly(acryl amide) [19], PVA [20][21][22], poly(ethylene imine) [23] and hydroxypropyl methylcellulose (HPMC) [24] have been reported.…”