Microchannel wall coatings for protein separations by capillary and chip electrophoresis (original) (raw)
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Tunable thick polymer coatings for on-chip electrophoretic protein and peptide separation
Journal of Chromatography A, 2012
We report a variety of procedures for fabricating confinement-induced polymer coatings, used to eliminate non-specific protein adsorption and to control electroosmotic flow for microchip capillary electrophoresis. The coating strategy generates relatively thick polymer wall coatings (100-700 nm) and can easily be tuned by adjusting the monomer concentration. 2-hydroxyethyl methacrylate (HEMA) polymer coating, photopatterned in microfluidic channels, effectively reduced protein non-specific adsorption and rendered high efficiency (N/m = ∼3 × 10 6 ) for protein separation. The coating strategy provides rapid and effective means to create robust wall coatings, with the ability to photograft various surface chemistries onto the coating. [2-(methacryloyloxy) ethyl] trimethylammonium chloride grafted HEMA coated channels showed high durability and reproducibility for generating EOF (RSD = 2.6%, n = 64) over a period of 15 days. Sulfobetaine methacrylate grafted HEMA coated channels allowed separation of BSA digest, 15 peaks resolved in 25 s, with an average N/m of 4 × 10 5 .
…, 2002
Physically adsorbed (dynamic) polymeric wall coatings for microchannel electrophoresis have distinct advantages over covalently linked coatings. In order to determine the critical factors that control the formation of dynamic wall coatings, we have created a set of model polymers and copolymers based on N,N-dimethylacrylamide (DMA) and N,N-diethylacrylamide (DEA), and studied their adsorption behavior from aqueous solution as well as their performance for microchannel electrophoresis of DNA. This study is revealing in terms of the polymer properties that help create an "ideal" wall coating.
Journal of Chromatography A, 2003
In this work, a new physically adsorbed coating for capillary electrophoresis (CE) is presented. The coating is based on a N,N-dimethylacrylamide-ethylpyrrolidine methacrylate (DMA-EPyM) copolymer synthesized in our laboratory. The capillary coating is simple and easy to obtain as only requires flushing the capillary with a polymer aqueous solution for 2 min. It is shown that by using these coated capillaries the electrostatic adsorption of a group of basic proteins onto the capillary wall is significantly reduced allowing their analysis by CE. Moreover, the DMA-EPyM coating provides reproducible separations of the basic proteins with RSD values for migration times lower than 0.75% for the same day (n55) and lower than 3.90% for three different days (n515). Interestingly, the electrical charge of the coated capillary wall can be modulated by varying the pH of the running buffer which makes possible the analysis of basic and acidic proteins in the same capillary. The usefulness of this coating is further demonstrated via the reproducible separation of whey (i.e. acidic) proteins from raw milk. The coating protocol should be compatible with both CE in microchips and CE-MS of different types of proteins.
Electrophoresis, 2003
We present the polymer poly-N-hydroxyethylacrylamide (PHEA) (trade name, polyDuramide ) as a novel, hydrophilic, adsorbed capillary coating for electrophoretic protein analysis. Preparation of the PHEA coating requires a simple and fast (30 min) protocol that can be easily automated in capillary electrophoresis instruments. Over the pH range of 3-8.4, the PHEA coating is shown to reduce electroosmotic flow (EOF) by about 2 orders of magnitude compared to the bare silica capillary. In a systematic comparative study, the adsorbed PHEA coating exhibited minimal interactions with both acidic and basic proteins, providing efficient protein separations with excellent reproducibility on par with a covalent polyacrylamide coating. Hydrophobic interactions between proteins and a relatively hydrophobic poly-N,N-dimethylacrylamide (PDMA) adsorbed coating, on the other hand, adversely affected separation reproducibility and efficiency. Under both acidic and basic buffer conditions, the adsorbed PHEA coating produced an EOF suppression performance comparable to that of covalent polyacrylamide coating and superior to that of adsorbed PDMA coating. The protein separation performance in PHEA-coated capillaries was retained for 275 consecutive protein separation runs at pH 8.4, and for more than 800 runs at pH 4.4. The unique and novel combination of hydrophilicity and adsorptive coating ability of PHEA makes it a suitable wall coating for automated microscale analysis of proteins by capillary array systems.
Journal of Chromatography A, 2008
In this work, a new copolymer synthesized in our laboratory is used as physically adsorbed coating for capillary electrophoresis (CE). The copolymer is composed of ethylpyrrolidine methacrylate (EPyM) and methylmethacrylate (MMA). The capillary coating is easily obtained by simply flushing into the tubing an EPyM/MMA solution. It is demonstrated that the composition of the EPyM/MMA copolymer together with the selection of the background electrolyte (BGE) and pH allow tailoring the direction and magnitude of the electroosmotic flow (EOF) in CE. It is also shown that the EOF obtained for the EPyM/MMA-coated capillaries was reproducible in all cases independently on pH or polymer composition. Thus, RSD values lower than 1.9% (n = 5) for the same capillary and day were obtained for the migration time, while the repeatability interdays (n = 5) was observed to provide RSD values lower than 0.5%. The stability of the coating procedure was also tested between capillaries (n = 3) obtaining RSD values lower than 0.6%. It is demonstrated with several examples that the use of EPyM/MMA coatings in CE can drastically reduce the analysis time and/or to improve the resolution of the separations. It is shown that EPyM/MMA-coated capillaries allow the separation of basic proteins by reducing their adsorption onto the capillary wall. Also, EPyM/MMA-coated capillaries provide a faster separation of samples containing simultaneously positive and negative analytes. Moreover, it is demonstrated that the use of EPyM/MMA-coated capillaries can incorporate an additional chromatographic-like interaction with nucleosides that highly improves the separation of this group of solutes.
Electrophoresis, 2004
We describe the use of a tri(ethylene glycol)-terminated alkyltrichlorosilane to create a very thin, protein-resistant "self-assembled monolayer" coating on the inner surface of a fused-silica capillary. The same compound has been demonstrated previously on flat silica substrates to resist adsorption of many proteins. As a covalently bound capillary coating, it displays good resistance to the adsorption of cationic proteins, providing clean separations of a mixture of lysozyme, cytochrome c, ribonuclease A, and myoglobin for more than 200 consecutive runs. Electroosmotic flow (EOF) was measured as a function of pH; the coated capillary retains significant cathodal EOF, with roughly 50% of the EOF of an uncoated capillary at neutral pH, making this coating promising for applications requiring some EOF. The EOF was reasonably stable, with a 2.9% relative standard deviation during a 24 h period consisting of 72 consecutive separations of cationic proteins. Efficiencies for cationic protein separations were moderate, in the range of 190 000-290 000 theoretical plates per meter. The coating procedure was simple, requiring only a standard cleaning procedure followed by a rinse with the silane reagent at room temperature. No buffer additives are required to maintain the stability of the coating, making it flexible for a range of applications, potentially including capillary electrophoresis-mass spectrometry (CE-MS).
2003
This paper presents systematic investigation on the surface properties of electroosmotic flows (EOF) inside microchannels for quartz, glass and PDMS based materials. Two novel methods to modify the surface properties of glass-based microchannels for capillary electrophoresis (CE) are developed. Instead of using complicated and time-consuming chemical silanization procedures for surface modification of the CE channels, two simple and reliable methods utilizing organic-based spin-on-glass (SOG) and water-soluble acrylic resin are reported, providing a fast and batch process for surface modification of glass-based CE channels. The proposed methods are evaluated using separation of @X-l 74 DNA makers. Experimental data sholv that separation efficiency is greatly improved. In addition, long-term stability of the SOG coating is also verified in this study.
Journal of Separation Science, 2011
A brush-like copolymer consisting of poly(ethylene glycol) methyl ether methacrylate and N,N-dimethylacrylamide (PEGMA-DMA) was synthesized and used as a novel static physically adsorbed coating for protein separation by capillary electrophoresis for the first time, in order to stabilize electroosmotic flow (EOF) and suppress adsorption of proteins onto the capillary wall. Very stable and low EOF was obtained in PEGMA-DMA-coated capillary at pH 2.2-7.8. The effects of molar ratio of PEGMA to DMA, copolymer molecular mass, and pH on the separation of basic proteins were discussed. A comparative study of bare capillary with PEGMA-DMA-coated capillary for protein separation was also performed. The basic proteins could be well separated in PEGMA-DMA-coated capillary over the investigated pH range of 2.8-6.8 with good repeatability and high separation efficiency because the copolymer coating combines good protein-resistant property of PEG side chains with excellent coating ability of PDMA-contained backbone. Finally, the coating was successfully applied to the fast separation of other protein samples, such as protein mixture and egg white, which reveals that it is a potential coating for further proteomics analysis.