Fuhu Cao

A novel PEG coating immobilized onto capillary through polydopamine coating for separation of proteins in CE

The antifouling PEG‐immobilized capillary was introduced for the protein separation in CE through mussel adhesive protein inspired polydopamine coating for the first time. The polydopamine, formed by spontaneous oxidative polymerization of dopamine at alkaline in the inner surface of capillary, was exploited to immobilize amine‐functionalized PEG onto the capillary surface. During the process, polydopamine‐graft‐PEG copolymer was formed via Michael addition or Schiff base reactions. The polymer coating was observed using X‐ray photoelectron spectroscopy and SEM. And both of them indicated the formation of the polymer coating. A comparative study of EOF showed that the novel coating could provide effective suppression of EOF and minimized adsorption of proteins. As a consequence, fast and efficient separations of three proteins such as lysozyme, cytochrome c, and ribounclease A were obtained within a broad pH range. Furthermore, the long‐term stability of polydopamine‐graft‐PEG coating in consecutive protein separation runs and the high separation efficiency proved that this novel coating was capable of minimizing protein adsorption during the capillary separation. The successful capillary performance also was demonstrated in the separation of protein mixture and milk powder samples at acidic pH.

Hydroxyethylcellulose-graft-poly(2-(dimethylamino)ethyl methacrylate) as physically adsorbed coating for protein separation by CE.

In this work, a novel graft copolymer, hydroxyethylcellulose‐graft‐poly(2‐(dimethylamino)ethyl methacrylate) (HEC‐g‐PDMAEMA), used as physical coatings of the bare fused‐silica capillaries, was synthesized by using ceric ammonium nitrate initiator in aqueous nitric acid solution. EOF measurement results showed that the synthesized HEC‐g‐PDMAEMA graft copolymer‐coated capillary in this paper could suppress EOF effectively compared to the bare fused‐silica capillary, and efficient separations of basic proteins were also achieved. The electrical charge of the coated capillary wall could be modulated by varying not only the pH of the running buffer, but also the grafting ratio of poly(2‐(dimethylamino)ethyl methacrylate) grafts, which makes possible the analysis of basic and acidic proteins in the same capillary. The effects of poly(2‐(dimethylamino)ethyl methacrylate) grafting ratio in HEC‐g‐PDMAEMA and buffer pH on the separation of basic proteins for capillary electrophoresis were investigated in detail. Furthermore, egg white proteins and milk powder samples were separated by the HEC‐g‐PDMAEMA‐coated capillary. The results demonstrated that the HEC‐g‐PDMAEMA copolymer coatings have great potential in the field of diagnosis and proteomics.

Brush-like copolymer as a physically adsorbed coating for protein separation by capillary electrophoresis

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.

A high efficiency approach for a titanium surface antifouling modification: PEG-o-quinone linked with titanium via electron transfer process

We explored a novel approach for the modification of titanium surfaces to improve the biocompatibility and antifouling properties using PEG-catechol. As is well-known, PEG-catechol can easily self-assemble onto titanium surfaces. However, the higher grafting density by this approach is hard to obtain. In our paper, o-quinone (the oxide of catechol) as the adhesive segment was used for the first time to graft PEG brushes onto titanium surfaces using the electroreduction process. Variable angle spectroscopic ellipsometer showed that the ultrahigh-density PEG brush adlayer could be grafted to the titanium surface when the o-quinone segment performs electrochemical reduction on the titanium. We called the adlayers that grafted onto the titanium surfaces by this kind of approach, electro-assembly monolayers (e-AMs). This distinguishes it from the PEG-catechol self-assembly monolayers (SAMs). The XPS, AFM and WCA techniques were also used to characterize the coating grafted onto the titanium surfaces via the two different ways. A clear result is that the grafted density of e-AMs can be higher than that of SAMs, and the grafted density of the e-AMs can be easily modulated. In addition, the long-term stability of e-AMs against full blood serum, FITC marked BSA and platelet adsorption was better than that of the SAMs.

Application of the copolymers containing sulfobetaine methacrylate in protein separation by capillary electrophoresis

This study describes the formation of highly efficient antiprotein adsorption random copolymer coating of poly(N,N-dimethylacrylamide-co-sulfobetaine methacrylate) (poly(DMA-co-SBMA)) on the fused-silica capillary inner wall. Firstly, the poly(DMA-co-SBMA)s with different feed ratio (SBMA/DMA) were synthesized via the reversible addition fragmentation chain transfer polymerization. And then, X-ray photoelectron spectroscopy (XPS) and water contact angle (CA) were used to investigate the composition and hydrophilicity of poly(DMA-co-SBMA) coating formed on the glass slide surfaces. CA measurements revealed that the poly(DMA-co-SBMA) coating became more hydrophilic with the increment of feed ratio (SBMA/DMA), and at the same time, the XPS results showed that the coating ability was also increased with the increment of feed ratio. Followed, the copolymer was applied to coat the fused-silica capillary inner wall, and the coated capillary was used to separate the mixture of proteins (lysozyme, cytochrome c, ribonuclease A, and α-chymotrypsinogen A) in a pH range from 3.0 to 5.0. Under the optimum conditions, an excellent separation of basic proteins with peak efficiencies ranging from 551,000 to 1509,000 N/m had been accomplished within 10 min. Furthermore, the effect of coating composition on protein separation was also investigated through the comparison of separation efficiency achieved by using bare, PSBMA- and poly(DMA-co-SBMA)-coated capillary, respectively.

A novel cationic triblock copolymer as noncovalent coating for the separation of proteins by CE.

A novel noncovalent adsorbed coating for CE has been prepared and explored. This coating was based on quaternized poly(2‐(dimethylamino)ethyl methacrylate)‐block‐poly(ethylene oxide)‐block‐poly(2‐(dimethylamino)ethyl methacrylate) (QDED) triblock copolymer which was synthesized by atomic transfer radical polymerization (ATRP) in our laboratory. The polycationic polymer and the negatively charged fused‐silica surface attracted each other through electrostatic interactions and hydrogen bonds. It was demonstrated that the coated capillaries provided an electroosmotic flow with reverse direction, and the magnitude of the electroosmotic flow can be modulated by varying the molecular mass of poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) block and pH value of the buffer. The effects of the molecular mass of PDMAEMA block in QDED triblock copolymer and pH value of the buffer on the separation of basic proteins were investigated in detail. The triblock copolymer coatings showed higher separation efficiency, better migration time repeatability and would apply to wider range of pH than bare fused‐silica capillary when used in separating proteins. Proteins from egg white were also separated through this QDED triblock copolymer‐coated capillary. These results demonstrated that the QDED triblock copolymer coatings are suitable for analyzing biosamples.

Synthesis of double-hydrophilic double-grafted copolymers PMA-g-PEG/PDMA and their protein-resistant properties

A series of double-hydrophilic double-grafted PMA-g-PEG/PDMA copolymers, which contained poly(methacrylate) (PMA) as backbone, poly(ethylene glycol) (PEG) and poly(N,N-dimethylacrylamide) (PDMA) as side chains synthesized successfully by using reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP), were used as physical coatings for the evaluation of protein-resistant properties by capillary electrophoresis (CE). Electroosmotic flow (EOF) measurement results showed that the PMA-g-PEG/PDMA copolymer coated capillaries could suppress electroosmotic mobility in a wide pH range (pH = 2.8–9.8) and EOF mobility decreased with the increase of copolymer molecular mass and PDMA content. At the same time, protein recovery, theoretical plate number of separation and repeatability of migration time demonstrated that antifouling efficiency was improved with the increase of molecular mass and PEG content.

Graft copolymer composed of cationic backbone and bottle brush‐like side chains as a physically adsorbed coating for protein separation by capillary electrophoresis

To stabilize electroosmotic flow (EOF) and suppress protein adsorption onto the silica capillary inner wall, a cationic hydroxyethylcellulose-graft-poly (poly(ethylene glycol) methyl ether methacrylate) (cat-HEC-g-PPEGMA) graft copolymer composed of cationic backbone and bottle brush-like side chains was synthesized for the first time and used as a novel physically adsorbed coating for protein separation by capillary electrophoresis. Reversed (anodal) and very stable EOF was obtained in cat-HEC-g-PPEGMA-coated capillary at pH 2.2-7.8. The effects of degree of cationization, PEGMA grafting ratio, PEGMA molecular mass, and buffer pH on the separation of basic proteins were investigated. A systematic comparative study of protein separation in bare and HEC-coated capillaries and in cat-HEC-g-PPEGMA-coated capillary was also performed. The basic proteins can be well separated in cat-HEC-g-PPEGMA-coated capillary over the pH range of 2.8-6.8 with good repeatability and high separation efficiency, because the coating combines good protein-resistant property of bottle brush-like PPEGMA side chains with excellent coating ability of cat-HEC backbone. Besides its success in separation of basic proteins, the cat-HEC-g-PPEGMA coating was also superior in the fast separation of other protein samples, such as protein mixture, egg white, and saliva, which indicates that it is a promising coating for further proteomics analysis.