title: Facile construction of sulfanyl-terminated poly(ethylene glycol)-brushed layer on a gold surface for protein immobilization by the combined use of sulfanyl-ended telechelic and semitelechelic poly(ethylene glycol)s.
abstract: A sulfanyl-terminated poly(ethylene glycol) (PEG)-brushed layer was constructed on a gold sensor platform by consecutive treatment with a sulfanyl-ended semitelechelic PEG (2 kDa, hereafter "MeO-PEG-SH (2k)") and a sulfanyl-ended telechelic PEG (5 kDa, hereafter "SH-PEG-SH (5k)"). Our strategy of constructing the sulfanyl-terminated PEG-brushed gold surface is based on mixed-PEG-brush formation from the longer SH-PEG-SH (5k) and the shorter MeO-PEG-SH (2k), where the preimmobilized shorter MeO-PEG-SH (2k) prevents loop formation in the longer SH-PEG-SH (5k) on the surface and the free sulfanyl group at one end of the longer SH-PEG-SH is exposed to the mixed-PEG tethered-chain surface. From the experimental results obtained from surface plasmon resonance analysis, it became apparent that the immobilization density and the orientation of the longer SH-PEG-SH (5k) on the gold surface could be controlled by the amount of preimmobilized shorter MeO-PEG-SH (2k). Under the optimized conditions of MeO-PEG-SH (2k) premodification, the constructed MeO-PEG-SH (2k)/SH-PEG-SH (5k) mixed layer conjugated efficiently with the maleimide-installed proteins and the antibody Fab' fragments, accompanied by an appreciable nonfouling characteristic against bovine serum albumin as strong as that of the MeO-PEG-SH (5k)/MeO-PEG-SH (2k) mixed surface, which was reported in our previous work; it also showed a superior nonfouling characteristic compared to the commercially available carboxymethylated dextran surface (Uchida, K.; et al. Biointerphase 2007, 2 (4), 126-130). Furthermore, from the experimental results of the X-ray photoelectron spectrometry analysis, the presence of both Au-bound and Au-unbound sulfur species was confirmed on the SH-PEG-SH (5k)/MeO-PEG-SH (2k)-modified gold surface. These results clearly indicate that the preimmobilized shorter MeO-PEG-SH (2k) not only increased the nonfouling characteristic of the PEG tethered-chain surface but also prevented loop formation in the longer SH-PEG-SH (5k) on the gold surface. Since the protein-installed SH-PEG-SH (5k)/MeO-PEG-SH (2k)-modified surface showed a strongly nonfouling characteristic and recognized the target molecules selectively, this new mixed-brush-formation technique using longer sulfanyl-ended telechelic PEGs and shorter semitelechelic PEGs is a simple yet effective method of constructing a strongly nonfouling terminal-functionalized gold surface for protein immobilization.
authors.affiliation: Graduate School of Pure and Applied Science, University of Tsukuba, 1-1-1 Ten-noudai, Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Keitaro
authors.initials: K
authors.lastname: Yoshimoto
authors.forename: Takumi
authors.initials: T
authors.lastname: Hirase
authors.forename: Seiko
authors.initials: S
authors.lastname: Nemoto
authors.forename: Tamao
authors.initials: T
authors.lastname: Hatta
authors.forename: Yukio
authors.initials: Y
authors.lastname: Nagasaki
mesh_terms: D000327:Adsorption; D002627:Chemistry, Physical / Q000379:methods; D006046:Gold / Q000737:chemistry*; D008301:Maleimides / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D020349:Surface Plasmon Resonance; D013499:Surface Properties; D013997:Time Factors; D014965:X-Rays
chemical_list: D008301:Maleimides; D011506:Proteins; C043592:maleimide; D012710:Serum Albumin, Bovine; D011092:Polyethylene Glycols; D006046:Gold