Abstract
Patterned poly(oligo ethylene glycol) methyl ether methacrylate (POEGMEMA) brush structures may be formed by using a combination of atom-transfer radical polymerization (ATRP) and UV photopatterning. UV photolysis is used to selectively dechlorinate films of 4-(chloromethyl)phenyltrichlorosilane (CMPTS) adsorbed on silica surfaces, by exposure either through a mask or using a two-beam interferometer. Exposure through a mask yields patterns of carboxylic acid-terminated adsorbates. POEGMEMA may be grown from intact Cl initiators that were masked during exposure. Corrals, traps, and other structures formed in this way enable the patterning of proteins, vesicles, and, following vesicle rupture, supported lipid bilayers (SLBs). Bilayers adsorbed on the carboxylic acid-terminated surfaces formed by C–Cl bond photolysis in CMPTS exhibit high mobility. SLBs do not form on POEGMEMA. Using traps consisting of carboxylic acid-functionalized regions enclosed by POEGMEMA structures, electrophoresis may be observed in lipid bilayers containing a small amount of a fluorescent dye. Segregation of dye at one end of the traps was measured by fluorescence microscopy. The increase in the fluorescence intensity was found to be proportional to the trap length, while the time taken to reach the maximum value was inversely proportional to the trap length, indicating uniform, rapid diffusion in all of the traps. Nanostructured materials were formed using interferometric lithography. Channels were defined by exposure of CMPTS films to maxima in the interferogram, and POEGMEMA walls were formed by ATRP. As for the micrometer-scale patterns, bilayers did not form on the POEGMEMA structures, and high lipid mobilities were measured in the polymer-free regions of the channels.
Highlights
Lipid membranes play a central role in biology: they form the cellular membrane, separating the interior of the cell from its external environment, and they provide the means by which the interior of the cell is compartmentalized into discrete organelles.[1]
A detailed investigation of the mechanism of dehalogenation of CMPTS films was reported previously by Sun et al.,[25] who reported a substantial decline in contact angle following exposure of films to UV light
Photolysis of C−Cl bonds in CMPTS films leads to the formation of carboxylic acid-functionalized surfaces
Summary
Lipid membranes play a central role in biology: they form the cellular membrane, separating the interior of the cell from its external environment, and they provide the means by which the interior of the cell is compartmentalized into discrete organelles.[1]. The high magnification image (Figure 5b) displays a clear contrast difference between the triangular lipid-free regions (dark) and the surrounding SLB (bright) These data confirm that POEGMEMA brushes resist the formation of an SLB, and are a highly effective and convenient means to organize SLBs into patterns. It involves fitting the recovery curve to yield a mathematical relationship between fluorescence intensity and time after bleaching, from which the diffusion coefficient and mobile fraction may be calculated.[38] Analysis of the data in Figure 5e using this method indicated that the mobile fraction was 98% and the diffusion coefficient was 0.84 μm[2] s−1, comparable to values obtained for SLBs formed from the same lipids on glass These data demonstrate that the carboxylic acid-functionalized surface produced by photochemical modification of the CMPTS film is an excellent substrate for SLB formation. The data presented here demonstrate that fabrication of polymer brush structures by IL is a convenient and effective way of producing structures that facilitate uniform confinement of SLBs over macroscopic areas
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