Polymer-modified surfaces

One approach utilizes the polymer-modified surface as a preconcentrating surface in which the analyte or some reaction product is collected and concentrated by reactive groups attached to the electrode. The preconcentrated analyte is then measured electro-chemically. Ideally, the collection process will be selective for the analyte species of interest. If not, the analyte must be elec-troanalytically discriminated from other collected species. The capacity of the polymer film on the modified electrode should be sufficient to prevent saturation by the analyte, and the electrochemical response during measurement should provide good sensitivity to the collected analyte [9]. 

In 1996, Gauglitz and coworkers coated surfaces with various amino-and carboxy-substituted polymers [198], The polymers tested were branched poly-(ethyleneimine), a,co-amino-functionalized PEG, chitosan, poly(acrylamide-co-acrylic acid) and an amino-modified dextran. The amino-substituted polymers were immobilized on glass by first immobilizing an aminosilane, followed by succinic anhydride/A-hydroxysuccinimide linker chemistry. Poly(acrylamide-co-acrylic acid) was directly coupled to an aminosilanized surface. When probed with 1 mg mL 1 ovalbumin solution, nonspecific adsorption was lowest for the dextran derivative. Notably, nonspecific adsorption increased in most cases when a hydrophobic hapten (atrazine) was coupled to the polymer-modified surface. 

Surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides dramatically reduce protein adsorption [26-28], The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavorable. Consequently, these polymer modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent nondenaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays, and biosensors. 

Fang, F., Szleifer, I. Controlled release of proteins from polymer-modified surfaces. Proc. Natl. Acad. Sci. 2006,103, 5769-74. 

Immobilization of the DNA onto polymer modified surface can be realized by electrodeposition, which is a well-known method [25]. Application of positive potential in this process can enhance the DNA immobilization as well as the stability of immobilized DNA. Diaz-Gonzalez etal. [26] studied the DNA immobilization onto a polylysine-modified electrode at different potentials. The best results were obtained using a potential of-1-0.5 V for 120 seconds. DNA was also electrodeposited onto a poly(p-aminobenzensulfonic acid)-modified glassy carbon electrode (GCE) at -fl.5 V for 30 minutes [27] or onto overoxidized Ppy-modified electrode at -1-1.8 V for 30 minutes [28]. 

Fig. 11.10 The polymer-modified surfaces can also be used as a template to pattern metallic films as outlined in (a). Evaporating a 250 nm thick silver film on a structured PS film and removing the polymer film after gluing the stack onto a convenient substrate allow producing a metallic film of controlled surface structiue with bumps (b) or holes (c). Adapted with permission from [21]. Copyright (2011) American Chemical Society...

Guo, L., Kawazoe, N., Fan, Y., Ito, Y., Tanaka, J., Tateishi, T., Zhang, X., and Chen, G. 2008. Chondrogenic differentiation of human mesenchymal stem ceUs on photoreactive polymer-modified surfaces. Biomaterials, 29, 23-32. 

Tang, Z., Akiyama, Y, Okano, T., 2012. Temperature-responsive polymer modified surface for cell sheet engineering. Polymer 4 (3), 1478-1498. 

In this chapter, the behavior of polymer-modified surfaces and polymeric fluids, in general, under confinement will be described. More specifically, direct and quantitative measurements of the lateral and normal interactions as a function of the separation distance between mica surfaces immersed in those fluids will be reviewed. Those polymers are often foimd in aqueous or nonaqueous solution, referred to as monomeric fluids. The monomeric fluids include salt-free (conductivity) water and aqueous salt solutions, as well as nonassodative organic solvents, such as toluene, tydohexane, or octa-methylcyclotetrasiloxane (OMCTS). The polymeric flirids indude dilute solutions of nonadsotbmg and adsorbing polymers as wdl as long and short end-attached neutral, dipolar, and charged polymers. ... 

Figure 6 Schematic summary of the normal forces F(D) between polymer-modified surfaces as a function of surface separation D. Adapted with slight changes from Klein, J. Molecular Conformation and Dynamics of Macromolecules in Condensed Systems Nagasawa, M., Ed. Elsevier Amsterdam, The Netherlands, 1988 pp 333-352, and Klein, J. Fundamentals of Tribology and Bridging the Gap Between the Macro- and MIcro/Nanoscale Bhushan, B., Ed. Kluwer Academic Publishers The Netherlands, 2001 pp 177-198." At low surface coverage (a), attractive bridging effect (cartoon in a) dominates the interactions. Rg indicates the gyration radius of the free polymer. The interactions in the case of high surface coverage are shown in b.

The different behavior of confined aqueous liquids compared to that of nonassodating liquids is wdl refieded in the properties of polymer-modified surfaces immersed in aqueous solutions. The earlier studies on confined pure liquids enabled a profound understanding of the interplay between electrostatic interactions and steric forces of flexible chains. 

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