Two-Layer Architecture Using Atom Transfer Radical Polymerization for Enhanced Sensing and Detection in Complex Media

A novel, two-layer hierarchical architecture based on surface-initiated atom transfer radical polymerization was investigated. It combines a thin and highly dense first layer, for nonfouling properties, with a loose second layer for high immobilization levels of active biomolecules. Sodium azide treatment, to reduce the concentration of macroinitiators on the first layer for reinitiation, and by controlling the polydispersity allowed one to achieve three polymer architectures with low, moderate, or high azide substitution. Moderate substitution enabled the highest immobilization levels with a nonfouling background. Integration with dual-functional zwitterionic poly­(carboxybetaine) made this platform suitable for applications in undiluted complex media such as blood. It was demonstrated via a surface plasmon resonance biosensor that antigen accessibility and antibody loading were greatly improved. These results indicate the two-layer strategy as a generic concept suitable for applications from diagnostics to medical coatings in order to maximize and minimize specific and nonspecific responses, respectively

Dry Film Refractive Index as an Important Parameter for Ultra-Low Fouling Surface Coatings

Here we demonstrate that the film refractive index (RI) can be an even more important parameter than film thickness for identifying nonfouling polymer films to undiluted human blood plasma and serum. The film thickness and RI are two parameters obtained from ellipsometry. Previously, film thickness has been correlated to ultra-low fouling properties. Practically, the film RI can be used to characterize polymer density but is often overlooked. By varying the water content in the surface-initiated atom transfer radical polymerization of zwitterionic carboxybetaine, a minimum of ∼1.5 RI units was necessary to achieve <5 ng/cm² of adsorption from undiluted human serum. A model of the film structure versus water content was also developed. These results point to an important parameter and simple approach for identifying surface coatings suitable for real-world applications involving complex media. Therefore, ultra-low fouling using a thin film is possible if it is densely packed

One-Step Dip Coating of Zwitterionic Sulfobetaine Polymers on Hydrophobic and Hydrophilic Surfaces

Zwitterionic sulfobetaine polymers with a catechol chain end (DOPA-PSB) were applied to a variety of hydrophobic polymer sheets and fibers. In addition, a silica surface was tested as a representative hydrophilic substrate. The polymer-coated surfaces showed significantly lower fouling levels than uncoated controls. Because of the anti-polyelectrolyte nature of sulfobetaine zwitterionic polymers, the effect of salt concentration on the coating solutions and the quality of the polymer coating against fouling are studied. The coating method involves only water-based solutions, which is compatible with most surfaces and is environmentally friendly. To demonstrate the versatility of the reported method, we evaluated the fouling levels of the polymer coating on commonly used polymeric surfaces such as polypropylene (PP), polydimethylsiloxane (PDMS), polystyrene (PS), nylon, polyvinyl chloride (PVC), and poly­(methyl methacrylate) (PMMA)