(571g) Characterization of Patterned, Surface Tethered, Environmentally Responsive Poly(acrylic acid) Brushes for Bioseparation Applications

The aim of this project is to characterize the fundamental molecular adsorption phenomena of model proteins on polymeric surfaces in order to improve bioseparation materials.  Bioseparation processes require specialized and sensitive techniques to selectively isolate and purify targeted biomolecules.  The focus for this project is adsorption as it relates to bioseparation applications.  Hence, for this project, separation materials are labeled into two distinct groups based on the desired adsorption behavior.  Materials are designed (1) to PROMOTE selective adsorption of targeted biomolecules or (2) to INHIBIT adsorption of non-targeted species, called foulants, which can create a barrier layer on the surface and impede material performance.  Molecular level transport phenomena and the fundamental adsorption behavior at solid-fluid interfaces can be monitored using surface plasmon resonance (SPR) spectroscopy.  Here, an SPR sensor was used to examine binding interactions and affinities of protein molecules in a real-time, label-free environment, with poly(acrylic acid) (PAA) brushes as an adsorbing and/or non-fouling surface ligand.  Using various molar ratios of precursor tethered molecules in ethanolic solutions, a mixture of self assembling monolayers (SAMs) were tethered to a homogeneous thin film substrate of gold (Au).  The resulting SAM formation on the gold substrate was then used to create a patterned PAA surfaces with different brush densities, configurations and thicknesses.  Results indicate that brush density and environmental temperature, pH, and salt concentrations are all dominant factors, which independently effect and also interact with one another, producing significant differences in the overall adsorptive/fouling performance of the material.  Special attention to brush configuration and swelling and shrinking behavior of the adsorptive material must be specifically controlled in order to improve control selective adsorption and to influence mass transport and diffusion limitations that inhibit molecular access to the brush.  Molecular accessibility to the active side chains (binding sites) nearing the brush surface can be dramatically improved by (a) spreading the brushes at least four times this diameter, and (b) accounting for the affinities (charge) and swelling-shrinking behavior of the brush (dependent upon environmental pH, temperature, and salinity).