Protein/Peptide Separation with Polymer Brush Nanosponges

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DESCRIPTION (provided by applicant): We will examine the adsorption of peptides and fluorescent dye molecules onto nanometer length-tethered polymer films (so-called polymer brushes) in order to rapidly fractionate mixtures of compounds and analyze the components by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. These hydrogel films can swell by more than an order of magnitude in aqueous solutions, depending on the pH. More specifically, the anionic brushes expand at high pH (>6) and collapse at low pH(<6) due to protonation of the anionic carboxylates; we refer to these films as nanosponges since the collapse triggers a release of the solvent (i.e. the sponge is squeezed). And this release of solvent offers a method to deliver an analyte that had previously been fractionated by selective adsorption from a mixture. In this two-year project we are primarily interested in examining the loading capacity of the brush films (i.e. the amount of adsorbed peptide per unit volume), along with the various structural parameters that control the loading and release of compounds from the brush film. Furthermore, we will examine the temporal response of uptake and release of analytes, along with the collapse and expansion of the brush films. Since these are nanofilms we anticipate that their response will be faster than traditional bulk hydrogel films. The specific objectives of this work include the following: 1) Design and synthesize polymer brush films that will adsorb peptides and/or ionic dyes based on the charge distribution of the molecules and the brush; 2) Demonstrate the rapid uptake and release of the peptides or fluorescent dyes by altering the pH of the solution; 3) Develop structure-property relationships that allow us to maximize the loading capacity and the selectivity of the adsorbed species; 4) Evaluate the efficacy of this approach for peptide/protein fractionation as applied to MALDI analysis for proteomic and metabolomic applications; and 5) Introduce our respective graduate students to biomedical research and encourage undergraduates to pursue Ph.D. degrees in related fields. The films will be synthesized by "grafting from" methodology from self-assembled monolayers that are tethered to gold coated silicon wafers. The resulting films will be characterized by a variety of techniques including: RAIRS, ellipsometry, QCM, AFM, and time-resolved fluorescence spectroscopy. This project is relevant to public health since our long-term goal is to rapidly separate proteins and other biologically relevant molecules from various fluids such as blood, urine, or cultured media. These novel materials act like smart sponges to selectively adsorb specific peptides based on ionic interactions, which will then be analyzed by mass spectrometry.