AVS 51st International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoM

Paper BI-MoM11
Probing the Conformation of Hydrated Molecular Adsorbates on Solid Interfaces Using Long Period X-ray Standing Wave Fluorescence

Monday, November 15, 2004, 11:40 am, Room 210D

Session: In-Situ Spectroscopy of Biomolecules at Interface
Presenter: C.A. Crot, University of Illinois at Chicago
Authors: C.A. Crot, University of Illinois at Chicago
C. Wu, University of Illinois at Chicago
M. Schlossman, University of Illinois at Chicago
T.P. Trainor, University of Alaska
P.J. Eng, University of Chicago
L. Hanley, University of Illinois at Chicago
Correspondent: Click to Email
Understanding the process of protein and biomolecular adsorption onto solid surfaces is of great importance in a wide variety of applications including biomaterials, tissue engineering, biosensors, immunoassays, and protein arrays. However, direct investigation of adsorption processes and the hydrated conformation of a molecular adsorbate is difficult since the majority of surface analysis techniques require ultra-high vacuum conditions. In this work long period x-ray standing wave fluorescence spectroscopy (XSW) is being developed as a spatial probe of molecular adsorption at the liquid-solid interface using a model surface-adsorbate system. A 25 nm thick polystyrene layer is spin coated on a thick silicon wafer, then the top of this layer is amine-functionalized via hyperthermal allyl amine ion deposition. X-ray photoelectron spectroscopy and atomic force microscopy are used to monitor the chemistry and morphology of this amine-polystyrene model surface. A thirteen residue peptide is covalently bound to a poly(ethyleneglycol) chain that is terminated with a bromine labeled amino acid and used as the model adsorbate. This Br-PEG-peptide construct is adsorbed onto the amine surface and its hydrated conformation is examined by XSW and x-ray reflectivity. Measurements of the bromine fluorescent yield as a function of incident angle provides information on the distance of the bromine layer from the silicon surface with an accuracy of several angstroms. Preliminary data analysis of the Br-PEG-peptide conformation indicates the peptide end is adsorbing directly onto the amine surface while the bromine atom on the Br-PEG end is extended ~13@+-@3 nm from the amine surface into the aqueous layer. Adsorbate configuration is probed as a function of adsorption time, amine film characteristics, and other experimental parameters. The general applicability of the XSW technique to probe the conformation of labeled adsorbates at the aqueous-solid interface is discussed.