X-ray Photoelecton Spectroscopy and Radiometry Studies of Biotin-Derivatized Poly(L-lysine)-grafted-Poly(ethylene glycol) Monolayers on Metal Oxides

摘要

This paper describes the first detailed analytical characterization of the surface roperties of a new class of biomolecular interfaces based on derivatized poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) coopolymers. Such copolymers spontaneously adsorb to negatively charged surfaces under physiological pH and efficiently repel nonspecific protein adsorption while providing PEG-tethered functional/active sites for specific biomolecular recognition. As a model system, we synthesized biotin-derivatized (PLL-g-PEG) copolymers, PLL-g-[(PEG)_(1-x)(PEG-biotin)_x], where x varies from 0 to 1. The copolymers were adsorbed on titaniumdioxide substrates. Surface characteristics and biorecognition properties were investigated using X-ray photoelectron spectroscopy and radiometry. We show that the onolayer formed is approx 20-25 A in thickness. It is organized with its PLL backbone located within the first 10 A on the substrate and with the PEG side chains located above the PLL. The resulting biotin surface concentration depends linearly onthe biotin concentration in the bulk copolymer. This biotinsurface concentration depends linearly on the biotin concentration in the bulk copolymer. This aspect implies that the surface concentration of functioal groups can be adjusted by adapting their concentration within the bulk copolymer. The PLL-g-PEG(-biotin) monolayers are efficient in repelling nonspecific protein asorption but can specifically bind streptavidin (SA). Within the biotin range considered, the SA surface concentration increases linearly with the biotin surface concentration of the monolayer.