title: Molecular and Thermodynamic Factors Explain the Passivation Properties of Poly(ethylene glycol)-Coated Substrate Surfaces against Fluorophore-Labeled DNA Oligonucleotides.
abstract: Poly(ethylene glycol) (PEG) nanofilms are used to avert the nonspecific binding of biomolecules on substrate surfaces in biomedicine and bioanalysis including modern fluorescence-based DNA sensing and sequencing chips. A fundamental and coherent understanding of the interactions between fluorophore-tagged DNA, PEG-films, and substrates in terms of molecular and energetic factors is, however, missing. Here we explore a large parameter space to elucidate how PEG layers passivate metal oxide surfaces against Cy3-labeled DNA probes. The driving force for probe adsorption is found to be the affinity of the fluorophore to the substrate, while the high-quality PEG films prevent adsorption to bare ITO surfaces. The amount of nonrepelled, surface-bound DNA strongly depends on oligonucleotide size, PEG chain length, and incubation temperature. To explain these observations, we develop an experimentally validated theory to provide a microscopic picture of the PEG layer and show that adsorbed DNA molecules reside within the film by end-tethering the fluorophore to the ITO surface. To compensate for the local accumulation of negatively charged DNA, counterions condense on the adsorbed probes within the layer. The model furthermore explains that surface passivation is governed by the interdependence of molecular size, conformation, charge, ion condensation, and environmental conditions. We finally report for the first time on the detailed thermodynamic values that show how adsorption results from a balance between large opposing energetic factors. The insight of our study can be applied to rationally engineer PEG nanolayers for improved functional performance in DNA analysis schemes and may be expanded to other polymeric thin films.
authors.affiliation: National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University , Nanjing 210093, China.
authors.forename: Chun-lai
authors.initials: CL
authors.lastname: Ren
authors.affiliation: Center for Advanced Bioanalysis GmbH, Linz, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Schlapak
authors.affiliation: Center for Advanced Bioanalysis GmbH, Linz, Austria.
authors.forename: Roland
authors.initials: R
authors.lastname: Hager
authors.affiliation: Department of Biomedical Engineering, Department of Chemistry and Chemistry of Life Processes Institute, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Igal
authors.initials: I
authors.lastname: Szleifer
authors.affiliation: Center for Advanced Bioanalysis GmbH, Linz, Austria.|Department of Chemistry, Institute of Structural and Molecular Biology, University College London , London, United Kingdom.
authors.forename: Stefan
authors.initials: S
authors.lastname: Howorka