PEG or Dextran surfaces

Application Note: 
A zero background surface is ideal for biophysical experiments, such as single molecule spectroscopy, biological atomic force microscopy, and as starting surfaces for bioconjugation .

It is well known that oligo- or poly(ethyleneglycol) (PEG) is the most “inert” chemical group toward protein adsorption. The inertness or non-fouling property of PEG is attributed to its hydrophilic nature. The PEG backbone is extensively hydrogen-bonded to water molecules, resulting in the formation of a partially structured hydration layer. Adsorption of a protein molecule requires the disruption of this structured water layer and is enthalpically inhibited. Protein adsorption also leads to the compression of the PEG layer towards the solid surface and is entropically unfavorable, Fig. 1. Indeed, PEG and other oligo- or poly-ethers have been successfully used as inert surfaces for the immobilization of protein molecules. Examples include oligoethyleneglycol (OEG) terminated alkanethiol self-assembled monolayers (SAMs) on Au, as demonstrated by Whitesides' group and others, as well as PEG films anchored to glass or other oxide terminated surface by silane coupling chemistry. The OEG-thiol SAM approach is restricted mainly to noble metal surfaces, particularly gold. The "graft-onto" strategy based on silane chemistry suffers from low PEG density and instability due to hydrolysis. To overcome the above limitations, we has successfully developed a proprietary high density brush of poly-ethyleneglycol (PEG). The density of grafted PEG groups is 1-2 orders of magnitude higher than those from the conventional silane coupling chemistry. Such high PEG density is the reason for the exceptional repulsiveness of the surface towards protein adsorption, as demonstrated in Fig. 2, which compares the adsorption of two protein molecules on the PEG brush surface and on a clean glass surface without PEG coating. The low background PEG surface can be directly used in a variety of experiments and applications demanding repulsiveness towards proteins. It is also the starting point to create functional surfaces for biomolecular immobilization, as detailed in other application notes. 


Fig, 1. How PEG resists protein adsorption. Protein adsorption on the PEG surface Fig. 2. Fluorescence microscope images of the adsorption of fibrinogen (FBN 1mg/ml) and membrane-type matrix metalloproteinase (MMP5, 1mg/ml) on clean and PEG coated glass surfaces. Detection was achieved by primary antibody and CY3-tagged secondary antibody.





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