Evidence of a Mobile Precursor State in Nonspecific Protein Adsorption

We study the dynamics of nonspecific protein adsorption using nanometer-micrometer-scale patterns involving hydrophobic domains in hydrophilic matrices. We report the discovery of a critical requirement for the sizes of the hydrophobic/adhesive pads for protein adsorption: the area of each adhesive pad must be more than 2 orders of magnitude larger than the footprint of a protein molecule before irreversible adsorption occurs. We attribute this to the minimal surface area sampled by a mobile protein molecule in a precursor state before irreversible adsorption occurs. Kinetic analysis based on the precursor model quantitatively accounts for the experimental observation and reveals that the distance sampled by the mobile precursor state before irreversible adsorption increases with the size of the protein molecule.