Relative Contribution of Lateral Packing Density to Albumin Adsorption on Monolayers

The effect of functional group density on protein adsorption is systematically studied to support ongoing efforts in molecular imprinting of surfaces and bulk materials. In these applications, functional commodity chemicals are molded to complement the shape and chemistry of the target molecule. Here, we study the relationship between bovine serum albumin adsorption and ligand density for carboxylate, alcohol, and alkyl terminal groups. Control surfaces consisting of densely packed self-assembled monolayers (SAMs) are contrasted with low-density SAMs formed through thiol-yne chemistry. Direct comparison consistently yielded greater protein adsorption on low-density SAMs than conventional pure component SAMs of the same functional group. Critically, the carboxylate and alcohol low-density SAMS are more hydrophobic than their analogous dense SAMs. Mixed functional group, dense SAMs were formed with alkyl diluents to match the hydrophobicity of the low-density SAMs. Once hydrophobicity is matched, the dense carboxylate and alcohol SAMs have higher adsorption than the low-density SAMs. We conclude (1) surface charge and hydrophobicity trends dominate over surface density contributions; (2) when hydrophobicity is matched, greater adsorption occurs on dense hydrophilic groups than on lower density hydrophilic groups; (3) when hydrophobicity is matched, greater adsorption occurs on lower density hydrophobic groups than on higher density hydrophobic groups.