Peptide adsorption on silica nanoparticles: evidence of hydrophobic interactions.

Molecular recognition and interactions at the interface between biomolecules and inorganic materials determine important phenomena such as protein adsorption, cell adhesion to biomaterials, or the selective response of biosensors. Events occurring at the biomolecule-inorganic interface, despite their importance, are still poorly understood, thus limiting control of interfacial properties and response. In this contribution, using well-characterized silica nanoparticles and a series of peptides having heterogeneous physicochemical properties (S1: KLPGWSG, S2: AFILPTG, and S3: LDHSLHS) identified from biopanning against the same particles, we identify the driving forces that govern peptide-silica binding. Binding isotherms obtained by fluorimetric assay under different pH conditions allowed us to demonstrate the impact of binding environment (pH) on adsorption behavior of a given peptide-surface silica nanoparticle. Our experimental data suggest a multistep adsorption mechanism leading to the formation of multilayers on silica, in which the prevailing interactions (i.e., electrostatic or hydrophobic/hydrogen bonding) and their relative contribution to the binding event are governed by the identity of the peptide itself, the substrate's surface functionality (hydrophilic or hydrophobic), and the peptide bulk concentration and solution bulk pH. Our studies show how it is possible to modulate peptide uptake on silica, or in fact on any particle, by changing either the surface properties or, more simply, the binding environment. In addition, the data reveal an intrinsic bias toward positively charged sequences in the elution conditions used in the biopanning protocol with much information about strong binder sequence diversity being lost during panning.