Tuning the orientation of an antigen by adsorption onto nanostriped templates

We investigate the adsorption of a globular protein (P.69 pertactin, also known as antigen 69k) on protein-repellent hydrophilic substrates bearing regularly spaced hydrophobic nanostripes, for stripe widths comprised between 20 and 160 nm. Protein adsorption is shown to be remarkably well-controlled by the templating substrates, with a near-to-perfect reproduction of stripes by the protein monolayer down to 20 nm width, except for a 5-10 nm broadening. However, whereas the ellipsoidal protein forms a dense monolayer with random orientation of its long axis for large stripe widths, it adsorbs in a predominantly side-on (flat-on) orientation for stripe widths below 50 nm, due to the easier reorientation (interfacial relaxation) of the proteins adsorbed at the edges of the stripes, which experience a decreased lateral interaction. These results show that protein confinement in regions of a size similar to their dimensions can be used to tune their orientation, which may be of interest for applications in high-density sensor devices.