Adsorption and Self-assembly of Proteins at Chemically Modified Surfaces

Our research is mostly focused on the subject of adsorption and self-assembly of proteins at modified surfaces. We employed atomic force microscopy (AFM) to study bovine serum albumin (BSA) and insulin adsorption at 1-decene- and methyl 10-undecenoate-modified Si(111) substrates. The results were compared to matrix-assisted laser desorption/ionization-mass spectroscopy (MALDI-MS) data previously published in the Morin group. The MALDI-MS spectra showed a big insulin signal, while BSA was not detected for 1 mg/mL BSA and 10% saturated insulin solutions. Our AFM images revealed considerable BSA adsorption, whereas it was not possible to observe insulin molecules. This clearly shows that in addition to the low quantity of the protein, a stronger interaction between the surface and the protein may result in a weak MALDI-MS signal and prevent quantitative analysis using this technique. Self-assembled monolayers on Au surfaces were used to investigate the oligomerization of truncated K122-4 (ΔK122-4) pilins into a new protein nanostructure. Employing AFM, we observed that at hydrophobic layers, with more than 10-30% accessible hydrophobic component, ΔK122-4 pilins oligomerize to a nanoweb. To differentiate the structure of ΔK122-4 nanoweb from the aggregation of the pilins at hydrophilic surfaces, electrochemical impedance spectroscopy was employed. Through equivalent circuit fitting, capacitance values of 3.7 ± 0.4 μF/cm2 and 2.5 ± 0.2 μF/cm2 were obtained for the aggregated pilins and the web pattern, respectively. Because of the higher average thickness of the former layer, this could support the presence of water in this layer. A dielectric constant (ε) of 5.1 ± 0.7 was obtained for the nanoweb. This low value could indicate a more compact and ordered assembly. Finally, conductive protein nanotube (PNTs) fabrication was performed by electroless copper deposition at ΔK122-4 PNTs in aqueous solution. The nanostructures were catalyzed by PdCl42-. At least 20% of the accessible amino acids of the PNTs have S-, N- and O-donor side chains which are able to form a complex with Pd(II). Metallization was verified using scanning electron microscopy (SEM).