Microscopic investigations of the interaction of proteins with surfaces

Combined electrochemical and microscopic study of porous enzymatic electrodes with direct electron transfer mechanism

In the present work electrochemical and microscopic methods have been utilized to get more insight into the complex relationship between the preparation route, structure and activity of porous enzymatic electrodes.

Relating material surface heterogeneity to protein adsorption: the effect of annealing of micro-contact-printed OTS patterns

We have investigated the influence of micrometer- and sub-micrometer-scale surface heterogeneities in patterned octadecyltrichlorosilane (OTS) films on human serum albumin (HSA) adsorption and its spatial distribution. 5-μm-wide OTS patterns were created on glass substrates by micro-contact printing and in some instances subsequent annealing was used to alter OTS molecule distribution within the patterns. Scanning force microscopy (SFM), advancing water contact angles and water vapor condensation figures were used to characterize the OTS films and to assess the nature of the heterogeneities within the various surface areas. High-resolution fluorescence microscopy was used to record images of fluorescently labeled albumin on OTS patterned films and fluorescence intensity was quantified and converted into the adsorbed amount. Adsorbed albumin was also characterized through SFM measurements. Combined SFM topography and lateral force microscopy (LFM) imaging revealed that micro-contact printing of OTS onto glass both replicated the stamp pattern and created small islands within the non-stamped regions between the patterns. The OTS coverage within stamped regions was not fully continuous but improved with subsequent annealing. Annealing also resulted in OTS island growth within the non-stamped regions and decreased average wettability on both the stamped and non-stamped areas. The extent of albumin adsorption was not proportional to OTS coverage, but correlated with the sub-μm distribution of OTS chains. We inferred that the surface distribution of ligands such as OTS on a sub-μm length scale determines the nature of albumin adsorption and its kinetics.

Application of atomic force microscopy and grating coupler for the characterization of biosensor surfaces

Atomic force microscopy (AFM) and an optical grating coupler system were used to improve the understanding of the biosensing layer on a Ta(2)O(5)-light-guiding surface. Exemplary, we investigated the immobilization of the protein avidin, the subsequent binding of biotinylated oligonucleotides and hybridization of a complementary 12-mer. The AFM measurements revealed the height of approximately 1.6 nm for a single avidin molecule, while the thickness of the avidin layer on the biosensor surface seemed to be 2.8-3.0 nm. This result lead to the conclusion that the protein was not forming a simple monolayer. However, the thickness of the avidin layer could not be determined directly, but only after shifting of protein by the tip of the AFM leading to grooves of 1 micro m(2) and approximately 3 nm depth. As the height of oxide particles forming the waveguide surface was also in the range of 1.5 nm, the depth of these grooves could also be a result of the deposition of proteins on top of the oxide particles. This was consistent with the increased roughness of the surface after protein binding. Thus, investigations with the grating coupler were used to determine quantitatively the amount of immobilized avidin. On a biotinylated surface the amount of immobilized avidin lead to the assumption of a complete monolayer, whereas simple adsorption proved to be less efficient. A binding ratio of 1:1.3 for avidin and a biotinylated oligonucleotide was achieved. Up to 83% of the bound single strand were accessible for a subsequent hybridization reaction with a 12-mer. These results supported the model of avidin being deposited mainly on top of the oxide particles leading to the picture of a 'rough' complete protein monolayer, which was postulated from the AFM investigations.