Ugo Valbusa

Bioactive surfaces for antibody-antigen complex detection by Atomic Force Microscopy

Recently there has been a great develop of new antibodies immobilization procedures, that keep antibodies to retain their orientation and functionality after the binding to a solid support. This allows the formation of immune-complexes useful for the detection of biomarkers from biological samples. We have developed a new method of functionalization for solid substrates that involves an initial surface activation, then a functionalization by means of 3-aminopropyltriethoxysilane-followed by another functionalization step with a layer of very small peptides, which have a high affinity to the Antibody Fc portion, acting as antibody linkers. These antibody binding peptides can immobilize the antibodies with a proper configuration that allows an unambiguous detection of antibody-antigen complexes by means of atomic force microscopy (AFM). The AFM can act as a powerful label free detection technique, which allows to detect, in principle, single molecule interactions, with the only limitation to use substrate with low-roughness surfaces; in this case, the roughness can be interpreted as background noise in the AFM analysis. Moreover, our functionalization method can be used to obtain bioactive surfaces on a wide range of solid supports, making them capable to suitably immobilize the antibodies for the antigenic binding.

Atomic Force Microscopy for DNA SNP Identification

The knowledge of the effects of single-nucleotide polymorphisms (SNPs) in the human genome greatly contributes to better comprehension of the relation between genetic factors and diseases. Sequence analysis of genomic DNA in different individuals reveals positions where variations that involve individual base substitutions can occur. Single-nucleotide polymorphisms are highly abundant and can have different consequences at phenotypic level. Several attempts were made to apply atomic force microscopy (AFM) to detect and map SNP sites in DNA strands. The most promising approach is the study of DNA mutations producing heteroduplex DNA strands and identifying the mismatches by means of a protein that labels the mismatches. MutS is a protein that is part of a well-known complex of mismatch repair, which initiates the process of repairing when the MutS binds to the mismatched DNA filament. The position of MutS on the DNA filament can be easily recorded by means of AFM imaging.

Nanostructuring Rh(110) Surfaces by Ion Etching

The ion irradiation of the Rh(110) surface results in the self-organised formation of various nano-structured morphologies like ripples, mounds, pyramids which have been thoroughly studied as a function of the incidence angle and of the impact energy of the impinging ions. A study of the evolution of the surface ripples at various impact energies above the hot-spot threshold, has been rationalized in terms of a contribution due to an ion-induced surface diffusion mechanism. In the very low ion incidence regime, where the formation of hot spots following ion impact is inhibited, the formation of a rhomboidal pyramid pattern is singled out and attributed to the predominant reorganization of surface adatom and vacancies produced in the topmost surface layers. The metastable rhomboidal pyramid pattern, was recently proven to have extraordinary chemical reactivity since it is endowed with a very high density of undercoordinated step sites runnin along the very open azimuthal direction.

Nanoindentations on SrTiO3 Substrates: Effects of Fractal Roughness on Contact Mechanics

The non-stationary character of roughness is a widely recognized property of surface morphology and suggests modelling several solid surfaces by fractal geometry. In the field of contact mechanics this demands for novel investigations attempting to clarify the role of multi-scale roughness during physical contact. Here we propose an experimental investigation of the mechanical response of SrTiO3 substrates probed by a commercial nanoindentor. Load-displacement curves have been acquired respectively on well-defined crystalline surfaces and on mechanically lapped surfaces. We observe the first-loading cycles to be considerably affected by surface roughness whenever the penetration depth is kept below the interface width. The obtained results are analyzed within an elasto-plastic deformation model for fractal surfaces and a picture is developed to describe the deformation process with respect to surface roughness and structural parameters.Copyright