Characterization of Biomaterials by Atomic Force Microscopy

AFM microscopy is a very promising tool for the understanding and the study of biological materials. This abstract briefly shows the results obtained during the period of my Ph.D. studies in the Chemistry and Industrial Chemistry Department at the University of Pisa. A commercial atomic force microscope (AFM) was used to investigate different kinds of biomaterials such as oligo peptides, polymers and proteins but also some hard materials as silicon and metals. The AFM consists of a microsized cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically made of silicon or silicon nitride with a tip radius of curvature on the order of few nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever ruled by Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact force, Van der Waals forces, capillary forces, chemical bonding, electrostatic forces etc. Traditionally, the sample is mounted on a piezoelectric scanner, that can move the object under examination in the z direction for maintaining a constant force, and in the x and y directions for scanning the sample. An image of the surface is obtained by mechanically moving the probe in a raster scan (that is the pattern of image detection and reconstruction in a computer image) over the specimen, line by line, and recording the probe-surface interaction as a function of position. The operating mode described above represents the typical way to use the atomic force microscope. But a whole world of capabilities of the instrument can be used. In particular we focused our attention on three research lines: • The phase imaging • The mechanical analysis of materials • The chemical force microscopy The AFM, developed first to explore atomic details on hard materials, has evolved to an imaging method capable of achieving fine structural details on biological samples and soft matter. ...