http://users.df.uba.ar/catalina/TBM/Rivetti_1996.pdf

Scanning force microscopy of DNA deposited onto mica: equilibration versus kinetic trapping studied by statistical polymer chain analysis.

The authors have measured the force-versus-indentation curves of different elastomers (polyurethane), rubber, cartilage, and living cells and deduced a parabolic tip shape from these curves. They have also calculated the radius of curvature of the AFM tip to be 50-100 nm. The calculated ranges of the local Young's moduli E are 0.6-2.4 MPa for rubber, 0.16-0.6 MPa for cartilage, and 0.013-0.15 MPa for a living cell. This means that an applied force of 1-10 pN is required to obtain high-resolution images of a living cell with about 1 nm vertical deformation and only a few nm2 area of contact. Therefore, understanding the deformation mechanism is not only important for determining local elasticities, but also to understand the 'height' information and the resolution limits of AFM images. Deformation without strong adhesive forces causes a soft sample on a hard substrate to appear thinner, a fact which has already been observed in many AFM images.

https://iopscience.iop.org/article/10.1088/0957-4484/4/2/006/pdf

Deformation and height anomaly of soft surfaces studied with an AFM

Imaging and manipulation of biological structures with the AFM

DNA binding to mica correlates with cationic radius: assay by atomic force microscopy

The newly developed atomic force microscope (AFM) provides a unique window to the microworld of cells, subcellular structures, and biomolecules. The AFM can image the three-dimensional structure of biological specimens in a physiological environment. This enables real-time biochemical and physiological processes to be monitored at a resolution similar to that obtained for the electron microscope. The process of image acquisition is such that the AFM can also measure forces at the molecular level. In addition, the AFM can interact with the sample, thereby manipulating the molecules in a defined manner--nanomanipulation! The AFM has been used to image living cells and the underlying cytoskeleton, chromatin and plasmids, ion channels, and a variety of membranes. Dynamic processes such as crystal growth and the polymerization of fibrinogen and physicochemical properties such as elasticity and viscosity in living cells have been studied. Nanomanipulations, including dissection of DNA, plasma membranes, and cells, and transfer of synthetic structures have been achieved. This review describes the operating principles, accomplishments, and the future promise of the AFM.

E. Delaine

Papers

Substrate preparation for reliable imaging of DNA molecules with the scanning force microscope.