Advances in atomic force microscopy investigations of biomolecules
Atomic Force Microscopy (AFM) methods have become central tools in analyzing the formation, topography, structure, dynamics and molecular action of biological materials. The prominent advantage is the ability of AFM to probe these properties in a liquid environment, without fixation, at sub-nanometer lateral and vertical resolution. The present issue of Microscopy Methods is dedicated to recent progress achieved by AFM in the study of biological molecules, complexes, and systems, including membranes, proteins, biological nanomachines and food. Future directions in using AFM for biotechnology and biomedical applications are also outlined.
An overview of AFM techniques applied in investigating soft matter systems is presented in the opening article by Cohen and colleagues. The paper details the various modes of operation, and the type of information each approach provides. While emphasizing the clear advantages AFM grants, that paper also discusses the limitations and artifacts associated with the technique. A section is dedicated to the selection of proper supporting surfaces and their treatment, to enable analysis of a wide range of biological materials. Finally, advances in AFM instrumentation, such as video AFM, are highlighted.
The paper by Milhiet and coworkers summarizes recent AFM research on the nanostructure and properties of planar model and native membranes, with emphasis on analyzing lipid phase separation and the formation of microdomains, and characterization of the lateral heterogeneity in the lipid bilayer. Measurements of the physicochemical and mechanical properties of the bilayers are discussed, as well as the localization and structure of proteins and protein complexes in the lipid microdomains. An extensive discussion is focused on the interactions of the lipid bilayers with their support and how this affects the bilayer physicochemical properties. The authors present ways to create supported lipid bilayers (SLBs), and discuss SLB analysis in contact and tapping modes. A section in this review highlights the use of AFM in studying membrane based biosensors for bionanotechnological applications. At the end of the paper, progress in device development is presented, providing details on AFM combined with other imaging tools, e.g., high-speed tapping mode AFM, and non-contact AFM for soft materials.
Mueller and Engel dedicated their review to high-resolution AFM studies of native membrane proteins and protein membranes. They discuss characterization of the oligomeric states of membrane proteins, identification of protein conformational changes at work, and studies tracking the diffusion of protein membranes. The authors also address in detail drawbacks in sample preparation methods that affect the native structure and limit the spatial resolution, and present