Atomic Force Microscopy (AFM) is a very high resolution imaging tool. Discovered in the 1980’s, it can be used to develop a topographic scan of the surface of a wide variety of materials. Unlike the technology that preceded it, scanning tunneling microscopy (STM), AFM does not require a surface to be conducting.

 

The actual structure is comprised of a probe or tip and a cantilever. The latter is a beam made of silicone that is widely utilized in nanotechnology. 

 

Although AFM can function under a number of different modes, the contact mode was the first employed. In this case, the tip brushes against the surface and as a result, the cantilever shifts. A laser points at the cantilever and reflects onto a position sensitive detector (a split photodiode detector). The deflection of the laser is used to create an image of the surface

 

Although imaging was its initial application, AFM is also utilized for force spectroscopy. In this case, the purpose is not to create an image, but to measure the forces occurring at the atomic scale (such as that required to break and form bonds). The probe can be coated so as to attract free molecules and is then brought toward and away from the surface. The result is that the probe pulls on individual particles, and the forces between them are measured.

 

The property of force spectroscopy has made AFM key in the study of molecular conformation, intramolecular forces, energy landscapes and failure mechanisms in different materials.

 

Figure 3: AFM Force Spectroscopy

 

Schematic diagram of bacteriorhodopsin unfolding using the AFM tip. One end of the molecule is picked up by the tip (A), and the alpha-helices are pulled out sequentially in pairs (B).

 

 

 

 

Webpage Author(s):

 

 

 

                                                            - Matthias Rief, University of Munich

                                                                

Figure 1: AFM

 

Stretching and breaking multiple parallel antibody-antigen bonds with Atomic Force Microscopy (AFM).

 

 

 

Figure 2: How AFM Works