The National Food Imaging Centre Equipment: Atomic Force Microscopy
Atomic force microscopy (AFM) is a completely new imaging technique for Teagasc researchers and provides fundamental data on the physicochemical properties of food materials, thus complementing SEM and CSLM data. AFM is very different from the other imaging techniques described above in that images are generated by moving a very small silicon nitride tip across the surface of the sample. The tip is attached to a cantilever, which deflects in response to minute surface variations in height. The deflection is converted to a brightness value that we see on the screen. This technique provides the highest possible imaging resolution of biological materials, permitting direct visualization of individual biomolecules including lipids, proteins and polysaccharides as well as microorganisms (Fig. 7). A resolution of one nanometer has been achieved on biological samples such as DNA. A unique feature of AFM is its ability to characterize the mechanical properties of food materials, including stiffness, elasticity, friction and stickiness in addition to surface topography. Samples can be analyzed under ambient conditions in liquid or gas environments and over a wide range of temperatures.
Figure 7. Atomic force microscope image of bacteria (Lactobacilli) embedded
in whey protein gel. Inset shows the principle of the technique.