Atomic force microscopy imaging probes

AFM/SPM Atomic Force Microscopy Scanning Probe Microscopy Surface imaging with near atomic spatial resolution Atomic scale morphology 0.1 A 50 A... 

The ability to control the position of a fine tip in order to scan surfaces with subatomic resolution has brought scanning probe microscopies to the forefront in surface imaging techniques. We discuss the two primary techniques, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) the interested reader is referred to comprehensive reviews [9, 17, 18]. 

The most popular of the scanning probe tecimiques are STM and atomic force microscopy (AFM). STM and AFM provide images of the outemiost layer of a surface with atomic resolution. STM measures the spatial distribution of the surface electronic density by monitoring the tiumelling of electrons either from the sample to the tip or from the tip to the sample. This provides a map of the density of filled or empty electronic states, respectively. The variations in surface electron density are generally correlated with the atomic positions. 

Atomic force microscopy (AFM) is a variant of STM and was introduced in 1986 by Binnig et al. (11). AFM belongs to a family of near-field microscopies and is capable of imaging a wide variety of specimens surface down to an atomic scale. The technique employs a probe (pyramidal tip) mounted at the end of a sensitive but rigid cantilever (see Fig. 2). The probe is drawn across the specimen under very light mechanical loading (1). Measurements of the probe s interaction with the sample s surface are accomplished with a laser beam reflected from the cantilever. 

Figure 4. Visualization of PARP-1-mediated chromatin compaction by atomic force microscopy. Chromatin assembled in vitro on a circular 10.5kb plasmid DNA was purified, incubated widi or without recombinant human PARP-1, and imaged by atomic force microscopy. Two types of images are shown scan probe oscillation amplitude (top) and topography (bottom height scale is indicated). The length scale is indicated. (See Colour Plate 6.)...

Among the many microscopy-based techniques for the study of biomolecular interactions on surfaces, scanning probe microscopies, and especially the atomic force microscopies (AFM), are the most used because of their molecular and sub-molecular level resolution and in situ imaging capability. Apart from the high resolution mapping of siuface nanotopographies, AFM can be used for the quantification and visualisation of the distribution of chemistry, hydrophobicity and local mechanical properties on surfaces, and for the fabrication of nanostructmes on surfaces. 

STM was the first of a class of techniqnes known as scanning probe microscopy. Atomic force microscopy (AFM), invented later in the 1980s, is currently the most widely used of these techniques. Both STM and AFM depend on probes with atomically sharp tips these probes are manenvred over the snrface of the sample to be imaged, maintaining atom-scale distances between the probe and sample. Both techniques are capable of picking np atoms individnally and placing them precisely on surfaces (7). 

Miquel, M.E., Carli, S., Couzens, P.J., Wille, H.J., and Hall, L.D. 2001. Kinetics of the migration of lipids in composite chocolate measured by magnetic resonance imaging. Food Res. Int. 34,773-781. Morris, V.J. 2004. Probing molecular interactions in foods. Trends Food Sci. Technol. 15, 291-297. Morris, V.J., Kirby, A.J., and Gunning, A.P. 1999. Atomic Force Microscopy for Biologists . Imperial College Press, London. 

---