Analysis of Human Fibroblasts by Atomic Force Microscopy
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The force-sensing members of the large family of scanning probe microscopies have become important tools during the past decade for visualizing, characterizing, and manipulating objects and processes on the meso- and nanoscale level. The atomic force microscope (AFM), in particular, has had an impact in the life sciences. In cell science, the pioneering work with AFM was conducted in the early 1990s (1-3). The methodologies have now reached a stage of relative maturity (4). The principal merit of the AFM is as a nonintrusive local probe of live cells and their dynamics in the biofluid environment. As well as offering high spatial resolution imaging in one or more operational modes, the AFM can deliver characterization of mechanical properties and local chemistry through operation in the force-vs-distance (F-d) mode (e.g., ref. 5). The lateral resolution delivered by the AFM will in most cases, and especially for soft materials, be inferior to that obtained by electron-optical techniques, but the z-resolution is routinely in the nanometer range with a depth of focus equal to the dynamic range of the z-stage travel. The instrument may be operated in one of several modes, of which the most common ones are as follows: the contact mode, using a soft lever in which contours of constant strength of interaction are traced out; the intermittent-contact mode, in which a relatively stiff lever is vibrated at a frequency near that of a free-running resonance and in which contours of constant decrement of the free-running amplitude or a constant phase shift are mapped; and the F-d mode, in which the local stiffness of interaction between tip and specimen is determined over a range of applied force (lever deflection and z-stage travel being the two measurable variables).
Atomic Force Microscopy: Biomedical Methods and Applications