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Jan. 22, 2001
Atomic Force Microscopy
Researchers map the topography of biological macromolecules
"Researchers use atomic force microscopy (AFM) to literally map the surface of inert and biological samples to obtain three-dimensional images."
"AFM is just one of a number of novel microscopy technologies collectively known as scanning probe microscopy (SPM). In principle, all SPM technologies are based on the interaction between a submicroscopic probe and the surface of some material. What differentiates SPM technologies is the nature of the interaction and the means by which the interaction is monitored.[:]
- electrostatic force microscopy
- magnetic force microscopy
- lateral force microscopy
- scanning tunneling microscopy
- atomic force microscopy (AFM) ... AFM can be carried out in ambient air or in a liquid environment, a critical feature for biological research.
"Nanolithography, a technique in which the probe exerts sufficient force on the sample to move individual atoms ... "
"The basic atomic force microscope is composed of a stylus-cantilever probe attached to the probe stage, a laser focused on the cantilever, a photodiode sensor (recording light reflected from the cantilever), a digital translator-recorder, and a data processor and monitor."
" ... AFM, also known as scanning force microscopy ... gained acceptance in biological research, where it has been used to study a broad range of biological questions ... "
"AFM is unlike other SPM technologies in that the probe makes physical, albeit gentle, contact with the sample. ... As the probe is dragged across the sample, the stylus moves up and down in response to surface features. This vertical movement is reflected in the bending of the cantilever, which is measured as changes in the light intensity from a laser beam bouncing off the cantilever and recorded by a photodiode sensor. The data from the photodiode is translated into digital form and processed by specialized software on a computer, then visualized as a three-dimensional topological image."
" ... a new intermittent-contact ("tapping mode") scanning method was developed. In this mode, the probe is made to vibrate and literally taps along the surface of sample, minimizing or eliminating any damage to the specimen. Another improvement in AFM technology is the introduction of the noncontact scanning mode ... "
"The magnification power achieved by atomic force microscopes rivals that of transmission and scanning electron microscopes (TEM and SEM, respectively). Atomic force microscopes also are capable of a wide field of view (similar to SEM) and extreme vertical resolution (like TEM). ... AFM has a Z-height resolution of 0.5 nm ... the typical globular protein diameter is approximately 3 nm or greater, AFM has the ability to rapidly detect protein-protein interactions without labeling." ... [more]
1:55:04 PM 
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