Imaging probes cantilevers

DNA templated protein arrays with predictable control at the nanometer scale could lead to single-molecule detection in proteomics studies. Individual proteins placed at unique locations on the nanoarray could be detected with single molecule imaging techniques such as recognition imaging, in which specific antibodies are attached to the scanning probe cantilever. 

For different modes and purposes, there are special AFM probes (cantilevers and tips). These differ in terms of their geometry, dimensions, force constants, resonance frequencies, tip position, shape and radius, material, etc. There are numerous commercial sources and we refer to these for finding the appropriate probes for the given experiment and sample. It is also clear based on the rudimentary treatment of tip sample interactions (Chap. 1) and the basic AFM features that the attainable information and resolution are in many cases dictated by the properties and characteristics of the probe tip. The tip physically interacts with the surface and its sharpness and aspect ratio, for instance, determine the degree of convolution in imaging small features or the limited success in the visualization of small pores (Fig. 2.23). 

CE Talley, MA Lee, RC Dunn. Single molecule detection and underwater fluorescence imaging with cantilevered near-field fiber optic probes. Appl Phys Lett 72 2954-2956, 1998. 

Talley, C. E., G. A. Cooksey arid R. C. Dunn (1996). "High resolution fluotescenee imaging with cantilevered near-field fibo optic probes." Applied Physics Letters 69(25) 3809-3811. 

Fig. 10. Scanning electron microscope (SEM) image of the probe with an MWCNT attached to a silicon cantilever [35]. Protruding of one individual MWCNT has been confirmed by transmission electron microscope (TEM) measurement (not shown here).

Figure4.1 Block diagram ofa SNOM apparatus (a), SEM images of a cantilever-type SNOM probe (b) and the aperture at the tip end (c).

AFM has been used to image surfaces by probing both the attractive and repulsive forces experienced by the tip as a result of its proximity to the sample surface. In both modes, the probe tip is mounted on a cantilever spring. Three main designs have been employed metal foil with a splinter of diamond, a shaped tungsten wire that acts both as spring and tip, and microfabricated tip/cantilever composites. 

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. 

Studies on fundamental interactions between surfaces extend across physics, chemistry, materials science, and a variety of other disciplines. With a force sensitivity on the order of a few pico-Newtons, AFMs are excellent tools for probing these fundamental force interactions. Force measurements in water revealed the benefits of AFM imaging in this environment due to the lower tip-sample forces. Some of the most interesting force measurements have also been performed with samples under liquids where the environment can be quickly changed to adjust the concentration of various chemical components. In liquids, electrostatic forces between dissolved ions and other charged groups play an important role in determining the forces sensed by an AFM cantilever. 

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