&lt;title&gt;Atomic force microscope for small cantilevers&lt;/title&gt;

Schaeffer, Tilman E.; Viani, Mario; Walters, D. A.; Drake, B.; Runge, Erik; Cleveland, J. P.; Wendman, Mark A.; Hansma, Paul K.

doi:10.1117/12.271228

Cited by 35 publications

(18 citation statements)

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“…A high resonance frequency in liquid is required to generate a high tapping frequency; also required is a low spring constant, so as to minimize the tip-sample interaction force. These conflicting requirements can be met only with small cantilevers (8,9). Every circuit in the feedback loop must have a wide bandwidth.…”

mentioning

confidence: 99%

A high-speed atomic force microscope for studying biological macromolecules

Ando

Kodera

Takai

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

994

796

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The atomic force microscope (AFM) is a powerful tool for imaging individual biological molecules attached to a substrate and placed in aqueous solution. At present, however, it is limited by the speed at which it can successively record highly resolved images. We sought to increase markedly the scan speed of the AFM, so that in the future it can be used to study the dynamic behavior of biomolecules. For this purpose, we have developed a high-speed scanner, free of resonant vibrations up to 60 kHz, small cantilevers with high resonance frequencies (450 -650 kHz) and small spring constants (150 -280 pN͞nm), an objective-lens type of deflection detection device, and several electronic devices of wide bandwidth. Integration of these various devices has produced an AFM that can capture a 100 ؋ 100 pixel 2 image within 80 ms and therefore can generate a movie consisting of many successive images (80-ms intervals) of a sample in aqueous solution. This is demonstrated by imaging myosin V molecules moving on mica (see http:͞͞www.s.kanazawa-u.ac.jp͞phys͞biophys͞bmvmovie.htm). One of the advantages of the atomic force microscope (AFM) (1) is its capacity to image individual biomolecules in, say, a buffered solution containing ions at physiological concentrations (2, 3). Such capacity suggests that the instrument can be used to record the dynamic behavior of such molecules. In practice, however, only very slow processes can be recorded (2, 4-6), because commercially available AFMs require minutes to form an acceptable image, and many interesting biological processes occur at much higher rates. To understand, and overcome, the factors that limit the scanning rate of an AFM, we begin by considering relations between the characteristics of the constituting components.We consider only the ''tapping mode'' of AFM operation (Digital Instruments, Santa Barbara, CA). This is the mode suitable for imaging biological macromolecules, because vertical oscillation of the cantilever at (or near to) its resonance frequency reduces lateral forces between the tip and the sample (7). The oscillating tip briefly taps the surface at the bottom of each swing, resulting in a decrease in oscillation amplitude. During the x-y scan of the sample stage a feedback loop (see below) keeps this decrease (and hence the tapping force) constant; this is necessary for minimizing the deformation of soft samples. The error signal-the difference between a preset signal and the rms amplitude of the cantilever-is fed into a proportional-integraldifferential (PID) feedback circuit. The PID output is amplified and then sent to the z-piezo actuator; this is repeated until the error signal returns to zero. For the three-dimentional movement of the sample stage to follow the sample topography accurately, the bandwidth of the feedback loop should be comparable to, or larger than, the frequency determined by the x-y scan velocity and the apparent width of the features on the surface. To increase the imaging bandwidth, all elements in the feedback loop have to be optimi...

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mentioning

confidence: 99%

A high-speed atomic force microscope for studying biological macromolecules

Ando

Kodera

Takai

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

994

796

View full text Add to dashboard Cite

show abstract

“…2bC), the DNA molecules again become visible-or, rather, the DNA molecule from the lower RNAP complex is visible, whereas the DNA molecule from the upper RNAP complex has moved out of this field of view. Faster AFM imaging is clearly desirable and is now being achieved with new small-cantilever AFMs (26,27), which have imaged DNA degradation by the DNase I enzyme as fast as 2 s per image (28)-20 times faster than the imaging rate of Fig. 2.…”

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confidence: 99%

Varieties of imaging with scanning probe microscopes

Hansma

1999

Proc. Natl. Acad. Sci. U.S.A.

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“…The bimetallic strip effect can be minimized by coating the cantilever on an area close to the tip only, whereby creating a "reflector pad" on which the laser can be positioned (Viani et al, 1999a). A coating process can be avoided by fabricating the cantilever entirely out of metal in the first place (Schäffer et al, 1997;Chand et al, 2000). Figure 13.7a shows an array of small aluminum cantilevers.…”

Section: Increasing the Resonant Frequency Of Cantileversmentioning

confidence: 98%

“…The image rate was 0.5 Hz for 128 × 128 pixels. A cantilever with L = 10 µm was used to image the surface of cleaved and bleached nacre, a high-performance biomineralized material from sea shells (Schäffer et al, 1997). The motion of calcite crystal step edges (Walters Viani et al (1999), by permission of the American Institute of Physics.…”

Section: Biological Applicationsmentioning

confidence: 99%

“…Standard commercial microscope objectives easily achieve such numerical apertures and can be used for generating small spots, but their large physical size makes them not optimal for use in an AFM setup that should be mechanically as rigid and compact as possible. Using raytracing software, a compact lens system with small spherical aberrations was designed that provides a nearly diffraction-limited spot diameter of about 1.6 µm (Schäffer et al, 1997).…”

Section: Small Focused Spot Sizementioning

confidence: 99%

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