Biology Reference
In-Depth Information
much narrower area to be scanned by AFM. Further, luorescence microscopy
provides complimentary information to high-speed AFM images, such as the
identiication of proteins observed by high-speed AFM, the simultaneous
recording of topographic changes in protein molecules and optical signals for
chemical reactions such as ATP hydrolysis.
In current high-speed AFM, a raster scanning is carried out by moving the
sample stage relatively to the ixed cantilever. In this design, the sample stage
should be very small so that the resonant frequency of the
-scanner is not
lowered. For simultaneous optical and AFM imaging, a stand-alone AFM, in
which the cantilever is scanned relative to the ixed sample, has to be adapted
to ensure optical transparency of the sample stage. Micro-electro-mechanical
fabrication techniques, which have been employed to produce self-sensing
and/or self-actuation cantilevers
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and sensor-combined scanners,
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could be
the key to the realization of a combined system as well as to the signiicant
enhancement of high-speed AFM performance.
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8.4.3 High-Speed AFM for Intracellular Imaging
Recently, it has been reported that AFM can have a capability of subsurface
imaging.
This new modal AFM is called scanning near-ield ultrasound
holography (SNFUH) and has been successfully used for intracellular imaging
under ambient conditions.
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In its application, a high-frequency acoustic wave
is launched from under the sample stage and propagates through the sample.
Materials embedded in the sample with different elastic moduli modulate the
phase and amplitude of the propagating acoustic wave. These modulations
affect the nonlinear acoustic interference that occurs at the cantilever tip
excited with another high-frequency acoustic wave with different frequency.
The interference produces a wave with a frequency corresponding to their
frequency difference. By adjusting the frequency difference to the cantilever
resonant frequency, the cantilever is effectively oscillated by the nonlinear
acoustic interference. SNFUH has no resolution in the
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-direction. However,
using multiple images obtained from different launching angles of the
ultrasonic wave, it is probably possible to reconstitute a 3D image. Combining
SNFUH with high-speed scanning techniques will enable the high-resolution
3D imaging of various intracellular processes in live cells which take place
spontaneously or as a result of their responses to extracellular stimuli.
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8.5 SUMMARY
We have described various studies on the instrumentation and imaging
of biomolecules carried out in the last decade. The direct and real-time
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