Biomedical Engineering Reference
In-Depth Information
related to the rhythms of the planet we live on. Interestingly, the gamma brain
rhythm (higher than 35Hz) can be measured using an electroencephalograph on
pilots when maximally concentrating on landing a plane, but also in the brains
of Buddhist monks who meditate for decades. What is this universal oscillation
at specific frequencies in our brains and in the brain of superior animals?
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5.2.7 The Scanning Kelvin Nanoprobe
Conventionally, a Kelvin probe of the macroscopic kind is used to detect work
function levels in metals or semiconductors—the work function being the
energy necessary to extract an electron from the Fermi level of the material to
infinity. A much greater resolution, high-sensitivity version of the instrument,
termed the scanning Kelvin nanoprobe (SKN), was developed at the University
of Toronto with applications in the field of biophysics in mind.
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The
instrument is capable of imaging both the work function and the topographical
maps for a scanned surface at an extremely high nanometric resolution. The
evidence for the high-sensitivity performance of the instrument came from its
ability to detect molecular events such as a single base mismatch in DNA.
Moreover, it is a non-contact and non-destructive technique that uses low-
intensity electric fields and small amplitude oscillations. As a result, this
technique causes minimal perturbations to the system under observation:
unlike patch-clamp techniques, it is an electrode-less method, does not require
the insertion of probing electrodes into the system under study.
The instrument functions by vibrating a tungsten probe over a neuron or
neuron network grown on a metallic surface connected to the conducting table
which is capable of movement in the X and Y directions (Figure 5.15). The
vibrating probe approaching the neurons vertically, generates a time variant
capacitance resulting in the generation of a Kelvin current, shown as i(t)in
Figure 5.16.
By applying a null current condition, the capacitance voltage can be
determined and the work function of cells can be extracted. In order to examine
the potential of the SKN for the study of neurons,
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Figure 5.15
Non-invasive investigation of neuron response to drugs by scanning
Kelvin nanoprobe technique.
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