Biomedical Engineering Reference
In-Depth Information
d
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t
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Figure 5.16
Schematic representation of the SKN detection principle for a neuron cell
culture. The probe vibrates at a distance d
0
,withanamplituded
1
over the
cells which are grown on a gold substrate. The presence of the neurons
alters the gold work function by a potential difference reflecting the
dielectric characteristics of the cell membrane and cytoplasm. The detected
Kelvin current, i(t), is very sensitive to any change in the metabolic state of
the neurons. A is the area of the probe, V
0
is the external backing variable
voltage, U is the voltage difference that reflects the dielectric properties of
cell layer and the contribution of the image force potential, d
1
is the
amplitude of the vibration and d
0
is the rest position of the probe; DF is
the work function and I is the thickness of neuron layer.
22
(Reprinted by kind permission of the Royal Society of Chemistry.)
n
3
.
hypothalamic mouse neurons were deposited on the gold electrode of a TSM
device much as described above in the section on acoustic wave sensors. For
this experiment, substrates were prepared using gold-covered silicon wafers
upon which a protein matrix of laminin and fibronectin in DMEM were used to
provide an appropriate surface for cellular adherence.
22
Immortalized hypo-
thalamic N-38 undifferentiated neurons were first separated from the main
frozen culture and grown in a flask in DMEM supplemented with 5% fetal
bovine serum (GIBCO). These were then left in an incubation chamber for 4 h
at 37 1C under 5% CO
2
for cells to deposit and attach by gravity. After this
time, a complete medium change was required to remove DMSO from the cell
culture. DMSO was present in the initial cell culture to enable faster freezing
and thawing during storage. When a substantial population was obtained, the
cells in the culture medium were added to the gold surfaces separated in plastic
Petri dishes. Usually the cell culture achieves 90-100% surface coverage in 48 h
and is fully differentiated. There is an optimum surface coverage related to
dendritic connection formation and to the fact that neurons prefer a less
crowded surface in cultures.
SKN measurements can be performed in both scanning and in localized, real-
time measurement modes. Figure 5.17(a) confirms the stability of the scanned
signal obtained from the bare gold surface in liquid.
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When there are neurons
on the surface, the scan (Figure 5.17(b)) shows a dramatic variation in the
potential (
550 mV). This change can be ascribed to the complex distribution
of charges and dielectric dipoles on the surface of the cell. If the cells are
B
