Biomedical Engineering Reference
In-Depth Information
their normal attachment phenotype on the QCM surface. To do this, the cell relies upon its
internal cytoskeleton attached via integrin cell surface receptors to its underlying ECM.
The multiple important components of the complex signal transduction system in the
biosensor are shown labeled in Figure 33B, which represents a schematic of individual ECs
attached to their ECM on the gold surface of the QCM biosensor. Small molecule drugs
that disrupt different components of this cellular structure, the cytoskeleton, the ECM, or
their integrin-mediated connectivity would be expected to have major effects upon the cell
QCM biosensor frequency and motional resistance values. To test the validity of this
hypothesis, we examined the small molecule drug nocodazole. The cellular targets of
nocodazole are the tubulin dimer components that comprise the majority of the mass of
the intracellular microtubules. Microtubules are long protein polymer structural compo-
nents of the cellular cytoskeleton that are required to maintain the spread state of the cell
following attachment to a surface. Upon binding, nocodazole is known from other studies
to cause dissociation of the microtubules (97).
Given the significant effect of nocodazole on the cellular cytoskeleton, we used the EC
QCM biosensor to examine the effect of adding varying nocodazole concentrations upon
the biosensor's frequency and motional resistance values (96). In Figure 1.34, we show the
significant detection capability of the biosensor when 2
M nocodazole was added (second
arrowhead) to a steady-state population of 20,000 cells on the biosensor surface. In forming
the biosensor, there was a rapid decrease in the frequency magnitude and increase in
motional resistance, from the values the attached cells exhibited immediately after addition
to the constant values after about 20 h. The 20 h constant values represented the steady state
of cell attachment characteristic of the biosensor that we used in all the nocodazole experi-
ments. The response to 2
M nocodazole addition at 22 h (second arrowhead) is shown to
be significant in magnitude. In different experiments between 0.11 and 15
M nocodazole,
we observed the frequency values of this biosensor to decrease significantly in magnitude,
100
250
2.0 µ m Nocodazole
ECs added
0
200
R
100
200
150
300
100
400
500
50
600
700
0
f
800
50
900
0
5
10
15
t (h)
20
25
30
FIGURE 1.34
Time-dependent
R behavior of the cell QCM biosensor created by the addition of 20,000 ECs at the first
arrowhead. After establishing stable steady-state properties, nocodazole was added to the biosensor at the sec-
ond arrowhead to a final concentration of 2
f and
M. Reprinted from Marx, K.A., Zhou, T., Montrone, A., Schulze, H.,
Braunhut, S. J. (2001). A Quartz Crystal Microbalance Cell Biosensor: Detection of Microtubule Alterations in
Living Cells at nM Nocodazole Concentrations. Biosen. Bioelectron. 16:773-782. With permission from Elsevier
Publishing.
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