Biomedical Engineering Reference
In-Depth Information
Next, we investigated the dynamics of the EC QCM biosensor response by studying the
kinetics of the frequency decrease in individual experiments at increasing nocodazole con-
centrations. Over the entire drug range, for each experiment the frequency decrease
remaining as a function of time measured by the EC QCM biosensor was found to possess
similar kinetics and was well fit by a single exponential decay equation. We present an
example of these single exponential fit data for 2
M nocodazole in Figure 1.36 (101). For
all the nocodazole doses studied,
t
0.5
, the time to reach half the total signal change, was
invariant, averaging
t
0.5
0.83
0.14 h. The exponential decay was 99% complete by
t
0.99
0.93 h, on average. The functional dependence of these data demonstrated that a
single dynamic sensing system within the cell, the microtubules, responded to the addi-
tion of nocodazole. This fact was confirmed by a fluorescence light microscopy investiga-
tion of the cells with increasing nocodazole dose, using a fluorescent antibody to tubulin.
Finally, reversibility of the cell QCM biosensor was demonstrated after a number of hours
by the return of the frequency and motional resistance shifts to their original values before
drug addition. And in another example of the cell QCM biosensor's versatility, this involv-
ing cell growth, we demonstrated that the effect of adding fibroblast growth factor protein
to stimulate ECs to grow could be followed continuously for up to 4 days (92).
These results indicated that the EC QCM biosensor could be used to detect and study
cytoskeletal alterations and dynamics. More broadly, we have previously suggested the
novel use of this class of cell QCM biosensor for the real-time identification or screening of
all classes of biologically active small-molecule drugs or biological macromolecules that
affect cellular attachment, regardless of their molecular mechanism of action (96,98). For
example, different cell types could be used that would make the biosensor more sensitive to
particular cytoskeleton-affecting drugs or classes of drugs. In a drug screening type of for-
mat, cell QCM biosensors could be studied comparing the response of a wild-type cell with
5.52
0
t
0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
t
(h)
FIGURE 1.36
The logarithm of the fraction of remaining
f
change, log[(
f
t
-
f
infinity
)/(
f
0
-
f
infinity
)], is plotted for 1-min interval
measurements as a function of time for the EC QCM biosensor following addition of 2
M nocodazole. A single
exponential decay fit to the data is presented, as is the position of the calculated half-time for the single expo-
nential decay,
t
0.5
. Reprinted from Marx, K.A., Zhou, T., Montrone, A., Braunhut, S. J. (2002). A Quartz Crystal
Microbalance Cell Biosensor: Detecting Nocodazole Dependent Microtubule Disruption Dynamics in Living
Cells.
Adv. Biomater. Character. Tissue Eng. Complex., Mater. Res. Soc.
711:125-132. With permission from the
Materials Research Society.
