Interfacing Biomolecules, Cells and Tissues with Nanowire-based Electrical Devices - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 89

top-down NW FETs by another group with high S/N and millivolts
amplitudes, 45a but not on bottom-up NW or CNT FETs.
Embryonic chicken cardiomyocytes were cultured on 100-500
Pm thick rectangular pieces of PDMS to form cell monolayers,
and then the PDMS/cardiomyocyte substrate was transferred into a
well, which contains extracellular medium, over a NWFET chip
fabricated on a standard substrate ( Fig. 7a-d ). PDMS/cardiomyo-
cyte cell substrates were positioned using a x-y-z manipulator un-
der an optical microscope to bring spontaneously beating cells into
direct contact with the NWFETs ( Fig. 7e ). This approach enabled
to manipulate the PDMS/ cells substrate independently of the
NWFET chip and to contact specific monolayer regions with spe-
cific devices, and subsequently change the region that is being
monitored with the NWFETs. Notably, the ability to identify and
register specific cellular regions over NWFET elements has not
been demonstrated previously for either planar or nanoscale FET
where cells have been cultured directly over device chips.
Measurement of the conductance versus time from a Si
NWFET in contact with a spontaneously beating cardiomyocyte
cell monolayer ( Fig. 7f ) yields regularly spaced peaks with a fre-
quency of ca. 1.5 Hz and S/N 4. Signal amplitudes that were
tuned by varying device sensitivity through changes in water gate-
voltage potential, V g , showed an average calibrated voltage of 2.8
± 0.5 mV. The calibration was further illustrated by data recorded
with V g values from -0.5 to 0.1 V ( Fig. 7g ), where the conduct-
ance signal amplitudes decrease from 31 to 7 nS, respectively, but
the calibrated voltage, 2.9 ± 0.3 mV, remained unchanged, indicat-
ing a robust NWFET/cell interface.
Signal amplitude was further increased by using a micropi-
pette to displace the PDMS/cells substrate at a fixed distance to-
wards the device, Figs. 7h and 7i . A direct comparison of single
peaks recorded for different ¨Z values shows a consistent mono-
tonic increase in peak amplitudes without any observable change
in peak shape or peak width over >2x change in amplitude, and
that the peak width is consistent with time-scales for ion fluxes
associated with ion-channel opening/closing 28a . A plot of the ex-
perimental results ( Fig. 7j ) summarizes the systematic 2.3-fold
increase in conductance and calibrated voltage peak amplitude,
and moreover, demonstrates that these amplitude changes are re-
versible for increasing and decreasing PDMS/cells displacement.