Interfacing Biomolecules, Cells and Tissues with Nanowire-based Electrical Devices - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 84

a beating heart. 41 Recording electrical signals in vitro and in vivo
from whole hearts is applied in areas ranging from basic studies of
cardiac function to patient healthcare. 42 Different techniques are
used across the surface of the heart to examine cardiac dysfunction
such as arrhythmia, 42,26c including macroscale metallic electrodes,
42 optical microscopy of dyed tissue, 26c or multielectrode arrays
(MEAs), but all suffer from relatively low resolution signals that in
part is related to their being planar rigid structures that cannot con-
form to organs, such as the heart, which are intrinsically three-
dimensional (3D) soft objects.
NW and nanotube device arrays, besides being exquisite sen-
sors, can be fabricated on flexible and transparent polymer sub-
strates, 18a, 18b allowing the chip to bent and conform to 3D curved
surfaces.
In this work, electrical recordings from whole embryonic
chicken hearts were recorded using p-type NWFET arrays in both
planar and bent conformations, Fig. 6A . Initially, planar NWFET
chip configuration was used to record a freshly isolated heart. Af-
ter a brief period of equilibration with medium, hearts beat sponta-
neously at a typical frequency of 1-3 Hz. Signals were recorded
simultaneously from the NWFET and from a conventional glass
pipette inserted into the heart, showing close temporal correlation
between peaks, with ca. 100 ms consistent time difference between
pipette and NW peaks since the pipette was inserted into a spatial-
ly remote region with respect to the NWFET devices, Fig. 6Ba .
Examination of individual NW signals revealed a peak shape with
a fast initial phase (full width at half maximum, FWHM = 6.8 ±
0.7 ms) followed by a slower phase (FWHM = 31 ± 9 ms), corre-
sponding to transient ion channel current and mechanical motion,
respectively. NW-FET signals were reproducible, with the chips
being stable for multiple experiments, exhibiting excellent S/N.
However, the voltage calibrated for these peaks depend on the de-
vice transconductance, that is, the water gate potential being ap-
plied which determines the sensitivity of the device, G/ Vg . While
the conductance of the fast transient decreased from ca. 55 to 11
nS with the water gate varied from -0.4 to 0.4 V ( Fig. 6Bc ) in cor-
relation with the decrease in device sensitivity, the voltage-
calibrated signal determined using the device transconductance
was essentially constant at 5.1 ± 0.4 mV for this same variation of
water gate voltage. These results confirm the stability of the inter-