Synthetically Encoded
Ultrashort-Channel Nanowire
Transistors for Fast, Pointlike Cellular Signal Detection
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Abstract
Nanostructures, which have sizes comparable to biological
functional
units involved in cellular communication, offer the potential for
enhanced sensitivity and spatial resolution compared to planar metal
and semiconductor structures. Silicon nanowire (SiNW) field-effect
transistors (FETs) have been used as a platform for biomolecular sensors,
which maintain excellent signal-to-noise ratios while operating on
lengths scales that enable efficient extra- and intracellular integration
with living cells. Although the NWs are tens of nanometers in diameter,
the active region of the NW FET devices typically spans micrometers,
limiting both the length and time scales of detection achievable with
these nanodevices. Here, we report a new synthetic method that combines
gold-nanocluster-catalyzed vapor–liquid–solid (VLS)
and vapor–solid–solid (VSS) NW growth modes to produce
synthetically encoded NW devices with ultrasharp (<5 nm) n-type
highly doped (n<sup>++</sup>) to lightly doped (n) transitions along
the NW growth direction, where n<sup>++</sup> regions serve as source/drain
(S/D) electrodes and the n-region functions as an active FET channel.
Using this method, we synthesized short-channel n<sup>++</sup>/n/n<sup>++</sup> SiNW FET devices with independently controllable diameters
and channel lengths. SiNW devices with channel lengths of 50, 80,
and 150 nm interfaced with spontaneously beating cardiomyocytes exhibited
well-defined extracellular field potential signals with signal-to-noise
values of ca. 4 independent of device size. Significantly, these “pointlike”
devices yield peak widths of ∼500 μs, which is comparable
to the reported time constant for individual sodium ion channels.
Multiple FET devices with device separations smaller than 2 μm
were also encoded on single SiNWs, thus enabling multiplexed recording
from single cells and cell networks with device-to-device time resolution
on the order of a few microseconds. These short-channel SiNW FET devices
provide a new opportunity to create nanoscale biomolecular sensors
that operate on the length and time scales previously inaccessible
by other techniques but necessary to investigate fundamental, subcellular
biological processes