Interfacing Biomolecules, Cells and Tissues with Nanowire-based Electrical Devices - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 95

ver, when interfacing with cells, the FETs process input/output
information without the need for direct exchange with cellular
ions, thus interfacial impedance and biochemical invasiveness to
cells can be minimized. Lastly, it could be integrated for multi-
plexed intracellular measurements.
Recently, it was demonstrated that variation of reactant partial
pressures during the VLS silicon nanowire (SiNW) growth could
introduce reproducible 120 o kinks, 49 and that the junction regions
could be doped to create p-n diodes and FETs. This methodology
was used to create a two-terminal FET probe in a cis crystal con-
formation that could be inserted into single cells by selective in-
situ doping during synthesis to localize the nanoscale FET element
( Figure 8a , magenta segments), and simultaneously wire-up the
FET channel with nanowire S/D components ( Fig. 8a , blue seg-
ments). The authors used heavy n ++ -type doping for the nanowire
S/D arms, and reduced the concentration to light n-type doping to
introduce a short ~200 nm region serving as the FET detector of
the overall probe.
In the next step, an unconventional nanoelectronic device fab-
rication approach was developed to allow these probes to be free
standing. Remote electrical interconnects were made to the S/D
nanowire arms on ultrathin SU-8 polymer ribbons above a sacrifi-
cial layer ( Fig. 8c , upper panel). The interfacial stress between
materials 50 was used to bend the probe upward after a final lift-off
process ( Fig. 8c , lower panel). The acute-angle kinked nanowire
geometry and the extended S/D arms spatially separate the func-
tional nanoscale FET from the bulky interconnects for a minimum
interference by a distance up to ~ 30 Pm, comparable to the size of
single cells. The sensitivity of the 3D nanoscale FET probes was
characterized and found to yield similar sensitivities to kinked
nanowire devices fabricated on planar substrates.
In order to use the 3D nanoFET probes in cells ( Fig. 8e, f ), the
negatively charged SiO 2 surface of the SiNWs was modified with
unilamellar vesicles of phospholipid bilayers, which can fuse with
cell membranes. 51 Examination of the dye-labeled modified probes
revealed a continuous shell on the acute-angle nanoprobes, and
< 1% changes in both the nanoFET conductance and sensitivity.

Initially, phospholipid-modified nanoFET probe was used to
monitor the calibrated
( Fig. 8g

potential change of an isolated HL-1 cell

), clamped by a micropipette to intracellular potential of