Relying on the local readout of minute electric currents within neurons and nerve cells, one way to improve electrophysiological human-machine interfaces, is to increase the resolution (both spatial and temporal) of the probes in use, moving from micrometer-sized devices to nanometre-sized probes.
Following this trend, a team of researchers from the University of Surrey and Harvard University have devised U-shaped nanowire field-effect transistor (U-NWFET) arrays, using a scalable production process whereby they could accurately tune the probes’ geometry. Because they could modulate the location, size and geometry of each probe (including the radii of curvature and the length of the FET sensing elements at the tips of the U-shaped nanowire probes), the researchers were able to systematically investigate how these parameters influenced intracellular electrophysiological recordings. Playing with various process parameters, they went on fabricating arrays of U-NWFET probes ranging from 15nm-diameter p-type Si nanowires with radii of curvature ranging from 0.75 to 2μm and active channel lengths from 50 to 2,000nm and then used them to probe cultured primary neurons and human cardiomyocytes.
The results published in a Nature Nanotechnology paper under the title “Scalable ultrasmall three-dimensional nanowire transistor probes for intracellular recording” revealed comparable recording signal-to-noise ratio and amplitude to those of patch clamp measurements, with the capability to record full amplitude intracellular action potentials from primary neurons and other electrogenic cells, while also offering the possibility to perform multiplexed recordings (with multiple wire tips of different curvatures).
“Our ultra-small, flexible, nanowire probes could be a very powerful tool as they can measure intracellular signals with amplitudes comparable with those measured with patch clamp techniques; with the advantage of the device being scalable, it causes less discomfort and no fatal damage to the cell (cytosol dilation). Through this work, we found clear evidence for how both size and curvature affect device internalisation and intracellular recording signal”, commented Dr Yunlong Zhao from the Advanced Technology Institute at the University of Surrey, lead author of the article.
“This work represents a major step towards tackling the general problem of integrating ‘synthesized’ nanoscale building blocks into chip and wafer scale arrays, and thereby allowing us to address the long-standing challenge of scalable intracellular recording” added co-author Professor Charles Lieber from the Department of Chemistry and Chemical Biology at Harvard University.