Intracellular recordings of action potentials by an extracellular nanoscale field-effect transistor

The ability to make electrical measurements inside cells has led to many important advances in electrophysiology(1-6). The patch clamp technique, in which a glass micropipette filled with electrolyte is inserted into a cell, offers both high signal-to-noise ratio and temporal resolution(1,2). Ideally the micropipette should be as small as possible to increase the spatial resolution and reduce the invasiveness of the measurement, but the overall performance of the technique depends on the impedance of the interface between the micropipette and the cell interior(1,2), which limits how small the micropipette can be. Techniques that involve inserting metal or carbon microelectrodes into cells are subject to similar constraints(4,7-9). Field-effect transistors (FETs) can also record electric potentials inside cells(10), and since their performance does not depend on impedance(11,12), they can be made much smaller than micropipettes and microelectrodes. Moreover, FET arrays are better suited for multiplexed measurements. Previously we have demonstrated FET-based intracellular recording with kinked nanowire structures(10), but the kink configuration and device design places limits on the probe size and the potential for multiplexing. Here we report a new approach where a SiO(2) nanotube is synthetically integrated on top of a nanoscale FET. After penetrating the cell membrane, the SiO(2) nanotube brings the cell cytosol into contact with the FET and enables the recording of intracellular transmembrane potential. Simulations show that the bandwidth of this branched intracellular nanotube FET (BIT-FET) is high enough for it to record fast action potentials even when the nanotube diameter is decreased to 3 nm, a length scale which is well below that accessible with other methods(1,2,4). Studies of cardiomyocyte cells demonstrate that when brought close, the nanotubes of phospholipid-modified BIT-FETs spontaneously penetrate the cell membrane to yield stable, full-amplitude intracellular action potential recording, showing that a stable tight seal forms between the nanotube and cell membrane. We also show that multiple BIT-FETs can record multiplexed intracellular signals from both single cells and networks of cells.