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

Duan X, Gao R, Xie P, Cohen-Karni T, Qing Q, Choe HS, Tian B, Jiang X, Lieber CM - Nat Nanotechnol (2011)

Bottom Line: Field-effect transistors (FETs) can also record electric potentials inside cells, and because their performance does not depend on impedance, they can be made much smaller than micropipettes and microelectrodes.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 well below that accessible with other methods.We also show that multiple BIT-FETs can record multiplexed intracellular signals from both single cells and networks of cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.

ABSTRACT
The ability to make electrical measurements inside cells has led to many important advances in electrophysiology. 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. 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, which limits how small the micropipette can be. Techniques that involve inserting metal or carbon microelectrodes into cells are subject to similar constraints. Field-effect transistors (FETs) can also record electric potentials inside cells, and because their performance does not depend on impedance, 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, but the kink configuration and device design places limits on the probe size and the potential for multiplexing. Here, we report a new approach in which a SiO2 nanotube is synthetically integrated on top of a nanoscale FET. This nanotube penetrates the cell membrane, bringing the cell cytosol into contact with the FET, which is then able to record the 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 well below that accessible with other methods. Studies of cardiomyocyte cells demonstrate that when phospholipid-modified BIT-FETs are brought close to cells, the nanotubes can spontaneously penetrate the cell membrane to allow the full-amplitude intracellular action potential to be recorded, thus showing that a stable and 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.

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Water gate characterization and bandwidth analysisa, SEM image of a BIT-FET device (S-D1) and control device (S-D2). b and c, Water gate, Vwg, responses prior to and after GeNW etching, respectively. Blue, (S-D1); red, (S-D2). d, pulsed Vwg with 0.1 ms rise/fall time, 1 ms duration and 100 mV amplitude (upper), and the corresponding conductance change of a BIT-FET device (black, lower). The red trace is the pure field-effect response after removing the capacitive signals of the passivated metal electrodes (see Supplementary Methods). e, baseline to plateau conductance change of the same BIT-FET device as in d versus pulse rise/fall time. The change was measured as an average over data 0.2-0.5 ms after the start of the pulse. Pulse amplitude was kept at 100 mV, and duration was ten times the rise/fall time in all measurements. f, Calculated bandwidth of the BIT-FET device versus nanotube inner diameter (ALD SiO2 thickness was the same as the nanotube inner diameter, and the nanotube length was fixed at 1.5 μm). The black and red symbols correspond to upper and lower limits, respectively (see Supplementary Methods). Inset, calculated change of the potential at the SiNW FET surface Vn (normalized with the step change V0 of potential at the nanotube opening) versus time.
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Figure 2: Water gate characterization and bandwidth analysisa, SEM image of a BIT-FET device (S-D1) and control device (S-D2). b and c, Water gate, Vwg, responses prior to and after GeNW etching, respectively. Blue, (S-D1); red, (S-D2). d, pulsed Vwg with 0.1 ms rise/fall time, 1 ms duration and 100 mV amplitude (upper), and the corresponding conductance change of a BIT-FET device (black, lower). The red trace is the pure field-effect response after removing the capacitive signals of the passivated metal electrodes (see Supplementary Methods). e, baseline to plateau conductance change of the same BIT-FET device as in d versus pulse rise/fall time. The change was measured as an average over data 0.2-0.5 ms after the start of the pulse. Pulse amplitude was kept at 100 mV, and duration was ten times the rise/fall time in all measurements. f, Calculated bandwidth of the BIT-FET device versus nanotube inner diameter (ALD SiO2 thickness was the same as the nanotube inner diameter, and the nanotube length was fixed at 1.5 μm). The black and red symbols correspond to upper and lower limits, respectively (see Supplementary Methods). Inset, calculated change of the potential at the SiNW FET surface Vn (normalized with the step change V0 of potential at the nanotube opening) versus time.

Mentions: We have characterized the electrical properties of the BIT-FETs and several control devices in solution to elucidate the behavior of this new device architecture. A SEM image (Fig. 2a) shows a representative two-FET structure, where a BIT-FET and conventional FET with similar channel length were fabricated with a common S electrode on the same SiNW. In both devices, the SiNW and electrodes exposed to solution are passivated with about 50 nm ALD SiO2 as described above. Measurements of conductance (G) for both devices as a function of water-gate voltage (Vwg) prior to etching the GeNW core of the BIT-FET (Fig. 2b) show very little change, with sensitivity of ca. -170 nS/V. Significantly, measurements made on the same devices after removal of the GeNW core to yield an open nanotube structure (Fig. 2c), demonstrate a large increase in the sensitivity of the BIT-FET to -4530 nS/V, while the control SiNW FET shows no change. Taken together these results validate that BIT-FET devices respond selectively and with high-sensitivity to the solution inside vs. outside the nanotubes, and thus meet the requirements for intracellular recording outlined schematically in Fig. 1a. The difference in sensitivity of the BIT-FET devices to solution inside vs. outside the nanotubes originates primarily from the gate capacitance difference11,12. Specifically, Ge over-coating on the SiNW may lead to a larger contact area between the SiNW and the internal solution of the nanotube (the active FET area) than defined by the nanotube inner diameter, which can increase this sensitivity difference (see Supplementary Methods).


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

Duan X, Gao R, Xie P, Cohen-Karni T, Qing Q, Choe HS, Tian B, Jiang X, Lieber CM - Nat Nanotechnol (2011)

Water gate characterization and bandwidth analysisa, SEM image of a BIT-FET device (S-D1) and control device (S-D2). b and c, Water gate, Vwg, responses prior to and after GeNW etching, respectively. Blue, (S-D1); red, (S-D2). d, pulsed Vwg with 0.1 ms rise/fall time, 1 ms duration and 100 mV amplitude (upper), and the corresponding conductance change of a BIT-FET device (black, lower). The red trace is the pure field-effect response after removing the capacitive signals of the passivated metal electrodes (see Supplementary Methods). e, baseline to plateau conductance change of the same BIT-FET device as in d versus pulse rise/fall time. The change was measured as an average over data 0.2-0.5 ms after the start of the pulse. Pulse amplitude was kept at 100 mV, and duration was ten times the rise/fall time in all measurements. f, Calculated bandwidth of the BIT-FET device versus nanotube inner diameter (ALD SiO2 thickness was the same as the nanotube inner diameter, and the nanotube length was fixed at 1.5 μm). The black and red symbols correspond to upper and lower limits, respectively (see Supplementary Methods). Inset, calculated change of the potential at the SiNW FET surface Vn (normalized with the step change V0 of potential at the nanotube opening) versus time.
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Figure 2: Water gate characterization and bandwidth analysisa, SEM image of a BIT-FET device (S-D1) and control device (S-D2). b and c, Water gate, Vwg, responses prior to and after GeNW etching, respectively. Blue, (S-D1); red, (S-D2). d, pulsed Vwg with 0.1 ms rise/fall time, 1 ms duration and 100 mV amplitude (upper), and the corresponding conductance change of a BIT-FET device (black, lower). The red trace is the pure field-effect response after removing the capacitive signals of the passivated metal electrodes (see Supplementary Methods). e, baseline to plateau conductance change of the same BIT-FET device as in d versus pulse rise/fall time. The change was measured as an average over data 0.2-0.5 ms after the start of the pulse. Pulse amplitude was kept at 100 mV, and duration was ten times the rise/fall time in all measurements. f, Calculated bandwidth of the BIT-FET device versus nanotube inner diameter (ALD SiO2 thickness was the same as the nanotube inner diameter, and the nanotube length was fixed at 1.5 μm). The black and red symbols correspond to upper and lower limits, respectively (see Supplementary Methods). Inset, calculated change of the potential at the SiNW FET surface Vn (normalized with the step change V0 of potential at the nanotube opening) versus time.
Mentions: We have characterized the electrical properties of the BIT-FETs and several control devices in solution to elucidate the behavior of this new device architecture. A SEM image (Fig. 2a) shows a representative two-FET structure, where a BIT-FET and conventional FET with similar channel length were fabricated with a common S electrode on the same SiNW. In both devices, the SiNW and electrodes exposed to solution are passivated with about 50 nm ALD SiO2 as described above. Measurements of conductance (G) for both devices as a function of water-gate voltage (Vwg) prior to etching the GeNW core of the BIT-FET (Fig. 2b) show very little change, with sensitivity of ca. -170 nS/V. Significantly, measurements made on the same devices after removal of the GeNW core to yield an open nanotube structure (Fig. 2c), demonstrate a large increase in the sensitivity of the BIT-FET to -4530 nS/V, while the control SiNW FET shows no change. Taken together these results validate that BIT-FET devices respond selectively and with high-sensitivity to the solution inside vs. outside the nanotubes, and thus meet the requirements for intracellular recording outlined schematically in Fig. 1a. The difference in sensitivity of the BIT-FET devices to solution inside vs. outside the nanotubes originates primarily from the gate capacitance difference11,12. Specifically, Ge over-coating on the SiNW may lead to a larger contact area between the SiNW and the internal solution of the nanotube (the active FET area) than defined by the nanotube inner diameter, which can increase this sensitivity difference (see Supplementary Methods).

Bottom Line: Field-effect transistors (FETs) can also record electric potentials inside cells, and because their performance does not depend on impedance, they can be made much smaller than micropipettes and microelectrodes.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 well below that accessible with other methods.We also show that multiple BIT-FETs can record multiplexed intracellular signals from both single cells and networks of cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.

ABSTRACT
The ability to make electrical measurements inside cells has led to many important advances in electrophysiology. 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. 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, which limits how small the micropipette can be. Techniques that involve inserting metal or carbon microelectrodes into cells are subject to similar constraints. Field-effect transistors (FETs) can also record electric potentials inside cells, and because their performance does not depend on impedance, 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, but the kink configuration and device design places limits on the probe size and the potential for multiplexing. Here, we report a new approach in which a SiO2 nanotube is synthetically integrated on top of a nanoscale FET. This nanotube penetrates the cell membrane, bringing the cell cytosol into contact with the FET, which is then able to record the 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 well below that accessible with other methods. Studies of cardiomyocyte cells demonstrate that when phospholipid-modified BIT-FETs are brought close to cells, the nanotubes can spontaneously penetrate the cell membrane to allow the full-amplitude intracellular action potential to be recorded, thus showing that a stable and 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.

Show MeSH