Flexible electrical recording from cells using nanowire transistor arrays

Abstract

Semiconductor nanowires (NWs) have unique electronic properties and sizes comparable with biological structures involved in cellular communication, thus making them promising nanostructures for establishing active interfaces with biological systems. We report a flexible approach to interface NW field-effect transistors (NWFETs) with cells and demonstrate this for silicon NWFET arrays coupled to embryonic chicken cardiomyocytes. Cardiomyocyte cells were cultured on thin, optically transparent polydimethylsiloxane (PDMS) sheets and then brought into contact with Si-NWFET arrays fabricated on standard substrates. NWFET conductance signals recorded from cardiomyocytes exhibited excellent signal-to-noise ratios with values routinely >5 and signal amplitudes that were tuned by varying device sensitivity through changes in water gate-voltage potential, V(g). Signals recorded from cardiomyocytes for V(g) from -0.5 to +0.1 V exhibited amplitude variations from 31 to 7 nS whereas the calibrated voltage remained constant, indicating a robust NWFET/cell interface. In addition, signals recorded as a function of increasing/decreasing displacement of the PDMS/cell support to the device chip showed a reversible >2x increase in signal amplitude (calibrated voltage) from 31 nS (1.0 mV) to 72 nS (2.3 mV). Studies with the displacement close to but below the point of cell disruption yielded calibrated signal amplitudes as large as 10.5 +/- 0.2 mV. Last, multiplexed recording of signals from NWFET arrays interfaced to cardiomyocyte monolayers enabled temporal shifts and signal propagation to be determined with good spatial and temporal resolution. Our modular approach simplifies the process of interfacing cardiomyocytes and other cells to high-performance Si-NWFETs, thus increasing the experimental versatility of NWFET arrays and enabling device registration at the subcellular level.

Fig. 1.

Schematic of the experimental approach. (A) NWFET chip, where NW devices are located at central region of chip. The visible linear features (gold) correspond to NW contacts and interconnect metal. Zoom-in showing a source (S) and 2 drain electrodes (D) connected to a vertically oriented NW (green arrow) defining 2 NWFETs. (B) Cardiomyocytes cultured on thin rectangular pieces of PDMS, where the black arrow highlights 1 piece in the culture medium, and the gray arrow indicates 1 piece being removed with tweezers (green). (C) PDMS piece with cultured cells oriented over the device region of NWFET chip. The green needle-like structure indicates the probe used to both manipulate the PDMS/cell substrate to specific NW device locations and to apply local force to the NWFET/cell junction. (D) Schematic view of a cardiomyocyte (black arrow) oriented over a NW (green arrow) FET device.

Fig. 2.

Measurement of cardiomyocyte signals. (A) Photograph of the experimental setup showing the PDMS piece (red dashed box) on top of a NWFET chip within a solution well that is temperature-regulated with an integrated heater (blue arrow). Additional yellow, purple, green, and red arrows highlight positions of the Ag/AgCl reference electrode, solution medium well (length × width × depth = 25–30 × 15–20 × 2 mm³), glass manipulator/force pipette connected to x-y-z manipulator, and plug-in connectors between NWFET interconnect wires and measurement electronics, respectively. (Scale bar, 10 mm.) (B) Representative gate responses of 3 Si NWFET devices. The sensitivity (G/V_g) of the separate devices represented by the green, cyan, and purple traces at V_g = −0.3 V are 13.8, 17.2, and 31.1 nS/mV, respectively. (Inset) Optical microscopy image of a 2 NWFET devices (dashed box) as illustrated schematically in Fig. 1. (Scale bar, 20 μm.) (C) Conductance vs. time traces recorded at V_g = −0.3 V (red) and 0 V (blue) for the same NWFET–cardiomyocyte interface; the device sensitivities at −0.3 and 0 V were 9.2 and 3.5 nS/mV, respectively. (D) Plots of peak conductance amplitude (filled triangles) and calibrated peak voltage amplitude (open squares) vs. V_g; data were obtained from the same experiments shown in C. Error bars correspond to ±1 SD. (E) Conductance vs. time data recorded as PDMS cardiomyocyte substrate was retracted from the NWFET chip (up arrow) and then brought back into contact with the device chip (down arrow).

Fig. 3.

Effect of applied force on recorded signals. (A) Schematic of the experiment illustrating displacement (Z) of the PDMS/cell substrate with respect to a NWFET device; displacement is accomplished with micromanipulator-controlled glass pipette. (B) Two representative traces recorded with ΔZ values of 8.2 μm (blue) and 18.0 μm (red) yield signal amplitudes of 44 ± 3 and 72 ± 4 nS, respectively. The same device was used to record both traces. (C) High-resolution comparison of single peaks recorded with ΔZ values of 0 (purple), 8.2 (blue), 13.1 (green), and 18.0 (red) with a corresponding signal increase from 31 to 72 nS. (D) Summary of the recorded conductance signals and calibrated voltages vs. ΔZ, where the open red circles (filled blue triangles) were recorded for increasing (decreasing) ΔZ; the small offset (within the error of the measurement) between these 2 directions was due to small lateral displacement during the experiment. (E) Data recorded in distinct experiment at large ΔZ close to cell failure with conductance signal amplitude of 299 ± 7 nS and calibrated voltage of 10.5 ± 0.2 mV.

Fig. 4.

Recording from distinct regions of cardiomyocyte monolayers. (A) A patch of beating cells (red dashed oval) over a NWFET (yellow arrow) with sensitivity of 12.8 nS/mV. (Scale bar, 40 μm.) (B) Conductance vs. time signals recorded from the cell patch presented in A. The average signal amplitude is 53.2 ± 4.0 nS. (C) Distinct patch of beating cells (red dashed oval) over a NW device (yellow arrow) with sensitivity of 9.2 nS/mV. (Scale bar, 20 μm.) (D) Conductance vs. time signals recorded from the cells in C. The average signal amplitude is 19.1 ± 3.1 nS.

Fig. 5.

Multiplexed NWFET recording. (A) Optical micrograph showing 3 NWFET devices (NW1, NW2, NW3) in a linear array, where pink indicates the area with exposed NW devices (metal passivated with Si₃N₄) and light green corresponds to the region further passivated with SU8. (Scale bar, 150 μm.) NW1, NW2, and NW3 device sensitivities are 10.9, 10.5, and 17.2 nS/mV, respectively. (B) Representative conductance vs. time signals recorded simultaneously from NW1, NW2, and NW3, where the average signals are 50.2 ± 4.6 (4.6 ± 0.4), 42.5 ± 3.2 (4.0 ± 0.3), and 102 ± 15 nS, (5.9 ± 0.9 mV), respectively. (C) High-resolution comparison of the temporally correlated peaks highlighted by the black dashed box in B. (D) Cross-correlation results from recorded signals in C. The time shifts Δt_1–2, Δt_2–3, and Δt_1–3 correspond to differences between NW1 and 2 (1.5 ms), NW2 and 3 (4.3 ms), and NW1 and 3 (5.9 ms), respectively.