Intracellular action potential recordings from cardiomyocytes by ultrafast pulsed laser irradiation of fuzzy graphene microelectrodes

Abstract

Graphene with its unique electrical properties is a promising candidate for carbon-based biosensors such as microelectrodes and field effect transistors. Recently, graphene biosensors were successfully used for extracellular recording of action potentials in electrogenic cells; however, intracellular recordings remain beyond their current capabilities because of the lack of an efficient cell poration method. Here, we present a microelectrode platform consisting of out-of-plane grown three-dimensional fuzzy graphene (3DFG) that enables recording of intracellular cardiac action potentials with high signal-to-noise ratio. We exploit the generation of hot carriers by ultrafast pulsed laser for porating the cell membrane and creating an intimate contact between the 3DFG electrodes and the intracellular domain. This approach enables us to detect the effects of drugs on the action potential shape of human-derived cardiomyocytes. The 3DFG electrodes combined with laser poration may be used for all-carbon intracellular microelectrode arrays to allow monitoring of the cellular electrophysiological state.

Fig. 1. 3DFG SEM imaging and optical characterization.

(A) SEM images of 5-μm 3DFG electrodes. Scale bars, 5 μm (I), 1 μm (II), and 0.5 μm (III). (B) UV-vis absorbance as a function of wavelength for fused silica (gray), 3DFG synthesized at 800°C for 10 min (red), and 3DFG synthesized at 800°C for 30 min (blue). (C) Real (ε₁) and imaginary (ε₂) parts of the dielectric constant of 3DFG in the visible and near-infrared range. (D) Photocurrent generated at the interface between 3DFG electrodes and PBS under excitation with ultrafast (picosecond) pulsed laser at 1064 nm at varying laser intensities. The pulse trains have a duration of 6 ms. (E) Capacitive and faradaic current components of the photocurrent generated by laser excitation. The capacitive values were taken as the maximum current peak at the onset of the laser excitation. The faradaic values were calculated as the average of the last 1-ms-long portion before the end of the laser pulse train.

Fig. 2. 3DFG MEA–cardiomyocyte interface.

(A) Bright-field (I and III) and immunofluorescence images (II and IV) of hiPSC-CMs cultured on 3DFG-MEAs for 7 days in vitro. Scale bars, 100 μm (I and II) and 50 μm (II and IV). (B) False-colored SEM images of hiPSC-CMs on 3DFG MEAs. Scale bars, 5 μm. (C) Cross-sectional SEM images of HL-1 cells on 3DFG. The right image shows the cell nucleus in green, the cytoplasm in blue, and 3DFG in red. Scale bars, 2 μm.

Fig. 3. Electrophysiological recordings.

(A) Representative extracellular FP recording of hiPSC-CMs using 3DFG-MEA with 50-μm electrodes (n = 80 electrodes). (B) Representative intracellular AP recording on 3DFG-MEA with 50-μm electrodes after optoporation (n = 70 electrodes). (C) Time stability of the intracellular coupling after optoporation with the cellular membrane reforming and the extracellular FP reappearing in the signal. On the right, the cardiomyocyte is excited a second time with laser, which produces new pores and recovers the intracellular AP recording.

Fig. 4. Compound effects on cardiomyocytes.

(A) Representative cardiac FPs (red trace) and APs (blue trace) after administration of 2 μM E-4031. The AP trace shows the presence of EADs after the main repolarization phase of the APs. (B) Representative cardiac APs before and after administration of nifedipine at various concentrations. (C) Representative cardiac APs before and after administration of 100 nM dofetilide (DOF). REF, reference signal in physiological conditions.