Iridium oxide nanotube electrodes for sensitive and prolonged intracellular measurement of action potentials

Abstract

Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive, and large scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes made up of nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow center. We show that this geometry enhances cell-electrode coupling and results in measuring much larger intracellular action potentials. The nanotube electrodes afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the electrode performance can be significantly improved by optimizing the electrode geometry.

Accurate nanoelectrode recording of human pluripotent stem cell-derived cardiomyocytes for assaying drugs and modeling disease

“…Using electron microscopy, we observed that the cardiomyocytes engulfed the nanopillars underneath them (Figure 1c). At the same time, we did not observe any mechanical penetration of the cells by these nanopillars, which agrees with our previous findings and those of others 15,16,20 .…”

“…The method of intracellular recording after electroporation is applicable for hESC-CMs (Figure 1e), hiPSC-CMs (Figure 1f), and mouse HL-1 cells (Figure 1g). For the hESC-CMs, we achieved a maximum intracellular action potential amplitude of 25.15 mV (Figure 1h), which is only approximately three times attenuated from the full amplitude recorded by patch clamp 18 and larger than any previous chip-based nanoelectrode recording of mouse HL-1 cardiomyocytes 15,16 . With a peak-to-peak noise level of 30 μV pp , we achieved a signal-to-noise ratio of 838 over a 5 kHz bandwidth.…”

“…After electroporation, we observed a dramatic amplitude increase and a signal shape that matches that of patch clamp-recorded intracellular action potentials. The magnitude of this increase in amplitude is variable and depends upon how the cells engulf the nanopillars 16 . The method of intracellular recording after electroporation is applicable for hESC-CMs (Figure 1e), hiPSC-CMs (Figure 1f), and mouse HL-1 cells (Figure 1g).…”

“…To achieve intracellular recording, we sent in a train of voltage pulses via the nanopillars to create nanometer sized holes in the basal cell membrane surrounding the nanopillars 15,16 . After electroporation, we observed a dramatic amplitude increase and a signal shape that matches that of patch clamp-recorded intracellular action potentials.…”

“…The nanopillar electrode array platform recently developed by our group and others [15][16][17] offers the opportunity to measure, in multiplex, intracellular action potentials of single cardiomyocytes in a beating, confluent monolayer. This measurement could yield the information relevant to pre-clinically monitor drug cardiotoxicity 3 , track cardiomyocyte maturation, and perform any variety of experiments enabled by multi-day current clamp-like measurements.…”