Instrumentation to evaluate neural signal recording properties of micromachined microelectrodes inserted in invertebrate nerve

An Algorithm for Tracking the Position and Velocity of Multiple Neuronal Signals Using Implantable Microelectrodes In Vivo

Increasingly complex multi-electrode arrays for the study of neurons both in vitro and in vivo have been developed with the aim of tracking the conduction of neural action potentials across a complex interconnected network. This is usually performed through the use of electrodes to record from single or small groups of microelectrodes, and using only one electrode to monitor an action potential at any given time. More complex high-density electrode structures (with thousands of electrodes or more) capable of tracking action potential propagation have been developed but are not widely available. We have developed an algorithm taking data from clusters of electrodes positioned such that action potentials are detected by multiple sites, and using this to detect the location and velocity of action potentials from multiple neurons. The system has been tested by analyzing recordings from probes implanted into the locust nervous system, where recorded positions and velocities correlate well with the known physical form of the nerve.

Towards pharmacological treatment screening of cardiomyocyte cells using Si nanowire FETs

Silicon nanowires (Si NWs) are the most promising candidates for recording biological signals due to improved interfacing properties with cells and the possibility of high-speed transduction of biochemical signals into detectable electrical responses. The recording of extracellular action potentials (APs) from cardiac cells is important for fundamental studies of AP propagation features reflecting cell activity and the influence of pharmacological substances on the signal. We applied a novel approach of using fabricated Si NW field-effect transistors (FETs) in combination with fluorescent marker techniques to evaluate the functional activity of cardiac cells. Extracellular AP signal recording from HL-1 cardiomyocytes was demonstrated. This method was supplemented by studies of the pharmacological effects of stimulations using noradrenaline (NorA) as a modulator of functional activity on a cellular and subcellular levels, which were also tested using fluorescent marker techniques. The role of calcium alteration and membrane potential were revealed using Fluo-4 AM and tetramethylrhodamine, methyl ester, perchlorate (TMRM) fluorescent dyes. In addition, chemical treatment with sodium dodecyl sulfate (SDS) solutions was tested. The results obtained demonstrate positive prospects for AP monitoring in different treatments for studies related to a wide range of myocardial diseases using lab-on-chip technology.

A single-cell correlative nanoelectromechanosensing approach to detect cancerous transformation: monitoring the function of F-actin microfilaments in the modulation of the ion channel activity

Cancerous transformation may be dependent on correlation between electrical disruptions in the cell membrane and mechanical disruptions of cytoskeleton structures. Silicon nanotube (SiNT)-based electrical probes, as ultra-accurate signal recorders with subcellular resolution, may create many opportunities for fundamental biological research and biomedical applications. Here, we used this technology to electrically monitor cellular mechanosensing. The SiNT probe was combined with an electrically activated glass micropipette aspiration system to achieve a new cancer diagnostic technique that is based on real-time correlation between mechanical and electrical behaviour of single cells. Our studies demonstrated marked changes in the electrical response following increases in the mechanical aspiration force in healthy cells. In contrast, such responses were extremely weak for malignant cells. Confocal microscopy results showed the impact of actin microfilament remodelling on the reduction of the electrical response for aspirated cancer cells due to the significant role of actin in modulating the ion channel activity in the cell membrane.

Nanoelectronics-biology frontier: From nanoscopic probes for action potential recording in live cells to three-dimensional cyborg tissues

Semiconductor nanowires configured as the active channels of field-effect transistors (FETs) have been used as detectors for high-resolution electrical recording from single live cells, cell networks, tissues and organs. Extracellular measurements with substrate supported silicon nanowire (SiNW) FETs, which have projected active areas orders of magnitude smaller than conventional microfabricated multielectrode arrays (MEAs) and planar FETs, recorded action potential and field potential signals with high signal-to-noise ratio and temporal resolution from cultured neurons, cultured cardiomyocytes, acute brain slices and whole animal hearts. Measurements made with modulation-doped nanoscale active channel SiNW FETs demonstrate that signals recorded from cardiomyocytes are highly localized and have improved time resolution compared to larger planar detectors. In addition, several novel three-dimensional (3D) transistor probes, which were realized using advanced nanowire synthesis methods, have been implemented for intracellular recording. These novel probes include (i) flexible 3D kinked nanowire FETs, (ii) branched intracellular nanotube SiNW FETs, and (iii) active silicon nanotube FETs. Following phospholipid modification of the probes to mimic the cell membrane, the kinked nanowire, branched intracellular nanotube and active silicon nanotube FET probes recorded full-amplitude intracellular action potentials from spontaneously firing cardiomyocytes. Moreover, these probes demonstrated the capability of reversible, stable, and long-term intracellular recording, thus indicating the minimal invasiveness of the new nanoscale structures and suggesting biomimetic internalization via the phospholipid modification. Simultaneous, multi-site intracellular recording from both single cells and cell networks were also readily achieved by interfacing independently addressable nanoprobe devices with cells. Finally, electronic and biological systems have been seamlessly merged in 3D for the first time using macroporous nanoelectronic scaffolds that are analogous to synthetic tissue scaffold and the extracellular matrix in tissue. Free-standing 3D nanoelectronic scaffolds were cultured with neurons, cardiomyocytes and smooth muscle cells to yield electronically-innervated synthetic or 'cyborg' tissues. Measurements demonstrate that innervated tissues exhibit similar cell viability as with conventional tissue scaffolds, and importantly, demonstrate that the real-time response to drugs and pH changes can be mapped in 3D through the tissues. These results open up a new field of research, wherein nanoelectronics are merged with biological systems in 3D thereby providing broad opportunities, ranging from a nanoelectronic/tissue platform for real-time pharmacological screening in 3D to implantable 'cyborg' tissues enabling closed-loop monitoring and treatment of diseases. Furthermore, the capability of high density scale-up of the above extra- and intracellular nanoscopic probes for action potential recording provide important tools for large-scale high spatio-temporal resolution electrical neural activity mapping in both 2D and 3D, which promises to have a profound impact on many research areas, including the mapping of activity within the brain.

Nanowire nanoelectronics: Building interfaces with tissue and cells at the natural scale of biology

The interface between nanoscale electronic devices and biological systems enables interactions at length scales natural to biology, and thus should maximize communication between these two diverse yet complementary systems. Moreover, nanostructures and nanostructured substrates show enhanced coupling to artificial membranes, cells, and tissue. Such nano–bio interfaces offer better sensitivity and spatial resolution as compared to conventional planar structures. In this work, we will report the electrical properties of silicon nanowires (SiNWs) interfaced with embryonic chicken hearts and cultured cardiomyocytes. We developed a scheme that allowed us to manipulate the nanoelectronic to tissue/cell interfaces while monitoring their electrical activity. In addition, by utilizing the bottom-up approach, we extended our work to the subcellular regime, and interfaced cells with the smallest reported device ever and thus exceeded the spatial and temporal resolution limits of other electrical recording techniques. The exceptional synthetic control and flexible assembly of nanowires (NWs) provides powerful tools for fundamental studies and applications in life science, and opens up the potential of merging active transistors with cells such that the distinction between nonliving and living systems is blurred.

Nanotechnology meets electrophysiology

Recording of electrical signals from electrogenic cells is an essential aspect to many areas, ranging from fundamental biophysical studies of the function of the brain and heart, through medical monitoring and intervention. Over the past decades, these studies have been primarily carried out by various well-established techniques that have greatly advanced the field, yet pose handicapping technical limitations. Nanotechnology allows the fabrication of devices small enough to enable recording of single cells, and even single neurites. The rise in knowledge in controlling nanostructures allows their tailoring to match cellular components, thus offering high level of interfacing to single cells. We will cover the latest developments in electrophysiology, applying new nanotechnology-based approaches for cellular electrical recordings, both extracellularly and intracellularly.

Design and Implementation of Functional Nanoelectronic Interfaces With Biomolecules, Cells, and Tissue Using Nanowire Device Arrays

Nanowire FETs (NWFETs) are promising building blocks for nanoscale bioelectronic interfaces with cells and tissue since they are known to exhibit exquisite sensitivity in the context of chemical and biological detection, and have the potential to form strongly coupled interfaces with cell membranes. We present a general scheme that can be used to assemble NWs with rationally designed composition and geometry on either planar inorganic or biocompatible flexible plastic surfaces. We demonstrate that these devices can be used to measure signals from neurons, cardiomyocytes, and heart tissue. Reported signals are in millivolts range, which are equal to or substantially greater than those recorded with either planar FETs or multielectrode arrays, and demonstrate one unique advantage of NW-based devices. Basic studies showing the effect of device sensitivity and cell/substrate junction quality on signal magnitude are presented. Finally, our demonstrated ability to design high-density arrays of NWFETs enables us to map signal at the subcellular level, a functionality not enabled by conventional microfabricated devices. These advances could have broad applications in high-throughput drug assays, fundamental biophysical studies of cellular function, and development of powerful prosthetics.

Nanowire transistor arrays for mapping neural circuits in acute brain slices

Revealing the functional connectivity in natural neuronal networks is central to understanding circuits in the brain. Here, we show that silicon nanowire field-effect transistor (Si NWFET) arrays fabricated on transparent substrates can be reliably interfaced to acute brain slices. NWFET arrays were readily designed to record across a wide range of length scales, while the transparent device chips enabled imaging of individual cell bodies and identification of areas of healthy neurons at both upper and lower tissue surfaces. Simultaneous NWFET and patch clamp studies enabled unambiguous identification of action potential signals, with additional features detected at earlier times by the nanodevices. NWFET recording at different positions in the absence and presence of synaptic and ion-channel blockers enabled assignment of these features to presynaptic firing and postsynaptic depolarization from regions either close to somata or abundant in dendritic projections. In all cases, the NWFET signal amplitudes were from 0.3-3 mV. In contrast to conventional multielectrode array measurements, the small active surface of the NWFET devices, approximately 0.06 microm(2), provides highly localized multiplexed measurements of neuronal activities with demonstrated sub-millisecond temporal resolution and, significantly, better than 30 microm spatial resolution. In addition, multiplexed mapping with 2D NWFET arrays revealed spatially heterogeneous functional connectivity in the olfactory cortex with a resolution surpassing substantially previous electrical recording techniques. Our demonstration of simultaneous high temporal and spatial resolution recording, as well as mapping of functional connectivity, suggest that NWFETs can become a powerful platform for studying neural circuits in the brain.

Flexible electrical recording from cells using nanowire transistor arrays

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.

Electrical recording from hearts with flexible nanowire device arrays

We show that nanowire field-effect transistor (NWFET) arrays fabricated on both planar and flexible polymeric substrates can be reproducibly interfaced with spontaneously beating embryonic chicken hearts in both planar and bent conformations. Simultaneous recordings from glass microelectrode and NWFET devices show that NWFET conductance variations are synchronized with the beating heart. The conductance change associated with beating can be tuned substantially by device sensitivity, although the voltage-calibrated signals, 4-6 mV, are relatively constant and typically larger than signals recorded by microelectrode arrays. Multiplexed recording from NWFET arrays yielded signal propagation times across the myocardium with high spatial resolution. The transparent and flexible NWFET chips also enable simultaneous electrical recording and optical registration of devices to heart surfaces in three-dimensional conformations not possible with planar microdevices. The capability of simultaneous optical imaging and electrical recording also could be used to register devices to a specific region of the myocardium at the cellular level, and more generally, NWFET arrays fabricated on increasingly flexible plastic and/or biopolymer substrates have the potential to become unique tools for electrical recording from other tissue/organ samples or as powerful implants.

The measurement of compound neural action potential in sciatic nerve using microelectrode array

As a method of observing regeneration of damaged nerves, research is being conducted on analyzing the electric signals of nerve fibers that are damaged and regenerating by implanting a microelectrode array between those nerves. Microelectrode arrays possess high impedance and a unique phase characteristic according to their structural features, thus it requires a phase linearity test and an impedance test to prevent neural signal distortion. Therefore, this paper analyzes the features of microelectrode array and designs a bioamplifier. We also measured signals from sciatic nerves in rats with microelectrode array.

The measurement of compound neural action potential in sciatic nerve using microelectrode array

As a method of observing regeneration of damaged nerves, research is being conducted on analyzing the electric signals of nerve fibers that are damaged and regenerating by implanting a microelectrode array between those nerves. Microelectrode arrays possess high impedance and a unique phase characteristic according to their structural features,thus it requires a phase linearity test and an impedance test to prevent neural signal distortion.Therefore, this paper analyzes the features of microelectrode array and designs a bioamplifier. We also measured signals from sciatic nerves in rats with microelectrode array.