Nanowire electrodes for high-density stimulation and measurement of neural circuits

Micronano Synergetic Three-Dimensional Bioelectronics: A Revolutionary Breakthrough Platform for Cardiac Electrophysiology

Cardiovascular diseases (CVDs) are the leading cause of mortality and therefore pose a significant threat to human health. Cardiac electrophysiology plays a crucial role in the investigation and treatment of CVDs, including arrhythmia. The long-term and accurate detection of electrophysiological activity in cardiomyocytes is essential for advancing cardiology and pharmacology. Regarding the electrophysiological study of cardiac cells, many micronano bioelectric devices and systems have been developed. Such bioelectronic devices possess unique geometric structures of electrodes that enhance quality of electrophysiological signal recording. Though planar multielectrode/multitransistors are widely used for simultaneous multichannel measurement of cell electrophysiological signals, their use for extracellular electrophysiological recording exhibits low signal strength and quality. However, the integration of three-dimensional (3D) multielectrode/multitransistor arrays that use advanced penetration strategies can achieve high-quality intracellular signal recording. This review provides an overview of the manufacturing, geometric structure, and penetration paradigms of 3D micronano devices, as well as their applications for precise drug screening and biomimetic disease modeling. Furthermore, this review also summarizes the current challenges and outlines future directions for the preparation and application of micronano bioelectronic devices, with an aim to promote the development of intracellular electrophysiological platforms and thereby meet the demands of emerging clinical applications.

Linking cortex and contraction-Integrating models along the corticomuscular pathway

Computational models of the neuromusculoskeletal system provide a deterministic approach to investigate input-output relationships in the human motor system. Neuromusculoskeletal models are typically used to estimate muscle activations and forces that are consistent with observed motion under healthy and pathological conditions. However, many movement pathologies originate in the brain, including stroke, cerebral palsy, and Parkinson's disease, while most neuromusculoskeletal models deal exclusively with the peripheral nervous system and do not incorporate models of the motor cortex, cerebellum, or spinal cord. An integrated understanding of motor control is necessary to reveal underlying neural-input and motor-output relationships. To facilitate the development of integrated corticomuscular motor pathway models, we provide an overview of the neuromusculoskeletal modelling landscape with a focus on integrating computational models of the motor cortex, spinal cord circuitry, α-motoneurons  and skeletal muscle in regard to their role in generating voluntary muscle contraction. Further, we highlight the challenges and opportunities associated with an integrated corticomuscular pathway model, such as challenges in defining neuron connectivities, modelling standardisation, and opportunities in applying models to study emergent behaviour. Integrated corticomuscular pathway models have applications in brain-machine-interaction, education, and our understanding of neurological disease.

Wireless and battery-free technologies for neuroengineering

Tethered and battery-powered devices that interface with neural tissues can restrict natural motions and prevent social interactions in animal models, thereby limiting the utility of these devices in behavioural neuroscience research. In this Review Article, we discuss recent progress in the development of miniaturized and ultralightweight devices as neuroengineering platforms that are wireless, battery-free and fully implantable, with capabilities that match or exceed those of wired or battery-powered alternatives. Such classes of advanced neural interfaces with optical, electrical or fluidic functionality can also combine recording and stimulation modalities for closed-loop applications in basic studies or in the practical treatment of abnormal physiological processes.

Impedance scaling for gold and platinum microelectrodes

Objective.Electrical measurement of the activity of individual neurons is a primary goal for many invasive neural electrodes. Making these 'single unit' measurements requires that we fabricate electrodes small enough so that only a few neurons contribute to the signal, but not so small that the impedance of the electrode creates overwhelming noise or signal attenuation. Thus, neuroelectrode design often must strike a balance between electrode size and electrode impedance, where the impedance is often assumed to scale linearly with electrode area.Approach and main results. Here we study how impedance scales with neural electrode area and find that the 1 kHz impedance of Pt electrodes (but not Au electrodes) transitions from scaling with area (r^-2) to scaling with perimeter (r^-1) when the electrode radius falls below 10µm. This effect can be explained by the transition from planar to spherical diffusion behavior previously reported for electrochemical microelectrodes.Significance.These results provide important intuition for designing small, single unit recording electrodes. Specifically, for materials where the impedance is dominated by a pseudo-capacitance that is associated with a diffusion limited process, the total impedance will scale with perimeter rather than area when the electrode size becomes comparable with the diffusion layer thickness. For Pt electrodes this transition occurs around 10µm radius electrodes. At even lower frequencies (1 Hz) impedance approaches a constant. This transition tor^-1scaling implies that electrodes with a pseudo-capacitance can be made smaller than one might expect before thermal noise or voltage division limits the ability to acquire high-quality single-unit recordings.

Nanovolcano microelectrode arrays: toward long-term on-demand registration of transmembrane action potentials by controlled electroporation

Volcano-shaped microelectrodes (nanovolcanoes) functionalized with nanopatterned self-assembled monolayers have recently been demonstrated to report cardiomyocyte action potentials after gaining spontaneous intracellular access. These nanovolcanoes exhibit recording characteristics similar to those of state-of-the-art micro-nanoelectrode arrays that use electroporation as an insertion mechanism. In this study, we investigated whether the use of electroporation improves the performance of nanovolcano arrays in terms of action potential amplitudes, recording durations, and yield. Experiments with neonatal rat cardiomyocyte monolayers grown on nanovolcano arrays demonstrated that electroporation pulses with characteristics derived from analytical models increased the efficiency of nanovolcano recordings, as they enabled multiple on-demand registration of intracellular action potentials with amplitudes as high as 62 mV and parallel recordings in up to ~76% of the available channels. The performance of nanovolcanoes showed no dependence on the presence of functionalized nanopatterns, indicating that the tip geometry itself is instrumental for establishing a tight seal at the cell-electrode interface, which ultimately determines the quality of recordings. Importantly, the use of electroporation permitted the recording of attenuated cardiomyocyte action potentials during consecutive days at identical sites, indicating that nanovolcano recordings are nondestructive and permit long-term on-demand recordings from excitable cardiac tissues. Apart from demonstrating that less complex manufacturing processes can be used for next-generation nanovolcano arrays, the finding that the devices are suitable for performing on-demand recordings of electrical activity from multiple sites of excitable cardiac tissues over extended periods of time opens the possibility of using the devices not only in basic research but also in the context of comprehensive drug testing.

High-Aspect-Ratio Nanostructured Surfaces as Biological Metamaterials

Materials patterned with high-aspect-ratio nanostructures have features on similar length scales to cellular components. These surfaces are an extreme topography on the cellular level and have become useful tools for perturbing and sensing the cellular environment. Motivation comes from the ability of high-aspect-ratio nanostructures to deliver cargoes into cells and tissues, access the intracellular environment, and control cell behavior. These structures directly perturb cells' ability to sense and respond to external forces, influencing cell fate, and enabling new mechanistic studies. Through careful design of their nanoscale structure, these systems act as biological metamaterials, eliciting unusual biological responses. While predominantly used to interface eukaryotic cells, there is growing interest in nonanimal and prokaryotic cell interfacing. Both experimental and theoretical studies have attempted to develop a mechanistic understanding for the observed behaviors, predominantly focusing on the cell-nanostructure interface. This review considers how high-aspect-ratio nanostructured surfaces are used to both stimulate and sense biological systems.

Nanoelectrode-mediated single neuron activation

Elucidating cellular dynamics at the level of a single neuron and its associated role within neuronal circuits is essential for interpreting the complex nature of the brain. To investigate the operation of neural activity within its network, it is necessary to precisely manipulate the activation of each neuron and verify its propagation path via the synaptic connection. In this study, by exploiting the intrinsic physical and electrical advantages of a nanoelectrode, a vertical nanowire multi electrode array (VNMEA) is developed as a neuronal activation platform presenting the spatially confined effect on the intracellular space of individual cells. VNMEA makes a distinct difference between the interior and exterior cell potential and the current density, deriving the superior effects on activating Ca2+ responses compared to extracellular methods under the same conditions, with about 2.9-fold higher amplitude of Ca2+ elevation and a 2.6-fold faster recovery rate. Moreover, the synchronized propagation of evoked activities is shown in connected neurons implying cell-to-cell communications following the intracellular stimulation. The simulation and experimental consequences prove the outstanding property of temporal/spatial confinement of VNMEA-mediated intracellular stimulation to activate a single neuron and show its potential in localizing spiking neurons within neuronal populations, which may be utilized to reveal the connection and activation modalities of neural networks.

High density nanowire electrodes for intracortical microstimulation

High-density electrodes with the nano feature size greatly enhance resolution and specificity during intracortical microstimulation. In this viewpoint, we fabricated and developed high-density nanowire (NW) electrodes, ~ 2.45×10⁹ / cm² that could directly stimulate specific region of the cortex with low current amplitude in the range of 120-180 μA. The proposed nanowire electrodes will help expand the capabilities of microstimulation and extend the range of dysfunctions that can be treated using microstimulation technique.

Interfacing human induced pluripotent stem cell-derived neurons with designed nanowire arrays as a future platform for medical applications

Nanostructured substrates such as nanowire arrays form a powerful tool for building next-generation medical devices.

Large-Scale, High-Resolution Microelectrode Arrays for Interrogation of Neurons and Networks

High-density microelectrode arrays (HD-MEAs) are increasingly being used for the observation and manipulation of neurons and networks in vitro. Large-scale electrode arrays allow for long-term extracellular recording of the electrical activity from thousands of neurons simultaneously. Beyond population activity, it has also become possible to extract information of single neurons at subcellular level (e.g., the propagation of action potentials along axons). In effect, HD-MEAs have become an electrical imaging platform for label-free extraction of the structure and activation of cells in cultures and tissues. The quality of HD-MEA data depends on the resolution of the electrode array and the signal-to-noise ratio. In this chapter, we begin with an introduction to HD-MEA signals. We provide an overview of the developments on complementary metal-oxide-semiconductor or CMOS-based HD-MEA technology. We also discuss the factors affecting the performance of HD-MEAs and the trending application requirements that drive the efforts for future devices. We conclude with an outlook on the potential of HD-MEAs for advancing basic neuroscience and drug discovery.

Optimized Real-Time Biomimetic Neural Network on FPGA for Bio-hybridization

Neurological diseases can be studied by performing bio-hybrid experiments using a real-time biomimetic Spiking Neural Network (SNN) platform. The Hodgkin-Huxley model offers a set of equations including biophysical parameters which can serve as a base to represent different classes of neurons and affected cells. Also, connecting the artificial neurons to the biological cells would allow us to understand the effect of the SNN stimulation using different parameters on nerve cells. Thus, designing a real-time SNN could useful for the study of simulations of some part of the brain. Here, we present a different approach to optimize the Hodgkin-Huxley equations adapted for Field Programmable Gate Array (FPGA) implementation. The equations of the conductance have been unified to allow the use of same functions with different parameters for all ionic channels. The low resources and high-speed implementation also include features, such as synaptic noise using the Ornstein-Uhlenbeck process and different synapse receptors including AMPA, GABAa, GABAb, and NMDA receptors. The platform allows real-time modification of the neuron parameters and can output different cortical neuron families like Fast Spiking (FS), Regular Spiking (RS), Intrinsically Bursting (IB), and Low Threshold Spiking (LTS) neurons using a Digital to Analog Converter (DAC). Gaussian distribution of the synaptic noise highlights similarities with the biological noise. Also, cross-correlation between the implementation and the model shows strong correlations, and bifurcation analysis reproduces similar behavior compared to the original Hodgkin-Huxley model. The implementation of one core of calculation uses 3% of resources of the FPGA and computes in real-time 500 neurons with 25,000 synapses and synaptic noise which can be scaled up to 15,000 using all resources. This is the first step toward neuromorphic system which can be used for the simulation of bio-hybridization and for the study of neurological disorders or the advanced research on neuroprosthesis to regain lost function.

Recent Progress on Microelectrodes in Neural Interfaces

Brain‒machine interface (BMI) is a promising technology that looks set to contribute to the development of artificial limbs and new input devices by integrating various recent technological advances, including neural electrodes, wireless communication, signal analysis, and robot control. Neural electrodes are a key technological component of BMI, as they can record the rapid and numerous signals emitted by neurons. To receive stable, consistent, and accurate signals, electrodes are designed in accordance with various templates using diverse materials. With the development of microelectromechanical systems (MEMS) technology, electrodes have become more integrated, and their performance has gradually evolved through surface modification and advances in biotechnology. In this paper, we review the development of the extracellular/intracellular type of in vitro microelectrode array (MEA) to investigate neural interface technology and the penetrating/surface (non-penetrating) type of in vivo electrodes. We briefly examine the history and study the recently developed shapes and various uses of the electrode. Also, electrode materials and surface modification techniques are reviewed to measure high-quality neural signals that can be used in BMI.

Scalable Nanostructured Carbon Electrode Arrays for Enhanced Dopamine Detection

Dopamine is a neurotransmitter that modulates arousal and motivation in humans and animals. It plays a central role in the brain "reward" system. Its dysregulation is involved in several debilitating disorders such as addiction, depression, Parkinson's disease, and schizophrenia. Dopamine neurotransmission and its reuptake in extracellular space takes place with millisecond temporal and nanometer spatial resolution. Novel nanoscale electrodes are needed with superior sensitivity and improved spatial resolution to gain an improved understanding of dopamine dysregulation. We report on a scalable fabrication of dopamine neurochemical probes of a nanostructured glassy carbon that is smaller than any existing dopamine sensor and arrays of more than 6000 nanorod probes. We also report on the electrochemical dopamine sensing of the glassy carbon nanorod electrode. Compared with a carbon fiber, the nanostructured glassy carbon nanorods provide about 2× higher sensitivity per unit area for dopamine sensing and more than 5× higher signal per unit area at low concentration of dopamine, with comparable LOD and time response. These glassy carbon nanorods were fabricated by pyrolysis of a lithographically defined polymeric nanostructure with an industry standard semiconductor fabrication infrastructure. The scalable fabrication strategy offers the potential to integrate these nanoscale carbon rods with an integrated circuit control system and with other complementary metal oxide semiconductor (CMOS) compatible sensors.

Talking to cells: semiconductor nanomaterials at the cellular interface

The interface of biological components with semiconductors is a growing field with numerous applications. For example, the interfaces can be used to sense and modulate the electrical activity of single cells and tissues. From the materials point of view, silicon is the ideal option for such studies due to its controlled chemical synthesis, scalable lithography for functional devices, excellent electronic and optical properties, biocompatibility and biodegradability. Recent advances in this area are pushing the bio-interfaces from the tissue and organ level to the single cell and sub-cellular regimes. In this progress report, we will describe some fundamental studies focusing on miniaturizing the bioelectric and biomechanical interfaces. Additionally, many of our highlighted examples involve freestanding silicon-based nanoscale systems, in addition to substrate-bound structures or devices; the former offers new promise for basic research and clinical application. In this report, we will describe recent developments in the interfacing of neuronal and cardiac cells and their networks. Moreover, we will briefly discuss the incorporation of semiconductor nanostructures for interfacing non-excitable cells in applications such as probing intracellular force dynamics and drug delivery. Finally, we will suggest several directions for future exploration.

Ultrasonic beamforming system for interrogating multiple implantable sensors

In this paper, we present an ultrasonic beamforming system capable of interrogating individual implantable sensors via backscatter in a distributed, ultrasound-based recording platform known as Neural Dust [1]. A custom ASIC drives a 7 × 2 PZT transducer array with 3 cycles of 32V square wave with a specific programmable time delay to focus the beam at the 800mm neural dust mote placed 50mm away. The measured acoustic-to-electrical conversion efficiency of the receive mote in water is 0.12% and the overall system delivers 26.3% of the power from the 1.8V power supply to the transducer drive output, consumes 0.75μJ in each transmit phase, and has a 0.5% change in the backscatter per volt applied to the input of the backscatter circuit. Further miniaturization of both the transmit array and the receive mote can pave the way for a wearable, chronic sensing and neuromodulation system.

Ultrasensitive gold micro-structured electrodes enabling the detection of extra-cellular long-lasting potentials in astrocytes populations

Ultra-sensitive electrodes for extracellular recordings were fabricated and electrically characterized. A signal detection limit defined by a noise level of 0.3-0.4 μV for a bandwidth of 12.5 Hz was achieved. To obtain this high sensitivity, large area (4 mm2) electrodes were used. The electrode surface is also micro-structured with an array of gold mushroom-like shapes to further enhance the active area. In comparison with a flat gold surface, the micro-structured surface increases the capacitance of the electrode/electrolyte interface by 54%. The electrode low impedance and low noise enable the detection of weak and low frequency quasi-periodic signals produced by astrocytes populations that thus far had remained inaccessible using conventional extracellular electrodes. Signals with 5 μV in amplitude and lasting for 5-10 s were measured, with a peak-to-peak signal-to-noise ratio of 16. The electrodes and the methodology developed here can be used as an ultrasensitive electrophysiological tool to reveal the synchronization dynamics of ultra-slow ionic signalling between non-electrogenic cells.

Nanowire FET Based Neural Element for Robotic Tactile Sensing Skin

This paper presents novel Neural Nanowire Field Effect Transistors (υ-NWFETs) based hardware-implementable neural network (HNN) approach for tactile data processing in electronic skin (e-skin). The viability of Si nanowires (NWs) as the active material for υ-NWFETs in HNN is explored through modeling and demonstrated by fabricating the first device. Using υ-NWFETs to realize HNNs is an interesting approach as by printing NWs on large area flexible substrates it will be possible to develop a bendable tactile skin with distributed neural elements (for local data processing, as in biological skin) in the backplane. The modeling and simulation of υ-NWFET based devices show that the overlapping areas between individual gates and the floating gate determines the initial synaptic weights of the neural network - thus validating the working of υ-NWFETs as the building block for HNN. The simulation has been further extended to υ-NWFET based circuits and neuronal computation system and this has been validated by interfacing it with a transparent tactile skin prototype (comprising of 6 × 6 ITO based capacitive tactile sensors array) integrated on the palm of a 3D printed robotic hand. In this regard, a tactile data coding system is presented to detect touch gesture and the direction of touch. Following these simulation studies, a four-gated υ-NWFET is fabricated with Pt/Ti metal stack for gates, source and drain, Ni floating gate, and Al2O3 high-k dielectric layer. The current-voltage characteristics of fabricated υ-NWFET devices confirm the dependence of turn-off voltages on the (synaptic) weight of each gate. The presented υ-NWFET approach is promising for a neuro-robotic tactile sensory system with distributed computing as well as numerous futuristic applications such as prosthetics, and electroceuticals.

Modulation of action potentials using PEDOT:PSS conducting polymer microwires

We describe the use of PEDOT:PSS conducting polymer microwires to modulate action potentials in single cells.

PEDOT

PSS conducting polymer microwires are electrochemically synthesized with diameters ranging from 860 nm to 4.5 μm and conductivities of ~30 S/cm. The length of the microwires is controlled by the spacing of the electrodes used for the electrochemical polymerization. We demonstrate the use of these microwires to control the action potentials of cardiomyocytes, showing that the cellular contractions match the frequency of the applied voltage. Membrane integrity assays confirm that the voltage delivered by the wires does not damage cells. We expect the conducting polymer microwires will be useful as minimally invasive devices to control the electrical properties of cells with high spatial precision.

High Density Individually Addressable Nanowire Arrays Record Intracellular Activity from Primary Rodent and Human Stem Cell Derived Neurons

We report a new hybrid integration scheme that offers for the first time a nanowire-on-lead approach, which enables independent electrical addressability, is scalable, and has superior spatial resolution in vertical nanowire arrays. The fabrication of these nanowire arrays is demonstrated to be scalable down to submicrometer site-to-site spacing and can be combined with standard integrated circuit fabrication technologies. We utilize these arrays to perform electrophysiological recordings from mouse and rat primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons, which revealed high signal-to-noise ratios and sensitivity to subthreshold postsynaptic potentials (PSPs). We measured electrical activity from rodent neurons from 8 days in vitro (DIV) to 14 DIV and from hiPSC-derived neurons at 6 weeks in vitro post culture with signal amplitudes up to 99 mV. Overall, our platform paves the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.

Conducting polymer nanowires for control of local protein concentration in solution

Interfacing devices with cells and tissues requires new nanoscale tools that are both flexible and electrically active. We demonstrate the use of PEDOT:PSS conducting polymer nanowires for the local control of protein concentration in water and biological media. We use fluorescence microscopy to compare the localization of serum albumin in response to electric fields generated by narrow (760 nm) and wide (1.5 μm) nanowires. We show that proteins in deionized water can be manipulated over a surprisingly large micron length scale and that this distance is a function of nanowire diameter. In addition, white noise can be introduced during the electrochemical synthesis of the nanowire to induce branches into the nanowire allowing a single device to control multiple nanowires. An analysis of growth speed and current density suggests that branching is due to the Mullins-Sekerka instability, ultimately controlled by the roughness of the nanowire surface. These small, flexible, conductive, and biologically compatible PEDOT:PSS nanowires provide a new tool for the electrical control of biological systems.

CMOS nanoelectrode array for all-electrical intracellular electrophysiological imaging

Developing a new tool capable of high-precision electrophysiological recording of a large network of electrogenic cells has long been an outstanding challenge in neurobiology and cardiology. Here, we combine nanoscale intracellular electrodes with complementary metal-oxide-semiconductor (CMOS) integrated circuits to realize a high-fidelity all-electrical electrophysiological imager for parallel intracellular recording at the network level. Our CMOS nanoelectrode array has 1,024 recording/stimulation 'pixels' equipped with vertical nanoelectrodes, and can simultaneously record intracellular membrane potentials from hundreds of connected in vitro neonatal rat ventricular cardiomyocytes. We demonstrate that this network-level intracellular recording capability can be used to examine the effect of pharmaceuticals on the delicate dynamics of a cardiomyocyte network, thus opening up new opportunities in tissue-based pharmacological screening for cardiac and neuronal diseases as well as fundamental studies of electrogenic cells and their networks.

A network engineering perspective on probing and perturbing cognition with neurofeedback

Network science and engineering provide a flexible and generalizable tool set to describe and manipulate complex systems characterized by heterogeneous interaction patterns among component parts. While classically applied to social systems, these tools have recently proven to be particularly useful in the study of the brain. In this review, we describe the nascent use of these tools to understand human cognition, and we discuss their utility in informing the meaningful and predictable perturbation of cognition in combination with the emerging capabilities of neurofeedback. To blend these disparate strands of research, we build on emerging conceptualizations of how the brain functions (as a complex network) and how we can develop and target interventions or modulations (as a form of network control). We close with an outline of current frontiers that bridge neurofeedback, connectomics, and network control theory to better understand human cognition.

Differential Collective- and Single-Cell Behaviors on Silicon Micropillar Arrays

Three-dimensional vertically aligned nano- and micropillars have emerged as promising tools for a variety of biological applications. Despite their increasing usage, the interaction mechanisms of cells with these rigid structures and their effect on single- and collective-cell behaviors are not well understood for different cell types. In the present study, we examine the response of glioma cells to micropillar arrays using a new microfabricated platform consisting of rigid silicon micropillar arrays of various shapes, sizes, and configurations fabricated on a single platform. We compare collective- and single-cell behaviors at micropillar array interfaces and show that glial cells under identical chemical conditions form distinct arrangements on arrays of different shapes and sizes. Tumor-like aggregation and branching of glial cells only occur on arrays with feature diameters greater than 2 μm, and distinct transitions are observed at interfaces between various arrays on the platform. Additionally, despite the same side-to-side spacing and gaps between micropillars, single glial cells interact with the flat silicon surface in the gap between small pillars but sit on top of larger micropillars. Furthermore, micropillars induced local changes in stress fibers and actin-rich filopodia protrusions as the cells conformed to the shape of spatial cues formed by these micropillars.

Determining the Time Window for Dynamic Nanowire Cell Penetration Processes

Nanowire (NW) arrays offer opportunities for parallel, nondestructive intracellular access for biomolecule delivery, intracellular recording, and sensing. Spontaneous cell membrane penetration by vertical nanowires is essential for these applications, yet the time- and geometry-dependent penetration process is still poorly understood. In this work, the dynamic NW-cell interface during cell spreading was examined through experimental cell penetration measurements combined with two mechanical models based on substrate adhesion force or cell traction forces. Penetration was determined by comparing the induced tension at a series of given membrane configurations to the critical membrane failure tension. The adhesion model predicts that penetration occurs within a finite window shortly after initial cell contact and adhesion, while the traction model predicts increasing penetration over a longer period. NW penetration rates determined from a cobalt ion delivery assay are compared to the predicted results from the two models. In addition, the effects of NW geometry and cell properties are systematically evaluated to identify the key factors for penetration.

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

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.

Nanotechnology and neurophysiology

Neuroscience would be revolutionized by a technique to measure intracellular electrical potentials that would not disrupt cellular physiology and could be massively parallelized. Though such a technology does not yet exist, the technical hurdles for fabricating minimally disruptive, solid-state electrical probes have arguably been overcome in the field of nanotechnology. Nanoscale devices can be patterned with features on the same length scale as biological components, and several groups have demonstrated that nanoscale electrical probes can measure the transmembrane potential of electrogenic cells. Developing these nascent technologies into robust intracellular recording tools will now require a better understanding of device-cell interactions, especially the membrane-inorganic interface. Here we review the state-of-the art in nanobioelectronics, emphasizing the characterization and design of stable interfaces between nanoscale devices and cells.

Nanotechnology, neuromodulation & the immune response: discourse, materiality & ethics

Drawing upon the American Pragmatic tradition in philosophy and the more recent work of philosopher Karen Barad, this paper examines how scientific problems are both obscured, and resolved by our use of language describing the natural world. Using the example of the immune response engendered by neural implants inserted in the brain, the author explains how this discourse has been altered by the advent of nanotechnology methods and devices which offer putative remedies that might temper the immune response in the central nervous system. This emergent nanotechnology has altered this problem space and catalyzed one scientific community to acknowledge a material reality that was always present, if not fully acknowledged.

Revealing neuronal function through microelectrode array recordings

Microelectrode arrays and microprobes have been widely utilized to measure neuronal activity, both in vitro and in vivo. The key advantage is the capability to record and stimulate neurons at multiple sites simultaneously. However, unlike the single-cell or single-channel resolution of intracellular recording, microelectrodes detect signals from all possible sources around every sensor. Here, we review the current understanding of microelectrode signals and the techniques for analyzing them. We introduce the ongoing advancements in microelectrode technology, with focus on achieving higher resolution and quality of recordings by means of monolithic integration with on-chip circuitry. We show how recent advanced microelectrode array measurement methods facilitate the understanding of single neurons as well as network function.

Cell responses to metallic nanostructure arrays with complex geometries

Metallic nanopillar/nanowires are emerging as promising platforms for biological applications, as they allow for the direct characterization and regulation of cell function. Herein we study the response of cells to a versatile nanopillar platform. Nanopillar arrays of various shape, size, and spacing and different nanopillar-substrate interfacial strengths were fabricated and interfaced with fibroblasts and several unique cell-nanopillar interactions were observed using high resolution scanning electron microscopy. Nanopillar penetration, engulfment, tilting, lift off and membrane thinning, were observed by manipulating nanopillar material, size, shape and spacing. These unique cell responses to various nanostructures can be employed for a wide range of applications including the design of highly sensitive nano-electrodes for single-cell probing.

Micro and Nano-Scale Technologies for Cell Mechanics

Cell mechanics is a multidisciplinary field that bridges cell biology, fundamental mechanics, and micro and nanotechnology, which synergize to help us better understand the intricacies and the complex nature of cells in their native environment. With recent advances in nanotechnology, microfabrication methods and micro-electro-mechanical-systems (MEMS), we are now well situated to tap into the complex micro world of cells. The field that brings biology and MEMS together is known as Biological MEMS (BioMEMS). BioMEMS take advantage of systematic design and fabrication methods to create platforms that allow us to study cells like never before. These new technologies have been rapidly advancing the study of cell mechanics. This review article provides a succinct overview of cell mechanics and comprehensively surveys micro and nano-scale technologies that have been specifically developed for and are relevant to the mechanics of cells. Here we focus on micro and nano-scale technologies, and their applications in biology and medicine, including imaging, single cell analysis, cancer cell mechanics, organ-on-a-chip systems, pathogen detection, implantable devices, neuroscience and neurophysiology. We also provide a perspective on the future directions and challenges of technologies that relate to the mechanics of cells.