Nanoelectrode-mediated single neuron activation

Combining PEDOT:PSS Polymer Coating with Metallic 3D Nanowires Electrodes to Achieve High Electrochemical Performances for Neuronal Interfacing Applications

This study presents a novel approach to improve the performance of microelectrode arrays (MEAs) used for electrophysiological studies of neuronal networks. The integration of 3D nanowires (NWs) with MEAs increases the surface-to-volume ratio, which enables subcellular interactions and high-resolution neuronal signal recording. However, these devices suffer from high initial interface impedance and limited charge transfer capacity due to their small effective area. To overcome these limitations, the integration of conductive polymer coatings, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is investigated as a mean of improving the charge transfer capacity and biocompatibility of MEAs. The study combines platinum silicide-based metallic 3D nanowires electrodes with electrodeposited PEDOT:PSS coatings to deposit ultra-thin (<50 nm) layers of conductive polymer onto metallic electrodes with very high selectivity. The polymer-coated electrodes were fully characterized electrochemically and morphologically to establish a direct relationship between synthesis conditions, morphology, and conductive features. Results show that PEDOT-coated electrodes exhibit thickness-dependent improved stimulation and recording performances, offering new perspectives for neuronal interfacing with optimal cell engulfment to enable the study of neuronal activity with acute spatial and signal resolution at the sub-cellular level.

Biology-guided engineering of bioelectrical interfaces

Bioelectrical interfaces that bridge biotic and abiotic systems have heightened the ability to monitor, understand, and manipulate biological systems and are catalyzing profound progress in neuroscience research, treatments for heart failure, and microbial energy systems. With advances in nanotechnology, bifunctional and high-density devices with tailored structural designs are being developed to enable multiplexed recording or stimulation across multiple spatial and temporal scales with resolution down to millisecond-nanometer interfaces, enabling efficient and effective communication with intracellular electrical activities in a relatively noninvasive and biocompatible manner. This review provides an overview of how biological systems guide the design, engineering, and implementation of bioelectrical interfaces for biomedical applications. We investigate recent advances in bioelectrical interfaces for applications in nervous, cardiac, and microbial systems, and we also discuss the outlook of state-of-the-art biology-guided bioelectrical interfaces with high biocompatibility, extended long-term stability, and integrated system functionality for potential clinical usage.

Considerations and recent advances in nanoscale interfaces with neuronal and cardiac networks

Nanoscale interfaces with biological tissue, principally made with nanowires (NWs), are envisioned as minimally destructive to the tissue and as scalable tools to directly transduce the electrochemical activity of a neuron at its finest resolution. This review lays the foundations for understanding the material and device considerations required to interrogate neuronal activity at the nanoscale. We first discuss the electrochemical nanoelectrode-neuron interfaces and then present new results concerning the electrochemical impedance and charge injection capacities of millimeter, micrometer, and nanometer scale wires with Pt, PEDOT:PSS, Si, Ti, ITO, IrO x , Ag, and AgCl materials. Using established circuit models for NW-neuron interfaces, we discuss the impact of having multiple NWs interfacing with a single neuron on the amplitude and temporal characteristics of the recorded potentials. We review state of the art advances in nanoelectrode-neuron interfaces, the standard control experiments to investigate their electrophysiological behavior, and present recent high fidelity recordings of intracellular potentials obtained with ultrasharp NWs developed in our laboratory that naturally permeate neuronal cell bodies. Recordings from arrays and individually addressable electrically shorted NWs are presented, and the long-term stability of intracellular recording is discussed and put in the context of established techniques. Finally, a perspective on future research directions and applications is presented.

3D Electrodes for Bioelectronics

In recent studies related to bioelectronics, significant efforts have been made to form 3D electrodes to increase the effective surface area or to optimize the transfer of signals at tissue-electrode interfaces. Although bioelectronic devices with 2D and flat electrode structures have been used extensively for monitoring biological signals, these 2D planar electrodes have made it difficult to form biocompatible and uniform interfaces with nonplanar and soft biological systems (at the cellular or tissue levels). Especially, recent biomedical applications have been expanding rapidly toward 3D organoids and the deep tissues of living animals, and 3D bioelectrodes are getting significant attention because they can reach the deep regions of various 3D tissues. An overview of recent studies on 3D bioelectronic devices, such as the use of electrical stimulations and the recording of neural signals from biological subjects, is presented. Subsequently, the recent developments in materials and fabrication processing to 3D micro- and nanostructures are introduced, followed by broad applications of these 3D bioelectronic devices at various in vitro and in vivo conditions.

Vertical Nanowire Electrode Array for Enhanced Neurogenesis of Human Neural Stem Cells via Intracellular Electrical Stimulation

Extracellular electrical stimulation (ES) can provide electrical potential from outside the cell membrane, but it is often ineffective due to interference from external factors such as culture medium resistance and membrane capacitance. To address this, we developed a vertical nanowire electrode array (VNEA) to directly provide intracellular electrical potential and current to cells through nanoelectrodes. Using this approach, the cell membrane resistivity and capacitance could be excluded, allowing effective ES. Human fetal neural stem cells (hfNSCs) were cultured on the VNEA for intracellular ES. Combining the structural properties of VNEA and VNEA-mediated ES, transient nanoscale perforation of the electrode was induced, promoting cell penetration and delivering current to the cell. Intracellular ES using VNEA improved the neuronal differentiation of hfNSCs more effectively than extracellular ES and facilitated electrophysiological functional maturation of hfNSCs because of the enhanced voltage-dependent ion-channel activity. The results demonstrate that VNEA with advanced nanoelectrodes serves as a highly effective culture and stimulation platform for stem-cell neurogenesis.

A Single-Neuron: Current Trends and Future Prospects

The brain is an intricate network with complex organizational principles facilitating a concerted communication between single-neurons, distinct neuron populations, and remote brain areas. The communication, technically referred to as connectivity, between single-neurons, is the center of many investigations aimed at elucidating pathophysiology, anatomical differences, and structural and functional features. In comparison with bulk analysis, single-neuron analysis can provide precise information about neurons or even sub-neuron level electrophysiology, anatomical differences, pathophysiology, structural and functional features, in addition to their communications with other neurons, and can promote essential information to understand the brain and its activity. This review highlights various single-neuron models and their behaviors, followed by different analysis methods. Again, to elucidate cellular dynamics in terms of electrophysiology at the single-neuron level, we emphasize in detail the role of single-neuron mapping and electrophysiological recording. We also elaborate on the recent development of single-neuron isolation, manipulation, and therapeutic progress using advanced micro/nanofluidic devices, as well as microinjection, electroporation, microelectrode array, optical transfection, optogenetic techniques. Further, the development in the field of artificial intelligence in relation to single-neurons is highlighted. The review concludes with between limitations and future prospects of single-neuron analyses.