Resident neuroelectrochemical interfacing using carbon nanofiber arrays

Carbon Nanoelectrodes for the Electrochemical Detection of Neurotransmitters

Carbon-based electrodes have been developed for the detection of neurotransmitters over the past 30 years using voltammetry and amperometry. The traditional electrode for neurotransmitter detection is the carbon fiber microelectrode (CFME). The carbon-based electrode is suitable for in vivo neurotransmitter detection due to the fact that it is biocompatible and relatively small in surface area. The advent of nanoscale electrodes is in high demand due to smaller surface areas required to target specific brain regions that are also minimally invasive and cause relatively low tissue damage when implanted into living organisms. Carbon nanotubes (CNTs), carbon nanofibers, carbon nanospikes, and carbon nanopetals among others have all been utilized for this purpose. Novel electrode materials have also required novel insulations such as glass, epoxy, and polyimide coated fused silica capillaries for their construction and usage. Recent research developments have yielded a wide array of carbon nanoelectrodes with superior properties and performances in comparison to traditional electrode materials. These electrodes have thoroughly enhanced neurotransmitter detection allowing for the sensing of biological compounds at lower limits of detection, fast temporal resolution, and without surface fouling. This will allow for greater understanding of several neurological disease states based on the detection of neurotransmitters.

Interfacing neurons on carbon nanotubes covered with diamond

Investigation of the interface and needed adhesion surface for neuronal cells on carbon nanotubes covered with diamond.

Carbon Nanomaterials Interfacing with Neurons: An In vivo Perspective

Developing new tools that outperform current state of the art technologies for imaging, drug delivery or electrical sensing in neuronal tissues is one of the great challenges in neurosciences. Investigations into the potential use of carbon nanomaterials for such applications started about two decades ago. Since then, numerous in vitro studies have examined interactions between these nanomaterials and neurons, either by evaluating their compatibility, as vectors for drug delivery, or for their potential use in electric activity sensing and manipulation. The results obtained indicate that carbon nanomaterials may be suitable for medical therapies. However, a relatively small number of in vivo studies have been carried out to date. In order to facilitate the transformation of carbon nanomaterial into practical neurobiomedical applications, it is essential to identify and highlight in the existing literature the strengths and weakness that different carbon nanomaterials have displayed when probed in vivo. Unfortunately the current literature is sometimes sparse and confusing. To offer a clearer picture of the in vivo studies on carbon nanomaterials in the central nervous system, we provide a systematic and critical review. Hereby we identify properties and behavior of carbon nanomaterials in vivo inside the neural tissues, and we examine key achievements and potentially problematic toxicological issues.

Exploring arrays of vertical one-dimensional nanostructures for cellular investigations

The endeavor of exploiting arrays of vertical one-dimensional (1D) nanostructures (NSs) for cellular applications has recently been experiencing a pronounced surge of activity. The interest is rooted in the intrinsic properties of high-aspect-ratio NSs. With a height comparable to a mammalian cell, and a diameter 100-1000 times smaller, NSs should intuitively reach far into a cell and, due to their small diameter, do so without compromising cell health. Single NSs would thus be expedient for measuring and modifying cell response. Further organization of these structures into arrays can provide up-scaled and detailed spatiotemporal information on cell activity, an achievement that would entail a massive leap forward in disease understanding and drug discovery. Numerous proofs-of-principle published recently have expanded the large toolbox that is currently being established in this rapidly advancing field of research. Encouragingly, despite the diversity of NS platforms and experimental conditions used thus far, general trends and conclusions from combining cells with NSs are beginning to crystallize. This review covers the broad spectrum of NS materials and dimensions used; the observed cellular responses with specific focus on adhesion, morphology, viability, proliferation, and migration; compares the different approaches used in the field to provide NSs with the often crucial cytosolic access; covers the progress toward biological applications; and finally, envisions the future of this technology. By maintaining the impressive rate and quality of recent progress, it is conceivable that the use of vertical 1D NSs may soon be established as a superior choice over other current techniques, with all the further benefits that may entail.

Vertically Aligned Carbon Nanofiber based Biosensor Platform for Glucose Sensor

Vertically aligned carbon nanofibers (VACNFs) have recently become an important tool for biosensor design. Carbon nanofibers (CNF) have excellent conductive and structural properties with many irregularities and defect sites in addition to exposed carboxyl groups throughout their surfaces. These properties allow a better immobilization matrix compared to carbon nanotubes and offer better resolution when compared with the FET-based biosensors. VACNFs can be deterministically grown on silicon substrates allowing optimization of the structures for various biosensor applications. Two VACNF electrode architectures have been employed in this study and a comparison of their performances has been made in terms of sensitivity, sensing limitations, dynamic range, and response time. The usage of VACNF platform as a glucose sensor has been verified in this study by selecting an optimum architecture based on the VACNF forest density.

Tuning InAs nanowire density for HEK293 cell viability, adhesion, and morphology: perspectives for nanowire-based biosensors

Arrays of nanowires (NWs) are currently being established as vehicles for molecule delivery and electrical- and fluorescence-based platforms in the development of biosensors. It is conceivable that NW-based biosensors can be optimized through increased understanding of how the nanotopography influences the interfaced biological material. Using state-of-the-art homogenous NW arrays allow for a systematic investigation of how the broad range of NW densities used by the community influences cells. Here it is demonstrated that indium arsenide NW arrays provide a cell-promoting surface, which affects both cell division and focal adhesion up-regulation. Furthermore, a systematic variation in NW spacing affects both the detailed cell morphology and adhesion properties, where the latter can be predicted based on changes in free-energy states using the proposed theoretical model. As the NW density influences cellular parameters, such as cell size and adhesion tightness, it will be important to take NW density into consideration in the continued development of NW-based platforms for cellular applications, such as molecule delivery and electrical measurements.

Silicon nanopillars as a platform for enhanced fluorescence analysis

The importance of fluorescent detection in many fields is well established. While advancements in instrumentation and the development of brighter fluorophore have increased sensitivity and lowered the detection limits of the method, additional gains can be made by manipulating the local electromagnetic field. Herein we take advantage of silicon nanopillars that exhibit optical resonances and field enhancement on their surfaces and demonstrate their potential in improving performance of biomolecular fluorescent assays. We use electron beam lithography and wafer scale processes to create silicon nanoscale pillars with dimensions that can be tuned to maximize fluorescence enhancement in a particular spectral region. Performance of the nanopillar based fluorescent assay was quantified using two model bioaffinity systems (biotin-streptavidin and immunoglobulin G-antibody) as well as covalent binding of fluorescently tagged bovine serum albumin (BSA). The effects of pillar geometry and number of pillars in arrays were evaluated. Color specific and pillar diameter dependent enhancement of fluorescent signals is clearly demonstrated using green and red labels (FITC, DyLight 488, Alexa 568, and Alexa 596). The ratios of the on pillar to off pillar signals normalized by the nominal increase in surface area due to nanopillars were found to be 43, 75, and 292 for the IgG-antibody assay, streptavidin-biotin system, and covalently attached BSA, respectively. Applicability of the presented approaches to the detection of small numbers of molecules was evaluated using highly diluted labeled proteins and also control experiments without biospecific analytes. Our analysis indicates that detection of fewer than 10 tagged proteins is possible.

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.

Nanoneurotoxicity to nanoneuroprotection using biological and computational approaches

Nanoparticles (NPs) that are ∼100 nm in diameter can potentially cause toxicity in the central nervous system (CNS). Although NPs exhibit positive aspects, these molecules primarily exert negative or harmful effects. Thus, the beneficial and harmful effects should be compared. The prevalence of neurodegenerative diseases, such as Alzheimer disease, Parkinson disease, and some brain tumors, has increased. However, the major cause of these diseases remains unknown. NPs have been considered as one of the major potential causes of these diseases, penetrating the human body via different pathways. This review summarizes various pathways for NP-induced neurotoxicity, suggesting the development of strategies for nanoneuroprotection using in silico and biological methods. Studies of oxidative stress associated with gene expression analyses provide efficient information for understanding neuroinflammation and neurodegeneration associated with NPs. The brain is a sensitive and fragile organ, and evolution has developed mechanisms to protect it from injury; however, this protection also hinders the methods used for therapeutic purposes. Thus, brain and CNS-related diseases that are the cause of disability and disorder are the most difficult to treat. There are many obstacles to drug delivery in the CNS, such as the blood brain barrier and blood tumor barrier. Considering these barriers, we have reviewed the strategies available to map NPs using biological techniques. The surface adsorption energy of NPs is the basic force driving NP gathering, protein corona formation, and many other interactions of NPs within biological systems. These interactions can be described using an approach named the biological surface adsorption index. A quantitative structural activity relationship study helps to understand different protein-protein or protein-ligand interactions. Moreover, equilibrium between cerebrovascular permeability is required when a drug is transferred via the circulatory system for the therapy of neurodegenerative diseases. Various drug delivery approaches, such as chemical drug delivery and carrier-mediated drug delivery, have been established to avoid different barriers inhibiting CNS penetration by therapeutic substances. Developing an improved understanding of drug receptors and the sites of drug action, together with advances in medicinal chemistry, will make it possible to design drugs with greatly enhanced activity and selectivity; this may result in a significant increase in the therapeutic index.

Macroporous nanowire nanoelectronic scaffolds for synthetic tissues

The development of three-dimensional (3D) synthetic biomaterials as structural and bioactive scaffolds is central to fields ranging from cellular biophysics to regenerative medicine. As of yet, these scaffolds cannot electrically probe the physicochemical and biological microenvironments throughout their 3D and macroporous interior, although this capability could have a marked impact in both electronics and biomaterials. Here, we address this challenge using macroporous, flexible and free-standing nanowire nanoelectronic scaffolds (nanoES), and their hybrids with synthetic or natural biomaterials. 3D macroporous nanoES mimic the structure of natural tissue scaffolds, and they were formed by self-organization of coplanar reticular networks with built-in strain and by manipulation of 2D mesh matrices. NanoES exhibited robust electronic properties and have been used alone or combined with other biomaterials as biocompatible extracellular scaffolds for 3D culture of neurons, cardiomyocytes and smooth muscle cells. Furthermore, we show the integrated sensory capability of the nanoES by real-time monitoring of the local electrical activity within 3D nanoES/cardiomyocyte constructs, the response of 3D-nanoES-based neural and cardiac tissue models to drugs, and distinct pH changes inside and outside tubular vascular smooth muscle constructs.

Vertically aligned carbon nanofiber as nano-neuron interface for monitoring neural function

Neural chips, which are capable of simultaneous multisite neural recording and stimulation, have been used to detect and modulate neural activity for almost thirty years. As neural interfaces, neural chips provide dynamic functional information for neural decoding and neural control. By improving sensitivity and spatial resolution, nano-scale electrodes may revolutionize neural detection and modulation at cellular and molecular levels as nano-neuron interfaces. We developed a carbon-nanofiber neural chip with lithographically defined arrays of vertically aligned carbon nanofiber electrodes and demonstrated its capability of both stimulating and monitoring electrophysiological signals from brain tissues in vitro and monitoring dynamic information of neuroplasticity. This novel nano-neuron interface may potentially serve as a precise, informative, biocompatible, and dual-mode neural interface for monitoring of both neuroelectrical and neurochemical activity at the single-cell level and even inside the cell.

FROM THE CLINICAL EDITOR

The authors demonstrate the utility of a neural chip with lithographically defined arrays of vertically aligned carbon nanofiber electrodes. The new device can be used to stimulate and/or monitor signals from brain tissue in vitro and for monitoring dynamic information of neuroplasticity both intracellularly and at the single cell level including neuroelectrical and neurochemical activities.

Vertical nanowire electrode arrays as a scalable platform for intracellular interfacing to neuronal circuits

Deciphering the neuronal code--the rules by which neuronal circuits store and process information--is a major scientific challenge. Currently, these efforts are impeded by a lack of experimental tools that are sensitive enough to quantify the strength of individual synaptic connections and also scalable enough to simultaneously measure and control a large number of mammalian neurons with single-cell resolution. Here, we report a scalable intracellular electrode platform based on vertical nanowires that allows parallel electrical interfacing to multiple mammalian neurons. Specifically, we show that our vertical nanowire electrode arrays can intracellularly record and stimulate neuronal activity in dissociated cultures of rat cortical neurons and can also be used to map multiple individual synaptic connections. The scalability of this platform, combined with its compatibility with silicon nanofabrication techniques, provides a clear path towards simultaneous, high-fidelity interfacing with hundreds of individual neurons.

Intact mammalian cell function on semiconductor nanowire arrays: new perspectives for cell-based biosensing

Nanowires (NWs) are attracting more and more interest due to their potential cellular applications, such as delivery of compounds or sensing platforms. Arrays of vertical indium-arsenide (InAs) NWs are interfaced with human embryonic kidney cells and rat embryonic dorsal root ganglion neurons. A selection of critical cell functions and pathways are shown not to be impaired, including cell adhesion, membrane integrity, intracellular enzyme activity, DNA uptake, cytosolic and membrane protein expression, and the neuronal maturation pathway. The results demonstrate the low invasiveness of InAs NW arrays, which, combined with the unique physical properties of InAs, open up their potential for cellular investigations.

Patternable nanowire sensors for electrochemical recording of dopamine

Spatially resolved electrochemical recording of neurochemicals is difficult due to the challenges associated with producing nanometer-scale patternable and integrated sensors. We describe the lithographic fabrication and characterization of patternable gold (Au) nanowire (NW) based sensors for the electrochemical recording of dopamine (DA). We demonstrate a straightforward NW-size-independent approach to align contact pads to NWs. Sensors, with NW widths as small as 30 nm, exhibited considerable insensitivity to scan rates during cyclic voltammetry, a nonlinear increase in oxidation current with increasing NW width, and the selectivity to measure submaximal synaptic concentrations of DA in the presence of interfering ascorbic acid. The electrochemical sensitivity of Au NW electrode sensors was much larger than that of Au thin-film electrodes. In chronoamperometric measurements, the NW sensors were found to be sensitive for submicromolar concentration of DA. Hence, the patternable NW sensors represent an attractive platform for electrochemical sensing and recording.

Carbon nanofibers and carbon nanotubes in regenerative medicine

Carbon nanotubes and carbon nanofibers have long been investigated for applications in composite structural materials, semiconductor devices, and sensors. With the recent well-documented ability to chemically modify nanofibrous carbon materials to improve their solubility and biocompatibility properties: a whole new class of bioactive carbon nanostructures has been created for biological applications. This review focuses on the latest applications of carbon nanofibers and carbon nanotubes in regenerative medicine.

Interactions Between Cultured Neurons and Carbon Nanotubes: A Nanoneuroscience Vignette

Carbon nanotubes, owing to their electrical, chemical, mechanical, and thermal properties, are one of the most promising nanomaterials for the electronics, computer, and aerospace industries. More recently, these unique materials are finding their niche in neuroscience. Here, we discuss the use of carbon nanotubes as scaffolds for neuronal growth. The chemical properties of carbon nanotubes can be systematically varied by attaching different functional groups. Such functionalized carbon nanotubes can be used to control the outgrowth and branching pattern of neuronal processes. We also discuss electrical interactions between neurons and carbon nanotubes. The electrical properties of nanotubes can provide a mechanism to monitor or stimulate neurons through the scaffold itself. The ease of which carbon nanotubes can be patterned makes them attractive for studying the organization of neural networks and has the potential to develop new devices for neural prosthesis. We note that additional toxicity studies of carbon nanotubes are necessary so that exposure guidelines and safety regulations can be set.

Flexible carbon nanotubes electrode for neural recording

This paper demonstrates a novel flexible carbon nanotubes (CNTs) electrode array for neural recording. In this device, the CNTs electrode arrays are partially embedded into the flexible Parylene-C film using a batch microfabrication process. Through this fabrication process, the CNTs can be exposed to increase the total sensing area of an electrode. Thus, the flexible CNTs electrode of low impedance is realized. In application, the flexible CNTs electrode has been employed to record the neural signal of a crayfish nerve cord for in vitro recording. The measurements demonstrate the superior performance of the presented flexible CNTs electrode with low impedance (11.07 kohms at 1 kHz) and high peak-to-peak amplitude action potential (about 410 microV). In addition, the signal-to-noise ratio (SNR) of the presented flexible CNTs electrode is about 257, whereas the SNR of the reference (a pair of Teflon-coated silver wires) is only 79. The simultaneous recording of the flexible CNTs electrode array is also demonstrated. Moreover, the flexible CNTs electrode has been employed to successfully record the spontaneous spikes from the crayfish nerve cord. The amplitude of the spontaneous peak-to-peak response is about 25 microV.

Easily made single-walled carbon nanotube surface microelectrodes for neuronal applications

The present work examines the feasibility of a simple method for using single-walled carbon nanotubes (SWNT) to fabricate multielectrode arrays (MEA) for electrophysiological recordings. A suspension of purified SWNTs produced by arc discharged was directly deposited onto standard platinum electrodes. The in vitro impedance and electrochemical characterizations demonstrated the enhanced electrical properties of the SWNT microelectrode array. To test its functionality we performed extracellular ganglion cell recordings in isolated superfused rabbit retinas. Our results showed that SWNT based electrode arrays have potential advantages over metal electrodes and can be successfully used to record the single and multi-unit activity of ganglion cell populations.

Positional control of catalyst nanoparticles for the synthesis of high density carbon nanofiber arrays

Precise arrangement of nanoscale elements within larger systems, is essential to controlling higher order functionality and tailoring nanophase material properties. Here, we present findings on growth conditions for vertically aligned carbon nanofibers that enable synthesis of high density arrays and individual rows of nanofibers, which could be used to form barriers for restricting molecular transport, that have regular spacings and few defects. Growth through plasma-enhanced chemical vapor deposition was initiated from precisely formed nickel catalyst dots of varying diameter and spacing that were patterned through electron beam lithography. Nanofiber growth conditions, including power, precursor gas ratio, growth temperature and pressure were varied to optimize fiber uniformity and minimize defects that result from formation and migration of catalyst particles prior to growth. It was determined that both catalyst dot diameter and initial plasma power have a considerable influence on the number and severity of defects, while growth temperature, gas ratio (C(2)H(2):NH(3)) and pressure can be varied within a considerable range to fine-tune nanofiber morphology.

Vertically aligned carbon nanofiber arrays: an electrical and genetic substrate for tissue scaffolding

We present a discussion of the use of vertically-aligned carbon nanofibers (VACNFs) as nanoscale elements that directly interface to biological whole-cell systems. VACNFs are compatible with a large subset of microfabrication processes, thereby enabling their incorporation into mesoscale hybrid systems that provide addressability of the VACNFs as either bulk electrode material, or as individually addressed nanoelectrodes. These VACNF devices are compatible with cell cultures, and electrochemical addressability of nanofibers can be maintained for extended periods within cell cultures. We present results that demonstrate possible use of VACNF devices as electrical and genetic substrates for tissue scaffolding applications.

Vertically aligned carbon nanofiber arrays record electrophysiological signals from hippocampal slices

Vertically aligned carbon nanofiber (VACNF) electrode arrays were tested for their potential application in recording neuro-electrophysiological activity. We report, for the first time, stimulation and extracellular recording of spontaneous and evoked neuroelectrical activity in organotypic hippocampal slice cultures with ultramicroelectrode VACNF arrays. Because the electrodes are carbon-based, these arrays have potential advantages over metal electrodes and could enable a variety of future applications as precise, informative, and biocompatible neural interfaces.

Biocompatible Conductive Architecture of Carbon Nanofiber-Doped Chitosan Prepared with Controllable Electrodeposition for Cytosensing

A novel architecture was designed by combining the biocompatibility of chitosan (CS) and excellent conductivity of carbon nanofiber (CNF). The controllable electrodeposition of soluble CNF-doped CS colloidal solution formed a robust CNF-CS nanocomposite film with good biocompatibility for the immobilization and cytosensing of K562 cells on an electrode. The formed architecture was characterized using scanning electron microscopic, infrared spectrum, contact angle, and thermogravimetric analyses. The adhesion of K562 cells on the nanocomposite film-modified electrode could be followed with electrochemical impedance spectroscopy and cyclic voltammetry. The presence of CNF facilitated the electrochemical behavior of K562 cells. The impedance of electronic transduction was related to the amount of the adhered cells, producing a highly sensitive impedance sensor for K562 cells ranging from 5 x 10(3) to 5.0 x 10(7) cells mL-1 with a limit of detection of 1 x 10(3) cells mL-1. This work suggested a strategy to prepare a biocompatible and conductive interface for immobilization and electrochemical detection of cells and opened a way for the application of CNF in cytosensing.