Nanoscale Electrodes Research Articles

Electrochemical properties of pre-lithiated nanorod-like LixV6O13 lithium ion battery cathode materials prepared by solvothermal method

Vanadium oxides have been proved to be prospective nanoscale electrode materials which are being extensively explored in electrochemical. However, low cycle stability and multiplier performance have limited the commercial application of materials. To overcome this disadvantage, a rod-like LixV6O13 was synthesized by solvothermal method using LiNO3, V2O5, C2H5OH (Ethanol absolute) as raw materials. The diameter of rod-shaped LixV6O13 was between 200 and 500 nm and presented excellent dispersibility. The results indicated that proper pre-lithiation improved the specific capacity and rate performance of V6O13. When x = 0.055 (VO-Li2), the rod-like LixV6O13 exhibited a capacity retention of 69.1% after 100 cycles at 0.1 C (42 mA/g) and a discharge capacity of 98.5 mAh/g after 100 cycles at 1 C, comparing to those of the pure V6O13 of only 39.5% and 39.7 mAh/g respectively. The results of SEM and CV tests demonstrated that the improved electrochemical properties were mainly attributed to the increase of material specific surface area and the change of internal structure caused by lithium insertion, which promoted the kinetics of the chemical reaction and the electrochemical performance of LixV6O13. The applicability of the method was further examined through the disassembly of the battery after the cycle, providing the possibility of commercialization of V6O13 lithium ion battery cathode materials.

Homogenization of carbon-nanotube brush electrodes

Carbon nanotube brushes (carbon nanotubes attached to a current collector) have been proposed for nanoscale electrodes. While the detailed molecular scale physics is important in its own right, often a more useful scale to examine electrode performances is the micro and meso scale continuum. The detailed structure of microscale material parameters results from statistical mechanics and will not be discussed here, rather we focus on the micro scale homogenization to the meso scale wherein material parameters result from a micro scale “cell” problem for a periodic lattice. We apply a matched asymptotic formulation to obtain the meso scale field equations and material parameters. The finite element method (FEM) and finite volume method (FVM) are employed to solve the micro scale cell problem and the mesoscale field equations, respectively. Numerical results are presented for the electrical potential field and concentration of cations and anions. For a test case, it is observed that a doubling of the electrode area can create a ten-fold increase in the potential which has interesting implications for electrode design.

(Invited) Electrodeposited Metallic Nanowires for Bioanalytic Nanofluidic Devices

Electrodeposited metallic nanowires have been demonstrated as electrode or sensing materials in many applications such as optoelectronic devices, energy devices, and biosensors due to their excellent electrical and optical properties. However, most of previous demonstrations utilized the metallic nanowires in the form of percolating networks. Individual nanowires also have potential as nanoscale electrodes or nanoscale sensing materials for the applications where electrical signals need to be extracted from nanoscale components of the device. In this sense, metallic nanowires are suitable electrode or sensing materials for bioanalytic nanofluidic devices where electrical signals from nanoscale single molecules need to be interrogated in a device with nanoscale components. This talk will present strategies and technical challenges to be resolved in applying individual metallic nanowires in bioanalytic nanofluidic devices. While high rate synthesis of metallic nanowires can be achieved via electrodeposition in a nanoporous template, the main challenges to produce nanofluidic devices with individual nanowire electrodes include position and aligning the nanowires at designated locations and cover-plate bonding in the presence of electrode structures. Also, the efforts on device fabrication need to be combined with the effort on engineering nanowires with both sufficient mechanical strength and improved electrical conductivity, so that the nanowires are compatible with both the fabrication and operational protocols. This work is a part of the effort from the NIH Center for BioModular Multiscale Systems for Precision Medicine (CBM2) where the center goal is to design, produce and deliver to the medical community mixed-scale tools for analyzing circulating biomarkers for disease management for precision medicine

Spherical Shaped Particle of Randomly Packed LiFePO4 Nanoplates for High-Rate of Li-Ion Batteries

Energy storage is the key factor for saving and using renewable energy. Among the various energy storage devices, Li-ion battery is the most promising storage device owing to its high energy density, efficiency and cycle life. Not only for the small application like mobile phone and laptop computer but also electric vehicles (EVs) and massive energy storage system (ESS), numerous applications have been used Li-ion battery. However its high energy density is like a double-edged sword, the safety issues have been a problem for the practical market. The safety problems from the Li-ion battery usually come from thermal runaway, which is mainly come from oxygen release from the cathode material. Lithium iron phosphate (LFP) has PO4 polyanion that oxygen atom is strongly bonded with phosphorus and prevents oxygen release, therefore, it is well known as the safe cathode material for the Li-ion battery. Also for the high power battery applications, LFP is a promising material owing to the ability of high-rate charge and discharge performance. For the high rate availability on LFP material, two important key factors should be satisfied; one is fast ion diffusion inside the material and the other is high electric conductivity. The Li-ion diffusivity coefficient and electron conductivity are intrinsic properties of the material, however, particle size or morphology and conducting agent coating can raise the speed of diffusion and conduction. Here, we demonstrated those factors by solvo-thermally synthesized plate shape nanoparticle and spherical secondary particle with carbon coating using spray-drying. The nanoparticle has a flat shape in b-axis, therefore, diffusion speed increase because the diffusion distance of lithium is greatly reduced. The nanoparticle without spray-drying showed low capacity and also poor C-rate performance even with the carbon coating. Besides, after forming the spherical particles, it showed 162mAh/g of initial capacity at the 0.1C rate and maintains more than 80% of initial capacity (~130.91mAh/g) at the 50C rate. Moreover, electrode density which is the intrinsic weakness of nanoscale electrode material has been improved and the spheres carried out excellent cycling ability which shows 98% capacity retention over 500cycles at 1C after the high C-rate test. In order to analyze the causes of such good characteristics, morphology and crystallographic directions were confirmed by SEM and TEM image, and electrical conductivity and diffusion coefficient were calculated by using Cyclic Voltammetry (CV), Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS). More details will be discussed at the meeting.

ALD HfO2 Films for Defining Microelectrodes for Electrochemical Sensing and Other Applications

Microelectrodes are used in a wide range of applications from analytical electrochemistry and biomolecular sensing to in vivo implants. While a variety of insulating materials have been used to define the microelectrode active area, most are not suitable for nanoscale electrodes (<1 μm2) due to the limited robustness of these films when the film thickness is on the order of the nanoelectrode dimension. In this study, we investigate atomic layer deposited hafnium dioxide (ALD HfO2) as an insulating film to coat planar platinum microelectrodes, with the active areas being defined where the HfO2 is etched. Thermally grown films with thicknesses between 10 and 60 nm were deposited by 100 to 550 ALD cycles and were initially characterized by measuring their standard electrical properties and imaging incipient texture development. Electrochemical measurements on the structures were made, including linear sweep voltammetry and electrochemical impedance spectroscopy, which identified the presence of pinholes in films deposited over the range of 100 to 350 cycles, resulting in leakage. These measurements also suggest a lower limit to the size of microelectrodes below which the electrochemical current detected is no longer dominated by that through the exposed active area. A bilayer insulator comprising ALD HfO2 coated with parylene-C was investigated to minimize the pinhole leakage. Steady-state currents were measured for different electrode areas, qualitatively agreeing with the theory for areas down to ∼1 μm2. For sub-square micrometer electrode areas, bilayer-insulated devices with parylene-C apertures that exposed the smallest microelectrode area showed measured currents that were consistent with extrapolations, indicating that it reduces leakage through HfO2.

Silicon nanowires to detect electric signals from living cells

The ability to merge electronic devices with biological systems at the cellular scale is an interesting perspective. Potential applications span from investigating the bio-electric signals in excitable (and non-excitable) cells with an insofar-unreached resolution to plan next-generation therapeutic devices. Semiconductor nanowires are well suited for achieving this goal because of their intrinsic size and wide range of possible configurations. However, production of such nanoscale electrodes can be pricey, time-consuming and affected by poor compatibility with the Complementary Metal-Oxide-Semiconductor integrated circuits (CMOS-IC) process standards. To take a step forward, we introduced a new method to fabricate small, high-density Silicon Nanowires (SiNWs) with a fast, relatively inexpensive and low-temperature (200 °C) process compatible with CMOS-IC standards, thus theoretically allowing on-site amplification of bioelectric signals from living cells in tight contact. Here, we report our preliminary data showing the biocompatibility of SiNWs, as a necessary step to produce a compact device providing super-resolved descriptions of bioelectric waveforms captured from the subcellular to the network level.

Enhanced pseudocapacitive energy storage properties of Nb 2 O 5 /C core‐shell structures with the surface modification

Pseudocapacitive energy storage is an attractive technology as it can achieve high energy density at high rate conditions. However, its practical application has been an issue because of low electrical conductivity of nanoscale electrode materials. Surface coating is an effective way to enhance the electrochemical properties of the electrochemical energy storage system by helping electron transfer between the electrode material and current collector. In order for surface coating technologies to be applied to pseudocapacitive energy storage field, providing fast ions and electrolyte transport through the coating layer as well as high electrical conductivity is essential because pseudocapacitors aim for high rate charge/discharge capability. In this paper, the Nb2O5/carbon core-shell structure is developed to meet these requirements. Simple microwave-assisted method is applied to create nanoscale (approximately 5 nm) conductive carbon layer on the surface of bare Nb2O5 nanoparticles, and the high power capability of Nb2O5/carbon core-shell is improved further by oxidation process providing open structure for electrolyte and ion diffusion. Thick electrode architecture containing oxidized Nb2O5/carbon core-shell shows superior high rate performance as capacities of 215 C g−1 are obtained at a 50 mV s−1 scan rate.

Effects of Atomic Layer Deposition of ZrO2 on Infiltrated Mixed Ionic and Electronic Conducting Solid Oxide Cell Electrodes

Infiltration of mixed ionic and electronic conducting (MIEC) nanoparticles into ionic or MIEC scaffolds has been employed to improve the performance of solid oxide cells (SOCs) designed to operate at relatively low temperatures (<600°C). However, the high MIEC specific surface area also hastens sintering and coarsening processes that can lead to a high rate of performance degradation for the electrodes over time. Atomic layer deposited (ALD) coatings have been investigated as a means of curbing the degradation of nano-scale MIEC electrodes. ALD is desirable for coating porous electrodes because of its self-limiting layer-growth characteristic — fully conformal coating can ideally be achieved throughout the depth of a porous electrode, including the most electrochemically active region near the electrolyte. However, results reported to date have yielded mixed results: in some cases, the ALD coating suppresses degradation, whereas in others the coating actually degrades electrode performance. Successful performance improvement seems to be dependent on a combination of factors from choice of electrode substrate and its architecture, to the coating species, its thickness throughout an electrode, and the experimental procedures for coating. This presentation seeks to better elucidate the nature of these dependencies via a study of Sr0.5Sm0.5CoO3-δ (SSC) infiltrated Gd-doped ceria (GDC) electrodes with ALD-ZrO2 coating. Life tests were carried out with degradation accelerated by using a relatively high ageing temperature of 750°C, with impedance spectroscopy measured periodically at 600°C. Rises in polarization resistance with time were substantially mitigated by 30 ALD deposition cycles, and to a lesser extent by 60 cycles, relative to uncoated samples. The overall 0-hour performance is virtually the same across the coated and uncoated samples after a short break-in period, with the benefit from ALD being entirely in the increased sustained performance. The mechanistic benefit of ALD-ZrO2 on these electrodes is parsed with the aid of microstructural and chemical characterization. Scanning electron microscopy with energy dispersive spectroscopy of cross-sections of the coated samples reveals a substantial gradient in the ZrO2 coating thickness, with several nm thickness near the free surface decreasing to sub-monolayer thickness near the electrode/electrolyte interface. This is sensible because thicker ZrO2 coatings on SSC powders were found by powder x-ray diffraction to react extensively, forming Sr- and Sm-zirconates and cobalt oxide species. The results suggest that sub-monolayer ALD-ZrO2 coatings form a very thin layer of reactants that do not cover electrochemically-active surface sites but can help suppress particle coarsening. Based on this mechanism, a coarsening model previously developed for infiltrated SSC-GDC electrodes is shown to fit the polarization resistance versus time data by assuming that the ALD layer decreases the cation diffusion. The ideal thickness is that which balances the negative effect of the reaction of active SSC material with the positive effect of a reduced effective diffusion coefficient. This thickness is sensitive to the number of ALD cycles deposited as well as the aspect ratio of the pores the ALD precursors must traverse within the electrode. The results will be contrasted to those obtained from ALD-ZrO2 on conventional La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrodes, which do not degrade by coarsening due to the larger feature sizes. In this case, there is no benefit from monolayer-thickness ALD-ZrO2, and thicker layers substantially degrade the performance. Figure 1

(Invited) Fast-Scan Nanogap Voltammetry at Double-Carbon-Fiber Ultramciroelectrodes

In this presentation, we discuss theory [1] and experiment [2] of double-carbon-fiber (CF) ultramicroelectrodes (UMEs) with nanometer-wide gaps to voltammetrically obtain high time resolution, signal-to-background ratio, and kinetic selectivity for dopamine (DA) against ascorbic acid (AA). The novel nanogap-based electrodes are fabricated by using a pair of ~7 µm-diameter CFs, which are inserted into a double-bore glass capillary, heat-pulled, and milled by focused-ion-beam technology to yield ~50 µm-long double-cylinder UMEs separated by a nanometer-wide gap without extensive nanolithography or nanoscale electrode positioning required for other nanogap electrodes. Double-CF UMEs are characterized electrochemically by investigating the redox cycling of the Ru(NH3)6 3+/2+ couple across a nanogap between voltammetric generator and amperometric collector electrodes to achieve quasi-steady states at fast scan rates of 100 V/s, which is ~1000 times faster than reported with any nanogap-based electrochemical cell. Importantly, the transient background of the amperometric collector response is suppressed ~100 times in comparison with that of the voltammetric generator response to enable the quantitative analysis of the collector response against the cycled generator potential without background subtraction. Finite element analysis of oxidative amperometric responses to Ru(NH3)6 2+ at the collector electrode at up to 100 V/s yield consistent gap widths of ~0.18 µm and a standard electron-transfer rate constant of 0.9 cm/s. Moreover, nanogap-mediated redox cycling can be initiated by DA oxidation at the generator electrode to largely improve the DA selectivity of the collector response against AA, which is also oxidized at the generator electrode to immediately and irreversibly produce a redox-inactive species, thereby minimizing the corresponding collector response. The probe-type design of double-CF UMEs as well as their high DA selectivity against AA is attractive for in-vivo applications. [1] Pathirathna, P.; Balla, R. J.; Amemiya, S. “Simulation of fast-scan nanogap voltammetry at double-cylinder ultramicroelectrodes.” J. Electrochem. Soc., Focus Issue on the Brain and Electrochemistry Honoring R. Mark Wightman and Christian Amatore, 2018, 165, G3026. [2] Pathirathna, P.; Balla, R. J.; Amemiya, S. “Nanogap-based electrochemical measurements at double-carbon-fiber ultramicroelectrodes.” Anal. Chem. 2018, 90, 11746.

Na2V6O16·2.14H2O nanobelts as a stable cathode for aqueous zinc-ion batteries with long-term cycling performance

Abstract Aqueous zinc-ion batteries (ZIBs) have been considered as one of the most promising electrochemical devices for large-scale energy storage system owing to their low cost and high safety. Herein, Na2V6O16·2.14H2O nanobelts are synthesized and applied as cathode material for ZIBs. The sample displays a high capacity of 466 mAh g−1 at 100 mA g−1 and stable cycling performance with a capacity retention of 90% over 2000 cycles at the 20 A g−1. Moreover, Na2V6O16·2.14H2O presents a capable rate ability and a high energy density of 312 Wh kg−1 at a specific power of 70 W kg−1. The superior electrochemical performance is attributed to the large interlayer spacing and outstanding structure stability, which promise the highly reversible intercalation and extraction of zinc ion. The electrochemical kinetics and zinc ion storage mechanism are also investigated. This work demonstrates that nanoscale electrode materials with large interlayer spacing can effectively enhance the electrochemical performance of aqueous ZIBs, which can be extended to other metal ion batteries, such as magnesium ion batteries and aluminum ion batteries.

Improving the processability and cycling stability of nano-LiFePO4 cathode by using PVDF/TX binary binder

ABSTRACTIn lithium-ion battery industry, the nanoscale electrode materials usually have difficulty to be dispersed well in the electrode slurry. The inferior processability thus results in deteriorated electrochemical performances of the cell. In this work, poly(vinylidene fluoride) (PVDF) and terpene resin (TX) as a binary binder are used to improve the dispersibility and cycling stability of nanoscale LiFePO4 (nano-LFP) cathode. The wettability, dispersibility, adhesion strength and electrochemical performance of nano-LFP cathode using PVDF/TX are measured and compared with that using only PVDF binder. Nano-LFP cathode using PVDF/TX binder (the optimal ratio of PVDF to TX is 97:3) exhibits better dispersibility and stronger adhesion strength than that of PVDF. In addition, nano-LFP cathode with PVDF/TX binder shows better cycling stability, rate capability, and electrochemical kinetics than that with PVDF, retaining 97.4% capacity after 100 cycles test at C/5 in room temperature and 93.4% capacity after 60 cycles test at C/2 in 55℃, respectively.

Investigation of Electrochemical Nanostructuring with Ultrashort Pulses by Using Nanoscale Electrode

Background: Electrochemical machining (ECM) is a non-traditional machining method for the metal material based on the principle of anode electrochemical dissolution which has been used in micro/nano fabrication with advantages as not influenced by materials intensity and hardness, no residual stress and no heat treatment born on the surface of the workpiece. Several researches and applications have shown that the surface quality can be improved effectively during the electrochemical machining by using ultrashort pulse power supply. Method: This paper presents a potential of electrochemical machining at the nanometer scale. First, a transient charging double layer mathematical model is developed to describe electrochemical nanostructuring of metallic materials with ultrashort (nanosecond) voltage pulses. And then, by using finite element method (FEM), the analysis model of electrochemical interface between poles is established to give a more realistic analysis of the comparison of transient currents at different separations between the tool and workpiece. Second, a nanoscale electrode is an essential tool in electrochemical nanostructuring. In this paper, electrodes with diameters of several ten to hundred nanometers are successfully prepared by the liquid membrane electrochemical etching. Finally, by using the nanometer scale electrodes above and the ultrashort pulse power supply, several nanostructures with physical dimension of several hundred nanometers are fabricated on nickelbased superalloys. Results: Using the optimal machining parameters, a tool electrode with 230 nm in diameter is obtained from the initial tungsten rod radius of 100 μm. By using 0.05 M H2SO4 solution, the pulse generator with 1μs in period, 100 ns in pulse on-time and 4 V in voltage, a micro/nano groove with the depth of 150 nm and maximum entrance width of 3 μm is obtained. Conclusion: Nanoscale electrodes with diameters of several ten to hundred nanometers is obtained successfully demonstrating that the liquid membrane electrochemical etching is a very effective method to fabricate nanoscale electrode. Several nanostructures with physical dimension of several hundred nanometers can be fabricated successfully demonstrating that ECM with ultrashort pulses is a highly promising nanostructuring technology.

Microwave-assisted synthesis of nano petal-like α-Ni(OH)2/RGO and its electrochemical performance

A nanoscale petal-like α-Ni(OH)2/reduced graphene oxide (α-Ni(OH)2/RGO) composite was synthesized with the one-step microwave method. α-Ni(OH)2 particles with sizes of approximately 200 nm are uniformly distributed on the reduced graphene oxide sheet in the sample. When used as an electrode for alkaline rechargeable batteries, the discharge capacity of the α-Ni(OH)2/RGO composite reaches 333.5 mAh/g at 0.2C and 247.1 mAh/g at 10 C, respectively, with an excellent rate capability. After 2000 cycles, the capacity of the electrode is insignificantly attenuated, indicating a high capacity retention and cycling stability. The outstanding electrochemical properties are attributed to the nanoscale petal-like structure α-Ni(OH)2 anchoring on the RGO sheets, which facilitates ion diffusion and increases the active surface, which is effectively reacting with the electrolyte. The nanoscale petal-like electrode material fabricated in this study provides clues to address the problem of energy applications of high-performance alkaline rechargeable batteries.

In situ chemical sensing by using scanning probe microscope

Scanning electrochemical microscopy (SECM), which utilizes microelectrodes as a probe to measure the chemicals released and consumed by cells as current signal, is a promising tool for measuring the metabolites of cells. We have improved SECM resolution for single cell imaging by miniaturizing the size of the electrode and developing hybrid system of SECM and scanning ion conductance microscopy (SICM), which utilizes nanopipette as a probe to measure live cell topography. SECM-SICM provides simultaneous imaging of concentration profiles of chemical substances and cell surface topography. Using this system, we successfully measured the release of neurotransmitters from PC12 cells. In addition, the nanoscale electrodes are useful for intracellular chemical detection by inserting the electrodes into cells and measured reactive oxygen species (ROS).

Nanopipette-assisted single cell metabolic glycan labeling.

Here, we report a single cell glycan labeling strategy by combining nanoscale intracellular glass electrodes with bioorthogonal reaction. With the tip diameter less than 100 nm, the nanopipette electrode can be spatially controlled to inject artificial monosaccharides into single living cells with minimal invasion. The injection process can be precisely regulated by electroosmotic flow inside the nanopipette, and fluorescence labeling of sialic acid at single cell level is achieved.

Design of Nano-scale Electrodes and Development of Avatar-Based Control System for Energy-Efficient Power Engineering

In this article is described the avatar-based energy-efficient power engineering control system, which is based on authors results published previously related to development of an Internet of Things and people (IOTAP) and the digital twins systems. The authors are described the development of the innovation tools for digital twins system, based on Avatar-based Control Techniques.

High rate capability electrode constructed by anchoring CuCo2S4 on graphene aerogel skeleton toward quasi-solid-state supercapacitor

Designing nano-scale electrode materials has been proven to be an efficient path for enhancing the rate capability and stability of supercapacitors. Herein, a novel electrode is designed by anchoring copper cobalt sulfide (CuCo2S4) nanoparticles on the graphene aerogel (GA) via a facile solvothermal method. The CuCo2S4 particles with an average size of 21 nm can guarantee the abbreviated ion diffusion paths and the GA can ensure a conductive skeleton and prevent CuCo2S4 from agglomeration, thus promoting kinetics and efficiency of electrochemical process synchronously. As a result, the CuCo2S4/GA electrode exhibits a high specific capacitance of 668 F g−1 at a current density of 1 A g−1 along with 72% retention as the current increases to 20 A g−1, showing a decent rate capability. The measurable analysis of charge storage reveals that the surface capacitive process plays a dominant role during the electrochemical process and its proportion raises with the increase of the scan rate, resulting in excellent rate capability. Additionally, a quasi−solid−state supercapacitor is assembled by using CuCo2S4/GA composite as the free-standing electrode, which delivers an energy density of 22 W h kg−1 together with a power density of 1080 W kg−1, implying the potential application in supercapacitors.

Nanogap-Based Electrochemical Measurements at Double-Carbon-Fiber Ultramicroelectrodes.

Electrochemical measurements with unprecedentedly high sensitivity, selectivity, and kinetic resolution have been enabled by a pair of electrodes separated by a nanometer-wide gap. The fabrication of nanogap electrodes, however, requires extensive nanolithography or nanoscale electrode positioning, thereby preventing the full exploration of this powerful method in electrode design and application. Herein, we report the simple fabrication of double-carbon-fiber ultramicroelectrodes (UMEs) with nanometer-wide gaps not only to facilitate nanogap-based electrochemical measurements but also to gain high time resolution, signal-to-background ratio, and kinetic selectivity for dopamine against ascorbic acid. Specifically, ∼7 μm-diameter carbon fibers are inserted into a double-bore glass capillary, heat-pulled, and milled by focused ion-beam technology to yield ∼50 μm-long double-cylinder UMEs. The redox cycling of the Ru(NH3)63+/2+ couple across a nanogap between voltammetric generator and amperometric collector electrodes reaches quasi-steady states at fast scan rates of 100 V/s as demonstrated experimentally and even 1000 V/s as predicted theoretically. The transient background of the amperometric collector response is suppressed ∼100 times in comparison with that of the voltammetric generator response. Nanogap voltammograms based on the collector response against the cycled generator potential are quantitatively analyzed without background subtraction to reproducibly yield nanogap widths of ∼0.18 μm and a standard electron-transfer rate constant of 0.9 cm/s. Moreover, nanogap-mediated redox cycling can be initiated by dopamine oxidation at the generator electrode to largely improve the dopamine selectivity of the collector response against ascorbic acid, which is also oxidized at the generator electrode to immediately and irreversibly produce a redox-inactive species.

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.

Potential-Controlled Adsorption, Separation, and Detection of Redox Species in Nanofluidic Devices.

Nanoscale channels and electrodes for electrochemical measurements exhibit extreme surface-to-volume ratios and a correspondingly high sensitivity to even weak degrees of surface interactions. Here, we exploit the potential-dependent reversible adsorption of outer-sphere redox species to modulate in space and time their concentration in a nanochannel under advective flow conditions. Induced concentration variations propagate downstream at a species-dependent velocity. This allows one to amperometrically distinguish between attomole amounts of species based on their time-of-flight. On-demand concentration pulse generation, separation, and detection are all integrated in a miniaturized platform.