Unified selective sorting approach to analyse multi-electrode extracellular data

Extracellular data analysis has become a quintessential method for understanding the neurophysiological responses to stimuli. This demands stringent techniques owing to the complicated nature of the recording environment. In this paper, we highlight the challenges in extracellular multi-electrode recording and data analysis as well as the limitations pertaining to some of the currently employed methodologies. To address some of the challenges, we present a unified algorithm in the form of selective sorting. Selective sorting is modelled around hypothesized generative model, which addresses the natural phenomena of spikes triggered by an intricate neuronal population. The algorithm incorporates Cepstrum of Bispectrum, ad hoc clustering algorithms, wavelet transforms, least square and correlation concepts which strategically tailors a sequence to characterize and form distinctive clusters. Additionally, we demonstrate the influence of noise modelled wavelets to sort overlapping spikes. The algorithm is evaluated using both raw and synthesized data sets with different levels of complexity and the performances are tabulated for comparison using widely accepted qualitative and quantitative indicators.

A diamond-based electrode for detection of neurochemicals in the human brain

Deep brain stimulation (DBS), a surgical technique to treat certain neurologic and psychiatric conditions, relies on pre-determined stimulation parameters in an open-loop configuration. The major advancement in DBS devices is a closed-loop system that uses neurophysiologic feedback to dynamically adjust stimulation frequency and amplitude. Stimulation-driven neurochemical release can be measured by fast-scan cyclic voltammetry (FSCV), but existing FSCV electrodes rely on carbon fiber, which degrades quickly during use and is therefore unsuitable for chronic neurochemical recording. To address this issue, we developed durable, synthetic boron-doped diamond-based electrodes capable of measuring neurochemical release in humans. Compared to carbon fiber electrodes, they were more than two orders-of-magnitude more physically-robust and demonstrated longevity in vitro without deterioration. Applied for the first time in humans, diamond electrode recordings from thalamic targets in patients (n = 4) undergoing DBS for tremor produced signals consistent with adenosine release at a sensitivity comparable to carbon fiber electrodes. (Clinical trials # NCT01705301).

High-performance supercapacitor electrode from cellulose-derived, inter-bonded carbon nanofibers

Carbon nanofibers with inter-bonded fibrous structure show high supercapacitor performance when being used as electrode materials. Their preparation is highly desirable from cellulose through a pyrolysis technique, because cellulose is an abundant, low cost natural material and its carbonization does not emit toxic substance. However, interconnected carbon nanofibers prepared from electrospun cellulose nanofibers and their capacitive behaviors have not been reported in the research literature. Here we report a facile one-step strategy to prepare inter-bonded carbon nanofibers from partially hydrolyzed cellulose acetate nanofibers, for making high-performance supercapacitors as electrode materials. The inter-fiber connection shows considerable improvement in electrode electrochemical performances. The supercapacitor electrode has a specific capacitance of ∼241.4 F g-1 at 1 A g-1 current density. It maintains high cycling stability (negligible 0.1% capacitance reduction after 10,000 cycles) with a maximum power density of ∼84.1 kW kg-1. They may find applications in the development of efficient supercapacitor electrodes for energy storage applications.

Reducing electrowetting-on-dielectric actuation voltage using a novel electrode shape and a multi-layer dielectric coating

This paper presents design and fabrication of an electrowetting-on-dielectric (EWOD) device using a novel electrode shape and a multi-layer dielectric coating that reduce the actuation voltage of the device to less than 12.6 V. The fabrication of the EWOD electrodes is carried out in several steps including laser exposure, wet developing, etching, and stripping. A high-dielectric-constant multi-layer dielectric coating containing a 770 nm thick Polyvinylidene difluoride (PVDF) layer and a 1 µm thick Cyanoethyl pullulan (CEP) layer, is deposited on the EWOD electrodes for insulation. This multi-layer dielectric structure exhibits a high capacitance per unit area, and the novel electrode shape changes the actuation force at the droplet contact line reducing the voltage required to operate the device. In addition, an overlaying Teflon layer of 50 nm is placed on top of the dielectric structure to provide a hydrophobic surface for droplet manipulation. It is observed from the experiments that the electrode shape and the dielectric structure have contributed to the reduction of the actuation voltage of the EWOD device.

Facile fabrication of supercapacitors with high rate capability using graphene/nickel foam electrode

High-performance reduced graphene oxide/nickel foam (rGO/NF) composite electrodes for high-performance supercapacitors were prepared by flame-induced reduction of dry graphene oxide (GO) coated on nickel foam. Flame reduction of GO is a facile, feasible and cost-effective reduction technique, which is conducted without the need of any reductant. Most importantly, the rGO obtained by flame reduction showed a typical disordered cross-linking network and randomly distributed pores, which provide accessible routes for fast transportation of ions. It was demonstrated that the rGO/NF electrode with embedded current collector (NF) exhibited better electrochemical performance than conventional rGO film counterparts, including a high gravimetric specific capacitance of 228.6 F g-1 at a current density of 1 A g-1, excellent rate capability (over 81% retention at 32 A g-1) and high cycling stability with only 5.3% capacitance decay over 10,000 cycles of cyclic voltammetry at a ultrahigh scan rate of 1000 mV s-1. This facile method for the fabrication of rGO/NF electrodes could envision enormous potential for high performance energy storage devices.

Determination of ascorbic acid by a gold–zinc Oxide Nanoparticle-Modified Glassy carbon electrode

.A novel electrochemical sensing platform was developed based on flower-like gold–zinc oxide core–shell nanoparticles and a graphene nanocomposite-modified glassy carbon electrode. The gold–zinc oxide core–shell nanoflowers were synthesized by seed growth and characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet-visible absorption spectroscopy. The modified electrode provided good electrocatalytic properties, rapid response, high stability, and favorable reproducibility for determination of ascorbic acid. The performance of the sensor included a linear dynamic range from 1.0 × 10−7 to 6.0 × 10−4 M, a limit of detection of 3.9 × 10−8 M, and a sensitivity of 24.12 µA/mM. The nanocomposite also provided excellent selectivity and lower potential for the oxidation of ascorbic acid. The sensor was used for the determination of ascorbic acid in tablets with satisfactory results. This device provides rapid, simple, and selective determination of ascorbic acid.

Diamond-based electrode for chronic sensing in deep brain stimulation

This thesis describes the development of a sensing electrode and electronic research platform that enables the measurement of fluctuating levels of neurotransmitters in the human brain. Boron doped diamond electrodes were created via a custom developed chemical vapor deposition reactor for measurement of neurotransmitters using Fast Scan Cyclic Voltammetry.

Promising biomass-derived activated carbon and gold nanoparticle nanocomposites as a novel electrode material for electrochemical detection of rutin

In this paper, six types of typical bio-wastes are used to prepare activated carbons (ACs) by high-temperature carbonization and activation with KOH. A novel electrochemical sensor for rutin was developed based on a peanut shell-derived activated carbon and gold nanoparticle composite modified glassy carbon electrode (P-AC/AuNPs/GCE). The as-synthesized ACs and composites were characterized by a variety of physicochemical techniques. The proposed sensor exhibits ideal electrochemical behavior for rutin with a wide linear range, low detection limit, and good selectivity. The desirable electrochemical performance enables the biomass-derived ACs and their composites to act as new sources of carbonaceous materials for electrochemical sensors.

Temperature dependence of the electrode potential of a cobalt-based redox couple in ionic liquid electrolytes for thermal energy harvesting

Increasing the application of technologies for harvesting waste heat could make a significant contribution to sustainable energy production. Thermoelectrochemical cells are one such emerging technology, where the thermal response of a redox couple in an electrolyte is used to generate a potential difference across a cell when a temperature gradient exists. The unique physical properties of ionic liquids make them ideal for application as electrolytes in these devices. One of the keys to utilizing these media in efficient thermoelectrochemical cells is achieving high Seebeck coefficients, Se: the thermodynamic quantity that determines the magnitude of the voltage achieved per unit temperature difference. Here, we report the Se and cell performance of a cobalt-based redox couple in a range of different ionic liquids, to investigate the influence of the nature of the IL on the thermodynamics and cell performance of the redox system. The results reported include the highest Se to-date for an IL-based electrolyte. The effect of diluting the different ILs with propylene carbonate is also reported, which results in a significant increase in the output powers and current densities of the device.