A Multi-Channel Stimulator With High-Resolution Time-to-Current Conversion for Vagal-Cardiac Neuromodulation

This paper presents an integrated stimulator for a cardiac neuroprosthesis aiming to restore the parasympathetic control after heart transplantation. The stimulator is based on time-to-current conversion. Instead of the conventional current mode digital-to-analog converter (DAC) that uses ten of microamp for biasing, the proposed design uses a novel capacitor time-based DAC offering close to 10 bit of current amplitude resolution while using only a bias current 250 nA. The stimulator chip was design in a 0.18 m CMOS high-voltage (HV) technology. It consists of 16 independent channels, each capable of delivering 550 A stimulus current under a HV output stage that can be operated up to 30 V. Featuring both power efficiency and high-resolution current amplitude stimulation, the design is suitable for multi-channel neural simulation applications

A Multichannel High-Frequency Power-Isolated Neural Stimulator With Crosstalk Reduction

In neuroprostheses applications requiring simultaneous stimulations on a multielectrode array, electric crosstalk, the spatial interaction between electric fields from various electrodes is a major limitation to the performance of multichannel stimulation. This paper presents a multichannel stimulator design that combines high-frequency current stimulation (using biphasic charge-balanced chopped pulse profile) with a switched-capacitor power isolation method. The approach minimizes crosstalk and is particularly suitable for fully integrated realization. A stimulator fabricated in a 0.6 & #x03BC;m CMOS high-voltage technology is presented. It is used to implement a multichannel, high-frequency, power-isolated stimulator. Crosstalk reduction is demonstrated with electrodes in physiological media while the efficacy of the high-frequency stimulator chip is proven in vivo. The stimulator provides fully independent operation on multiple channels and full flexibility in the design of neural modulation protocols

A Bidirectional ASIC for Active Microchannel Neural Interfaces

Closed-loop neural prostheses have been widely used as a therapeutic strategy for a range of neurological, inflammatory, and cardiac disorders. Vagus nerve stimulation has shown promising results for the monitoring and treatment of post-operation symptoms of heart transplant recipients. A prime candidate for selective control of vagal fibres is the microchannel neural interface (MNI), which provides a suitable environment for neural growth and enables effective control of the neural activity in a bidirectional system. This paper presents the design and simulation of an ASIC in 180-nm high-voltage CMOS technology, capable of concurrent stimulation and neural recording with artifact reduction in a seven-channel MNI. The analog front-end amplifies action potentials with a gain of 40 dB, presenting a common-mode rejection ratio of 81 dB at 1 kHz and a noise efficiency factor of 5.13 over the 300 Hz to 5 kHz recording bandwidth. A 42-V-compliant stimulation module operates concurrently and independently across the seven channels

Photoelectrochemistry of two-dimensional and layered materials: a brief review

Two-dimensional (2D) materials have unique band structure and show a great promise for optoelectronic and solar energy harvesting applications. Photoelectrochemical (PEC) processes are intensively studied employing these materials, due to their high specific surface area, and the possibility of surface modification by defect engineering/catalyst deposition. The PEC activity of different 2D and layered materials was scrutinized for water oxidation/reduction and for inorganic ion oxidation by a statistical analysis to reveal any specific trends. Furthermore, some frequently studied performance improvement strategies (i.e., heterojunctions, tunnelling, and co-catalysts) are also discussed. Overall, exploring novel materials of 2D family, and new directions are both needed to initiate further discussions and additional research activity, which might enable to harness the full potential of these exciting materials

Photoelectrocatalytic Study of Gold-Modified Bismuth Vanadate for the Degradation of 4-Chlorophenol

This project details a study on the modification of monoclinic BiVO4 photocatalyst with gold nanoparticles for the degradation of 4-chlorophenol. It adapts methodologies in the literature for the synthesis of thin film semiconductor photocatalyst electrodes and photoelectrochemical characterization techniques, including voltammetry and chronoamperometry, to compare BiVO4 modified with 0.5, 0.75, 1, 2, and 4 wt% gold to its unmodified form. Additional parameters explored were the material of the counter electrode, the electrical potential bias, the spectra of illumination, and the addition of hydrogen peroxide. Analysis of data suggested that 2 wt% Au/BiVO4 was the most suitable thin film electrode for the degradation of 4-chlorophenol in a H2O2-Na2SO4 electrolyte

Fotoelektrohemijska ćelija na bazi nanocevi titan-dioksida modifikovanih gvožđe oksidom.

The fast reaction of forced hydrolysis of iron(III) nitrate in hypochlorite solution at room temperature, leads to the formation of mainly hematite, α-Fe2O3. Successive ion adsorption and reaction (SILAR) is applied to decorate an electrochemically formed TiO2 nanotube electrode. The anodic photoelectrochemical behavior of pure TiO2-NT’s and modified electrodes are investigated in a sulfate containing solution at pH=9.2. It is shown that such a modification leads to an increase of anodic photoactivity, as well as that at the same current density, the photoelectrochemical cell with a modified electrode operates at a voltage lower by 0.7 V. The band gap and flat band potentials are estimated, and the structure of the band gap and possible charge transfer reactions and mechanism are discussed. The electrochemical oxidation of the urea in near neutral pH is investigated on platinum electrode. It is shown that oxidation reaction is practically inhibited up to the potentials of ~0.9 V. The same reaction is investigated onto electrochemically obtained titanium dioxide nanotubes modified by hematite using SILAR method. It is shown that such system possesses electrocatalytic activity at very low potentials, and activity can be further improved by the illumination of the electrode in the photo-assisted reaction. The possible application of the photoactive anode is considered in the application of urea based water electrolysis and urea based fuel cell.Brza reakcija prisilne hidrolize gvožđa (III) nitrata u rastvor hipohlorita na sobnoj temperaturi, dovodi do stvaranja uglavnom hematita, α-Fe2O3. Sukcesivna jonska adsorpcija i reakcija (SILAR) primenjena je za modifikaciju elektrohemijski formirane elektrode od TiO2 u obliku nanocevi. Anodno fotoelektrohemijsko ponašanje čistih TiO2-NT i modifikovanih elektroda ispitano je u rastvoru sulfata pri pH = 9.2. Pokazano je da takva modifikacija dovodi do povećanja anodne fotoaktivnosti, kao i da kod iste gustine struje fotoelektrohemijska ćelija sa modifikovanom elektrodom radi na naponu manjem za 0,7 V. Procenjena je vrednost širine energetske barijere i potencijala izravnatih zona. Diskutovano je o strukturi energetske barijere ispitivanih materijala, mogućim reakcijama i mehanizmu prenosa naelektrisanja. Elektrohemijska oksidacija uree u rastvoru pH=9,2 je ispitana na platinskoj elektrodi. Pokazano je da je reakcija oksidacije praktično inhibirana do vrednosti potencijala od ~ 0,9 V. Ista reakcija je ispitana na elektrohemijski dobijenim nanocevima titan-dioksida modifikovanim hematitom koristeći SILAR metodu. Pokazano je da takav sistem poseduje elektrokatalitičku aktivnost pri veoma niskim potencijalima, a aktivnost se može dodatno poboljšati osvetljavanjem elektrode. Moguća primena fotoaktivne anode je razmatrana za primenu u elektrolizi vode na bazi uree i gorivne ćelije na bazi uree

A DVD-MoS2/Ag2S/Ag nanocomposite thiol-conjugated with porphyrins for an enhanced light-mediated hydrogen evolution reaction

We have recently demonstrated in a previous work an appreciable photoelectrocatalytic (PEC) behavior towards hydrogen evolution reaction (HER) of a MoS2/Ag2S/Ag nanocomposite electrochemically deposited on a commercial writable Digital Versatile Disc (DVD), consisting therefore on an interesting strategy to convert a common waster product in an added-value material. Herein, we present the conjugation of this MoS2/Ag2S/Ag-DVD nanocomposite with thiol-terminated tetraphenylporphyrins, taking advantage of the grafting of thiol groups through covalent S-S bridges, for integrating the well-known porphyrins photoactivity into the nanocomposite. Moreover, we employ two thiol-terminated porphyrins with different hydrophilicity, demonstrating that they either suppress or improve the PEC-HER performance of the overall hybrid, as a function of the molecule polarity, sustaining the concept of a local proton relay. Actually, the active polar porphyrin—MoS2/Ag2S/Ag-DVD hybrid material presented, when illuminated, a better HER performance, compared to the pristine nanocomposite, since the porphyrin may inject photoelectrons in the conduction band of the semiconductors at the formed heterojunction, presenting also a stable operational behavior during overnight chopped light chronoamperometric measurement, thanks to the robust bond created

Optimizing the neural response to electrical stimulation and exploring new applications of neurostimulation

Electrical stimulation has been successful in treating patients who suffer from neurologic and neuropsychiatric disorders that are resistant to standard treatments. For deep brain stimulation (DBS), its official approved use has been limited to mainly motor disorders, such as Parkinson\u27s disease and essential tremor. Alcohol use disorder, and addictive disorders in general, is a prevalent condition that is difficult to treat long-term. To determine whether DBS can reduce alcohol drinking in animals, voluntary alcohol consumption of alcohol-preferring rats before, during, and after stimulation of the nucleus accumbens shell were compared. Intake levels in the low stimulus intensity group (n=3, 100&mgr;A current) decreased by as much as 43% during stimulation, but the effect did not persist. In the high stimulus intensity group (n=4, 200&mgr;A current), alcohol intake decreased as much as 59%, and the effect was sustained. These results demonstrate the potent, reversible effects of DBS.^ Left vagus nerve stimulation (VNS) is approved for treating epilepsy and depression. However, the standard method of determining stimulus parameters is imprecise, and the patient responses are highly variable. I developed a method of designing custom stimulus waveforms and assessing the nerve response to optimize stimulation selectivity and efficiency. VNS experiments were performed in rats aiming to increase the selectivity of slow nerve fibers while assessing activation efficiency. When producing 50% of maximal activation of slow fibers, customized stimuli were able to activate as low as 12.8% of fast fibers, while the lowest for standard rectangular waveforms was 35.0% (n=4-6 animals). However, the stimulus with the highest selectivity requires 19.6nC of charge per stimulus phase, while the rectangular stimulus required only 13.2nC.^ Right VNS is currently under clinical investigation for preventing sudden unexpected death in epilepsy and for treating heart failure. Activation of the right vagal parasympathetic fibers led to waveform-independent reductions in heart rate, ejection ratio, and stroke volume. Customized stimulus design with response feedback produces reproducible and predictable patterns of nerve activation and physiological effects, which will lead to more consistent patient responses

Electrochemical Transformation of Alkanes, Carbon Dioxide and Protons at Iron-Porphyrins and Iron-Sulfur Clusters

Abstract The work contained in this thesis focuses on (i) chemical and electrochemical alkane oxidation using Fe-porphyrin complexes as catalysts (ii) electrochemical and photoelectrochemical CO2 reduction using Fe-porphyrin complexes (iii) electrochemical and photoelectrochemical generation of hydrogen using iron-sulfur cluster. Chapter 1 gives a general overview of the electrochemical techniques which underpin the work presenedt in this thesis. Chapter 2 reports the chemical and electrocatalytic oxidation of hydrocarbons to alcohols and epoxides by using iron (III) porphyrins as catalysts. A series of new basket-handle thiolate Fe (III) porphyrins have been used to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation. The electrocatalytic and chemical catalytic activity oxidation of the thiolate porphyrins are benchmarked against Fe (III) tetraphenyl porphyrin chloride and its tetrapentafluorophenyl analogue. Chapter 3 describes the electrochemical and photoelectrochemical reduction of carbon dioxide to carbon monoxide. This chapter shows that iron (III) porphyrin complexes are capable of carrying out electrocatalytic reduction of carbon dioxide at both vitreous carbon and illuminated p-type silicon surfaces, with reasonable current efficiencies. At illuminated p-type silicon photovoltages of ca 500mV are obtained. 7 Chapter 4 describes the electrochemical and photoelectrochemical reduction of proton to H2 using [Fe4S4 (SPh)4]2- as an electrocatalyst at both vitreous carbon and at illuminated p-type Si electrodes