Bioelektronické materiály a systémy

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Elevating Platinum to Volumetric Capacitance: High Surface Area Electrodes through Reactive Pt Sputtering
(WILEY, 2024-05-17) Gryszel, Maciej; Jakešová, Marie; Vu, Xuan Thang; Ingebrandt, Sven; Glowacki, Eric Daniel
Platinum is the most widespread electrode material used for implantable biomedical and neuroelectronic devices, motivating exploring ways to improve its performance and understand its fundamental properties. Using reactive magnetron sputtering, PtOx is prepared, which upon partial reduction yields a porous thin-film form of platinum with favorable properties, notably record-low impedance values outcompeting other reports for platinum-based electrodes. It is established that its high electrochemical capacitance scales with thickness, in the way of volumetric capacitor materials like IrOx and poly(3,4-ethylenedioxythiophene), PEDOT. Unlike these two well-known analogs, however, it is found that PtOx capacitance is not caused by reversible pseudofaradaic reactions but rather due to high surface area. In contrast to IrOx, PtOx is not a reversible valence-change oxide, but rather a porous form of platinum. The findings show that this oxygen-containing form of Pt can place Pt electrodes on a level competitive with IrOx and PEDOT. Due to its relatively low cost and ease of preparation, PtOx can be a good choice for microfabricated bioelectronic devices. Platinum is used in many medical implants, but lags behind next-generation electrode materials in performance. How sputtered platinum oxide is a microfabricatable thin film material that provides bioelectronics electrodes with volumetric capacitance and low impedance that tweaks platinum to compete at the level of conducting polymers and IrOx is shown. image
ChemFET gas nanosensor arrays with alignment windows for assembly of single nanowires
(Springer, 2023-04-13) Chmela, Ondřej; Gablech, Imrich; Sadílek, Jakub; Brodský, Jan; Vallejos Vargas, Stella
This work focuses on the fabrication and characterization of ChemFET (Chemical Field-Effect Transistor) gas nanosensor arrays based on single nanowire (SNW). The fabrication processes include micro and nanofabrication techniques enabled by a combination of ultraviolet (UV) and e-beam lithography to build the ChemFET structure. Results show the integration and connection of SNWs across the multiple pairs of nanoelectrodes in the ChemFET by dielectrophoresis process (DEP) thanks to the incorporation of alignment windows (200-300 nm) adapted to the diameter of the NWs. Measurements of the SNW ChemFET array's output and transfer characteristics prove the influence of gate bias on the drain current regulation. Tests upon hydrogen (H-2) and nitrogen dioxide (NO2) as analyte models of reducing and oxidizing gases show the ChemFET sensing functionality. Moreover, results demonstrate better response characteristics to H-2 when the ChemFET operates in the subthreshold regime. The design concepts and methods proposed for fabricating the SNW-based ChemFET arrays are versatile, reproducible, and most likely adaptable to other systems where SNW arrays are required.
Faradaic Fenton Pixel: Reactive Oxygen Species Delivery Using Au/Cr Electrochemistry
(Wiley-VCH, 2023-09-01) Miglbauer, Eva; Abudllaeva, Oliya S.; Gryszel, Maciej; Glowacki, Eric Daniel
Reactive oxygen species (ROS) are an integral part of many anticancer therapies. Fenton-like processes involving reactions of peroxides with transition metal ions are a particularly potent and tunable subset of ROS approaches. Precise on-demand dosing of the Fenton reaction is an area of great interest. Herein, we present a concept of an electrochemical faradaic pixel that produces controlled amounts of ROS via a Fenton-like process. The pixel comprises a cathode and anode, where the cathode reduces dissolved oxygen to hydrogen peroxide. The anode is made of chromium, which is electrochemically corroded to yield chromium ions. Peroxide and chromium interact to form a highly oxidizing mixture of hydroxyl radicals and hexavalent Cr ions. After benchmarking the electrochemical properties of this type of device, we demonstrate how it can be used under in vitro conditions with a cancer cell line. The faradaic Fenton pixel is a general and scalable concept that can be used for on-demand delivery of redox-active products for controlling a physiological outcome.
Direct measurement of oxygen reduction reactions at neurostimulation electrodes
(IOP Publishing Ltd, 2022-06-01) Ehlich, Jiří; Migliaccio, Ludovico; Sahalianov, Ihor; Nikić, Marta; Brodský, Jan; Gablech, Imrich; Vu, Xuan Thang; Ingebrandt, Sven; Glowacki, Eric Daniel
Objective. Electric stimulation delivered by implantable electrodes is a key component of neural engineering. While factors affecting long-term stability, safety, and biocompatibility are a topic of continuous investigation, a widely-accepted principle is that charge injection should be reversible, with no net electrochemical products forming. We want to evaluate oxygen reduction reactions (ORR) occurring at different electrode materials when using established materials and stimulation protocols. Approach. As stimulation electrodes, we have tested platinum, gold, tungsten, nichrome, iridium oxide, titanium, titanium nitride, and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). We use cyclic voltammetry and voltage-step amperometry in oxygenated versus inert conditions to establish at which potentials ORR occurs, and the magnitudes of diffusion-limited ORR currents. We also benchmark the areal capacitance of each electrode material. We use amperometric probes (Clark-type electrodes) to quantify the O-2 and H2O2 concentrations in the vicinity of the electrode surface. O-2 and H2O2 concentrations are measured while applying DC current, or various biphasic charge-balanced pulses of amplitude in the range 10-30 mu C cm(-2)/phase. To corroborate experimental measurements, we employ finite element modelling to recreate 3D gradients of O-2 and H2O2. Main results. All electrode materials support ORR and can create hypoxic conditions near the electrode surface. We find that electrode materials differ significantly in their onset potentials for ORR, and in the extent to which they produce H2O2 as a by-product. A key result is that typical charge-balanced biphasic pulse protocols do lead to irreversible ORR. Some electrodes induce severely hypoxic conditions, others additionally produce an accumulation of hydrogen peroxide into the mM range. Significance. Our findings highlight faradaic ORR as a critical consideration for neural interface devices and show that the established biphasic/charge-balanced approach does not prevent irreversible changes in O-2 concentrations. Hypoxia and H2O2 can result in different (electro)physiological consequences.
High-Conductivity Stoichiometric Titanium Nitride for Bioelectronics
(Wiley-VCH GmbH, 2023-02-02) Gablech, Imrich; Migliaccio, Ludovico; Brodský, Jan; Havlíček, Marek; Podešva, Pavel; Hrdý, Radim; Ehlich, Jiří; Gryszel, Maciej; Glowacki, Eric Daniel
Bioelectronic devices such as neural stimulation and recording devices require stable low-impedance electrode interfaces. Various forms of nitridated titanium are used in biointerface applications due to robustness and biological inertness. In this work, stoichiometric TiN thin films are fabricated using a dual Kaufman ion-beam source setup, without the necessity of substrate heating. These layers are remarkable compared to established forms of TiN due to high degree of crystallinity and excellent electrical conductivity. How this fabrication method can be extended to produce structured AlN, to yield robust AlN/TiN bilayer micropyramids, is described. These electrodes compare favorably to commercial TiN microelectrodes in the performance metrics important for bioelectronics interfaces: higher conductivity (by an order of magnitude), lower electrochemical impedance, and higher capacitive charge injection with lower faradaicity. These results demonstrate that the Kaufman ion-beam sputtering method can produce competitive nitride ceramics for bioelectronics applications at low deposition temperatures.

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