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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

Objective. The wireless transfer of power for driving implantable neural stimulation devices has garnered significant attention in the bioelectronics field. This study explores the potential of photovoltaic (PV) power transfer, utilizing tissue-penetrating deep-red light-a novel and promising approach that has received less attention compared to traditional induction or ultrasound techniques. Our objective is to critically assess key parameters for directly powering neurostimulation electrodes with PVs, converting light impulses into neurostimulation currents. Approach. We systematically investigate varying PV cell size, optional series configurations, and coupling with microelectrodes fabricated from a range of materials such as Pt, TiN, IrO x , Ti, W, PtO x , Au, or poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate). Additionally, two types of PVs, ultrathin organic PVs and monocrystalline silicon PVs, are compared. These combinations are employed to drive pairs of electrodes with different sizes and impedances. The readout method involves measuring electrolytic current using a straightforward amplifier circuit. Main results. Optimal PV selection is crucial, necessitating sufficiently large PV cells to generate the desired photocurrent. Arranging PVs in series is essential to produce the appropriate voltage for driving current across electrode/electrolyte impedances. By carefully choosing the PV arrangement and electrode type, it becomes possible to emulate electrical stimulation protocols in terms of charge and frequency. An important consideration is whether the circuit is photovoltage-limited or photocurrent-limited. High charge-injection capacity electrodes made from pseudo-faradaic materials impose a photocurrent limit, while more capacitive materials like Pt are photovoltage-limited. Although organic PVs exhibit lower efficiency than silicon PVs, in many practical scenarios, stimulation current is primarily limited by the electrodes rather than the PV

Electrolyte-gated field effect transistors and electrochemical transistors have emerged as powerful components for bioelectronic sensors and biopotential recording devices. A set of parameters must be considered when developing devices to amplify weak electrophysiological signals. These include maximum transconductance values, cut-off frequencies, and large on/off current ratios. Organic polymer-based devices have recently dominated the field, especially when considering flexibility as a key factor. Oxide semiconductors may also offer these features, as well as advantages like higher mobility. Herein, flexible, ultrathin, indium tin oxide (ITO) electrolyte-gated transistors are reported. These accumulation-mode devices combine n-type operation with mu e = 9.5 cm2 Vs-1, high transconductance (gm = 44 mS), and on/off ratios (105) as well as optically transparent layouts. While oxides are normally considered brittle, mechanically flexible ITO layers are obtained by room temperature deposition of amorphous layers onto parylene C. This process results in low strain, producing devices that survive bending. ITO electrochemically degrades, however, with cycling. To overcome this, the surface is passivated with high dielectric constant inert capping layers of Ta2O5 or Ta2O5/AlN. This greatly improves stability while preserving low gate voltages. Based on their overall performance, ITO-based EGFETs are promising for bioelectronics. Conducting polymers is not the only way, inorganic oxides can make electrochemical transistors too. It is shown that ultrathin, flexible, ITO electrolyte-gated transistors are designed for bioelectronics. These transistors demonstrate high transconductance, excellent on/off ratios, and mechanical flexibility. Via surface passivation strategies are used to enhance the electrochemical stability of ITO, making these devices promising candidates for future in vivo and in vitro bioelectronic applications. image, Funding Agencies|European Research Council [LM2023051]; MEYS CR [949191]; European Research Council (ERC) under the European Union; City council of Brno, Czech Republic [2023-05459]; Swedish Research Council; Swedish Government [2009-00971]; Czech Science Foundation [24-10775S]

Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De-centralized production of hydrogen peroxide (H2O2) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e-refinery) for H2O2 by means of electrocatalysis-controlled comproportionation reaction (2(H)O + O -> 2(HO)), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H2O2 on the cathode. The reactions were evaluated in both half-cell and device configurations. The performance of the H2O2 e-refinery, assembled on anion-exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%., Funding: Swedish Agency for Innovation Systems (Vinnova) [2016-05156]; Swedish Energy Agency [42022-1]; Swedish Research Council [VR 2021-04427, VR 2019-05577, VR 2016-05990]; Centre in Nanoscience and Technology (CeNano, Linkoeping Institute of Technology (LiTH), Linkoeping University, 2020, 2021); Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoeping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Knut and Alice Wallenberg Foundation (H2O2) [KAW 2018.0058]

Organic electrochemical transistors (OECTs) have emerged as promising candidates for various fields, including bioelectronics, neuromorphic computing, biosensors, and wearable electronics. OECTs operate in aqueous solutions, exhibit high amplification properties, and offer ion-to-electron signal transduction. The OECT channel consists of a conducting polymer, with PEDOT:PSS receiving the most attention to date. While PEDOT:PSS is highly conductive, and benefits from optimized protocols using secondary dopants and detergents, new p-type and n-type polymers are emerging with desirable material properties. Among these, low-oxidation potential oligomers are highly enabling for bioelectronics applications, however the polymers resulting from their polymerization lag far behind in conductivity compared with the established PEDOT:PSS. In this work we show that by careful design of the OECT geometrical characteristics, we can overcome this limitation and achieve devices that are on-par with transistors employing PEDOT:PSS. We demonstrate that the vertical architecture allows for facile electropolymerization of a family of trimers that are polymerized in very low oxidation potentials, without the need for harsh chemicals or secondary dopants. Vertical and planar OECTs are compared using various characterization methods. We show that vOECTs are superior platforms in general and propose that the vertical architecture can be expanded for the realization of OECTs for various applications., Funding agencies: European Research Council (AdG 2018 Magnus Berggren, 834677), the Swedish Research Council (2018-06197), and the Swedish Foundation for Strategic Research (RMX18-0083), the Swedish Research Council (2022-04807, 2023-05459), the Swedish Government Strategic Research Areas in Materials Science on Functional Materials at Linköping University (Faculty Grant SFOMat-LiU No. 2009-00971).

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., Funding Agencies|European Research Council (ERC) under the European Union [949191]; Grant Agency of the Czech Republic [23-07432S]; Brno City Municipality; Knut and Alice Wallenberg foundation; LTU labbfond

Photocatalytic generation of hydrogen peroxide, H2O2, has gained increasing attention in recent years, with applications ranging from solar energy conversion to biophysical research. While semiconducting solid-state materials are normally regarded as the workhorse for photogeneration of H2O2, an intriguing alternative for on-demand H2O2 is the use of photocatalytic organic dyes. Herein we report the use of water-soluble dyes based on perylene diimide molecules which behave as true molecular catalysts for the light-induced conversion of dissolved oxygen to hydrogen peroxide. In particular, we address how to obtain visible-light photocatalysts which are stable with respect to aggregation and photochemical degradation. We report on the factors affecting efficiency and stability, including variable electron donors, oxygen partial pressure, pH, and molecular catalyst structure. The result is a perylene diimide derivative with unprecedented peroxide evolution performance using a broad range of organic donor molecules and operating in a wide pH range., Funding Agencies|National Science Centre, Poland [2019/33/B/ST5/01212]; Bavarian State Ministry for Science and the Arts; European Research Council (ERC) under the European Union [949191, 787937]; city council of Brno, Czech Republic; Knut and Alice Wallenberg Foundation

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.

Organic electrochemical transistors (OECTs) are promising building blocks for bioelectronic devices such as While the majority of OECTs use simple planar geometry, there is interest in exploring how these devices operate with much shorter channels on the submicron scale. Here, we show a practical route toward the minimization of the channel length of the transistor using traditional photolithography, enabling large-scale utilization. We describe the fabrication of such transistors using two types of conducting polymers. First, commercial solution-processed poly(dioxyethylenethiophene):poly(styrene sulfonate), PEDOT:PSS. Next, we also exploit the short channel length to support easy in situ electropolymerization of poly(dioxyethylenethiophene):tetrabutyl ammonium hexafluorophosphate, PEDOT:PF6. Both variants show different promising features, leading the way in terms of transconductance (gm), with the measured peak gm up to 68 mS for relatively thin (280 nm) channel layers on devices with the channel length of 350 nm and with widths of 50, 100, and 200 m. This result suggests that the use of electropolymerized semiconductors, which can be easily customized, is viable with vertical geometry, as uniform and thin layers can be created. Spin-coated PEDOT:PSS lags behind with the lower values of gm; however, it excels in terms of the speed of the device and also has a comparably lower off current (300 nA), leading to unusually high on/off ratio, with values up to 8.6 × 104. Our approach to vertical gap devices is simple, scalable, and can be extended to other applications where small electrochemical channels are desired.

Visible-light-driven semiconductor photoelectrodes are promising new devices for on-demand photocathodic generation of hydrogen peroxide. Herein, the fabrication of organic polymeric photocathodes employing poly(4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole) (pThBTD), and comparatively seven other related derivatives is reported. The monomer dithienobenzodithiazole can be directly polymerized on an electrode via two methods: electropolymerization or iodine-vapor-assisted polymerization. Both give polymers with wide visible light absorption and suitable stability for photoelectrodes. These methods yield different active layer morphologies, with electropolymerization yielding photocathodes with better performance. Critical issues affecting oxygen reduction photocurrents are evaluated, namely thickness, wettability, and pH. Photocathodic oxygen reduction currents, as well as photovoltages, are among the highest reported for an organic photoelectrocatalyst, and pThBTD films can stably produce H2O2 with high faradaic yield over at least 8 h. This work shows that single-component organic semiconductor devices can be highly competitive versus more complex heterostructures and that such low-bandgap organic polymers can afford remarkable stability.

This review is dedicated to electronics materials enabling thin-film-based neural interface and bioelectronics devices. First-generation bioelectronic medicine devices feature hand-crafted bulk interface electrodes, wires and interconnects, and insulators. This review discusses how modern materials science, especially know-how repurposed from semiconductor and microdevice technologies, enables next-generation bioelectronics. Those are divided into two subgroups: second and third generation. The former refers to rigid microscaled devices, while the latter is defined as soft, ultrathin, and flexible microdevices. A critical assessment of different biointerface electrodes, conductors for interconnects, and insulators for substrates, passivation, and encapsulation layers is made. The goal is not to give an exhaustive account of every use-example of given materials, but to point out specific aspects that are relevant to making the right choices for materials for a given device or application. Unique advantages of specific materials are highlighted, while also focusing on weaker points and caveats that those materials may have. The goal is to have an up-to-date handbook for persons entering the field which also points out tips and tricks as well as challenging problems that researchers can be inspired to confront and overcome.

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 esta

Optically driven electronic neuromodulation devices are a novel tool in basic research and offer new prospects in medical therapeutic applications. Optimal operation of such devices requires efficient light capture and charge generation, effective electrical communication across the device's bioelectronic interface, conformal adhesion to the target tissue, and mechanical stability of the device during the lifetime of the implant-all of which can be tuned by spatial structuring of the device. We demonstrate a 3D structured opto-bioelectronic device-an organic electrolytic photocapacitor spatially designed by depositing the active device layers on an inverted micropyramid-shaped substrate. Ultrathin, transparent, and flexible micropyramid-shaped foil was fabricated by chemical vapour deposition of parylene C on silicon moulds containing arrays of inverted micropyramids, followed by a peel-off procedure. The capacitive current delivered by the devices showed a strong dependency on the underlying spatial structure. The device performance was evaluated by numerical modelling. We propose that the developed numerical model can be used as a basis for the design of future functional 3D design of opto-bioelectronic devices and electrodes.

Increasing the electrochemical surface area of noble metal electrodes is vital for many applications, including catalysis and bioelectronics. Herein, a method is presented for obtaining porous noble metal thin films via reactive magnetron sputtering of noble metal oxides, MOx, followed by their reduction using chemical reducers or electrochemical current. Variation of reduction conditions yields a range of different electrochemical and morphological properties. This method for obtaining porous noble metals is rapid, facile, and compatible with microfabrication processes. The resulting metallic films are porous and have competitively high capacitance and low impedance.

The nervous system poses a grand challenge for integration with modern electronics and the subsequent advances in neurobiology, neuroprosthetics, and therapy which would become possible upon such integration. Due to its extreme complexity, multifaceted signaling pathways, and similar to 1 kHz operating frequency, modern complementary metal oxide semiconductor (CMOS) based electronics appear to be the only technology platform at hand for such integration. However, conventional CMOS-based electronics rely exclusively on electronic signaling and therefore require an additional technology platform to translate electronic signals into the language of neurobiology. Organic electronics are just such a technology platform, capable of converting electronic addressing into a variety of signals matching the endogenous signaling of the nervous system while simultaneously possessing favorable material similarities with nervous tissue. In this review, we introduce a variety of organic material platforms and signaling modalities specifically designed for this role as "translator" , focusing especially on recent implementation in in vivo neuromodulation. We hope that this review serves both as an informational resource and as an encouragement and challenge to the field.

H2O2 plays a significant role in a range of physiological processes where it performs vital tasks in redox signaling. The sensitivity of many biological pathways to H2O2 opens up a unique direction in the development of bioelectronics devices to control levels of reactive-oxygen species (ROS). Here a microfabricated ROS modulation device that relies on controlled faradaic reactions is presented. A concentric pixel arrangement of a peroxide-evolving cathode surrounded by an anode ring which decomposes the peroxide, resulting in localized peroxide delivery is reported. The conducting polymer (poly(3,4-ethylenedioxythiophene) (PEDOT), is exploited as the cathode. PEDOT selectively catalyzes the oxygen reduction reaction resulting in the production of hydrogen peroxide (H2O2). Using electrochemical and optical assays, combined with modeling, the performance of the devices is benchmarked. The concentric pixels generate tunable gradients of peroxide and oxygen concentrations. The faradaic devices are prototyped by modulating human H2O2-sensitive Kv7.2/7.3 (M-type) channels expressed in a single-cell model (Xenopus laevis oocytes). The Kv7 ion channel family is responsible for regulating neuronal excitability in the heart, brain, and smooth muscles, making it an ideal platform for faradaic ROS stimulation. The results demonstrate the potential of PEDOT to act as an H2O2 delivery system, paving the way to ROS-based organic bioelectronics.

Electrical stimulation of peripheral nerves is a cornerstone of bioelectronic medicine. Effective ways to accomplish peripheral nerve stimulation (PNS) noninvasively without surgically implanted devices are enabling for fundamental research and clinical translation. Here, it is demonstrated how relatively high-frequency sine-wave carriers (3 kHz) emitted by two pairs of cutaneous electrodes can temporally interfere at deep peripheral nerve targets. The effective stimulation frequency is equal to the offset frequency (0.5 - 4 Hz) between the two carriers. This principle of temporal interference nerve stimulation (TINS) in vivo using the murine sciatic nerve model is validated. Effective actuation is delivered at significantly lower current amplitudes than standard transcutaneous electrical stimulation. Further, how flexible and conformable on-skin multielectrode arrays can facilitate precise alignment of TINS onto a nerve is demonstrated. This method is simple, relying on the repurposing of existing clinically-approved hardware. TINS opens the possibility of precise noninvasive stimulation with depth and efficiency previously impossible with transcutaneous techniques., Funding Agencies|European Research Council (ERC) under the European Union [716867, 949191]; City Council of Brno, Czech Republic; European Research Council [834677]; Swedish Research Council; MedTechLabs

Objective. Vagus nerve stimulation (VNS) is a promising approach for the treatment of a wide variety of debilitating conditions, including autoimmune diseases and intractable epilepsy. Much remains to be learned about the molecular mechanisms involved in vagus nerve regulation of organ function. Despite an abundance of well-characterized rodent models of common chronic diseases, currently available technologies are rarely suitable for the required long-term experiments in freely moving animals, particularly experimental mice. Due to challenging anatomical limitations, many relevant experiments require miniaturized, less invasive, and wireless devices for precise stimulation of the vagus nerve and other peripheral nerves of interest. Our objective is to outline possible solutions to this problem by using nongenetic light-based stimulation. Approach. We describe how to design and benchmark new microstimulation devices that are based on transcutaneous photovoltaic stimulation. The approach is to use wired multielectrode cuffs to test different stimulation patterns, and then build photovoltaic stimulators to generate the most optimal patterns. We validate stimulation through heart rate analysis. Main results. A range of different stimulation geometries are explored with large differences in performance. Two types of photovoltaic devices are fabricated to deliver stimulation: photocapacitors and photovoltaic flags. The former is simple and more compact, but has limited efficiency. The photovoltaic flag approach is more elaborate, but highly efficient. Both can be used for wireless actuation of the vagus nerve using light impulses. Significance. These approaches can enable studies in small animals that were previously challenging, such as long-term in vivo studies for mapping functional vagus nerve innervation. This new knowledge may have potential to support clinical translation of VNS for treatment of select inflammatory and neurologic diseases., QC 20230113

The approach of using polyether, aka glycol, side chains to afford amphiphilicity to conducting polymers has recently emerged as a powerful technique for next-generation materials for bioelectronics and electrochemical devices. Herein we apply this synthetic logic to the archetypical conducting polymer poly(3,4-ethylenedioxythiophene), PEDOT, to generate a glycolated PEDOT analogue, G-PEDOT. We report on the electropolymerization of this material, and its electrochemical properties: including spectroelectrochemistry, electrochemical capacitance, and operation of microelectrodes and electrochemical transistors. While in many respects performing like PEDOT, G-PEDOT has electrochemical switching within lower potentials with complete de-doping at lower potentials, affording transistors with higher on/off ratios than PEDOT, and electrochromic switching within a smaller electrochemical window. Overall, G-PEDOT emerges as a useful, functional alternative to other PEDOT derivatives, and could be a building block in copolymers., Funding Agencies|National Science Centre, Poland [2019/33/B/ST5/01212]; European Research Council (ERC) under the European Union [949191]; city council of Brno, Czech Republic; MEYS CR [LM2018110]

Deep brain stimulation (DBS) is a technique commonly used both in clinical and fundamental neurosciences. Classically, brain stimulation requires an implanted and wired electrode system to deliver stimulation directly to the target area. Although techniques such as temporal interference (TI) can provide stimulation at depth without involving any implanted electrodes, these methods still rely on a wired apparatus which limits free movement. Herein organic photocapacitors as untethered light-driven electrodes which convert deep-red light into electric current are reported. Pairs of these ultrathin devices can be driven using lasers at two different frequencies to deliver stimulation at depth via temporally interfering fields. This concept of laser TI stimulation using numerical modeling, tests with phantom brain samples, and finally in vivo tests is validated. Wireless organic photocapacitors are placed on the cortex and elicit stimulation in the hippocampus, while not delivering off-target stimulation in the cortex. This laser-driven wireless TI evokes a neuronal response at depth that is comparable to control experiments induced with deep brain stimulation protocols using implanted electrodes. This work shows that a combination of these two techniques-temporal interference and organic electrolytic photocapacitors-provides a reliable way to target brain structures requiring neither deeply implanted electrodes nor tethered stimulator devices. The laser TI protocol demonstrated here addresses two of the most important drawbacks in the field of DBS and thus holds potential to solve many issues in freely moving animal experiments or for clinical chronic therapy application., Funding Agencies|European Research Council (ERC) under the European Union [716867, 949191]; European Research Council [834677]; Knut and Alice Wallenberg Foundation within the framework of the Wallenberg Centre for Molecular Medicine at Linkoping University; Swedish Research Council (Vetenskapsradet) [2018-04505]

Implantable devices for the wireless modulation of neural tissue need to be designed for reliability, safety and reduced invasiveness. Here we report chronic electrical stimulation of the sciatic nerve in rats by an implanted organic electrolytic photocapacitor that transduces deep-red light into electrical signals. The photocapacitor relies on commercially available semiconducting non-toxic pigments and is integrated in a conformable 0.1-mm(3) thin-film cuff. In freely moving rats, fixation of the cuff around the sciatic nerve, 10 mm below the surface of the skin, allowed stimulation (via 50-1,000-mu s pulses of deep-red light at wavelengths of 638 nm or 660 nm) of the nerve for over 100 days. The robustness, biocompatibility, low volume and high-performance characteristics of organic electrolytic photocapacitors may facilitate the wireless chronic stimulation of peripheral nerves. An organic electrolytic photocapacitor transducing deep-red light into electrical signals and implanted within a thin cuff around the sciatic nerve of rats allows for wireless electrical stimulation of the nerve for over 100 days.

Objective. For decades electrical stimulation has been used in neuroscience to investigate brain networks and been deployed clinically as a mode of therapy. Classically, all methods of electrical stimulation require implanted electrodes to be connected in some manner to an apparatus which provides power for the stimulation itself. Approach. We show the use of novel organic electronic devices, specifically organic electrolytic photocapacitors (OEPCs), which can be activated when illuminated with deep-red wavelengths of light and correspondingly do not require connections with external wires or power supplies when implanted at various depths in vivo. Main results. We stimulated cortical brain tissue of mice with devices implanted subcutaneously, as well as beneath both the skin and skull to demonstrate a wireless stimulation of the whisker motor cortex. Devices induced both a behavior response (whisker movement) and a sensory response in the corresponding sensory cortex. Additionally, we showed that coating OEPCs with a thin layer of a conducting polymer formulation (PEDOT:PSS) significantly increases their charge storage capacity, and can be used to further optimize the applied photoelectrical stimulation. Significance. Overall, this new technology can provide an on-demand electrical stimulation by simply using an OEPC and a deep-red wavelength illumination. Wires and interconnects to provide power to implanted neurostimulation electrodes are often problematic in freely-moving animal research and with implanted electrodes for long-term therapy in patients. Our wireless brain stimulation opens new perspectives for wireless electrical stimulation for applications in fundamental neurostimulation and in chronic therapy.

Peroxid vodíku (H2O2) je metastabilní reaktivní forma kyslíku, která reguluje mnoho biologických drah. Úloha H2O2 v biologických procesech závisí na jeho lokální koncentraci, v malém množství (nM) může působit jako signální molekula, zatímco vyšší koncentrace mohou mít cytotoxické účinky. Cílem této práce bylo vytvoření fotosenzitivních mikročástic, které by produkovaly fyziologické množství peroxidu vodíku pro regulaci signálních drah v kultivovaných buňkách. Navrhované mikročástice jsou organické fotovoltaické struktury bez substrátu, které produkují H2O2 fotofaradickou redukcí molekulárního kyslíku. Produkce peroxidu probíhá za současné oxidace donoru elektronů přítomného v elektrolytu. Částice mají rozměry v řádu mikrometrů, zatímco jejich tloušťka nepřekračuje 100 nm. Fotofaradické reakce jsou poháněny červeným světlem (660 nm), které může pronikat tkáněmi, což umožňuje potenciální aplikace mikročástic in vivo. Práce se bude zabývat optimalizací výroby mikročástic a charakterizací produkce H2O2., Hydrogen peroxide (H2O2) is a metastable reactive oxygen species regulating many biological pathways. The role of H2O2 in biological processes depends on its local concentration, in the nM range H2O2 can act as a signalling molecule, while exposure to higher levels of H2O2 can have cytotoxic effects. The aim of this work is to create photosensitive microparticles that would produce physiological amounts of hydrogen peroxide to regulate signalling pathways in cultured cells. The proposed microparticles are substrate-free organic photovoltaic elements that produce H2O2 by photofaradaic reduction of molecular oxygen with the concurrent oxidation of an electron donor present in the electrolyte. The detailed fabrication methods to achieve them were described. The particles have lateral dimensions in the range of micrometres, while a thickness of less than 100 nm. Photofaradaic reactions are driven by tissue-penetrating deep red light (660 nm) to enable potential in vivo applications of the technology. The thesis will discuss optimization of the photofaradaic microparticles production and characterization of the H2O2 evolution.

Předmětem této práce byla konstrukce a měření dlouhodobé stability mikro-referentních elektrod na bázi anodizovaných Ag drátů a Ti drátů s Ag/AgCl pastou. V rámci této práce byl také sestrojen měřicí aparát, pomocí něhož byla dlouhodobá stabilita měřena. V dnešní době jsou na trhu dostupné komerční referentní elektrody. Tyto komerční produkty se vyznačují především výbornou dlouhodobou stabilitou, ale jsou příliš velké a drahé pro využití v bioelektronických systémech. Ve vědecké komunitě proto dochází v posledních letech o pokusy miniaturizace referentních elektrod. Bez nich není možné provádět velkou část elektrochemických měření. Na základě měření dlouhodobé stability bylo zjištěno, které ze zkoumaných vzorků splňují požadavky pro použití v bioelektronických systémech. Také bylo určeno, který ze zkoumaných vzorků je nejvhodnější. Posledním výsledkem této práce je měřicí aparát, pomocí něhož je možné měřit dlouhodobou stabilitu až třiceti dvou elektrod., The subject of this work was the construction and long term stability measurement of micro-reference electrodes based on anodized silver wire and titanium wire with Ag/AgCl paste. A measuring apparatus, with which the long term stability was measured, was constructed as a part of this work. These days, commercial reference electrodes are available on the market. These reference electrodes are characterized by their excellent long term stability, however, they are too large and too expensive to be used in bioelectronic systems. Because of this, the science community has been trying to miniaturize reference electrodes in the past years. Without reference electrodes, it is impossible to do most electrochemical measurements. Based on the long term stability of measured samples it was determined which of the samples meet the criteria for bioelectronic measurements. It was also determined which of the studied samples were most suitable. The last result of this work is a measuring apparatus that can measure the long term stability of up to thirty-two electrodes.

V této práci jsou popsány obecné vlastnosti základních senzorů plynů, zaměřuje se zejména na chemorezistivní typ a chemicky citlivý unipolární tranzistor, kterým se dále věnuje v praktické části. Dále popisuje vlastnosti vybraných 1D a 2D materiálů, metody jejich přípravy a přenosu. Praktická část práce popisuje návrh a výrobu čipů, které kombinují výše uvedené senzorické principy pro využití 1D a 2D materiálů jako aktivní vrstvy. Poté jsou popsány postupy přenosů jednotlivých materiálů na vyrobené čipy, a tyto materiály jsou charakterizovány pomocí Ramanovy spektroskopie a měření charakteristik unipolárního tranzistoru z těchto materiálů. Na závěr jsou měřeny odezvy zvolených materiálů na vybrané oxidační a redukční plyny., In this work, general properties of fundamental gas sensors are described. Thesis is mainly focused on chemoresistive and ChemFET types, which are further used in experimental part. Subsequently, properties, preparation and transfer methods of chosen 1D and 2D materials are described. Experimental part of this work describes design and fabrication of chips, which combine the sensing principals mentioned above for utilization of 1D and 2D materials as an active layer. Transfer methods of individual materials on fabricated chips are described and these materials are characterized by Raman spectroscopy and field effect transistor characteristics measurements. Finally, the response of chosen materials to oxidative and reductive gases is measured.

Předmětem této práce byla konstrukce a měření dlouhodobé stability mikro-referentních elektrod na bázi anodizovaných Ag drátů a Ti drátů s Ag/AgCl pastou. V rámci této práce byl také sestrojen měřicí aparát, pomocí něhož byla dlouhodobá stabilita měřena. V dnešní době jsou na trhu dostupné komerční referentní elektrody. Tyto komerční produkty se vyznačují především výbornou dlouhodobou stabilitou, ale jsou příliš velké a drahé pro využití v bioelektronických systémech. Ve vědecké komunitě proto dochází v posledních letech o pokusy miniaturizace referentních elektrod. Bez nich není možné provádět velkou část elektrochemických měření. Na základě měření dlouhodobé stability bylo zjištěno, které ze zkoumaných vzorků splňují požadavky pro použití v bioelektronických systémech. Také bylo určeno, který ze zkoumaných vzorků je nejvhodnější. Posledním výsledkem této práce je měřicí aparát, pomocí něhož je možné měřit dlouhodobou stabilitu až třiceti dvou elektrod., The subject of this work was the construction and long term stability measurement of micro-reference electrodes based on anodized silver wire and titanium wire with Ag/AgCl paste. A measuring apparatus, with which the long term stability was measured, was constructed as a part of this work. These days, commercial reference electrodes are available on the market. These reference electrodes are characterized by their excellent long term stability, however, they are too large and too expensive to be used in bioelectronic systems. Because of this, the science community has been trying to miniaturize reference electrodes in the past years. Without reference electrodes, it is impossible to do most electrochemical measurements. Based on the long term stability of measured samples it was determined which of the samples meet the criteria for bioelectronic measurements. It was also determined which of the studied samples were most suitable. The last result of this work is a measuring apparatus that can measure the long term stability of up to thirty-two electrodes.

V této práci jsou popsány obecné vlastnosti základních senzorů plynů, zaměřuje se zejména na chemorezistivní typ a chemicky citlivý unipolární tranzistor, kterým se dále věnuje v praktické části. Dále popisuje vlastnosti vybraných 1D a 2D materiálů, metody jejich přípravy a přenosu. Praktická část práce popisuje návrh a výrobu čipů, které kombinují výše uvedené senzorické principy pro využití 1D a 2D materiálů jako aktivní vrstvy. Poté jsou popsány postupy přenosů jednotlivých materiálů na vyrobené čipy, a tyto materiály jsou charakterizovány pomocí Ramanovy spektroskopie a měření charakteristik unipolárního tranzistoru z těchto materiálů. Na závěr jsou měřeny odezvy zvolených materiálů na vybrané oxidační a redukční plyny., In this work, general properties of fundamental gas sensors are described. Thesis is mainly focused on chemoresistive and ChemFET types, which are further used in experimental part. Subsequently, properties, preparation and transfer methods of chosen 1D and 2D materials are described. Experimental part of this work describes design and fabrication of chips, which combine the sensing principals mentioned above for utilization of 1D and 2D materials as an active layer. Transfer methods of individual materials on fabricated chips are described and these materials are characterized by Raman spectroscopy and field effect transistor characteristics measurements. Finally, the response of chosen materials to oxidative and reductive gases is measured.

Peroxid vodíku (H2O2) je metastabilní reaktivní forma kyslíku, která reguluje mnoho biologických drah. Úloha H2O2 v biologických procesech závisí na jeho lokální koncentraci, v malém množství (nM) může působit jako signální molekula, zatímco vyšší koncentrace mohou mít cytotoxické účinky. Cílem této práce bylo vytvoření fotosenzitivních mikročástic, které by produkovaly fyziologické množství peroxidu vodíku pro regulaci signálních drah v kultivovaných buňkách. Navrhované mikročástice jsou organické fotovoltaické struktury bez substrátu, které produkují H2O2 fotofaradickou redukcí molekulárního kyslíku. Produkce peroxidu probíhá za současné oxidace donoru elektronů přítomného v elektrolytu. Částice mají rozměry v řádu mikrometrů, zatímco jejich tloušťka nepřekračuje 100 nm. Fotofaradické reakce jsou poháněny červeným světlem (660 nm), které může pronikat tkáněmi, což umožňuje potenciální aplikace mikročástic in vivo. Práce se bude zabývat optimalizací výroby mikročástic a charakterizací produkce H2O2., Hydrogen peroxide (H2O2) is a metastable reactive oxygen species regulating many biological pathways. The role of H2O2 in biological processes depends on its local concentration, in the nM range H2O2 can act as a signalling molecule, while exposure to higher levels of H2O2 can have cytotoxic effects. The aim of this work is to create photosensitive microparticles that would produce physiological amounts of hydrogen peroxide to regulate signalling pathways in cultured cells. The proposed microparticles are substrate-free organic photovoltaic elements that produce H2O2 by photofaradaic reduction of molecular oxygen with the concurrent oxidation of an electron donor present in the electrolyte. The detailed fabrication methods to achieve them were described. The particles have lateral dimensions in the range of micrometres, while a thickness of less than 100 nm. Photofaradaic reactions are driven by tissue-penetrating deep red light (660 nm) to enable potential in vivo applications of the technology. The thesis will discuss optimization of the photofaradaic microparticles production and characterization of the H2O2 evolution.