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Prussian blue nanoparticles (PB NPs) stabilized with surface capping agents as functional mimics of majorantioxidant enzymes are attracting attention for use in reactions mediated by reactive oxygen species. However,influence of a stabilizing agent or interface on the enzyme-like properties of the nanomaterial remains unclear. Inthis study, we investigate the effect of the chemically reduced graphene oxide (rGO) interface on themorphology, stability, and multienzymatic activity of PB NPs. The rGO stabilized PB NPs nanocomposite (PB/rGO) demonstrated different morphology, dynamics of the superoxide scavenging, and lower peroxidase- andcatalase-mimicking activities in comparison with the non-stabilized PB NPs. Electrochemical studies showedimproved immobilization of PB/rGO on the graphite felt, while the sensitivity of hydrogen peroxide determinationwas higher for the non-stabilized PB NPs. This study enhances our understanding of the role of the rGOstructuring interface in altering the properties of nanomaterials for oxidation protection and nanozyme-basedsensing approaches.

Electrochemical sensors that can determine single/multiple analytes remain a key challenge in miniaturized analytical systems and devices. In this study, we present in situ synthesis and modification of gold nanodendrite electrodes to create an electrochemical system for the analysis of hydrogen peroxide. The sensor system consisted of the reference and counter electrodes as well as the working electrode. Electrochemical reduction of graphene oxide, ErGO, on the thin-film gold and gold nanodendrite working electrodes was used to achieve an efficient sensor interface for the adsorption of a biomimetic electrocatalytic sensor material, Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin complex, with as high as 10–10 mol cm−2 surface coverage. The sensor system demonstrated a detection limit of 0.3 µM H2O2 in the presence of oxygen. Electrochemical determination of hydrogen peroxide in plant material in the concentration range from 0.09 to 0.4 µmol (gFW)−1 using the electrochemical sensor system was shown as well as in vivo real-time monitoring of the hydrogen peroxide dynamics as a sign of abiotic stress (intense sunlight). Results of the electrochemical determination were in good agreement with the results of biochemical analysis with the spectrophotometric detection. We anticipate that this method can be extended for the synthesis and integration of multisensor arrays in analytical microsystems and devices for the quantification and real-time in vivo monitoring of other analytes and biomarkers.

The aim of this study was to investigate biomimetic activity of water-soluble manganese porphyrin complexes with a series of meso-substituents of the porphyrin macrocycle in the electrocatalytic reduction of hydrogen peroxide in aqueous solutions and to obtain information on possible intermediates, processes, and mechanisms. Mn porphyrins were compared in the process of the electrocatalytic reduction of hydrogen peroxide at pH 4, 7.4, and 10 in the deoxygenated solutions and in the presence of oxygen. The highest sensitivity, defined as the reduction current increase in relation to the concentration of hydrogen peroxide, was found in the case of Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin, MnTMPyP, in alkaline 2.9·10−2 A M−1 and acidic 1.6·10−2 A M−1 solutions in the presence of oxygen. The reduction currents at pH 7.4, 10, and 4 in the presence of H2O2 were about 4, 7, and 12 times higher, respectively, in the solutions with the MnTMPyP complex than those at a GCE without a porphyrin complex in the solution. The electrocatalytic reduction of hydrogen peroxide occurs in parallel with an oxidative degradation of the porphyrin catalyst depending on the conditions of the experiment and was most significant in the presence of oxygen. The effect of the functional substituents at the meso-positions of a porphyrin ligand on the electrocatalytic activity of the water-soluble Mn(III) porphyrins complexes is discussed and reaction mechanisms are proposed.

We report a new type of solid-state electrode (type I) of a simple design with polyvinyl chloride membranes based on Mn(III) tetraphenylporphyrin and with graphite as the electronically conducting substrate. Enlargement of the membrane/graphite contact area by soaking graphite in the plasticizer with subsequent conditioning of the electrode at 30 °C allowed us to shorten the time required to achieve steady potential values of the sensors to just 3 days. These electrodes do not require a specially added RedOx system in the transducer layer. Stabilization of the EMF response of type I electrodes is compared to type II electrodes which contain a Cu0/Cu2+ RedOx couple in the transducer layer. Type I sensors are suitable for measuring the salicylate ion concentration in the clinically important concentration range down to 2.5 × 10−4 M with a sensitivity to salicylate ion of −59.0 mV decade−1 in solutions with a high constant background of chloride ions of 0.12 M at pH = 5.3, making this a promising technique for an effective design of solid-contact ion-selective electrodes with polymeric sensing membranes.

This study establishes the relationships between the structure of a series of meso-substituted tin(IV) porphyrins and their efficiency as photosensitizers for hydrogen generation in the Sn(IV)P/Pt–TiO2 nanocomposite system. The electrochemical properties of a series of SnPs, the catalytic performance of Pt nanomodifications, and the morphology of the Pt/TiO2 nanocomposites were characterized by electrochemical and electron microscopy methods. The dependence of photocatalytic performance on the structure for a series of Sn(IV) meso-substituted phenyl porphyrins was studied, and possible mechanisms are discussed employing the results of the electrochemical studies. It was found that the time course and type of the photochemically reduced species of Sn(IV)Ps, which are essential intermediates, are important factors and depend on the electronegativity of the metal center, the character of meso-substituents of the porphyrin ring, and pH and are correlated with the redox potential sequence of the respective Sn(...

Bioinspired molecular complexes that mimic the enzymatic catalysis of redox transformations offer a versatile platform for the development of non-enzymatic mediatorless sensors with high sensitivity, selectivity, and robustness without the use of precious metals. The aim of this study was to prepare and investigate biomimetic sensors based on the electrocatalytic reduction of hydrogen peroxide and oxygen by a series of immobilized complexes of iron and manganese with porphyrin macrocycles for the detection of hydrogen peroxide and glucose. The influence of substitution of the macroheterocyclic ligand, composition of the adsorption solution, Nafion membrane, and amino acids on the properties of the sensors was studied. Optimized sensor function is based on the electrogenerated reduced form of Mn(II) meso-tetra(N-methyl-4-pyridyl) porphyrin as a catalyst and allows high sensitivity of the hydrogen peroxide detection of 1.8 A M−1 cm−2 and 0.071 A M−1 cm−2 to be achieved in the lower and higher concentration ranges, respectively, with a low detection limit of 5⋅10−7 M at physiological pH 7.4 and in the presence of oxygen. The MnTMPyP electrode was investigated as an electrochemical transducer in the glucose-oxidase-based biosensor. The sensors were successfully applied for the detection of hydrogen peroxide and glucose in human serum samples. Along with a simple fabrication procedure and robustness of the sensor, the biomimetic electrocatalytic properties of the MnTMPyP complex facilitate excellent performance of the proposed sensors for hydrogen peroxide and glucose determination in biological media, emphasizing the importance of bioinspired electrocatalytic metalloporphyrin complexes for the development of sensors and point-of-care devices.

The present study of nanoelectrochemical sensors prepared by directed electrochemical nanowire assembly (DENA) is defined by the requirements of electrochemical analysis, where the transducer function of metallic nanowires is synergetically combined with their electrochemical catalytic activity with respect to a particular analyte. We show for the first time that this technique can be employed for metals (Pd, Au) and their bimetallic compositions to create various multicomponent sensor nanomaterials on a single chip without the use of multistep lithography for the spatially resolved analysis of solutions. The nanostructures of various compositions can be individually addressed when used in liquid media, so that the particular surface properties of the individual nanoarray elements can be used for the electrochemical analysis of specific analytes. The sensor application of these devices in electrolytes and cell culture conditions has been demonstrated for the first time. As an example, the Pd-Au nanowires prepared by DENA were used for a non-enzymatic analysis of H2O2 with a linear concentration interval of 10−6–10−3 M, sensitivity of 18 μA M−1, and detection limit of 3 × 10−7 M at as low absolute value of the detection potential as − 0.05 V. This sensor was also proven for the detection of hydrogen peroxide in HL-1 cell culture, demonstrating good biocompatibility and support for the cell culture conditions. Using various DENA-grown electrochemical compositions on a single chip, a novel multisensor platform is proposed for the determination of various analytes in electrolyte solutions for biocompatible sensor arrays, flexible multianalyte environmental and technological process monitoring, and healthcare areas.

The tunable characteristics of the porphyrin molecular tectons have given rise to interest in investigating the self-assembled porphyrin nanoarchitectures for designing new materials. Nanostructures created by the self-assembly of meso-tetrakis(4-sulfonatophenyl)porphine and Co(III) meso-tetra(4-pyridyl)porphine chloride and their photoconductivity are reported here. These nanostructures were characterized by electron microscopy. The ratio of porphyrin tectons in the binary porphyrin nanostructures is about 3:2. The nanostructures demonstrate a high photoconductivity of about 5 × 10−5 S m−1. The dependence of the photoconductivity of the porphyrin nanostructures on the path length and temperature is demonstrated.

The report describes the Ostwald ripening process in a nanocomposite comprising gold nanoparticles and TiO2 semiconductor under electrochemical conditions. The phenomenon is considered in relation to previous observations on the Ostwald ripening process in metallic nanostructures. Possible processes involved are discussed, and a mechanism is proposed based on the size dependence of the electrochemical parameters of gold nanostructures.

New membrane materials were studied for thallium (I)-selective chemical sensors based on chalcogenide glasses in the TlI-Ag 2 S-As 2 S 3 system. Using these studies on the radioactive tracers diffusion ( 108m Ag и 204 Tl) and electrical conductivity, an ionic conductivity of σ ion = 10 −7 Ohm −1 cm −1 (20 °C) was found for the glass composition 27%TlI-20%Ag 2 S-53%As 2 S 3 . This composition of chalcogenide glass was selected as a membrane material for the Tl-selective chemical sensor displaying a value of the electrode function of 57 mV/pTl and a detection limit of 3 × 10 −6 mol l −1 .

Two types of gold nanostructures are discussed: charge(citrate)-stabilized and sterically(OA)-stabilized gold nanostructures and their assembly with heme-containing metalloproteins, cyt c and horseradish peroxidase (HRP) enzyme into a bioelectrochemically active nanoarchitecture as well as a sensor application. The assembly of the nanostructures on the thin-film gold electrodes and the immobilization and electrochemical properties of metalloproteins on these electrodes are presented. The nanostructured bioelectrochemical interfaces provide a good environment for the stable and reproducible immobilization of electroactive proteins. We show that both molecules preserve their functionalities (electrochemical and biocatalytic activities). The amount of electroactive proteins immobilized on the nanostructured electrode surfaces is significantly increased compared to the flat electrode surfaces. The kinetic parameters of the heterogeneous direct electron transfer reaction of cyt c on the nanostructured electrodes are compared. The thin-film gold electrodes modified with OANWs, OANPs, and citrate-stabilized NPs and covalently immobilized HRP exhibit an excellent catalytic activity toward the oxidation of hydrogen peroxide with a working concentration range from 20 μM to 500 μM, a sensitivity of 0.031 A M−1 cm−2 (RSD 0.005), 0.027 A M−1 cm−2 (RSD 0.004), and 0.022 A M−1 cm−2 (RSD 0.0035), and a detection limit of 5 μM, 8 μM, and 14 μM, respectively (RSDs near the detection limits were 9–12%). The HRP sensor characteristics are improved significantly compared to the flat thin-film sensors by using gold nanostructures. Our study shows that ultrathin gold nanowires and nanoparticles with two different types of stabilizing agents are promising materials for assembling biomolecules into functional nanoarchitectures for metalloprotein-based bioelectrochemical sensors.

A one-step photoreduction method was applied to the synthesis of platinum colloids of 15 nm in aqueous solution without the need for organic solvents and templates. The formation process of these Pt nanostructures was studied by means of scanning electron microscopy and UV-visible absorption spectroscopy, and the morphology of the Pt nanoparticles (NPs) was illustrated by transmission electron microscopy. The Pt nanostructures were electrochemically characterized by determining the polarization curve and Tafel plot of the hydrogen evolution reaction. The active and easily accessible surface was demonstrated by the self-assembly of these Pt NPs into perfect dendritic structures on the surface of an indium-tin-oxide thin film after the appropriate addition and evaporation of water, which can be explained by diffusion-limited aggregation theory. Further evidence of the easily accessible surface of Pt NPs, is the coordination interaction between the Pt NPs as prepared and the amine ligand of metalloporphyrin resulting in the appearance of nanospheres. In contrast, the two phenomena were not found in citrate ions-stabilized Pt NPs under the same condition, indicating the Pt NPs synthesized with the photoreduction method have great potential in the fields of nanoelectronics, sensors and catalysis, as the “clean” and active surface might improve electrochemical and catalytic performance. Self-assembly and coordination of the Pt nanoparticles due to the easily accessible surface were verified by the formation of Pt dendrites and metalloporphyrin/Pt nanospheres, which might offer perspective to the design of functional materials.

This paper describes ultrathin gold nanowires (NWs) and nanoparticles (NPs) prepared by oleylamine (OA) synthesis and their assembly with horseradish peroxidase enzyme (HRP) for bioelectrochemical sensing of hydrogen peroxide for the first time. The immobilization of oxidoreductase enzyme HRP on the electrodes modified with OA gold nanostructures (OANSs) is discussed. The HRP-sensor characteristics, namely sensitivity, working concentration range, sensor-to-sensor and measurement-to-measurement reproducibility as well as long-term stability, are improved significantly compared to the planar thin-film sensors by using OANSs. The thin-film gold electrodes modified with OANWs and OANPs exhibit a catalytic activity towards oxidation of hydrogen peroxide with a working concentration range from 20 µM to 500 µM, a sensitivity of 0.031 A M(-1) cm(-2) (RSD 0.046) and 0.027 A M(-1) cm(-2) (RSD 0.045), and a detection limit of 5 µM and 8 µM, respectively (RSD near the detection limits was 9-12%). Our study shows that ultrathin gold nanowires and nanoparticles prepared by oleylamine synthesis are prospective materials to assemble biomolecules into functional nanoarchitectures for enzyme-based bioelectrochemical sensors, metalloprotein bioelectronics, and energy research.

Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer.

Methods to prepare ultrathin gold nanowires and monodisperse nanoparticles based on the intrinsic property of gold(I) ions to form aurophilic interactions stabilized by oleylamine and long-chain alkylamine have been widely explored. Due to the low thermodynamic stability of the high aspect ratio nanostructures, their conjugation and assembly into functional nanosystems have not been explored so far. One of the reasons for this is that the surface of the nanostructures is insulated by stabilization compounds, which preserve the integrity of the nanostructures but at the same time form an insulating barrier in electronic and electrochemical systems in contact areas and for the charge transfer reactions. Conjugation of a metalloprotein cytochrome c (Cyt c) with oleylamine-stabilized gold ultrathin nanowires and nanoparticles into a bioelectrochemically active nanoarchitecture is presented here for the first time. Methods of preparing and assembling the ultrathin nanowires and nanoparticles on the thin-film gold electrodes are shown. Thermodynamic and kinetic parameters were obtained for the direct electron transfer reaction of cyt c on these surfaces. Nanowires are responsible for an approximately −20 mV shift in the redox potential of the ferri/ferro-cyt c couple relative to a thin-film gold electrode.

The fabrication of ultrathin single-crystal Au nanowires with high aspect ratio and that are stable in air is challenging. Recently, a simple wet-chemical approach using oleylamine has been reported for the synthesis of Au nanowires with micrometer length and 2 nm in diameter. Despite efforts to understand the mechanism of the reaction, an ultimate question about the role of oxygen (O(2)) during the synthesis remained unclear. Here we report that the synthesis of ultrathin Au nanowires employing oleylamine is strongly affected by the amount of O(2) absorbed in the reaction solution. Saturating the solution with O(2) leads to both a high-yield production of nanowires and an increase in their length. Nanowires with diameters of about 2 nm and lengths of 8 μm, which corresponds to an aspect ratio of approximately 4000, were produced. The role of oxygen is attributed to the enhanced oxidation of twin defects on Au nanoparticles formed in the first stage of the reaction. Understanding the role of oxidative etching is crucial to significantly increasing the yield and the length of ultrathin Au nanowires.

Little is known about the chemical equilibrium formed between the micellar complex of oleylamine and aurous halide during the synthesis of Au nanoparticles employing an Au(I) precursor. In this paper, we determine for the first time the stability constant of the intermediate oleylamine/Au complex during the first stages of the reaction that produces Au nanoparticles using an amine compound as a reducing agent. We found that the intermediate complex has two stability constants that were dependent on the concentration of AuCl. These results were supported by Fourier transform infrared and mass spectroscopy analysis, which indicated that an unstable secondary amine was produced during the oxidation of oleylamine and reduction of Au(I). Our findings demonstrate that the reduction of Au(I) species promotes substeps of structural changes in the oleylamine molecule. We anticipate our assays to be a starting point for a more comprehensive understanding of the synthesis of Au nanoparticles based on a templateless ...

Nanostructured surfaces have recently gained in importance for electrochemical applications because of an enhanced surface area compared to planar substrates. Due to this property, structured substrates are well suited for electrochemical (bio-)sensors, capacitive coupling with electrogenic cells, and other bioelectronic applications. However, the relationship between electrolytically exposed and redox-active surface areas of nanostructured electrodes compared to planar electrodes is still under discussion. Here, we performed a series of comparative studies to elucidate processes taking place at the electrochemically active surface of gold nanopillars. The pillars, approximately 200 nm in height and 50 nm in diameter, were fabricated using template-assisted nanostructuring. The surface area increase compared to planar electrodes was determined by scanning electron microscopy (SEM), and the redox-active surface area of the same sample was derived from cyclovoltammetric studies. We found consistency between the SEM results and the electrochemically active surfaces determined by cyclic voltammetry of immobilized ferrocenylhexanethiol, immobilized cytochrome c, and oxidation/reduction of gold for small scan rates. Similar values were derived from the capacitance measured by cyclic voltammetry, whereas impedimetric measurements revealed values twice as high. Commonly used diffusion-controlled systems, such as hexacyanoferrate, showed a smaller increase of the electroactive surface area. Finally, we conclude that the sterically restricted diffusion of redox-active species leads to an inaccurate determination of the electroactive surface area of nanosized electrodes.

A novel effective bioelectrochemical sensor interface for enzyme biosensors is proposed. The method is based on in situ synthesis of gold nanostructures (5–15 nm) on the thin-film electrode surface using the oleylamine (OA) method, which provides a high-density, stable, electrode interface nanoarchitecture. New method to activate the surface of the OA-stabilized nanostructured electrochemical interface for further functionalization with biomolecules (glucose oxidase enzyme) using Meerwein's salt is proposed. Using this approach a new biosensor for glucose determination with improved analytical characteristics: wide working range of 0.06–18.5 mM with a sensitivity of 22.6 ± 0.5 μA mM− 1 cm− 2, limit of detection 0.02 mM, high reproducibility, and long lifetime (60 d, 93%) was developed. The surface morphology of the electrodes was characterized by scanning electron microscopy (SEM). The electrochemical properties of the interface were studied by cyclic voltammetry and electrochemical impedance spectroscopy using a Fe(II/III) redox couple. The studies revealed an increase in the electroactive surface area and a decrease in the charge transfer resistance following surface activation with Meerwein's reagent. A remarkably enhanced stability and reproducibility of the sensor was achieved using in situ synthesis of gold nanostructures on the electrode surface, while surface activation with Meerwein's salt proved indispensable in achieving an efficient bioelectrochemical interface.

A spatially resolved delivery of substances integrated with cell culture substrates shows promise for application in pharmacological assays, bioanalytical studies on cell signaling pathways and cell-based biosensors, where control over the extracellular biochemical environment with a cellular resolution is desirable. In this work, we studied a biohybrid system where rat embryonic cortical neuronal networks are reconstructed on microstructured silicon chips and interfaced to microfluidics. The design of cell–cell and cell–medium interactions in confined geometries is presented. We developed an aligned microcontact printing technique (AμCP) for poly(lysine)-extracellular matrix proteins on microstructured chips, which allows a high degree of geometrical control over the network architecture and alignment of the neuronal network with the microfluidic features of a substrate. Spatially resolved on-chip delivery of compounds with a cellular resolution is demonstrated by chemical stimulation of patterned rat cortical neurons within a network with a number of solutions of excitatory neurotransmitter glutamate delivered via microfluidics. The combination of the system described with a patch-clamp technique allowed both modulation of the biochemical environment on a cellular level and the monitoring of electrophysiological properties in the reconstructed rat embryonic cortical networks changed by this microenvironment.

Poly(dimethylsiloxane) (PDMS)-PDMS and hybrid PDMS-glass devices have been characterized and compared in terms of current-voltage linearity, contact angle, electroosmotic velocity, electroosmotic mobility, and electrokinetic potential in dependence on the surface treatment. The hybrid PDMS-glass microfluidic devices have further been tested as on-chip capillary electrophoresis systems for the separation of fluorescently labeled amino acids. It has been demonstrated that different methods of surface pretreatment of the PDMS-glass devices result in significantly different separation performance, with plate numbers varying from 650 to 57 000 in dependence on the surface state and the nature of the amino acids. Electrophoretic separations of amino acids have been achieved within tens of seconds with detection limits of less than 2 microM (approximately 2 x 10(-16) to 2.5 x 10(-16) mol quantities at injection volumes of 110-120 pL). The detected amounts of fluorescein isothiocyante (FITC)-amino acids are at least ten times lower, since the amino acid:FITC ratio is 10:1 mol. The results demonstrate the perspective of such hybrid PDMS-glass microfluidic systems and the methods to modify their surfaces for on-chip separation methods for biomolecules.

The technological aspects of manufacturing three dimensional microstructures for BioMEMS in glass wafers are demonstrated and discussed. The microchannels have been etched in Pyrex glass to a depth of 6–16 μm. Special attention has been paid to the composition and the optimization of the deposition process of the thin film sacrificial metal layers as etch masks for chemical wet etching of glass, and to the influence of the composition of the etch solution on glass etch velocity, undercut phenomenon and the quality of the structures. The structures have been visualized by means of REM to observe the profile and the edge roughness.

A first step towards a microfabricated potentiometric thin-film sensor array for the simultaneous detection of Pb 2+ , Cd 2+ and Cu 2+ has been realized. The sensitive layers used are on the basis of chalcogenide glass materials. These thin-film chalcogenide glass materials that consist of mixtures of Pb-Ag-As-I-S, Cd-Ag-As-I-S or Cu-Ag-As-Se have been prepared by pulsed laser deposition technique. The developed sensor array has been physically characterized by means of scanning electron microscopy and Rutherford backscattering spectrometry. The electrochemical sensor characterization has been performend by potentiometric measurements. Keywords: heavy metal detection, thin-film sensor array, chalcogenide glass material, microfabrication technique, pulsed laser deposition, potentiometry. Introduction Nowadays, the development of cost-effective sensors and sensor systems for analytical tasks becomes more and more important. Under the aspect of a growing demand for environmental analysis as well as monitoring and process control systems, the request of these market segments are an easy to

Variable resistors were constructed from epitaxial SrRuO3 (SRO), La0.67Sr0.33MnO3 (LSMO) and SrTiO3 layers with perovskite crystal structure. Each layer was patterned separately by lithographic methods. Optimized wet chemical etchants and several polishing steps in organic solvents allowed good epitaxy of subsequent layers, comparable to epitaxy on pristine substrates. Periodate as the oxidizing agent for SRO and iodide with ascorbic acid as the reducing agents for LSMO were used to attack these chemically resistant oxides. The final devices changed their conductance in a similar manner to previously described variable resistors that were defined with shadow masks.

The origin of the interface formation appearing due to the realization of contacts to ultrathin gold nanowire devices is revealed. Such interfaces play an important role in transport mechanisms in nanowire structures and can determine the electrical and operating parameters of a nanodevice. Based on experimental results, the specific electrical properties of bundles of ultrathin gold nanowires fabricated by wet chemical synthesis and subsequently assembled and contacted with gold electrodes are reported. It is demonstrated that these properties are strongly affected by the monolayers of organic molecules inevitably present on the surface of the nanowires due to synthetic conditions. In particular, such layers form a potential barrier to tunneling of the electrons from contacts to the nanowires. The electric transport behavior of the investigated nanowire structures in the temperature range from 500 mK to 300 K obeys the model of thermal fluctuation-induced tunneling conduction through the nanowire-metal electrode molecular junction. Application of this model allows calculation of the parameters of the molecular potential barrier. The formation of such a molecular barrier is verified by scanning tunneling microscope (STM) and transmission electron microscope (TEM) measurements performed using a supporting graphene layer. These findings are important for designing novel nanodevices for molecular electronics on the basis of ultrathin nanowires.

Ion-sensitive field effect transistors with gates having a high density of nanopores were fabricated and employed to sense the neurotransmitter dopamine with high selectivity and detectability at micromolar range. The nanoporous structure of the gates was produced by applying a relatively simple anodizing process, which yielded a porous alumina layer with pores exhibiting a mean diameter ranging from 20 to 35 nm. Gate-source voltages of the transistors demonstrated a pH-dependence that was linear over a wide range and could be understood as changes in surface charges during protonation and deprotonation. The large surface area provided by the pores allowed the physical immobilization of tyrosinase, which is an enzyme that oxidizes dopamine, on the gates of the transistors, and thus, changes the acid-base behavior on their surfaces. Concentration-dependent dopamine interacting with immobilized tyrosinase showed a linear dependence into a physiological range of interest for dopamine concentration in the changes of gate-source voltages. In comparison with previous approaches, a response time relatively fast for detecting dopamine was obtained. Additionally, selectivity assays for other neurotransmitters that are abundantly found in the brain were examined. These results demonstrate that the nanoporous structure of ion-sensitive field effect transistors can easily be used to immobilize specific enzyme that can readily and selectively detect small neurotransmitter molecule based on its acid-base interaction with the receptor. Therefore, it could serve as a technology platform for molecular studies of neurotransmitter-enzyme binding and drugs screening.

We present a new biocompatible nanostructured microelectrode array for extracellular signal recording from electrogenic cells. Microfabrication techniques were combined with a template-assisted approach using nanoporous aluminum oxide to develop gold nanopillar electrodes. The nanopillars were approximately 300-400 nm high and had a diameter of 60 nm. Thus, they yielded a higher surface area of the electrodes resulting in a decreased impedance compared to planar electrodes. The interaction between the large-scale gold nanopillar arrays and cardiac muscle cells (HL-1) was investigated via focused ion beam milling. In the resulting cross-sections we observed a tight coupling between the HL-1 cells and the gold nanostructures. However, the cell membranes did not bend into the cleft between adjacent nanopillars due to the high pillar density. We performed extracellular potential recordings from HL-1 cells with the nanostructured microelectrode arrays. The maximal amplitudes recorded with the nanopillar electrodes were up to 100% higher than those recorded with planar gold electrodes. Increasing the aspect ratio of the gold nanopillars and changing the geometrical layout can further enhance the signal quality in the future.

Gold nanopillars are grown in patterns inside a porous anodic alumina template. On selected positions, defined by a gold "seed" pattern, gold is electroplated into the pores, while a barrier layer underneath the porous template blocks the deposition on the rest of the surface. Large-scale arrays of free-standing nanopillar islands are obtained after selective etching of the alumina template.

A new method based on surface treatment with triethyloxonium tetrafluoroborate is proposed for the activation of a gold electrode modified by gold nanoparticles using an oleylamine technique in order to improve the electrochemical signals of a gold surface.

A biohybrid system composed of neuronal cells and silicon-supported nanoporous membranes has been designed to facilitate control of the biochemical environment of neuronal networks with cellular resolution. The membranes may exhibit variable pore sizes and interpore distances and are interfaced to a microfluidic device. Different porosity parameters give rise to changes in the transconductance of the nanopores and can therefore be used to control diffusion of molecules through the membranes. It was shown that the porous membranes are biocompatible with primary vertebrate as well as insect neurons. Our results indicate that nanoporous membranes may be used to interface with biological materials in a biohybrid system, for example as an artificial chemical synapse interface.

Functional coupling of reconstructed neuronal networks with microelectronic circuits has potential for the development of bioelectronic devices, pharmacological assays and medical engineering. Modulation of the signal processing properties of on-chip reconstructed neuronal networks is an important aspect in such applications. It may be achieved by controlling the biochemical environment, preferably with cellular resolution. In this work, we attempt to design cell–cell and cell–medium interactions in confined geometries with the aim to manipulate non-invasively the activity pattern of an individual neuron in neuronal networks for long-term modulation. Therefore, we have developed a biohybrid system in which neuronal networks are reconstructed on microstructured silicon chips and interfaced to a microfluidic system. A high degree of geometrical control over the network architecture and alignment of the network with the substrate features has been achieved by means of aligned microcontact printing. Localized non-invasive on-chip chemical stimulation of micropatterned rat cortical neurons within a network has been demonstrated with an excitatory neurotransmitter glutamate. Our system will be useful for the investigation of the influence of localized chemical gradients on network formation and long-term modulation.

In the present work, on-chip capillary electrophoresis for the separation of neuromediators is demonstrated. The influence of separation buffer (composition, pH, SDS additive), on-chip electrokinetic sample stacking, and surface pretreatment of the PDMS-PDMS and hybrid PDMS-glass devices on the electrokinetic characteristics of microfluidics (nu(eo), mu(eo), zeta) and separation performance of on-chip capillary electrophoresis of neuromediators have been investigated. It is demonstrated that for the effective separation of neuropeptides on elastomer-based microfluidic devices, on-chip sample stacking is necessary. Field-amplified sample stacking for electroosmotic flow supported on-chip separations of neuromediators and without special design of the sample injection scheme has been demonstrated. Electrophoretic separations of fluorescently labeled analytes have been achieved within tens of seconds at injection volumes of about 110pL, with plate numbers varying from

Pb–Ag–As–I–S chalcogenide glass was deposited on the surface of a light-addressable potentiometric sensor (LAPS) by means of the pulsed laser beam deposition (PLD) technique. The deposited layer worked as a Pb 2+ -ion-sensitive transducer, and the sensor showed Nernstian response with a sensitivity of 29±1 mV/decade. The detection limit of the sensor for Pb 2+ -ions was 1×10 −6 mol/l. The response time does not exceed 50 s for Pb 2+ -ion concentrations higher than 1×10 −3 mol/l, while for lower concentration range the response time increases up to 3–5 min.

Au nanowires (AuNWs) were produced by electroless reduction of HAuCl4 in a micellar structure formed by oleylamine and investigated by means of high-resolution transmission electron microscopy (HRTEM). Micrometer long ultra-thin flexible AuNWs with 1—2 nm diameter and AuNWs with about 12 nm diameter and a few hundred nm length were produced. Their extremities show a characteristic bulging. In contradiction with previous work, the bodies of the 12 nm nanowires are defect-free along the axial direction, their extremities, however, show the presence of twin boundaries. Ultra-thin AuNWs were often found as bundles presenting lengths of few micrometers. Although they are stable in solution for months, they were found to be quite sensitive to electron beam irradiation during HRTEM experiments, with a tendency to break up into face centered cubic (fcc) Au droplets. It is proposed that the micellar configuration of oleylamine plays a fundamental role in the atomic arrangement of nanowires. Finally, we anticipate our results to be a starting point for a more realistic experimental investigation of surface effects on the mechanical properties of ultra-thin nanowires with high aspect ratio, which have been only widely exploited theoretically.