Optical-transparent and flexible glucose sensor with ITO electrode

The glucose sensor was constructed by immobilizing glucose oxidase (GOD) with glutaraldehyde solution onto the sensitive area of the transparent oxygen electrode. The oxygen electrode was fabricated by sealing KCl electrolyte solution including the Indium-Tin Oxide (ITO)-electrode with both metal-weldable film and gas-permeable membrane coated with Ag/AgCl electrode. The sensor behavior was evaluated using standard glucose solutions in a batch measurement system with a computer-controlled potentiostat at a reduction potential of -900 mV. The sensor device has flexible structure and good optical transparency (less than 0.6 abs) at the visible wavelength from 400 to 700 nm. The sensor was possible to be used for measuring glucose from 0.06 to 1.24 mmol/l (correlation coefficient: 0.999), including the reported concentration of tear glucose in normal (0.14 mmol/l), with good reproducibility.     

A portable potentiostat for the bilirubin-specific sensor prepared from molecular imprinting

A portable amperometric potentiostat was designed and implemented in this work. It was developed to acquisit the current signals produced from bilirubin by an electrochemical sensor. Based on an SOC-based chip, this potentiostat has the merits of moderate accuracy, small size, low cost, and high portability. The bilirubin electrode was prepared by synthesizing a thin layer of bilirubin imprinted poly(methacrylic acid-co-ethylene glycol dimethacrylate) onto the Au layer. With the molecularly imprinted polymer (MIP) film, specific detection of bilirubin was successfully achieved. The cyclic voltammogram of the electrode was measured from this assembled potentiostat. The performance from a commercial potentiostat was considered rather stable and was used as a reference to examine and evaluate the performance of the assembled potentiostat. The detected current signals by the bilirubin sensing were obtained. Linear calibration with a sensitivity of 1.344+/-0.38 microA/mg dl was achieved. Our experimental results showed that the proposed potentiostat's performance could achieve sufficient performance. The evaluation was also made from the aspects such as reset time and steady-response time. The self-assembled potentiostat thus demonstrated its ability in precise detection of bilirubin from an electrode layered with the imprinted polymer film.     

A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration

Here, we present the proof-of-concept for a subsurface bioelectrochemical system (BES)-based biosensor capable of monitoring microbial respiration that occurs through exocellular electron transfer. This system includes our open-source design of a three-channel microcontroller-unit (MCU)-based potentiostat that is capable of chronoamperometry, which laboratory tests showed to be accurate within 0.95 ± 0.58% (95% Confidence Limit) of a commercial potentiostat. The potentiostat design is freely available online: http://angenent.bee.cornell.edu/potentiostat.html. This robust and field-ready potentiostat, which can withstand temperatures of -30°C, can be manufactured at relatively low cost ($600), thus, allowing for en-masse deployment at field sites. The MCU-based potentiostat was integrated with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration in drained thaw lake basins outside Barrow, AK. At three different depths, the working electrode of a microbial three-electrode system (M3C) was maintained at potentials corresponding to the microbial reduction of iron(III) compounds and humic acids. Thereby, the working electrode mimics these compounds and is used by certain microbes as an electron acceptor. The sensors revealed daily cycles in microbial respiration. In the medium- and deep-depth electrodes the onset of these cycles followed a considerable increase in overall activity that corresponded to those soils reaching temperatures conducive to microbial activity as the summer thaw progressed. The BES biosensor is a valuable tool for studying microbial activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide-scale use in remote areas.     

Effect of some carbon nanomaterials on ethanol oxidation by <Emphasis Type="Italic">Gluconobacter oxydans</Emphasis> bacterial cells

The effect of carbon nanomaterials (carbon nanotubes, thermally expanded and pyrolytic graphite) on the bioelectrochemical activity of Gluconobacter oxydans bacterial cells was studied during sorption contact with nanomaterials. For bacterial immobilization, the surface of a working bioelectrode was modified via the application of bacterial suspension in the studied nanomaterial and chitosan. The bioelectrochemical electrode characteristics (the amplitude of generated potential, cyclic volt–ampere characteristics, resistance) were estimated before and in the process of bacterial interaction with ethanol (3-electrode measurement scheme). Modification of the spectral graphite electrode by carbon nanotubes allowed a decrease in the resistance of the charge transfer by 48% and an increase in the oxidation current on cyclic volt—ampere characteristics at a voltage of 200 mV by 21% as compared with nonmodified electrode. The thermally expanded and pyrolytic graphite increased the bioelectrode resistance to 4050 and 8447 Ohm cm², respectively. Mathematical modeling demonstrated that from 75 to 100% of biomaterial (depending on the used nanomaterial) were involved in the process of electricity generation with the selected method of the bacterial immobilization. The use of data obtained during the development of microbial biosensors and electrodes of biofuel cells is discussed.     

Uniform Lithium Deposition Assisted by Single‐Atom Doping toward High‐Performance Lithium Metal Anodes

For a long time lithium (Li) metal has been considered one of the most promising anodes for next‐generation rechargeable batteries. Despite decades of concentrated research, its practical application is still hindered by dendritic Li deposition and infinite volume change of Li metal anodes. Here, atomically dispersed metals doped graphene is synthesized to regulate Li metal nucleation and guide Li metal deposition. The single‐atom (SA) metals, supported on the nitrogen‐doped graphene can not only increase the Li adsorption energy of the localized area around the metal atomic sites with a moderate adsorption energy gradient but also improve the atomic structural stability of the overall materials by constructing a coordination mode of M‐N_x‐C (M, N, and C denoted as metal, nitrogen, and carbon atoms, respectively). As a result, the as‐obtained electrode exhibits an ultralow voltage hysteresis of 19 mV, a high average Coulombic efficiency of 98.45% over 250 cycles, and a stable Li plating/stripping performance even at a high current density of 4.0 mA cm^?2. This work demonstrates the application of SA metal doping in the rational design of Li metal anodes and provides a new concept for further development of Li metal batteries.     

Effects of Electrode Material on the Voltage of a Tree-Based Energy Generator

The voltage between a standing tree and its surrounding soil is regarded as an innovative renewable energy source. This source is expected to provide a new power generation system for the low-power electrical equipment used in forestry. However, the voltage is weak, which has caused great difficulty in application. Consequently, the development of a method to increase the voltage is a key issue that must be addressed in this area of applied research. As the front-end component for energy harvesting, a metal electrode has a material effect on the level and stability of the voltage obtained. This study aimed to preliminarily ascertain the rules and mechanisms that underlie the effects of electrode material on voltage. Electrodes of different materials were used to measure the tree-source voltage, and the data were employed in a comparative analysis. The results indicate that the conductivity of the metal electrode significantly affects the contact resistance of the electrode-soil and electrode-trunk contact surfaces, thereby influencing the voltage level. The metal reactivity of the electrode has no significant effect on the voltage. However, passivation of the electrode materials markedly reduces the voltage. Suitable electrode materials are demonstrated and recommended.     

Long-term in vivo experience of an electrochemical sensor using the potential step technique for measurement of mixed venous oxygen pressure

An implantable amperometric blood oxygen sensor was developed to improve rate adaptation of heart pacemakers. Two different working electrode materials in direct contact with the blood were tested, smooth glassy carbon and gold. Reference electrodes of Ag/AgCl and porous pyrolytic carbon were evaluated. A counter electrode being the titanium housing of the pulse generator was partly coated with carbon. An implantable pacemaker system with chronocoulometric oxygen detection was developed. Heart synchronous potential steps were periodically applied to the 7.5 mm² working electrode in the atrium. Both single and double potential step techniques were evaluated. The oxygen diffusion limited current was used to calculate the stimulation rate. Bench tests and studies on 31 animals were performed to evaluate long-term stability and biocompatibility. In five dogs, the AV node was destroyed by RF ablation to create a realistic animal model of a pacemaker patient. Sensor stability and response to exercise was followed up to a maximum implantation time of 4 years. Post-mortem examinations of the electrode surfaces and tissue response were performed. The results show that a gold electrode is more stable than glassy carbon. The Ag/AgCl reference was found not to be biocompatible, but activated carbon was stable enough for use as reference for the potentiostat. Double potential steps stabilize the sensor response in comparison to single steps. Blood protein adsorption on the gold surface decreased the oxygen transport but not the reaction efficacy. No adverse tissue reactions were observed.     

Long-term in vivo experience of an electrochemical sensor using the potential step technique for measurement of mixed venous oxygen pressure

An implantable amperometric blood oxygen sensor was developed to improve rate adaptation of heart pacemakers. Two different working electrode materials in direct contact with the blood were tested, smooth glassy carbon and gold. Reference electrodes of Ag/AgCl and porous pyrolytic carbon were evaluated. A counter electrode being the titanium housing of the pulse generator was partly coated with carbon. An implantable pacemaker system with chronocoulometric oxygen detection was developed. Heart synchronous potential steps were periodically applied to the 7.5 mm² working electrode in the atrium. Both single and double potential step techniques were evaluated. The oxygen diffusion limited current was used to calculate the stimulation rate. Bench tests and studies on 31 animals were performed to evaluate long-term stability and biocompatibility. In five dogs, the AV node was destroyed by RF ablation to create a realistic animal model of a pacemaker patient. Sensor stability and response to exercise was followed up to a maximum implantation time of 4 years. Post-mortem examinations of the electrode surfaces and tissue response were performed. The results show that a gold electrode is more stable than glassy carbon. The Ag/AgCl reference was found not to be biocompatible, but activated carbon was stable enough for use as reference for the potentiostat. Double potential steps stabilize the sensor response in comparison to single steps. Blood protein adsorption on the gold surface decreased the oxygen transport but not the reaction efficacy. No adverse tissue reactions were observed.     

Direct electrochemical sensor for label-free DNA detection based on zero current potentiometry

A direct electrochemical DNA biosensor based on zero current potentiometry was fabricated by immobilization of ssDNA onto gold nanoparticles (AuNPs) coated pencil graphite electrode (PGE). One ssDNA/AuNPs/PGE was connected in series between clips of working and counter electrodes of a potentiostat, and then immersed into the solution together with a reference electrode, establishing a novel DNA biosensor for specific DNA detection. The variation of zero current potential difference (ΔE(zcp)) before and after hybridization of the self-assembled probe DNA with the target DNA was used as a signal to characterize and quantify the target DNA sequence. The whole DNA biosensor fabrication process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy with the use of ferricyanide as an electrochemical redox indicator. Under the optimized conditions, ΔE(zcp) was linear with the concentrations of the complementary target DNA in the range from 10nM to 1μM, with a detection limit of 6.9nM. The DNA biosensor showed a good reproducibility and selectivity. Prepared DNA biosensor is facile and sensitive, and it eliminates the need of using exogenous reagents to monitor the oligonucleotides hybridization.     

Amperometric biosensor for determining human salivary phosphate

An amperometric biosensor was constructed for analysis of human salivary phosphate without sample pretreatment. The biosensor was constructed by immobilizing pyruvate oxidase (PyOD) on a screen-printed electrode. The presence of phosphate in the sample causes the enzymatic generation of hydrogen peroxide (H(2)O(2)), which was monitored by a potentiostat and was in proportion to the concentration of human salivary phosphate. The sensor shows response within 2s after the addition of standard solution or sample and has a short recovery time (2 min). The time required for one measurement using this phosphate biosensor was 4 min, which was faster than the time required using a commercial phosphate testing kit (10 min). The sensor has a linear range from 7.5 to 625 microM phosphate with a detection limit of 3.6 microM. A total of 50 salivary samples were collected for the determination of phosphate. A good level of agreement (R(2)=0.9646) was found between a commercial phosphate testing kit and the phosphate sensor. This sensor maintained a high working stability (>85%) after 12h operation and required only a simple operation procedure. The amperometric biosensor using PyOD is a simple and accurate tool for rapid determinations of human salivary phosphate, and it explores the application of biosensors in oral and dental research and diagnosis.     

Computer programs for calibrating control electrode voltages and for conditioning working electrodes for a neurochemical voltammetry system

Two computer programs are described which are used to set voltages, calibrate the system, and cyclically condition electrodes electrically in an electrochemical system. This voltammetry system is normally used for measurement of monoamines in neurochemical studies. The system uses an Apple II, a potentiostat, and a DAS-5 interface between the two. The calibration program is used to establish the numerical values needed by the DAS-5 interface from the computer to yield desired potentiostat voltages, to calibrate the potentiostat, and to set output voltages of the system to be safe for the electrode and neural tissue before the potentiostat is turned on. Another program is used to condition electrodes as required in some cases to establish discriminably different oxidation potentials for different electroactive compounds (monoamines and ascorbate).     

Parenteral penicillin in rats: an experimental model of periodic EEG activity]

Parenteral G Penicillin has been administered to 10 rats and EEG pattern has been recorded. High voltage spikes appeared on one hemisphere, 12 to 25 minutes after injections. Gradually spike frequency and voltage increased till periodical EEG was observed on both hemispheres. Such activity was synchronous, symmetrical, stereotyped and often accompanied by myoclonias. This pattern lasted from 45 to 100 minutes. The authors underline the analogies with the Ouabain model of epilepsy and with periodical EEG patterns in man.     

The somatic shunt cable model for neurons.

The derivation of the equations for an electrical model of nerve cells is presented. The model consists of an equivalent cylinder, a lumped somatic impedance, and a variable shunt at the soma. This shunt was introduced to take into account the fast voltage decays observed following the injections of current pulses in some motoneurons and hippocampal granule cells that could not be explained by existing models. The shunt can be interpreted either by penetration damage with the electrode or by a lower membrane specific resistance at the soma than in the dendrites. A solution of the model equations is presented that allows the estimation of the electrotonic length L, the membrane time constant tau m, the dendritic dominance ratio rho, and the shunt parameter epsilon, based only on the measurement of the first two coefficients and time constants in the multiexponential voltage response to injected current pulses.     

Current-to-voltage convertor for measurement of oxygen

A highly sensitive, miniature, inexpensive circuit for the measurement of PO2 in vivo has been described. The circuit is constructed from a current-to-voltage convertor, clamping circuit, differential amplifier, and reverse voltage and overvoltage protector. The design of the circuit allows us to apply voltage bias to the measuring electrode while grounding the preparation. The clamping circuit holds the selected bias voltage constant while the differential amplifier subtracts this bias potential from the PO2 signal yielding an output voltage that is proportional to the current sensed by the oxygen electrode. The circuit is protected from reverse voltage and overvoltage.     

Polyphenol biosensor based on laccase immobilized onto silver nanoparticles/multiwalled carbon nanotube/polyaniline gold electrode

Laccase purified from Ganoderma sp. was immobilized covalently onto electrochemically deposited silver nanoparticles (AgNPs)/carboxylated multiwalled carbon nanotubes (cMWCNT)/polyaniline (PANI) layer on the surface of gold (Au) electrode. A polyphenol biosensor was fabricated using this enzyme electrode (laccase/AgNPs/cMWCNT/PANI/Au electrode) as the working electrode, Ag/AgCl as the reference electrode, and platinum (Pt) wire as the auxiliary electrode connected through a potentiostat. The biosensor showed optimal response at pH 5.5 (0.1 M acetate buffer) and 35 °C when operated at a scan rate of 50 mV s⁻¹. Linear range, response time, and detection limit were 0.1–500 μM, 6 s, and 0.1 μM, respectively. The sensor was employed for the determination of total phenolic content in tea, alcoholic beverages, and pharmaceutical formulations. The enzyme electrode was used 200 times over a period of 4 months when stored at 4 °C. The biosensor has an advantage over earlier enzyme sensors in that it has no leakage of enzyme during reuse and is unaffected by the external environment due to the protective PANI microenvironment.     

Inhibition of Enzyme Induction in E. Coli by Anodic Silver

A silver anode, but not a cathode, is bactericidal at microampere current levels because of the electrochemical reactions occurring at the metal electrode surface. This has been clinically useful as a local anti-infective agent even though the mechanism of action on the bacterial cell has not been determined. We investigated the effect by inducing β-galactosidase while passing current though cultures of Escherichia coli. Enzyme induction was depressed in the silver anode chamber within twenty minutes of initiation of current (0.04 to 40 μA); induction in the connected silver cathode chamber was normal. The inhibition at the anode is not the result of electrolysis of the medium nor is the electric current itself required, since pre-anodized silver is inhibitory. The electrochemical products are effective even after derepression has occurred. They appear to act on the process of protein production itself rather than directly on the liberated β-galactoside enzyme.     

Rapid Changes in the Pattern of Electric Current around the Root Tip of Lepidium sativum L. following Gravistimulation

Using a highly sensitive vibrating electrode, the pattern of naturally occurring electric currents around 1-day-old primary roots of Lepidium sativum L. growing vertically downward and the current pattern following gravistimulation of the root has been examined. A more or less symmetrical pattern of current was found around vertically oriented, downward growing roots. Current entered the root at the root cap, the meristem, and the beginning of the elongation zone and left the root along most of the elongation zone and in the root hair zone. After the root was tilted to a horizontal position, we observed current flowing acropetally at the upper side of the root cap and basipetally at the lower side within about 30 seconds in most cases. After a delay of several minutes, acropetally oriented current was also found flowing along the upper side of the meristematic zone. The apparent density of the acropetal current in the root cap region increased and then decreased with time. Gravitropic curvature was first visible approximately 10 minutes after tilting of the root to the horizontal position. Since the change in the pattern of current in the root cap region precedes bending of the root and is different for the upper and lower side, a close connection is suggested between the current and the transduction of information from the root cap to the elongation zone following graviperception in the cap.     

The use of differential measurements with a glucose biosensor for interference compensation during glucose determinations by flow injection analysis

A novel detection system for the determination of glucose in the presence of clinically important interferents, based on the use of dual sensors and flow-injection analysis (FIA), is described. The normalisation methodology involves measurement of the interference signal at a reference sensor; this signal can then be subtracted from the glucose sensor signal (post-run) to give a corrected measurement of the glucose concentration. The detection system consists of a thin layer cell with dual glassy carbon working electrodes. One electrode was surface modified to act asglucose biosensor by immobilisation of glucose oxidase (GOx) (from Aspergillus niger) with 1% glutaraldehyde and bovine serum albumin. The second electrode (glucose oxidase omitted) was utilised to measure the interference signal responding only to electroactive species present in the injected sample. A computer controlled multichannel potentiostat was used for potential application and current monitoring duties. The sensor responses were saved in ASCII format to facilitate post-run analysis in Microsoft Excel. Cyclic voltammetry (CV) was utilised to investigate the manner in which the interference signal contributed to the total signal obtained at the biosensor in the presence of glucose. The kinetic parameters I_max and the apparent Michaelis-Menten constant, K′_m, were calculated for the sensor operating under flow-injection conditions.     

Ultrasensitive biosensing on the zepto-molar level

Detection of analytes on the zepto-molar (10(-21) M) level has been achieved using a field-effect bio-detector. By applying a gating voltage to enzymes immobilized on the working electrode of the detector, amplification of the biocatalytic current was observed. The amplification is attributed to the modification of the tunnel barrier between the enzyme and the electrode by the gating voltage-induced electric field which exists at the solution-electrode interface. The detection was demonstrated with the glucose oxidase (GOx)-glucose and alcohol dehydrogenase (ADH)-ethanol biocatalytic systems. Glucose at zepto-molar level was detected with zepto-molar detection resolution. Equivalently, 30 glucose molecules present in the sample were detected and the detection system responded distinctively to the incremental change in the number of glucose molecules in unit of 30 molecules. The enzyme's biospecificity was also preserved in the presence of the applied field. We present possible processes that could give rise to the electrical charges required to produce the observed current level.     

Study of low-temperature plasma between rotating electrodes

Results are presented from experimental studies of the electrophysical and spatiotemporal characteristics of a dielectric barrier discharge operating in atmospheric-pressure air in a discharge cell with a dielectric barrier in the form of a rotating disc. One of the electrodes of the discharge cell was stationary and placed at a certain distance from the dielectric surface, and the following two versions of the second electrode were used: (i) a metal disc electrode was attached to the surface of the rotating dielectric disc, while on the opposite surface of the disc, there was a rectangular strip electrode that was at the same potential as a metal disc electrode and had a sliding contact with the dielectric; (ii) only the strip electrode with the sliding contact was connected to the high-voltage source, while the metal disc electrode was disconnected. Due to barrier rotation, the discharge operated in a pulse mode, although it was supplied from a dc voltage source. The current-voltage characteristic of such a dielectric barrier discharge was measured and analyzed. The number of microdischarge channels arising at the stationary electrode, the geometrical parameters of the microdischarge channels, and the discharge current were studied as functions of the supplied voltage, the distance between the stationary electrode and the dielectric surface, and the rotation velocity of the barrier disc.