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PubMed1983

Application of antimony microelectrodes to intracellular pH monitoring.

Some novel studies of the properties of the antimony microelectrode used for intracellular pH measurements are described. First, it is shown that currents in the picoampere range, such as those encountered as leakage in some electrometers, induce important changes in pH sensitivity. The response time of the electrode has also been measured and indicates that the electrode exhibits a rapid time course which would be very useful for dynamic cytoplasmic pH investigations. An example of internal pH recording during cellular acidification in Xenopus laevis oocyte is also presented.

Animals↗

PubMed1981

Microelectrode recordings from transected nerves in amputees with phantom limb pain.

Intraneural microelectrode recordings were made from the nerve supplying the phantom area in two patients suffering from phantom limb pain. Spontaneous activity was prominent in both cutaneous and muscle fascicle of the nerves. Tapping the neuromata which accentuated the phantom limb pain, induced afferent discharges with both short and long latencies, the latter from fibres with a conduction velocity of only 0.5 m/sec. Blocking the neuromata with lidocaine completely abolished the tap-induced afferent discharges and the tap-induced accentuation of the phantom pain. The spontaneous pain was, however, unchanged, as was the spontaneous activity recorded.

Afferent Pathways↗

PubMed1986

Laminar localization of the sites of release of immunoreactive substance P in the dorsal horn with antibody-coated microelectrodes.

The localization of the sites of release of immunoreactive substance P (SP) in the spinal cord after peripheral nerve stimulation has been examined in the anaesthetized cat. A new technique using antibodies bound to the outside of glass microelectrodes has allowed the identification of these sites with a spatial precision previously unobtainable. A basal release of SP was detected and this was not increased by electrical stimulation of large myelinated primary afferent fibres. Excitation of unmyelinated primary afferents resulted in the release of high concentrations of SP confined to the region of the substantia gelatinosa and lamina V-VI.

Animals↗

PubMed1996

Microinjection of fluorescence dye in a plant cell and its intercellular translocation using a multi-channel microelectrode system.

Lucifer yellow CH dye (LY) was electrophoretically injected into a cell of a cultured tobacco (BY-2) using a multi-channel microelectrode (MME). Pulsing electricx potential (pulse width:90 ms, pulse interval: 80 ms) was applied between the potential-applying (PA) electrodes of both MMESs . The PA-electrode positioned in the LY-bearing cell was set negative against the other PA-electrode. When the pulse height was 340 V, intercellular translocation of LY from the LY-bearing cell to the neighboring cell was observed within 10 s.

Cells, Cultured↗

PubMed1994

Effects of repeated treatments with an extract of Ginkgo biloba (EGb 761), bilobalide and ginkgolide B on the electrical activity of pancreatic beta cells of normal or alloxan-diabetic mice: an ex vivo study with intracellular microelectrodes.

1. The effects of repeated (5-day) treatments with an extract of Ginkgo biloba leaves (EGb 761), bilobalide, and ginkgolide B on the in vitro electrical activity of insulin-secreting pancreatic beta cells of mice have been examined using intracellular microelectrodes. 2. EGb 761 (200 mg/kg/day, p.o.) protected beta cells against the toxic effects of alloxan (50 mg/kg, i.v.), an effect characterized by a restoration of membrane potential (Vr) and an increase in spike frequency (Fs/30), an indicator of insulin secretion. 3. Treatment of non-diabetic mice with EGb 761 (200 mg/kg/day, p.o.) increased Fs/30 of their beta cells, as tested by in vitro exposure of the cells to 11.1 mM glucose, an effect that also occurred with bilobalide (8 mg/kg/day, i.p.) but not with ginkgolide B (4 mg/kg/day, i.p.). 4. Since bilobalide and ginkgolide B caused opposite effects on the sensitivity of beta cells to glucose, the stimulatory effect of EGb 761 on Fs/30 may be attributed to its content of bilobalide. 5. In contrast to its ex vivo effect, the direct in vitro effect of EGb 761 (10 and 25 micrograms/ml) on beta cells favors a decrease in electrical activity, indicating that its in vivo action might be indirect (e.g. via the formation of an active metabolite).

Action Potentials↗

PubMedDate not supplied

An improved simple tungsten microelectrode.

An improvement to tungsten-in-glass microelectrode has been made which requires to special skills. It involves the introduction of a gel solution into the glass micropipette which surrounds and binds the tungsten wire along its full length. A significant damping of microphonic effects is produced and a good fit between tungsten and glass near their tips becomes less critical for success. The electrode was found to be very stable over long recording sessions.

Animals↗

PubMed1995

Improved detection limit for catecholamines using liquid chromatography-electrochemistry with a carbon interdigitated array microelectrode.

The detection limit of catecholamines can be lowered by using a carbon-based interdigitated array (IDA) microelectrode as a detector for liquid chromatography (LC). The IDA electrode is more sensitive than conventional glassy carbon electrodes due to the high current density caused by radial diffusion at each microband, and redox cycling between two microband arrays. Since the number of redox cycles increases at lower flow-rates, the carbon IDA is particularly useful for microbore LC. In an LC system with a 1-mm microbore column and a carbon IDA electrode, the peak height of dopamine (DA) and DOPAC did not decrease with decreasing flow-rate because of this redox cycling. A low detection limit of 5 fg (32 amol) and 9.6 fg (57 amol) was obtained for DA and DOPAC due to the high current density and low background noise level (0.1 pA) at the carbon IDA electrode. The total charge generated by oxidizing DA at the anodic array was more than the value calculated by assuming that all the DA molecules were oxidized.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1990

An extracellular microelectrode array for monitoring electrogenic cells in culture.

This paper describes a planar array of microelectrodes developed for monitoring the electrical activity of cells in culture. The device allows the incorporation of surface topographical features in an insulating layer above the electrodes. Semiconductor technology is employed for the fabrication of the gold electrodes and for the deposition and patterning of an insulating layer of silicon nitride. The electrodes have been tested using a cardiac cell culture of chick embryo myocytes, and the physical beating of the cultured cells correlated with the simultaneous extracellular voltage measurements obtained. It was found that extracellular stimulation of the cells was possible via the same electrodes used for recording.

Action Potentials↗

PubMed1994

Extracellular recording in neuronal networks with substrate integrated microelectrode arrays.

A photolithographically produced array of 60 substrate-integrated microelectrodes was used for extracellular recording. Neuronal electrical activity was recorded from chicken retinal ganglion cells with or without stimulation by diffuse light. The retina was removed from chicken embryos of embryonic day 14-18. Only cells recorded from day 18 retina would react to photostimulation, increasing their activity when stimulated, corresponding to the developmental time course of photoreceptor differentiation.

Animals↗

PubMed2005

Classification of the mode of inhibition of high-affinity choline uptake using capillary electrophoresis with electrochemical detection at an enzyme-modified microelectrode.

A nonradiochemical in vitro assay using capillary electrophoresis with electrochemical detection at an enzyme-modified microelectrode has been developed to evaluate the inhibition of high-affinity choline transport in synaptosomes. Quantitative analysis of high-affinity choline transporter rates as a function of inhibitor and substrate concentrations allowed determination of the mode of inhibition for the quaternary ammonium-catechol-based inhibitors 3-[(trimethylammonio)methyl]catechol, N,N-dimethylepinephrine, and 6-hydroxy-N,N-dimethylepinephrine. The results are compared to the well-characterized inhibitor of choline transport, hemicholinium-3.

Acetylcholinesterase↗

PubMed2005

Noninvasive and continuous recordings of auxin fluxes in intact root apex with a carbon nanotube-modified and self-referencing microelectrode.

Auxin (also known as indole-3-acetic acid, IAA) represents an ancient signaling molecule of plants that also exerts bioactive actions on yeast and animal cells. Importantly, IAA emerges as a new anticancer agent due to the ability of oxidatively activated IAA to selectively kill tumor cells. IAA acts as a pheromone-like molecule in brown algae, whereas the hormone concept of IAA dominates current plant biology. However, recent advances also favor the morphogen- and transmitter-like nature of IAA in plants, making this small molecule one of the most unique molecules in the eukaryotic superkingdom. Here, we introduce new technology for the continuous measuring of IAA fluxes in living cells, tissues, and whole organs that is based on a carbon nanotube-modified and self-referencing microelectrode specific for IAA. This technique not only will advance our knowledge of how IAA regulates plant development but will also be applicable in medicine for its potential use in cancer therapy.

Biological Transport↗

PubMed2004

A low noise multichannel integrated circuit for recording neuronal signals using microelectrode arrays.

This paper reports on the development of a fully integrated 32-channel integrated circuit (IC) for recording neuronal signals in neurophysiological experiments using microelectrode arrays. The IC consists of 32 channels of low-noise preamplifiers and bandpass filters, and an output analog multiplexer. The continuous-time RC active filters have a typical passband of 20-2000 Hz; the low and the high cut-off frequencies can be separately controlled by external reference currents. This chip provides a satisfactory signal-to-noise ratio for neuronal signals with amplitudes greater than 50 microV. For the nominal passband setting, an equivalent input noise of 3 microV rms has been achieved. A single channel occupies 0.35 mm(2) of silicon area and dissipates 1.7 mW of power. The chip was fabricated in a 0.7 microm CMOS process.

Action Potentials↗

PubMed2004

Dielectrophoretic registration of living cells to a microelectrode array.

We present a novel microfabricated device to simultaneously and actively trap thousands of single mammalian cells in alignment with a planar microelectrode array. Thousands of 3 micromdiameter trapping electrodes were fabricated within the bottom of a parallel-plate flow chamber. Cells were trapped on the electrodes and held against destabilizing fluid flows by dielectrophoretic forces generated in the device. In general, each electrode trapped only one cell. Adhesive regions were patterned onto the surface in alignment with the traps such that cells adhered to the array surface and remained in alignment with the electrodes. By driving the device with different voltages, we showed that trapped cells could be killed by stronger electric fields. However, with weaker fields, cells were not damaged during trapping, as indicated by the similar morphologies and proliferation rates of trapped cells versus controls. As a test of the device, we patterned approximately 20000 cells onto a 1cm(2) grid of rectangular adhesive regions, with two electrodes and thus two cells per rectangle. Our method obtained 70+/-1% fidelity versus 17+/-1% when using an existing cell-registration technique. By allowing the placement of desired numbers of cells at specified locations, this approach addresses many needs to manipulate and register cells to the surfaces of biosensors and other devices with high precision and fidelity.

Animals↗

PubMed2004

Interdigitated microelectrode (IME) impedance sensor for the detection of viable Salmonella typhimurium.

Interdigitated microelectrodes (IMEs) were used as impedance sensors for rapid detection of viable Salmonella typhimurium in a selective medium and milk samples. The impedance growth curves, impedance against bacterial growth time, were recorded at four frequencies (10Hz, 100Hz, 1kHz, and 10kHz) during the growth of S. typhimurium. The impedance did not change until the cell number reached 10(5)-10(6) CFUml(-1). The greatest change in impedance was observed at 10Hz. To better understand the mechanism of the IME impedance sensor, an equivalent electrical circuit, consisting of double layer capacitors, a dielectric capacitor, and a medium resistor, was introduced and used for interpreting the change in impedance during bacterial growth. Bacterial attachment to the electrode surface was observed with scanning electron microscopy, and it had effect on the impedance measurement. The detection time, t(D), defined as the time for the impedance to start change, was obtained from the impedance growth curve at 10Hz and had a linear relationship with the logarithmic value of the initial cell number of S. typhimurium in the medium and milk samples. The regression equations for the cell numbers between 4.8 and 5.4 x 10(5) CFUml(-1) were t(D) = -1.38 log N + 10.18 with R(2) = 0.99 in the pure medium and t(D) = -1.54 log N + 11.33 with R(2) = 0.98 in milk samples, respectively. The detection times for 4.8 and 5.4 x 10(5) CFUml(-1) initial cell numbers were 9.3 and 2.2 h, respectively, and the detection limit could be as low as 1 cell in a sample.

Animals↗

PubMed2004

Dielectrophoretic registration of living cells to a microelectrode array.

We present a novel microfabricated device to simultaneously and actively trap thousands of single mammalian cells in alignment with a planar microelectrode array. Thousands of 3 Ipm diameter trapping electrodes were fabricated within the bottom of a parallel-plate flow chamber. Cells were trapped on the electrodes and held against destabilizing fluid flows by dielectrophoretic forces generated in the device. In general, each electrode trapped only one cell. Adhesive regions were patterned onto the surface in alignment with the traps such that cells adhered to the array surface and remained in alignment with the electrodes. By driving the device with different voltages, we showed that trapped cells could be killed by stronger electric fields. However, with weaker fields, cells were not damaged during trapping, as indicated by the similar morphologies and proliferation rates of trapped cells versus controls. As a test of the device, we patterned approximately 20,000 cells onto aI cm2 grid of rectangular adhesive regions, with two electrodes and thus two cells per rectangle. Our method obtained 70 +/- 1% fidelity versus 17 +/- 1% when using an existing cell-registration technique. By allowing the placement of desired numbers of cells at specified locations, this approach addresses many needs to manipulate and register cells to the surfaces of biosensors and other devices with high precision and fidelity.

Animals↗

PubMed2004

Immunoassays based on electrochemical detection using microelectrode arrays.

We show that CombiMatrix's VLSI arrays of individually addressable electrodes, using conventional CMOS integrated circuitry, can be used in detecting various analytes via immunoassay protocols. These microarrays provide over 1000 electrodes per square centimeter. The chips are coated with a porous material on which specific affinity tags are synthesized proximate to selected electrode sites. CombiMatrix microarrays are used to develop spatially multiplexed assay formats for biological entities over a wide range of sizes, from small molecules to cells. Antibodies are tagged with coded affinity labels and then allowed to self-assemble on the appropriate electrode assay sites. Each analyte-specific antibody is chaperoned to individual, predetermined locations by the self-assembly process. The resulting chip can perform numerous different analyte-specific immunoassays, simultaneously. We present new detection technologies based upon the use of the active individually addressable microelectrodes on the chip: redox enzyme amplified electrochemical detection. The results for human alpha1 acid glycoprotein, ricin, M13 phage, Bacillus globigii spores, and fluorescein indicate that this method is one of the most sensitive available, with limits of detection in the attomole range. The detection range is 4-5 logs of analyte concentration, with an assay volume of 50 microl or less. The system provides for a host of multiplexed immunoassays because of the large number of electrodes available. We show how the assays can be optimized for maximum performance on the CombiMatrix microarray platform.

Biosensing Techniques↗

PubMed2005

A high density microelectrode array biosensor for detection of E. coli O157:H7.

A high density microelectrode array biosensor was developed for the detection of Escherichia coli O157:H7. The biosensor was fabricated from (100) silicon with a 2 microm layer of thermal oxide as an insulating layer, an active area of 9.6 mm2 and consists of an interdigitated gold electrode array. The sensor surface was functionalised for bacterial detection using heterobifunctional crosslinkers and immobilised polyclonal antibodies to create a biological sensing surface. Bacteria suspended in solution became attached to the immobilised antibodies when the biosensor was tested in liquid samples. The change in impedance caused by the bacteria was measured over a frequency range of 100 Hz-10 M Hz. The biosensor was evaluated for E. coli O157:H7 detection in pure culture and inoculated food samples. The biosensor was able to discriminate between cellular concentrations of 10(4)-10(7)CFU/mL and has applications in detecting pathogens in food samples.

Antibodies↗

PubMed2005

A carbon fiber microelectrode-based third-generation biosensor for superoxide anion.

Implantable and miniature carbon fiber microelectrode (CFME)-based third-generation biosensor for superoxide anion (O(2)(-)) was fabricated for the first time. The CFME-based biosensor was constructed by electro-deposition of Au nanoparticles on the CFMEs and then modification of the Au nanoparticles by cysteine followed by immobilization of superoxide dismutase (SOD) on the electrodes. The direct electrochemistry of the SOD immobilized on the CFME-based electrodes was efficiently realized by electron transfer promoter - cysteine molecules confined on the Au nanoparticles deposited on the CFMEs. The CFME-based biosensors were demonstrated to possess striking analytical properties for O(2)(-) determination, such as optional operation potentials, high selectivity and sensitivity as well as good stability. Along with the implantable capacity inherent in the CFMEs, these striking analytical properties of the CFME-based biosensors substantially make them potential for in vivo determination of O(2)(-).

Adsorption↗