Microelectrode Research Articles

Passivation and corrosion of microelectrode arrays

The application of silicon based microsensors in aqueous environments is hindered by unsatisfactory barrier properties and poor corrosion resistance of common passivation layers which give insufficient protection to electronic microstructures. This paper reports on investigations of the protective effect of various types of layers (compatible to silicon planar technology) against 1 M NaCl at pH 2 to 10. Failures of the passivation layers were detected by leak current and conductivity measurements with subsequent investigations of failure mechanisms by scanning electron microscopy (SEM). Both organic and inorganic films were tested with chips which were completely covered with the passivation layer. Organic films had a time to failure of at best 500 h, achieved by Probimer® and plasma treated polyimide. The poor barrier properties of PECVD-SiO2 and Si3N4 monolayers (only a few hours) were clearly surpassed by combining the monolayers to SiO2 / Si3N4- duplex and SiO2 / Si3N4 / SiO2 triplex (ONO) layers. The most promising barrier properties were achieved by the triplex (ONO) layer which yielded a time to failure of 1200 h compared to 500 h for the duplex layer on non-buried conducting tracks. Burying the conducting tracks into the thermal SiO2 layer significantly improved the performance of the duplex (2000 h) and the SiC layer (1000 h compared to 700 h on non-buried tracks) once again. In the case of open electrodes the Si3N4 layer quickly failed, whereas the duplex and the SiC layer revealed better protective properties. Organic films failed due to swelling and the formation of blisters. Intrinsic mechanical stress with chemical interaction resulted in stress corrosion cracking (SCC) and finally lead to the failure of the inorganic PECVD layers. Passivierung und Korrosion von Mikroelektrodenarrays Die Anwendung Silizium-basierter Mikrosensoren in wassrigen Medien wird duch die unzureichenden Barriereeigenschaften und schlechten Korrosionsbestandigkeiten ublicher Passivierungsschichten beeintrachtigt, welche die elektronischen Mikrostrukturen nur ungenugend schutzen. In dieser Arbeit wird uber Untersuchungen zur Schutzwirkung unterschiedlicher Passivierungsschichttypen (kompatibel mit der Silizium-Planartechnologie) in 1 M NaCl bei pH 2 bis 10 berichtet. Das Versagen der Passivierungsschichten wurde durch Leckstrom- und Leitfahigkeitsmessungen mit anschliessender elektronenmikroskopischer Untersuchung der Schadigungsmechanismen ermittelt. Es wurden sowohl organische als auch anorganische Schichten auf Chips getestet, welche vollstandig mit der Passivierungsschicht bedeckt waren. Organische Schichten hatten bestenfalls Standzeiten von 500 h, so erreicht mit Probimer® und plasma-behandeltem Polyimid. Die schlechten Barriereeigenschaften der PECVD-SiO2- und Si3N4- Monoschichten (Schutzwirkung nur wenige Stunden) wurden weit ubertroffen durch Kombination dieser Monoschichten zu SiO2 / Si3N4- Duplex and SiO2 / Si3N4 / SiO2 Triplex (ONO) Schichten. Die besten Barriereeigenschaften wurden mit den Triplex(ONO)-Schichten erzielt, welche auf nicht vergrabenen Leiterbahnen erst nach 1200 h versagten. Unter sonst gleichen Bedingungen hielten Duplex-Schichten nur 500 h stand. Durch Vergraben der Leiterbahnen in die thermische SiO2- Schicht wurde die Schutzwirkung von Duplex-Schichten auf 2000 h und von SiC-Schichten auf 1000 h (nur 700 h auf nicht vergrabenen Leiterbahnen) verbessert. Im Bereich geoffneter Elektroden versagte die Si3N4- Schicht sehr schnell, wohingegen die Duplex- und SiC-Schichten wesentlich bessere Bestandigkeit aufwiesen. Organische Filme versagten durch Schwellen und Blasenbildung. Die PECVD-Schichten erlitten neben abtragender Korrosion auch Spannungsriskorrosion durch gemeinsame Einwirkung intrinsischer mechanischer Spannungen und chemischer Belastungen.

Effects of locus coeruleus stimulation on the responses of SI neurons of the rat to controlled natural and electrical stimulation of the skin.

1. The effects of microstimulation of the locus coeruleus (LC) region on the spontaneous discharge and the response of SI neurons to natural and electrical stimulation of the skin have been investigated in 26 urethane anesthetized Sprague-Dawley rats. In particular, one or two air puffs, 5-10 msec in duration, 1-2 psi, usually separated by an interval of 40 msec, were applied on the hairy skin of the wrist or the forepaw at the presentation rate of 1/sec. For units unresponsive to air puffs, similar presentation of low intensity electrical stimuli (0.2-5.0 V, 0.2-0.4 msec pulses) were applied through two needles inserted on the most effective area of the skin. Both natural and electrical stimulations of the skin were applied under control conditions, as well as 50 msec after a 250 msec train of 0.3 msec pulses at 40 Hz. 20-30 microA applied stereotaxically to the LC complex through a tungsten microelectrode. 2. Not all cortical units exhibited spontaneous discharge. Most of the units, however, which were spontaneously active, were inhibited by electrical stimulation of the LC complex, while the remaining ones were excited. The sites of stimulation, which included either the LC proper or the locus subcoeruleus, were identified following both anatomical and physiological criteria. 3. SI neurons recorded at sites between 400 and 950 microns below the surface of the cortex, thus being most likely granule cells of layers III and IV, responded to cutaneous stimuli with spikes which occurred with a latency of 20-30 msec in response to single air puffs and a latency of 15-20 msec in response to single electrical pulses to the skin. In both instances the response to the second stimulus applied at the interstimulus interval of 40 msec was markedly reduced or abolished due to postexcitatory inhibition following the response to the first stimulus (in-field inhibition). In contrast, units particularly located at or below 1000 microns from the cortical surface, which were of very large size probably corresponding to large layer V pyramidal cells, were often difficult to activate with air puffs applied at the centre of the receptive field (RF) and were submitted to electrical stimulation of the skin. 4. Among the 59 isolated SI units tested either to air puffs (45 neurons) or to electrical skin stimulation (14 neurons), 15 units (i.e., 25.4%) were facilitated, while 12 units (i.e., 20.3%) were inhibited following stimulation of the LC complex. 5. A marked feature of the facilitatory effects which usually involved the predominant response to the first air puff, but also the smaller response to the second puff, was that the increase in the number of spikes per stimulus was accompanied by a temporal focusing of the responses characterized by a clear tightening of the latency and narrowing of the peak of activity, which was often accompanied by some level of tonic inhibition of the background discharge. Thus, LC stimulation increased the signal-to-noise ratio of SI neuronal responses to skin stimulation. When inhibitory effects were induced by LC stimulation, they clearly affected the unit response to the first air puff, which was severely depressed. However, the response to the second puff could be facilitated, suggesting that LC stimulation might have produced inhibition of those inhibitory interneurons responsible for the postexcitatory inhibition of the units under examination. Evidence for spatial focusing of the response was not easily documented. In some units, however, LC stimulation produced either facilitation of the responses to puffs at the receptive field center and inhibition of the responses to puffs at the edge at the receptive field or vice versa. 6. Since the LC complex contains in the rat a predominant population of noradrenergic neurons, it is likely that the effects described above were mainly due to activation of these noradrenergic neurons. 7. (ABSTRACT TRUNCATED)

Effect of rinse with calcium enriched milk on plaque fluid.

Previous research has shown that rinsing the mouth with milk significantly diminished the pH in dental plaque fluid; however, the degree of saturation with respect to the dental enamel (DS) was not significantly decreased because of an increase in the calcium ion concentration in plaque fluid. The aim of this study was to investigate the cariostatic effect of adding calcium to milk on the DS value of the plaque fluid after rinsing. Plaque samples were collected from 8 Japanese male dental students. Prior to plaque collection, all subjects refrained from practicing oral hygiene for 48 hr and fasted overnight. Supragingival plaque samples were collected from one side of the mouth of each subject, and then collected from the other side, following a 30-second rinse with 15 mL of calcium-enriched milk, which was prepared by adding calcium carbonate to ordinary milk, and a 10-minute waiting period. The samples were cleared by centrifugation, and the plaque fluid was analyzed for inorganic ions and pH, using an ion chromatograph and pH microelectrode, respectively. The calcium ion concentration of the milk was 6.4 mM, which was about 36% higher than that of ordinary milk. The pH decreased significantly (p<5%) from 6.4 to 6.1 following the rinse with calcium enriched milk, as tested by the paired t-test. The decrease in pH might have caused a reduction of the DS value; however, it was compensated for by a significant (p<0.5%) increase in the calcium ion concentration of plaque fluid.

Microelectrodes with Leak of Solution

Microelectrodes with Leak of Solution

Arrays of gold microelectrodes made from split integrated circuit chips

AbstractA simple and inexpensive way to fabricate arrays of gold microelectrodes is proposed. Integrated circuit chips are sawed through their middle, normal to the longest axis, leading to destruction of the silicon circuit and rupture of the gold wires that interconnect it with the external terminals. Polishing the resulting rough surface converts the tips of the wires embedded in the chip halves into arrays of gold microdisks of about 25 μm diameter. The number of active microelectrodes (MEs), of an array depends on the number of pins in the chip, n, being typically (n/2)‐4. These MEs can be used individually or externally interconnected in any combination. X‐ray images of the chips and micrographs of the resulting surface of the polished arrays have revealed variable distances between neighbor MEs, which are however, larger than 10 times the radius of the disks. This feature of the MEs prevents diffusional cross‐talk between electrodes. The use of these microdisk electrodes for analytical purposes exhibits sigmoidal voltammograms, and chronoamperometric experiments confirm the nonlinear i vs. t1/2 plots, typical for processes where radial diffusion prevails, Satisfactory uniformity was observed for the response of each electrode of an array, indicating similarity of geometry and disk areas. The potentialities of these MEs were demonstrated by the determination of cadmium at ppb levels using square wave voltammetry with preconcentration. Due to the relative ease with which these MEs can be manufactured and their good performance in (chemical) analysis, wide applications in electrochemistry and electroanalysis is envisioned.

Development of a rapid and sensitive determination method of carbohydrates and their related compounds by capillary electrophoresis with amperometric detection at a copper microelectrode.

糖類及びその関連物質を迅速分離するために,陽イオン性界面活性剤を含む強アルカリ溶液を電気泳動液として用いるキャピラリーゾーン電気泳動法について検討した.試料ゾーンは直径30μmの銅円盤マイクロ電極を用い,0.7V(対Ag/AgCl)の一定電位でアンペロメトリーによって電気化学的に検出した.この銅マイクロ電極は,陽イオン性界面活性剤を含む強アルカリ溶液中において界面活性剤を含まない場合に比べて,糖類及びその関連物質に対して約2倍の触媒酸化電流を示した.糖類及びその関連物質の分離時間は15分以下と従来法に比べて約1/3で済んだ.糖類及びその関連物質の検出限界は約2.5fmol(S/N=3)と従来法に比べて約20倍の高感度が得られた.

Electrochemical characteristics of H2O2 microarray electrodes as base elements of biosensors

The electrochemical characteristics were examined of band- and square-type MAEs (microarray electrodes) with 10, 20 and 30 μm band width and side length prepared by using standard planar processing in K3Fe(CN)6 solution. Among them, S1–5 square-type MAE with 10 μm side length and 9.0×10−3 mm2 in the total area exhibits the largest current density and the shortest response time. The H2O2 calibration curve obtained at the S1–5 shows linearity from 0.1 to 5.0 mmol/l, a mean slope of 550 nA/mmol/l with a CV (variation coefficient) of 16.1%. A glucose sensor based on the S1–5 was prepared and its sensitivity was 21 nA/mmol/l, ten-fold greater than that of a single ME (microelectrode) reported lately.

The functional linkage among the "ZSL"-spinal dorsal horn-SN.

Electrical stimulation of the Zusanli point (ZSL) and solitary tract nucleus (SN) as well as microelectrode recording from the laminae III-V of the lumbar spinal dorsal horn have been used on the pentobarbital anesthetized rats, finding and identifying 57 spinal neurons responding to the stimulations of both ZSL and SN. Among them, 34 responded antidromically to SN; the others responded orthodromically to SN. Among them, the low-threshold mechano-receptive (LTM) neurons and wide-dynamic-range (WDR) neurons were 50 percent respectively. The results indicate that (i) a single spinal dorsal horn neuron receives somatic afferent input and then conveys it to the visceral sensory nucleus-SN; (ii) some spinal dorsal horn neurons receive, in turn, innervation from the SN; (iii) the convergence and integration between somatic and visceral sensory inputs might occur in the spinal dorsal horn neurons and/or SN.

Manufacture of sharpened microelectrodes from varnished wire

Manufacture of sharpened microelectrodes from varnished wire

The projection linkage between the spinal dorsal horn neurons and both the solitary tract and dorsal column nuclei.

Electrical stimulation of the solitary tract nucleus (SN) and dorsal column nuclei (DCN) as well as microelectrode recording from the lumbal spinal dorsal horn have been used to find and identify the axonal projection of and the afferent innervation on the spinal neurons of pentobarbital-anesthetized rats. A total of 92 neurons was recorded and identified mainly in laminae III-V of the lumbar spinal dorsal horn. Of them, 38 neurons were activated antidromically from stimulation of both the SN and DCN. The other 54 neurons responded synaptically to both the SN and DCN stimulations. The initial antidromic responses of 8 neurons in the first group were followed by one or more responses synaptically driven from the SN and/or DCN stimulation. Conduction velocities were in the range of A delta fibers, but faster in the antidromic responses and slower in the synaptic responses. These results indicate that (i) some spinal neurons issue branched axons of larger-sized A delta fibers and double project to both the SN and DCN; (ii) some of these double projection neurons receive in turn smaller A delta fiber innervation from the SN and/or DCN; and (iii) some other neurons in the spinal cord are dually innervated by smaller A delta fibers originating from both nuclei.

Measurements of diffusion coefficients and concentrations of electroactive species in hydrogel by cyclic voltammetry with a microelectrode

Mesures du coefficient de diffusion et de la concentration de Mo(CN) 8 4− au-dessus et au-dessous de la transition de phase d'un gel de poly(N-isopropylacrylamide). Le coefficient de diffusion dans l'etat contracte est tres inferieur a celui mesure dans l'etat gonfle

Chloride ion-selective microelectrodes

Microelectrodes have attracted considerable interest in electrochemistry [1,2] One of the unique characteristics of the microelectrode is its applicability to in vivo electrochemical measurements without damaging the cell So far, many amperometnc measurements have been carried out using microelectrodes in vivo [3], especially in brain tissue, to detect neurotransmitters However, these amperometnc microelectrodes cannot be used for important measurements such as those of intracellular ion activities in living cells For such purposes, glass capillary microelectrodes provided with an internal filling solution have been used in the field of modern electrobiology [4] The internal resistance of their tips is usually quite large, so noise is frequently a serious problem in the measurement of weak responses Furthermore, although several recent papers report the use of polymer-modified electrodes as ion-selective sensors [5], such electrodes are not suitable for in vivo electrochemical measurements because of their large size In this paper, we report a convenient and straightforward method for the fabrication of a Cl --selective microelectrode, the Ag/AgC1 microelectrode sealed in a thin glass sheath, which can be used as a micropotentiometnc electrode, and we describe its behavior in a microcapsule and a single cell

Re-development of synaptic connections after implanted single 5-HT containing neuron in isolated leech ganglia.

Single mature Retzius cells which contain 5-HT have been implanted in isolated ganglia of Whitmania pigra. The properties of the implanted Retzius cell and its connections with the original identified nerve cells of the ganglia have been measured by intracellular microelectrodes. At 3 days in culture an implanted Retzius cell maintains its normal electrical membrane properties. It also forms the non-rectifying electronic coupling with the original Retzius cell and rectifying junctions with the L motor neuron of the host ganglion. In addition it receives chemical inputs of the impulse from T and N sensory neurons of ganglion. Impulses in the implanted Retzius cell evoke synaptic potentials in the L motor neuron. In this paper the appearance of novel synapses, which are formed by implanting an extra mature neuron as a pre- or post-synaptic element, is described. It might represent functional development of central nervous system at an earlier stage.

Physiological identification and property of afferents from the masseter muscle to the caudal part of the trigeminal nucleus in rat.

The present study was to identify the physiological properties of the afferent fibers from the masseter muscle to the caudal part of the spinal trigeminal nucleus of rat using a microelectrode technique. When electrical stimulation was applied to the masseter muscle, the evoked potentials were recorded with a shorter latency (the S-response) or a longer latency (the L-response). The threshold current intensity of the S-response was lower than that of the L-response. There were statistical significant differences between the S-response and the L-response in latency and in threshold current intensity. Both the S- and L-responses could follow by stimulation of low frequencies (10 to 30 Hz), indicating that the evoked responses were the component of the secondary neuron activities. On the anatomical and physiological assumption, the conduction velocities of the S- and the L-responses were calculated and they were in the range of that of A-delta fibers. We also observed that both the S- and the L-responses could not follow high frequency stimulation of the masseter muscle. This effect may reflect the phenomenon of fatigue in the finely myelinated fibers or polymodal nociceptors. Thus, the present study suggested the involvement of the afferents from the masseter muscle to the spinal trigeminal nucleus in the transmission and the relay of the masticatory muscle pain.

In Behavior of, MICROELECTRODES

in Behavior of, MICROELECTRODES

Segregation of gastric Na and Cl transport: a vibrating probe and microelectrode study.

The short-circuit current (Isc) of resting Necturus gastric mucosa (approximately 20 microA/cm2) can be attributed to the algebraic sum of the net Cl- secretion and amiloride-inhibitable net Na+ absorption. We have attempted to identify the cell types [surface epithelial cells (SCs) or oxyntic cells (OCs)] responsible for the transport of these ions in Necturus gastric mucosa using microelectrodes (ME) and a vibrating probe (VP). Mucosae were mounted horizontally in an open-topped Plexiglas chamber either serosal side up for basolateral ME impalements of OCs or mucosal side up for apical impalements of SCs and VP measurements. Cell impalements were made under open-circuit conditions, and VP measurements were performed under short-circuit conditions. Impalements of OCs indicate that neither the ratio of their apical to basolateral cell membrane resistances (Ra/Rb = 1.3 +/- 0.2) nor their cell membrane potentials were affected by 10(-6) M mucosal amiloride. In contrast, impalements of SCs indicate that amiloride increased their Ra/Rb from 3.5 +/- 0.2 to 15.6 +/- 1.8 and hyperpolarized both cell membrane potentials by greater than 20 mV. VP measurements showed that the amiloride-induced change in the current from SCs (5.6 microA/cm2) accounted for the amiloride-induced change in the Isc (5.5 microA/cm2). A non-zero current (4.4 +/- 1.0 microA/cm2) measured over SCs in the presence of amiloride was due to contamination from current arising from the gastric crypts that contain the OCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Further improvement of the elgiloy microelectrode

Further improvement of the elgiloy microelectrode

The simultaneous discharges of two neurons in N. Pf and RF and the influences on them by stimulating central gray matter.

This paper employs the method of simultaneous recording of the electric discharges of two neurons with two microelectrodes to study the interrelationship of simultaneous electric activities of pain excitation neurons (PEN) and pain inhibition neurons (PIN) in N. parafascicularis (Pf) of thalamus and reticular formation (RF) of midbrain in 42 rats. The results prove: (i) There are both PEN and PIN in RF in midbrain and they act coordinately; (ii) noxious messages may simultaneously act on PEN and PIN in N. Pf and RF, and the reciprocal coordination of electric activities of these two kinds of neurons is very obvious; (iii) stimulating central gray matter or injecting morphine may weaken the activities of PEN simultaneously, with the opposite effects on PIN.

8. Micro-electrodes for in vivo neuro-electrochemistry

8. Micro-electrodes for in vivo neuro-electrochemistry

Long voltammetric microelectrode for in vivo monitoring of acetaminophen in primate species

A long (45 cm) voltammetric microelectrode for in vivo monitoring of acetaminophen in primate species is described. Due to its length, intravascular insertion is feasible into regions of effective blood circulation. The working electrode is made of carbon paste, placed at the end of a Teflon tubing. Acetaminophen is detected in vivo, in rhesus monkey blood stream, following its intravenous (i.v.) administration. Differential pulse voltammetry with a relatively fast scan rate (2 V/min) is employed to allow rapid assessment of blood concentration of a drug (up to 90 measurements per hour). Well defined peak voltammograms are obtained. In the anodic potential range of whole blood voltammograms, no differential pulse peaks are observed. Despite the obvious problems associated with voltammetric measurements in a complex environment such as whole blood, the method appears to be suited for in vivo monitoring of oxidizable drugs.