Μm Tip Research Articles

Improved ceramic-based multisite microelectrode for rapid measurements of l-glutamate in the CNS

This paper describes improvements and further characterization of a ceramic-based multisite microelectrode for in vivo measurements of l-glutamate. Improvements include increased recording area, insulation deposition using photolithography for more uniform recording sites and forming the microelectrodes using a diamond saw providing smoother microelectrode edges. The new microelectrodes are triangular in shape, 1 cm in length and taper from 1 mm to a 2–5 μm tip. Details on performing in vivo measurements are given, including microelectrode preparation, pitfalls of the recording method and approaches to enhance reproducibility of the technique. The detection limit for l-glutamate was lowered to ∼0.5 μM and a self-referencing recording technique was utilized to remove interferents as well as decrease noise. Applications of the microelectrodes to study l-glutamate uptake and release in rat prefrontal cortex, cortex, cerebellum and striatum are included.

Continuous anti-stiction coatings using self-assembled monolayers for gold microstructures

We have experimented with using continuous self-assembled monolayer (SAM) coatings on different surfaces, such as gold and silicon nitride, as anti-stiction coatings for radio-frequency microelectromechanical systems (RF MEMS). SAMs are coated on gold and silicon nitride surfaces in order to fabricate stiction-free gold structures after the wet release process. SAM coatings on gold and silicon nitride surfaces change the contact angle of a water droplet from 70.6° to 112.6° and from 36.7° to 115.8°, respectively. From atomic force microscopy, we can see that there is little change in the roughness of the gold and silicon nitride before and after the SAM coating. Using the electroplating technique and the wet release process, we have fabricated 4 μm thick gold cantilevers and bridges on a gold surface with a 6.5 μm gap from the substrate. Cantilevers and bridges are fabricated with different lengths in the range of 100–1000 μm with separations of 100 μm. It is observed that cantilevers and bridges with a length of 1000 μm on a gold substrate are released and standing free. A 1000 μm long gold cantilever has only 16.5 μm tip end deflection after the wet release process and SAM coating, much smaller compared with the 120 μm tip end deflection with the dry release process. Gold cantilevers, 100–500 μm long, on silicon nitride are released free and gold bridges on silicon nitride are released with a length of 1000 μm with continuous SAMs. The SAMs are coated on gold and silicon nitride surface in order. This method enables the gold cantilever and bridge on the gold or silicon nitride surface to be released with low deflection.

Conduction of hyperpolarization along hamster feed arteries: augmentation by acetylcholine.

The conduction of vasodilation along resistance vessels has been presumed to reflect the electrotonic spread of hyperpolarization from cell to cell along the vessel wall through gap junction channels. However, the vasomotor response to acetylcholine (ACh) encompasses greater distances than can be explained by passive decay. To investigate the underlying mechanism for this behavior, we tested the hypothesis that ACh augments the conduction of hyperpolarization. Feed arteries (n = 23; diameter, 58 +/- 4 microm; segment length, 2-8 mm) were isolated from the hamster retractor muscle, cannulated at each end, and pressurized to 75 mmHg (at 37 degrees C). Vessels were impaled with one or two dye-containing microelectrodes simultaneously (separation distance, 50 microm to 3.5 mm). Membrane potential (E(m)) (rest, approximately -30 mV) and electrical responses were similar between endothelium and smooth muscle, as predicted for robust myoendothelial coupling. Current injection (-0.8 nA, 1.5 s) evoked hyperpolarization (-10 +/- 1 mV; membrane time constant, 240 ms) that conducted along the vessel with a length constant (lambda) = 1.2 +/- 0.1 mm; spontaneous E(m) oscillations (approximately 1 Hz) decayed with lambda = 1.2 + 0.1 mm. In contrast, ACh microiontophoresis (500 nA, 500 ms, 1 microm tip) evoked hyperpolarization (-14 +/- 2 mV) that conducted with lambda = 1.9 +/- 0.1 mm, 60% further (P < 0.05) than responses evoked by purely electrical stimuli. These findings indicate that ACh augments the conduction of hyperpolarization along the vessel wall.

Finite element analysis of a IBM suspension integrated with a PZT microactuator

This paper presents a piezoelectric-based microactuator concept that could provide an economical and easily integrated option for dual stage actuation used in hard disk drives (HDDs). A simple cantilever beam integrated with the PZT actuator was simulated first in order to testify the driving mechanics of the new design. A modern suspension (IBM Deskstar DTLA-307015) integrated with the developed PZT actuator was then simulated by finite element method (FEM). Theoretical dynamic and electrostatic analyses were performed to investigated the resonant frequency and displacement sensitivity. Good dynamic characteristics were obtained. Further simulation was done based on the optimized structure of the actuator/suspension assembly and results show that >1 μm tip stroke can be obtained while the driving voltage is only 20 V. A 10 V is sufficient to get >1 μm tip stroke if double layer PZT actuator is used.

Reduced brightness of the ZrO/W Schottky electron emitter

The reduced brightness for a 〈100〉 ZrO/W Schottky electron emitter with a tip radius of 0.8 μm has been measured. The maximum reduced brightness measured was 2×108 A/(m2 sr V). The measurements of the reduced brightness are compared with the extended Schottky theory and the theory on stochastic Coulomb interactions. At high angular current densities the reduced brightness is limited by statistical Coulomb interactions in the gun lens region. The limits to the maximum reduced brightness in an ideal configuration are explored and found to be 2×109 A/(m2 sr V) for a 0.2 μm tip and a current limiting aperture in the extractor electrode.

Adhesive strength of electroplated copper films

A study has been conducted to characterise the scratch resistance and adhesive strength of copper films electroplated on to thin layers of W/TiN/Si(1 0 0) and Cu/Ta/Si(1 0 0) substrates. The properties were characterised with a microscratch tester using diamond indenter of different sizes. For the electroplated copper film on W seed, a 200 μm tip with an increased loading produced initially a minor delamination corresponding to damage along the sides of the scratch path followed by cracking at the centre of the scratch. A complete delamination of the film, causing tearing of the film from the underlying substrate, occurred at a critical load of 16 N. In the case of the film on Cu seed, no delamination was observed within the loading range up to 22 N under a 200 μm tip. When a 50 μm indenter was used a minor delamination was seen initially at a force of 4 N, and this delamination subsequently increased with increasing load, but no full delamination was found within the loading range of up to 22 N. The full delamination of the film on Cu seed occurred at 3 N when the scratch testing was performed using a 20 μm diamond tip. The failure phenomenon for the film on Cu seed is different from that on W seed. The initial failure was caused by radial cracking in the film, which turned into chipping of the film as the loading force increased. The film then completely delaminated, causing substantial debris to be strewn along the scratch path.

Imaging cytosolic free-calcium distribution and oscillations in pollen tubes with confocal microscopy: A comparison of different dyes and loading methods

A steep, oscillating tip-focused gradient in cytosolic free calcium ([Ca2+]c) has been implicated in pollen tube growth. Further understanding of the biological causes and consequences of these processes relies on the precise imaging of [Ca2+]c during the different growth phases. In this work, the minimum technical requirements for confocal [Ca2+]c imaging ofAgapanthus umbellatus pollen tubes were examined. A range of dyes, dye forms, and loading methods were compared. Non-ratio and ratio imaging were critically analysed, in terms of the detection of the [Ca2+]c gradient and its fluctuations over time. Both ratiometric and nonratiornetric methods detected relative changes in [Ca2+]c. However, visualisation of the [Ca2+]c gradient, with an accurate spatial definition, was only possible with ratiometric methods. The gradient observed in this study ranged from 1.8 μM (tip) to 180–220 nM (basal level), within the first 4–10 μm. Apical [Ca2+]c fluctuations with an amplitude between 415 nM and 1.8 μM showed a period of 40 to 75 s. All protocols for dye-loading proved to have strengths and weaknesses. Thus, the choice of a dye and its loading procedure should consider the required imaging period, extent of sequestration, effect on cell performance and viability, ease of loading procedure, and aim of the study. The present study constitutes an examination of the [Ca2+]c gradient in pollen tubes by these criteria.

A novel technique for micro-dissection of neuronal processes

A simple system for cutting dendrites of single neurons without damaging the viability of the cell is described. The system utilizes a rapidly vibrating (100 Hz) micropipette (< 1 μm tip diameter), which is dragged under direct visual control across the dendrite of a selected neuron. We used this system in a thin slice preparation to dissect the apical dendrites of rat hippocampal Ca1 pyramidal cells. We then used the patch-clamp technique in the whole-cell configuration to record from the isolated somata of these cells and to inject a dye into them. Both a functional and an anatomical disconnection of the dendrites from their somata were verified.

The influence of periphyton on boundary layer conditions: a pH microelectrode investigation

The effect of the physical presence and activity of an increasing layer of periphyton on the pH, CO 2, and thickness of the boundary layer surrounding artificial plants was investigated. Details of a microelectrode apparatus suitable for use in natural water, with probes 5 μm tip diameter and with a sensitivity of 0.01 pH are given. Detailed pH gradients illustrate an increase in length of gradient and amplitude of pH shift with increased periphyton abundance. A logarithmic increase in pH at the leaf surface was found with increasing periphyton abundance measured as areal chlorophyll density and periphyton thickness, which translated into an exponential decline in calculated free CO 2 availability. Periphyton was capable of reducing the estimated free CO 2 concentration to less than 2 μmol l −1. Boundary layer thickness increased linearly with periphyton thickness. The outer edge of the periphyton effectively became the surface of the object, with interstitial water static. Periphyton has the potential to detrimentally affect the growth of the host plant through its effects on the rate of carbon supply.

Electron field emission from polycrystalline silicon tips

Arrays of 10 polysilicon field emitter tips were fabricated using plasma etch and oxidized to form sharp tips. Phosphorus doped polysilicon tips emit at around 10–15 V regardless of the degree of their sharpness. Similarly, intrinsic polysilicon tips emit at around 50 V (at 2 μm tip to anode spacing). The same turn on voltages have been observed on flat polysilicon surfaces. Field emission data of the diode structures revealed a significant difference between phosphorous doped and intrinsic polysilicon tips and flat surfaces. The φ3/2/β versus applied voltage was obtained from the transconductance data and was used to compare the performance of the doped and intrinsic polysilicon tips. A qualitative comparison of φ3/2/β ratio reveals an increase in the effective work function of the intrinsic polysilicon device which is related to the field penetration inside the emitting surfaces. Furthermore, field emission data reveal the conduction limitation of the intrinsic polysilicon films associated with the single carrier injection mechanism.

Adhesion Quantification of Post-CMP Copper to Amorphous SiN Passivation by NanoIndentation

ABSTRACTIn this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reliably and repeatably produce these delaminations a TiW (10wt% Ti) superlayer was sputter deposited on to the test structures.[2,3] Mechanical properties, including elastic modulus and hardness of SiN, electrodeposited copper, and TiW measured by nanoindentation are also reported here.

Mechanical properties of plasma-deposited SiOxNy coatings on polymer substrates using low load carrying capacity techniques

Amorphous hydrogenated silicon oxynitride thin films were deposited on polycarbonate by plasma-enhanced chemical vapour deposition (PECVD) using a dual mode microwave/radio frequency (MW/RF) plasma system. The film composition was adjusted by varying the nature of the silicon gas precursor (silane or hexamethyl–disiloxane), and the flow rate ratio of nitrous oxide (N2O) and ammonia (NH3). The mechanical properties of the film (residual stress, hardness and scratch resistance) were determined by means of curvature method and by low load techniques (0.1–10 mN), such as depth sensing indentation and cantilever microscratch testing. Adequate contact conditions were evaluated using a simple analytical model of stress field distribution. Coating-specific properties were determined by using a low contact load (1 mN) and a sharp indenter (2 μm tip radius). The highest scratch resistance is obtained for hard coatings possessing low internal stress.

Characterization of point-plane corona in air at radio frequency using a FE-FCT method

The development of corona under RF conditions in point-plane configuration has been investigated in this paper, using the recently developed finite-element flux-corrected transport (FE-FCT) method. The study was made in air for a 1 cm gap with 50 µm tip radius needle at 40 MHz and the effects of different parameters, such as the peak applied voltage (in the range 3-4.5 kV) on the coronal development and particularly on the current and light output, are examined. Polarity and hysteresis effects are observed, as well as a plateau in the current waveform, which are confirmed by previously published experimental results. Finally, a Fourier analysis on the steady-state current waveform is performed.

Local field emission features of thick diamond films on various silicon substrates

The field emission of diamond is promising for high-power applications. According to theoretical analyses, the field emission (FE) of insulating diamond should be governed by the diamond-substrate interface. Therefore, we have investigated the influence of differently p- and n-doped Si(100)-substrate types on the FE properties of thick, oriented, and locally insulating diamond films, grown in a microwave plasma-assisted chemical vapor deposition setup. Local FE measurements were performed by means of a field emission scanning microscope with variable lateral resolution R⩾100 nm. By using anodes of 1 μm tip diameter, very high maximum reproducible local current densities JREP (from μm2-sized areas) up to 8860 A/cm2 could be achieved at vacuum field strengths E of typical 1200–3000 V/μm, corresponding to 20–50 V/μm in the diamond near the substrate. The current I vs E behavior, the reproducibility, and JREP depended strongly on the substrate type. FE mapping over a 10×10 μm2 sized area revealed a uniform emission on a 100 nm scale. In order to realize high currents for power applications, the uniformity of the substrate-diamond interface, as well as of the film smoothness, should be improved.

A new technique for measuring the temporal characteristics of the carbon fibre microelectrodes in in vivo voltammetry at millisecond time intervals

A common approach to test the time-response of carbon fibre microelectrodes entails the use of a flow injection system which allows delivery of a bolus of test compound in the flow stream to a detector electrode. The introduced bolus is distorted from its original form by convective and dispersive forces during the period of transport from the injector to the detector electrode in the connection tubing and couplings. Thus, the flow injection system allows one to change the medium in the vicinity of the electrode in about 100–200 ms. We describe here a simple falling drop system, which is an easy to use for calibration of the carbon fibre microelectrodes with respect to their sensitivity and time-response. This system does not have a loop injector and minimizes problems associated with convective and dispersive bolus distortion. It allows one to change the medium in the vicinity of the electrode in less than 10 ms. With this system, the sensitivity and the temporal resolution of the electrodes may be easily and rapidly estimated in a single experiment. The temporal resolution of the untreated, uncoated carbon fibre cylinder electrode of 300 μm tip length in response to dopamine was estimated as 1.49±0.1 μM/ms (M±SEM, n=36, rise) and 0.051±0.003 μM/ms ( n=36, wash-out) on the half of amplitude of electrochemical response which was monitored by constant potential amperometry.

High-Power Diode Laser in Neurosurgery: Clinical Experience in 30 Cases

Background High-power semiconductor diode lasers were recently introduced and have been tested in ophthalmology and general surgery. These lasers are attractive from the practical and economical standpoint, and have enough power to perform most surgical procedures. They could replace other surgical lasers such as CO 2, argon, 1.06 μm, and 1.32 μm Nd-YAG lasers for many applications in neurosurgery. We report our initial experience with the first available 0.805-μm surgical diode laser, the Diomed 25 (Diomed, Ltd, Cambridge, U.K.) in a series of 30 patients. Methods The diode laser was evaluated during surgical resection of various types of central nervous system tumors in 30 patients. It was used free-hand in 27 patients in contact and non-contact, continuous wave (cw) and pulsed modes, and during ventricular endoscopy in three patients. Average time of laser use during a procedure was 248 seconds. Output power ranged from 1 to 25 watts, with an average power per patient of 2.64 to 15.5 watts (mean, 8.78 watts). Total energy delivered ranged from 65 to 11,051 joules per patient. Results Using 600- or 400-μm non-contact optic fiber, well pigmented tumor tissue hemostasis was obtained at cw 3 to 10 watts with a defocused beam, whereas vaporization required 10-25 cw or pulsed watts with a focused beam. Soft and tough tissue section could be obtained using a sculpted cone-shaped (600-300 μm tip) contact fiber at 7-10 cw watts after fiber tip charring. Because of the deeper penetration of 0.805-μm light in non-pigmented tissues, non-contact mode is not recommended for white matter or poorly vascularized tumors. The contact mode was not efficient on very soft tissues such as edematous brain parenchyma. The contact fibers proved to be very fragile because of heat generation. Conclusions The high power diode laser proved to be efficient for hemostasis, section and vaporization, using contact and non-contact modes, at different output powers. Economical and ergonomical advantages of this new generation of surgical lasers may cause them to replace other surgical lasers such as argon, CO 2, and Nd-YAG lasers, mostly for tumor surgery.

Properties of electrolyte-filled glass microelectrodes: an experimental study

The electrochemical and electrical properties of geometrically defined electrolyte-filled microelectrodes were studied at various transelectrode current passages, using radiotracer ( 38Cl and 42K) and electrical techniques. Geometrically, the electrodes were defined by their tip properties that, for standard (single-barrelled, 3.0 M KCl-filled, ≈10 MΩ) electrodes implied a tip opening radius of 0.135 μm and a tip taper of 0.0215 μm/ μm in the most distal (0–150 μm), and of 0.0105 μm/ μm in the next most distal (150–1000 μm) tip regions. From the radiotracer studies it followed that (a) in the absence of transelectrode current passage, K + and Cl − are leaking from the electrode tip in amounts corresponding to currents of ±3.8 nA, and (b) in the presence of transelectrode current passage, the flow of K + and Cl − through the electrode tip changes with the transelectrode current in a statistically linear fashion so that K + carries about 80% and Cl − about 20% of any electrode-injected current. From the electrical measurements it appeared that the standard electrodes are characterized by (a) a tip potential of −2.6 mV, and (b) a resistance that changes from an instantaneous, non-rectifying type to a steady state, outwardly rectifying type, within tenths of a second of constant current flow. The outward current rectification was seen to be reduced by raising [KCl] in the immersing solution, or by lowering it in the filling solution. Together, the observed electrode properties are consistent with the electrode electrolyte's solute and solvent turnover being governed by electro-osmotic as well as by electrodiffusion laws.

Characteristics of electrically evoked somatodendritic dopamine release in substantia nigra and ventral tegmental area in vitro.

Somatodendritic dopamine (DA) release from neurons of the midbrain represents a nonclassical form of neuronal signaling. We assessed characteristics of DA release during electrical stimulation of the substantia nigra pars compacta (SNc) in guinea pig midbrain slices. With the use of parameters optimized for this region, we compared stimulus-induced increases in extracellular DA concentration ([DA]o) in medial and lateral SNc, ventral tegmental area (VTA), and dorsal striatum in vitro. DA release was monitored directly with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Detection of DA in SNc was confirmed by electrochemical, pharmacological, and anatomic criteria. Voltammograms of the released substance had the same peak potentials as those of DA obtained during in vitro calibration, but different from those of the indoleamine 5-hydroxytryptamine. Similar voltammograms were also obtained in the DA-rich striatum during local electrical stimulation. Contribution from the DA metabolite 3,4-dihydroxyphenylacetic acid to somatodendritic release was negligible, as indicated by the lack of effect of the monoamine oxidase inhibitor pargyline (20 microM) on the signal. Lastly, DA voltammograms could only be elicited in regions that were subsequently determined to be positive for tyrosine hydroxylase immunoreactivity (TH-ir). The frequency dependence of stimulated DA release in SNc was determined over a range of 1-50 Hz, with a constant duration of 10 s. Release was frequency dependent up to 10 Hz, with no further increase at higher frequencies. Stimulation at 10 Hz was used in all subsequent experiments. With this paradigm, DA release in SNc was tetrodotoxin insensitive, but strongly Ca2+ dependent. Stimulated [DA]o in the midbrain was also site specific. At the midcaudal level examined, DA efflux was significantly greater in VTA (1.04 +/- 0.05 microM, mean +/- SE) than in medial SNc (0.52 +/- 0.05 microM), which in turn was higher than in lateral SNc (0.35 +/- 0.03 microM). This pattern followed the apparent density of TH-ir, which was also VTA > medial SNc > lateral SNc. This report has introduced a new paradigm for the study of somatodendritic DA release. Voltammetric recording with electrodes of 2-4 microns tip diameter permitted highly localized, direct detection of endogenous DA. The Ca2+ dependence of stimulated release indicated that the process was physiologically relevant. Moreover, the findings that somatodendritic release was frequency dependent across a range characteristic of DA cell firing rates and that stimulated [DA]o varied markedly among DA cell body regions have important implications for how dendritically released DA may function in the physiology and pathophysiology of substantia nigra and VTA.

Detection of glutamate released by neurons with an enzyme-based microelectrode: applications and limitations

Pharmacological evidence suggests that the neurotransmitter released by vertebrate photoreceptors is L-glutamate. To confirm and study this release, we developed a glutamate-sensitive microelectrode (10–30 μm tip diameter) consisting of a glass-encased Pt-wire whose exposed extremity was coated with a polypyrrole layer containing glutamate oxidase. Glutamate was detected amperometrically as hydrogen peroxide produced from oxidized L-glutamate (Pt-wire polarized at 500 mV against Ag AgCl ). Exposure to 100 μM L-glutamate caused an increase in microelectrode current of about 50 pA; glutamate concentration changes down to about 1 μM were detectable. Electrode sensitivity was 100-fold greater for L-glutamate than for other major amino-acids. However, oxidizable compounds ( eg catecholamines) crossing the polypyrrole layer were also detected. We used this microelectrode to measure activity-dependent glutamate release from single presynaptic terminals of solitary photoreceptors from salamander retina; various strategies were followed, but we failed to detect any release of glutamate. In contrast, on a slice of insect retina where non-vesicular release of glutamate occurs, we measured a glutamate concentration of about 10 μM close to the surface of the retina. Possible reasons for our failure to detect glutamate released from vertebrate photoreceptors are discussed.

SLCP—The scanning diffusion limited current probe: A new method for spatially resolved analysis

A new analytical method of measuring absolute concentration profiles inside microstructures called SLCP is presented. The combination of chronoamperometry at microelectrodes of 15–20 μm with scanning and positioning techniques (precision in x, y, z: 1 μm) sets up this SXM/SXP † † Scanning X-Microscopy and Scanning X-Probe, where X denotes the measuring principle. -type method. The SLCP method is capable of ion selective and localized absolute concentration measurement. It is applicable to microstructures with high aspect ratios. The measured parameter is the diffusion limited current I lim which is directly proportional to concentration. It is recorded at a substance specific potential. The principle works with all metal ions and electroactive substances that can be deposited or consumed almost quantitatively and under diffusional control. By using potential/time programs with two deposition potentials, the simultaneous concentration measurement of two ion species is possible. The multiple pulse sequence is successfully applied to alloy deposition. Three experimental modes have been developed; in addition to local concentration measurement, local cyclic voltammograms can be measured as well. Local resolution is 10–20 μm. Very thin microdisk analysis electrodes of 15–20 μm tip diameter have been developed.