On microelectrode distortion of tissue oxygen tensions

This article demonstrates that the gentlest insertion of an oxygen measuring electrode into living tissue may distort the normal distribution of oxygen in the tissue, and thereby cause the electrode to determine erroneous oxygen tensions. A model tissue is studied. An electrode inserted into this tissue is found to distort tissue oxygen tensions, and to measure incorrect values. The effect can be minimized by using the smallest electrodes.     

Iridium oxide pH microelectrode

The manufacture, calibration, and signal conditioning during construction of an iridium/iridium oxide pH microsensor is described. The microsensor was designed to be used extracellularly, primarily in biofilm research. The sensing tip diameters were typically in the range of 3-15 mum. The iridium oxide was formed by potential cycling in dilute sulfuric acid. A pH profule across a denitrifying biofilm was measured as an example of an application. The higher Nernstian slope (70-80 mV/pH for fresh electrodes), increased rigidity, and restriction of the sensing tip to the outermost end of the electrode are features which make the iridium/iridium oxide pH microelectrode superior to a glass microelectrode. (c) 1992 John Wiley & Sons, Inc.     

Ion-exchange thin-layer chromatography and paper ionophoresis of dinucleoside monophosphates

The thin-layer chromatography of dinucleoside monophosphates on plates coated with DEAE-cellulose powder and on plates coated with cellulose impregnated with polyethyleneimine, together with their ionophoretic mobilities on DEAE-cellulose paper, is described. It is shown that the 2′→5′ dinucleoside monophosphates can be separated from the corresponding 3′→5′ isomers by ion-exchange thin-layer chromatography and paper ionophoresis. The method is very sensitive and can replace the commonly used enzymic hydrolysis for analyzing the nature of the phosphodiester linkage of a given dinucleoside monophosphate.     

An improved pCO2 microelectrode

By utilizing the recently developed glass-membrane pH microelectrode an improved pCO₂ microelectrode has been manufactured. The new pCO₂ microelectrode described here has been made with tip diameters ranging from 2 to 200 μm. In addition, the sensitivity (slope) was nearly theoretical, 56 to 60 mV/log pCO₂, the response time was 1–3 min, and the intercept stability (drift) was less than 3 mV/20-min time interval. Finally, the lifetime of this electrode was several days to a week when stored correctly. The most unique quality of this pCO₂ microelectrode was that the eperatienal characteristics, tip diameter, sensitivity, and response time, could be controlled by adhering to predetermined design considerations.     

Illuminated microelectrode for tissue culture

Conventional glass microelectrodes acting as light guides have been used to facilitate the accurate approach and penetration of selected cells maintained in vitro. The device is a simple, inexpensive modification of conventional microelectrode holders and facilitates electrophysiological and microinjection studies of cells in vitro.     

A carbon dioxide air-gap microelectrode based on a neutral hydrogen ion exchanger pH microelectrode

A relatively simple potentiometric pCO2 gas-sensing microelectrode is described. It is based on an ion-exchanger pH electrode, has a 2- to 5-microns tip, and has an air gap which is formed by means of hydrophobic treatments. The microelectrode exhibits a linear response in the range 10(-4)-10(-2) M with a Nernstian slope of 59 to 62 mV/decade at 25 degrees C. Ninety-five percent of the steady-state response time is about 20-30 s at the flow system when the concentration of sodium bicarbonate in buffer solution (pH 4.5) suddenly shifts from 0.2 to 2 mM and the lifetime is longer than 1 week.     

An ammonia-sensing air gap microelectrode

An ammonia-sensing air gap microelectrode has been designed on the basis of a neutral carrier pH-sensing inner electrode. This electrode has a tip diameter of 2 to 5 microns, has a simple design, is easy to fabricate, and has a long shelf life. Its response to ammonium is linear in the range 3 x 10(-5) to 10(-2) M and its response time (95%) is 10 to 15 s. The electrode was converted to a microsensor for urea by immobilization of urease within its tip. The linear response to urea ranged from 3 x 10(-4) to 10(-2) M and the response time was 15 to 20 s.     

A glass-membrane pH microelectrode.

By miniaturizing the original MacInnes and Dole glass-membrane pH electrode a new pH microelectrode has been developed. The technique developed utilizes the tip of a high electrical resistance glass pipet that can be sealed with a thin membrane of H⁺-sensitive glass. Single-barreled electrodes have been made with tip diameters ranging from 1.5 to 100 μm and double-barreled electrodes with tip diameters from 2 to 28 μm. The glass-membrane pH microelectrode provided a means for sensing the pH of biological solutions with an electrode having theoretical slope and tip configurational control. The most unique characteristics of the electrode were: the pH sensing surface was quite small, the tip diameter could be controlled, and the problem of electrode insulation was eliminated.     

A submicrometer glass-membrane pH microelectrode.

The glass-membrane pH microelectrode (GMpHME) described previously (Anal. Biochem.73, 501, 1976) had a limitation in the minimum size (tip diameter) that could be manufactured (about 1 μm). In addition, when made at this small size the electrical resistance was usually high (10¹¹ Ω) and the response time long (greater than 5 min). The inability to manufacture the GMpHME with tip diameters less than 1 μm was primarily due to the thickness of the pH glass used to form the H⁺-sensitive membrane. In this report we detail a method for thinning the pH glass in such a way that the manufacture of submicrometer glass-membrane pH microelectrodes is possible. These submicrometer pH electrodes have rapid response times (1 to 3 min) and maintain the desirable characteristics of all GMpHMEs, that is, near theoretic slope and a well-defined sensing surface area.     

Voltage clamping with a single microelectrode

A technique is described which allows neurons to be voltage clamped with a single microelectrode, and the advantages of this circuit with respect to conventional bridge techniques are discussed. In this circuit, the single micro electrode is rapidly switched from a current passing to a recording mode. The circuitry consists of: (1) an electronic switch; (2) a high impedance, ultralow input capacity amplifier; (3) a sample-and-hold module; (4) conventional voltage clamping circuitry. The closed electronic switch allows current to flow through the electrode. The switch then opens, and the electrode is in a recording mode. The low input capacity of the preamplifier allows the artifact from the current pulse to rapidly abate, after which time the circuit samples the membrane potential. This cycle is repeated at rates up to 10 kHz. The voltage clamping amplifier senses the output of the sample-and-hold module and adjusts the current pulse amplitude to maintain the desired membrane potential. The system was evaluated in Aplysia neurons by inserting two microelectrodes into a cell. One electrode was used to clamp the cell and the other to independently monitor membrane potential at a remote location in the soma.     

Graphene microelectrode arrays for neural activity detection

We demonstrate a method to fabricate graphene microelectrode arrays (MEAs) using a simple and inexpensive method to solve the problem of opaque electrode positions in traditional MEAs, while keeping good biocompatibility. To study the interface differences between graphene–electrolyte and gold–electrolyte, graphene and gold electrodes with a large area were fabricated. According to the simulation results of electrochemical impedances, the gold–electrolyte interface can be described as a classical double-layer structure, while the graphene–electrolyte interface can be explained by a modified double-layer theory. Furthermore, using graphene MEAs, we detected the neural activities of neurons dissociated from Wistar rats (embryonic day 18). The signal-to-noise ratio of the detected signal was 10.31 ± 1.2, which is comparable to those of MEAs made with other materials. The long-term stability of the MEAs is demonstrated by comparing differences in Bode diagrams taken before and after cell culturing.     

Measurement of purine release with microelectrode biosensors

Purinergic signalling departs from traditional paradigms of neurotransmission in the variety of release mechanisms and routes of production of extracellular ATP and adenosine. Direct real-time measurements of these purinergic agents have been of great value in understanding the functional roles of this signalling system in a number of diverse contexts. Here, we review the methods for measuring purine release, introduce the concept of microelectrode biosensors for ATP and adenosine and explain how these have been used to provide new mechanistic insight in respiratory chemoreception, synaptic physiology, eye development and purine salvage. We finish by considering the association of purine release with pathological conditions and examine the possibilities that biosensors for purines may one day be a standard part of the clinical diagnostic tool chest.