A technique for the long-term application of surface electrodes

A technique is reported for the long-term application of surface electrodes for ambulatory electromyographic (EMG) recording. Prior to electrode application the surrounding skin is lightly painted with tincture of benzoin. This treatment improves adherence to the skin of disposable electrodes and electrode attachment collars, reduces skin trauma associated with electrode removal, and minimizes sensitivity to electrode adhesives.This research was supported in part by NIH grant No. NS25114.     

Rechargeable glucose electrodes for long-term implantation

A unique enzyme electrode was designed using glucose oxidase immobilized on fine graphite powder. The graphite-enzyme is in a fluid state which enables recharging of the system when the enzyme activity decreases, therefore allowing the system to have a long lifetime in a diabetic patient. The sensor was tested using glucose concentration in the range of 20–300 mg d⁻¹. The electrode construction includes a hydrophobic membrane and a platinum electrode for detection of hydrogen peroxide. The signal output is large with minimal noise when tested in buffer. The sensor has been performing at ambient temperature for 4 months when stored overnight at 4° C.     

A computer-assisted technique for long-term gastric pH monitoring

A computer-assisted technique for prolonged gastric pH monitoring has been developed using a personal computer. Segments of signal from several studies performed in controls and on patients with duodenal ulcers were chosen for comparison between manual and digital pH readings; no significant difference was detected. In clinical practice this system might provide an additional tool in the diagnostic and therapeutic treatment of peptic ulcer disease.     

A technique for long-term venous cannulation in rats

We require repeated blood samples from rats over long periods in our studies on obese hyperlipemic animals and normal controls. Under our conditions of lipid adnormality and exercise previously reported techniques did not give long-term cannula patency. We have thus developed a technique using thromboresistant heparin-treated Silastic tubing and a mesh-stabilized metal cannula at the base of the skull. The tubing is inserted into the vena cava without occlusion and the tip lying in the region of the termination of the hepatic veins. The tubing exists from the abdomen through the incision and runs subcutaneously to a metal tube protruding from the skin. It is closed with a short length of polyethylene tubing folded over and secured with a tight Teflon sleeve. Heparinized saline is used to fill the cannula and flush it at biweekly intervals. The cannulas remain patent for long periods with 59% permitting withdrawal of blood at 120 days. Loss of function is random after 30 days when 100% were patent. A significant number remain functional at 200 days.     

A technique for long-term collection of uterine contents from mares

A technique for collection of uterine contents from mares is described: it uses a purse-string suture of the cervix to retain a collecting device. Its use during collection of uterine fluids in various experiments is evaluated. The procedure was satisfactory for at least eight-hour collection periods.     

Evolution in impedance at the electrode-skin interface of two types of surface EMG electrodes during long-term recordings.

The evolution in impedance at the electrode-skin interface of Beckman and Red Dot electrodes was assessed during long-term recordings. Impedance was measured between each pair of electrodes, arranged in a bipolar configuration on tibialis anterior (n=13). A waveform constructed of sinusoids of known frequencies, evenly distributed on a log scale from 1-16,384 Hz, was applied through the electrodes, and the result recorded by a DAQ system. SEMG signals were recorded at 1000 Hz during isometric dorsiflexion contractions of 30 s, performed every 15 min for 2 h. Impedance data were acquired at 65,536 Hz immediately before and after SEMG recordings. Large individual differences in impedance levels were observed at low frequencies. At high frequencies, impedance values depended only on the electrode type. Impedance decreased steadily with time for Beckman electrodes (p < 0.05), but did not decrease significantly for Red Dot electrodes. The magnitude of the reduction over time varied widely between individuals, and was related to the initial impedance values. The impedance-bandwidth product remained constant for each electrode type (95% confidence intervals 146.2-148.2 and 126.1-127.8 for Beckman and Red Dot electrodes respectively). When skin impedance is electrically modelled with a simple network containing a resistor and a capacitor, the capacitance varies with the properties of the electrode used, whereas resistance is dependent on the subject. Furthermore, the EMG spectrum is unaffected by impedance provided skin preparation is sufficient to reduce the impedance below 55 komega.     

A new technique for the long-term study of the physiology of plant fruit tissue slices

Parkin, K. L. 1987. A new technique for the long-term study of the physiology of plant fruit tissue slices.
A modified tissue culture medium, devoid of plant growth hormones, was evaluated as a means to allow long-term study of the physiology of plant fruit tissue slices. Tomato ( Lycopersicon esculentum Mill, cvs New Yorker and Caruso) tissue slices, prepared from mature green fruits, were mounted in this medium and examined for their capability to undergo ripening. Over a 30 day period the changes in color, firmness and respiratory activity for the slices appeared to be temporally associated as is the case for the intact fruit. A less distinct respiratory climacteric was noted for the incubated discs compared to the intact fruit. This new technique might be applicable to long-term study of other plant tissues.     

Design and application of electrodes for the determination of dissolved oxygen

The design and circuitry of solid electrodes of the Clark type for the determination of oxygen dissolved in microbial cultures and the suitable techniques are described. For the electrodes a portable battery instrument with an amplifier and recorder was developed. The electrode materials tested were: Au, Pt, Ag (cathode) and Ag/Ag₂O and Ag/AgCl (anode). The effect of the presence of carbon dioxide on the course of the polarographic curves was determined. The temperature effect was determined for various membrane materials and its compensation with a thermistor was investigated. The effect of the circuit and design of the electrodes on stability, response time, reproducibility of measurement, durability of the electrodes and applicability in microbiology are discussed.     

Analytical application of self assembled monolayers on gold electrodes: critical importance of surface pretreatment

Polycrystalline bare gold electrodes have been used as substrate for the preparation of self assembled monolayers (SAMs) of alkanethiols. Chemical cleaning and several mechanical polishing procedures of the electrode have been carefully tested in order to prepare monolayers of octadecyl-, mercaptans. By analyzing the cyclic voltammetric curves of hexacyanoferrate III and chlorpromazine and the electrochemical desorption of the coated monolayer, it appeared that the response at the bare electrodes is related to the cleaning procedure and that the structure of SAM coated gold electrodes is influenced by the polishing material used, i.e. diamond or alumina slurry. Electrochemical results have been confirmed by Auger analysis of the electrode surface.     

A simple and economic technique for long-term continuous intravenous infusion in the unrestrained rat

A reliable, inexpensive and ethically acceptable method for long-term intravenous infusion in unrestrained rats is described. This system absorbs rotational forces produced by the animal turning without kinking of the tube.     

A technique for labelling the sample surface for quick-freeze,deep-etch,rotary replication electron microscopy: application to the study of geletin gel structure

A method using magnesium oxide crystals to label the surface of physical gels, such as gelatin gel before quick-freezing is described and discussed. The quick-freeze, deep-etch, rotary replication technique is most adapted to 3-D visualization of physical gel structure. However, it is known that the depth which ultrarapid freezing may reach is limited by the growth of ice crystals as the distance from the surface of the specimen (rapidly cooled by smashing against a cooled metal plate) increases. Consequently, intact preservation of structures occurs only in superficial zones of the specimen. The MgO surface labelling technique provides a simple means for surface recognition. It enables the estimation of a given replicated area depth, taking into account the angle of specimen scraping before etching and replicating. By comparison of views of the same replica at different depths, freezing artifacts may be recognized even when they cause only slight deformations in the structure. This is particularly necessary for interpretation of gel network geometry: interpretation can be made with certainty only if a reliable surface reference marker exists. For gelatin gels, the depth of best freezing can be estimated to be around 5 μm from the frozen sample surface.     

Enzyme electrodes and their application

Starting from the state of the art, principles for improving the analytical characteristics of enzyme electrodes are discussed. Coupling of appropriate amperometric electrode processes with enzyme systems, e.g. urease or aminopeptidases, results in a simplification of operation. Optimal sample frequencies are realized on the basis of enzyme membranes, with both a small characteristic diffusion time and a high enzyme activity, applied in a well-designed sample-processing system. Coupled enzyme reactions of the sequence or competition type are successfully used for extension to new analytes, e.g. inhibitors, cofactors or alternative substrates. Cyclization of the analyte enhances the sensitivity of enzyme electrodes to the nanomolar concentration range. Enzymic anti-interference layers are a tool for improving the sensor specificity. The operational characteristics of enzyme electrodes are thus adaptable to any given analytical problem.