Metal microelectrodes wires

Scanning electrochemical microscopy seeks to overcome the lack of sensitivity and selectivity of the probe tip in STM and AFM to the substrate identity and chemical composition. It does this by using both tip and substrate as independent working electrodes in an electrochemical cell, which therefore also includes auxiliary and reference electrodes. The tip is a metal microelectrode with only the tip active (usually a metal wire in a glass sheath). At large distances from the substrate, in an electrolyte solution containing an electroactive species the mass-transport-limited current is therefore... 

In terms of the mechanics of assembly, metal microelectrodes are the simplest to produce. They are simply metal wires or needles which have very small tips. All of the electrode, save the tip, is insulated with a suitable material as shown in Figure 4.2. The only mechanical problem associated... 

For more than 300 platinum microelectrodes produced, the average metallic wire radius is 30 + 3 pm (i.e. an accuracy of 10%). This value is coherent with the wire radius commercially indicated and shows the good repeatability of microelectrodes fabrication. In addition, more than 100 reproducible cyclic voltammograms can be recorded successively in the ferricyanide solution without modification of the curve shape. 

Two further techniques to realize microelectrodes should be mentioned. Thin metal wires have been embedded into relatively soft ionic crystals such as AgCl and... 

Stabilization of BLMs at the surface of electrodes has been reported by a number of groups [28-30]. For example, the tip of a Teflon-coated platinum microelectrode was cut in situ with a scalpel while immersed in a lipid solution (lipid in a hydrocarbon solvent). Upon immersion of the wire into an aqueous solution of 0.1 M KCl, the phospholipid coating adhering to the metal surface spontaneously thinned to form a BLM directly adjacent to the electrode surface... 

Microelectrodes, also called ultra-microelectrodes, have some very special diffusion properties. The electrode can be prepared by melting an ultra-thin metal wire into a glass rod. The small radius of the wire with only a few micrometers leads to a situation in which the radial resistance of the electrolyte in front of the electrode snbstitntes the diffusion limitation by the diffusion layer. A microelectrode and the current distribution in front of the microelectrode are shown in Figure 5.14. 

There are several commercially available materials for building microelectrodes suitable for in vivo measurements [3, 4]. Electrode construction is generally based on microscopic wires of noble metals or carbon fibers, and there are various types of microelectrodes such as... 

One method for producing a well-insulated microelectrode is to start with a glass capillary tube and bond it to an internal metallic wire. Several techniques exist. A low-melting-point metal can be used to fill the tube, or a wire of the same diameter as the internal diameter of the tube can be passed through the glass capillary, which is then heated to produce bonding. One must be careful to select glasses and metals which have nearly the same temperature coefficients of expansion. Three basic techniques exist as described below. 

The electrical connection from a glass microelectrode to its accompanying electronics is made by a metal wire inserted in the stem end of the lumen and in contact with the filling electrolyte. Early literature frequently refers to tungsten wire for this purpose, but there seems to be no valid basis for using this metal. Apparently it was available and had been used in place of antimony in certain pH electrodes. Because of its metallurgical properties, tungsten is difficult to form, and it has undesirable electrical characteristics. 

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