Click on the desired tip profile below to view electrode selections and pricing.  A - Standard tip profile  H - Heat treated tapered tip profile  F - Extra fine tip profile  B - Blunted tip profile Selecting or customizing the optimum electrode configuration for your application What metal type is best for my application? What length do I need? What electrode configuration do I need? What is the insulation thickness? What impedence of exposure do I need? What tip profile is best for my application? What shaft diameter is best for my application? What type of connectors are used with MPI's electrodes? What are the tip exposures for different electrode impedance values? What metal type is best for my application? WE-Tungsten is the most versatile and widely used probe material because of it's stiffness, biocompatability and cost. It is ideal for demanding recording situations and most stimulation protocols. Tungsten comes in a variety of lengths and widths including the very popular 5" electrode which is used when recording from deeper structures in the brain. It is also used extensively for "Deep Brain" studies in Parkinson disease and other studies requiring an electrode configuration longer than 8". PI-Platinum/Iridium is extremely inert and is much more resistant to corrosion than either tungsten or stainless steel when used in extensive stimulation protocols. Platinum/Iridium also has a lower concomitant tip impedance than tungsten or stainless steel and therefore has a lower tip impedance for the same amount of metal exposure. This normally equates to a higher signal to noise ratio when recording. Because it is extremely biocompatible it is an excellent selection for chronic implants. SS-Stainless Steel (Elgiloy) is widely used in doing "Vibrating Probe Studies" because of its stiffness and it can be easily electrochemically coated with other metals used in these type of studies. Our stainless steel is very unique in that it is an alloy, Elgiloy, which is used for dental implants, so it is also very corrosion resistant and biocompatible. It has also been used extensively for Prussian blue staining by passing very low dc anodal current through it for histological marking. IR-Pure Iridium is the newest addition to our line of microelectrodes. Iridium has recently found its way into many journal articles especially for chronic implants and devices being tested for potential neural prosthesis. Iridium has by far the lowest concomitant tip impedance of any of the noble metals. It is extremely inert and very resistant to corrosion. Electrochemical cyclic voltometry can be used to "activate" the surface of electrodes to increase charge storage capabilities up to an order of magnitude over bright iridium making it an excellent stimulating electrode. A similar decrease in impedance is also effected by the activation techniques. Return to List What length do I need? The overall length of any electrode system is determined primarily on the depth of the tissue one wishes to record or stimulate and the micro-drive system being employed. Tungsten microprobes come in 3 or 5 inch lengths or can be custom ordered in any length less than 5 inches. Special mounting schemes are possible employing stainless steel and polymide tubing for longer lengths. Platinum/Iridium typically comes in two inch lengths and stainless steel in 3 inch lengths but either can also be specified in shorter lengths or in longer lengths using stainless steel and polymide tubing. Because of the high expense of pure iridium it is always mounted in stainless steel and polymide tubing and is typically 3 inches long. Return to List What Electrode configuration do I need? We presently offer three different electrode configurations at this time, although we have fabricated many custom designs for customers in the past. As you observe what our part numbers look like for our probes, as seen under our Product section, you will notice they have a part number like WE30031.0A5. The 00 portion of the part number specifies the microprobe configuration. 00 implies no special mounting with the sharpened probe being insulated with Parylene-C, having the length, width, tip profile and impedance as specified in the tables for ordering your electrodes. PT are electrodes which have been mounted into polymide tubing in order to increase the stiffness and provide additional insulation thickness. This mounting is typically recommended when fairly high impedance electrodes must penetrate deeper layers of the brain or spinal cord specifies our bipolar or stereotrodes. These electrodes when ordered with impedances less than 0.5 megohms are excellent for localizing stimulation current fields. Higher impedance stereotrodes are excellent for enhancing the isolation of single neural elements by simultaneous recording of multiple units on two closely spaced microelectrodes. The tip spacing is typically equal to the shaft diameter of one of the electrodes used in making the stereotrode. Different tip spacing is available upon request. Return to List What is the insulation thickness? All except the 3 inch Extra Fine-F profile tungsten microprobe, which has a 1 micron coat of Parylene-C insulation, have 3 microns of Parylene-C. It has been proven that this thickness works best for most all electrode tip profiles we offer. We selected 3 microns to provide a sufficiently small tip profile for getting close to neural elements, ease of electrode insertion and to minimize attenuation for higher impedance electrodes. Attenuation of the signal can occur as a result of capacitive shunting when recording with higher impedance microprobes in deep structures, so additional insulation maybe required in the form of our PT, polymide microprobes. The F-Extra Fine profile for the 3 inch tungsten electrodes provides an extremely fine microprobe tip which is excellent when recording from small densely packed cell structures. Return to List What tip impedance or exposure do I need? Because of our unique fabrication process and the special properties of Parylene-C we are able to expose any microprobe with microscopic precision and reproducibility. Each microprobe is individually exposed under a high power microscope, inspected and electrically characterized. Our microprobes have a lower impedance value for the same tip exposure as other commercially available electrodes. It is therefore recommended that those who have not used our electrodes before specify a range of impedance in order to select the best impedance value for their application. Also since we have been providing microprobes to researchers for over 20 years we can provide expert advice in selecting the best electrode design for your experimental paradiagm. Please email us on the Feedback page and provide information regarding your experimental protocol. There is no additional charge for specifying a range of impedance values for any box of microprobes. Return to List What tip profile is best for my application? The tip profile is another subtle specification which will determine the ultimate success of your recording or stimulation paradigm. It is however, a microprobe parameter for which there is some debate. Many first time users will want to experiment with different tip profiles in order to see which one works best for their recording or stimulation protocols. A-General Use microprobes are the most widely used tip profile. It works best for most recording situations and is recommended for stimulation. The insulation at the tip of the microprobe is abruptly sheared using a proprietary high voltage arcing technique, leaving a clean exposed metal surface. H-Heat treated tapered configuration should be used mainly by those investigators who must penetrate their microprobes through tough membranes such as the dura mater of larger mammals. By applying a small local heat source near the electrode tip under a microscope we are able to provide a microprobe that has a more gradual tip profile than the "A" type. The heat treatment also will have the effect of toughening the insulation near the tip making it less likely to push back when penetrating tougher membranes. This profile is not recommended for chronic studies because the heated portion of the Parylene-C at the tip maybe unstable in the biological environment and degrade after several days or weeks of implantation causing the impedance to drop. F-Extra fine tip profile is available in 3 inch (76mm) in both the 0.003" and 0.005" (75 and 125 micron) diameter tungsten microprobes. The WE3001X.XF series is intended for generally shallow penetrations where one requires extremely good isolation. For penetrations greater than 3 millimeters in which the tip impedance is greater than 1.5 megohms the addition of polymide tubing (WE3PT1X.XF) series is recommended to reduce capacitive shunting. B-Blunted is a recent addition to our inventory as a result in feedback from many of our users. By making the tip bullet shaped the electrode's exposed length is less than it would be if it was sharp for the same impedance. Isolation can therefore be improved in some situations since the exposed tip looks more like a point source. Many investigators feel that this provides greater selectivity than the conventional sharper tip profiles and that they hold up better for heavy stimulation protocols. Some investigators have also reported that they feel there is less puncturing of cells with the blunted tips. Return to List What Shaft diameter is best for my application? We offer three different microprobe diameters, 0.003" (75 microns), 0.005" (175 microns) and 0.01" (250 microns). Whereas our tungsten electrodes are offered in all three diameters, the Platinum/Iridium electrodes are offered in 0.01" (250 microns) and 0.003" (75 microns)diameters. The 0.01" diameter Pt/Ir electrodes are excellent for most recording and stimulation protocols. The finer 0.003" diameter Pt/Ir electrodes have a 70/30% Platinum to iridium ratio for greater stiffness and have been used now for many of the same applications as well as for chronic implant studies. Stainless Steel (Elgiloy) is actually 0.009" dia. and the Pure Iridium microprobes use 0.003" dia. iridium rod. The 0.003" diameter tungsten and Platinum/Iridium microprobes are new and were developed in response from researchers who wanted microprobes which produced minimal tissue damage, especially when used for chronic implantation protocols. The 0.005" inch microprobe is the most common size for tungsten users although many users require the heavier 0.01" dia. microprobe for penetrating tougher tissue and are viewed as being slightly less fragile.  Return to List What type of connectors are used with MPI's electrodes?The M201 pin connectors are attached to the distal end of our electrodes. You can purchase these connectors as well as the mating connector, M202, by clicking here and going to our Accessory Page. Many users prefer to use our electrodes without any connector, which is fine. We will simply remove the connectors for you if requested. There is no discount for this since the connectors are attached at the beginning our fabrication process. Gold-plated pins (#M201) and sockets (#M202) may be attached to 24-, 26-, or 28-gauge wire. Return to List What are the tip exposures for different electrode impedance values? Return to List