Frequently Asked Questions

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 76 mm or 125 mm (don’t see 125 um on WPI website) lengths or can be custom ordered in any length less than 5 inches. Platinum/Iridium typically comes in two inch lengths and stainless steel in 51 mm lengths but either can also be specified in shorter lengths or in longer lengths using stainless steel and polyimide tubing. Because of the high expense of pure iridium it is always mounted in stainless steel and polyimide tubing and is typically 50 mm long.
What is the insulation thickness?
All electrodes except the 3 inch Extra Fine-F profile tungsten microprobe, that have 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 WPI’s KT, polyimide microprobes. The Extra Fine profile (ex. TM31C10) for the 3 inch tungsten electrodes provides an extremely fine microprobe tip which is excellent when recording from small densely packed cell structures.
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 30 years, we can provide expert advice in selecting the best electrode design for your experimental paradigm. Please contact us and provide information regarding your researcher’s requirements. There is no additional charge for specifying a range of impedance values for any box of microprobes
What tip profile is best for my application?
We offer a variety of different tip alternatives for those that prefer a specialized electrode profile for their research. The tip selection can provide subtle yet important changes to the performance of the electrode, as described below. It is recommended that first time users consider experimenting with different tip profiles to determine which works best for their recording or stimulation protocols. A-Standard Our standard tip profile features a sharp yet robust point that offers versatile performance and an effective balance between penetration and durability. The most widely used tip profile, we recommend our standard tip for most neural recording applications, though it is also effective for most stimulation protocols. We employ an arc exposure method that provides precise and consistent performance as well as a very wide range of available impedances. While this method results in a small variability in impedance from electrode to electrode, most researchers find it very acceptable for their application. For those that need a more exact tip exposure, we offer a laser exposure service for a small premium. Please contact us if you feel this service is right for you. B-Blunted Our blunted electrodes are engineered to have a more rounded, bullet-shaped tip. For many applications the blunted tip can offer superior stimulation performance, as its shorter profile can lead to the electrode acting more as a point source and providing improved isolation. Many investigators feel that this profile both provides greater selectivity than the conventional sharper tip profiles and is more appropriate for higher-intensity stimulation protocols. Some investigators have also reported observations that the use of blunted tips leads to fewer occurrences of punctured cells. F-Extra fine Our extra-fine tip profile features a significantly sharper taper as well as a thinner insulation layer. This type of electrode is commonly used for shallow preparations where it is necessary to record from small tightly-packed cell populations, such as the striate layers of the visual and auditory cortices. Due to the very delicate nature of these tips, they are only available in tungsten electrodes, in 3-inch (76mm) length and both 0.003" and 0.005" (75 and 125 micron) shaft diameter. For penetrations greater than 4 mm in which the tip impedance is greater than 1.5 MΩ, we recommend that an additional layer of polyimide tubing be specified to reduce capacitive shunting and to increase the stiffness of the electrode. H-Heat Treated Our heat-treated electrodes are intended for those investigators who must penetrate their probes through tough membranes, such as the dura mater of larger mammals. By applying a heat source near the electrode tip under a microscope, we have the ability to provide an electrode with a more gradual tapering tip than our standard profile, while also toughening the polymer insulation near the tip. These modifications allow the electrode to be pushed through tough membranes easier and with less risk of tip and insulation damage.
Problems reading the impedance of your metal microelectrodes?
1. Check your impedance tester, maybe you are testing the impedance values at a different frequency than the 1 Kilohertz. 2. Check if your impedance tester doesn’t have a sample and hold circuit in which case the impedance is measured immediately upon pressing the test button and the impedance does not have a chance to stabilize. 3. Usually the impedance will drop after a few minutes of the electrode being in the saline solution. 4. Sometimes the electrodes can oxidize increasing the impedance in which case we recommend passing about negative 3 to 4.5 volts across the electrode in saline to clean and de-oxidize the electrode.
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. Monopolar Electrodes - 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. Polyimide Tubing - PT Electrodes which have been mounted into polyimide 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. ST Specifies our bipolar or stereotrodes. These electrodes when ordered with impedances less than 0.5 meohms 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.
What type of connectors are used with our electrodes?
The 5482, 5483 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.
What are the tip exposures for different electrode impedance values?
Tip exposures for Heat Tapered "H" tip profiles have approximately 15 to 20 percent MORE exposure. Tip exposures for Blunted "B" tip profiles have approximately 15 to 20 percent LESS exposure. Tip exposures for Extra Fine "F" tip profiles have approximately 10 to 15 percent MORE exposure.
Problems reading the impedance of your metal microelectrodes?
1. Check your impedance tester, maybe you are testing the impedance values at a different frequency than the 1 Kilohertz. 2. Check if your impedance tester doesn’t have a sample and hold circuit in which case the impedance is measured immediately upon pressing the test button and the impedance does not have a chance to stabilize. 3. Usually the impedance will drop after a few minutes of the electrode being in the saline solution. 4. Sometimes the electrodes can oxidize increasing the impedance in which case we recommend passing about negative 3 to 4.5 volts across the electrode in saline to clean and de-oxidize the electrode.
Troubleshooting Unstable Resistance Readings from an ENDOHM
One of our frequently asked questions (FAQs) concerns TEER measurements with an EndOhm. If the resistance readings from your ENDOHM don't stabilize, you may need to do some troubleshooting. Test the EVOM2 : First, test your EVOM2 meter. The 1000Ω test resistor (WPI # 91750) can be used for this purpose. Insert the RJ-11 plug at the end of the test resistor into the Input port on the meter. Set the Function Switch to Ohms. Disconnect the EVOM2 from the charger and turn the Power on (I). The meter should display 1000Ω. If not, adjust the R ADJ screw with a small slot-head screwdriver until the meter shows a reading of 1000Ω. If the EVOM2 reads 1000 ± 2-3 ohms, and the reading remains stable, then the EVOM2 is working correctly. Test the ENDOHM : Next, test the ENDOHM. You can still test the ENDOHM qualitatively by exposing it to different KCl concentrations. The readings should always be a stable, lower TEER value at higher concentrations, and a higher but potentially less stable value at lower concentrations. In general, if the TEER reading is falling, it means that the current is finding an alternative path of lower resistance than through the media alone, or the preparation is somehow adopting a charge. If the problem is truly in the ENDOHM, it will typically be caused by a leak of culture media beneath the electrode surfaces, where it can attack wire bonds to the Ag/AgCl disks. A delayed reaction may take time for the media to creep into very fine fissures where the glue bond has lost seal integrity. If the TEER reading continually drifts downward well below the expected value, then the ENDOHM most likely has a leak at the electrode bond or corrosion somewhere in the current or voltage pathways. If the ENDOHM has developed fine fissures, it needs to be replaced.
Will the EVOM3 work with Endohm’s?
Yes, but the 99672 adaptor is required or the new EVOM3 cable 99916.
Why would I want to use the blank function?
The blank feature is used when you want to subtract out any measurement that is not from the membrane, such as the electrode and fluid resistances.
Does the EVOM3 system automatically calculate TEER?
No, TEER measurement requires an area calculation. To compute TEER, divide the measured resistance by the appropriate surface area (below). For example, a 12 mm insert measures 565 Ω, the TEER is 565 Ω/1.13 or 500 Ω. 6 well plate (24 mm inserts) 4.53 cm2, 12 well plate (12 mm inserts) 1.13 cm2, 24 well plate 6.5 mm inserts) 0.3316 cm2, 96 well plate (4.3 mm inserts) 0.143 cm2.
EVOM3 data is stored automatically when the last well is reached. How do I store the data when I only want to measure 8 of 96 wells?
Clear any data in memory by opening settings, store menu then press new plate, that will clear any prior readings. Return to the main screen, open the preview screen, select each well to measure (the selection turns green), place the electrode, then measure. When you’re done measuring the selected wells, open the settings, press the store screen menu, then press store new to save the plate data to the USB drive.
I forgot my password for login.
Click on the "My Account" link that is located in the top right corner of this webpage. Enter your user name and click on the Forgot Password link.
I purchased a product and need to speak to someone in Technical Support about its use.
Inside the USA, our Technical Support Department is available from 8am - 6pm EST. You can call our toll-free phone number 866-606-1974 to speak with someone. If you are outside the USA, please contact your distributor. Alternatively, you can submit an online ticket by going to (Support>Technical Support). We will respond in a timely manner, because your satisfaction is our goal.
How do I place an order?
Orders can be placed online by adding your products to the shopping cart. If you would like to talk with a knowledgeable representative, you can locate your distributor's information by clicking here. To speak with someone from North America, contact our main office: World Precision Instruments 175 Sarasota Center Boulevard Sarasota, FL 34240-9258 wpi@wpiinc.com Tel: 941-371-1003 Toll-free (US only): 866-606-1974 Our Customer Service Representatives are available 8am - 6pm EST. Payment Methods For payment, we accept Visa, MasterCard, American Express credit cards, and Purchase Orders with approved credit. International Orders WPI has offices and distributors worldwide. Orders from countries covered by our international network should be directed to the appropriate office or distributor. View our Distributors page for information. If your country is not listed in our office and distributor network list, please contact our U.S. office to place an order. Terms & Conditions Track your Order
I need to return or exchange a product, what do I do?
All returns must go through our RMA (Return Merchandise Authorization) process. Please go to the Returns and Exchanges page, fill out the form and the RMA administrator will contact you with complete instructions.
Are electrical resistance and transepithelial electrical resistance (TEER) the same thing?
No. We obtain the TEER value by multiplying the raw/obtained resistance value on an epithelial voltmeter (such as, EVOM2) by the cell growth area (e.g., area of a cellular monolayer grown onto a cell culture insert). For example, if you grow cells onto a cell culture insert with area of 0.5 cm^2. The resistance readout on an epithelial voltmeter (e.g., EVOM2) shows a value of 300 Ω. TEER= 300 Ω × 0.5 cm^2 = 150 Ω- cm^2
What is an EndOhm?
The EndOhm is a chamber designed for the EVOM2 where you place a removable well into it to make the resistance measurements. This chamber has electrodes in fixed positions and the electrode positioning and stillness has a major affects when measuring tissue resistance.
How is an EVOM2 used for Measuring Confluence?
The EVOM2 works on the principal that once you measure what we call the “blank” well, this first resistance measurement contains the summation of the electrode resistance, the electrode gap and the resistance due to the volume and the molarity of the liquid media. (Any electrode charge differences are negated by the EVOM2's measurement method of reversing the polarity and averaging the results.) The successive periodic measurements of the well are a plot of the growth of the membrane by a resistance measurement, and once this resistance graph has plateaued, we can say that the membrane has reached confluence. The EVOM2 system works just like a Voltage clamp amplifier and Ussing system, but without the special Ussing chamber. The EVOM2 system is not as accurate as an Ussing can be, but the purpose of the EVOM2 system is to to determine if a membrane is confluent, not perform detailed analysis. (Some membrane permeability analysis can be studied by the EVOM2 system, but as a percent of change rather than an absolute value of change.)
Why use an EndOhm instead of a STX?
The EVOM2 will detect pin holes and voids in the membrane above all else as the flow of electricity will seek the lower point of resistance. The STX2 general purpose electrodes can flex and change the spacing of the electrodes, and also the act of not holding them still in a well can add to a significant resistance error. On the other hand, the EndOhm electrodes are fixed in position. When properly cared for and pretreated in media, they give the most stable, repeatable and reliable resistance readings. The addition of the centered concentric electrodes also insure that the entire area of the membrane is exposed to the electrical current flow so there are no shadow areas due to an edge placement as there can be with the STX2. (It should be noted that the baseline expected TEER value of the tissue, if it is of a low resistance value, can add to measurement difficulties with large area membranes. For Example: If the TEER value is 200Ω-cm2 then a 12mm well will be 1.13 times less for the same confluent measurement (176.9Ω). The same 200Ω tissue in a 24mm diameter well is 4.52 times less or 44.2Ω. As this resistance number decreases below about 100Ω, we see more electrode instability and those readings can vary. We have found that electrode “cleaning” and preconditioning are essential for stable readings.)
How do I Clean my Electrode?
Electrode cleaning consists of the periodic use of an enzymatic cleaner (Enzol, Tergazyme) and – or a soak in unscented household bleach (3% NaClO). The bleach serves to recoat Ag surfaces to AgCl and dissolve accumulated proteins. Both of these effects lead to electrode instability. The enzymatic cleaner is a safe agent to remove residue from the electrodes deposited by media components like DMEM. If this is allowed to accumulate, the resistance reading goes up and also can be unstable.
What about Electrode Preconditioning?
Electrode preconditioning is presoaking the electrodes in the measurement media for a time to allow any foreign liquids to migrate out of the permeable pellets. Alcohol is commonly used to sterilize these electrodes and the alcohol will soak into them and act as a high resistance to electrical flow. As the alcohol slowly exchanges with saline based media inside the electrode, the resistance reading results are seen as a downward drifting value.
Can you give me a Simple Data Acquisition System for TEER?
The Lab-Trax-4 is a quiet, 12-bit, four channel, analog-to-digital data recorder that has sampling speeds up to 10,000 samples per second or 2500 s/S for all four channels. This unit is powered directly by the USB2 port and can be used on a laptop in the field as a portable unit. The hardware has four digital inputs and four digital outputs, if needed. The LabScribe3 software is easy to use and frequently updated to meet the most current demands. As Microsoft continues to update to newer operating systems, the hardware will continue to be supported by newer revsions of LabScribe. It is also now supported on Mac and Linux based computers. If you are using a STX2 to make these measurements, you may need an extra pair of hands to enter text for you. If you enter your text into the Marks field before making measurements, then you only need to press the Enter key to place the mark when your TEER reading has stabilized. If you are using an STX100, you will have your hands free to make notations.
What are the TEER measurement challenges that I may encounter?
This was written to address issues with the STX2, but it also applies to the EndOhm. Any of these items can change the resistance reading: • Electrode spacing gap. Do not spread or compress the electrode gap of the STX2 electrode. • Electrode resistance. Keep the electrodes clean and conditioned. • Electrode depth. Always submerge the electrodes at least 2 mm. • Electrodes near the plastic walls. Try to keep the electrodes away from plate walls, if possible. • Electrode placement. If you typically rest the longer leg of the electrode on the bottom plate, then repeat that placement for consistency. • Fluid resistance. Do not let the media evaporate and do not dilute it. • Fluid levels. Try to maintain the same volume of fluid for every reading. A small variation may have a large effect in a small insert. Excessive movement. Try to hold the electrodes still. In some cases, a mechanical electrode holder may be used. • Washing/media change may cause a rupture in the membrane of the cell culture insert. Fluid change should be done cautiously along the wall of the inserts. A small gap of lifted tissue/cellular layer from the membrane of the cell culture insert can open a clear path for the EVOM2 to read a lower resistance. The current leaks through this gap rather than going through the membrane containing the cellular monolayer, since electricity tends to take the path of least resistance. In such cases, you will notice a drastic drop in the resistance. When you notice such a large decrease in the resistance value, we recommend that you check your sample (e.g., cellular monolayer on a cell culture insert) under a microscope to see if there is a rupture in the filter or large empty region on the filter indicating that a cluster of cells has detached. Acquiring multiple readings in the same well (3-5 times) and calculating the average can be used to decrease the variability.
Can you suggest some experimental parameters that can be controlled to obtain consistent TEER results?
• Temperature is known affect TEER values. We recommend that you maintain a consistent temperature to obtain consistent values. Since the reading are obtained in cell culture media/ buffer. We recommend that you use a water bath with a fixed temperature to warm the media/buffer to be used during the experiment. A consistent media/buffer temperature ensures a consistent experimental condition. We recommend taking the well plate, containing cells grown on culture inserts, out of the incubator for at least 20 minutes to stabilize the well plate at room temperature before making measurements. • If you are using an EndOhm chamber, make sure you maintain the same fixed distance between the top and bottom electrodes to obtain consistent read outs. If you are using a chop-stick electrode (STX2), try to hold it in a vertical position while obtaining results. Consistency in maintaining the same holding position of the chop-stick electrodes while performing an experiment is expected to show consistent read outs. • We recommend using the same fluid with the same ionic concentration both in the apical (e.g., top of a cell culture insert) or basolateral side (e.g., lower part of the cell culture insert sitting inside a well of a 12 well-plate). During the measurement, if you are using 1X PBS buffer in the apical side, we recommend using 1X PBS buffer in the basolateral side. We also recommend that both fluid levels (inside and outside of cell culture inserts) be at the same height in order to minimize pressure differentials. During experiments, the apical well/side is filled first with fluid to prevent dislodging of the membrane from the filter by hydrostatic pressures. • Application of consistent volumes of the fluid (media/buffer) during all experiments will reduce data variability.
I want to measure TEER of alveolar epithelial cells which are cultured without media in the apical side. Do I need to add media/buffer in the apical side to measure the TEER of these monolayers?
Yes. In simple terms, electrodes (e.g., EndOhm/ STX2) maintain electrical connection via fluid (cell culture media/buffer). Not having any fluid on the top of the cell culture insert will disrupt the electrical connection. However, since these cells are cultured without media in the apical side, we recommend exposure to apical fluid for shortest time possible. It is safe to assume that around 5 minutes of exposure to apical media/buffer should not affect the cells. We suggest that you perform a pilot experiment to determine the duration of time that your cells can tolerate apical fluid. As mentioned previously, we recommend using the same fluid with same ionic concentration (for example, 1X PBS buffer or media) in both apical and basolateral sides.
How can I get a formal quote?
For a simple quote, you can place your items in the shopping cart and simply print the page before ordering. For a formal quote, locate your distributor by clicking here. If you are in the United States, you have options: • Contact us at quotes@wpiinc.com or by calling 866.606.1974 (US only), and we will help you find what you need. • If you know exactly what you want, place the products in your cart. Then, when you check out, select "Do Not Ship, Quote Only" for the Shipping Method and "Quote Request" for the Payment Type. These options are found on the second page after you enter your contact information. We will put together a formal quote and get it back to you as soon as possible.

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