Frequently Asked Questions

Does the CARDIOPHYS include an output cable?  
The CARDIOPHYS system does not include and output cable like the CBL102 (BNC- 3.5 mm MiniPhone plug) because the data acquisition system can vary according to what the customer may already have. If the customer already has a data acquisition system then we can offer a cable to connect the CARDIOPHYS to their system, if one is available. The output connection on the CARDIOPHYS is a 3.5 mm MiniPhone plug. If the customer does not have a data acquisition system then we offer along with the CARDIOPHYS a LAB-TRAX-4, 505195 (ECG Analysis Module), 2851, and CBL-102 cable. We only offer two cables with 3.5 mm MiniPhone plug: CBL100- 3.5 mm MiniPhone plug to 3.5 mm MiniPhone plug and CBL102- 3.5 mm MiniPhone plug to BNC (male).
How large of an area can the CleanRay-3000 disinfect?
The CleanRay can work in areas as large at 30' x 30' (900 sf), but the larger the space, the longer the unit needs to run for effective use. As a general rule, the unit should run for 15 minutes for every 10 feet. Applying the rule, a 30' x 30' room would require a 45 minute cycle.
Why am I getting dashes as reading on EVOM3, even if I have the STX2-PLUS electrode inside the sample?
The electrode in the air or partially immersed in the liquid can show dashes since it records unstable read outs. The electrode tip portion (sensing region) must stay fully immersed. You may also notice unstable read outs when the electrode tip is not fully immersed. Make sure to select apical and basolateral volumes so that electrode tip stays fully immersed. You need to use apical and basolateral volumes greater than what is suggested by the insert manufacturer. For example, for Corning-24 well Transwell (example Corning 3470) we recommend minimum 300 µL on the top (apical) and 850 µL on the bottom (basolateral). [These volumes are a little more than the least required for STX2-PLUS electrode.] Here are the steps: 1: STX2-PLUS Adjustment of Electrode Height. Rotate the front ring clockwise so that the electrode can enter to the maximum depth inside the well. 2: STX2-PLUS Electrode tip and liquid volume requirements. Make sure the electrode sensing tip (red boxed portions) on both blades stay fully immersed in a conductive liquid, such cell culture media or buffer during measurement. You need to have adequate apical and basolateral volumes to get a stable reading. Since STX2-PLUS stays hung, the increased volume must be used to make sure electrode sensing region fully immersed. NOTE: You must use more liquid volumes than recommended by the insert manufacturer. Insert manufacturer’s recommended volumes will not keep electrode tip fully immersed. [As mentioned as an example previously, for Corning-24 well Transwell (e.g., Corning 3470) we recommend using minimum 300 µL on top (apical) and 850 µL on bottom (basolateral). These volumes are a little more than the least required for STX2-PLUS electrode. You can check visually to make sure the apical and basolateral volumes are adequate to keep the electrode tips fully immersed, and then consistently use those volumes.] Even if the unstable reading or dashes issue is still seen, the electrode most probably need chloriding. The chloriding refers to keeping electrode tips immersed in 3-6% sodium hypochlorite or bleach for 10-15 minutes followed by rinsing with distilled water. It is a part of STX2-PLUS maintenance and a critical maintenance process. Please refer to maintenance instruction below (step 1). ** Below are the steps that can be followed for STX2-PLUS cleaning or maintenance. 1. Before using them, chloride the electrode by keeping the electrode tips immersed in 3-6% sodium hypochlorite (bleach) for 10-15 minutes. Chloriding needs to be done every 3 days when the electrodes are used frequently or after more than a week storage. ** 2. Rinse with sterile DI water/buffer. 3. Optional step: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 4. Use the electrode for measurements. 5. Optional step in between measuring samples: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 6. After measurements soak/immerse electrode tips in 70% isopropanol or ethanol for 5-10 minutes. 7. Rinse with DI water. Let it air dry. Store electrode dry and in a place away from light/minimal light. 8. When used frequently, every week soak electrode tips in 1% Tergazyme for 15 minutes. Follow by rinse with DI water. 9. Next, chloride by keeping the electrode tips immersed in 3-6% sodium hypochlorite (bleach) for 10-15 minutes. (Same as step #1.) 10. Rinse with sterile DI water/buffer. 11. Use for measurements. 12. Repeat from step 5.
Can increasing or changing sample liquid volumes change my resistance values?
You can expect to see a change of raw resistance values. However, you subtract the blank values (blank Transwell with no cells) from the sample values (Transwell with cells). This way, you subtract the blank value with increased volume from samples with increased volume. Thus, any change of resistance contributed by increased volume is omitted. Consistently use the same volumes for all your samples in an experiment.
Is there an electrode cleaning or maintenance instruction that I can follow?
Below are the steps that can be followed for STX2-PLUS cleaning or maintenance. Make sure you use enough liquid levels during cleaning or maintenance at least up to the red boxed region. 1. Before using them, chloride the electrode by keeping the electrode tips immersed in 3-6% sodium hypochlorite (bleach) for 10-15 minutes. Chloriding needs to be done every 3 days when the electrodes are used frequently or after more than a week storage. 2. Rinse with sterile DI water/buffer. 3. Optional step: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 4. Use the electrode for measurements. 5. Optional step in between measuring samples: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 6. After measurements soak/immerse electrode tips in 70% isopropanol or ethanol for 5-10 minutes. 7. Rinse with DI water. Let it air dry. Store electrode dry and in a place away from light/minimal light. 8. When used frequently, every week soak electrode tips in 1% Tergazyme for 15 minutes. Follow by rinse with DI water. 9. Next, chloride by keeping the electrode tips immersed in 3-6% sodium hypochlorite (bleach) for 10-15 minutes. (Same as step #1.) 10. Rinse with sterile DI water/buffer. 11. Use for measurements. 12. Repeat from step 5.
Are there any other electrode handing instruction that WPI recommends?
1. Do NOT hold the electrode by the cable. It can physically break the internal connections gradually. 2. Hold the electrode by the arrowed region (plastic). 3. Limit liquid immersion or liquid spray level somewhere up to here (maximum). You do not want the liquid to get inside and reach up to internal the cables or connectors that’s why. You can wipe with the rest of the electrode with a paper towel sprayed with isopropanol or ethanol (do not spray directly).
Will the EVOM™ Manual work with Endohm’s?
Yes, but the 99672 adaptor is required or the new EVOM3/EVOM Manual 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 EVOM™ Manual system automatically calculate TEER?
No, TEER measurement requires an area calculation. To compute TEER, multiply 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 cm2 = 638.5 Ω- cm2. Here are the surface areas generally applicable to different transwell/insert formats: 6 well plate (24 mm inserts) 4.52 cm2, 12 well plate (12 mm inserts) 1.13 cm2, 24 well plate (6.5 mm inserts) 0.33 cm2, 96 well plate (4.3 mm inserts) 0.14 cm2. For Automated TEER Measurements, consider using the WPI REMS Automated TEER Measurement System.
EVOM™ Manual 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.
How should you store the EVOM™ Manual and electrodes if they will be exposed to UV light in a laminar hood for extended periods of time?
Take the EVOM™ Manual out of the laminar hood after use. Next time, turn on the UV inside the hood. Once the hood is disinfected by UV, turn off UV, next spray 70-100% ethanol or isopropanol onto paper towel and wipe the EVOM™ Manual. Do not spray alcohol directly onto EVOM™ Manual.
Why am I getting dashes as reading on EVOM™ Manual, even if I have the STX4 electrode inside the sample?
The electrode in the air or partially immersed in the liquid can show dashes since it records unstable read outs. The electrode tip portion (sensing region) must stay fully immersed. You may also notice unstable read outs when the electrode tip is not fully immersed. Make sure to select apical and basolateral volumes so that electrode tip stays fully immersed. You need to use apical and basolateral volumes greater than what is suggested by the insert manufacturer. For example, for Corning-24 well Transwell (example Corning 3470) we recommend minimum 300 µL on the top (apical) and 850 µL on the bottom (basolateral). [These volumes are a little more than the least required for STX4 electrode.]. Here are the steps: 1. STX4 Adjustment of Electrode Height. Rotate the front ring clockwise so that the electrode can enter to the maximum depth inside the well. 2. STX4 Electrode tip and liquid volume requirements. Make sure the electrode sensing tip (red boxed portions) on both blades stay fully immersed in a conductive liquid, such cell culture media or buffer during measurement. You need to have adequate apical and basolateral volumes to get a stable reading. Since STX4 stays hung, the increased volume must be used to make sure electrode sensing region fully immersed. NOTE: You must use more liquid volumes than recommended by the insert manufacturer. Insert manufacturer’s recommended volumes will not keep electrode tip fully immersed. [As mentioned as an example previously, for Corning-24 well Transwell (e.g., Corning 3470) we recommend using minimum 300 µL on top (apical) and 850 µL on bottom (basolateral). These volumes are a little more than the least required for STX4 electrode. You can check visually to make sure the apical and basolateral volumes are adequate to keep the electrode tips fully immersed, and then consistently use those volumes.]
Can increasing or changing sample liquid volumes change my resistance values?
You can expect to see a change of raw resistance values. However, you subtract the blank values (blank Transwell with no cells) from the sample values (Transwell with cells). This way, you subtract the blank value with increased volume from samples with increased volume. Thus, any change of resistance contributed by increased volume is omitted. Consistently use the same volumes for all your samples in an experiment.
Is there an electrode cleaning or maintenance instruction that I can follow?
Below are the steps that can be followed for STX4 cleaning or maintenance. Make sure you use enough liquid levels during cleaning or maintenance at least up to the red boxed region. 1. Rinse with sterile DI water/buffer. 2. Optional step: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 3. Use the electrode for measurements. 4. Optional step in between measuring samples: Quick dip in 70% ethanol or isopropanol and quick dip in DI water/buffer. 5. After measurements soak/immerse electrode tips in 70% isopropanol or ethanol for 5-10 minutes. 6. Rinse with DI water. Let it air dry. Store electrode dry and in a place away from light/minimal light. 7. When used frequently, every week soak electrode tips in 1% Tergazyme for 15 minutes. Follow by rinse with DI water. 8. Use for measurements.
Why do my readings appear to be drifting*?
*Drift–Readings that continuously increase or decrease significantly (either voltage or resistance) over time. Example: At 1000 Ω, the reading is increasing 100 Ω/ minute. (A drift of 10 Ω/minute is acceptable.) Excessive drift may be caused by changes in the pH or temperature, or the electrode needs cleaning. There are a few things that can be a possible cause of this drift. Ensure that the electrodes are fully immersed in culture media solution, and the fluid temperature in the plate is consistent by equilibrating at room temperature or using a plate warmer. -Another common cause of drift is the electrode tips may have deposits of cell culture media constituents- the electrode (tips) requires enzymatic cleaning (Tergazyme or Enzol) periodically up to 1x per week depending on the use. Handheld electrodes also must be kept as motionless as possible during a measurement. Excessive movement will cause the measurement to fluctuate. Additionally, in a 5% CO2 environment, a loss of CO2 causes the media pH to change, and the resistance reading may change. This is mainly applicable in the context of continuous measurement for an extended period (hours, as compared to a few minutes).
Why are my electrode readings unstable*?
*Instability–At 500 Ω, the reading jumps from 450 to 550 Ω and does not settle down (an instability ±5 Ω is acceptable in the 500 Ω range). In the higher ranges, up to ±1000 Ω is acceptable at the 100K range. Electrodes showing instability may require enzymatic cleaning. The most common causes of reading instability can be fixed by fully immersing the tips in solution or performing enzymatic cleaning. The electrode tips are not fully immersed in adequate conductive liquid (media or buffer). Add extra liquid to bring the liquid level up to the electrode tips. (Use consistent apical and basolateral volumes to make consistent comparisons.) The electrode tips (sensing region) may have deposits of cell culture media constituents, this can be resolved with enzymatic cleaning.
How do I check whether my EVOMTM Manual system is functioning properly?
Use the 1000-ohms test resistor to test and calibrate the EVOM meter itself. Verify the screen display shows a 1000 ohm reading +/- 1 ohm. Refer to the user manual for more specifics on calibration, a pdf version of the manual can be found under the ‘support’ tab of our website labelled ‘manuals’. To test the function of your electrode, a KCl resistance test is used. Prepare 40-, 80- and 160-mM concentrations of KCl using deionized (DI) water. As the KCl solution concentration doubles, the resistance reading should decrease by around half. If you are experiencing drifting resistance values with 80 and 160 mM KCl solutions, ensure that- Electrode tip portion or sensing region is fully immersed in the conductive liquid (media or buffer) during measurement. Electrode needs cleaning. A regular cleaning/ maintenance of the electrode is strongly recommended and needed for functional longevity of the electrode.
I want to use KwikSil surgical glue in my "imaging" experiments in rats. How do I get rid of the bubbles completely, or at least reduce them as much as possible?
The bubbles are hydrogen gas that is released as a by-product of the curing process. The cure happens in such a short period that the gas can't escape. A slower cure time might help. To slow the cure process, cool the material before mixing.
Can the adhesive be removed safely from rodent fur after use after it has cured?
If Kwik-Cast/Sil is applied to rodent fur, the cured adhesive can be removed from fur. Just gently and slowly pull the cured adhesive away from fur. Naturally, there are oils on fur and hair.
How many bulbs comes in the CleanRay-1000?
One bulb comes with the lamp.
How long do the bulbs last?
The bulb usually lasts 3000 hour on average.
Does the lamp produce ozone also, or is it only using UV rays?
The UV lamp also gives off ozone.
How long does it takes for the CLEANRAY-1000 to disinfect small objects?
Typical cycle times for disinfecting small items range from 30-60 minutes. If you wish to disinfect a room, consider the CleanRay-2000 or CleanRay-3000. Cycle times can be set from 30 to 150 minutes depending on the model. For example, a small bathroom can be disinfected in 30 minutes using the CleanRay-2000.
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, multiply 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 cm2 = 638.5 Ω- cm2. Here are the surface areas generally applicable to different transwell/insert formats: 6 well plate (24 mm inserts) 4.52 cm2, 12 well plate (12 mm inserts) 1.13 cm2, 24 well plate (6.5 mm inserts) 0.33 cm2, 96 well plate (4.3 mm inserts) 0.14 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.
How should you store the EVOM3 and electrodes if they will be exposed to UV light in a laminar hood for extended periods of time?
Take the EVOM3 out of the laminar hood after use. Next time, turn on the UV inside the hood. Once the hood is disinfected by UV, turn off UV, next spray 70-100% ethanol or isopropanol onto paper towel and wipe the EVOM3. Do not spray alcohol directly onto EVOM3.
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.
What is the advantage of using oil back-filled glass micropipettes?
The term “back filling” refers to the process of filling the pipette from the large, non-pulled end. “Front filling” is the term which is used to describe filling a micropipette through the small, pulled front end of the pipette. The glass micropipettes are first backfilled completely with mineral oil and secured to the NANOLITER Injector Head. Then, some mineral oil is dispensed through the tip. This creates the space and generates the pressure to front-fill samples through the tip. Front filling sample prevents the spillage or loss of costly or scarce sample involved with back-filling samples. When the sample volume is low, first back-filling glass micropipettes with oil and then front-filling the sample may be the only option.
Can I use WPI’s old standard controller to run the 300704 Injector head?
WPI NANOLITER2020 Injector Head (300704) needs the MICRO2T controller (recommended). WPI’s MICRO4 controller may be used to control the pump. The 300704 Injector Head cannot be used with WPI’s old standard controller.
Can I use same MICRO2T controller that I use with UMP3 pump? Do I need an additional adapter to use the 300704 pump with my existing MICRO2T controller?
Yes, the same MICRO2T controller can be used to control the UMP3 pump and the Nanoliter2010. No additional adapter is needed. 300704 connects directly to MICRO2T controller.
Can I run the pump using a footswitch?
Yes, you can use the footswitch 13142. This is not included in the NANOLITER2020 system and is sold separately.
What do I do when glass micropipettes come off after attaching or I am unable to front-fill a sample?
Odorless and colorless mineral oil is used for backfilling glass micropipettes. While the glass micropipette is installed and with gradual spillage over multiple uses, the gaskets become too slippery to hold glass micropipette in place. Use Kimwipes to soak up oil spillage inside the injector head, outside the glass micropipettes and to clean the gaskets. If needed, install a new set of gaskets to resolve the issue.
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.
I position the O-rings in the right order and orientation per your video but still don’t get an air tight seal .What can be done?
If the rear seal is loose or mounted backwards then it can leak from air passage. This gasket needs to be tight on the plunger wire. If the pipette is pull tested, then it can be easily unseated from the middle gasket and leak by air infusion. The butt end of the glass needs to be smooth (and without any cracks in the glass) and firmly held down onto the middle seat while the collet is being screwed down. That plastic seat will deform a small amount and "mold" itself to the end of the glass. The fluids can also flow out on their own without any added back pressure even if there is a good seal, but that amount of mixing at a 10 um tip is very small. If either rear gasket allows for air flow, then it will leak.
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