Hello,
My lab recently purchased a pre-owned EVOM 1, and I'm uncertain if it's functioning correctly. I've replaced all the batteries and run the self-test, which seems fine. I'm using brand new Millicell® ERS-2 (MERSSTX01) electrodes to measure TEER in Caco-2 monolayers (passage 18, cultured in Transwell 12-well inserts with 0.4 µm pores; media DMEM + 20% FBS + 1% PenStrep + 1% NEAA).
The main issue I'm facing is that the measurements are inconsistent—values are above 1000 Ω·cm² in 14-day cultures (with blanks around 500 Ω), and the readings on the EVOM display do not stabilize. Additionally, the measurements are inconsistent even in replicates, with significantly different values obtained from the same well. I've tried several troubleshooting steps, including using a heat plate, re-chloriding the electrode tips, and ensuring the apical and basolateral media volumes are equal, but the issue persists.
What additional steps can I take to verify that both the EVOM and electrodes are functioning properly? Any tips or advice would be greatly appreciated!
Thanks in advance!
The following procedures can be performed to confirm the operation of an EVOM (Epithelial Volt Ohm Meter), which is frequently used to measure the electrical resistance across cell monolayers or epithelial tissue:
1. Initial Setup:
· Power On: Verify that the EVOM 1 is either connected to a power source or turned on and completely charged (if it runs on batteries).
· Electrode Calibration: Make sure the electrodes are clean and correctly calibrated if the gadget needs them.
2. Performing a Baseline Check:
· Zero Adjustment: To guarantee accurate readings, set the EVOM 1 to zero before taking any measurements. Usually, you can accomplish this by using the zero adjustment knob.
· Test in Air: Determine the air resistance. If there is no current flow, the device should display an infinite or extremely high resistance.
3. Testing with a Known Resistor:
· Connect a Known Resistor: Make use of a known-value resistor (that falls within the EVOM 1's normal range). Measure the resistance after connecting it to the electrodes.
· Verify Reading: The resistance can be measured by inserting the electrodes into the saline solution. This ought to provide a precise resistance value based on the saline concentration. The resistance ought to line up with established saline solution values.
4. Checking with a Simple Saline Solution:
· Prepare Saline Solution: In a small container, prepare a saline solution (0.9% NaCl).
· Measure Resistance: Insert the electrodes into the saline solution and measure the resistance. This should give a specific resistance value depending on the concentration of the saline. The resistance should be consistent with known values for saline solutions.
5. Test on a Cell Culture Model:
· Prepare a Cell Culture: Caco-2 cells are a well-established cell culture with tight connections.
· Measure TEER (Transepithelial Electrical Resistance): TEER (transepithelial electrical resistance) measurement involves placing electrodes on opposing sides of the epithelial layer and measuring the resistance. Given the cell type and culture parameters, this should be compared to the predicted TEER values.
· Consistency Check: Repeat the measurement at various intervals to guarantee consistent readings.
6. Maintenance and Recalibration:
· Clean Electrodes: To avoid contamination and guarantee precise measurements, clean the electrodes following each usage per the manufacturer's instructions.
· Regular Recalibration: To guarantee continued accuracy, periodically recalibrate the instrument using known resistors and solutions.
7. Software Verification (if applicable):
· Check Software: If there is software included with the EVOM 1, make sure it is connected correctly and that data is accurately logged.
· Run Diagnostics: Some models' software may include built-in diagnostic tools that allow for additional functionality verification.
You can make sure your EVOM 1 is operating properly and giving precise measurements by following these procedures.