Here are some general checks to ensure that there are no issues with the Exoid fluid cells.
These checks can be performed regularly to ensure your Exoid is performing as expected, and should be your first port of call when an issue arises. If you are having issues, please make a 3-minute measurement recording so that you can send this to support for analysis.
Check for issues with the level of the baseline current
Check the baseline with no nanopore: In the absence of a nanopore, place the upper fluid cell and shielding cap on, then apply 0 V. The current should be 0 ± 3nA.
Check the baseline current at 0 V: Put the nanopore back on. After the current has been established at a higher voltage, ensure that when the voltage is set to 0 V, the current is 0 ± 3 nA. Anything outside of this suggests an issue.
Check the baseline current at equal positive and negative voltages: After the current has been established, apply an equal positive and negative charge and ensure the difference between the two resulting voltages is ≤ 10nA.
Troubleshoot these issues: Remove the upper fluid cell and ensure there is no liquid on top of the nanopore. If there is, remove this. Remove the nanopore and dry and clean the lower fluid cell. Replace the nanopore (place the same nanopore back on) and the upper fluid cell, replace the electrolyte and re-establish current. If this does not fix the issue, check the upper and lower fluid cells for signs of damage and contact support.
Check for visible signs of lower fluid cell paste damage
Check for visible signs of cracks, holes, ‘lifting up’ (i.e., paste lifting up from the electrode at the edges), and flaking of the silver chloride paste in the lower fluid cell. If these are present, or if you are otherwise having issues with an unstable or noisy baseline, then please see the dedicated support article for lower fluid cell paste issues.
Check for salt buildup in the fluid cells
As Tunable Resistive Pulse Sensing (TRPS) requires the use of an electrolyte, salt can build up in the fluid cells if they are not cleaned properly. Visually inspect the fluid cells for buildup of white salt deposits. If these are present, clean the fluid cells with 70% ethanol. Moving forward, you may need to intensify your cleaning process.
Check for bubbles
First, remove the shielding cap. Visually inspect the upper fluid cell for visible bubbles. Next, gently remove the upper fluid cell and place on top of the shielding cap. Visually inspect the lower fluid cell through the nanopore and check for visible bubbles. If bubbles are present, clean and dry the fluid cells and replace the electrolyte/sample. If this is a recurrent problem, please see the dedicated support article and contact support.
Check for expected behaviour when using the reference cell
If you cannot identify the issue with the Exoid, the 10 MΩ reference cell can be used to diagnose the issue. It should be noted that it is often difficult to distinguish between a nanopore issue, a setup issue, and a fluid cell issue. Contact Izon support for advice if unsure.
Remove the fluid cell from the Exoid and replace the lower fluid cell with the reference cell. At 0 mV the current should be 0 ± 3 nA, at 1000 mV the current should be 100 ± 3 nA, and at -1000 mV the current should be -100 ± 3 nA. Contact Izon support if this is not the case.