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Troubleshoot: The FluidFM probe cannot be filled

The FluidFM probe cannot be filled

If a fresh probe cannot be filled despite using the protocol given here it can have several reasons. Please follow the following steps to localize the problem:

  1. Fill the reservoir of the probe with distilled, filtered, degassed water
  2. Apply 1 bar of pressure for 30 s.
  3. Release the pressure

Now observe the water meniscus between the reservoir and the FluidFM chip. We can have 4 cases:

Case 1: The water meniscus never moved towards the FluidFM chip.

There is a leak between pressure controller and probe. Typically the leak is at the connector. This can be tested by mounting the CONNECTOR to a dead-end CYTOCLIP, where the old chip is removed and the opening is blocked with glue. You can then immerse this test setup in a water-filled beaker and apply high pressure with a syringe. Any leaks will reveal themselves through bubbles.

Case 2: The meniscus moved towards the chip when pressure was applied, yet is back the reservoir after releasing the pressure.

The probe opening or the channel is blocked. Discard the probe, write us a mail and we will replace it for free with your next order. 

Case 3: The meniscus moved a bit towards the FluidFM chip, yet has not reached it yet.

The probe is open, but the pressure and time were not sufficient to fill the channel yet. Either wait for a few minutes with 1 bar applied or use a syringe as pressure source to achieve a higher pressure.

Case 4: The meniscus reached the FluidFM chip.

This means the probe could be successfully filled. Continue with your experiment.

There are air bubbles in the probe

Air bubbles in the FluidFM probe channel impede most experiments and must be avoided. Gas in the probe shows as compressible phase domain whenever the pressure is changed.

Eliminate bubbles

To get rid of the bubbles in the channel you can follow and repeat the following steps:

  1. Dry the probe by touching the FluidFM chip (avoid the tip) with a kimwipe. 
  2. Apply 1 bar pressure to the probe while it is still in air
  3. Make sure the liquid reaches the opening of the probe
  4. Immerse the probe into your liquid medium/petridish while the pressure is still set to 1 bar
  5. Release the pressure

Bubbles in the channel can be hard to loose, and sometimes require long times of pressure cycling or simply waiting. Thus it is better to prevent bubbles as follows.

Prevent bubbles

General rules to prevent air bubbles in the probe channel:

  1. When working in air always leave at least 10 mbar overpressure applied. This prevents bubbles coming in from the front aperture.
  2. Always degas the liquid before filling it into the FluidFM probe. This is especially important when you work with negative pressures, e.g. for cell adhesion.
  3. Pretreat and coat the FluidFM probe such that the probe surface chemistry matches the liquid. A good example is plasma activation for hydrophilic solutions.
  4. Never let your probe dry out. Mixing water with glycerol will reduce this risk strongly.

There is no droplet coming out at the end during filling

No worries, this is completely normal. The probe is ready to use as soon as the liquid reaches the tip opening. No need to form a droplet.

The exact pressure at which liquid can exit the FluidFM probe opening against air and form a droplet depends of: the probe geometry, of the liquid itself, of the air properties and of the chemical fictionalization of the FluidFM probe.

As rule of thumb:

For FluidFM nanopipettes and nanosyringes you will not see a droplet. The surface tension at the opening is too high to overcome with 1000 mbar. They will still be fully operational once in the sample or on the substrate.

For FluidFM micropipettes you will see a droplet at the exit building up while applying 1000 mbar, not with lower pressures though.

Fluorescent tracer in the liquid can be used to visualize filling of probes. 

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