How can I avoid air bubbles in the probe?

Sometimes, when I fill the FluidFM probes I have tiny air bubbles in the microchannel which make e.g. force measurements difficult. How can I get rid of them? Or is there a way to avoid them altogether?

It is better and much easier to avoid bubbles in the probe from the start, rather then eliminating them once they occurred.

Prevent bubbles

General rules to prevent air bubbles in the probe channel:

  1. When working in air always leave at least 10 mbar over-pressure applied. This prevents bubbles from 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.

Dissolve bubbles

f you could for some reason not avoid bubbles forming in the channel, applying pressure to the probe for extended amounts of time can dissolve the bubble. Sometimes this requires 30 minutes or more of pressure cycling or simply waiting.

Try the following steps to dissolve bubbles:

  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 while the pressure is still set to 1 bar.
  5. Wait until all bubbles are dissolved.

Some customers reported that cycling between positive and no pressure in this phase can accelerate the dissolution.

As you can see this is a long procedure, which is why we recommend following best practices above to avoid bubbles altogether. 

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