Exchange of probe content is not possible

Generally speaking the content of a probe cannot be changed for two reasons:

1. It would take far too long

2. It leads to cross-contamination

It takes too long to exchange the liquid in the probe even if the reservoir is emptied, e.g. with a pipette, because there is a dead volume between the reservoir and the probe opening.  This volume is in the range of 500 nL. With maximum flow rates of 0.2 nL/s (FluidFM micro pipette @ 1 bar, water in water) replacing a liquid would take about an hour. Ten times more for FluidFM nanopipettes.

This exchange of the liquid also is likely to introduce cross-contamination for the subsequent liquid.

The complete exchange of the liquid is therefore not recommended.

One exception - Front loading

However, you can apply front-loading to use several liquids in a row. Here a small amount of liquid is aspirated through the probe opening in the front, only to dispense it again shortly after.

This tactic is also used when performing single cell extraction, where oil serves as back-fill and the cell content is aspirated from the front.

We advise aspirating less than 10 pL, such that the aspirated volume is visible in the microscope, can be quantified, and does not get lost in the reservoir or dead volume leading to it.