What can I measure on?

When you make your own sample vial (see Make sample vial) there are certain requirements. We go through these requirements below.

Sample vial requirements

Parameter	Allowed range	Notes
Concentration	< 5 000 000 total/mL	Target 0.5–4 million total/mL when you make the sample vial. Start low and then move to higher concentrations.
Particle size	0.5–5 µm	Equivalent spherical size. BactoBox® detects particles (e.g., cells) in this range. Larger sized objects will not be detected by BactoBox.
Electrical conductivity	1500–2200 µS/cm	This is the default range for the BacTotal-v2024-10 gating. Custom gating may change the allowed range. See the Measure with low conductivity program for an example.
pH	5–9
Volume	4–12 mL	Target 10 mL when you make the sample vial.

Concentration

High concentrations may clog your BactoBox® setup. This is why the 5 000 000 total/mL concentration limit is important.

If the concentration is too high then this may prematurely clog the flow cell, which makes it an expensive lesson.

Don't know the concentration of your sample?

Make a dilution series and measure the most diluted sample first. This avoids clogging your BactoBox® setup. It also avoids carry-over from your previous sample vial.

Once you are above the lower limit of detection (30 000 cells/mL), target a concentration of 0.5–4 million cells/mL.

Do not measure on turbid sample liquid

If the sample liquid is turbid (not transparent) this strongly indicate that the concentration is too high.

Particle size

The BactoBox® setup has microfluidic flow paths. The smallest cross-sectional area is 10×10 µm, which is approximately one-tenth the width of a human hair. Therefore, even a tiny particle may clog the entire setup! To avoid that, always make sure that the external filter is in place.

Use a 10 µm cell sieve to avoid large particles

Filter the sample liquid with a 10 µm cell sieve before you measure on it.

Electrical conductivity

BactoBox® uses an electrical measurement principle. Therefore, the electrical conductivity is important for accurate results.

BactoBox® has a built-in conductivity sensor. It gives an error if the conductivity is outside the allowed range.

Use SBT dilution vial or SBT dilution liquid

Use an SBT dilution vial or SBT dilution liquid. Both have the right electrical conductivity already.

When you dilute your sample (1:1000 or more), the conductivity of the diluent dominates over that of your sample. This puts the conductivity within the allowed range.

Try the Measure with low conductivity program

BactoBox® comes with several gating settings. One of these is part of the Measure with low conductivity program. It accepts sample vials in the 500–1 100 µS/cm range.

See Gating.

Electrical conductivity changes with temperature

Keep your sample vial at room temperature to avoid surprises

For example, if your sample is refrigerated then wait for it to reach room temperature.

The electrical conductivity of the diluent changes a lot even for small temperature changes. A mere +5 ℃ increase in temperature becomes a 200 µS/cm increase in conductivity.

See Hit the right conductivity for details.