What are the "Particle" and "Aggregate" thresholds? How do I define them?

The Particle Threshold corresponds to the minimum impedance signal defined for a cell which helps to distinguish particles of interest from debris and other non-relevant particles. Below this value, particles are not detected during dispensing. A default threshold of 200 ohms is set-up in the analysis software (threshold defined for mammalian cells >10µm). This value can of course be adjusted depending on the experimental conditions (cell line and medium used).

The Aggregate Threshold, in contrary, defines the maximal impedance signal from which more than one cell is detected. By default, the software does not apply any aggregate threshold and this can be defined by the end-user. By setting this threshold, the dispenser can avoid dispensing clusters of cells or aggregates.

How to define thresholds?

Most of the time, the Particle Threshold is between 150-500 ohms.

The Aggregate Threshold can be estimated upon cell visualization to identify the typical size range or number of cells that constitute an aggregate for your specific application.

Additionally, thresholds can also be adjusted based on the sample distribution (see FAQ: How do I evaluate the concentration of my sample ?).

The distribution of the sample should follow a gaussian curve. Events detected before or after the curve can be considered as debris or maybe non-relevant particles.

Figure | Particle distribution of a sample.

The signal detected before the gaussian curve (450 ohm) can be defined as the particle threshold . The signal above 4000 ohms, in contrary can be defined as the aggregate threshold since the events are rare and outside of the gaussian curve.