If there is just one particle in one milliliter of e.g. water it is very difficult to predict the likelihood of detecting this one particle because the particle could pass by the detection window and go unseen.
If the particle is larger i.e. Large Particle Counts in the micrometer range, it becomes more likely to detect the single particle. We are working on a module which looks at the whole measuring cell (capillary). This module will be available from mid-2025.