Abstract: A microfluidic system is described comprising a plurality of fluidly connected microfluidic chambers, each microfluidic chamber comprising: a fluid sample inlet; a fluid sample outlet; a selectably closable valve operable to enable gas to be vented from the chamber; a pressurisation system operable to apply an overpressure to one or more first microfluidic chambers being fluidly most upstream. A method is also described comprising supplying a fluid sample to the system via the one or more first microfluidic chambers being fluidly most upstream; operating the pressurisation system to apply an overpressure to the one or more first microfluidic chambers; selectively operating the valves of the fluidly connected microfluidic chambers to cause the fluid sample to move successively between the microfluidic chambers.

Abstract: A particle concentrator system for the concentration of particulate material is described. The particle concentrator system comprises a prefilter module comprising a first inertial classifier configured to retain a flow in which particles smaller than a predetermined cut point size tend to segregate differentially; and a concentrator module comprising at least one second inertial classifier, and optionally more than one fluidly in series, configured to retain a flow in which particles larger than a predetermined cut point size tend to segregate differentially. The inertial classifiers are preferably virtual impactors. A gas sampler system, a gas sampler, concentrator and collection system, a method for the collection of a sample of aerosolised particulate material using such systems are also described.