A device for counting particles on a sample surface includes a scanner probe having a first opening for receiving particles from a sample surface and one or more second openings, a particle detector for detecting particles passed there-through, a modulator for modulating air flowing there-through, a pump for producing a first airstream flowing from the first opening and through the particle detector, and for producing a second airstream flowing through the modulator and to the one or more second openings, and control circuitry for controlling the modulator to modulate an amplitude of the second airstream.