The inventive concept relates to a device for detecting particles in air, said device comprising a receiver for receiving a flow of air comprising particles, a sample carrier, and a particle capturing arrangement. The particle capturing arrangement is configured to separate the particles from the flow of air for and to collect a set of particles on a surface of the sample carrier. The device further comprises a light source configured to illuminate the particles on the sample carrier, such that an interference pattern is formed by interference between light being scattered by the particles and non-scattered light from the light source. The device further comprises an image sensor configured to detect the interference pattern. The device further comprises a cleaner configured for cleaning the surface of the sample carrier for enabling re-use of the surface for collection of a subsequent set of particles.