The present invention provides devices and methods for detection of particles, such as biological cells, in samples using a photosensitive waveguide. The photosensitive waveguide changes its transmissivity in a detectable manner in response to controlling radiation emitted from the particles. In preferred embodiments, the waveguide is two-dimensional and the position of the particles as well as their presence is obtained by scanning the waveguide in two non-parallel directions. The provided devices are preferably used to locate labeled cells. The present invention also includes control systems and methods for detecting and locating cells using the devices provided.