The invention relates to a device for detecting the emission of a target particle at an emission wavelength. This device has a photo detector e.g. complementary MOS type semiconductor, comprising a sensible detection surface with high optical index in the order of 3.5. A target particle is positioned closed to the surface in an analysis medium with low optical index in the order of 1.33. A mask e.g. metallic or aluminum film, comprises opaque zones with emission wave length and holes for receiving the target particle, where the mask covers the sensible surface.