Abstract: The present disclosure relates to mass spectrometers and ion mobility spectrometers and methods for utilizing them and, in particular, to efficient detection of large size ionic species by attaching fluorescent agents to such species and utilizing high intensity light and appropriate optics to define a detection plane. A mechanism to detect fluorescence photons with high efficiency is coupled thereto. In an exemplary embodiment, a mass or ion mobility analyzer is utilized to separate fluorescent ionic species in space or time. The ionic species absorb and re-emit photons as they transverse the detection plane. The photons are directed to a photon detector that generates an electric signal that defines time or position (or position and time of intersection) of ionic species with the detection plane.