This invention generally relates to optical devices that can collect and detect signal emissions effectively while allowing the excitation light path and the sample flow path to coexist non-obstructively in a compact format. More specifically, this invention relates to a compact device having a multilayer coating on the structure surface and a wave guiding structure. In the device, using the surface plasmon coupling effect, the majority of the optical emission from the emitter on top of the multilayer coating is distributed toward the wave guiding structure. The wave guiding structure then further directs on signal to the detector with a high efficiency.