An assay unit for carrying-out fluorescence-detected assays on physiological samples comprises a microfluidic chip with a microfluidic system to convey a physiological sample or analyte solution through one or more microfluidic channels arranged on the chip, and a photonic system with two or more rectangular waveguide structures arranged on the chip to guide excitation light in the near IR, visible, or near UV range. The microfluidic channels and the waveguide structures cross each other at a detection site. In an assay area, where a certain microfluidic channel and a certain waveguide structure cross each other, one or more lateral surfaces of the core of the waveguide structure at least partially face an inner volume of the microfluidic channel, such that an evanescent field of light guided within the waveguide structure overlaps with a certain part of the inner volume of the microfluidic channel. In the assay areas, one or more capture spots are located on the surface of the waveguide core, the capture spo
