A waveguide absorption filter for fluorescence measurements

Filtering strategies are a crucial aspect for signal detection in many fluorescence based systems such as chemical and/or biochemical sensors. Here we present the design, fabrication and characterization of a new waveguide absorption filter capable of maximizing the fluorescence signal collection thanks to its high numerical aperture. The comparison in terms of performance with an interference filter demonstrates how this new type of absorption filter still works well even when the fluorescence light forms large incidence angles with the perpendicular at the filter input face, a condition for which any other filtering strategy fails. Finally, as a proof of concept, a preliminary fluorescence measurement carried out on an IgG - anti IgG bioassay shows the potentiality of our absorbing waveguide filter in comparison to that of the interference one. The use of such filtering strategy can improve and simplify the fluorescence signal detection in several fields of sensing application, from Point of Care Testing to environmental monitoring.