Polymer on Quartz Waveguide Sensing Platform for Enhanced Evanescent Fluorescence Spectroscopy

This paper presents the study of the performance of a novel SU-8 waveguide on a quartz substrate for evanescent fluorescence spectroscopy. The sensitivity of the sensing platform (SU-8/quartz) was compared to an SU-8 waveguide on silica fabricated with the standard protocol. The physical properties of the SU-8/quartz waveguide resulting from a novel fabrication process allowed for a higher fluorescence coupling and lower optical losses than the SU-8/silica waveguide. The impact of the different indices of refraction of both waveguides on the fluorescence collection efficiency was calculated with three-dimensional finite-difference time-domain simulations by simulating randomly oriented and phased dimensionless current dipoles in the vicinity of their sensing layers. An evanescent fluorescence spectroscopy experiment was performed with different concentrations of Alexa-647 labeled-BSA proteins immobilized on the two polymer waveguides to compare the sensitivity of both sensing platforms. The SU-8/quartz waveguide revealed to have a higher calculated fluorescence collection efficiency and also a greater measured fluorescence light output compared to the SU-8/silica waveguide.