<p>A fluorescence reader for an optical assay arrangement that includes a polymeric sample substrate having a reaction site-surface and a substrate surface. The fluorescence reader includes a light source arranged to illuminate the reaction site-surface through the substrate surface, and a detector device arranged to detect fluorescent light emitted from the reaction site-surface and transmitted through the substrate surface, the substrate surface being configured to increase transmission of emitted fluorescent light by suppression of total internal reflection.</p>
