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left: Schematic optical set-up used for first model-assays for ‘volume detection’, interference filters were used for selection of the excitation or emission light and photodiodes or photomultiplier for signal detection; right: comparison of set-ups for volume detection and detection of backcoupled and guided luminescence light, using a second outcoupling grating where different wavelength can be discriminated by the outcoupling angle. From [31], Copyright Elsevier (1997).
