High sensitivity on-chip fluorescence detection based on cross-polarization and thin-film organic photodetectors

In this paper we present a novel, high-sensitivity, cost-effective cross-polarization scheme to filter out excitation light from a fluorescent dye emission spectrum. With this scheme, it is possible to achieve a detection limit of 10 nM which is a 1,000 fold reduction from previously published results. The concept is demonstrated using an inverted microscope with a halide lamp as the excitation source and an organic photodiode as the intensity detector. The excitation light is linearly polarized and used to illuminate a microfluidic device containing 1 mu L of Rhodamine 613 dye dissolved in ethanol. The detector is shielded by a second polarizer, orientated orthogonally to the excitation light. The resulting emission signal was detected by the organic photodiode down to a concentration of 10 nM. This scheme opens the possibility to fabricating integrated microfluidic devices with fluorescence detection, suitable for point-of-care (POC) diagnostics, biomedical and environmental applications.