A polarization isolation method for measurement of fluorescence assays in a microfluidic system using organic electronics for application to point-of-care diagnostics

This dissertation demonstrates a cheap, disposable, integrated on-chip fluorescence detector with limit of detection (LOD) of 1 nanomoles(nM) of a fluorescence dye which is 1000 times less than that reported in current literature. The on-chip fluorescence detector has been fabricated from scratch using novel organic electronic devices with a potential to go down to picomolar detection limits when properly optimized. A high-sensitivity MEMS based on-chip fluorescence detection system consisting of a light source, sample chamber, detector and couple of polarizers was integrated into a set of 3"x1" glass slides. A green organic light-emitting diode (OLED) has been used as the excitation source and organic photodiode (OPD) has been used as the fluorescence detector. A novel integrated cross-polarization scheme was used to filter out excitation light from the fluorescent dye emission spectrum. Two commonly used dyes in biotechnology applications, Rhodamine 6G and Fluorescein have been detected down to ten's of nanomoles which is several orders of magnitude improvement in detection limits over existing literature using OPD. A theoretical model has been developed to study fluorescence signal variation with dye concentration for this particular system. A theoretical curve fitting has been performed based on the model. The theoretical fit matches closely with experimental data. The parameters for an optimized system for the theoretical lowest limit of detection (LOD) of the dyes have been tabulated. The minimum achievable LOD with optimized parameters is potentially as low as 10 picomoles(pM) which is 106 lower than the micromolar detection regime found in current literature for on-chip detection devices using organic photodiodes. A portable picomolar on-chip detection system can have wide applications in detection of pathogens for point-of-care diagnostics systems and also in water purification plants.