Towards a low-cost optical biosensor system for biomedical immunoassay applications

A novel, low-cost optical measurement system has been designed for biomedical applications such as immunoassays. The system comprises a rapid-prototyped ABS plastic housing, 500 nm LED source, 530 nm UV filter, and 540 nm silicon photodiode receiver with a custom-built high gain precision amplifier. The sensor system has been designed to measure the fluorescence of different bioliquids in a standard glass test-tube. In addition, a small disc magnet can be inserted to enhanced signal-to-noise in liquids containing fluorophore-labelled magnetic beads. Our preliminary results show that the baseline optical signal depends weakly on the refractive index of the liquid and more strongly on its opaqueness. Removing this baseline signal permits the measurement of FTIC solutions down to concentrations of about 100 nMol. In addition, the insertion of the magnet was found to enhance significantly the optical signal in translucent liquids with low bead concentrations but, interesting, not in opaque ones. We believe that this low-cost (less than 150) optical immunoassay sensor has potential applications such as detecting progesterone and bacteria levels in milk, water, saliva, urine, and blood.