Development of small-sized fluorescence detector for pipette tip-based biosensor for on-site diagnosis

A small-sized fluorescence detector (referred to as a pipette tip [PT]-reader) was developed for a pipette tip-based biosensor. The PT-reader allows us to measure the fluorescence intensity of a solution in a truncated cone-shaped pipette tip with only the tip inserted into the PT-reader. A pipette holder made from a mixture of polydimethylsiloxane (PDMS) and carbon black was capable of the rigorous position arrangement of a truncated cone shaped-pipette tip and the prevention of stray light. The detection performance of the PT-reader was evaluated by measurement of resorufin. The limit of detection (LOD; 3σ) and the relative standard deviation (RSD, n = 4) were estimated to be 0.46 μM and 0.47-4.1%, respectively. This performance was comparable to that of a desktop-type fluorescence microplate reader. In addition, the PT-reader was applied to the quantification of immunoglobulin A (IgA), and the LOD (3σ) of IgA was estimated to be 1.0 ng/mL. The quantitation values of IgA in human saliva obtained by the PT-based enzyme-linked immunosorbent assay (PT-ELISA) were in agreement with those obtained by conventional ELISA. The PT-reader is expected to be useful for low-cost and user-friendly measurements, and the technique of device development proposed in this study will contribute to the progress of on-site medical diagnosis.

Development of a fluorescence microplate reader using an organic photodiode array with a large light receiving area

We developed a small fluorescence microplate reader with an organic photodiode (OPD) array. The OPD array has nine OPDs that have a large light receiving area (9.62 mm² per one OPD). Since the OPD array is fabricated on a flat glass plate, it can be placed just below microwells and can detect fluorescence emitted through the entire surface of the microwell bottom. The analytical performance of the developed plate reader was evaluated by measuring an aqueous solution of resorufin. The limit of detection (LOD) for resorufin (0.01-0.05 μM) was lower than that obtained with a plate reader equipped with nine inorganic photodiodes developed in a previous study (0.30 μM) and a commercially available microplate reader (0.16 μM). These results indicate that the large light receiving area improves the detection performance of the system. In addition, the developed reader was successfully used to quantify immunoglobulin A (IgA) in human saliva. The LOD for IgA was estimated to be 1.2 ng/mL, which is low enough to objectively evaluate human stress.