Development of Quantitative Analysis Technique Based on an On-Chip Flow Rate Measurement Using Organic Photodiodes

A novel quantitative analysis method was developed using a microchip with organic photodiodes (OPDs). This quantitative method is based on measurement of the flow rate of an ink solution flowed in a microchannel on the microchip by the gas generated in a sealed sample reservoir through chemical reaction of the analyte with the enzyme. The amount of gas generated in the sample reservoir is dependent on the concentration of the analyte; therefore, the flow rate of the ink solution is also dependent on the concentration of the analyte. The concentration of the analyte can thus be estimated by measurement of the ink solution flow rate. The ink solution flow rate was estimated by measuring the migration time of the ink solution between two points using two OPDs placed under the microchannel. This quantitative analysis method was demonstrated by the measurement of catalase using the microchip. In addition, the developed method was applied to the determination of C-reactive protein (CRP), a biomarker of inflammation, based on a catalase-linked immunosorbent assay (C-LISA). The limit of detection for CRP was estimated to be 2.0×102 ng/mL. The method was also applied to the determination of CRP in human serum, and the quantitative value (2.7±0.1 µg/mL) obtained by this method was in excellent agreement with that obtained by the conventional enzyme-linked immunosorbent assay (ELISA) method (2.5±0.1 µg/mL). The developed quantitative analysis method does not require a photodetector with high sensitivity and is thus capable of downsizing; therefore, this will be useful for on-site analyses such as point-of-care testing and field measurements.