High coupling efficiency contact imaging system having micro light pipe array for a digital enzyme-linked immunosorbent assay

The enzyme-linked immunosorbent assay (ELISA) is a diagnostic technique used for detecting the presence of viruses or tumor markers. To detect target biomarkers, antigen-antibody reactions followed by fluorescent reactions are carried out in an ELISA. Recently, digital ELISAs have been proposed to achieve higher sensitivity. In the digital ELISA, fluorescent reactions are carried out in an array of femtoliter-scale microchambers. The concentration of the target biomarkers is determined by counting the number of microchambers with and without fluorescence using a fluorescence microscope. We have been developing compact digital ELISA systems by replacing the fluorescence microscope with a dedicated stacked photodiode CMOS image sensor as a fluorescence detection tool. High coupling efficiency for fluorescence and low coupling efficiency for excitation light are key problems that need to be overcome to achieve a practical contact fluorescence imaging system. Here, we present an array of light pipe absorption filters directly connected with microchambers. The manufacturing processes are also described. Our structure makes it possible to achieve a high sensitivity that is comparable to that achieved by employing the digital ELISA with a fluorescence microscope and provides a miniaturized digital ELISA system.