In clinical practice, such as in the hospital setting, various diseases are diagnosed and treated using associated biomarker analyses. Biomarkers are biogenic substances, and enzyme immunoassay (EIA) is widely used for their quantification. Since EIA procedures include complicated handling of solutions, such as dispensing and washing, large-scale automated analyzers are used in hospital laboratories. The aim of our group is to develop systems for clinical analysis that can contribute to daily health management at home. By applying semiconductor microfabrication technologies, we have developed a system that uses a CD-type device in which microfluidic processes are integrated. This integrated CD-type microfluidic system can perform a series of biochemical tests used in hospital laboratories, but on a miniaturized scale, thus requiring extremely small volumes of solutions (on the nanoliter scale).
During an assay with the integrated CD-type microfluidic system, samples and reagents are applied onto reservoir wells located in the area around the center of the CD-sized disc, and then distributed outward through microflow passages under centrifugal force generated by spinning of the disc. A series of analysis procedures can be performed based on this fluid flow mechanism. The conventional pump-based fluid flow system requires extra sample and reagent volume, in addition to the volume directly required for the reaction itself, for filling pump connection tubes and fluid transfer tubes. On the other hand, the integrated CD-type microfluidic system uses centrifugal force for fluid flow, and requires extremely small volumes of solutions. More importantly, every solution applied on the disc is under the influence of centrifugal force while the disc is spinning, so one motor for disc rotation is sufficient for simultaneous analysis of multiple samples and multiple biomarkers; an individual pumping force for each solution, seen in the conventional system, is not necessary.
For example, we have developed an integrated CD-type microfluidic system that performs EIA for salivary secretory immunoglobulin A (s-IgA), a biomarker indicative of stress status, which enables quantification of s-IgA from a saliva sample as small as 1 µl. Further, in clear contrast to the conventional system, the integrated CD-type microfluidic system uses disposable devices, and thus no complicated washing mechanism is necessary. This is an added advantage in miniaturizing the whole assay system. The assay system will become as compact as a portable CD drive in the future, and will contribute to successful health management in various settings such as individual households, workplaces, and schools. We believe that our integrated CD-type microfluidic technology will play a key role in future home-based medical care.