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In this paper, we report the demonstration of a flow sequencing method in a centrifugal microfluidic device rotated at a constant speed. The simple poly-dimethylsioxiane chip, which consists of microchannels, chambers, and vent holes, was integrated in a compact disk substrate, and multistep flow sequencing was executed by simply spinning the device at a constant rotational speed. All the triggers were controlled by a water clock using the liquid meniscus as the clock hand. The flow modes to the sample chambers were switched by switching the air supply to the sample chambers, depending of on whether the meniscus water clock was inside the channel connection (disabling air supply) or outside it (enabling air supply). A four-step flow sequence was successfully executed using two different connections of the chambers, namely, parallel connection and serial connection. Highly reproducible autonomous trigger timing with a typical error of less than 3% was achieved. Delicate adjustment of the flow sequencing by varying the channel geometry was also demonstrated. The time-scaling of the flow sequencing was accomplished by changing the viscosity of the fluid in the water clock. Additionally, a four-step flow sequencing involving a flow injection chain was successfully demonstrated by serial connection. Through combinations and further variations of these concepts, it is expected that the proposed method would be used to realize higher-order flow programs in steadily spinning centrifugal microfluidic devices. [ABSTRACT FROM AUTHOR]

We have developed a method to fabricate higher order surface enhanced Raman scattering (SERS) active structure with gold-decorated polystyrene microparticles (Au/PS microparticles) to serve a wide range of applications in life science and environmental analysis using alternating-current dielectrophoresis (DEP). It is within several tens of seconds to form or gather the SERS—active ‘hot spots’ and analyte. The immobilization of Au/PS microparticles can be demonstrated and qualitatively explained by DLVO and DEP calculation. Our method enables us to detect 4, 4′-bipyridine (4bpy) at 100 pM by an easy operation of in situ SERS platform using fiber-type simple Raman spectrometer. This platform can easily generate SERS-active ‘hot spots’ with SERS enhancement factor ∼ 10 8 in specific region on demand. [ABSTRACT FROM AUTHOR]

Abstract: A stacked-type centrifugal microfluidic device with three-dimensional (3D) microchannel networks and multifunctional capillary bundle structures is developed, and an immunoassay for the detection of immunoglobulin G (IgG) is demonstrated. The device consists of multiple layers of disk-like chips with conventional planar microchannels and vertical capillary bundle structures that are constructed on disks of poly(dimethylsiloxane) and poly(methyl methacrylate). The integration of multiple reactors up to 10 reactors on a disk with 8cm in diameter is realized by reducing the area of reservoir but increasing the thickness. Moreover the thick optical detection reservoir is also realized for absorption spectroscopy in the 3D centrifugal microfluidics. 3D liquid valving on the vertical capillary bundle structures and liquid transportation through these structures are successfully demonstrated. The results show the successful control of the multistep liquid injection without problems such as blockage of capillary bundle by bubbles that expected to be caused due to 3D structure. The results of the immunoassay show clear response to analyte concentration suggesting successful unit operations in developed 3D centrifugal microfluidic device for immunoassay. Finally, the advantages and impact of the 3D design for the development of high-performance centrifugal microfluidic systems are summarized. [Copyright &y& Elsevier]

Abstract: The advantages of vertical microreactor stack with three-dimensional (3D) structure for immunoassay are discussed. The vertical microreactor stack uses vertical fluid flow operation with multifunctional fluid filters. The multifunction of fluid filter is very effective for micromixing and passive valve operation. The mechanism of micromixing is discussed by using computational fluid dynamics (CFD), and the results suggest that the mixing mechanism based on two main effects. One is Coanda effect and the other is Taylor dispersion induced in enormously high aspect ratio capillary and liquid plug. We demonstrated enzyme reaction with unique repeat mixing operation, to evaluate the micromixing performance of fluid filter. As the results, we proved that the fluid filter has very effective mixing performance. The detection limit, which demonstrated by competition enzyme-linked immunosorvent assay (ELISA), is comparable with recommended detection limit, which suggested by Japanese ministry for the environment. [Copyright &y& Elsevier]