Kazuo Hosokawa

A polydimethylsiloxane (PDMS) deformable diffraction grating for monitoring of local pressure in microfluidic devices

In this paper, a novel optical method for monitoring of local pressure in microfluidic devices using a deformable diffraction grating is presented. A test device was fabricated with transparent silicone elastomer - polydimethylsiloxane (PDMS) - using the replica moulding technique. The moulded PDMS chip and a flat glass plate have a bonding interface, which defines a 2xa0mm×2xa0mm diffraction grating and a 200xa0µm wide, 20xa0µm deep microchannel. The grating consists of 5xa0µm wide, 2xa0µm deep rectangular grooves arrayed with a period of 10xa0µm. All the grooves are connected to the microchannel, and deformed by internal pressure. The optical response of the device to pressure ranging from -80 to 100xa0kPa is presented and compared with the theoretical prediction. It is also demonstrated that the test device can be used for measurement of air flow rates ranging from 0 to 0.3xa0mlxa0min-1. The major advantages of this method are simple design and inexpensive fabrication. This method is not only desirable for flow characterization of microfluidic devices, but also opens up the possibility of producing new types of fibre-optic pressure sensor and pressure-driven optical modulator.

Droplet-based nano/picoliter mixer using hydrophobic microcapillary vent

A mixing device for liquid droplets with pL-nL volume was developed for the first time. Two droplets with volume of 5 nL were pneumatically manipulated and joined together in a microchannel. For drawing off the air between two droplets, Hydrophobic Microcapillary Vent (HMCV)-a vent valve driven by the negative capillary action-was utilized. The mixer can be used as a diffusion-based optical chemical detector, or as a basic component in integrated multistep Micro Total Analysis Systems (/spl mu/TAS). Since the mixer has planar structure without moving parts, it can be fabricated by molding technique at low cost.

Two-dimensional micro-self-assembly using the surface tension of water

Several self-assembling microstructures have been fabricated, and approximately 100 units floating on the surface of water were self-assembled two-dimensionally. The basic assembly units are 400 /spl mu/m large, and consist of both polyimide and polysilicon thin films. Surface tension was used in this system as the bonding force. The surface tension is the local interaction between the units, and is dominant in the microscale. Each unit was bonded selectively by employing the following characteristics of the surface tension: 1) objects located at equal heights are attracted to each other, 2) large attractive forces act on sharp parts, and 3) objects located at different heights are mutually repulsed. The curling-up property of the thin films was used to obtain the different heights. Self-assembling behaviour was also predicted by using a rate equation.

Development of a Microfabricated Biochemical Workbench — Improving the Mixing Efficiency —

Unlike the existing μTAS, we have tried to conduct cell-free translation on a chip as the first step toward the highly automated biochemical microsystems named, “Micro Work Bench”. This paper describes the detailed design of the reactor chip and the experimental results of the cell-free translation on the chip. Based on the experiments with the first version of the reactor, two types of structures for laminated flow generation are newly proposed to improve the mixing efficiency in the microreactor to achieve the detectable amount of yield in the cell-free system. Using luminescence imaging, it can be observed that the flow profiles in the microreactor can be improved by the mixing device.

The occurrence of 19,28-bisnorlanostane derivatives in a plant fossil: A novel geochemical degradation process of triterpenoids

Abstract Four novel triterpene ketones bearing 24-methyl-28-nor- and 24-methyl-19,28-bisnor-5α-lanostane skeletons were identified in a fossil of a stem of a plant belonging to the Lauraceae family. The structures of these compounds have been determined by comparison of their spectral data with those of authentic specimens derived from lanosterol and 24-methylenecycloartanol. This is the first finding of compounds bearing a 19,28-bisnorlanostane skeleton, which implies a novel possible microbiological pathway of degradation of lanostanes in the sedimentary environment.

Hydrophobic Microcapillary Vent for Pneumatic Manipulaiton of Liquid in μtas

For integrated multi-step μTAS, pneumatic manipulation of liquid reagents is a promising way to minimize dead volume and contamination. In such a system, passive vent valves are required for positioning and mixing of reagent droplets. This paper presents design, fabrication, and testing of a novel microstructure named Hydrophobic Microcapillary Vent (HMCV). By utilizing the negative capillary action of aqueous liquid against hydrophobic microcapillaries, one can position the liquid accurately without sensors: a water droplet of 400 pL volume was successfully positioned using air pressure up to 30 kPa. Since the HMCV has no moving parts and can be fabricated by molding technique at low cost, it can be built in a disposable unit of microdevices.