Masaki Kanai

Fabrication of quartz microchips with optical slit and development of a linear imaging UV detector for microchip electrophoresis systems

We have developed quartz microchips for electrophoresis and a linear imaging UV detector along with the microchip. The microchips have an optical slit, which cut off the stray light in order to improve the sensitivity of UV absorption detection on the chip, at the bonding interface. They have been successfully fabricated on synthesized quartz glass substrates using the hydrofluoric acid (HF) solution bonding method. The signal level of UV absorption detection was effectively improved by applying microchips with the “on‐chip” optical slit. It is also possible to improve the signal‐to‐noise ratio by repetitive scanning of linear photodiode array located along the separation channel, and signal averaging during elimination of the potential. Furthermore, the analysis may be performed until the separation of the target component is complete, because the real‐time migration pattern of each component in the sample can be seen just as in a slab‐gel electrophoresis, thus enabling a shorter analysis time.

Condition optimization, reliability evaluation of SiO2-SiO2 HF bonding and its application for UV detection micro flow cell

Abstract In order to apply SiO2–SiO2 bonding with hydrofluoric acid (HF bonding) for micro-electro-mechanical systems (MEMS) fabrication, the optimal bonding conditions were examined under different temperature, HF concentration and bonding time. The necessary HF concentration and the necessary time for bonding are reduced by elevating the bonding temperature. The time for bonding was reduced from 24 h at room temperature to 30 min at 80°C, 60 min at 60°C under the conditions of 0.5 wt.% HF concentration and 1.3 MPa applied pressure. The bonding time is comparable to that of anodic bonding. Reliability of the HF bonding was confirmed by the results of temperature cyclic tests and thermal shock tests. A long term stability of the bonded sample was also evaluated by helium (He) leak detection. The measured He leak rate was less than 2.0×10−9 atm cm3/s which is much smaller than that calculated value through component materials of the sample. A novel quartz UV detection micro flow cell for chemical analysis having Si shade structure was fabricated by the HF bonding. The absorbance unit for UV absorption detection of the cell was improved remarkably.

A disposable, dead volume-free and leak-free monolithic PDMS microvalve

A new fabrication method of a membrane-inserted pneumatically-driven microvalve is presented. The device is entirely made from PDMS. To ensure dead volume-free and leak-free, the valve chamber is formed with smooth surface using molding of UV-curable bond. Also, to place a PDMS membrane on the molded PDMS substrate, bonding with spin-coated PDMS membrane is performed, indicating to align-less assembly. As a reference of bonding characterization, the curing ratio, defined as the ratio of soft bake time and hard cure time of PDMS at the same soft cure temperature, is introduced. The best bonding feature is obtained at the curing ratio of 0.06. The maximum tensile bonding strength is examined. Finally, the performance of the membrane-inserted monolithic PDMS valve is tested.

Integrated micro chamber for living cell analysis with negligible dead volume sample injector

We develop the micro chamber for real-time monitoring of living cell. It is integrated with an extremely low dead volume sample injector. The chamber was fabricated by the combination of isotropic etching and deep trench etching using CCP-RIE and ICP-RIE. The reproducible sample injection of the order of 1 nL is performed. Biological cell culture of HeLa is also demonstrated in a prototype device.

Optimal Design of the Micromixer using Nonhomogeneous Multilayer Laminar Flow

An efficient micromixer using nonhomogeneous multilayer in the laminar flow regime is described. In order to increase the mixing efficiency, the CFD simulation was used to optimize the width of the multilayers. It is estimated that the reagents mixing is proceeded more than 10 times faster compared to previous multilayer micromixers. The optimized micromixer was fabricated, and its mixing efficiency was evaluated.

Development of an All-Fluoroplastic Microfluidic Device Applied as a Nanoliter Sample Injector

A method was developed to fabricate an all-fluoroplastic microfluidic device using NEOFLON EFEP, a new fluoroplastic material. The device was successfully used as a nanoliter sample injector, which is very useful for various biological assays and chemical syntheses. The advantages of NEOFLON are that it is easily structured, it bonds at low temperatures, and it has chemical/physical robustness. NEOFLON microchannels 5 µm in width and 5 µm in height were successfully fabricated for the prototype sample injector. The injector enabled the sample injection and metering of a 1.9 nL sample with less than 2% volume change. This suggests that the NEOFLON flow device is capable of the precise fluidic handling of a few nanoliter samples in volume.

Microfabricated CE Chips with Optical Slit for UV Absorption Detection

We have developed novel μ-CE chips with “on chip” optical slit which cut off the stray light in order to improve the sensitivity of the optical absorption detection on μ-CE chips. Our chips which have an optical slit at the bonding interface have been successfully fabricated on synthesized quartz glass substrates using HF (hydrofluoric acid solution) bonding method [1],[2]. The signal level of UV absorption detection was improved about ten times by applying the “on chip” optical slit compared with that of conventional µ-CE chips.

Spatially Focused Reagent Injection System for Cell Analysis using 3-D Sheath Flow Scanner

We developed a spatially focused reagent injection system using 3-D sheath flow scanner. The proposed 3-D sheath flow scanner enables to introduce reagent specifically to target cell colonies cultivated in a microchamber. SiO2 mesh strainer is formed in the microwell to improve spatial resolution of the reagent flow. This enables selective delivery of the reagent to target cell colonies cultivated in the microwell. The specific reagent flow is shifted by eight buffer flows which are controlled by four electro- osmotic flow (EOF) pumps. High performance positioning is realized by PC control with a joystick. Observation of confocal fluorescent image confirmed that the reagent flow is focused to small spot of about 100mumPhi on the mesh strainer where biological cells are cultivated.

Multiple flow switch using stepwise sheath flow

In this paper, A concentration-conservative multiple flow switch using the stepwise sheath flow is fabricated. The functional flow switch was designed using CFD flow simulation in the microchannel.

Monitoring Cellular Events in Living Mast Cells Stimulated with an Extremely Small Amount of Fluid on a Microchip

We successfully developed a measurement system for real-time analysis of cellular function using a newly designed microchip. This microchip was equipped with a micro cell incubation chamber (240 nl) and was stimulated by a very small amount of stimuli (as small as 24 nl). Using the microchip system, cultivation of mast cells was successfully carried out. Monitoring of the cellular events after stimulation with an extremely small amount of fluid on a microchip was performed. This system could be applicable for various types of cellular analysis including real-time monitoring of cellular response by stimulation.