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In this study, a rapid prototyping method for droplet generators using pipette tips and glass capillaries (pipette-tip-shelled capillary microfluidic device (PiT-CMD)) is described. The proposed de...

We present droplet manipulation using a digital microfluidic device comprising downward electrodes. Using this device, we demonstrated droplet transportation, programmable dispensing, and droplet c...

This paper describes the performance of organic droplet mixing using a digital microfluidic (DMF) device. DMF devices have been applied to the dispensation and transportation of aqueous droplets us...

Microchannels used for high-precision handling of small amounts of liquids are employed in various fields. However, technical limitations with respect to complex channel structure fabrication exist...

Nanoparticle (NP) concentration is crucial for liquid biopsies and analysis, and various NP concentrators (NPCs) have been developed. Methods using ion concentration polarization (ICP), an electrochemical phenomenon based on NPCs consisting of microchannels, have attracted attention because samples can be non-invasively concentrated using devices with simple structures. The fabrication of such NPCs is limited by the need for lithography, requiring special equipment and time. To overcome this, we reported a rapid prototyping method for NPCs by extending the previously developed hydrogel molding method, a microchannel fabrication method using hydrogel as a mold. With this, we fabricated NPCs with both straight and branched channels, typical NPC configurations. The generation of ICP was verified, and an NP concentration test was performed using dispersions of negatively and positively charged NPs. In the straight-channel NPC, negatively and positively charged NPs were concentrated &gt, 50-fold and &gt, 25-fold the original concentration, respectively. To our knowledge, this is the first report of NP concentration via ICP in a straight-channel NPC. Using a branched-channel NPC, maximum concentration rates of 2.0-fold and 1.7-fold were obtained with negatively and positively charged NPs, respectively, similar to those obtained with NPCs fabricated through conventional lithography. This rapid prototyping method is expected to promote the development of NPCs for liquid biopsy and analysis.

We herein report a method for the preparation of a glass microchannel capable of forming multiple emulsion droplets (i.e., water-in-oil-in-water and oil-in-water-in-oil) by locally controlling the wettability of the glass microchannel. Production of multiple emulsion droplets using a glass microchannel requires partial control of its wettability using a method that consists of two steps: (1) hydrophobization of a whole glass microchannel by filling the microchannel with octadecyltrichlorosilane (OTS) solution, and (2) local hydrophilization of the OTS-treated glass microchannel by exposure to ultraviolet light through a mask. However, conditions for the preparation of OTS-SAMs for controlling microchannel wettability and subsequent multiple emulsion droplet formation have not yet been reported. In this study, we investigated the conditions required to form multiple emulsion droplets and demonstrated formation of multiple emulsion droplets using a treated glass microchannel with multiple junctions. The glass microchannel prepared according to this method was able to form various aqueous and organic droplets due to its resistance to swelling.

Electric and magnetic dual-driven twisting ball display had realized handwriting by using a permanent magnet and changing colors electrically in our previous work. Janus particles used in the dual-driven twisting ball display had electric and magnetic anisotropy simultaneously caused by a charge control agent (CCA) and magnetic nanoparticles in one hemisphere. However, we found that magnetic handwriting was impossible right after electric color changing. In this study, we examined this phenomenon changing the property of Janus particles.

We describe the behavior of droplet formation within 3D cross-junctions and 2D T-junctions with various cross-sectional geometries that were manually fabricated using the hydrogel-molding method. The method utilizes wire-shaped hydrogels as molds to construct 3D and 2D microchannel structures. We investigated the flow patterns and droplet formation within the microchannels of these microfluidic devices. Despite being fabricated manually, the microchannels with 3D cross-junctions and 2D T-junctions were reproducible and formed highly monodispersed droplets. Additionally, the sizes of the droplets formed within the microchannels could be predicted using an experimental formula. This technique of droplet formation involves the use of a device fabricated by hydrogel molding. This method is expected to facilitate studies on droplet microfluidics and promote the use of droplet-based lab-on-a-chip technologies for various applications.

We report a novel technique to fabricate alginate–TiO2 composite particles with densely packed TiO2 nanoparticles. Using a microfluidic device, monodisperse sodium alginate droplets containing low-density TiO2 nanoparticles (1 or 5 w/v%) were formed in the oil phase. The sodium alginate droplets formed in the oil phase were subsequently placed on a Ca2+-loaded agarose-gel plate to induce shrinkage by water removal (from the droplets to the Ca2+-loaded agarose-gel plate) and gelation by Ca2+ transport (from the Ca2+-loaded agarose-gel plate to the droplets). Thus, the produced alginate–TiO2 composite particles containing densely packed TiO2 nanoparticles were significantly smaller than the microchannel. We also investigated the optimal conditions to successfully produce spherical composite particles by varying the oil phases, surfactants, calcium concentrations and gel strength of the agarose-gel plate. Moreover, our method could decrease the probability of channel clogging that often occurs when a colloidal suspension (e.g., nanoparticles) is used as the dispersed phase. This method facilitates the stable production of monodisperse alginate–inorganic composite particles for a wide range of applications.

We describe a simple and robust technique for fabricating monodisperse Janus hydrogel beads with magnetic anisotropy smaller than the microchannel used to produce them.

We present a lithography-free procedure for fabricating intrinsically three-dimensional smooth-walled microchannels within poly(dimethylsiloxane) (PDMS) elastomer using hydrogel molds. In the fabrication process, small pieces of agarose gel ("wires" or "chips") are embedded in uncured PDMS composite, arranged in the shape of the desired microchannels, and used as molds to form the microchannels. The point of the process is that molds for creating junctions of microchannels such as T-junctions or cross-junctions can be robustly formed by simply grafting gel wires in uncured PDMS composite without using adhesive agents. The technical advantage of this method is that three-dimensional microstructures such as microchannels with circular cross sections, three-dimensionally arranged junctions or interchanges of microchannels can be flexibly designed and fabricated with a straightforward procedure without the need for any specialized equipment or layer-by-layer assemblage processes. This method provides a low-cost, green procedure for fabricating microfluidic devices and promises to make microfluidic processes more accessible and easy to implement in a variety of scientific fields.

In this study, we report the mass production of monodisperse emulsion droplets and particles using microfluidic large-scale integration on a chip. The production module comprises a glass microfluidic chip with planar microfabricated 16-256 droplet-formation units (DFUs) and a palm-sized stainless steel holder having several layers for supplying liquids into the inlets of the mounted chip. By using a module having 128 cross-junctions (i.e., 256 DFUs) arranged circularly on a 4 cm x 4 cm chip, we could produce droplets of photopolymerizable acrylate monomer at a throughput of 320.0 mL h(-1). The product was monodisperse, having a mean diameter of 96.4 microm, with a coefficient of variation (CV) of 1.3%. Subsequent UV polymerization off the module yielded monodisperse acrylic microspheres at a throughput of approximately 0.3 kg h(-1). Another module having 128 co-flow geometries could produce biphasic Janus droplets of black and white segments at 128.0 mL h(-1). The product had a mean diameter of 142.3 microm, with a CV of 3.3%. This co-flow module could also be applied in the mass production of homogeneous monomer droplets.

In order to form large micro-droplet-arrays, we have developed a device that can merge and transport microdroplets in two directions. Transportation of droplets is performed by electrostatic actuation technique. The speciality of this method is that it uses only one electrode panel, based on standard printed circuit board (PCB), and in it, only 18 independent controls are needed. We have also developed disposable plastic films cards, which can substantialy reduce the development cost because the actuation chip has been separated into two parts: a fixed electrode panel and a less costly removable card. The droplets array is formed and analyzed in the card.

A new dispenser made of Teflon that uses electrostatic manipulation technique to dispense nano-liter size droplets based on the electrostatic actuation mechanism has been developed. Two types of dispensers were developed, viz. a single-hole type (Teflon tube) and a multiple-hole dispenser (Teflon block). The single-hole type dispenser successfully dispensed droplets of a solution supplied by a syringe pump on an electrode panel surface; and thus the droplets become available for subsequent manipulation on the electrode panel. Based on the same principle, a compact Teflon block dispenser was designed that can simultaneously dispense five different solutions in a small area (30 mm). The size of dispensed droplets can be controlled by various factors, e.g., flow rate of solution, dispensing height, applied voltage, frequency of voltage pattern. We could dispense the droplets in the range of 55–210 ± 8 nL. This technique can be applied for automation of repetitive pipetting and screening operations in protein crystallization.

New methods for improving the quality of protein crystals are always being sought. Electric-field-induced protein crystallization is one of them. A few devices have already been developed. We conducted a series of experiments for several years and fabricated many electrode panels to realize a device for electric-field induced protein crystallization for the microbatch method. The review mainly deals with the application of the various devices that have so far been reported in the literature on the subject, including an overview of the work that has already been conducted. The factors affecting the electric-field-induced protein crystallization are also discussed.

In this paper, a method for fabricating a microfluidic valve made of polydimethylsiloxane (PDMS) using a rapid prototyping method for microchannels through hydrogel cast molding is discussed. Currently, the valves in microchannels play an important role in various microfluidic devices. The technology to prototype microfluidic valves rapidly is actively being developed. For the rapid prototyping of PDMS microchannels, a method that uses a hydrogel as the casting mold has been recently developed. This technique can be used to prepare a three-dimensional structure through simple and uncomplicated methods. In this study, we were able to fabricate microfluidic valves easily using this rapid prototyping method that utilizes hydrogel cast molding. In addition, we confirmed that the valve displacement could be predicted within a range of constant pressures. Moreover, because microfluidic valves fabricated using this method can be directly observed from a cross-sectional direction, we anticipate that this technology will significantly contribute to clarifying fluid behavior and other phenomena in microchannels and microfluidic valves with complex structures.

This paper reports the preparation of encapsulated particles as models of cells using an alternating droplet generation encapsulation method in which the number of particles in a droplet is controlled by a microchannel to achieve one-to-one encapsulation. Using a microchannel in which wettability is treated locally, the fluorescent particles used as models of cells were successfully encapsulated in uniform water-in-oil-in-water (W/O/W) emulsion droplets. Furthermore, 20% of the particle-containing droplets contained one particle. Additionally, when a surfactant with the appropriate properties was used, the fluorescent particles within each inner aqueous droplet were enclosed in the merged droplet by spontaneous droplet coalescence. This one-to-one encapsulation method based on alternating droplet generation could be used for a variety of applications, such as high-throughput single-cell assays, gene transfection into cells or one-to-one cell fusion.

A new scheme for the polymer beads production using a microfluidic technique is described. This technique is based on the fact that droplets formation at a junction in microchannels is caused by shear stress acting on the dispersed-phase flow by the continuous-phase flow. The Reynolds number in a microchannel was very low which indicated the flow in the microchannel was laminar, therefore, uniform droplet formation was generated. The diameter of the droplets is widely varied from 50% to 300% to the diameter of the dispersed phase flow. Various monomers were used as a dispersed phase, and aqueous solution of polyvinyl alcohol as a continuous phase. Droplets produced in the microchannel were introduced from the drain to the server, and then polymerized by the thermal polymerization method or photo polymerization method. The droplet diameter was monodisperse with CV of less than 5%. Various polymer beads were produced by changing the geometry of the microchannel structure. By using this technique, two colored polymer beads, with different electrical potential for the electronics paper, were produced. We are now approaching to the mass production of the two colored polymer beads which is used for the manufacturing of electronic papers.

A microfluidic device having both hydrophobic and hydrophilic components is exploited for production of multiple-phase emulsions. For producing water-in-oil-in-water (W/O/W) dispersions, aqueous droplets ruptured at the upstream hydrophobic junction are enclosed within organic droplets formed at the downstream hydrophilic junction. Droplets produced at each junction could have narrow size distributions with coefficients of variation in diameter of less than 3%. Control of the flow conditions produces variations in internal/external droplet sizes and in the internal droplet number. Both W/O/W emulsions (with two types of internal droplets) and oil-in-water-in-oil emulsions were prepared by varying geometry and wettability in microchannels.

A novel technique is described for preparing multiple polymeric microspheres of the same size. A monodisperse droplet suspension of an acrylic monomer was prepared in a T-shaped microchannel, and particles of accurately the same size were produced by subsequent polymerization. The droplet/particle size was varied flexibly in the range of diameters 30–120 μm by changing the flow conditions in a microfluidic device. The resulting products have a coefficient of variation (CV) below 2%. A diagram of the flow parameters showed a clear region in which monosized drops were formed successfully. Furthermore, using another microfluidic device, hemispherically colored acrylic microspheres of 90–190 μm in diameter were engineered with a coefficient of variation of less than 1%.

To develop a rapid bacterial testing device, a microfluidic PCR device was designed. We simulated temperature distribution in a microchannel, and measured the temperature control from thermoelectric elements. In addition, we fabricated and evaluated the microfluidic pneumatic valve device which is one of the fundamental elements on our PCR device. As a result, because the PCR temperature distribution along the microchannel was visualized, the thermoelectric elements could be controlled on the basis of the result. Fabricated pneumatic valve was also tested to control the fluid. These results allow one to fabricate microfluidic PCR device for rapid bacterial testing.

Much research on automation in agriculture has been presented in recent years at the annual meetings of the Japanese Society of Agricultural Machinery (JSAM). This research has been performed in universities and government institutes, and by agricultural machinery manufacturers. Because of funding limitations, research in universities has concentrated on methodologies, such as navigation, sensing, and application of control theory. Development of a one dimensional image sensor, and application of neural networks and genetic algorithms, has taken place at Hokkaido University; vision guidance and fuzzy logic application at the University of Tokyo; an automatic follow-up vehicle has been developed at Kyoto University; and an automatic transport vehicle at Ehime University. At research institutes and manufacturers, with their greater financial freedom, more practical systems have been developed. A tilling robot and a driver-less air blast sprayer is being developed in the Bio-oriented Technology Research Advancement Institute (BRAIN); and an autonomous rice planter, a tillage robot and autonomous forage tractor in the research institute of the Ministry of Agriculture, Forestry, and Fishery (MAFF). Kubota Co. Ltd has developed autonomous rice planting and husbandry vehicles. In Asian countries an autonomous speed sprayer is under study in Korea and an autonomous power sprayer in Taiwan, but little research is performed elsewhere in Asia.

A new device has been fabricated for electric field-induced protein crystallization with the microbatch method. In conjunction with this, a specialized tray using inexpensive plastic film has been developed for economical set-up of the experiments. Crystallization can be conducted using AC or DC voltage.

The use of wildflowers has become popular for creating aesthetic public landscaping. As weeding costs are rather expensive, automation of weeding would help reduce maintenance costs. In this study, as a step towards automation of weeding, identification of plants for wildflower gardens was performed by image processing. Shape feature analysis was applied to the binary images to identify the plant as one of four species (aster, pansy, treasure flower, and California Poppy). As features, roundness, first invariant central moment, area, and perimeter were studied for each plant type. Mahalanobis’ generalized distance was used in identification of the plants. The results showed that the best shape features for identifying these plants were roundness and first invariant central moment.

以上, キュウリに炭そ病菌を接種して人為的に可視害を作り, 自動診断システムを構築するために必要となる可視害の認識について, フィルター画像を用いて以下のことを実験し考察した.1.可視害部の識別に関してその識別しやすい波長を同定するために, (1) ？ƒk, (2) 画像のクラス分離度ηmax, (3) D.I.で評価した反射率で行い, この三つの評価量に共通して650nmのフィルター画像が認識に適していることが判明した.2.外界での診断に向けて環境条件を除去する基本的なフィルター情報融合法を検討した.これにより環境条件を除去して病気による反射率の変化を得る二つの波長情報はλ650とλ400かλ800であることが判明した.またλ800は反射率が高く葉脈の影響がλ400より強いため, 葉を認識しながら接近する際や比較的遠隔から葉脈に対する可視害部の位置を知りたい場合はλ800を選択し, 近接して可視害部を詳細に調べる時は葉脈の影響が小さいλ400が適すると考察した.問題点と今後の課題は,実際に光源変化や対象の傾きをつくり,環境条件が変化しても同じ診断が下せるよう今回の結果を用いて検証することである.対象である葉は風により静止していない上に外界では光源が太陽光となるために,可視害に至った葉の診断部を構築するためには葉の動きや測定距離にも対応した画像処理に改良していくことも必要である.立毛中の植物を外界で診断するためには上記のような天候・時刻に左右されない測定が可能となることがまず必要である.そして実際には環境ストレス,他の病気を原因とするストレスに植物が侵されると予想される.環境ストレスは主に水不足,土壌環境,日照不足に分けられる.水不足については,今回は800nmまでのフィルター画像しか得られなかったが,Fig.10より植物の水吸収帯が1,400nm付近にあることがわかるため,このフィルター画像を用いた含水診断を行えば良いのではないかと考えている.また他のものはそれぞれ土壌診断,天候のデータの使用により診断できると推測する.病害によるストレスに関しては,対象とした植物に対して発生しやすい病害を特定して基礎データを得て各病害の特徴を統計的に求め,Fig.1に示したように識別のしやすいものから診断することで原因の特定が可能になると考える.また室内で得られた病害のデータが自然界で発生する病害とは多少異なることが予想されるが,その点に関しては新たに得られたデータを入力していけば診断規準が変更できるよう自動診断を学習型とすることで対応できるのではないかと考えている.

The main goal of this study was to develop a method to diagnose when roots had sufficiently recovered from transplanting injury. Plant responses to light intensity, such as changes in stem diameter and vapour transpiration, were measured. The light intensity was varied by a pseudo random signal. Cross-correlation functions of light intensity and plant responses were calculated to understand the similarity of the response to the input quantitatively. The results showed that the recovery from the transplanting injury could be diagnosed when the response time lag of plant stem diameters from the top to the lower part of the plant approached the original pre-transplanting level.

本研究では, 植物の移植後における回復状態の判定法として, 植物の体内水分状態に着目し, 水ストレスを与えたときの葉温変動, 茎径変動の応答を計測し, 回復時と移植後の変化を評価した.その結果, 以下の結論を得た.1.光と各種応答との相互相関関数を求め, タイムラグを比較した結果, 茎径変化のタイムラグが移植前の値に収束することで回復状態を判定できることが判明した.2.茎径のステップ応答は, 根が回復するにつれて一次遅れ系からオーバーシュートを示す二次遅れ系に近い状態に変化することが確認された.3.葉温のステップ応答は, 根が回復するにつれて一次遅れ系から気孔開閉による振動現象が現れるようになることが確認された.4.回復状態の診断を定量的に示すには, 相互相関関数のタイムラグで評価することが最も良い方法であると考えられる.

We develop a novel technique for fabricating monodisperse Janus hydrogel beads with magnetic anisotropy smaller than the microchannel based on coagulation of Fe3O4 nanoparticles and shrinkage-gelation technique. This technique can avoid the problem of limits to the minimum biphasic droplet size due to the high risk of clogging, and the problem of a blurring boundary on fabricated Janus particles by convective mixing across the interface inside the biphasic droplets. Therefore, this technique has potential for the further development of electronic paper.

超音波によるトマト果実の熟度推定を行った結果以下の結論を得た.1.トマト果実の色が緑色の間は音速400m/s以下で一定であった.2.トマト果実の色が緑色から赤色に変化するにつれて, 音速が800m/s位まで上昇した.これにより, 果実の熟度判定を音速で行えるものと思われる.3.果実に亀裂が生じると音速は低下した.

We report a simple method for forming monodispersed, uniformly shaped gel microbeads with precisely controlled sizes. The basis of our method is the placement of monodispersed sodium alginate droplets, formed by a microfluidic device, on an agarose slab gel containing a high-osmotic-pressure gelation agent (CaCl(2) aq.): (1) the droplets are cross-linked (gelated) due to the diffusion of the gelation agent from the agarose slab gel to the sodium alginate droplets and (2) the droplets simultaneously shrink to a fraction of their original size (100 μm in diameter) due to the diffusion of water molecules from the sodium alginate droplets to the agarose slab gel. We verified the mass transfer mechanism between the droplet and the agarose slab gel. This method circumvents the limitations of gel microbead formation, such as the need to prepare microchannels of various sizes, microchannel clogging, and the deformation of the produced gel microbeads.

Mass culture of plant cell and tissues in a bioreactor are widely used for production of plant metabolites or seedlings. Packed Cell Volume (PCV) and Optical Density (OD) are used for off-line measurement, and Electric Conductivity (EC) and pH are used for on-line measurement of growth rate in bioreactors. In these measurement, the samples are derived from a part of a reactor, and these sample may not indicate the actual status of bioreactor, because the growth rate may change in height or radius of bioreactor.An ultrasonic technique was used to measure the growth rate in a bioreactor.The material used were plant cell of Rice plant (Oryza sativa), and adventive root of Atropa belladonna. The frequency of ultrasonic sensors were 0.5, 1, 2, 3, 5, and 7 MHz. It was found that the attenuation of ultrasonic wave propagated through the bioreactor had linear relation with the growth rate and that the stronger attenuations were measured in higher frequencies. The velocity of waves were almost constant with the growth rate. A simple model using a wave equation was used to simulate the attenuation of ultrasonic wave in the bioreactor, and the results showed good agreement with the experiment. The ultrasonic wave can propagate across the bioreactor, and it seems that the results correspond to the actual status of the bioreactor.

A method is given for generating droplets in a microchannel network. With oil as the continuous phase and water as the dispersed phase, pico/nanoliter-sized water droplets can be generated in a continuous phase flow at a -junction. The channel for the dispersed phase is 100 microm wide and 100 microm deep, whereas the channel for the continuous phase is 500 microm wide and 100 microm deep. For given experimental parameters, regular-sized droplets are reproducibly formed at a uniform speed. The diameter of these droplets is controllable in the range from 100-380 microm as the flow velocity of the continuous phase is varied from 0.01 m s(-1) to 0.15 m s(-1).

Two sorts of optimal control techniques, the modern control theory based on optimal regulator and the intelligent control based on neural network and genetic algorithm, were applied to the control of two physiological processes of plant, the water status to light intensity and the net photosynthetic rate to the drainage and supply of the nutrient solution in hydroponics, respectively. In the modern control, the ARMA model of the water status to light intensity was identified by using least squares method. The Kalman filter was used to estimate state variables. The covariance of the Kalman filter was decided by simulation. In the experiment, the ratio of the weight matrices were varied between 0.1 to 10.0. The optimal control performances showed good agreement with the simulation, and it showed good results for control of water status of plants. In the intelligent control, on the other hand, the neural network was used for the identification of the net photosynthetic rate to the drainage and supply of the solution, and the genetic algorithm was used for the search of optimal value through the model simulation. The three-layer neural network made it possible to identify the nonlinear behavior of the net photosynthetic rate to the drainage and supply. The use of genetic algorithm allowed to quickly search the optimal value of the drainage and supply times which maximizes the net photosynthetic rate through the model-simulation. The optimal value could be obtained within 5-generation when both rates of crossover and mutation take high values as 0.8 and 0.8, respectively. It was found that the optimal regulator is useful for the control of the plant water status to light intensity, and the combination of neural network and genetic algorithm is effective for the control of such complex process as net photosynthetic rate to the drainage of the solution

When quantitative analysis or quantitative chemical synthesis is performed using a micrototal analysis system (microTAS), the technologies for precise metering, transporting, and mixing of droplets are required. In this chapter, several technologies for the handling of droplets are described. For metering, dispensing and transporting of droplets, pneumatic and electrokinetic forces are used. Separation of cells and particles is also performed by electrical operation. Other handling technique, such as ultrasonic or centrifugal force applications, are also reviewed. Robotic synthesis devices or high throughput screening devices are promising applications for these technologies.

To control the water stress to the plant requires one of the advanced technologies for the greenhouse and the field cultivation. The highest quality of the crops is obtained when the optimal water stress is provided. In this study, the plant's responses to the randomly varying two levels of light intensity were measured, and the frequency characteristics of the plant were calculated. For the mathematical model of the plant, auto-regressive model (AR model) was assumed, and its parameters were identified. From this model, the simulation of the experiment and the frequency characteristics were calculated. The results of the simulation corresponded to those of the experiment. The step response of the lighting to the plant was also measured, and the frequency response functions were calculated. The frequency characteristics under random lighting condition, from step response, and by AR model showed good agreement. These results showed that the AR model would be a possible model to explain the plant responses.

In this work, we describe the synthesis of novel electrically and magnetically dual-driven Janus particles for a handwriting-enabled twisting ball display via the microfluidic technique. One hemisphere of the Janus particles contains a charge control agent, which allows the display color to be controlled by applying a voltage and superparamagnetic nanoparticles, allows handwriting by applying a magnetic field to the display. We fabricated a twisting ball display utilizing these Janus particles and tested the electric color control and handwriting using a magnet. As a result, the display was capable of permitting handwriting with a small magnet in addition to conventional color control using an applied voltage (80 V). Handwriting performance was improved by increasing the concentration of superparamagnetic nanoparticles and was determined to be possible even when 80 V was applied across the electrodes for 4 wt. % superparamagnetic nanoparticles in one hemisphere. This improvement was impossible when the concentration was reduced to 2 wt. % superparamagnetic nanoparticles. The technology presented in our work can be applied to low-cost, lightweight, highly visible, and energy-saving electronic message boards and large whiteboards because the large-size display can be fabricated easily due to its simple structure.

A microchemical reaction method involving microdroplets is proposed. Microdroplets are formed in a chemically stable medium on electric panel devices. These devices are substrates which have electrode arrays or electrode dots, and its surfaces are coated by an insulating film (such as Teflon or polypropylene) to prevent discharge and electrolysis of solutions. Microdroplets can be separately manipulated by a traveling electric field, which arises on applying a sequential voltage to the electrodes. Droplets moved smoothly at 1 Hz and voltage 400 V(0-p). Reagents were then put in droplets that were collided and coalesced, resulting in chemical reactions that included alkalization of phenolphthalein and the luciferin-luciferase reaction.

A bubble-based chemical reaction/analysis system is proposed that uses electrostatic micromanipulation. Micro/nanoliter-sized bubbles are set in a liquid layer below an electrode array device. The micro bubbles are manipulated smoothly by the electrostatic force generated by the electrode array. A chemical reaction between two gas reagents, exemplified by 2NO+O/sub 2//spl rarr/2NO/sub 2/, has been demonstrated.

We study the formation of micro droplets in confluent two-phase flows in a microfluidic system. Instability at the interface of two immiscible liquids undergoing laminar flow generates micro droplets of highly uniform size. Under high shear stress the droplets form rapidly, and more than 2000 droplets can be prepared of similar size. Droplet size can be controlled by varying the flow conditions. Also, the effect of tension at the interface is studied by comparing results from PMMA/glass devices. Monodisperse polymeric microspheres were successfully obtained by polymerization of prepared monomer droplets.

We have developed a new method to measure the hydraulic conductivity of cell membrane (L/sub p/), based on the principle that two liquids flow in laminar flow though relatively narrow space. The developed method has advantages that the number of the required cell sample is only one, and accurate measurement can be made as compare with the conventional method.

Feasibility study of PCR using electrostatic manipulation of micro droplets is discussed. Adherence of droplets to the surface has been a difficult hindrance to overcome when controlling PCR solution in liquid medium. Different types of medium immiscible with the droplets are tested and n-octane enables electrostatic manipulation of PCR droplets. The concept of a novel micro PCR device is proposed.

This paper presents a new method for preparing micro droplets inside the liquid layer at a T-junction in a microchannel network. The relations between droplet size, flow speed, and channel size are studied. The droplet size is easily varied by changing the flow conditions in the microchannels. The size distribution of the resulting droplets is very narrow.