<p>Conventional solution-phase synthesis of azo compounds is complicated by the need for precise pH and temperature control, high concentrations of pH control reagents, and by-product removal. The microdroplet synthesis method has solved these problems.</p>

This paper presents a method for utilizing three-dimensional microfluidic channels fully to realize multiple functions in a single device. The final device structure was achieved by combining three independent modules that consisted of horizontal and vertical channels. The device allowed for the one-step generation of water-in-oil-in-water droplets without the need for partial treatment of the polydimethylsiloxane channel surface using separate modules for generating water-in-oil droplets on the horizontal plane and oil-in-water droplets on the vertical plane. The second vertically structured module provided an efficient flow for the generation of highly wettable liquid droplets, and tuning of the first horizontally structured module enabled different modes of inner-core encapsulation within the oil shell. The successful integration of the vertical and horizontal channels for core-shell droplet generation and the chemical synthesis of a metal complex within the droplets were evaluated. The proposed approach of integrating independent modules will expand and enhance the functions of microfluidic platforms.

© 2018, The Author(s). In synthetic biology, the control of gene expression requires a multistep processing of biological signals. The key steps are sensing the environment, computing information and outputting products1. To achieve such functions, the laborious, combinational networking of enzymes and substrate-genes is required, and to resolve problems, sophisticated design automation tools have been introduced2. However, the complexity of genetic circuits remains low because it is difficult to completely avoid crosstalk between the circuits. Here, we have made an orthogonal self-contained device by integrating an actuator and sensors onto a DNA origami-based nanochip that contains an enzyme, T7 RNA polymerase (RNAP) and multiple target-gene substrates. This gene nanochip orthogonally transcribes its own genes, and the nano-layout ability of DNA origami allows us to rationally design gene expression levels by controlling the intermolecular distances between the enzyme and the target genes. We further integrated reprogrammable logic gates so that the nanochip responds to water-in-oil droplets and computes their small RNA (miRNA) profiles, which demonstrates that the nanochip can function as a gene logic-chip. Our approach to component integration on a nanochip may provide a basis for large-scale, integrated genetic circuits.

Bacterial persisters are phenotypic variants that survive the treatment of lethal doses of growth-targeting antibiotics without mutations. Although the mechanism underlying persister formation has been studied for decades, how the persister phenotype is switched on and protects itself from antibiotics has been elusive. In this study, we focused on the lactate dehydrogenase gene (ldhA) that was upregulated in an Escherichia coli persister-enriched population. A survival rate assay using an ldhA-overexpressing strain showed that ldhA expression induced persister formation. To identify ldhA-mediated persister formation at the single-cell level, time-lapse microscopy with a microfluidic device was used. Stochastic ldhA expression was found to induce dormancy and tolerance against high-dose ampicillin treatment (500 μg/ml). To better understand the underlying mechanism, we investigated the relationship between ldhA-mediated persister formation and previously reported persister formation through aerobic metabolism repression. As a result, ldhA expression enhanced the proton motive force (PMF) and ATP synthesis. These findings suggest that ldhA-mediated persister formation pathway is different from previously reported persister formation via repression of aerobic metabolism.

This paper presents mechanically reinforced low-concentration alginate fibers by embedding inner cores of high-concentration alginate. 3D structures by stacking multiple polydimethylsiloxane (PDMS) layers allow the microfluidic formation and control of the isolated cores in the continuous flow. The alginate hydrogel fibers are simply spun, and the compartments, central core, surrounding cores, and outer shell layer are successfully verified. The results demonstrate the great potential for the development of complex fibrous materials, particularly for biological applications, which require specific morphology and composition of the fibers.

In this paper, an investigation of a vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymer film for use in a nonpolarized energy harvester is presented. The Fourier transform infrared spectroscopy and X-ray diffraction analysis of a nonpolarized VDF/TrFE copolymer film indicate that polymer crystallinity depends on film thickness. Furthermore, the growth of the polar structure (β phase) is observed upon the reduction in the thickness. However, power generation does not exhibit a linear behavior because the generation capacity increases with the thickness. These results indicate that the film thickness for a nonpolarized harvester must be optimized to obtain the maximum output.

This paper presents the formation of complex cross-sectional microfibers using three-dimensional microfluidic devices. The compartments and shapes of core and shell layers in the microfibers were independently controlled via three-dimensional fluidic channels fabricated by the combination of sheath units. The number of layers is easily expanded by the stacking of these units. Therefore, the highly heterogeneous microfibers of alginate hydrogel are obtained in polydimethylsiloxane structures. This widely expandable method has great potential for the development of functional and complex fiber-shaped materials.

This paper presents the formation of complex cross-sectional microfibers using three-dimensional microfluidic devices. The compartments and shapes of core and shell layers in the microfibers were independently controlled via three-dimensional fluidic channels fabricated by the combination of sheath units. The number of layers is easily expanded by the stacking of these units. Therefore, the highly heterogeneous microfibers of alginate hydrogel are obtained in polydimethylsiloxane structures. This widely expandable method has great potential for the development of functional and complex fiber-shaped materials.

An ex vivo brain lactic acid (LA) monitoring system for investigating brain activity at the organ level was constructed and tested in continuous LA monitoring. Our system consists of a micro-fluidic dual-analyte (LA and glucose) biosensor and a special brain chamber that is suitable for organ level experiments. The biosensor utilizes the redox reactions of osmium-wired horseradish peroxidase (Os-HRP) to detect hydrogen peroxide produced by enzyme reactions. The sensor had sufficient sensitivity (LA: ∼ 0.01 mM, glucose: ∼ 0.01 mM) and selectivity for assessment of extracellular LA. The ex vivo monitoring of brain LA was performed using the proposed system. As a result, the change in extracellular LA was successfully monitored continuously, and the change in the LA level was considered the result of metabolic activity of the sample. Our system is expected to be useful not only for ex vivo brain monitoring, but also for monitoring other organs.

<p>A new fabrication process of a superrepellent surface using a doubly reentrant structure pillar array was developed. The proposed process applying a soft-lithography is simple, low-cost, and mass-productive process compared to the conventional process. It enables to fabricate a doubly reentrant structure pillar array on glass, silicon, and PDMS substrates.</p>

A fully passive volume-dependent droplet sorter is presented in this research. Repeated and multiple on-rail transfer of microdroplets in a cascade channel resulted in high resolution sorting of droplet-phase samples. Microdroplets with volumes of 0.89-3.26 nl were successfully sorted in eight steps, and a maximum sorting resolution of about 0.21 nl was obtained over three transfer stages. Line rails and dot rails employed in the cascading channels allowed volume-dependent droplet transfer, and shape recovery of the transferred droplet for the repeatable transfer, respectively. This simple device and method can be applied to droplet-based chemical or biological research.

This study describes the synthesis of an azo-Mn(II) complex requiring an accurate pH control. The reaction conditions for the delicate azo-Mn(II) complex could be precisely controlled using a microfluidic device. The microfluidic method showed the following advantages over the conventional method: the concentration of the pH-control reagent was reduced (1/15), the reaction time was remarkably decreased from 4 h to less than 1 s, and the reaction temperature was lowered from 40 to 23 degrees C. Moreover, the microfluidic device suppressed the oxidation of the compound and did not require cooling to remove the heat of reaction. In addition, the conventional method uses harsh pH control, whereas the microfluidic device permits mild pH control.

A simple printing process to design a novel piezoelectric energy-harvesting device made from vinylidene fluoride/trifluoroethylene copolymers is presented. Fabrication using a metal nanoink and a household printer dramatically reduced the fabrication complexity. In addition, this process employed low-temperature steps, and thus the structural damage to the polymers resulting from high-temperature annealing was avoided. By stacking the devices and connecting them in parallel, the generated energy was increased and electric power of approximate to 1.12 J was obtained.

This study reports a fast and quantitative determination method for phenylalanine (Phe) and tyrosine (Tyr) in human plasma using on-chip pressure-driven liquid chromatography. A pillar array column with low-dispersion turns and a gradient elution system was used. The separation of fluorescent derivatives of Phe, Tyr, and other hydrophobic amino acids was successfully performed within 140 s. Under the optimized conditions, Phe and Tyr in human plasma were quantified. The developed method is promising for rapid diagnosis in the clinical field.

A microfluidic stamping method to form functional shapes on a cross section in fibre-shaped flow is presented by D. H. Yoon and co-workers on page 3224. Microfluidic stamping and overstamping allowed various cross sectional shapes on the three-dimensional flow. Dimension of the flows is controlled via a change in combination of 3D structures and fluidic conditions, which correspond to stamp type and stamping force.

To realize efficient, fast separations on pillar array columns with turns, a novel turn with low-dispersion and low-pressure-drop properties was developed. This "pillar-distribution controlled" (PDC) turn was designed as a constant-radius-turn filled with octagonal pillars that were arranged to control the linear velocity of the mobile phase in the radial direction. After the pillar positions were adjusted by computational fluid dynamics analysis, 27 mm long pillar array columns with two turns were fabricated on a 20 x 20 mm(2) silicon glass plate. The PDC turns suppressed the sample dispersion to a similar extent as the previously developed tapered turn, and the pressure drop of the newly designed turn was reduced to similar to 1/6 that of the tapered turn. Moreover, the C18-modified pillar array column with the PDC turns showed good bioanalytical applicability; five fluorescendy labeled amino acids were separated in only 24 s at a linear velocity of 7.5 mm/s. The developed turn structure offers the advantages of longer pillar array columns with more turns for the fast analysis of complex samples.

To realize efficient, fast separations on pillar array columns with turns, a novel turn with low-dispersion and low-pressure-drop properties was developed. This "pillar-distribution controlled" (PDC) turn was designed as a constant-radius-turn filled with octagonal pillars that were arranged to control the linear velocity of the mobile phase in the radial direction. After the pillar positions were adjusted by computational fluid dynamics analysis, 27 mm long pillar array columns with two turns were fabricated on a 20 x 20 mm(2) silicon glass plate. The PDC turns suppressed the sample dispersion to a similar extent as the previously developed tapered turn, and the pressure drop of the newly designed turn was reduced to similar to 1/6 that of the tapered turn. Moreover, the C18-modified pillar array column with the PDC turns showed good bioanalytical applicability; five fluorescendy labeled amino acids were separated in only 24 s at a linear velocity of 7.5 mm/s. The developed turn structure offers the advantages of longer pillar array columns with more turns for the fast analysis of complex samples.

A microfluidic stamping method to form functional shapes on a cross section in fiber-shaped flow is proposed. Microfluidic stamping and overstamping allow various cross sectional shapes on the 3D flow. The shapes can be controlled by a change in combination of structures and fluidic conditions which correspond to stamp type and stamping force.

Environmental microbes are a great source of industrially valuable enzymes with potent and unique catalytic activities. Unfortunately, the majority of microbes remain unculturable and thus are not accessible by culture-based methods. Recently, culture-independent metagenomic approaches have been successfully applied, opening access to untapped genetic resources. Here we present a methodological approach for the identification of genes that encode metabolically active enzymes in environmental microbes in a culture-independent manner. Our method is based on activity-based single-cell sequencing, which focuses on microbial cells showing specific enzymatic activities. First, at the single-cell level, environmental microbes were encapsulated in water-in-oil microdroplets with a fluorogenic substrate for the target enzyme to screen for microdroplets that contain microbially active cells. Second, the microbial cells were recovered and subjected to whole genome amplification. Finally, the amplified genomes were sequenced to identify the genes encoding target enzymes. Employing this method, we successfully identified 14 novel beta-glucosidase genes from uncultured bacterial cells in marine samples. Our method contributes to the screening and identification of genes encoding industrially valuable enzymes.

Environmental microbes are a great source of industrially valuable enzymes with potent and unique catalytic activities. Unfortunately, the majority of microbes remain unculturable and thus are not accessible by culture-based methods. Recently, culture-independent metagenomic approaches have been successfully applied, opening access to untapped genetic resources. Here we present a methodological approach for the identification of genes that encode metabolically active enzymes in environmental microbes in a culture-independent manner. Our method is based on activity-based single-cell sequencing, which focuses on microbial cells showing specific enzymatic activities. First, at the single-cell level, environmental microbes were encapsulated in water-in-oil microdroplets with a fluorogenic substrate for the target enzyme to screen for microdroplets that contain microbially active cells. Second, the microbial cells were recovered and subjected to whole genome amplification. Finally, the amplified genomes were sequenced to identify the genes encoding target enzymes. Employing this method, we successfully identified 14 novel beta-glucosidase genes from uncultured bacterial cells in marine samples. Our method contributes to the screening and identification of genes encoding industrially valuable enzymes.

Previously, we have developed a gradient elution system for pillar array columns, which achieved faster separation than isocratic elution. In this study, we validated gradient elution in microchip liquid chromatography (LC) and investigated the retention and bandwidth predictions of fluorescently labeled aliphatic amines in fast gradient elution chromatography using semi-empirical retention models. The retention times and peak widths under different gradient elution programs were predicted by three solvent strength models and compared with the experimental results. The relative errors of prediction for the retention times and peak widths were below 14 % and 12 %, respectively. The results showed that the solvent strength models could be utilized for predicting the retention times and peak widths under gradient elution in the microchip LC system and that the gradient elution program for pillar array columns worked efficiently. The prediction by the retention model promises to be a potential tool for essential compound identification in biological samples.

Efficient microfluidic synthesis of chiral salen Mn(II) and Co(II) complexes containing lysozyme was achieved. The reaction conditions for the delicate protein were controlled precisely with a separation barrier in the microfluidic device. The microfluidic method has the following advantages over the conventional method: a remarkable reduction in the reaction time from 4.5 h to less than 1 s for the synthesis of Mn(II) and Co(II) complexes, a reduction in the reaction temperature from 40 to 23 degrees C, and no need for an N-2 atmosphere because all the reagents are isolated from the air. A three-fold yield improvement was achieved for Mn(II) and Co(II) complexes containing lysozyme compared with conventional synthesis.

This research proposed a sheath flow formation method for complex 3D structure such as multi-core and multi-sheath using multi-stacked PDMS units. Cross sectional shape of the flow and the number of sheath layer were defined simply by combination of different PDMS units. The stacked PDMS units allowed independent fluid injection of different layers and the short sheath area realized low diffusion between each layer. Furthermore, the proposed 3D device fabrication method requires only one point alignment. The sheath flow formation method is useful for wide applications which require fiber materials of specific cross sectional shapes and layers.

Efficient microfluidic synthesis of chiral salen Mn(II) and Co(II) complexes containing lysozyme was achieved. The reaction conditions for the delicate protein were controlled precisely with a separation barrier in the microfluidic device. The microfluidic method has the following advantages over the conventional method: a remarkable reduction in the reaction time from 4.5 h to less than 1 s for the synthesis of Mn(II) and Co(II) complexes, a reduction in the reaction temperature from 40 to 23 degrees C, and no need for an N-2 atmosphere because all the reagents are isolated from the air. A three-fold yield improvement was achieved for Mn(II) and Co(II) complexes containing lysozyme compared with conventional synthesis.

Previously, we have developed a gradient elution system for pillar array columns, which achieved faster separation than isocratic elution. In this study, we validated gradient elution in microchip liquid chromatography (LC) and investigated the retention and bandwidth predictions of fluorescently labeled aliphatic amines in fast gradient elution chromatography using semi-empirical retention models. The retention times and peak widths under different gradient elution programs were predicted by three solvent strength models and compared with the experimental results. The relative errors of prediction for the retention times and peak widths were below 14 % and 12 %, respectively. The results showed that the solvent strength models could be utilized for predicting the retention times and peak widths under gradient elution in the microchip LC system and that the gradient elution program for pillar array columns worked efficiently. The prediction by the retention model promises to be a potential tool for essential compound identification in biological samples.

This paper presents a simple printing process to design a novel piezoelectric energy harvest device made from (VDF/TrFE) copolymers. The fabrication process using metal nano-ink and a household printer dramatically reduced the fabrication complexity. Additionally, this process employed low temperatures and thus the structural damage of the polymers resulting from high temperature annealing could be avoided. An electric power of about 0.06 mu J was generated using this device.

We conducted an experiment on the fabrication of fluidic devices for producing fine droplets. In our proposed method, multiple channels were fabricated by using a focused ion beam (FIB) system. The minimum feature top width was found to be approximately 56 nm. When both the target width and depth of one channel were set to 500 nm, the resultant top width was 750-780 nm, the bottom width was 250-320 nm, and the depth was 560 nm, almost achieving the target size for the channel depth.

This paper proposes a high-throughput, function-based screening approach of a metagenomic library for isolating novel microbial enzymes by droplet-based microfluidics. We used gel microdroplets (GMDs) dispersed in oil as picoliter-volume reaction vessels for lipolytic enzyme by encapsulating cells in individual GMDs. Using this approach, we monitored the growth of individual cells encapsulated in GMDs and assessed the enzyme reaction activities at the level of an individual GMD. We then applied this method to screen lipolytic enzyme genes from the metagenomic library constructed from soil collected from a quercus serrate forest of Mount Tsukuba, Ibaraki, Japan. In the workflow presented in this study, metagenomic library clones were encapsulated in 100-pL GMDs with a fluorogenic reporter substrate. A total of 67,000 metagenomic library clones can be screened in only 24 h with reduced consumption of reagents (i.e., &lt; 10 mu L). As a result, we identified a novel lipolytic enzyme, EstT1, belonging to the EstD2 family of esterases and containing a putative signal peptide, which facilitates enzyme export and catalyzation of substrates in the periplasm. Our study demonstrates the potential of microfluidic GMDs as an efficient tool for metagenomic library screening of industrially relevant enzymes with the potential of significantly reducing the cost and time factors involved in successful practical application of microbial enzymes. (C) 2014 Elsevier B.V. All rights reserved.

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 mu m. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

This paper proposes a high-throughput, function-based screening approach of a metagenomic library for isolating novel microbial enzymes by droplet-based microfluidics. We used gel microdroplets (GMDs) dispersed in oil as picoliter-volume reaction vessels for lipolytic enzyme by encapsulating cells in individual GMDs. Using this approach, we monitored the growth of individual cells encapsulated in GMDs and assessed the enzyme reaction activities at the level of an individual GMD. We then applied this method to screen lipolytic enzyme genes from the metagenomic library constructed from soil collected from a quercus serrate forest of Mount Tsukuba, Ibaraki, Japan. In the workflow presented in this study, metagenomic library clones were encapsulated in 100-pL GMDs with a fluorogenic reporter substrate. A total of 67,000 metagenomic library clones can be screened in only 24 h with reduced consumption of reagents (i.e., &lt; 10 mu L). As a result, we identified a novel lipolytic enzyme, EstT1, belonging to the EstD2 family of esterases and containing a putative signal peptide, which facilitates enzyme export and catalyzation of substrates in the periplasm. Our study demonstrates the potential of microfluidic GMDs as an efficient tool for metagenomic library screening of industrially relevant enzymes with the potential of significantly reducing the cost and time factors involved in successful practical application of microbial enzymes. (C) 2014 Elsevier B.V. All rights reserved.

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 mu m. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

We report a real time method to monitor the chemical reaction in microdroplets, which contain an organic dye, 5(6)-carboxynaphthofluorescein and a CdSe/ZnS quantum dot using fluorescence spectra. Especially, the relationship between the droplet size and the reaction rate of the two reagents was investigated by changing an injection speed.

We report a real time method to monitor the chemical reaction in microdroplets, which contain an organic dye, 5(6)-carboxynaphthofluorescein and a CdSe/ZnS quantum dot using fluorescence spectra. Especially, the relationship between the droplet size and the reaction rate of the two reagents was investigated by changing an injection speed.

We report a real time method to monitor the chemical reaction in microdroplets, which contain an organic dye, 5(6)-carboxynaphthofluorescein and a CdSe/ZnS quantum dot using fluorescence spectra. Especially, the relationship between the droplet size and the reaction rate of the two reagents was investigated by changing an injection speed.

This paper presents a droplet sampling device driven by horizontal pneumatic actuators. A high aspect ratio and highly flexible PDMS (polydimethylsiloxane) structure was proposed for carrying out larger number of sampling than the number of actuators. Large deformation of the actuators caused domino-deformation of parallel walls, and the deformations allowed for selective collection of target droplets. The dimensions of the PDMS structure and the ratio of resin to curing agent were optimized for efficient sampling under the low pressure applied to the actuators. Five sampling modes were achieved in the simple one-layer structure consisting of one inlet, four walls, one drain channel, and two pneumatic actuators, formed by single-step soft lithography process.

This research presents efficient coaxial sheath flow formation using a three-dimensional PDMS device. In the device, one core and five sheaths are simply formed with low diffusion between different samples. Stacking and alignment of six PDMS layers of same structure allowed for fabrication of the proposed 3D device. Only one point alignment of center channel for the sheath provides free from misalignment that was a critical problem of multi-stacked PDMS device. Furthermore, the number of samples is infinitely expandable by increase in the number of stacking layers. The coaxial sheath flow is useful for biological fiber formation which requires multilayer of different materials such as artificial blood vessels or muscles.

This paper reports a highly controllable three-dimensional (3D) sheath flow device for fabrication of artificial capillary vessels. Three step sheath injection type 3D flow device which realizes wide core and sheath structure variations by simply flow rate control was applied to fabricate double-layer coaxial Core-Sheath microfibers applicable for long micro capillary vessels by aligning and cultivating vascular endothelial cells. As a result, about a 3-centimeter-long microfiber which has the vascular endothelial cells fused mutually in the center was successfully formed after three days culture.

This paper presents a droplet sampling device driven by horizontal pneumatic actuators. A high aspect ratio and highly flexible PDMS (polydimethylsiloxane) structure was proposed for carrying out larger number of sampling than the number of actuators. Large deformation of the actuators caused domino-deformation of parallel walls, and the deformations allowed for selective collection of target droplets. The dimensions of the PDMS structure and the ratio of resin to curing agent were optimized for efficient sampling under the low pressure applied to the actuators. Five sampling modes were achieved in the simple one-layer structure consisting of one inlet, four walls, one drain channel, and two pneumatic actuators, formed by single-step soft lithography process.

High-efficient synthesis of Mn(II) and Co(II) complexes containing lysozyme using a reaction area-separated-type microfluidic device was realized.
The proposed method has the following advantages compared to the conventional method: reduction of reaction temperature from 40 degrees C to 23 degrees C; remarkable reduction of reaction time from 4 hours to less than 1 second for synthesis of Mn(II) and Co(II) complexes; and atmosphere control (in N-2) of the previous steps is not required because all reagents are isolated from the air.
A three-fold yield improvement was achieved in the synthesis of metal complexes containing lysozyme.

We report a novel real-time method to monitor the reaction of an organic dye, 5(6)-carboxynaphthofluorescein succinimidyl ester and a CdSe/ZnS quantum dot (QD) using fluorescence spectra of microdroplets formed in a microfluidic device. Dual fluorescence peaks (at lambda = 605 and 670 nm) were observed via a fluorescence energy transfer (FRET) process from the CdSe/ZnS QD to the organic dye; the rate of the chemical reaction of the two reagents was estimated by the ratio of the two fluorescence peaks, defined as the fluorescence intensity ratio. In addition, well-controlled microdroplets were continuously generated (with a diameter of similar to 150 mu m) in the microfluidic device and the reaction time was determined as the length from the mixing point to the sampling point using fluorescence spectroscopy. The fluorescence intensity ratio increased with increasing reaction time after mixing of the two reagents indicating that the chemical reaction was observed directly in the microdroplet. Therefore, the real-time monitoring of the chemical reaction was successfully achieved by measuring the fluorescence intensity ratio as a function of the reaction time. When compared with a conventional batch process, a fast reaction time of &lt;1 s and a high fluorescence intensity ratio was achieved in the microdroplets formed in the microfluidic device. (C) 2014 Elsevier B.V. All rights reserved.

We report a novel real-time method to monitor the reaction of an organic dye, 5(6)-carboxynaphthofluorescein succinimidyl ester and a CdSe/ZnS quantum dot (QD) using fluorescence spectra of microdroplets formed in a microfluidic device. Dual fluorescence peaks (at lambda = 605 and 670 nm) were observed via a fluorescence energy transfer (FRET) process from the CdSe/ZnS QD to the organic dye; the rate of the chemical reaction of the two reagents was estimated by the ratio of the two fluorescence peaks, defined as the fluorescence intensity ratio. In addition, well-controlled microdroplets were continuously generated (with a diameter of similar to 150 mu m) in the microfluidic device and the reaction time was determined as the length from the mixing point to the sampling point using fluorescence spectroscopy. The fluorescence intensity ratio increased with increasing reaction time after mixing of the two reagents indicating that the chemical reaction was observed directly in the microdroplet. Therefore, the real-time monitoring of the chemical reaction was successfully achieved by measuring the fluorescence intensity ratio as a function of the reaction time. When compared with a conventional batch process, a fast reaction time of &lt;1 s and a high fluorescence intensity ratio was achieved in the microdroplets formed in the microfluidic device. (C) 2014 Elsevier B.V. All rights reserved.

An electrohydrodynamic (EHD) ion-drag micropump using three-dimensional carbon micromesh electrodes was developed. The carbon micromesh electrodes were created by the pyrolysis of SU-8 structures. The carbon electrodes and microchannel were formed on a quartz substrate, and the microchannel was sealed by an SU-8 slab structure. The pumping behaviors were evaluated using Fluorinert as a non-conductive sample solution. The maximum pressure and volume flow rate were approximately 23 Pa and 400 nL/min, respectively, under an applied voltage of 500 V.

This paper describes a microdroplet merging device that can actively control the merging of various droplets under a wide range of flow conditions, using a simple structure. The microdroplets were trapped and merged in a wide chamber divided by pillars, and their behavior was controlled by two horizontal pneumatic microactuators. Hydrodynamic flow control by the actuation was evaluated numerically, and the trapping and merging of droplets were achieved experimentally and controlled via pressure applied to the microactuators. Furthermore, two independently generated droplets were merged under four different modes, ranging from no merging to four-droplet merging, with different ratios and volumes. The pneumatic actuators allowed not only the control of the number of merged droplets, but also a wide range of applied droplet volumes. The device was fabricated simply using a single-layer PDMS (polydimethylsiloxane) structure, and the continuous merging performance operated using only hydrodynamic flow control without any surfactant. Finally, chemical synthesis of a metal complex was performed by the droplet merging method. Crystallization of the complex was visualized in real time, and the synthesis was verified by ultraviolet-visible spectroscopy. © 2014 the Partner Organisations.

This paper describes a microdroplet merging device that can actively control the merging of various droplets under a wide range of flow conditions, using a simple structure. The microdroplets were trapped and merged in a wide chamber divided by pillars, and their behavior was controlled by two horizontal pneumatic microactuators. Hydrodynamic flow control by the actuation was evaluated numerically, and the trapping and merging of droplets were achieved experimentally and controlled via pressure applied to the microactuators. Furthermore, two independently generated droplets were merged under four different modes, ranging from no merging to four-droplet merging, with different ratios and volumes. The pneumatic actuators allowed not only the control of the number of merged droplets, but also a wide range of applied droplet volumes. The device was fabricated simply using a single-layer PDMS (polydimethylsiloxane) structure, and the continuous merging performance operated using only hydrodynamic flow control without any surfactant. Finally, chemical synthesis of a metal complex was performed by the droplet merging method. Crystallization of the complex was visualized in real time, and the synthesis was verified by ultraviolet-visible spectroscopy.

This paper describes a microdroplet merging device that can actively control the merging of various droplets under a wide range of flow conditions, using a simple structure. The microdroplets were trapped and merged in a wide chamber divided by pillars, and their behavior was controlled by two horizontal pneumatic microactuators. Hydrodynamic flow control by the actuation was evaluated numerically, and the trapping and merging of droplets were achieved experimentally and controlled via pressure applied to the microactuators. Furthermore, two independently generated droplets were merged under four different modes, ranging from no merging to four-droplet merging, with different ratios and volumes. The pneumatic actuators allowed not only the control of the number of merged droplets, but also a wide range of applied droplet volumes. The device was fabricated simply using a single-layer PDMS (polydimethylsiloxane) structure, and the continuous merging performance operated using only hydrodynamic flow control without any surfactant. Finally, chemical synthesis of a metal complex was performed by the droplet merging method. Crystallization of the complex was visualized in real time, and the synthesis was verified by ultraviolet-visible spectroscopy.

The effect of the annealing temperature on the magnetostrictive properties of Fe–Co alloy thin films on quartz glass was systematically investigated. The saturation magnetostriction was 56 ppm for the Fe32Co68-sputtered thin film quenched from 673 K, and it increased to 159 ppm with increasing annealing temperature up to 1073 K. The magnetostriction above 1093 K significantly decreased with the emerging fcc phase in the Fe–Co alloy. SEM images showed that the crystal grains present in the fcc phase aggregated to form a discontinuous surface, which resulted in a decrease in the effective magnetostriction. Measurements of the magnetic properties by vibrating sample magnetometer and magnetic force microscopy revealed the enhancement of the magnetization at the crystal grain boundaries of Fe–Co alloy thin films with large magnetostriction. Thus, the heterogeneity of the magnetization can play a key role in inducing the large magnetostrictive effect.

The effect of the annealing temperature on the magnetostrictive properties of Fe–Co alloy thin films on quartz glass was systematically investigated. The saturation magnetostriction was 56 ppm for the Fe32Co68-sputtered thin film quenched from 673 K, and it increased to 159 ppm with increasing annealing temperature up to 1073 K. The magnetostriction above 1093 K significantly decreased with the emerging fcc phase in the Fe–Co alloy. SEM images showed that the crystal grains present in the fcc phase aggregated to form a discontinuous surface, which resulted in a decrease in the effective magnetostriction. Measurements of the magnetic properties by vibrating sample magnetometer and magnetic force microscopy revealed the enhancement of the magnetization at the crystal grain boundaries of Fe–Co alloy thin films with large magnetostriction. Thus, the heterogeneity of the magnetization can play a key role in inducing the large magnetostrictive effect.

This paper presents a multiple size-oriented passive droplet sorting utilizing a balance between surface free energy and flow force. We proposed a simple multi-stage sorting structure which consists of a microchannel and guide grooves formed in parallel. Passive five different-sized droplets sorting of up to 200 droplets/s is achieved without any active elements. Also, we fabricated a prototype of the integrated micro fluidic system for droplet generation, merging and sorting for digital chemical synthesis.

A hydrodynamic droplet pass filter for droplet-phase sample sorting was developed in this study. Using only groove rails, without additional components or external controls, droplets were sorted based on their physical properties. This is the first report of a droplet pass filter used for effective sorting, and the sorting structure provides a novel fluidic component for fluidic circuits for many applications. Depending on the number of rails, we obtained high-pass, low-pass, band-pass, and multi band-pass filters for sorting droplet samples, and their filtration performance was controlled by varying the dimensions of the rail structures. We evaluated in detail the effect of the rail width on sorting, threshold size of droplets sorted into each rail, and capillary number-dependent sample sorting. Furthermore, band-pass droplet sorting, useful for sample quantification, was provided, and multi-step rail ways allowed multi band-pass droplet sorting that was independent of flow conditions. The proposed sorting method does not require any external systems or skilled operation, and thus, it is expected that the device can contribute to on-site sample treatment and analysis in various fields such as medical care or the military.

In this study, a fast and quantitative determination method for branched-chain amino acids (BCAAs), namely leucine, isoleucine, and valine, was developed using a pillar array column. A pillar array column with low-dispersion turns was fabricated on a 20 x 20-mm(2) microchip using multistep ultraviolet photolithography and deep reactive ion etching. The BCAAs were fluorescently labeled with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), followed by reversed-phase separation on the pillar array column. The NBD derivatives of the three BCAAs and an internal standard (6-aminocaproic acid) were separated in 100 s. The calibration curves for the NBD-BCAAs had good linearity in the range of 0.4-20 mu M, using an internal standard. The intra- and interday precisions were found to be in the ranges of 1.42-3.80 and 2.74-6.97 %, respectively. The accuracies for the NBD-BCAA were from 90.2 to 99.1 %. The method was used for the analysis of sports drink and human plasma samples. The concentrations of BCAAs determined by the developed method showed good agreements with those determined using a conventional high-performance liquid chromatography system. As BCAAs are important biomarkers of some diseases, these results showed that the developed method could be a potential diagnostic tool in clinical research.

This paper presents a microfluidic system for the active and precise control of microdroplet division in a micro device. Using two horizontal pneumatic valves formed at downstream of bifurcating microchannel, flow resistances of downstream channels were variably controlled. With the resistance control, volumetric ratio of downstream flows was changed and water-in-oil microdroplets were divided into two daughter droplets of different volume corresponding to the ratio. The microfluidic channels and pneumatic valves were fabricated by single-step soft lithography process of PDMS (polydimethylsiloxane) using SU-8 mold. A wide range control of the daughter droplets' volume ratio was achieved by the simple channel structure. Volumetric ratio between large and small daughter droplets are ranged from 1 to 70, and the smallest droplet volume of 14 pL was obtained. The proposed microfluidic device is applicable for precise and high throughput droplet based digital synthesis.

We present an active droplet merging device, which can merge various sizes of micro droplets in different numbers by using pneumatically controlled horizontal PDMS microvalves. The merging part consists of a main and side channels separated by a pillar array. The pillar array structure is contained within a microfuidic channel. The function of the pillar array provides a bypass path to the continuous flow (oil) inside the merging chamber. Droplets are successfully generated within the channel and achieve merging by controlling the selective different numbers and diameters of droplets through varying the flow resistance of main and side channel. In the merging chamber, a droplet will enter and slow down its movement. It will wait and then merge with the sequential droplets. These experiments demonstrate that such a merging device can controllably select and adjust the distance between the different adjacent micro droplets without any generation of sister droplets in the side channel. The device has no desynchronization problems. Thus, it can be applied for efficiently mixing the droplets in various diameters and numbers without changing the structure of the merging chamber. Hence, this device can be a more effective choice when applying microfluidics to chemical and biological applications.

Live-cell imaging of inflammatory cytokine secretion from human monocytes was successfully performed on a microfabricated well array chip by time-resolved fluoroimmunoassay using total internal reflection fluorescence microscopy. The system enabled to monitor secretion activity from tens of cells at a time resolution of 1 min. We first observed the close correlation between the loss of cell membrane integrity and "non-classical secretion" of IL-1β cytokine of inflammasome activated human peripheral monocytes.

MEMS liquid chromatography (LC) microchip with low dispersion and a low pressure drop turn structure was fabricated. In the turn structure, we used higher density pillar array at the inner side while lower density pillar array was used at the outer side to control inner and outer speed of a sample flow. An LC chip with an improved turn structure can obtain similar theoretical plate number (1233) compared to the previously proposed tapered turn (1135). The necessary inlet pressure is also reduced from 2.7 to 0.4 MPa under a flow rate of 10 mu L/min. These results show the improved turn structure is applicable for fast analysis time under high flow rate conditions.

We present an active droplet merging device, which can merge various sizes of micro droplets in different numbers by using pneumatically controlled horizontal PDMS microvalves. The merging part consists of a main and side channels separated by a pillar array. The pillar array structure is contained within a microfuidic channel. The function of the pillar array provides a bypass path to the continuous flow (oil) inside the merging chamber. Droplets are successfully generated within the channel and achieve merging by controlling the selective different numbers and diameters of droplets through varying the flow resistance of main and side channel. In the merging chamber, a droplet will enter and slow down its movement. It will wait and then merge with the sequential droplets. These experiments demonstrate that such a merging device can controllably select and adjust the distance between the different adjacent micro droplets without any generation of sister droplets in the side channel. The device has no desynchronization problems. Thus, it can be applied for efficiently mixing the droplets in various diameters and numbers without changing the structure of the merging chamber. Hence, this device can be a more effective choice when applying microfluidics to chemical and biological applications.

Multiple core-sheath flow was realized using matrix arrangement of 3D sheath flows. The sheath flow was hydrodynamically formed in a flow shift area which has symmetrical microgrooves on channel walls. Vertical and horizontal alignments of the sample streams are a key element of matrix configuration. The flow shift areas were connected in parallel to achieve horizontal alignment of the sheath flow. The cascade connection of the flowshift areas is used for vertical alignment of the sheath flow. In order to achieve matrix arrangement of core-sheath flow, combination of the parallel and cascade connections was utilized. In this work, the horizontal and vertical configurations of the 2-sample sheath flow were demonstrated. Two streams of the vertically aligned 2-sample sheath flow were joined horizontally, and, as a result, 4-sample core-sheath flow of matrix configuration was obtained successfully.

Electrical resistivity measurements in the temperature range from 6 to 300K were carried out in order to investigate the effects of the hydrogen absorption on the transport properties of Ni36Nb24Zr40 amorphous alloy ribbon. The electrical resistivity basically behaved negative temperature dependence in all prepared specimens of (Ni0.36Nb 0.24Zr0.40)100-xHx with 0 ≤ x &lt
15. The absolute value of temperature coefficient of the resistivity, TCR, increased with increasing the amount of the absorbed hydrogen. In addition, it was also clear that the electrical resistivity gradually increased with the time just after electrochemically charging, and tended to saturate after about 800 ks at 300 K. The behavior of the gradual increase in the electrical resistivity with the time was explained by the model including two kinds of the relaxation times, being associated with the migration of the hydrogen from the sample surface. © 2013 The Japan Institute of Metals and Materials.

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A gradient elution system for pressure-driven liquid chromatography (LC) on a chip was developed for carrying out faster and more efficient chemical analyses. Through computational fluid dynamics simulations and an experimental study, we found that the use of a cross-Tesla structure with a 3 mm mixing length was effective for mixing two liquids. A gradient elution system using a cross-Tesla mixer was fabricated on a 20 mm x 20 mm silicon chip with a separation channel of pillar array columns and a sample injection channel. A mixed solution of water and fluorescein in methanol was delivered to the separation channel 7 s after the gradient program had been started. Then, the fluorescence intensity increased gradually with the increasing ratio of fluorescein, which showed that the gradient elution worked well. Under the gradient elution condition, the retention times of two coumarin dyes decreased with the gradient time. When the gradient time was 30 s, the analysis could be completed in 30 s, which was only half the time required compared to that required for an isocratic elution. Fluorescent derivatives of aliphatic amines were successfully separated within 110 s. The results show that the proposed system is promising for the analyses of complex biological samples.

Live-cell imaging of inflammatory cytokine secretion from human monocytes was successfully performed on a microfabricated well array chip by time-resolved fluoroimmunoassay using total internal reflection fluorescence microscopy. Some of the lipopolysaccharide primed monocytes secreted small amounts of interleukin-1 beta (IL-1 ), whereas the monocytes stimulated with an ATP signal secreted large amounts of IL-1 from 10% of observed cells. These two types of secretion patterns corresponded to the proposed models of IL-1 secretion, "rescue and redirect" and "terminal release", respectively. Morphological changes in ATP-stimulated cells also indicated that the cells underwent necrotic cell death, also known as "pyroptosis".

We propose a novel droplet sorting method utilizing the reduction of surface free energy. Droplets are guided by a groove due to the decrement of surface energy. 'Guiding power' is different by droplet size and we successfully observed size dependant directional movement of droplets. This principle can be applied to the size-based passive sorting device without any complex operation. Because of that simplicity, this method has large ability to apply for point of care system.

This paper proposes a high accuracy fabrication method for multilayer PDMS (polydimethylsiloxane) devices. Based on newly developed multi-stacking process using three-dimensional (3D) alignment marks of the concave-convex pair structures, a multilayer PDMS device was fabricated without skillful handling for alignment. Total misalignment of smaller than 10 mu m is achieved for fabrication of a five-layer PDMS device. The precisely aligned multilayer structure was applied to a novel type of particle separation. By 3D secondary rotation flow in the 3D fluidic microchannel, two types of microparticles of 10 mu m and 20 mu m in diameter were successfully separated with high throughput.

This paper presents the one intet - five outlets droplet sorting device driven by the horizontal pneumatic actuators. The flexible high aspect ratio PDMS wall structures were proposed to realize five different sorting modes with only two pneumatic actuators. This multi sorting device has very simple structure and is fabricated by single PDMS mold process. Five different mode droplets sorting were confirmed using micro droplets from about 25 mu m to 300 mu m in the diameter.

This paper presents the EHD (electro-hydrodynamic) micro pump using 3-D carbon mesh electrodes. The carbon electrodes were fabricated by pyrolysis of SU-8 micro mesh structures [1]. Low temperature SU-8 bonding method under 90 degrees C was developed to realize wafer level carbon structure packaging. The pumping behaviors were evaluated using fluorinert as a sample solution. The maximum pressure and volume flow rate are about 23Pa and 400nL/min under applied voltage of 500V.

A microfluidic gas-intake device for measurement of gaseous substances was fabricated and tested. The gas-intake device has a window that provides direct absorption of gas into liquid in microchannels the membrane-type microfluidic device which uses a gas permeability of the PDMS membrane for gas-intake is fabricated and compared gas intake efficiency to the gas-intake device using the dissolution velocity of oxygen into D1 water channel. The degree of oxygen saturation was significantly improved (17.5 %) in case of the pillar-type device. This indicates that the pillar-type microstructure is effective for the gas-intake purpose. © The Electrochemical Society.

3D sheath flow was realized using hydrodynamic position control of the sample flow. The symmetric microgrooves formed on the channel walls were utilized to generate local directional streams. The sample introduced into the grooved area was shifted to the center region of the microchannel, and 3D sheath flow was formed passively. Using CFD ( computational fluid dynamics) simulation, the flow shift area was designed to achieve 3D sheath flow no longer than 500 mu m in channel length. Sample flow shift behavior was observed by using a confocal microscope. Since the structure of the inlets was very simple, it was possible to fabricate an in-plane multi-sample 3D sheath flow device. As a demonstration, a two-sample 3D sheath flow device was fabricated. The separated two-sample 3D sheath flow configuration was clearly observed.

A novel flow type electrochemical immuno sensing system using 3-D comb electrodes, which enables high-speed enzyme immunoassay on a single microchip, has been developed. A trap-and-release system of magnetic beads and a sheath flow sorting system are integrated on the chip. The integrated system realizes repeatable sample preparation and sensing. Using this system, AFP detection in the range from 25ng/mL to 500ng/mL was obtained within 30 minutes. This system can be applied widely for high sensitive enzyme immunoassays.

過大な侵襲が加わると消化管粘膜は早期から組織低酸素に傾きやすく,その悪化は生存率にも影響する。臨床的な指標として胃粘膜PCO₂ (PiCO₂)があり,消化管に留置したシリコンバルンの生理食塩水PCO₂から算出するトノメトリ法(PiCO_2-TONO)が開発されたが,間接法であり,手技上の煩雑さもある。今回,ion-sensitive field effect transistor (ISEFT)センサを用いたPiCO₂ (PiCO_2-ISFET)の直接測定装置を開発したので両者について比較した。麻酔下に人工呼吸管理したイヌ(n=9)を用い,3時間の急速心室ペーシングによる発作性頻拍モデルを作製した。心室ペーシングにより動脈圧は軽度に低下した。動脈血,混合静脈血および呼気終末のPCO₂は心室ペーシングにより上昇した。PiCO_2-TONOおよびPiCO_2-ISFETは,それぞれ67～72mmHg(基礎値56±5)および79～84mmHg(基礎値62±5)に上昇し,両者は相関(r²=0.53, p<0.01)したが,両者間に有意差(p<0.05)を認めた。Bland-Altman解析ではbias 8.5mmHg, precision 7.7mmHgであった。PiCO_2-ISFETはPiCO_2-TONOよりも高値を呈し,後者では過小評価の危険性があるのではないかと推察した。一方,ISFETセンサによる方法は自動的,連続的に実測値が表示され,簡便な応答性の優れた測定法であると考えた。

High performance flow monitoring systems are needed to monitor the particles and biomolecules flow in micro channels. For the design of microfluidic devices and systems, the finite element analysis tools play an important role. These systems are useful to evaluate the correspondence between the computational fluid dynamics (CFD) simulation and the actual flow in micro channels. The micro flow cell realizing 3D sheath flow was designed and the prototype was fabricated and evaluated. Since the flow distribution of the sample is critically changed with the pressure and the flow rate of the carrier, the 3D CFD analysis is indispensable to design the micro flow cell. The principle of 3D sheath flow is applicable to realize particles and biomolecules observation and handling systems. Novel micro flow switches using thermal gelation of methylcellulose (MC) have been developed. Since the local plug is formed illuminating the laser beam, the flow can be stopped at any point in the microchannels. The switching time of about 1 sec both open-to-close and close-to-open was achieved. By using the MC as a carrier flow, DNA, protein and biological cell sorting micro flow systems can be realized in the simple 2D microchannel structures. © 2003 Elsevier B.V. All rights reserved.

A novel automatic biomolecules sorter using thermal gelation of methyl cellulose (MC) solution was realized. In our previous work, we already reported the sol-gel transformation of MC could be used for the flow switch. The flow switch was applied for the prototype of the particles handling system with manual control. The sorting time in this case was about 2 seconds. However the time of sol-gel transformation was estimated within a second. To achieve faster sorting speed, we fabricated a PC controlled sorting system consisting of an automatic fluorescence sample detector, focused IR laser source, and two galvano mirrors for switching and scanning of the laser. As a result the sorting time was reduced to around 100 msec.

Novel micro flow switches using thermal gelation of methyl cellulose (MC) are proposed. The Cross-linked methyl cellulose changes its state from liquid to gel by elevating the temperature. We applied this phenomenon to form a solid structure by irradiating a focused IR laser beam at any points inside of the micro channel. The switching time is fast enough for both open-to-close and close-to-open. By using the MC of optimal concentration as a carrier flow, biomolecules handling systems are realized without any mechanical valve structures.

Immunological Helicobacter pylori (H. pylori) urease analyzer (HPUA), based on a solid-phase tip coated with a monoclonal antibody toward H. pylori's urease and ion-sensitive field effect transistor (ISFET), was developed. In this system, H. pylori urease adsorbed on the solid-phase tip, after a 15-min immunological reaction with gastric mucus sample solution, was measured with a urease analyzer composed of a flow-through cell for urea solution equipped with the measuring and reference ISFETs. The pH change (Delta pH) of urea solution after 55 s of the enzymatic reaction inside the tip was measured by withdrawing about 1 mu l of the urea solution toward the upstream of the tip, where the measuring ISFET is installed. It was confirmed that the present system could detect 0.2 mIU/ml of H. pylori urease. Clinical evaluations of the system were performed for 119 patients using urea breath test (UBT) as a gold standard, resulting in the sensitivity = 33/36 = 92% and specificity = 81/83 = 98%, respectively. (C) 2000 Elsevier Science S.A. All rights reserved.

In order to realize high performance particles and biomolecules handling systems, micro flow cell realizing three-dimensional (3-D) sheath flow was designed and the first prototype was fabricated. A finite element fluidic analysis is applied to realize optimal design of the flow cell. Especially, the structure of the sample injection part was considered to realize 3-D sheath flow. The high resolution flow monitoring method was studied and was applied to evaluate the flow behavior in the first prototype. The results indicated that the two steps introduction of the carrier flow is quite effective to put the sample flow away from the channel wall. This is very useful to avoid adsorption of the particles and the biomolecules on the wall due to the small flow rate near the wall. A simple micro flow switch for biomolecular separation is also proposed.

A variety of reliable methods are available for the detection of H. pylori during upper gastrointestinal endoscopy. We evaluated the clinical utility of an analyzer for H. pylori urease composed of a solid-phase tip coated with a monoclonal antibody against H. pylori urease and ion-sensitive field effect transistor-based pH sensor system. Samples of both gastric mucus and gastric mucosal specimens were collected and the results from this system were compared. Sensitivity and specificity were 97% and 100% for mucus samples and 92% and 97% for mucosal specimens in the present system
compared to 95% and 96% for histological examination, 92% and 100% for bacteriological test, and 89% and 100% for rapid urease test, respectively. These results confirmed that the present system had high clinical sensitivity and specificity, especially for testing of mucus samples. This method has the advantage of requiring only one sample per patient because mucus can be collected from a broad area of the stomach lumen by stroking the mucosal surface with a brush.

Gastric P-CO2 monitoring during canine hemorrhagic shock encountered occasional baseline drift to higher direction when conventional P-CO2 sensor was used. As a result of chemical analysis of gastric juice of dogs and human, hydrogen sulfide and acetic acid were identified as causative compounds. It was speculated that these weak acid molecules would permeate gas-permeable silicone membrane to be accumulated in the inner solution of Severinghaus-type P-CO2 sensors. In order to prevent this phenomenon, double-membrane type P-CO2 sensor was constructed. In this sensor, acid-neutralizing solution was installed between the inner and the outer membranes in order to dissociate weak acid molecules into corresponding ions, which can not diffuse into the inner silicone membrane. In addition, Cu2O particles were mixed in the inner silicone membrane to trap hydrogen sulfide in this membrane. It was confirmed by experiments in vitro that the readings of improved gastric P-CO2 sensors were not affected by acetic acid or hydrogen sulfide. As a result of a preliminary clinical evaluation, continuous monitoring of gastric was carried out for 72 h without detectable baseline drift or the change of sensitivity. (C) 1998 Elsevier Science S.A. All reserved.

A very low-power consumption wireless system for monitoring ECG (ElectroCardioGram) is proposed. It consists of ECG detector/transmitter located on the chest and the relay transmitter placed at the wrist. Between the detector part and relay transmitter, the signal is send as the AC micro current flown through the tissue of the body. Since this method obtains very low-power signal transmission of about 8 mu W(400mV(RMS) x 20 mu A(RMS)), the system can be driven by very small power source like a thin film battery. The similar wireless transmission method can be applied for other medical signal/data sensing micro systems sharing the same relay transmitter.