Tetsushi Sekiguchi

A very low-power consumption wireless ECG monitoring system using body as a signal transmission medium

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

Droplet-based microfluidics for high-throughput screening of a metagenomic library for isolation of microbial enzymes

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., <10 μL). 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.

Integration of pillar array columns into a gradient elution system for pressure-driven liquid chromatography.

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 × 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.

A Novel Biomolecule Sorter Using Thermosensitve Hydrogel in Micro Flow System

A novel biomolecule sorter using thermoreversible hydrogel was developed. Thermosensitive block copolymer changes its state from sol to gel when it is heated. The solution containing fluorescent biomolecules and thermosensitive polymer was introduced to a Y-shaped microchannel. The sol-gel transition was locally induced by site directed IR (infrared) laser irradiation in order to plug the microchannel and sort out the biomolecules. The sorting time of 120 ms was achieved. As an application of this sorter, fluorescently labeled λ-phage DNA molecules were separated and collected.

Immunological Helicobacter pylori urease analyzer based on ion-sensitive field effect transistor

Abstract Immunological Helicobacter pylori ( H. pylori ) urease analyzer (HPUA), based on a solid-phase tip coated with a monoclonal antibody toward H. pyloris 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 (ΔpH) of urea solution after 55 s of the enzymatic reaction inside the tip was measured by withdrawing about 1 μl 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.

Active and Precise Control of Microdroplet Division Using Horizontal Pneumatic Valves in Bifurcating Microchannel

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.

3D sheath flow using hydrodynamic position control of the sample flow

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 µm 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.

Comparison of the relationship between blood pressure and pulse wave transit times at different sites

In order to know the effect of the change in the pre-ejection period (PEP) included in the pulse wave transit time (PWTT), PWTT of the toe, finger and nose was measured in a clinical situation and the difference between each sites PWTT was calculated in order to eliminate the PEP. The slope of PWTT against systolic blood pressure (SBP) after administration of ephedrine and phenylephrine was calculated. The result suggested that because change in PEP caused inconsistency of the relationship between PWTT and blood pressure (BP), PEP had less effect on the toe PWTT than on the PWTT of other sites.

A Particles and Biomolecules Sorting Micro Flow System Using Thermal Gelation of Methyl Cellulose Solution

A novel micro flow system for particles and biomolecules sorting using thermal gelation of methyl cellulose (MC) solution was proposed and evaluated. The fabricated system is to sort out the target biomolecules from the samples in a simple Y-shape microchannel. The cross-linked MC (1wt%, 1000cP) changes its state from sol to gel by elevating the temperature up to 55°C. This phenomenon was applied to plug the channel by the IR laser irradiation. The switching time was within 1 second both open-to-close and close-to-open. By using the MC as a carrier flow, biomolecules sorting system was realized without any mechanical valve structures.

Gastric PCO2 monitoring system based on a double membrane type PCO2 sensor

Abstract Gastric PCO2 monitoring during canine hemorrhagic shock encountered occasional baseline drift to higher direction when conventional PCO2 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 PCO2 sensors. In order to prevent this phenomenon, double-membrane type PCO2 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 PCO2 sensors were not affected by acetic acid or hydrogen sulfide. As a result of a preliminary clinical evaluation, continuous monitoring of gastric PCO2 was carried out for 72 h without detectable baseline drift or the change of sensitivity.