Biomedical subjects

A Hibara

Publications and source records attributed to A Hibara.

5 recordsLinked to original sources

PubMed2001

On-chip integration of sequential ion-sensing system based on intermittent reagent pumping and formation of two-layer flow.

A sequential ion-sensing system using a single microchip was successfully realized. The system developed here involves intermittent pumping of plural organic phases into a microchannel, followed by contact with a single aqueous phase to form a stable organic-aqueous two-layer flow inside the microchannel. Because the plural organic phases created by intermittent flow contain the same lipophilic pH indicator dye but different ion-selective neutral ionophores, different ions can be sequentially and selectively extracted into the different organic phases, where they can be determined by thermal lens microscopy (TLM). We used KD-A3 as the lipophilic pH indicator dye and valinomycin and DD16C5 as neutral ionophores to demonstrate sequential ion sensing of potassium and sodium ions by measuring the deprotonated dye caused by the ion extraction. The integrated microfluidic system proposed here allows multi-ion sensing, which is not easily demonstrated by conventional ion sensor technology using a solvent polymeric membrane. The minimum volume of single organic phase needed to obtain an equilibrium response without dilution by cross dispersion of two organic phases was ca. 500 nL in our system, indicating that the required amounts of expensive reagents in one measurement could be reduced to 1.7 ng and 2.8 ng for the dye and ionophore molecules, respectively.

Biosensing Techniques↗

PubMed2001

Determination of subyoctomole amounts of nonfluorescent molecules using a thermal lens microscope: subsingle-molecule determination.

The photothermal effect of an ultratrace amount of nonfluorescent molecules in liquid was determined by optimizing the optical arrangement for a thermal lens microscope. The optimized experimental setup could be determined from the evaluation of probing volume and the concentration of the sample solutions even when the expectation of the molecule number in the probing region was less than a single molecule. The minimum expectation, which is explained as being the time average, was 0.4 molecule of Pb(II) octaethylporphyrin (OEP) in benzene. The concentrations in the 9.7 x 10(-11)-7.8 x 10(-10) M region used in this work corresponded to the expected number of 0.4-3.4 molecules, and the calibration curve in this region showed good linearity. Taking into account the enhancement factor of solvent, the molar absorption coefficient of solute, and the optimization of the optical arrangement, the present result, which was the determination limit of 0.34, was consistent with that previously reported. The relation between molecular behavior in the probing volume and the signal was discussed. The average temperature rise in the probing volume by the photothermal effect for the single OEP molecule was estimated as 3.1 muK, and this value was detectable, based on conventional thermal lens measurements for bulk scale sample.

Journal Article↗

PubMed2001

Use of a thermal lens microscope in integrated catecholamine determination on a microchip.

A new method for determination for catecholamines (CA) utilizing microchip technology and a thermal lens microscope has been developed. Microchannels with a 250 microm x 10 microm cross section were used for mixing, reaction, and detection. Epinephrine (EP), nor-epinephrine (NE), dopamine (DA), and L-dopa (LD) were determined by using coloring oxidization to aminochromes by sodium metaperiodate. A thermal lens microscope (TLM) was used for detection of the product. The sensitivity of the system was comparable for the four CA and required only 15 s for mixing of sample and reagent. The calibration lines indicated excellent linearity for concentrations of 5-20 microg mL(-1). The relative standard deviations for 10 microg mL(-1) solution were 1.08, 2.18, 2.2, and 2.5% for EP, NE, DA, and LD, respectively. CA in pharmaceutical injections were also determined by use of the system and the results correlated very well with nominal values. Results obtained by use of the integrated system suggested there was a sufficient possibility to realize high-throughput medical diagnosis systems.

Calibration↗

PubMed2001

Integrated multilayer flow system on a microchip.

We utilized microchip technology and found that the multilayer flow of liquids can be formed in microchannels. Liquid/liquid interfaces were formed parallel to the side wall of the microchannels, because the surface tension and friction force are stronger than the force of gravity. A water/ethylacetate/water interface was formed in a 70-microm-wide and 30-microm-deep channel. The interface was observed to be quite stable and to be maintained for a distance of more than 18 cm. As an example of a multilayer flow application, we demonstrated the liquid/liquid extraction of Co-dimethylaminophenol complex in a microchannel. The solvent-extraction process of the complex into m-xylene in the multilayer flow was found to reach equilibrium in 4 s, while it took 60 s in a simple two-phase extraction.

Journal Article↗

PubMed2000

Non-contact photothermal control of enzyme reactions on a microchip by using a compact diode laser.

Photothermal temperature control of an enzyme-catalyzed reaction in a microchip using a diode laser was demonstrated. A laser beam with energy of 10 mW was used to irradiate an absorbing target placed on top of the microchip cover plate. Theoretical calculations have shown that temperature in the microchannel can be locally increased by 5-7 degrees C during short time intervals, due to heat released by the target. The rate of the enzyme reaction, which was initially inhibited due to cooling of the chip to low temperature, was increased when the target was irradiated. The products were detected by a thermal lens microscope. The product concentration was shown to depend on irradiation time, laser intensity and substrate concentration. Reaction characteristics (rate constant of the reaction) were then derived from these dependencies. The reaction volume and absolute quantity of the reaction product were estimated as 10 nl and 100 fmol, respectively. It was also demonstrated that a direct solvent heating method using infrared radiation could control the reaction in the microchannel.

Lasers↗