Atsushi Seki

Novel sensors for potassium, calcium and magnesium ions based on a silicon transducer as a light-addressable potentiometric sensor

Abstract Potentiometric cation sensors using a silicon transducer, light-addressable potentiometric sensor (LAPS) and ion-recognition elements are described, and their performance are discussed. In the silicon transducer, an Al 2 O 3 layer was used as an insulating layer. On the surface of the Al 2 O 3 layer, ion-recognition element such as valinomycin, 18-crown-6 ether, bis [di( n -octylphenyl)phosphato]calcium(II) and ETH1117 were immobilized in the matrix of poly(vinyl chloride) film. Potassium tetrakis ( p -chlorophenyl)borate was used as a lipophilic salt. The K + , Ca 2+ and Mg 2+ sensitive-silicon electrodes showed responses similar to those of the corresponding ion-selective electrode. Furthermore, calcium sensing properties of lipophilic anion concentration were studied. It was shown that the presence of lipophilic anion increased the slope.

Phosphatidylcholine monolayers observed with Brewster angle microscopy and π-A isotherms

Abstract Monolayers of distearoyl phosphatidylcholine (DSPC), dimyristoyl phosphatidylcholine (DMPC), and mixtures of these phospholipids, and distearoyl phosphatidylcholine (DPPC), were observed at the air–water interface with Brewster angle microscopy. Their properties were compared to π-A isotherms. The length of the alkyl chain of phosphatidylcholine affected the morphological properties. At low surface pressure DSPC and DPPC formed the condensed domain; however, DMPC did not form a condensed domain and displayed a larger limiting area per molecule than DSPC. When DSPC and DMPC were mixed together at the same concentration, the property of the spread monolayer in a π-A isotherm was more likely to be DMPC; however, the BAM images were different from that of DMPC or DSPC at various surface pressures. The phase in π-A isotherms was not necessarily the same as the BAM images. Even when surface pressure increased with compression, a small collapse was observed in a microscopic region by BAM.

A hydrogen curing effect on surface plasmon resonance fiber optic hydrogen sensors using an annealed Au/Ta 2 O 5 /Pd multi-layers film

In this paper, a response time of the surface plasmon resonance fiber optic hydrogen sensor has successfully improved with keeping sensor sensitivity high by means of hydrogen curing (immersing) process of annealed Au/Ta2O5/ Pd multi-layers film. The hydrogen curing effect on the response time and sensitivity has been experimentally revealed by changing the annealing temperatures of 400, 600, 800°C and through observing the optical loss change in the H2 curing process. When the 25-nm Au/60-nm Ta2O5/10-nm Pd multi-layers film annealed at 600°C is cured with 4% H2/N2 mixture, it is found that a lot of nano-sized cracks were produced on the Pd surface. After H2 curing process, the response time is improved to be 8 s, which is two times faster than previous reported one in the case of the 25-nm Au/60-nm Ta2O5/3-nm Pd multi-layers film with keeping the sensor sensitivity of 0.27 dB for 4% hydrogen adding. Discussions most likely responsible for this effect are given by introducing the α-β transition Pd structure in the H2 curing process.

Enzyme Sensor for the Detection of Herbicides Inhibiting Acetolactate Synthase

Abstract An enzyme sensor for the detection of sulfonylurea herbicides inhibiting acetolactate synthase II (ALS) was developed using an oxygen electrode. ALS, which has an oxygen consumption side reaction, was entrapped in the matrix of PVA-SbQ polymer, and the enzyme membrane was attached to the electrode. The inhibition of side oxygen reaction of ALS II is measured as decreased consumption of O2 monitored by an oxygen electrode. Preliminary results show that 10−6 M herbicide concentration can be determined by this method.

Proliferation assay of mouse embryonic stem (ES) cells exposed to atmospheric-pressure plasmas at room temperature

Proliferation assays of mouse embryonic stem (ES) cells have been performed with cell culture media exposed to atmospheric-pressure plasmas (APPs), which generate reactive species in the media at room temperature. It is found that serum in cell culture media functions as a scavenger of highly reactive species and tends to protect cells in the media against cellular damage. On the other hand, if serum is not present in a cell culture medium when it is exposed to APP, the medium becomes cytotoxic and cannot be detoxified by serum added afterwards. Plasma-induced cytotoxic media hinder proliferation of mouse ES cells and may even cause cell death. It is also shown by nuclear magnetic resonance spectroscopy that organic compounds in cell culture media are in general not significantly modified by plasma exposure. These results indicate that if there is no serum in media when they are exposed to APPs, highly reactive species (such as OH radicals) generated in the media by the APP exposure are immediately converted to less reactive species (such as H2O2), which can no longer readily react with serum that is added to the medium after plasma exposure. This study has clearly shown that it is these less reactive species, rather than highly reactive species, that make the medium cytotoxic to mouse ES cells.

A monitoring of breathing using a hetero-core optical fiber sensor

A monitoring human breath has been seen as an important source of factor for vital status for emergency medical service. The monitoring of breathing has been tested and evaluated in a possible breath condition of a person to be monitored. A hetero-core optical fiber humidity sensor was developed for in order to monitor relative humidity in a medial mask. Elements for determent breath condition were extracted from the light intensity changing at some human breath condition, which were Breath depth, Breath cycle, Breath time and Check breathing. It is found that the elements had differences relative to normal breathing.

A new anion-sensitive biosensor using an ion-sensitive field effect transistor and a light-driven chloride pump, halorhodopsin

A new biosensor sensitive to chloride anion using a light-driven chloride pump protein, halorhodopsin (hR), and an ion-sensitive field effect transistor (ISFET) has been developed. Membrane vesicles of halophilic bacteria containing hR were immobilized in the matrix of polyvinylbutyral resin on the surface of the ISFET. The gate voltage of this device changed in the min time scale under yellow light illumination. The response for chloride anion increased according to the increase of chloride anion concentration in the bulk aqueous phase. In the dark, the gate potential did not change even in the presence of chloride anion. These chloride-dependent gate potential changes of the hR-ISFET indicate that the chloride pumping by hR is active on the ISFET and that ISFET detects the light-dependent chloride transport by hR.

Surfactant cytotoxicity assay based on a silicon transducer.

A cytotoxicity assay for surfactants was developed using a potentiometric silicon transducer and Lactobacillus plantarum (NBRC3070), and the results are reported here. L. plantarum was used as the test microorganism for assaying the cytotoxicity of the surfactants. The extracellular pH change resulting from the metabolic pathway was measured by a light-addressable potentiometric sensor. This potentiometric sensor system measured the acidification of the L. plantarum medium; acidification resulting from metabolic activity was inhibited by the toxic activity of the surfactant. Results indicated that the anionic surfactant did not exhibit inhibitory activity in either cell growth or extracellular acidification until 0.2mM. By contrast, the inhibition activity of cationic surfactants toward cellular growth and metabolic activity was greater than that of anionic surfactants. These results are consistent with those from the growth inhibition assay.

Bending effect on fiber optic evanescent absorption sensor for sensitivity enhancement in hetero-core structured fiber optic

Hetero-core structured fiber optic was applied to evanescent field absorption spectroscopy. The sensing part of the fiber optic was immersed in a dye solution, then the bending was applied to the fiber optic probe, and propagating loss spectra were measured. The effects of refractive index of the dye solution and the degree of the bending to the sensor part were studied. According to increasing of the degree of bending, the peak strength of the spectra of the dye increased. This is because that the increasing of the bending degree changes the angle of incidence in the propagating ray following the evanescent wave is generated effectively, hence the number of the dye molecules that can interact with the evanescent wave increases. As a result, the sensitivity enhancement of the peak strength was performed. In addition, the increase of the refractive index of the dye solution enhanced the peak intensity in the absorption spectra. It has been shown that the sensitivity enhancement of the fiber optic sensor would be performed by physical shape control and physical property of the solution such as refractive index.

Multipoint measurement based on hetero-core structured optical fiber SPR sensor employing OTDR equipment

In this paper, multipoint refractive index measurement is described using surface plasmon resonance (SPR) sensors based on hetero-core structured fiber optic technique. The sensor simply consists of two different core diameters fibers, which are connected by thermal fusion splicing, in order to deliberately leak the transmitted light wave into the cladding layer of the sensing fiber region. Chromium film and gold film were uniformly deposited around the cladding surface with a layer thickness of 5 nm and 45 nm, respectively, for SPR excitation. Multipoint measurement system consists of three SPR sensors, whose hetero-core insertion length are employed as 2-mm, located in a single transmission optical fiber and an optical time domain reflectometer (OTDR) to be used to measure refractive index. As a result, a hetero-core insertion length has trade off between sensitivity for refractive index and the number of sensors in tandem. The proposed multipoint refractive index measurement has been successfully demonstrated using three hetero-core SPR sensors and OTDR.