Satoru Iiyama

Evaluation of water quality and pollution using multichannel sensors

Abstract We studied and discussed the characteristics and the application of a multichannel electrode type sensor. It was based on eight membranes using various lipids as an effective and a simple potentiometric sensor for detecting water quality. The response of the sensor was calibrated using a standard solution, adjusted as an artificial river water. Especially, we researched the response patterns of the sensor to the river water at Kitakyushu in Japan. In general, cations increase the membrane potential of negatively charged membranes, while anions decrease that of positively charged membranes. The water quality of the upper stream was clearly distinguished from the water quality of the other sites. The original data obtained with the sensor were expressed on an eight-dimensional space, so they were visualized on the two-dimensional plane using principal component analysis. That is, the water quality of the upper stream was the same, and the quality of middle and down stream was different. The multichannel sensor system will contribute to control water quality and water pollution.

Measurements of soy sauce using taste sensor

Abstract The taste of soy sauce was studied using a taste sensor with lipid membranes. Stable measurements were made by synthesizing a standard solution for soy sauce. Twenty-five kinds of soy sauce were clearly distinguished with the sensor, but classification into three conventional groups, i.e., koikuchi (high amino acid, low NaCl), usukuchi (low amino acid, high NaCl) and sashimi, could not be made. Contrary to this, it was found that the tastes of three types of soy sauce, which were produced by the same manufacturer, resembled each other. The similarity of soy sauce by the same manufacturer was also confirmed by amino acid analysis and a sensory test. The taste sensor will contribute to automated soy sauce brewing.

Objective scaling of taste of sake using taste sensor and glucose sensor

Abstract The taste of Japanese sake was investigated using a taste sensor with eight kinds of lipid membranes and an enzymatic glucose sensor. The electric-potential pattern constructed of eight outputs from the taste sensor has information on the taste quality and intensity. A standard solution for sake measurement was synthesized. Therefore, chemical meanings were assigned to two perpendicular axes transformed from the nine variables of outputs from the two sensors; commercial brands of sake were scattered on this plane. The taste of sake was discussed objectively.

Effect of taste substances on electric characteristics of a lipid cast membrane with a single pore

Abstract The effect of taste substances was investigated for a lipid membrane constructed by casting complexes of synthetic lipid (double-chain ammonium salt) and sodium polystyrenesulfonate on a silicon wafer with a single minute pore. Reproducibility of the electric properties was improved remarkably by the use of the present construction method for the lipid membrane. It was found that this membrane showed a sensitive response to negatively-charged chemicals having strong bitterness such as picric acid because the lipids are positively charged. A membrane with non-equimolar lipid-polymer complexes showed a phase separation between two phases composed of liquid-crystal lipid multi-bilayers and crystal lipid-polymers within a limited temperature range. This membrane in the phase-separation state generated a self-sustained electric oscillation, whose mechanism was explained with the aid of a non-equilibrium theory. The waveform of the oscillation changed by using picric acid on the membrane. This bio-mimetic membrane has the possibility of acting as a biological chemoreceptor.

Relation of growth process to spatial patterns of electric potential and enzyme activity in bean roots

The electric spatial pattern and invertase activity distribution in growing roots of azuki bean (Phaseolus chrysanthos) have been studied. The electric potential near the surface along the root showed a banding pattern with a spatial period of about 2 cm. It was found that the enzyme activity has a peak around 3-7 mm from the root tip, in good agreement with the position of the first peak of the electric potential, which is located a little behind the elongation zone. An inhomogeneous distribution of ATP content was also detected along the root. Experiments on the electric isolation of the elongation zone from the mature zone and acidification treatment showed that H+ is transported from the mature-side to elongation-side regions, causing tip elongation through an acid-growth mechanism. Both acidification and electric disturbance on growing roots affected growth significantly. Simultaneous measurements of electric potential and enzyme activity clearly showed a good correlation between these two quantities and growth speed. From an analogy with the Characean banding, the spatio-temporal organization via the cell membrane in electric potential and enzyme activity can be regarded as a dissipative structure arising far from equilibrium. These experimental results can be interpreted with a new mechanism that the dissipative structure is formed spontaneously along the whole root, accompanied by energy metabolism, to make H+ flow into the root tip.

Study of astringency and pungency with multichannel taste sensor made of lipid membranes

Abstract Pungent and astringent substances have been studied using a multichannel taste sensor. The electric-potential pattern made up of eight outputs from the membranes of the sensor has information about taste quality and intensity. Pungent substances including capsaicin, piperine and allyl isothiocyanate have no effect on the electric potentials of the liquid membranes. On the other hand, astringent substances such as catechin, tannic acid, chlorogenic acid and gallic acid change the potentials remarkably. A principal-component analysis of the patterns in electric-potential change caused by the taste substances reveals that the taste quality of astringency is located between bitterness and sourness. A model for astringency is presented.

Electric oscillation in an excitable model membrane impregnated with lipid analogues

A model membrane constructed from a Millipore filter, whose pores were impregnated with dioleyl phosphate, exhibited an electric self-oscillation under nonequilibrium conditions. The membrane interposed between two solutions with the same KCl concentrations showed no temporal change in membrane potential. However, the potential became oscillatory on application of an electric current to the membrane. The frequency was proportional to the magnitude of the electric current. When both KCl solutions were replaced by NaCl solutions, a similar trend was observed, although the oscillation was not as regular as in the case of KCl. A membrane placed between equimolar solutions of KCl and NaCl, on the other hand, gave rise to an oscillation even without current application. When a membrane was placed between 5 mM KCl and 100 mM KCl, it was found that NaCl added to the 5 mM KCl side had a pronounced effect on the membrane with respect to the frequency response of the oscillation. These results indicate that the dioleyl phosphate membrane discriminates Na+ from K+.

Growth and electric current loops in plants

A theory is presented for a relationship between ion accumulation and electric current loops in multicellular systems such as the roots and stems of higher plants. A network of electric circuits shows that the electric current transported across the cell membrane flows between an elongating region and a mature region, not only in roots but also in stems. In roots, ions constituting the extracellular electric current flow in the external aqueous medium, while in stems an electric current of comparable density flows within the epidermal cell wall. Based on this theoretical result, electric isolation between the elongating and mature regions was made in the case of both roots and stems. The speed of growth during the initial stage was greatly decreased due to a change in the distribution of protons around the surfaces of the plant by cutting off the electric current loop. Electrochemical calculation shows that ions are not always accumulated at the efflux site, since the ion distribution is strongly affected by the relation of the magnitudes between the electric field and electric current. The results calculated for the electric potential and pH distributions around the root agree with experimental data.

Peculiar change in membrane potential of taste sensor caused by umami substances

Monosodium glutamate (MSG) induces a favorable taste, termed umami. The action of MSG on lipid membranes of a taste sensor was investigated. In general, food constituents monotonously increase the electric potential of the negatively charged membranes. Contrary to this, MSG decreases the potential at lower concentration and increases it at higher concentration, thus the effect of MSG on lipid membrane is biphasic. On the decrease of the membrane potential, a model was proposed in which the dissociated carboxyl group of MSG accelerates the dissociation of phosphate group of the membrane lipid.

Band-Type Dissipative Structure in Ion Transport Systems with Cylindrical Shape

A theory is presented for an appearance of band-type pattern of electric potential accompanied with electric current surrounding a unit or many-cell system of a cylindrical shape. A flux continuity at the membrane is reduced to a nonlinear equation composed of passive and active fluxes through a diffusion equation for protons. Another equation concerns the concentration of a diffusive substance weakening the pump activity. It is shown that, when an external parameter is varied from the homogeneous state, a symmetry breaking along a longitudinal axis usually appears before the one along a circumferential direction. A TDGL equation for spatial modes, which can describe both normally and invertedly bifurcating cases, is derived. An observation of hysteretic bands of chloroplasts in the green alga Acetabularia is discussed within the present theoretical scheme.