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In this study, 2,4,6-trinitrotoluene (TNT) binding peptide was synthesized and screened for TNT specific detection using surface plasmon resonance (SPR) sensor. The TNT binding peptide was rational design and synthesized through amino acid sequence from complementarity determining region (CDR) in the anti-TNT monoclonal antibody, which was produced from hybridoma cell using TNP-KLH conjugate as antigen. Three TNT binding peptide sequences were obtained from the heavy chain of CDR1 named TNTHCDR1, TNTHCDR2 from CDR2 and TNTHCDR3 from CDR3 of anti-TNT antibody. Screening process of three candidate peptides were carried out by using the SPR sensor with direct determination, which the peptide was directly immobilized on the sensor chip CM7 surface through amine coupling reaction. The results demonstrated that peptide TNTHCDR3 was determined as TNT binding peptide and no non-specific binding was observed. The selectivity of TNT binding peptide TNTHCDR3 was also testified by six kinds of TNT analogues. The results indicated the specific binding between TNT and peptide TNTHCDR3.

We investigated the bitter compounds in coffee brews using multivariate analysis of the data obtained from analytical instrument and electronic taste sensor experiments. Coffee brews were prepared from coffee beans roasted to four different degrees. Each brew was fractionated into four fractions by liquid-liquid extraction. The relative amounts of 30 compounds in each fraction were analyzed by analytical instruments, and the bitterness response value of each fraction was analyzed by a taste sensor. Candidate bitter compounds in the coffee brews were identified with reference to their variable importance in projection and by coefficient of projection to latent structure regression (PLS-R) analysis. PLS-R analysis suggested that nicotinic acid, l-lactic acid, and nicotinamide contributed to the bitterness of the coffee brews. In fact, the coffee brews with added nicotinic acid, l-lactic acid, and nicotinamide had an increased bitterness response value compared to those without.

A taste sensor based on lipid/polymer membranes has been reported being possible to detect the masking of bitter substances or masking on bitterness receptors (physical masking or biochemical masking). However, it was difficult to express the bitterness suppression by sweeteners, which is decided by the balance of substances produced in human’s brain (functional masking). High-potency sweeteners are one of the sweeteners used for bitterness-masking in food and pharmaceutical industry. The objective of this study is to evaluate the bitterness-masking effect of high-potency sweeteners using the taste sensor. A bitterness sensor was used to evaluate the bitterness of quinine hydrochloride, and sweetness sensors for high-potency sweeteners were used to evaluate the sweetness of aspartame and saccharine sodium. The sensory evaluation was also carried out to examine the bitterness suppression effect of high-potency sweeteners. The bitterness-prediction formulas were proposed with the aid of a model regression analysis using two outputs from the bitterness sensor and the sweetness sensor for high-potency sweeteners. As a result, the predicted bitterness showed a good correlation with the human taste when aspartame or saccharine sodium was added to quinine hydrochloride. Thus, this study provided an effective method to evaluate the bitterness suppressed by high-potency sweeteners.

A novel peptide-based three-dimensional probe called “peptide matrix,” inspired by the antibody paratope region, was fabricated on a surface plasmon resonance (SPR) sensor chip to enhance the sensitivity of detecting the explosive 2,4,6-trinitrotoluene (TNT). Although peptide aptamer is an attractive candidate for a molecular recognition probe because of its ease of synthesis and chemical stability, it still has difficulty in applying to highly sensitive (i.e. parts-per-billion (ppb) or sub-ppb level) detections. Thus, we developed the concept of peptide matrix structure, which is constructed by consecutive disulfide bond formation between a large number of peptide fragments. This robust three-dimensional structure displays multiple binding sites which can efficiently associate with each TNT molecule. The peptide matrix lowered the dissociation constant (KD) by two orders of magnitude compared to the linear peptide aptamer, estimating KD as 10.1 nM, which is the lowest concentration reported by using peptide-based TNT probe. Furthermore, the concentration limit of detection of peptide matrix modified SPR sensor was 0.62 ppb, and hence comparable to single-chain variable fragment (scFv)-based TNT sensors. To our knowledge, this is the first report demonstrating peptide matrix fabrication and its application for small explosive molecule detection. This peptide matrix-based approach, which has the advantage of simple synthesis and high sensitivity, will be applicable to many other small-molecule label-free detections.

Electronic tongues have been identified as useful tools for quantifying the taste of food and beverages. However, the bitterness evaluation of coffee in the presence of high-potency sweeteners has not been performed yet. In this study, we investigated an approach to quantify the bitterness of coffee with different roasting degrees and the sweetness of acesulfame potassium (Ace K) added to the coffee using taste sensors with lipid polymer membranes. A formula for predicting coffee bitterness with the addition of Ace K was proposed using the responses of a bitterness sensor and a sweetness sensor. We found that the predicted coffee bitterness showed a good correlation with human taste.

Objective taste evaluation has been much in demand in the food, beverage and pharmaceutical industries. A taste-sensing system, which is an electronic tongue with “global selectivity,” is one of the methods used for objective taste evaluation. A taste sensor electrode responds to only one of the basic tastes (saltiness, sourness, sweetness, bitterness and umami) as a change in membrane potential caused by interactions with tastants. Sweet substances are compounds with diverse chemical structures and sizes. Since the taste-sensing system is a potentiometric measurement system using a change in membrane potential, three types of sweetness sensors are required, one for sweeteners with each type of electric charge (uncharged, positively charged and negatively charged). A sweetness sensor for uncharged sweeteners has been developed. Therefore, negatively charged sweeteners, such as saccharine sodium and acesulfame potassium, were chosen as the target substances in this study. We investigated the responses of various sensor membranes using a lipid and nine kinds of plasticizers to each basic taste sample. Furthermore, not only the selectivity of the membranes but also the concentration dependence of their response to sweeteners was investigated. As a result, one of the developed sensors showed responses of over 20 mV to 5 mM saccharine sodium and 10 mM acesulfame potassium in CPA value measurement (CPA: change in membrane potential caused by adsorption). On the other hand, the sensor also showed nearly zero responses to other basic taste samples. In addition, saltiness was the only interfering taste, and the responses to target substances in relative value measurement were over 140 mV. The developed sweetness sensor had high selectivity and concentration-dependent responses. Hence, we concluded that the sensor is suitable for use as a sweetness sensor for high-potency sweeteners with a negative electric charge.

In rapid-melting-crystallization of network Ge-on-insulator (GOI), coalescence of growth-fronts inevitably occurs. To clarify crystallinity of the coalesced regions of two growth-fronts in GOI stripes, scanning electron microscopy and transmission electron microscopy analyses are performed. These analyses reveal that lattice planes of two growth-fronts coherently align without strains for short growth-distance (≤ 5 μm). The lattice planes at growth-fronts start to tilt gradually for growth-distance above 5 μm. For intermediate growth-distance (5–150 μm), slightly-tilting lattice-planes coherently align without generating any defects, where locally-distributed strains are induced in the coalesced regions. On the other hand, for long growth-distance (≥ 150 μm), grain-boundaries are generated in coalesced regions, and the locally-distributed strains are relaxed. The coherent lattice-alignment for growth-distance below 150 μm is attributed to atomic reordering in the coalesced regions, where coalescence occurs at high temperatures around the solidification point of Ge.

In this study, we quantified the tastes of branched-chain amino acids (BCAAs) and demonstrated the bitterness suppression effect using taste sensors that can selectively evaluate two basic taste qualities. Bitterness and sweetness sensors with a lipid/polymer membrane were used to quantity bitterness and sweetness of amino acids, respectively. Simple linear regression analysis revealed that the response values obtained from the corresponding taste sensor (bitterness, sweetness) and the scores obtained in the sensory test showed a strong correlation, demonstrating that the intensity of bitterness and sweetness of amino acids can be estimated. Moreover, a significant decrease in the response value of the bitterness sensor was observed when l -arginine ( l -Arg) was added to bitter amino acids, indicating that the bitterness suppression effect perceivable by humans can be demonstrated.

A chemiresistive sensor based on polyaniline (PANI) nanofibers decorated with highly dispersed gold nanoparticles (AuNPs) is developed to detect the volatile sulfur compounds (VSCs) of human expired breath. The PANI nanofibers with a characteristic of horizontal orientation on the insulating gap area of an interdigitated electrode are prepared by a temple-free electrochemical polymerization. The formation of the fine AuNPs on the PANI nanofibers is realized by the redox reaction between HAuCl 4 and PANI in the form of emeraldine. The PANI/AuNPs sensors exhibit good sensing responses to H 2 S and CH 3 SH gases. The sensing ability of the fabricated electrodes on VSCs contained in human breath is confirmed by their response upon exposure to the expired breath of a healthy volunteer after ingesting raw garlic. The developed nanosensors, together with a multichannel sensing system, are expected to be used in breath analysis and disease diagnose related to malodor biomarker gases.

Liquid-phase epitaxial growth of Ge islands on insulator (GOI) using Ni-imprint-induced Si (1 1 1) micro-crystal seeds (∼1 μmϕ) is proposed. As a result, single-crystalline GOI (1 1 1) structures with large area (∼10 μmϕ) are realized. The transmission electron microscopy observations reveal no dislocation or stacking fault in the laterally grown regions. Moreover, the Raman measurements show that the tensile strain (∼0.2%) which enhances the carrier mobility is induced in the growth regions. This new method can be employed to realize the multi-functional SiGe large scale integrated circuits.

In order to obtain practicable nano-conducting polymer resistive sensors, we investigated the electrochemical deposition of polyaniline (PANI) on the insulating gap area of an interdigitated electrode with a gap width as great as 100 μm. We revealed that the nucleation and growth of PANI on the insulating substrate were influenced by the surface character of the substrate such as hydrophilicity and roughness. By controlling the polymerization conditions, homogeneous PANI films with various nanostructures could be obtained across the insulating gap to form resistive junctions. Among them, a loose 2D nanowire network structure showed the best sensing performance upon exposure to ammonia gas with a low concentration. Keywords: Polyaniline, Nanowire network, Resistive junction, Gas sensor, Electropolymerization

A surface plasmon resonance (SPR) immunosensor for detection of 2,4-dinitrotoluene (2,4-DNT), which is a signature compound of 2,4,6-trinitrotoluene-related explosives, was developed by using a novel oligo (ethylene glycol) (OEG)-based sensor surface. A rabbit polyclonal antibody against 2,4-DNT (anti-DNPh-KLH-400 antibody) was prepared, and the avidity for 2,4-DNT and recognition capability were investigated by indirect competitive ELISA. The sensor surface was fabricated by immobilizing a 2,4-DNT analog onto an OEG-based self-assembled monolayer formed on a gold surface via an OEG linker. The fabricated surface was characterized by Fourier-transform infrared-refractive absorption spectrometry (FTIR-RAS). The immunosensing of 2,4-DNT is based on the indirect competitive principle, in which the immunoreaction between the anti-DNPh-KLH-400 antibody and 2,4-DNT on the sensor surface was inhibited in the presence of free 2,4-DNT in solution. The limit of detection for the immunosensor, calculated as three times the standard deviation of a blank value, was 20 pg mL(-1), and the linear dynamic range was found to be between 1 and 100 ng mL(-1). Additionally, the fabricated OEG-based surface effectively prevented non-specific adsorption of proteins, and the specific response to anti-DNPh-KLH-400 antibody was maintained for more than 30 measurement cycles.

Taste sensor responds to different taste qualities by unique patterns of output signals. The sensor uses lipid membranes as recognition element of tastes. Food constituents affect the membrane potential of the sensor mainly with shielding effect and/or adsorption. However suitable concentration of lipid in membrane has not been studied up to now. In this paper, we changed the concentration of lipid dioctyl phosphate (C) and trioctylmethyl ammonium chloride (T) in membranes, and investigated the response of the sensor to taste substances. Dilution of lipid improved the detection limit of the sensor to adsorptive taste substances, whereas the detection limit to non-adsorptive taste substances did not remarkably changed.

By a chemical oxidative polymerization of aniline on solid substrates treated with Au nanoparticles (Au-NPs) deposition and 4-aminothiophenol (ATP) modification, polyaniline (PANI) fibers were obtained in micro-/nanosize with two-dimensional network structures. The observation by laser scanning microscopy (LSM) indicated that the formation of PANI fibrous network occurred during the drying process rather than the polymerization. It was suggested the ATP modification on Au-NPs deposited substrate resulted in an inhomogeneous grafting of solution-formed PANI on the solid substrates, which self-aggregated to the fibrous network structure with the evaporation of water due to interchain interactions. The influence of polymerization conditions on the formation of fibrous network and the conducting property of the prepared film were discussed. Results from the gas sensing of the as-prepared PANI sensor upon exposure to NH 3 confirmed that the sensitivity and responding rapidity was improved greatly by the PANI 2D fibrous network structure. Especially, a rapid response in resistance change on NH 3 with low concentration indicated that the developed method in this work can be used to fabricate highly sensitive PANI gas sensors.

This paper describes the fabrication and evaluation of new sensor chip technology based on application of polyamidoamine (PAMAM) dendrimer generation 4 (G4) for enhancing surface loading capacity and efficiency for selective and sensitive detection of explosive molecule trinitrotoluene (TNT) under competitive inhibition assay format. The fabrication process of a nano-scale biosensor chip surface was optimized at various steps involving thiol layer, cross-linker, dinitro phenylated-keyhole limpet hemocyanin (DNP-KLH) protein conjugate as ligand. The top ligand layer is supported by underlying 11-amino 1-undecanethiol hydrochloride (AUT) self-assembled monolayer (SAM) and PAMAM dendrimer G4. Bis-sulfosuccinimidyl suberate (BS 3 ) was used as homobifunctional crosslinker to react with amine groups at both the ends. PAMAM dendrimer activation was achieved over 11-amino 1-undecanethiol SAMs over gold chip. PAMAM sensor surfaces scored many advantages over the planer surfaces such as enhanced antibody immobilization, allowing the use of lower concentrated antibody to work under the regime of lower detection limit besides stable and robust surface leading to longer life. Bioactive thin films were fabricated over gold chip via layer-by-layer self-assembly methods. Biomolecular interaction between DNP-KLH conjugate surface and specific TNP-gly-KLH mouse IgG antibody was monitored through surface plasmon resonance (SPR) based real-time optical transducer. The quantitation of TNT on this bioactive surface was done using the competitive inhibition immunoassay. The DNP-KLH surface biosensor has shown a detection limit of 110 ppt for TNT molecule. This TNT specific biosensor holds the promise to be most sensitive, easy to regenerate, highly stable, low response loss sensor surface under competitive assay format. A 12 s injection of 10 mM glycine–HCl solution or 50 mM NaOH solution was found adequate for regeneration of DNP-KLH surface for repeated use. DNP-KLH sensor platform was checked for its repeatability and storability.

In order to develop the fully integrated portable surface plasmon resonance (SPR) system for detection of explosives, the amplification strategy of SPR signal was investigated. Indirect competitive inhibition method allowed the middle-sized SPR sensor to detect trinitrotoluene (TNT) at ppt level. However, this enhanced SPR signal was not high enough to detect TNT at ppt level by a miniaturized SPR sensor. Therefore, localized surface plasmon resonance (LSPR) effect using Au nanoparticle as further signal amplification approach was used. The amplification method of indirect competitive inhibition and LSPR were combined together for fabrication of the immunosurface using Au nanoparticle. TNT detectable range of this immunosurface was from 10 ppt (10 pg/ml) to 100 ppb (100 ng/ml), which was almost comparable to that without Au nanoparticle. The observed resonance angle change due to binding monoclonal TNT antibody (M-TNT Ab) with the immunosurface modified with Au nanoparticle was amplified to four times higher than that in absence of Au nanoparticle.

It was attempted to detect a smoldering fire which was mainly caused by a cigarette in a general house. Same types of eight sensors are adopted in this experiment to detect the fire. The sensor is a type of a tin oxide gas sensor which is used to detect various kinds of reducing gases. It is on a market as a gas detector. The sensor is mounted at a supporting bar and its height can be changed. The height was set at 50, 100 and 150 cm in the experiment. The lit cigarette was put on a cotton cloth and the generated gases were detected. The cloth was adopted as a subjective material for the fire. The sensor output near the fire source fluctuates largely. It was attempted to identify the position and burning material of the fire. The moving average characteristics of the sensor outputs were derived and the differential characteristic of the sensor output was also derived. The characteristics are effective to identify the fire position. The scattering diagram for two sensor outputs near the fire source was introduced and the slope of the characteristic was derived. The slope is effective to distinguish the material of fire source. As for the result, it can be distinguished the fire position within about 30 s and fire material roughly. Tin oxide gas sensor is good for detecting the smoldering fire.

A biological olfaction system is one of the highest performance chemical sensing systems for low-molecular-weight compounds. An ability of recognizing a various molecular properties based on their structures is essential for a biological odor recognition process. For the development of a sensor mimicking the olfactory system, we have formed benzene-patterned self-assembled monolayer (SAM) on the sensor surface using SAMs with nanostructure that serves as adsorption sites for benzene ring, which is representative substructure of aromatics. The structure of the benzene-patterned SAM surface was analyzed by contact-angle measurement, ellipsometry, cyclic voltammetry (CV) and atomic force microscopy (AFM). Moreover, the electrodes evaluated as sensor surfaces with cyclic surface-polarization impedance (cSPI) sensor that measures changes in impedance of the electrode surface by adsorption of substances. The results of cSPI indicated the benzene-patterned SAM surface could distinguish benzene by recognizing of the hydrophobicity and the molecular size.

This paper describes the development and comparison of two immunoassays for the detection of 2,4,6-trinitrotoluene (TNT) based on competitive inhibition. Two polyclonal antibodies were used in the immunoassay; one was prepared from 2,4,6-trinitrophenol–bovine serum albumin conjugate (anti-TNP-BSA Ab, goat IgG) and another from 2,4,6-trinitrophenyl–keyhole limpet hemocyanine conjugate (anti-TNPh-KLH Ab, rabbit IgG). A solid-phase immunoassay that consisted of physically immobilized TNP-BSA conjugate was allowed to interact with these antibodies and the resonance angle changes due to the biomolecular interactions were monitored by surface plasmon resonance (SPR). The quantification of TNT was based on the change in the resonance angle shift for binding of antibodies with a TNP-BSA conjugate, which occurred in the presence of TNT in solution. Both antibodies showed a high degree of affinity for TNT and varying degrees of cross-reactivity to the related nitroaromatic derivative compounds, such as 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB), 2-amino-4,6-dintitrotoluene (2A-4,6-DNT), 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) and TNP. The anti-TNPh-KLH Ab prepared in our laboratory showed a detection limit of 0.006 ng/ml (6 ppt), which was comparable to or even better than the detection limit (0.095 ng/ml or 95 ppt) of a commercially available anti-TNP-BSA Ab for detection of TNT. A pepsin solution prepared with a glycine–HCl buffer (pH 2.0) was used for regeneration of the sensor surface. The duration for a single immunocycle was ∼19 and ∼13 min for anti-TNP-BSA Ab and anti-TNPh-KLH Ab immunosystems, respectively. The proposed immunoassay is simple and possesses good analytical characteristics for quantification of TNT.

A surface plasmon resonance (SPR) immunosensor based on a competitive immunoreaction for the determination of trinitrophenol (TNP) is described. A goat anti-mouse IgG (1st antibody), which recognizes an Fc moiety of an antibody, was immobilized on a gold film of an SPR sensor chip by physical adsorption. A TNP solution containing a fixed concentration of a mouse anti-TNP monoclonal antibody (2nd antibody) and a TNP-keyhole limpet hemocyanin (KLH) conjugate was incubated in one-pot and introduced into the sensor chip. The TNP-KLH conjugate competes with TNP for binding with the 2nd antibody. The resulting complex of the 2nd antibody with the TNP-KLH conjugate was bound to the 1st antibody, which is immobilized on the sensor chip. The SPR sensor signal based on resonance angle shift is dependent on the concentration of TNP in the incubation solution in the range from 25 ppt to 25 ppb, and the coefficient of variation of the SPR signals for the 25 ppb TNP solution was determined to be 13% (n = 4). The experimental results for the adsorption constant of the 1st antibody on the sensor chip and the binding constant of the 1st antibody complex with the 2nd antibody are discussed, together with theoretical considerations.

The global demands for landmine abolition become stronger, whereas the development of landmine detection technology progresses slowly. At present, the detection activities are mainly performed by means of a metal detector or a well-trained dog that needs much time and cost. Therefore, a more efficient landmine detection technique is desired. Most landmines contain aromatic nitro compounds, such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) as explosive charges; therefore, these substances are clues for landmines. In this study, we tried to detect amount of aromatic nitro compounds high-sensitively using a surface-polarization controlling method that measures electrochemical impedance of an electrode surface where explosive compounds adsorbed. As a result, we could detect the aromatic nitro compounds at detection limits of sub-μM level and distinguish the aromatic nitro compounds from other aromatic compounds at 100 μM at least. Furthermore, in order to improve specificity and sensitivity to aromatic nitro compounds, the electrode surface was modified with arenes that makes charge-transfer complex with aromatic nitro compounds. We adopted anthracene as the arene to functionalize the electrode surface. The modified electrode makes it possible to detect the aromatic nitro compounds selectively. This method enables us to develop a sensor for landmine detection.

We have examined the sensing characteristics of a surface plasmon resonance (SPR) immunoassay for the detection of 2,4,6-trinitrotoluene (TNT) using an immunoreaction between 2,4,6-trinitrophenol-ovalbumin (TNP-OVA) conjugate and anti-2,4,6-trinitrophenol antibody (anti-TNP antibody). TNP-OVA conjugate was attached to a SPR-gold sensing surface by means of physical immobilization, which undergoes binding interaction with anti-TNP antibody. Both the immobilization and binding processes were studied from a change in the SPR-resonance angle. The quantification of TNT is based on the principle of indirect competitive immunoassay, in which the immunoreaction between the TNP-OVA conjugate and anti-TNP antibody was inhibited in the presence of free TNT in solution. The decrease in the resonance angle shift is proportional to an increase in concentration of TNT used for incubation. The immunoassay exhibited excellent sensitivity for the detection of TNT in the concentration range from 0.09 to 1000 ng/ml with good stability and reproducibility. The immunosensor developed could detect TNT as low as 0.09 ng/ml, within a response time of approximately 22 min. The sensor surface was regenerated by a brief flow of pepsin solution, which disrupts the antigen-antibody complex without destroying the conjugate biofilm. Cross-reactivity of the SPR sensor to some structurally related nitroaromatic derivative and the detection of TNT in the presence of these nitroaromatic compounds were investigated. The cross-reactivity of the SPR sensor to 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 2-amino-4,6-dinitrotoluene (2A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) were very low (or =1.1%). The analytical characteristics of the proposed immunosensor are highly promising for the development of new field-portable sensors for on-site detection of landmines.

A novel odor sensing system which imitates the process of reception of odorants in biological olfactory system had been developed, utilizing surface polarity controlling method as a transducer of the sensor. In biological system, odorants are received by a large number of receptors, which recognize not whole structures but partial structures of molecules. The present sensor responded partial structures of odorants and adsorption interaction of the partial structures were controlled by the surface polarity of the electrode. Sensor output signals were analyzed on the stand point of partial structures of odorants. As a result, the responses to alcohols, aromatic compounds and aromatic alcohols as odorants could be discriminated by similar molecular structures, with principal component analysis (PCA). In addition, regression models of the response to partial structures of odorants were developed by multiple regression analysis, and odor qualities of aromatic alcohols could be evaluated quantitatively by partial structures of odor molecules.

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.

Taste qualities were studied using a method for detecting the change in interactions between an electrode surface and taste substances in aqueous solution. The present method to detect chemicals was categorized into impedance spectroscopy in electrochemistry. Taste substances affect the electrochemical impedance by adsorption to the electrode surface. Dependences of the impedance on the electrode potential showed different patterns for five basic taste substances with different taste qualities. Furthermore, the response profiles obtained for capsaicin, piperine and allyl isothiocyanate, which are natural pungent-taste substances and have strong hydrophobic groups, were discriminated from those for bitter taste substances using a new method detecting the change of electrode impedance by addition of the mediators of chemical interactions to the taste substances. Hydrophobic substances, which were difficult to discriminate using the electrochemical method, could be discriminated by a proposed method; hence, it was possible to detect wide range of chemical substances from hydrophilic electrolytes to various hydrophobic non-electrolytes.

Phospholipids, such as phosphatidic acid, suppress bitter taste without affecting other taste qualities. In the present study, we detected and quantified this suppression effect with an electronic tongue whose transducer is composed of several kinds of lipid/polymer membranes with different characteristics. We measured a phospholipid cocktail and various kinds of taste substances with five basic taste qualities. The responses to quinine hydrochloride and L-tryptophan, which have a bitter taste, were reduced as the phospholipid concentration was increased, and the responses to the other taste substances were not affected by the phospholipids, as with the human sensation test. Furthermore, the change of bitter intensity caused by phospholipid was quantified by principal component analysis and the tau scale, which expresses the relationship between taste intensity and taste substance concentration. The results are compared with those of the human sensory test and discussed.

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.

The taste of milk with homogenization treatment was discriminated using a taste sensor. The transducer is composed of seven electrodes with lipid/polymer membranes. Sensory evaluations by humans for expressing taste characteristics of “richness” showed that there were no significant differences among the milk samples, which were treated with different homogenization pressure; on the contrary, it was possible to discriminate the slight differences in quality of milk with the taste sensor. The response electric potential pattern was much different below and above 100 kg cm −2 of homogenization pressure. The electric potential decreased systematically with increasing homogenization pressure higher than 100 kg cm −2 . The distribution of fat globule size had two peaks with homogenization pressure below 100 kg cm −2 , but had one peak over 100 kg cm −2 . Thus, the taste sensor responds to some physico-chemical changes accompanied by change in globule size and has the discrimination ability superior to humans. The present result will contribute to automated real-time control of homogenization of milk.

A recently developed multichannel taste sensor with global selectivity is being reviewed. This sensor is composed of several kinds of lipid/ polymer membranes for transforming information of taste substances into electric signals, which are analysed by a computer. The sensor output shows different patterns for chemical substances which have different taste qualities such as saltiness and sourness, while it shows similar patterns for chemicals with similar tastes. The sensor responds to taste in itself, as can be understood from the fact that taste interactions such as the suppression effect, which appears between sweet and bitter substances, can be well reproduced. Amino acids can be classified into several groups according to their own tastes with sensor outputs. The taste of foodstuffs such as beer, coffee, mineral water and vegetables can be discussed quantitatively using the taste sensor, which provides the objective scale for the human sensory expression. The taste sensor will open the door to a new stage of food culture.

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.

The titrable acidity of and the ethanol concentration in sake mash were measured using a multichannel taste sensor system. A positively charged membrane responded to ethanol and the electric response of the membrane showed good agreement with those determined by gas chromatography in the measurement of sake mash. It was considered that the responses were induced by a change in the activity coefficient of anions. The titrable acidity of sake mash was measured using an electrode with a negatively charged membrane, because the electric response of the membrane showed a strong correlation with the titrable acidity of sake. The result showed good agreement with the value determind by titration, and the agreement was slightly increased by multiple regression together with the electric response of the positively charged membrane. Therefore, it is concluded that this method is useful for determination of the ethanol concentration in and the titrable acidity of sake mash. The results show that the taste sensor can be used for monitoring of those values in sake fermentation.

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.

Lipid membranes are useful materials to transform information about taste substances into electric signals. A lipid monolayer membrane for a taste sensor has been prepared by adsorbing lipid materials to the hydrophobic surface of a polymer membrane. The lipid-modified membranes respond to such electrolytic taste substances as HCl (sourness) or NaCl (saltiness) with large response magnitudes and such non-electrolytic substances as caffeine (bitterness) or sugar (sweetness) with high sensitivities. Thus the present membrane has a high ability to detect taste.

The critical current density, Jc, is discussed theoretically to explain the exponential dependence of Jc on the flux density, B, given typically by Jc∝exp( −B B 0 (T) ), which has been widely observed for single crystals of high-Tc superconductors in an external magnetic field parallel to the crystal c-axis. It is pointed out that Jc shows an exponential-type dependence, Jc∝exp( −ƒf(B, T) ), when the tilt modulus, C44, of fluxoids shows a remarkable softening for higher values of the wave number. It is also shown that the present expression of Jc is reduced to the observed B dependence of ƒ(B, T)⋍ B B 0 (T) by taking account of th e effects of the layered crystal structure on C44 and the correlation length, l44.

A taste sensor with a multichannel electrode was developed by using lipid membranes as a transducer of taste substances. The sensor can detect the taste in a similar manner to the human gustatory sensation by response patterns of electric potential to taste substances. The sensitivity, reproducibility and durability were superior to those of humans. The same taste as that elicited by some commercial aqueous drink was reproduced by making aqueous solution mixed from four kinds of basic taste substances, the concentrations of which were determined so that the electric-potential pattern of this mixed solution could agree well with the pattern by the drink. Different brands of beer were easily distinguished by the electric-potential patterns.

The expression for the thermal-fluctuation-induced depinning line, T = TP (Be), is derived theoretically for weakly pinning high-Tc superconductors. In the derivation, it is shown that the thermal displacement of pinned fluxoids, uth reduces the critical current density as J c = J c0 ( − 〈u 2 th 〉/d 2 p ) 3 2 , where J c0 is the critical current density in the absence of u th and d p is the effective half width of the summed-up pinning potential. Then T p (itB e) is determined as the temperature at which Jc becomes zero due to the increase of 〈u2th〉 with the increase of T in the external flux density of Be. The relation of Tp(Be) with the irreversibility line of Ti(Be) and the flux melting line of Tm(Be) is also discussed.

A series of n-alkanols from ethanol to tridecanol interacted with a negatively charged lipid membrane composed of dioleyl phosphate, which exhibited a

We have developed a taste sensor consisting of a multichannel electrode with transducers composed of lipid membranes immobilized with a polymer, i.e., eight different kinds of lipid analogs mixed with poly(vinyl chloride) and plasticizer. This multichannel sensor responds to five basic taste substances in five different ways; the taste patterns composed of eight electric-potential responses could be clearly distinguished from each other for the five basic taste substances. Moreover, similar but distinguishable patterns were obtained for substances eliciting a similar taste in humans. The reproducibility is noticeably improved from those of lipid membranes which were previously investigated for application in a taste sensor. The present results imply that the multichannel lipid membrane device has the ability to sense tastes like a human being.

The local anesthetics, tetracaine, procaine and lidocaine, interacted with a negatively charged lipid membrane composed of dioleyl phosphate (DOPH), which exhibited a self-sustained oscillation of the membrane potential. The anesthetics depolarized the membrane potential when present in increasing concentrations, whereas they increased the membrane resistance at low concentrations and decreased it at high concentrations. The above results were analyzed on the basis of electrochemical theory taking into account ion flux across the membrane. The electrical characteristics are affected by both the hydrophobicity and the diffusion constant of local anesthetics within the membrane.

Higher plants exhibit an oscillation of electrical potential near the surface along the root. The oscillation was studied with the aid of both the usual intracellular microelectrode technique and the extracellular multielectrode technique, the latter making it possible to measure simultaneously electrical potentials along the root. It was found that the oscillation of extracellular surface potential showed the largest amplitude in the elongation region, and the phase of the oscillation in this region differed by 180 degrees from that in the mature region, where the oscillation appeared coherent. The measurement of the intracellular electrical potential suggested the existence of oscillatory components localized to the parenchyma/xylem interface in the elongation region. A theoretical analysis based on an electrical circuit network described the above-mentioned behavior. It was shown that the oscillation was propagated along the root over several centimeters without substantial decay in the mature region.

Mutual entrainment of spatial pattern without temporal oscillations is demonstrated using a giant cell of the green alga. The possibility of spatial entrainment is shown theoretically.

To clarify an essential mechanism on the formation of alternating alignment of acid and alkali bands along cell walls of Characean algae as Nitella and Chara, the behaviour of proton transport in a simplified model system is investigated theoretically from the viewpoint of nonequilibrium thermodynamics. The present model system is described by a linear diffusion equation for proton concentration with a nonlinear boundary condition on the flux continuity across the cell membrane under an integral constraint on the total flux connected with the light intensity. It is confirmed by numerical calculations that the present model can reproduce band-type spatial patterns of proton concentration above a critical light intensity, as has been observed experimentally. An expression for the pattern of proton flux with a characteristic M-shape is also derived analytically. It is shown that a formation of the spatial patterns can be described analogously to the occurrence of a phase separation if a local potential proposed in this paper is used in place of a chemical potential. An essential mechanism on the formation of spatial patterns in the Characean algae as a kind of dissipative structure is discussed with the aid of a kinetic equation of reaction-diffusion type derived from the local potential near the bifurcation point of the present system.

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.

Ordered-fluid phase transitions of methylphosphatidic and phosphatidic acid bilayers are discussed theoretically to explain comprehensively various observed data in the presence of Ca2+ or protons. It is shown that the observed data can be explained reasonably by taking account of the interaction among neighboring head-groups with the aid of Ca2+ or protons. As a result, a quantitative explanation is given for the dependence of the phase-transition temperature on pH as well as Ca2+ concentration with the coexistence of monovalent cations. The dependence of the cooperativity of the transition on pH and monovalent cation concentration is also well explained. It is also pointed out that in the ordered-fluid phase transitions, a hysteresis metastable state and phase separation can be expected to appear under some conditions.

A theory is presented for a phase transition between resting and depolarized states of a protoplasmic droplet of Nitella induced by variation of Ca2+ and Na+ concentrations. In the theory, a membrane formed on a surface of the droplet by lipids and proteins is regarded as a kind of adsorbed bilayer. Effects of bridging among adsorbed molecules through Ca2+ are taken into account, besides an electrostatic interaction between polar groups of adsorbed molecules and monovalent and divalent cations. It is shown that an excitable membrane is stabilized only in a certain range of Ca2+ and Na+ concentrations, where a phase separation through the Ca2+-bridging occurs between Ca2+-rich membranous and Ca2+-depleted domains. This kind of phase separation is mainly subject to a competitive effect between monovalent cations and Ca2+ at lower Ca2+ concentrations but an ionic strength at higher Ca2+ concentrations. The present results can explain fairly well quantitative features of existing observed data.

A new flux-pinning mechanism is proposed for moderately strong pins showing a saturation of macroscopic pinning force density Fp at high fields. For moderately strong pins, a shear correlation length in a pinned fluxoid lattice decreases to the order of lattice spacing at high fields. It is shown that a phase separation between an amorphous-like, dense-dislocation phase and a crystal-like, dilute-dislocation phase occurs to minimize the free energy of the pinned fluxoid lattice. In this case, the derived expression for Fp at high fields shows a saturation tendency which is almost insensitive to an increase of the elementary pinning force, fp. As fp becomes stronger, the volume fraction of the dense-dislocation phase increases and, finally, the whole fluxoid lattice is occupied only by the amorphous-like, dense-dislocation phase. A nonsaturation of Fp then appears even at high fields.

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.

The relaxation of the magnetization due to thermally activated flux creep in a bulk sample of a nonideal type II superconductor is discussed theoretically. Firstly, an expression for the average volume of a flux bundle characterizing its coherent thermal hopping motion is derived by starting with an equation for the local force balance on pinned fluxoids. Secondly, a thermal hopping rate of flux bundles is derived from the Fokker-Planck equation of pinned flux bundles. These results are used to derive expressions for both the time dependence of the magnetization and the induced electric field due to flux creep. It is shown that the present theory can quantitatively explain the existing observed data of the flux-creep rate, not only in conventional superconductors such as Nb-Ta and Pb-Tl but also in strongly-pinning bulk samples of the high- T c oxide superconductors such as Y-Ba-Cu-O.

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.