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A multichannel taste sensor, namely an electronic tongue, with global selectivity is composed of several kinds of lipid/polymer membranes for transforming information about substances producing taste into electrical signals, which are input to a computer. The sensor output exhibits different patterns for chemical substances which have different taste qualities such as saltiness, sourness and bitterness, whereas it exhibits similar patterns for chemical substances with similar tastes. The sensor responds to the taste itself, as can be understood from the fact that taste interactions such as the suppression effect, which appears for mixtures of sweet and bitter substances, can be reproduced well. The suppression of the bitterness of quinine and a drug substance by sucrose can be quantified. Amino acids can be classified into several groups according to their own tastes on the basis of sensor outputs. The tastes of foodstuffs such as beer, coffee, mineral water, milk, sake, rice, soybean paste and vegetables can be discussed quantitatively using the taste sensor, which provides the objective scale for the human sensory expression. The flavour of a wine is also discriminated using the taste-odour sensory fusion conducted by combining the taste sensor and an odour-sensor array using conducting polymer elements. The taste sensor can also be applied to measurements of water pollution. Miniaturization of the taste sensor using FET produces the same characteristics as those of the above taste sensor by measuring the gate-source voltage. Use of the taste sensor will lead to a new era of food and environmental sciences.

To use Nature as a model for a new sensor technique - that is a concept that has become very attractive in recent years. This biomimetic approach deals with sensors and sensor systems based on mechanisms found in biological systems. One branch consists of the concept of biosensors, a biosensor being a combination of a biologically active material with a transducer element. Another branch consists of the concept of artificial senses, such as so-called electronic noses and electronic tongues. The principles of these are analogous to the sense of smell: a signal pattern from a sensor array with different selectivities is processed with multivariate data analysis for recognition and learning. Electronic noses have already become an established technique, and the establishment of electronic tongues is rapidly growing. Professor K Toko at Kyushu University, who is a pioneer in these fields, has now written a book to introduce the biomimetic approach to sensor technology. He has also developed an electronic tongue based on lipid/polymer membranes. The aim of this system is to mimic the human taste sensation; therefore it is called a `taste sensor'. This taste sensing system has now also been commercialized. The book also covers this taste sensing system in detail. In the introductory part, the principles of measurement systems and different techniques of multivariate data analysis are described and discussed. This also includes some discussions concerning the five human senses and their integration to form an overall decision of quality. In the next part, reception mechanisms of biological systems are briefly described with emphasis on the taste system of the tongue. A large section on properties of some lipid membranes then follows, including their potential as membranes for the taste sensing system. The next section covers principles and properties of biosensors, followed by a chapter on odour sensors - so-called electronic noses. The principles of olfaction and its basis for the electronic nose are discussed. The taste sensing system is thoroughly described in a large section. The abilities of different membranes to detect the five tastes of the tongue (sweet, sour, bitter, salt and umami) are described. Details of many applications, mainly in the food industry, are given. In the last part, other methods to measure taste based on impedance, surface plasmon resonance and surface photovoltage are described. Finally, some future aspects towards a common sensing system based on artificial analogues to all human senses are touched upon. To summarize the book, it covers all essential areas in biomimetic sensor technologies, biosensors, electronic noses and electronic tongues. It also covers multivariate data processing techniques, which are a very important aspect of these systems. It examines the term `deliciousness', which actually is the combination of the information from all five human senses to give an overall impression of the experience of the food. The initial part on sensors and measurement methods is very valuable in putting the subsequent chapters in perspective. The section dealing with artificial membrane properties, however, is rather large, and there is little description of how biological membranes work. Thus, a section dealing more deeply with olfaction and biological receptors would have made the book more complete. The hypothesis of how membrane binding can start excitation in a receptor cell and how this can be a used as a prototype for a taste sensor, however, is interesting. Although the term `electronic tongue' suggests measurements on taste, most of the research groups working with this concept are trying to find not the taste but the quality. The taste sensing system describes the result in terms of the five basic senses of the tongue. It is a little confusing, then, when in some cases this system also refers to more general properties of quality. It is also surprising that no other concepts of electronic tongues are mentioned in the book. This book is recommended to researchers in the field of electronic noses and tongues. Part of it could also be useful for introducing postgraduate students to the biomimetic approach in sensor technology. Fredrik Winquist

The effect of heat treatment on the taste of milk was investigated using a taste sensor. The transducer is composed of seven electrodes with different kinds of lipid membranes. Sensory evaluations by humans were made in terms of three taste characteristics of “richness (koku),” “cooked flavor” and “deliciousness” together with a measurement of whey protein denaturation. This study provided a quantitative description of the taste change caused by heat treatment of milk, because the output showed high correlations with richness and the degree of protein denaturation.

Taste of amino acids was studied using a multichannel taste sensor with lipid membranes as the transducer of taste substances. The study on taste of amino acids has drawn much attention so far because each of them elicits complicated mixed taste. The response of the sensor to amino acids was compared with results of panel tests, and response potentials from the eight membranes were transformed to terms representing five basic tastes by multiple linear regression. This expression of five basic tastes reproduced human taste sensation very well. The taste was expressed more quantitatively by assuming new channels, which are represented by multiplication of the response potentials of the original channels. This new set of channels implies the existence of processes involving the nervous system which is connected with taste cells.

An artificial excitable lipid membrane, which is composed of a porous filter filled with lipids, exhibits self-sustained oscillation of the membrane potential by DC electric current imposed across the membrane. The system yielded various electric oscillatory responses to sinusoidal AC electric currents superimposed on the DC current. At adequate frequency and amplitude of the sinusoidal stimulation, the oscillation was entrained (or synchronized) to the stimulation; the oscillation was desynchronized when the parameter (frequency or amplitude) was deviated to some extent from the initial value. Aperiodic oscillations appeared for parameter values located between entrained regions. Detailed analyses revealed that the aperiodic oscillations were chaotic, which was first shown quantitatively in artificial membrane systems.

It is known that thiol-containing compounds form monolayer membranes on a gold surface via chemisorption from organic solvents in terms of a strong connection ability between thiol and the metal. Here we prepared different kinds of thiol-containing lipids and fabricated monolayer membranes on the gold disk electrode whose surface structures were similar to biological membranes. Responses of this lipid-coated electrode to odor substances were examined by an electrochemical method of a cyclic voltammetry. Blocking ability for the redox reaction of Fe(CN)6 3- was found to change upon adsorption of odor substances into monolayer membranes. The order of threshold values to detect the odorants was β-ionone

The normalized decay rate R of magnetization due to thermally activated flux creep is typically given by R≃k B T/U c, where k B is the Boltzmann constant, T is the absolute temperature and U c is the effective pinning potential. Some observed data for high-T c superconductors show that R increases with increasing T, while in other studies, R takes a peak at a certain temperature T m below the critical temperature T c, where T m decreases with increasing external magnetic field. These temperature dependences of R are explained systematically on the basis of a recent theory of flux creep developed by the authors.

A correlation dimension and a distribution pattern of spectrum intensities of a self-sustained electric oscillation were studied for an aperiodic oscillation induced by an application of electric current on a membrane of a synthetic lipid, dioleyl phosphate. The estimated dimension showed a remarkable deviation in the presence of taste substances such as quinine (above a certain threshold value) from that in the absence of these taste substances; this deviation was accompanied by a change in spectrum pattern. The present result indicates that the two variables extracted from the aperiodic oscillations will be useful as sensing information in a chemical taste sensor using lipid membranes.

A formal theory of macroscopic pinning force FP is presented from a viewpoint that FP of is a value of Lorentz force FL at a bifurcation point, JT=Jc, above which a nondissipative state fluxoi'd lattice carrying a transport current with the density JT becomes unstable and a dynamic dissipative state called the flux flow appears. It is shown that correlation lengthes among pinned fluxoids diverge at the bifurcation point Jc, as these do in other bifurcation phenomena.