Biomimetic Sensor Technology

Abstract

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