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Introduction
Hamida Hallil1,2 and Hadi Heidari3
1 Univ. Bordeaux, CNRS, IMS, UMR 5218, Bordeaux INP, Fâ33405 Talence, France
2 CINTRA, CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Singapore 637553, Singapore
3 School of Engineering, University of Glasgow, Glasgow, UK
1.1 Overview
Scientific and technological advances of recent years allow considering the realâtime detection of toxic pollutants or chemical or biological substances in gaseous or liquid environments adequately. It is possible to easily find on the market portable devices that allow, for investments of a few hundred to a few thousand dollars, sensor or diagnostic platforms, or low concentrations of chemical or biological species. A smooth, fast, and costâeffective detection of the presence of a chemical or biological element and the quantification of its concentration in real time are criteria that help to amplify the distribution of these sensors and access to highly soughtâafter measurements particularly in demanding areas of scientific knowledge at the boundaries between applied mathematics, physics, chemistry, and biology. This enthusiasm is particularly noticeable in applications dedicated to the issues from the environment, food, and health.
Nowadays, the various commercialized systems existing to answer these issues can be presented in two different approaches: the sensors dedicated to the identification of the risks and consequently to alarm the user; and sensors dedicated to the specific detection of target species at very low concentrations in real time.
However, despite these remarkable technological advances, the development of sensors with: (i) high sensitivity, (ii) real selectivity to a biological or chemical species, (iii) low limit of quantification, (iv) energy autonomy, and (v) reasonable cost remain ultimate challenges for manufacturers and academic researchers.
In recent years based on academic literature, an enormous surge of works has been carried out to develop robust, reliable, accurate, and highâresolution chemical sensing platforms. Also, many efforts have been attempted to convert them into miniaturized, more portable, and costâeffective systems and to study protocols currently used in advanced sensor networks.
A surge of interest, yet an unmet market demand for reliable and highâperformance chemical sensors from different perspectives from materials (polymer, metal oxide, carbon material, etc.) and technology (electrochemical, Field Effect Transistor [FET], acoustic, microwave, optic, electronic tongue and nose, etc.) to applications (food spoilage monitoring, odor, medical, environmental, IOT, etc.), and the accurate interpretation of biochemical processes by readily measurable signals still exists. Such biochemical sensors need to provide fast response, highâsensitivity and selectivity, large dynamic range, and lowâcost to be considered as viable products. These sensors can serve as various applications such as biothreat detection, epidemic disease control, lowâcost home healthcare, and cellâbased and environmental monitoring.
This book titled Smart Sensors for Environmental and Medical Applications addresses the limitations and challenges in obtaining the stateâofâtheâart smart biochemical sensors. It includes ten chapters of contributions from leading experts in bio and chemical sensing. We believe that the approaches developed, and the issues raised in this book will enable the reader to identify the requirements, challenges, and future directions related to the burgeoning field of biochemical detection systems. It should be noticed that in this introduction it is important to recall and explain some basic principles and metrological characteristics common to various sensors categories. These basic notions will provide the reader with a foundation and knowledge for understanding the different technologies and issues raised in the presented chapters.
Furthermore, this book will allow the readers to identify new opportunities in this emerging research field.
1.2 Sensors: History and Terminology
Scientific knowledge has developed through a double effort:
- First, the reflection on the mechanisms, that is to say on the nature of interactions between physical and chemical quantitiesârelated phenomena; this thinking is reflected by the mathematical tool by the laws of physics, abstract relationships between physical quantities.
- Second, experimentation based on the measurement of physical and chemical quantities and which, by associating a numerical value allows to quantitatively define the properties of objects, digitally verify the physical laws, or to empirically establish the form.
Whereas science seeks to grasp and then to express coherent mathematical theories and the laws governing the relationships of physical quantities, technology uses these laws and the properties of matter to develop new devices or materials that enable humans to increase their means of action to better support their wellbeing, facilitate their exchanges, and improve their life. Indeed, at first, the technique was a collection of experimental processes, fruits of the observation, random groupings, or successive tests; the knowledge of the laws of nature allowed the technique to rationalize its approach and to become a science of realization. The measure therefore plays a crucial role. In order to be carried out successfully, the measuring operation generally requires that the information be transmitted remotely from the point where it is captured, protected against alteration by parasitic phenomena, and amplified, before being operated in various ways: displayed, saved, and processed by calculator.
In this respect, electronics offer a variety of influential means: to benefit from measurements of all types of physical quantities, such as their processing and exploitation, it is very desirable to transpose each of the physical quantities immediately into the form of an electrical signal. It is the role of the sensor to ensure this duplication of information by transferring it, at the very point where the measurement is made, of the physical quantity (nonelectric) of its own, on an electrical quantity: current, voltage, load, or impedance.
A sensor is first of all the result of the ingenious exploitation of physical law: this is why an important place is given in this book to the physical principles which are at their base. This is the result of specific properties of each type of sensor: performance, field of application, and rules of good use.
The electrical characteristics of the sensor impose on the user the choice of associated electrical circuits that are perfectly adapted. Therefore, the delivered signal is obtained and can be processed under the best conditions. Indeed, physical principles, specific properties, and associated electrical assemblies are the three main aspects under which each type of sensor will be studied.
1.2.1 Definitions and General Characteristics
The physical quantity that is the object of measurement (temperature, pressure, magnetic, humidity, gas molecules, biomarker, deformation, etc.) is designated as the measurand and represented by M; all the experimental operations which contribute to the knowledge of the numerical value of the measurand constitute its measurement [1].
The sensor is a device that is subjected to the action of a physical or chemical phenomenon measurand, which has a characteristic of electrical nature (load, voltage, current, or impedance) designated by R and which is a function of the measurand: R = F(M) (Figure 1.1). R is the response or the output quantity of the sensor. The measurement of R should allow to know the value of M.
The relati...
