Polymers in sensor applications

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Abstract

Because their chemical and physical properties may be tailored over a wide range of characteristics, the use of polymers is finding a permanent place in sophisticated electronic measuring devices such as sensors. During the last 5 years, polymers have gained tremendous recognition in the field of artificial sensor in the goal of mimicking natural sense organs. Better selectivity and rapid measurements have been achieved by replacing classical sensor materials with polymers involving nano technology and exploiting either the intrinsic or extrinsic functions of polymers. Semiconductors, semiconducting metal oxides, solid electrolytes, ionic membranes, and organic semiconductors have been the classical materials for sensor devices. The developing role of polymers as gas sensors, pH sensors, ion-selective sensors, humidity sensors, biosensor devices, etc., are reviewed and discussed in this paper. Both intrinsically conducting polymers and non-conducting polymers are used in sensor devices. Polymers used in sensor devices either participate in sensing mechanisms or immobilize the component responsible for sensing the analyte. Finally, current trends in sensor research and also challenges in future sensor research are discussed.

Introduction

During the last 20 years, global research and development (R&D) on the field of sensors has expanded exponentially in terms of financial investment, the published literature, and the number of active researchers. It is well known that the function of a sensor is to provide information on our physical, chemical and biological environment. Legislation has fostered a huge demand for the sensors necessary in environmental monitoring, e.g. monitoring toxic gases and vapors in the workplace or contaminants in natural waters by industrial effluents and runoff from agriculture fields. Thus, a near revolution is apparent in sensor research, giving birth to a large number of sensor devices for medical and environmental technology. A chemical sensor furnishes information about its environment and consists of a physical transducer and a chemically selective layer [1]. A biosensor contains a biological entity such as enzyme, antibody, bacteria, tissue, etc. as recognition agent, whereas a chemical sensor does not contain these agents. Sensor devices have been made from classical semiconductors, solid electrolytes, insulators, metals and catalytic materials. Since the chemical and physical properties of polymers may be tailored by the chemist for particular needs, they gained importance in the construction of sensor devices. Although a majority of polymers are unable to conduct electricity, their insulating properties are utilized in the electronic industry. A survey of the literature reveals that polymers also acquired a major position as materials in various sensor devices among other materials. Either an intrinsically conducting polymer is being used as a coating or encapsulating material on an electrode surface, or non-conducting a polymer is being used for immobilization of specific receptor agents on the sensor device.

Section snippets

Classical materials for sensor application

The principle of solid-state sensor devices is based on their electrical response to the chemical environment, i.e. their electrical properties are influenced by the presence of gas phase or liquid phase species. Such a change in electrical properties is used to detect the chemical species. Although silicon based chemical sensors, such as field effect transistors (FETs), have been developed, they are not currently produced commercially because of technological and fundamental problems of

Gas sensor

The emission of gaseous pollutants such as sulfur oxide, nitrogen oxide and toxic gases from related industries has become a serious environmental concern. Sensors are needed to detect and measure the concentration of such gaseous pollutants. In fact analytical gas sensors offer a promising and inexpensive solution to problems related to hazardous gases in the environment. Some applications of gas sensors are included in Table 2. Amperometric sensors consisting of an electrochemical cell in a

Trends in sensor research

A consolidated picture of the development of sensors and their applications is presented in Table 2, indicating the wide range of sensor research. Some insight into recent trends in sensor research is obtained from the number of papers being published per year in various analytical journals, which are useful indicators of systems that are directly applied to solving real problems. Fig. 14 shows the number of hits for various subgroups of sensors, including ISEs, optical sensors, amperometric,

Challenges in sensor research

Following the discussion in Section 4, several challenges to the future sensor devices may be considered:

  • 1.

    The search and selection of proper materials, as well as improved and novel recognition mechanisms necessary for instant identification of a target component, and the mechanism to create the signal that will be obtained from the sensor.

  • 2.

    The development of new materials for use as matrices to effectively immobilize receptor molecules to obtain stable and reproducible sensor function, including

Conclusion

The majority of sensor devices utilize many polymers with definite roles, either in the sensing mechanism or through immobilizing the species responsible for sensing of the analyte component. This has become possible only because polymers may be tailored for particular properties, are easily processed, and may be selected to be inert in the environment containing the analyte. While some polymers are intrinsically responsible for a sensor function, other polymers are made to augment the sensing

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