Sensor is defined as primary device which selectively reacting or responding to change in particular properties of the surrounding
medium and which enables recording of this response in the form of a corresponding electrical signal. Chemical sensors respond to concentration changes of chemical substances in liquid and gaseous media. The need for continuous monitoring of critical parameters in clinical chemistry, biotechnology, pharmaceutical, chemical and nuclear industries, chemical warfare and environmental control is the driving force behind sensor research. Numerous sensing schemes have been developed in the past twenty years, most of them based on optical or electrochemical methods which form the majority of sensors. In order to achieve certain selectivity, a specific interaction takes place between a receptor and the target analyte. This usually occurs at a membrane or coating or a thin film located at the sensor-sample interface. Typical receptors include organic molecules such as immobilised chelating agents; more complex species such as enzyme, antibodies, DNA; as well as natural synthetic receptors. Aside from covalent immobilisation, which is the preferred but tedious method, embedding the receptor into an inert matrix is another frequently applied method. Numerous polymers have been used for incorporating or chemically immobilising indicators, chelators and biomolecules. This presentation will generally discuss all the relevant aspects and principles, which include the application of fundamental sciences in conducting chemical sensors research.