The exploitation of metalloporphyrins as chemically interactive material in chemical sensors

The main features of a chemical sensor are given by the properties of the chemically interactive membranes that accomplish the selective capture of molecules from the environment. The capture of molecules on the surface can originate the variation of a number of different properties of the materials so that a number of different kinds of chemical sensors can be based on the same chemically interactive membrane. In this paper the utilization of metalloporphyrins and related compounds as chemically interactive materials is discussed and preliminary data concerning the performance of mass sensitive sensors and conductivity sensors are reported. Very interesting results have been obtained with quartz microbalances. In this case metalloporphyrin coated sensors show, beside good sensitivity, a selectivity which depends mostly on the metallic ion complexed at the center of the macrocycle. This results in the possibility of changing the sensor selectivity with minor modification of the synthesis process. This property makes metalloporphyrins interesting for electronic nose applications. Results concerning the applications of an electronic nose based on metalloporphyrin coated quartz microbalances are illustrated and discussed. Conductivity measurements confirmed the previously reported character of the charge transport inside the metalloporphyrins. A certain sensitivity to triethylamine and NOx has also been found. Among the measured compounds, a polymer of porphyrins has been included, conductivity measurements indicate the occurrence of a different conduction mechanism.