Enriching the selectivity of metalloporphyrins chemical sensors by means of optical technique

In the electronic nose, the sensing elements must demonstrate high selectivity feature toward various kinds of gases. This paper reports the use of the optical technique to enrich the selectivity of four metallo-octaethyl porphyrins (with the metal atoms of Mn, Fe, Co and Ru) Langmuir-Blodgett (LB) films toward four vapor samples; 2-propanol, ethanol, acetone and cyclohexane. The optical system was developed using these materials as sensing elements and four LED's of different colors; red, yellow, green and blue, as light sources. The sensing sensitivity was based on the change on the light intensity at the peak wavelength of light sources after being reflected by the films. The sensitivity of the films was observed to depend on the wavelength of the light source used and the metal atom at the center of the metalloporphyrins molecules. Each thin film produced four response signals or 16 signals for the whole system for a particular vapor. These 16 signals constituted the pattern of the signature of a vapor. The signature of each vapor was found to be different from each other. This work indicated that the amount of the sensing elements used to create a high selectivity gas sensor system may be reduced. (C) 2002 Elsevier Science B.V. All rights reserved.