Fabrication of optical gas sensors using porphyrin-based nano-assembled thin films: A comparison with bulk materials

In this study two kinds of biological origins, porphyrin and bacteriorhodopsin that were embedded into polymer matrix and into inorganic sol-gel matrix, respectively, were employed as active elements for an optical sensor. To confirm the usefulness of the consequent nano-scale matrix in the detection of volatile organic compounds (VOCs), aromatics and amine compounds, anionic tetrakis-(4-sulfophenyl)porphine (TSPP) was alternately assembled with cationic poly(diallyldimethylammonium chloride) (PDDA) on quartz plates. The performance and sensor parameters of the nano-scale thickness porphyrin-based thin film and bacteriorhodopsin thick film are compared. The sensing principle is based on monitoring the optical changes of the Q-band at 700 nm for the porphyrin film and at 570 nm for the bacteriorhodopsin film. This work was a first step in the development of a fiber-optic gas sensor which employs thin films as sensitive elements for the detection of different gases.