This work describes the preparation of a polyaniline (Pani)-porous Vycor glass (PVG) nanocomposite and its use as sensing phase in an optical fibre pH sensor. Nanocomposites of Pani-PVG were prepared by in situ polymerisation of aniline absorbed inside the pores of a PVG (Corning 7930) with an average porous size of 8 nm. The optical sensor was constructed by fixing a PVG slide onto a distal end of bifurcated optical fibre bundle, with a cyanoacrylic resin. The sensor response was found to be reversible in the pH range from 5 to 12 and linear from pH 7.4 to 9.5. Response times of 4, 8 and >16 min were obtained for slide thickness' of 0.5, 1 and 1.5 mm, respectively. Changes of temperature, ranging from 20 to 40°C, showed minor effect on the dynamic range. Similarly, the ionic strength (0.15, 0.30 and 0.50 mol l-1) and the nature of the ions (NaCl, KCl and NaClO4) showed minor influence on the sensor response. Leaching of Pani was not observed and the sensor lifetime was determined as being at least 5 months. These results indicate that a Pani-PVG nanocomposite is suitable for the construction of optical pH sensors, with good analytical performance, since the glass slides can be prepared with good reproducibility and durability. © 2001 Elsevier Science B.V.741-3157162Kosch, U., Klimant, I., Wolfbeis, O.S., Long-lifetime based pH microoptodes without oxygen interferences (1999) Fresenius J. Anal. Chem., 364, pp. 48-53Mahutte, C.K., On-line arterial blood gas analysis with optodes: Current status (1998) Clin. Biochem., 31, pp. 119-130Song, A., Parus, S., Kopelman, R., High-performance fibre-optic pH microsensors for practical physiological measurements using a dual-emission sensitive dye (1997) Anal. Chem., 69, pp. 863-867Motellier, S., Toulhoat, P., Modified acid-base behaviour of resin-bound pH indicator (1993) Anal. Chim. Acta, 271, pp. 323-329Moreno, M.C., Jiménez, M., Pérez, C., Cámara, C., Analytical performance of an optical pH sensor for acid-base titration (1990) Anal. Chim. Acta, 230, pp. 35-40McGlip, J., Glass cages make sense (1991) Phys. World, 11, pp. 23-25Baldini, F., Bracci, S., Cossi, F., Bechi, P., Pucciani, F., Controlled-pore glasses embedded in plastic optical fibres for gastric pH sensing purposes (1994) Appl. Spectrosc., 48, pp. 549-552Shulman, S.G., Chen, S., Bai, F., Leiner, M.J.P., Weis, L., Wolfbeis, O.S., Dependence of the fluorescence of immobilised 1-hydroxypirene-3,6,8-trisulphonate on solution pH: Extension of the range of applicability of a pH fluorosensor (1995) Anal. Chim. Acta, 304, pp. 165-170Jones, J.P., Porter, M.D., Optical pH sensor based on the chemical modification of a porous polymer film (1988) Anal. Chem., 60, pp. 404-406Kosch, U., Klimant, I., Werner, T., Wolfbeis, O.S., Strategies to design pH optodes with luminiscence decay times in the microsecond time regime (1998) Anal. Chem., 70, pp. 3892-3897Wolfbeis, O.S., Marhold, H., A new group of fluorescent pH-indicators for an extended pH-range (1987) Fresenius Zeitschift für Analytische Chemie, 337, pp. 347-350Posch, H.E., Leiner, M.J.P., Wolfbeis, O.S., Towards a gastric pH-sensor: An optrode for pH 0-7 range (1989) Fresenius Zeitschift für Analytische Chemie, 334, pp. 162-165Wolfbeis, O.S., Offenbacher, H., Fluorescence sensor for monitoring ionic strength and physiological pH values (1986) Sens. Actuators, 9, pp. 85-91Geniès, E.M., Boyle, A., Lapkowski, M., Tsintavis, C., Polyaniline: A historical survey (1990) Synth. Met., 36, pp. 139-182Watanabe, A., Mori, K., Iwabuchi, A., Iwasaki, I., Nakamura, Y., Electrochemical polymerisation of aniline and N-alkylanilines (1989) Macromolecules, 22, pp. 3521-3525Bodalia, R., Stern, R., Batich, C., Duran, R., Synthesis and polymerisation of 2-alkilanilines (1993) J. Polym. Sci.: Part A. Polym. Chem., 31, pp. 2123-2127Mattoso, L.H.C., Polianilinas: Síntese, estrutura e propriedades (1996) Quimica Nova, 19, pp. 388-398Kitani, A., Yano, J., Sasaki, K., ECD materials for the three primary colours developed by polyanilines (1986) J. Electroanal. Chem., 209, pp. 27-232Cushman, R.J., McManus, P.M., Yang, S.C., Spectroelectrochemical study of polyaniline: The construction of a pH potential phase diagram (1986) J. Electroanal. Chem., 219, pp. 335-346Taboada, M.P.S., De Paoli, M.A., De Oliveira, W.A., Fibre-optic sensor based on poly(o-methoxyaniline) (1997) Anal. Chim. Acta, 353, pp. 275-280De Marcos, S., Wolfbeis, O.S., Optical sensing of pH based on polypyrrole films (1996) Anal. Chim. Acta, 334, pp. 149-153Fabrizio, M., Furlanetto, F., Mengoli, G., Musiani, M.M., Paolucci, F., Polyaniline-based membranes for gas electrodes (1992) J. Electroanal. Chem., 323, pp. 197-212Li, S., Cao, Y., Xue, Z., Inoue, M.B., Soluble polyaniline (1987) Synth. Met., 20, pp. 141-149Macinnes D., Jr., Funt, D.B.L., Poly-o-methoxyaniline: A new soluble conducting polymer (1988) Synth. Met., 25, pp. 235-242Abe, M., Ohtani, A., Umemoto, Y., Akisuki, S., Ezoe, M., Higushi, H., Nakamoto, K., Noda, Y., Soluble and high molecular weight polyaniline (1989) J. Chem. Soc., Chem. Commun., pp. 1736-1738Inoue, M., Navarro, R.E., Inoue, M.B., New soluble polyaniline: Synthesis, electrical properties and solution electronic spectrum (1989) Synth. Met., 30, pp. 199-207Bergeron, J.Y., Chevalier, J.W., Dao, L.H., Water-soluble conducting poly(aniline) polymer (1990) J. Chem. Soc., Chem. Commun., pp. 180-182Ge, Z., Brown, C.W., Sun, L., Yang, S.C., Fibre-optic pH sensor based on evanescent wave absorption spectroscopy (1993) Anal. Chem., 65, pp. 2335-2338Pringsheim, E., Terpetschnig, E., Wolfbeis, O.S., Optical sensing of pH using thin films of substituted polyanilines (1997) Anal. Chim. Acta, 357, pp. 247-252Zarbin, A.J.G., Paoli, M.A., Alves, O.L., New polyaniline/porous glass composite (1997) Synth. Met., 84, pp. 107-108Zarbin, A.J.G., Paoli, M.A., Alves, O.L., Nanocomposite glass/conductive polymers (1999) Synth. Met., 99, pp. 227-235Neoh, K.G., Kang, E.T., Protonation and deprotonation behaviour of amine units in polyaniline (1993) Polymer, 34, pp. 1630-1636Perrin, D.D., Dempsey, B., (1974) Buffers for pH and Metal Ion Control, p. 156. , Chapman & Hall, LondonZarbin, A.J.G., (1997) Novos nanocompósitos obtidos pelas Interações de compostos organometálicos e polímeros condutores com vidros porosos, , Ph.D. Thesis, UNICAMP, Campinas, BrazilNaraynaswamy, R., Optical chemical sensors: Transduction and signal processing (1993) Analyst, 118, pp. 317-322Kirkbright, G.F., Narayanaswamy, R., Welti, N.A., Fibre-optic pH probe based on the use of an immobilised calorimetric indicator (1984) Analyst, 109, pp. 1025-1028Taib, M.N., Andres, R., Narayanaswamy, R., Extending the response range of an optical fibre pH sensor using artificial neural network (1996) Anal. Chim. Acta, 330, pp. 31-40Huang, W.S., Humphrey, B.D., McDiarmind, A.G., Polyaniline, a novel conducting polymer (1986) J. Chem. Soc., Faraday Trans., 1 (82), pp. 2385-2400