A new type of microstructured optical fiber, with a transverse slot running along its length, has been fabricated from polymethylmethacrylate. The slot exposes the fiber core over long lengths, allowing for materials to be directly introduced into the vicinity of the evanescent waves of the core modes. The use of this fiber as an evanescent wave chemical sensor has been demonstrated.7004 Hale, Z.M., Payne, F.P., A tapered single-mode optical fibre as an intrinsic pH sensor (1992) Procedings of IEE Colloqium on Fibre Optics Sensor Technology Digest number 128, pp. 81-84. , Institute of Electrical Engineers, LondonCulshaw, B., Muhammad, F., Stewart, G., Murray, S., Pinchbeck, D., Norris, J., Cassidy, S., McGhee, A., Evanescent wave methane detection using optical fibers (1992) Electron. Lett, 28, pp. 2232-2234Knight, J.C., Birks, T.A., Russell, P.S.J., Atkin, D.M., All silica single-mode optical fiber with photonic crystal cladding (1996) Opt. Lett, 21, pp. 1547-1549Cordeiro, C.M.B., dos Santos, E.M., Brito Cruz, C.H., de Matos, C.J., Ferreiia, D.S., Lateral access to the holes of photonic crystal fibers - selective filling and sensing applications (2006) Opt. Express, 14, pp. 8403-8412Cordeiro, C.M.B., De Matos, C.J.S., Dos Santos, E.M., Bozolan, A., Ong, J.S.K., Facincani, T., Chesini, G., Brito Cruz, C.H., Towards practical liquid and gas sensing with photonic crystal fibres: Side access to the fibre microstructure and single-mode liquid core fibre (2007) Meas. Sci. Technol, 18, pp. 3075-3071van Brakel, A., Grivas, C., Petrovich, M.N., Richardson, D.J., Micro-channels machined in microstructured optical fibers by femtosecond laser (2007) Opt. Express, 15, pp. 8731-8735Barton, G., van Eijkelenborg, M.A., Henry, G., Large, M.C.J., Zagari, J., Fabrication of microstructured polymer optical fibres (2004) Opt. Fiber Techno, 10, pp. 325-335