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A broad-range fibre optic pH sensor based on evanescent wave absorption is presented in this paper. This sensor is prepared by immobilizing a mixture of three pH sensitive indicators (dyes): cresol red, bromophenol blue and chlorophenol red onto the unclad fibre surface using a sol-gel cladding technology. Triton is introduced into the sol-gel cladding to improve the cladding quality. Smooth and strong sol-gel cladding with entrapped indicators and triton has been fabricated and observed using a scanning electron microscope (SEM), an energy dispersive X-ray detector (EDX) and an atomic force microscopy (AFM). The pH sensor based the cladding has shown a linear, reversible and repeatable response over a broad range of pH values between 4.5 and 13.0. (C) 2007 Elsevier B.V. All rights reserved.