Fibre side-polishing technology allows for refractive index measurements using optical fibre Bragg grating sensors. Evanescent field interaction between the guided fibre light mode and the analyte near to the core of the side-polished optical fibre yields a Bragg wavelength shift in dependence on the refractive index of the analyte. This refractometric sensor technique has been extended to opto-chemical measurements with specific sensitivity using transducer layers with selective absorption properties deposited on the side-polished fibre core region. Experimental results are presented for the case of a hydrogen gas sensor (palladium transducer) and a pH sensor (polyaniline transducer).