An optrode sensor has been constructed by coating fumed silica particles incorporating covalently attached organoironcarbonyl probe groups onto a ZnSe attenuated total reflectance (ATR) element, The sensor may be interrogated remotely using Fourier transform infrared (FTIR) spectroscopy by coupling IR transparent optical fibres to the ATR element. The organometallic probe groups act as components of a sensing system in which analyte/sensor interactions are transduced through shifts in the sharp v(CO) bands of the metal carbonyl reporting group. The potential of the device is demonstrated for pH sensing in the range 7-13 and as a sensor of solvent environment. Coating two different immobilised probe groups onto the ATR element, combined with FTIR measurement, allows the optrode to be used for the independent, multi-component sensing of two analytes. (C) 2002 Elsevier Science B.V. All rights reserved.