The design of low-cost and low-power optical transducers on plastic foil for colorimetric gas sensors is proposed. The transducer was fabricated from PET or PEN foil on which polymeric micro-mirrors and colorimetric film were patterned using additive techniques. It consisted of a planar optical waveguide that was covered with an inkjet printed ammonia sensitive film for its evaluation. A parametric study was performed on the waveguide configuration to reduce the light loss and improve the gas sensing characteristics. The use of polymeric substrate made the device more cost effective and compatible with large scale fabrication, such as roll-to-roll processes. Combined with a low-power interface circuitry operating in pulsed mode, the limit of detection was defined as a function of the power consumption. Sub-ppm concentrations of NH3 were measured at a consumption of 868 mu W. Such potentially low-cost and low-power sensors foresee applications in the field of wireless systems, for environmental and safety monitoring. (C) 201 1 Elsevier B.V. All rights reserved.