Optical transduction of chemical sensing by thin films of colour reagents and molecular receptors using piezo-optical and surface plasmon resonance methods

Two novel chemical sensing systems using thin organic films have been elaborated and compared, one involving well established colour reagents used with a novel piezo-optical transduction system and the other using alkylviologen films for molecular recognition of phenols, with transduction via surface plasmon resonance (SPR) techniques. In the piezo-optical technique, chopped light absorbed by the thin sensing film deposited on piezoelectric polyvinylidene fluoride (PVDF) is converted into heat by non-radiative decay. This expands the film, stressing the PVDF and generating an electric charge which is measured using a lock-in amplifier. The signal dependence on optical absorption length, thermal diffusion length, film uniformity and porosity, chopper frequency and amplifier phase synchronisation are reviewed. The design and selection of molecular receptors for phenols, and the fabrication of thin films suitable for SPR, are described together with results demonstrating response patterns to different phenols and products of atmospheric aging of phenol solutions. The relative advantages of these two very different generic transduction techniques for organic thin film sensing layers are discussed with reference to the data presented on the selected sensing systems.