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 elabo rated and compared, one involving well established colour reagents used wit h a novel piezo-optical transduction system and the other using alkylviolog en films for molecular recognition of phenols, with transduction via surfac e plasmon resonance (SPR) techniques. In the piezo-optical technique, chopp ed light absorbed by the thin sensing film deposited on piezoelectric polyv inylidene fluoride (PVDF) is converted into heat by non-radiative decay. Th is expands the film, stressing the PVDF and generating an electric charge w hich is measured using a lock-in amplifier. The signal dependence on optica l absorption length, thermal diffusion length, film uniformity and porosity , chopper frequency and amplifier phase synchronisation are reviewed. The d esign and selection of molecular receptors for phenols, and the fabrication of thin films suitable for SPR, are described together with results demons trating response patterns to different phenols and products of atmospheric aging of phenol solutions. The relative advantages of these two very differ ent generic transduction techniques for organic thin film sensing layers ar e discussed with reference to the data presented on the selected sensing sy stems.