Photonic modulation of surface properties: A novel concept in chemical sensing

In this paper we discuss the challenges and opportunities afforded by surface-based photoswitchable chemical sensors. We focus on spiropyrans as it is a well-studied system that can be photonically switched between two states, only one of which exhibits ion-binding behaviour. Surface immobilization and protection within a polymer matrix is identified as a route that can successfully address the need for a localized hydrophobic environment in which a user can maintain control over the spiropyran-merocyanine equilibrium and at the same time improve photo-fatigue resistance. Furthermore, we discuss the excellent potential of light emitting diodes as light sources and detectors for photoswitching between the states of spiropyran and measurement of bound species. A simple, low-cost, low-power experimental setup provides spatial and temporal control of surface illumination and surface binding. This, coupled with low irradiance, is shown to generate significant improvement in fatigue resistance of spiropyrans-modified films, and may prove to be an important step towards the realization of chemical sensors that can be deployed in large-scale wireless chemical sensor networks.