Silicone Films for Optical Sensing of Other Species

6 Silicone Films for Optical Sensing of Other Species 

In spite of the prominence of molecular oxygen luminescence sensing due to its manifold applications, several other chemical species may also be monitored with silicone-based sensors using a pluraHty of indicator-based and label-free mechanisms. A representative account of these chemical optosensors is outHned here to allow the reader to realize how versatile sihcones are for manufacturing such devices, including those for non-gaseous species. 

Hydrogen sulfide (H S) can reversibly be quantified down to 10 ppm(v) with silicone thin films doped (after curing) with nanometer-sized CdSe/CdS luminescent quantum dots [12]. The sensor response is due to donor (H Sf-acceptor (QD) interactions. The indicator layer does not display any response to water, volatile hydrocarbons or alcohols, but shows some response to amines such as 1-butylamine, due to the higher nucleophihcity of the latter. 

The optical indicator dye need not be embedded into the silicone film itself. For instance, a usual way to monitor gases that are able to cross a siUcone thin membrcuie but require water to provide the analytical signal change, is to dissolve the indicator dye (typically a pH-sensitive one) in water or a hydrated hydrogel and separate this sensitive layer from the sample by means of the undoped silicone film. Typical 

The silicone thin film is only used to avoid penetration (and therefore, interference) of non-gaseous species into the (internal) acidity-sensitive indicator layer. 

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