Optical sensor with active matrix built from polyelectrolytes–smart molecules mixture

Light propagating in optical fibres totally reflects from internal glass surfaces, but to some extent optical energy known as evanescent waves crosses glass surfaces and penetrates the surroundings of the optic fibre core. Thin films, built on the surface of optic fibre enriched in smart molecules, changes the spectroscopic properties under influence of the surrounding conditions, and may serve as an active matrix for optic sensors. We have synthesised two polyelectrolytes with aliphatic main chains: one with anionic groups (sulfonated poly(vinyl alcohol)) and a second one with cationic groups (quaternized poly( N,N-dialkylaminoalkylacrylamide)). Thin films composed of up to 50 polyelectrolyte pairs were characterised by contact angle, ellipsometric, and UV-visible spectral measurements. Thin films composed from aliphatic polyelectrolytes and smart molecules, viz. fluorescent dye (eosin) and pH-sensitive dye (phenol red), were deposited on the surface of etched optic fibres. The possibility of pH-sensitive quenching of eosin fluorescence was examined.