NEAR-INFRARED FLUORESCENCE PROBE FOR PH DETERMINATION

Nafion, a perfluorosulfonated ion-exchange polymer, has been evaluated as a substrate for immobilizing a near-infrared absorbing fluorophore to determine pH in solutions. Following simple preparation procedures a cyanine dye with a pH-sensitive functional group (a bis(carboxylic acid) derivative) was entrapped within the Nafion matrix and fabricated into thin film. The fabrication of a thin-film probe gives greater versatility for the method. This dye exhibits great stability inside the Nafion matrix and has relatively long absorption and fluorescence wavelengths which allow researchers to utilize the lower interference of this region. Since the absorption maximum of the study system is around 800 nm in aqueous solutions, semiconductor lasers can be used. In the study the feasibility of this approach was illustrated and the analytical utility of near-infrared laser diodes for pH determination was evaluated.