Cross-linked dodecyl acrylate microspheres: novel matrices for plasticizer-free optical ion sensing

Hexanedioldiacrylate (HDDA) cross-linked dodecyl acrylate (DDA) microspheres ranging from approximately 1 to 10 mum in diameter have been prepared via photoinitiated dispersion polymerization and used as polymer matrices in the development of a new class of "plasticizer-free" ion-selective optical sensors (optodes). Incorporation of a fluorescent Nile Blue derivative (ETH 5294) into the microspheres produced independent self-referencing optodes capable of measuring the activities of various anions in aqueous media. In order to increase sensitivity and signal reproducibility, changes in the fluorescence intensity of two emission peaks, corresponding to the protonated and deprotonated forms of the chromoionophore, were used to perform ratiometric analysis. Spatial and 3D spectral resolution of individual sensing microspheres is reported, providing analytically useful information about the local sensing environment. Physical properties of the polymeric microspheres that affect sensor function such as size, morphology, surface topography, dispersity, and glass transition temperature (Tg) are also reported here.