Selective fluorescence sensors for Cu²⁺ and Hg²⁺ ions using acridinium-polymer complexes

The photophysical properties of two acridinium derivatives, 9-phenyl-10-methylacridinium (Ph-Arc⁺) and 9-mesityl-10-methyl acridinium (Mes-Acr⁺) were investigated in aqueous solutions of poly(methacrylic acids) (PMAA) at various pH values with various polymer to dye (R/D) ratios. In acidic conditions, PMAA effectively turned on the emission of both acridinium derivatives. Micromolar concentrations of copper (II) ions can selectively turn off the emission of dye/PMAA mixtures with a linear response range from 0.50 to 10.0 µM and a detection limit as low as 0.38 µM. In near neutral conditions, Mes-Acr⁺ in PMAA solutions displayed extremely weak emission. However, trace amounts of Hg²⁺ ions can instantly turn on the emission with a low detection limit of 43.6 nM and a linear range between 1.0 to 10.0 µM. This analytical method is fast, cost-effective, and environmentally friendly, as it is conducted in 100 % aqueous solution with commercial acridinium derivatives and a biocompatible polymer.