The Hofmeister Anion Effect on Ionophore-based Ion-selective Nanospheres Containing Solvatochromic Dyes

Recently reported ionophore-based ion-selective nanospheres contained pH-independent and positively charged solvatochromic dyes. Here, we evaluate systematically the effect of anions to the fluorescence response of the nanospheres. The anion interference was found significant for anion concentrations above 10 mM. The sensor responses in the presence of various anion background was studied. While target ion (K+) causes the fluorescence of the nanospheres to decrease, increasing anion background also leads to lower fluorescence intensity. Lipophilic anions such as ClO4-, SCN-, and I- exhibited much more interference than hydrophilic anions (e. g., NO3-, Cl-, F-, SO42-). The trend of the anion interference followed the Hofmeister series. A theoretical model was also demonstrated based on anion adsorption on the surface of the nanospheres.