Fundamental investigation on fluorous nanoemulsion optodes: effect of matrix fluorination on selectivity

As fundamental investigation on fluorous nanoemulsion (NE) optodes for highly selective perfluorooctanesulfonate (PFOS⁻) sensing, the effect of matrix fluorination on selectivity was investigated. Due to the high hydrophobicity of PFOS⁻ itself, it responded in exhaustive mode regardless of the fluorination ratio of the matrix, and the lowest detectable PFOS⁻ concentration was on the order of 10⁻⁷ to 10⁻⁶ M. On the other hand, the response of non-fluorous interfering anions was suppressed as the fluorination ratio of the matrix increased. It was revealed that the relative selectivity of PFOS⁻ for hydrophobic anions, ClO₄⁻, SCN⁻, and 1-octanesulfonate (OS⁻) was improved by more than one order of magnitude, up to nearly two orders of magnitude, and that it was also improved by less than one order of magnitude for hydrophilic anions, Br⁻, Cl⁻, and SO₄⁻, in logarithmic selectivity coefficient (log \({K}_{{PFOS}^{-}, j}^{opt}\) $K_{{\mathit{PFOS}}^{-},j}^{\mathit{opt}}$ ).