Towards selective fluorimetric nanospheres sensor for perfluorooctanoic acid anions

A fluorimetric approach allowing monitoring of perfluorooctanoic acid anions concentration changes in solution is proposed. The sensing mechanism explored is based on interactions of perfluorooctanoic anions with Nile red dye on the interface of organic liquid (plasticizer) and aqueous solution embedded within the polymeric nanospheres. In the presence of perfluorooctanoic acid a new emission band appears at approximately 660 nm, accompanied by a decrease in the emission characteristic for Nile Red in the organic phase (observed in the absence of the analyte) at ca 600 nm. The ratio of emission intensities recorded was increasing for increasing analyte concentration in the solution within the range from 0.1 to 400 ppm. Interestingly, this behaviour was observed only for perfluorooctanoic acid anions, offering selectivity over other perfluoroalkyl compounds bearing longer side chains, tested in parallel (perfluoroundecanoate and perfluorotetradecanoate anions). Other relatively lipophilic inorganic anions tested (ClO₄^- or PF₆^-) were also able to interact with Nile Red within the spheres, as proven by emission spectra change, however at much higher concentrations compared to that of perfluorooctanoic acid anions.