Perfluorooctanesulfonate detection and removal with simple imidazolium macrocycles

Simple polycationic macrocycles act as effective receptors for the binding and precipitation-based removal of PFAS "forever chemicals" from aqueous solution. Recognition of perfluoroalkylsulfonates, such as perfluorooctanosulfonate (PFOS), is seen. This occurs even in the presence of inorganic salts and in biofluids, with the binding event "masking" the sulfonate headgroup in PFOS. This triggers self-aggregation of the macrocycle : PFOS complex and formation of disordered micron-scale aggregates that can be removed from solution through a single filtration step using sub-stoichiometric amounts of receptor. The process is highly efficient, with 99.8% PFOS removal being seen upon a single treatment with the cationic receptor. By pairing the recognition with an indicator dye, selective and sensitive PFOS detection can be achieved (LOD ≤48 nM), exploiting hydrophobic association of the dye with the receptor : PFOS aggregates. Molecular dynamics simulations show a three-step aggregation mechanism, with an initial single receptor complex forming, which triggers the formation of micelle-like species that incorporate supra-stoichiometric levels of PFOS. The detection sensitivity and selectivity can be enhanced by pairing the receptors with lipid vesicles, which associate with the receptor : PFOS : dye aggregates, but not the individual components. The net result is a highly sensitive dual-mode detection and removal strategy for a class of environmentally important targets.