Guanidinocalix[5]arene for sensitive fluorescence detection and magnetic removal of perfluorinated pollutants

Abstract

Perfluorinated alkyl substances, such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are toxic materials that are known to globally contaminate water, air, and soil resources. Strategies for the simultaneous detection and removal of these compounds are desired to address this emerging health and environmental issue. Herein, we develop a type of guanidinocalix[5]arene that can selectively and strongly bind to PFOS and PFOA, which we use to demonstrate the sensitive and quantitative detection of these compounds in contaminated water through a fluorescent indicator displacement assay. Moreover, by co-assembling iron oxide nanoparticle with the amphiphilic guanidinocalix[5]arene, we are able to use simple magnetic absorption and filtration to efficiently remove PFOS and PFOA from contaminated water. This supramolecular approach that uses both molecular recognition and self-assembly of macrocyclic amphiphiles is promising for the detection and remediation of water pollution.

Selectivity of Per- and Polyfluoroalkyl Substance Sensors and Sorbents in Water

“…(a) A “turn-on” fluorescent sensor using fluorescein (Fl) as the emissive species and guanidinocalix[5]arenes (GC5A) as the quencher and the PFAS-capturing probe. Reprinted with permission from ref ( 30 ). Copyright 2019 Springer Nature.…”

“…For “turn-on” types, the fluorescent probe is either originally weakly emissive (e.g., a molecularly imprinted chitosan-doped carbon quantum dot), 44 nonemissive (e.g., aggregation-induced emission luminogens), 47 or emissive but quenched by a paired quencher (e.g., fluorescein and guanidinocalix[5]arenes) ( Figure 3 a). 30 After this fluorescent probe conjugates with PFAS molecules, the fluorescence emission is activated or strengthened, and the degree of this signal change can be correlated to PFAS concentrations. Similarly, “turn-off” fluorescence sensors exhibit decreasing fluorescent signal when the fluorescent probe interacts with PFAS molecules, and the extent of the fluorescence reduction can be converted to PFAS concentrations.…”

“…In one fluorescence sensor, for example, the LOD of the device for PFOS increased from 10.7 μg/L (21.4 nM) to 60.4 μg/L (120.8 nM) when the sample matrices changed from buffer solution to real lake water. 30 Therefore, preconcentration and pretreatment are typically required for PFAS sensors. Solid-phase extraction is the standard method for preconcentration used by the EPA, 26 , 27 and it has also been frequently applied in various sensing devices.…”

“…However, there are a limited number of studies on PFAS sensors that mention or demonstrate those properties. 30 , 64 , 65 , 67 Many sensors are advertised as “real-time”, but usually there are limited quantitative data provided regarding the specific response time. Even when fast response is demonstrated, there may be time required to prestabilize the sensor signal, which may take several hours.…”

“…By extracting solutes from those real water samples, the selectivity in individual modes could also be tested. 30 …”