Detection of PFAS and Fluorinated Surfactants Using Differential Behaviors at Interfaces of Complex Droplets

Abstract

Contamination of per- and polyfluoroalkyl substances (PFAS) in water supplies will continue to have serious health and environmental consequences. Despite the importance of monitoring the concentrations of PFAS at potential sites of contamination and at treatment plants, there are few suitable and rapid on-site methods. Many nonconventional techniques do not possess the necessary selectivity and sensitivity to distinguish PFAS from other surface-active components and to quantify the low concentrations in real-world conditions. Herein, we report a novel and rapid method for the detection of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) by leveraging their differential behaviors at the interfaces of emissive complex droplets. Measurement of surface and interfacial tensions via a force tensiometer reveals that PFAS preferentially self-assemble at the water–fluorocarbon oil interface (F/W) rather than the water–hydrocarbon oil interface (H/W). We also observe an opposite behavior for hydrocarbon surfactants. This difference in interfacial behavior produces distinct effects on the morphological change and optical emission of biphasic oil-in-water droplets. The change in the intensity of fluorescence emission, measured with a simple spectroscopic setup, correlates with the concentrations of PFAS. We also demonstrate that the range of detection and sensitivity can be tuned by adjusting the initial composition of the complex droplets. Our results illustrate an alternative mode of sensors that may provide a rapid and on-site detection of PFAS.

Dynamic In Situ Monitoring of the Salt Counter-ion Effect on Surfactant Effectiveness Using Reconfigurable Janus Emulsions

“…Selectively influencing their effectiveness then allows to dynamically and controllably alter the interfacial tension equilibrium and thus droplet morphology. To this end, a series of active surfactants have been developed that can be selectively attached to specific droplet interfaces, e.g., in order to target specific stimuli, such as light, electric or magnetic fields, − environmental contaminants, , biomacromolecules, or bacteria . Based on the unique chemical-morphological-optical coupling inside reconfigurable complex droplets and depending on a fine-adjustment of the droplets’ starting morphology, marginal variations of the interfacial tension balance can then cause significant variations of the macroscopic optical properties of the emulsion.…”

“…Reconfigurable complex emulsions have emerged as a novel triggerable material platform of interest for a wide range of transformative application concepts, including as dynamic optical components, for the encapsulation and release of active agents, signal transmitters and amplifiers in liquid sensing platforms, , and as scaffolds for the generation of precision objects . Biphasic emulsion droplets present the intrinsic ability to dynamically switch their morphology between encapsulated and Janus geometries .…”

Multiplexed and continuous microfluidic sensors using dynamic complex droplets

“…S4 (ESI†), the emission intensity reaches a maximum value at f SDS = 0.2, which agrees well with previous reports that measured directional emission in a batch-to-batch manner. 11,20,39 This behavior limits the effective range of complex droplets to be from f SDS = 0.2 to 1. In this work, we sought to demonstrate the ability to faithfully reproduce the full range of responses from complex droplets, including the nonmonotonic response, in real-time via continuous and multiplexed measurement.…”

“…[5][6][7][8][9][10][11] For example, they have previously been demonstrated as effective detection platforms for biological analytes-such as E. coli, 12,13 Listeria monocytogenes, 14,15 SARS-CoV-2, 16,17 and bacteriophages 18 -as well as environmental contaminants. 19,20 While these examples served as successful proofs-of-concept, crucial limitations exist that prevent the development of an on-site sensing platform for real-world samples and situations. Specifically, many of the current platforms lack the capacity to generate multiplexed or continuous sensing signals.…”

“…Previous works by our group and others have used the coupling between the dynamic morphology and optical properties of complex emulsions for the selective detection of targeted analytes. 11,12,15,[17][18][19][20]38,39 For example, Zeininger et al reported detections of Salmonella enterica using the relationship between the internal geometry of the droplets (induced by the presence of the bacteria) and the angular distribution of fluorescent emission. 11 This transduction mechanism, called directional emission, has also been used to detect trace concentrations of per-and polyfluoroalkyl substances (PFAS) 20 and hydrogen peroxide.…”