Real-Time Standoff Detection of Trace Levels of PFAS in Water Using Photothermal Nanomechanical Spectroscopy.

Real-time detection of hazardous chemicals in water that appear at parts-per-trillion level concentrations with high sensitivity and selectivity is challenging. Achieving ultrahigh sensitivity using techniques based on immobilized receptors and electrochemistry requires the use of preconcentrators for sample enrichment, which imposes a time penalty. In addition, the use of immobilized receptors results in sensor-to-sensor irreproducibility challenges. Here, we demonstrate a real-time standoff technique for the ultrasensitive detection of chemical species in water based on a nanomechanical photothermal technique. This method involves exciting trace amounts of molecules in water by using tunable infrared light and directing the scattered light onto a cantilever, inducing mechanical deflections. The wavelength-dependent nanomechanical deflections were then used to quantify the contaminants in the water. We demonstrate this technique by selective detection of 1 part-per-trillion perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and fluorotelomer alcohol (FTOH) in distilled and deionized water without using preconcentrators, labels, or receptors and demonstrate its functionality in industrial surface water samples. The proposed method also does not require sample preparation and is amenable to deployment in field applications.