Plasmonic synergism in tailored metal–carbon interfaces for real-time single molecular level sniffing of PFOS and PFOA

Generating plasmonic hot-spots through engineering of nanoscale interfaces offers exciting opportunities towards point-of-care analytical detection. The mutual trade-off between ultra-high sensitivity, specificity and reliability are major drawbacks for practical applicability with real-time samples. Fundamentally these originate from low photonic mode density, high ohmic losses, temporally fluctuating and chemically indistinguishable nature of electromagnetic hot-spots. This work describes synergism of metallic plasmons from tailored interfaces of Ag-Au nanoalloys with conical nanocavities of nanocarbon florets (NCF), leading to strong metal-dielectric interfacial coupling. Such, Ag-Au-NCF nanohybrid delivers an unprecedented 1517-fold enhancement in surface-plasmon coupled directed emission (SPCE) of Rhodamine B (RhB) leading to robust (relative standard deviation, RSD < 10 %) single-molecular-level detection of spectroscopically-silent perfluoroalkyl substances (PFAS). The limit-of-detection demonstrated (PFOS = 0.005 ppt) is one-thousand times better than WHO recommendation and surpasses all existing reports. The specific cation–anion interactions between RhB and PFAS are substantiated through density functional calculations that concur with experimental findings. Finally, the emission from this SPCE platform can be visually tracked through a smartphone camera over wide range of PFOS concentrations (0.005–5000000 ppt) in water samples (lake, river, tap, drinking and ocean) and blood-plasma, offering transformative opportunities in analytical sciences.