Surfactant-Sensitized Covalent Organic Frameworks-Functionalized Lanthanide-Doped Nanocrystals: An Ultrasensitive Sensing Platform for Perfluorooctane Sulfonate

Abstract

Perfluorooctane sulfonate (PFOS) known as a persistent organic pollutant has been attracting great interests due to its potential ecotoxicity. An approach capable of sensing ultra-trace PFOS is in urgent demand. Here, we developed an approach for highly sensitive sensing PFOS using surfactant-sensitized covalent organic frameworks (COFs)-functionalized upconversion nanoparticles (UCNPs) as a fluorescent probe. COFs-functionalized UCNPs (UCNPs@COFs) were obtained by solvothermal growth of 1,3,5-triformylbenzene and 1,4-phenylenediamine on the surface of UCNPs. COF's layer on the surface of UCNPs not only provides recognition sites for PFOS but also improves the fluorescence quantum yields from 2.15 to 5.12%. Trace PFOS can quench the fluorescence emission of UCNPs@COFs at 550 nm due to the high electronegativity of PFOS. Moreover, the fluorescence quenching response can be significantly strengthened in the presence of a surfactant, which causes more sensitivity. The fluorescence quenching degrees (F ₀ - F) of the system are linear with the concentration of PFOS in the range of 1.8 × 10^-13 to 1.8 × 10^-8 M. The present sensor can sensitively and selectively detect PFOS in tap water and food packing with the limit of detection down to 0.15 pM (signal-to-noise ratio = 3), which is comparable to that of the liquid chromatography-mass spectrometry technique. The proposed approach realized a simple, fast, sensitive, and selective sensing PFOS, showing potential applications in various fields.

Scheme 1. (a) Illustration of the Synthesis of Core–Shell UCNPs@COFs Nanoparticles and (b) Schematic Illustration of UCNPs@COFs Fluorescent Nanoparticles for Sensing PFOS

Figure 1

TEM images of UCNPs (a), UCNPs@NH₂ (b), and UCNPs@COFs (c). (d) Fourier transform infrared (FT-IR) spectra of UCNPs (black), UCNPs@NH₂ (red), and UCNPs@COFs (blue). (e) Powder X-ray diffraction (PXRD) patterns of JCPDS standard card number 16-0334 (green), UCNPs (pink), UCNPs@NH₂ (blue), COFs (red), and UCNPs@COFs (black). (f) Thermogravimetry analysis (TGA) patterns of UCNPs (black) and UCNPs@COFs (red).

Figure 2

(a) Effect of the concentration of UCNPs@COFs on fluorescence quenching. (b) Effect of the reaction time on fluorescence quenching. (c) Effect of different surfactants on fluorescence quenching. (d) Effect of the concentration of SDBS on fluorescence quenching (F₀ and F are the fluorescence intensities of UCNPs@COFs at 550 nm in the absence and presence of PFOS, respectively).

Figure 3

(a) Fluorescence intensity response of UCNPs@COFs (dispersed in DMF) to different amounts of PFOS. (b) Plot of F₀ – F vs log[PFOS] (F₀ and F are the fluorescence intensities of UCNPs@COFs at 550 nm in the absence and presence of PFOS, respectively).

Figure 4

Selectivity of the sensing platform.