Preparation of nonconjugated fluorescent polymer nanoparticles for use as a fluorescent probe for detection of 2,4,6-trinitrophenol.

Water-soluble nonconjugated fluorescent polymer nanoparticles (NFPNs) were prepared from branched polyethylenimine (PEI) and citric acid through an amide condensation reaction in the aqueous phase. The NFPNs were characterized using a transmission electron microscope, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectra (XPS). The NFPN fluorescence (with excitation/emission peaks at 360/450 nm) was quenched by 2,4,6-trinitrophenol (TNP) at trace concentrations through the inner filter effect and the formation of self-assembled non-fluorescent Meisenheimer complexes of TNP on the NFPN surfaces through acid-base interactions. The complexes effectively enriched TNP from the bulk solution on the NFPN surfaces through acid-base interactions, and the strong overlap between NFPN excitation and TNP absorption peaks contributed to NFPNs having good sensitivity and selectivity for TNP. The method was selective for TNP and was not sensitive to other interfering species. The calibration plot of log(F0/F) versus TNP concentration shows a linear relationship (R2 = 0.999) for TNP concentration in the range of 0.5-150 μM. The detection limit for TNP was 0.7 μM. The assay was successfully used to determine TNP in spiked lake water samples, and the recoveries were 96.6-102.7%.