Efficient Near-infrared AIE Nanoparticles for Cell Imaging

Near-infrared fluorescence signals are highly desirable to acheieve high resolution in biological imaging. We encapsulated hydrophobic AIE (aggregation-induced emission) fluorophores into the biocompatible Pluronic F-127 NPs for cellular imaging and efficiently enhance the near-infrared AIE fluorophore emission. AIE molecule 2-(4-bromophenyl)-3-(4-(4-(diphenylamino)styryl)phenyl) fumaronitrile (TPABDFN) with near-infrared emission was synthesized and selected as the fluorescence resonance energy transfer (FRET) acceptor. (2-p-tolylethene-1,1,2-triyl)tribenzene (TPE-Me) was a blue-emitting AIE molecule, which spectrum was matching with TPABDFN. TPE-Me@F127 NPs emission was 480 nm, TPABDFN@F127 NPs maximum absorption wavelength was also 480 nm, that the absorption had a large area of overlapping with the TPE-Me@F127 NPs emission spectrum and leaded to efficient energy transfer, so TPE-Me was selected as the FRET donor. By encapsulating both TPE-Me donor and TPABDFN acceptor simultaneously within the NPs, a significant FRET effect was induced. FRET pairs of different ratios was co-encapsulated into the F127 NPs to optimize the fluorescence signals. The maximum of fluorescence quantum yield was 19.9%, energy transfer efficiency was 43.5%. TPABDFN@F127 NPs only had weak fluorescence, but the TPABDFN/TPE-Me@F127 NPs showed bright fluorescence signal. Fluorescence resonance energy transfer contributed to the notable increase of acceptor emission The fluorescence quantum yield had 10-fold enhancement of the TPABDFN. In addition, the obtained TPABDFN/TPE-Me@F127 NPs showed a large Stokes shift of 265 nm, which can be used to avoid the interference between excitation and emission light, as well as the near-infrared emission spectrum away from the organism auto-fluorescence, which was beneficial for the bio-application. Fluorescent probe emission in the far red/near-infrared (FR/NIR) (650 similar to 900 nm) region for biological detection also can greatly reduce the damage to living body. And TPABDFN/TPE-Me@F127 NPs had low cytotoxicity, good biocompatibility, stability and anti-photobleaching. The TPABDFN/TPE-Me@F127 NPs achieved good imaging result on HepG2 cell cytoplasm.