A novel bioimaging probe based on a conjugated
polymer, poly(9,9-dihexylfluorene-alt-2,1,3-benzoxadiazole) (PFBD), is demonstrated. Transfer of the hydrophobic
polymer into water using a short chain poly(
ethylene glycol) (PEG) resulted in conjugated
polymer nanoparticles (PEG-PFBD) with a fluorescence quantum yield of 46%. The PEG-PFBD nanoparticles possessed several desirable structural and photophysical properties, such as colloidal stability in a broad range of pH values, sub-20 nm particle size, the presence of surface chemical functionality, as well as desirable excitation and emission spectra, for bioimaging applications. PEG-PFBD nanoparticles were conjugated with
cyclic RGDfK targeting
peptide for labeling of membrane α(V)β(3)
integrin receptors on live HT-29
adenocarcinoma cells. Single nanoparticle microscopy revealed that the PEG-capped PFBD nanoparticles exhibit at least ten times higher emitted photon counts than single
quantum dots (QD655) of comparable size. In addition, Fluorescence Lifetime Imaging Microscopy (FLIM) of single PEG-PFBD nanoparticles revealed that the nanoparticles display a clearly resolvable single nanoparticle fluorescence lifetime.