Bright far-red/near-infrared fluorescent conjugated polymernanoparticles for targeted imaging of HER2-positive cancer cells

We report the design and synthesis of a far-red/near-infrared (FR/NIR) fluorescent conjugated polymer, PFDBT-POSS, bearing poly{[9,9-di(hexyl)fluorene]-alt-co-[4,7-bis(thiophen-2-yl)-2,1,3-benzothiazole]} (PFDBT) as the backbone and bulky polyhedral oligomeric silsesquioxane (POSS) as side chains. PFDBT-POSS based nanoparticles (NPs) with maleimide (Mal) groups on the surface are prepared by encapsulating the polymer using DSPE-PEG2000 and DSPE-PEG2000-Mal as matrix. The obtained PFDBT-POSS-Mal NPs show a maximum absorption at ∼536 nm and a FR/NIR emission centred at ∼687 nm. It has a quantum yield (QY) of 13.6% in water, which is 6-fold higher than that of PFDBT-Mal NPs (QY = 2%), indicating that incorporation of POSS segments as pendants can efficiently suppress fluorescence quenching. The presence of Mal functional groups allows for efficient bioconjugation with anti-HER2 affibody by click reaction. The resultant PFDBT-POSS-Affibody serves as a reliable fluorescent probe with low cytotoxicity and high photostability in targeted detection and cellular imaging of HER2-overexpressed cancer cells using SKBR-3 as an example. Of particular interest is that the absorption maximum of PFDBT-POSS-Mal NPs overlaps well with the commercial 543 nm laser line, which ensures the most efficient utilization of the light harvesting property of the probe to generate bright fluorescence signals. This study provides an efficient strategy to design bright FR/NIR fluorescent CP NPs with long wavelength absorption and emission for biological applications.