Reversible photoswitching conjugated polymer nanoparticles for cell and ex vivo tumor imaging

Fluorescent photoswitchable conjugated polymer nanoparticles (PCPNPs) bearing poly(9,9-dihexylfluorene-alt-2,1,3-benzoxadiazole) (PFBD) as the fluorescent host polymer and the photochromic diarylethene as toggle are synthesized via a modified nano-precipitation method using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG-NH₂) as the encapsulation matrix. The PCPNPs are spherical in shape with diameters around 34 nm. The fluorescence switching processes upon UV and white light illumination are successfully demonstrated with high contrast up to 90-fold, recovery efficiency of 95%, and excellent repeatability in solution. The cationic PCPNPs can be easily internalized into cancer cells, and accumulate in tumor tissues, where the fluorescence photoswitching processes can be used to self-validate the imaging results.