Far‐Red/Near‐Infrared Conjugated Polymer Nanoparticles for Long‐Term In Situ Monitoring of Liver Tumor Growth

The design and synthesis is reported for a fluorescent conjugated polymer (CP), poly{[4,4,9,9‐tetrakis(4‐(octyloxy)phenyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene)]‐alt‐co‐[4,7‐di(thiophen‐2‐yl)‐2,1,3‐benzothiadiazole]} (PIDT‐DBT), with absorption and emission profiles fallen within far‐red/near infrared (FR/NIR) region and further demonstrate its application in long‐term in vitro cell tracing and in vivo imaging of liver tumor growth. PIDT‐DBT‐Tat nanoparticles (NPs) have an absorption maximum at ≈600 nm with an emission maximum at ≈720 nm in water. In vitro cell tracing studies reveal that PIDT‐DBT‐Tat NPs can trace HepG2 liver cancer cells over 8 d. In vivo imaging results indicate that PIDT‐DBT‐Tat NPs can monitor liver tumor growth for more than 27 d in a real‐time manner. Both in vitro and in vivo studies demonstrate that PIDT‐DBT‐Tat NPs are superior to commercial Qtracker 705 as fluorescent probes. This study demonstrates for the first time the feasibility for long‐term in vivo imaging of tumor growth by utilizing CP‐based fluorescent probes, which will encourage the development of NIR fluorescent CPs for in vivo bioimaging.