In vivo optical performance of near infrared-emitting borylated polyfluorene-alt-benzothiadiazoles embedded within biodegradable PEG-PLGA nanoparticles

Borylated polyfluorene-benzothiadiazoles (PF8-BT) are π-conjugated polymers (CPs) with deep-red/near infrared (NIR) absorption and emission profiles suitable for in vivo optical imaging. A fully borylated PF8-BT derivative (P4) was encapsulated in PEG-PLGA nanoparticles and compared with a reference NIR-emitting CP (PCPDTBT) or indocyanine green (ICG). All formulations satisfied quality requirements for parenterally administered diagnostics. P4 nanoparticles had higher quantum yield (2.3%) than PCPCDTBT (0.01%) or ICG nanoparticles (1.1%). The signal:background ratios (SBR) of CP systems, P4 and PCPDTBT in a phantom mouse (λem=820 nm) increased linearly with fluorophore mass (12.5-100 µg/mL), while the SBR of ICG decreased above 25 µg/mL. P4 nanoparticles experienced < 10% photobleaching over 10 irradiations (PCPDTBT: ~25% and ICG: > 44%). In a mouse tumour xenograft model, P4 nanoparticles showed a 5-fold higher SBR than PCPDTBT particles with fluorophore accumulation in the liver > spleen > tumour. Blood chemistry and tissue histology showed no abnormalities compared to untreated animals after a single administration