Effects of hydrophilic/hydrophobic blocks ratio of PEG-b-PLGA on emission intensity and stability of over-1000 nm near-infrared (NIR-II) fluorescence dye-loaded polymeric micellar nanoparticles

Polymeric micellar nanoparticles (PNPs) composed of an amphiphilic block copolymer formed from hydrophilic and hydrophobic blocks and over-thousand-nanometer (OTN) near-infrared (NIR) fluorescent dye are promising fluorophores for the dynamic imaging of deep tissue. In this study, we examined the effect of the ratio of hydrophilic/hydrophobic blocks of a block copolymer, poly(ethylene glycol) (PEG)-b-poly(lactide-co-glycolide) (PLGA), on the properties of OTN-PNPs encapsulating IR-1061. OTN-PNPs with a higher molecular weight of PLGA cores showed higher emission and stabilities under physiological conditions. The PEG ratio to PLGA in the block copolymer decreased the stability of OTN-PNPs probably due to the invasion of water molecules into the polymer core. The results show that the in vivo stability and fluorescence properties can be tuned by adjusting the chain lengths of block copolymers and estimated using in vitro assays, which evaluates the brightness retention rate of the OTN-PNPs under physiological conditions.