Bio-conjugated ultrabright fluorescent nanoparticles for targeted cancer-cell imaging: independent size control and brightness.

Ultrabright fluorescent nanoparticles are promising for biomedical imaging, yet engineering their size, brightness, and surface chemistry remains a central challenge. Here, we establish a rational design framework for dye-encapsulated cellulose acetate nanoparticles assembled with Pluronic F127 via nanoprecipitation. By systematically varying the solvent choice, phase mixing protocols, and dialysis duration, we reveal how the synthesis parameters govern the optical and biological properties of the nanoparticles. Two-day dialysis yields ultrabright, stable nanoparticles (650-980 MESF per particle) with tunable sizes from 30 to 650 nm. Longer dialysis (4 days) causes particle contortion and dye leakage. We demonstrated the conjugation of folic acid at controlled densities (541-1050 molecules per particle) for cancer targeting. These nanoparticles selectively target breast cancer cells, which are known for overexpressed folate receptors, with superior uptake. Demonstrated cytotoxicity assays confirm the biocompatibility of the nanoparticles. Scalable synthesis of particles demonstrates their reliable, reproducible production. Our work provides a quantitative blueprint for engineering next-generation ultrabright nanoprobes optimized for biomedical imaging.