Determination of nanoparticle density profiles using centrifugal field-flow fractionation coupled with multi-angle light scattering.

Centrifugal field-flow fractionation (CFFF) coupled with multi-angle light scattering (MALS) provides complementary information on nanoparticle retention behavior and particle size, enabling determination of effective particle mass and radius of gyration under native solution conditions. In this work, an analytical approach is presented for continuously determining effective particle density as a function of retention time by combining mass information derived from CFFF retention with particle size measured by MALS. The methodology was evaluated using three representative nanoparticle systems with distinct structural characteristics: liposomes, porphysomes (empty and BSA-loaded), and lentiviral particles. BSA-loaded porphysomes exhibited an approximately constant density across the retained population, indicating proportional scaling of particle mass and particle volume, whereas empty porphysomes and liposomes showed progressively increasing density with retention time. Lentiviral particles exhibited the largest density gradient, demonstrating substantial variation in mass-to-volume relationships within the retained population. These results demonstrate that CFFF-MALS extends the analytical capability of field-flow fractionation by providing continuous density profiles of heterogeneous nanoparticle populations and establish effective particle density as a complementary parameter for nanoparticle characterization.