Particle Tracking Analysis (PTA) PTA measurements were performed to measure the number-based distribution of the spherical-equivalent hydrodynamic diameter of particles suspended in PBS (control particles and particles recovered following incubation in proteincontaining medium) and treatment medium (in situ analysis). These measurements were performed using the NanoSight NS300 system (Malvern Panalytical, Malvern, UK) equipped with a 488 nm laser module and a high-sensitivity CMOS camera. Five, 60 second videos were acquired for all measurement and averaged. All samples were analysed under constant flow conditions (flow setting 100) and at ambient temperature (~25 °C). The video capture parameters were set at a camera level of 6, with post-processing analyses being performed at a detection threshold of 4. Three independent replicate measurements were performed for each sample which were then used to calculate a mean diameter with associated standard error. Data were analysed using the NTA software (v3.4.0.0.3).