The plastic nanoparticles were prepared following a precipitation and solvent evaporation technique as previously described. Briefly, 50 mg amorphous PET film (product code ES303015, Goodfellow GmbH, London, UK) or PCL flakes were dissolved in 1,1,3,3,3,hexafluoro-2-propanol (5 mL) for at least one hour. This solution was added dropwise (1 mL/min) to MilliQ ® water (50 mL, cooled in an ice bath). At the same time the water was rigorously stirred using an Ultra Turrax ® stirrer at 8000 rpm (IKA, Germany). The suspension was filtered using Whatman filter paper (8 µm diameter) and the remaining solvent was evaporated. Particle sizes of d=131.7 nm for PET and d=184.9 nm for PCL were obtained using dynamic light scattering (Zetasizer Nano S).