2.5. Determination and characterization of protein size by dynamic light scattering

Particle size analysis of native and oxidized amylin and AFA samples was carried out by photon correlation spectroscopy measurements employing a ZS90 dynamic light scattering (DLS) device (Malvern instruments, USA) equipped with a helium-neon laser light source (632 nm). Proteins (Material RI = 1.45, absorption = 0.001) in a buffer similar to water (Dispersant RI = 1.33, viscosity = 0.954) were measured in capillaries (2 μL). The samples were not diluted before this analysis, keeping the total protein concentration constant (25 μM, 0.1 mg mL⁻¹). DLS measurements were carried out at a set angle of 90° and attenuator at 11. Size was measured at 22 °C, with an equilibration time of 120 s and cuvette position at 3 mm. Backscatter-angled detection was performed at 173° with a scattering collection angle of 147.7°. Each biological replicate was measured in several replicates with minimal time between repeats.