Dts 1070 disposable folded capillary cells

Particle size distribution and polydispersity index (PdI) were measured by via Zetasizer Nano ZS (Malvern Instruments, Ltd., UK). All protein samples were dissolved in imidazole buffer solution (pH 7.0) with a final protein concentration of 0.004% (w/w). No further filtration was applied. DTS-1070 disposable folded capillary cells (Malvern Instruments, Ltd., UK) were used for measurements. Analysis were completed at 25 C as triplicate.

The ζ-potential measurements were done using a Zetasizer Nano ZS (Malvern Instruments, Ltd., Malvern, Worcestershire, UK) coupled with an autotitrator (MPT-2, Autotitrator, Malvern Instruments Ltd.) to determine the surface charge of the protein as a function of the pH. To adjust the pH of the solution (from 2.0 -8.0), 0.1 M NaOH and 0.1 M HNO3 were used. Measurements were done at 25 °C. Protein solutions were prepared at 0.2% final concentration at pH 7.0 using 0.05 M imidazole buffer and left to dissolve overnight on a magnetic stirrer at room temperature. For measurements, DTS-1070 disposable folded capillary cells (Malvern Instruments, Ltd.) were used. ζ-Potential was calculated by the software with the instrument using Henry's equation:
where η is the solution viscosity (Pa s -1 ), µ is the electrophoretic mobility (V Pa -1 s -1 ), ε is the medium dielectric constant (ε = 80) and 𝑓𝑓(𝜅𝜅𝑅𝑅 𝐻𝐻 ) is the Henry's function. κ is the Debye length (nm) and RH is the particle radius (nm) and the RH is accepted as 1.5 due to the aqueous medium used for the analysis, referred to as the Smoluchowski approximation. Isoelectric point (pI) was determined by the intersection on the x-axe at 0 mV. The values between -2.2 and +1.8 mV (dotted lines) were not possible to calculate properly due to the presence of aggregates.