3.4 Protein stability in electrolyte at sequential time frame
The major concern of selecting the bio-NPs as RM was its degradation and
deactivation. To learn the stability of bio-NPs, the candidate proteins
selected as the sub-10 nm RM, BSA and ubiquitin, which exhibited
consistent results with literature [6,19,21], were suspended in 20
mM AmAc with the respectively protein concentrations of 0.1 mg/ml and
0.5 mg/ml. The size distribution and representative diameter of BSA and
ubiquitin were monitored as a function of time to confirm the dispersive
and structural stabilities of these proteins. In Table S2 , the
diameters of BSA and ubiquitin measured on sequential days were recorded
and the size variance of their representative diameters remained
< 10 % difference from literature.
On the 63th day of BSA suspension, the detected
diameter declined to 6.6 nm and had a 4.3 % difference from the value
obtained on the 1st day. A new BSA solution at the
sample protein concentration was prepared and tested on the same day to
approve the change in size, which contributed to the structural
alternation of BSA in electrolyte. Figure S3 indicated the
similar size distributions and the same measured representative diameter
of BSA generated from both the 63th-day BSA solution
and the fresh BSA solution measured on the same day. In association with
the diameter of the 1st-day BSA solution, the shift in
size distribution was evident, from which not only the change in monomer
but also dimer. On the 120th day of BSA suspension,
the representative diameter of BSA was again measured as 6.9 nm, which
suggested the slight change in diameter was the floating of the ES-SMPS
system. As a result, the consistent diameters of BSA and ubiquitin
obtained in this experiment and reported in literature illustrated the
repeatability of BSA and ubiquitin and presented their suitability as
the sub-10 nm and sub-5 nm RM.