2.2 Protein suspension preparation
Four biological macromolecules, bovine serum albumins (BSA;
Sigma-Aldrich), ubiquitin (Sigma-Aldrich), low-density lipoproteins
(LDL; Sigma-Aldrich), and high-density lipoproteins (HDL;
Sigma-Albumin), were selected for testing. 10 mg proteins were suspended
in 10 ml 20 mM NH4CH3COO solution in an ultrasonic both for 15 minutes
for the good dispersion of proteins. Protein suspension samples with
different concentrations were prepared by serial dilutions. For the
stability monitoring, protein suspensions were stored at 4 ˚C and
sonicated for 15 minutes at 20 ˚C.