Using DLS to characterize protein stability
The ability to characterize proteins will become increasingly important as the study of the human genome leads to the discovery of proteins with therapeutic properties or with actions involving specific diseases.
Bovine Serum Albumin (BSA) is a protein with a molecular weight of 69,000 Daltons that is commonly used in protein studies. Properly dispersing BSA is important to obtaining clean particle size distributions. Figure 1 contains the particle size distribution of 35% BSA in saline diluted in filtered distilled water. The sample was centrifuged for 2 minutes using special glass sample tubes to remove large particle contaminates from the diluent. The tubes can go from the centrifuge straight into the particle analyzer.
As can be seen in this intensity-weighted PSD, there are two peaks, one at 6 nm which is the primary BSA and another peak at 40 nm which are aggregates (dimers, trimers, etc) with an intensity contribution of 40%. Figure 2 contains the particle size distribution of the same BSA but diluted in saline. The PSD is still a bimodal with a primary particle size at about 7 nm however the aggregate peak seems to be larger, with an almost a 50% intensity contribution. Finally, Figure 3 contains the same BSA but in PBS. The particle size distribution has changed considerably. The size of the primary particle size grew to 10 nm. These results indicate how important the chemical environment is to the dispersion of BSA.