Applications

Analytical ultracentrifugation (AUC) is the method of choice when characterizing mixtures in solution. Offering much higher resolution than DLS and size exclusion chromatography, AUC represents the gold standard for characterizing many different solution-based systems and colloids. AUC is most appropriate for particles in the nanoscale regime, which includes all proteins, nucleic acids, carbohydrates, lipids, membrane vesicles, as well as inorganic and synthetic materials such as quantum dots, metal nanoparticles, carbon nanotubes and industrial materials like flocculants.

The experimentalist can modulate the sedimentation force by varying the speed, and modulate the sedimenting speed by adjusting density and viscosity of the solution and thereby cover a wide range of molecules with variable size, shape, molecular weight, density, and composition.

Application examples include:

• Particle Sizing: Particle size distributions are frequently used to compare size variations between samples and provide sensitive indicators for variations in the manufacturing process.
• Aggregation Determination Irreversible aggregation of proteins, antibodies and other colloids represents undesirable contaminations of the product that must be precisely measured and quantified. AUC rpovides a very sensitive method to identify and characterize the presence of aggregation.
• Oligomerization Behavior: Determining the presence of reversible oligomerization and stoichiometry of the resulting oligomers, as well as their thermodynamic binding strength can be performed by AUC with high accuracy for most protein samples.
• Heteroassociation: Many systems require the investigation of binding events between proteins and nucleic acids, small molecules, peptides and drugs, as well as with other proteins. By labeling on of the components (generally the smaller one) we can take advantage of the exquisite selectivity of the attached fluorophore label and meare Kds of binding
• Density Determination: Functionalization of nanoparticles and quantum dots generally causes a shift in density of the entire particles. Since metal core and organic layer generally differ significantly in density, AUC allows us to follow the change in sedimentation based on density variations. This can also be applied to the measurement of phage packing with DNA and other systems where the anisotropy doesn't change even though the density does.