Advanced Colloid Characterization

Advanced Colloid Characterization

Knowledge about the size, shape and optical properties of macromolecules and nanoparticles is of high importance for many applications in life sciences and particle technology because physiological and product properties are directly influenced by these parameters. Combined analysis of mass, size and shape or the determination of size and shape dependent optical properties is a major challenge and requires strong and versatile methods.

In our research, we take advantage of the powerful and versatile analytical ultracentrifugation (AUC) platform. The temporal and spatial distribution of macromolecules and nanoparticles can be measured in solution in the presence of centrifugal accelerations reaching up to 290,000 g. This allows studying the sedimentation and diffusion properties of very small analytes having just a few hundred Daltons. These transport properties can be linked to the analyte’s disperse properties such as size, shape and interactions. As a direct and first-principle based technique, AUC requires no calibration on a daily basis or measurement of standards. The setup comprises several potential detector options, which makes it highly interesting for the field of photonic technologies, too.

Our custom-made AUC equipped with a fiber-coupled multiwavelength detector (UV-VIS-NIR) allows determination of size and shape dependent extinction spectra in a single experiment. Currently, a novel experimental setup is developed, which allow us to study the emission properties of particles as a function of mass, size, shape and chemical composition. Moreover, a third device with combined refractive index and UV-VIS detector will soon complement our versatile measurement platform. This setup will be in particular useful for quantitative particle size analysis and highly concentrated systems to study non-ideality of sedimentation and diffusion phenomena. In such way, it will further provide access to the specific and non-specific interactions of macromolecules and nanoparticles.

In summary, AUC permits the multidimensional analysis of proteins and colloids and allows us to determine precisely:

  • Hydrodynamic and structure properties of colloids (molar masses, hydrodynamic diameters, effective densities, shape anisotropies),
  • Specific and non-specific interactions (concentration effects, binding constants, oligomerization states),
  • Optical properties (size dependent extinction and emission).

In addition to our strong AUC platform, we use analytical centrifugation (AC) in the form of the LUMiSizer from LUM GmbH for characterization of larger particle systems. In order to benefit from the numerous possibilities offered by AUC, we transfer methodologies developed for AUC to AC.