Wyatt Technology Möbiuζ mobility instrument

Wyatt Technology’s Möbiuζ mobility instrument incorporates several innovations to realise fast and reliable measurements of macromolecular electrophoretic mobilities.

Besides being capable of swiftly measuring mobilities of large particles such as liposomes and VLPs, the laser-based instrument achieves reproducible measurements of traditionally very challenging protein samples including antibody formulations, bovine serum albumin and lysozyme. It is designed specifically to address the measurement of protein mobilities rather than modification of a device designed to measure particulates.

Electrical charge is a fundamental property of all macromolecules. In colloidal suspensions, the amount of charge and screening developed at the interfaces between particles and media is of utmost importance in determining the formulation stability. For many biomolecules such as proteins, electrostatic interactions also exercise a profound influence on their conformations and functions. Since a direct measurement of the interfacial potential is rarely feasible, the electrophoretic mobility has become the most popular and widely accepted proxy for molecular charge.

As well as being a non-invasive method, laser light scattering is prized for its ability to carry out physical, first-principle measurements of macromolecules’ electrophoretic mobilities. However, when it comes to proteins, satisfactory results have been difficult to come by due to their small sizes (<5 nm) and their more conspicuous Brownian motions. Lengthier measurements are therefore necessary to average out the mobility-masking diffusion and reveal the macromolecular electrophoresis. In the process, these fragile molecules are subjected to electrical currents and often irreversibly damaged and degraded, rendering the results unreliable. As the solution ionicity increases, the situation deteriorates because even more current is required to drive measurable electrophoresis. Existing products on the market notoriously ‘cook’ their protein samples and struggle to measure any macromolecule smaller than 5 nm at a reasonable concentration.

The key to the successful measurement of proteins’ mobilities lies in a much shortened measurement time and the availability of sufficient data to average away molecular diffusion. Möbiuζ achieves these goals through massive parallelism of detection and extends the measurable molecular size range below 2 nm. A reduced measurement time (<60 s in most cases) contributes to the preservation of precious and fragile protein samples.

In a specific example, size exclusion chromatography (SEC) corroborated the preserved integrity of a sample of monoclonal antibody after the mobility measurement. A sample recovery rate of >98% was obtained. Another important advantage of Möbiuζ which results from the detection process is its much increased detection sensitivity: 2 mg/mL lysozyme or 0.5 mg/mL BSA.

Simultaneous measurement of the macromolecular hydrodynamic radius is available with the WyattQELS option, which utilises backward scattered light to determine the sample translational diffusion coefficient. Both re-usable flow-through cells and disposable cells are offered for mobility (and QELS) measurements. (Stop-flow is required during mobility measurements.) Samples can be introduced by manual injection, an auto-sampler, syringe pump or an auto-titrator. The Möbiuζ also has temperature control capability and is able to perform automated temperature studies.