image "fill the gap" of subvisible particulate measurements

Greetings! Over the last decades I have been involved in nanometrics – the characterization of nanosized objects, from small molecules, proteins & antibodies to the mesoscale. We may have crossed paths already on one of my frequent Webex presentations, recorded powerpoints (the most popular of mine is the “Dynamic Light Scattering primer”, followed closely by “Protein Characterization” ) or on youtube.

DLS still rising

The use of dynamic light scattering (DLS) as an almost standard technique in pharmaceutical research is still gaining popularity. Is  it really a surprise? While there are some shortfalls (baseline resolution, quantification challenge) the advantages of low volume, ease-of-use, high sensitivity and comparatively reasonable cost have attracted a considerable following. At PEGS 2011 in Boston last week, about half of the presentations in the “Biophysical & Biochemical Characterization of Biotherapeutics” pipeline contained a reference to DLS. Aggregation remains a ‘hot topic’, often in conjunction with thermal stability, characterization of stress due to heat, stirring, or chemical (GuanidiniumHCl, urea) perturbation. Several presenters investigated ionic strength effects for protein (primarily antibody) solutions at high concentration, where the second virial coefficient (from static light scattering) and the dynamic interaction parameter (from dynamic light scattering) may give insight into the underlying forces driving both reversible and irreversible aggregation.

Rule of thumb?

Is there an easy rule-of-thumb? No. But DLS has well deserved its place to help fill the ‘measurement gap’ between 100nm (i.e. the cutoff for typical Size Exclusion Chromatography) and a few microns (i.e. the cutoff for typical flow imaging microscopy systems). Protein-protein interactions can lead to the formation of oligo- and higher -meric species, that may show up as an overall larger z-average size, an increased polydispersity index, or a separate peak in the size distribution analysis, removing – as one of the presenters eloquently put it – the “cloak of invisibility” [Donna Luisi]. Happy uncloaking!

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