Electrospray-Differential Mobility Analysis of Bionanoparticles
Zachariah, Michael R
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The growth of the multibillion dollar bionanoparticle industry has spurred the development of new physical characterization methods. One such method, electrospray-differential mobility analysis (ES-DMA) constitutes an electrospray for aerosolization of bionanoparticles (such as viruses, gold-nanoparticles, proteins, nanoparticle-protein complexes) and an ion mobility method that operates at atmospheric conditions, and separates bionanoparticles spatially. This dissertation identifies some relevant "problem" areas for ES-DMA by reviewing selected applications. Some such problems are: proteins while passing through ES capillaries are found to interact with it and thus produce time dependent size distributions. Further, it is thought that adsorbed proteins may subsequently desorb and influence size distributions with the ES-DMA which may concomitantly affect quantification of aggregates. These artifacts are studied systematically and it is demonstrated that ES-DMA can quantify adsorption-desorption of complex protein mixtures at high shear rates. Further, it is shown that desorbing proteins do not have a significant effect on size distributions. Another artifact of the ES takes place during the aersolization process. Two units (called monomers) of a bionanoparticle may get encapsulated in the same ES droplet and upon drying of the droplet create artificial dimers thus affecting quantification with ES-DMA. Assuming Poisson distribution, this thesis provides a systematic approach that can be undertaken to eliminate this artifact. A third artifact arises from the low sensitivity of the DMA to size increase. When a ligand (for e.g. protein) adsorbs to a bionanoparticle it creates an increase in the size of the later, which can be used to quantify the amount of ligand adsorbed per bionanoparticle. As ligands can change conformations upon adsorption, using ES-DMA for such applications may be flawed. This issue has been identified and a solution has been provided by integrating a mass analyzer after the ES-DMA. After correcting for these artifacts, this dissertation delves into characterization of different types of bionanoparticles and demonstrates that ES-DMA has several advantages over other traditional techniques such as transmission electron microscopy, size exclusion chromatography, analytical ultracentrifugation, dynamic light scattering and plaque assay and thus has immense potential to become a process analytical technique in biomanufacturing environments.