Introduction
(Bio-) nanoparticle analysis employing a nano Electrospray Differential Mobility Analyzer (nES DMA) aka nES Gas-phase Electrophoretic Mobility Molecular Analyzer (nES GEMMA) is based on surface-dry analyte separation in the gas-phase at ambient pressure (Kaufman, 1996). Analytes are aerosolized via a nativ nES source with subsequent surface-drying and concomitant charge equilibration in a bipolar atmosphere induced e.g. by a 210Po α-particle source. Based on electrophoretic principles, single-charged nanoparticles are then separated only according to their electrophoretic mobility diameter (EMD) corresponding to the particle size for spherical analytes. Subsequently, correlation of the (bio-) nanoparticle EMD to their molecular weight (MW) is possible yielding a dependency for an analyte class (as shown for proteins by Bacher et al. (2001)). Based on such a correlation, (bio-) nanoparticle MW determination based on EMD values within one analyte class is possible. Turning our attention on icosahedral, non-enveloped virus-like particles (VLPs), proteinaceous shells encapsulating an aqueous interior applied for shielded cargo transport or for vaccination, we set up an EMD / MW correlation. This analyte class has previously not been targeted by gas-phase electrophoresis in detail.
Methods
Gas-phase electrophoresis was carried out on a nES DMA instrument (TSI Inc, Shoreview, MN, USA) consisting of a nES (model 3480) including a 210Po α-particle source, an electrostatic classifier based on a nano differential mobility analyzer (model 3080) and a n-butanol driven ultrafine condensation particle counter (model 3025A or 3776C). VLPs were aerosolized in native form from aqueous ammonium acetate. In case VLP storage buffers contained non-volatile components, their removal was accomplished via spin filtration (Weiss, 2013).
Conclusions
VLPs can be analyzed via native ESI MS and gas-phase electrophoresis - obtained EMD and MW values can be correlated. This resulting correlation was found to be significantly different from a correlation obtained for viruses (Weiss, 2015).
EMD based calculation of a particle MW represents an interesting alternative to native ESI MS. Both methods relate bionanoparticle MW values but differ significantly in (i) sample purity and analyte homogeneity requirements, (ii) ease of instrument handling, (iii) costs of instrumentation and (iv) accuracy of obtained MW values. Therefore, both methods can be regarded as being complementary.
A larger VLP dataset will further improve our EMD / MW correlation for VLPs and hence calculated MW values.
This work was supported by the Austrian Theodor Körner Fonds.
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