dc.description.abstract
Introduction
Gas-phase electrophoresis of single-charged bioanalytes (bionanoparticles) enables their separation according to the surface-dry particle size (Electrophoretic Mobility Diameter, EMD), which corresponds to the diameter of spherical shaped nanoparticles (Kaufman et al., 1996). Employing a native nano Electrospray Differential Mobility Analyzer (nES DMA) (aka nES Gas-phase Electrophoretic Mobility Molecular Analyzer, nES GEMMA), allows sizing/size-separation and determining of bionanoparticle-number concen-trations. Separations are based on a constant high laminar sheath flow and a tunable, orthogonal electric field enabling scanning of EMDs in the nanometer size range. Additionally, keeping the voltage constant, only bionanoparticles of a given EMD pass the instrument and can be collected by means of an ENPC (Electrostatic Nano Particle Collector) on corresponding supporting materials (e.g. mica, nitrocellulose, gold) for subsequent bionanoparticle analyses applying e.g. atomic force microscopy, immunologic or spectroscopic techniques (e.g. Havlik et al., 2015; Wieland et al., 2019; Weiss et al., 2016; Weiss et al., 2019).
Methods
In our proof-of-concept study we now focus for the first time on MALDI (Matrix-Assisted Laser Desorption Ionization) mass spectrometric (MS) characterization of nDMA size-selected biomaterial. We carried out size-selection of liposomes, vesicles consisting of a lipid bilayer and an aqueous lumen employed as carriers in e.g. pharmaceutic, cosmetic or nutritional applications. Gas-phase electrophoresis of the quite labile liposomes has previously been demonstrated successfully (Weiss et al., 2016). These bionanoarticles of defined (e.g. 85 nm) EMDs were collected on gold-coated silicon wafers (Fig. 1, left inset) by a modified ENPC. Subsequently, MALDI MS matrix was applied (Fig. 1, right inset), fixed microtiter-format target (Fig. 1, top) and MALDI reflectron MS carried out generating exact molecular weight data of the complex lipid composition. However, we not only focused on plain liposomes but also demonstrated the applicability of our approach for very low density lipoprotein particles (VLDL), important biomedical marker particles. Subsequently detailed fragmentation by CID (collision induced dissociation) was performed in the tandem MS to elucidate the fine structure of the detected molecules.
Conclusions
Our novel hyphenation of native (i.e. keeping very labile nano-object intact during the spray process) nES DMA size fractionation and MALDI MS opens the avenue to detailed structural investigation of size-selected bionanoparticles of complex nature by a "soft ionization" MS/MS (tandem MS) approach in very different areas as environmental chemistry, biomedicine and nanotechnology.
This work was supported partly by the Austrian Science Fund P25749-B20.
Kaufman, S. L., et al. (1996) Anal. Chem., 68,1895-904.
Havlik, M., et al. (2015) Anal. Chem., 87, 8657-64.
Wieland, K., et al. (2019) Nano Res., 12, 197-203.
Weiss. V. U., et al. (2016). Analyst, 141, 6042-6050.
Weiss V. U. et al. (2019). Anal. Chem., 91, in press.
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