Separation and Detection of Charged Unilamellar Vesicles in Vacuum by a Frequency-Controlled Quadrupole Mass Sensor

Extracellular vesicles (EVs) are membranous particles released by cells and are considered to be promising sources of biomarkers for various diseases. Mass spectrometry (MS) analysis of EVs requires a sample of purified and detergent-lysed EVs. Purification of EVs is laborious, based on size, density, or surface nature, and requires large amounts of the source material (e.g., blood, spinal fluid). We have employed synthetically produced large unilamellar lipid vesicles (LUVs) as analogs of EVs to demonstrate an alternative approach to vesicle separation for subsequent mass spectrometry analysis of their composition. Mass-to-charge ratio m/z separation by frequency-controlled quadrupole was employed to filter narrow-size distributions of LUVs from a water sample. Lipid vesicles were positively charged with nanoelectrospray and transferred into a vacuum using two wide m/z-range frequency-controlled quadrupoles. The m/z, charges, and masses of individual vesicles were obtained by the nondestructive single-pass charge detector. The resolving mode of the second quadrupole with m/z RSD < 10% allowed to separate size selected distributions of vesicles with modal diameters of 88, 112, 130, 162, and 190 nm at corresponding quadrupole m/z settings of 2.5 × 10⁵, 5 × 10⁵, 8 × 10⁵, 1.5 × 10⁶, and 2.5 × 10⁶, respectively with a rate of 20-100 counts per minute. The distributions of bioparticles with masses between 10⁸ and 10¹⁰ Da were separated from human blood serum in the pilot experiment. The presented approach for lipid vesicle separation encourages the development of new techniques for the direct mass-spectrometric analysis of biomarkers in MS-separated EVs in a vacuum.