Disruption and nebulization of lipid vesicles using surface acoustic waves for direct mass spectrometry

Characterizing extracellular vesicles (EVs) using mass spectrometry (MS) provides several advantages. The molecular compositions within EVs can be analyzed at very low concentrations and can also distinguish lipids and molecules with similar structures. However, there are some challenges when analyzing EVs directly using MS, mainly due to their variations in size and biological composition, as well as their tendency to form large clusters. Here, we present a novel surface acoustic wave (SAW) sample preparation system capable of simultaneous disruption and nebulization of liposomes as a model for direct EV analysis by MS. This approach provides a mechanical alternative to traditional chemical methods, which minimizes sample preparation time, volume loss, and chemical interference while enhancing ionization efficiency. We study the influence of frequency on SAW nebulization for MS analysis of DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes as well as liposome mixture. Through high-frequency Rayleigh SAW excitation, we demonstrate improved liposome disruption and enhanced ionization signals during MS analysis when combined with corona discharge ionization. We systematically investigate key parameters of device frequency, input radio frequency (RF) power, nebulization rate, acoustic heating, aerosolized droplet sizes, and surface preparation. The nebulization process was captured by high-speed imaging, which reveals the critical role of surface treatment and jetting dynamics in achieving efficient nebulization at different frequencies. Our findings reveal the frequency-dependent nature of Rayleigh SAW nebulization, highlighting its ability to generate fine, aerosolized particles that enhance MS sampling reliability and ionization efficiency. This work represents a significant advance in MS sample preparation techniques, with broad implications for lipidomics and growing interest in the analysis of biologically relevant vesicles such as EVs.