Surface acoustic wave nebulization (SAWN) is a novel method to transfer nonvolatile analytes directly from the aqueous phase to the gas phase for mass spectrometric analysis. The lower ion energetics of SAWN and its planar nature make it appealing for analytically challenging lipid samples. This challenge is a result of their amphipathic nature, labile nature, and tendency to form aggregates, which readily precipitate clogging capillaries used for electrospray ionization (ESI). Here, we report the use of SAWN to characterize the complex glycolipid, lipid A, which serves as the membrane anchor component of lipopolysaccharide (LPS) and has a pronounced tendency to clog nano-ESI capillaries. We also show that unlike ESI SAWN is capable of ionizing labile phospholipids without fragmentation. Lastly, we compare the ease of use of SAWN to the more conventional infusion-based ESI methods and demonstrate the ability to generate higher order tandem mass spectral data of lipid A for automated structure assignment using our previously reported hierarchical tandem mass spectrometry (HiTMS) algorithm. The ease of generating SAWN-MS(n) data combined with HiTMS interpretation offers the potential for high throughput lipid A structure analysis.
[Show abstract][Hide abstract] ABSTRACT: Generating aerosol droplets via the atomization of thin aqueous films with high frequency surface acoustic waves (SAWs) offers several advantages over existing nebulization methods, particularly for pulmonary drug delivery, offering droplet sizes in the 1-5-μm range ideal for effective pulmonary therapy. Nevertheless, the physics underlying SAW atomization is not well understood, especially in the context of thin liquid film formation and spreading and how this affects the aerosol production. Here, we demonstrate that the film geometry, governed primarily by the applied power and frequency of the SAW, indeed plays a crucial role in the atomization process and, in particular, the size of the atomized droplets. In contrast to the continuous spreading of low surface energy liquids atop similar platforms, high surface energy liquids such as water, in the present case, are found to undergo transient spreading due to the SAW to form a quasisteady film whose height is determined by self-selection of the energy minimum state associated with the acoustic resonance in the film and whose length arises from a competition between acoustic streaming and capillary effects. This is elucidated from a fundamental model for the thin film spreading behavior under SAW excitation, from which we show good agreement between the experimentally measured and theoretically predicted droplet dimension, both of which consistently indicate a linear relationship between the droplet diameter and the mechanical power coupled into the liquid by the SAW (the latter captured by an acoustic Weber number to the two thirds power, and the reciprocal of the SAW frequency).
Physical Review E 11/2012; 86(5-2):056312. DOI:10.1103/PhysRevE.86.056312 · 2.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fluid manipulations at the microscale and beyond are powerfully enabled through the use of 10-1,000-MHz acoustic waves. A superior alternative in many cases to other microfluidic actuation techniques, such high-frequency acoustics is almost universally produced by surface acoustic wave devices that employ electromechanical transduction in wafer-scale or thin-film piezoelectric media to generate the kinetic energy needed to transport and manipulate fluids placed in adjacent microfluidic structures. These waves are responsible for a diverse range of complex fluid transport phenomena - from interfacial fluid vibration and drop and confined fluid transport to jetting and atomization - underlying a flourishing research literature spanning fundamental fluid physics to chip-scale engineering applications. We highlight some of this literature to provide the reader with a historical basis, routes for more detailed study, and an impression of the field's future directions.
[Show abstract][Hide abstract] ABSTRACT: Advances in the field of ambient sampling/ionization mass spectrometry with a focus on mechanistic and instrumentation studies are discussed. The first attention to the concept of ambient ionization/sampling prior to MS analysis was the introduction of desorption electrospray ionization (DESI) by Cooks and coworkers in 2004. Ionization techniques with built-in sample preparation steps include paperspray ionization, extractive electrospray ionization (EESI), and fused droplet ESI (FDESI). EESI and FD-ESI incorporate a continuous liquid-liquid extraction step into the ionization process, leading to a much higher salt tolerance than with ESI. DESI MSI approaches have also been coupled to matrix-assisted laser desorption ionization (MALDI) MSI for the joint imaging of lipids and protein ions on the same tissue section. TM-DESI has been used to detect the formation of organo-functionalized silanes from nanofilm products used in coating ceramic tiles and nonabsorbent flooring materials.
Chemical Reviews 01/2013; 113(4). DOI:10.1021/cr300309q · 46.57 Impact Factor
F. Logarinho, T. Rosado, C. Lourenço, E. Gallardo, A. Araujo
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