June 29, 2017 by John Toon          The DRILL device is connected to a mass spectrometer to sort    charged droplets and improve desolvation of ionized    biomolecules for analysis. The device requires no modification    of the mass spectrometer, and can be accommodated within the    standard work flow now used by researchers. Credit: Rob Felt,    Georgia Tech    
      Adding the equivalent of a miniature tornado to the interface      between electrospray ionization (ESI) and a mass spectrometer      (MS) has allowed researchers to improve the sensitivity and      detection capability of the widely-used ESI-MS analytical      technique. Among the scientific fields that could benefit      from the new technique are proteomics, metabolomics and      lipidomics  which serve biomedical and health applications      ranging from biomarker detection and diagnostics to drug      discovery and molecular medicine.    
    Known as Dry Ion Localization and Locomotion (DRILL), the new    device creates a swirling flow that can separate electrospray    droplets depending on their size. In this application, one of    many potential uses for DRILL, the smaller droplets are    directed to enter the mass spectrometer, while the larger ones  which    still contain solvent  remain in the vortex flow until the    solvent evaporates. Removing the solvent allows analysis of    additional ions that may be lost in current techniques and    reduces the chemical "noise" that inhibits selectivity of the    mass spectrometer.  
    "A major challenge for detecting small quantities of    biomolecules using mass spectrometry technology is that we    can't see everything that is actually in the sample," said    Matthew Torres, an assistant professor in Georgia Tech's School    of Biological Sciences. "The DRILL device provides a new way to    solve that problem by increasing the number of ions we can get    into the mass spec instrument so we can productively detect    them. The ions are there now, but not necessarily in a form    that the mass spec can handle."  
    Developed by researchers at the Georgia Institute of Technology    with support from North Carolina State University, DRILL can be    added to existing electrospray ionization mass spectrometers    without modifying them.  
    "The principle is to make the droplets rotate and use inertia    to separate them out by size," explained Andrei Fedorov, a    professor in Georgia Tech's Woodruff School of Mechanical    Engineering. "We want the droplets to stay in the flow long    enough to remove the solvent. In practice, smaller droplets    remain in the center, where they are can be removed first for    analysis, while the larger ones remain on the edge of the flow    until they are dried."  
    The key idea of DRILL is based on Fedorov's 2007 invention    "Confining/Focusing Vortex Flow Transmission Structure, Mass    Spectrometry Systems, and Methods of Transmitting Particles,    Droplets, and Ions." (US Patent No. 7,595,487). In the past    three years, the DRILL device has been developed with support    from the National Institute of General Medical Sciences of the    National Institutes of Health, and its latest version was    described June 14 in the American Chemical Society journal    Analytical Chemistry.  
    In electrospray ionization (ESI), an electric potential is    applied to a solution inside a capillary, producing a strong    electric field at the spray capillary tip.    That leads to the expulsion of an aerosol containing charged    droplets that carry the molecules to be analyzed. The ejected    droplets then break up into smaller droplets, creating a plume    that expands spatially beyond the inlet intake capacity of the    mass spectrometer, resulting in sample loss. The DRILL device    provides an effective interface for collection and transmission    of charged analytes from ionization sources, such as ESI, to    detection devices, such as mass spectrometers, resulting in    significantly improved detection capability.  
    As much as 80 to 90 percent of large biopolymers (proteins,    peptides, and DNA) are currently lost to analysis using    existing ESI-MS techniques, which have grown in importance to    the life sciences community. Capturing all of the biopolymers    could lead to new discoveries, said Torres, whose lab studies    post-translational changes in proteins. By allowing analysis of    large biomolecules, DRILL could facilitate top-down proteomics    in which complete protein molecules could be studied without    the need to enzymatically break them up into smaller pieces    before MS analysis.  
    "This could allow us to see combinatorial modifications that    exist on a single protein molecule," said Torres. "It's very    important for us to understand how proteins communicate with    one another, and DRILL may allow us to do that by more    effectively removing the solvent from these types of samples."  
    The Georgia Tech researchers are using DRILL in their lab to    interface between liquid chromatography and the ESI-MS    instrument. Multiple electrodes and inlet/outlet ports enable    precise control over the flow generation and guiding electric    field inside the DRILL, so the device can be configured for a    variety of uses, Fedorov noted. In a general sense, DRILL adds    a new approach for manipulating the trajectory of charged    droplets, which, when combined with hydrodynamic drag forces    and electric field forces, provides a rich range of possible    operational modes.  
    DRILL can improve the signal-to-noise ratio by a factor of 10    in the detection of angiotensin I, a peptide hormone, and boost    the sensitivity for angiotensin II ten-fold to picomole levels.    DRILL demonstrated improved signal strength  up to 700-fold     for eight of nine peptides included in a test extract of    biological tissue.  
    DRILL could potentially allow the study of entire cell    contents, analyzing thousands of different molecule types    simultaneously. That could allow researchers to see how these    molecules change over time to detect problems in chemical    pathways and to determine why drugs work in some people and not    others.  
    "This could be a huge advance for biologists and others who are    interested in protein biochemistry and cell biology because it    enhances the sensitivity of the analytical technical and    overcomes a major hurdle in studying large biological    molecules," Torres added. "We expect to be able to see things    we haven't been able to see before."  
    The Georgia Tech researchers have been collaborating with David    Muddiman, a professor in the Department of Chemistry at North    Carolina State University, on developing DRILL and its    analytical characterization using state-of-the-art mass spectrometry experiments. A unique    contribution of the North Carolina State University researchers    is in using a powerful statistical method called "design of    experiments" to guide the multi-parameter optimization of the    DRILL device, resulting in identification of a sweet spot for    optimal operation.  
    Fedorov and Torres hope to expand use of the DRILL device    beyond Georgia Tech laboratories and further enhance its    design. Among the near-term improvements planned is the    addition of internal heating to accelerate the removal of    solvent. "We see many additional improvements that will allow    DRILL to further enhance the ESI-MS process," said Fedorov. "We    plan to continue evolving it as more labs start to use the    device."  
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    More information: Peter A. Kottke et al. DRILL: An    ESI-MS interface for improved sensitivity via inertial droplet    sorting and electrohydrodynamic focusing in a swirling flow,    Analytical Chemistry (2017). DOI: 10.1021/acs.analchem.7b01555
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