WO2011060369A1 - Ions générés par un dispositif à ondes acoustiques de surface détectés par spectrométrie de masse - Google Patents

Ions générés par un dispositif à ondes acoustiques de surface détectés par spectrométrie de masse Download PDF

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Publication number
WO2011060369A1
WO2011060369A1 PCT/US2010/056724 US2010056724W WO2011060369A1 WO 2011060369 A1 WO2011060369 A1 WO 2011060369A1 US 2010056724 W US2010056724 W US 2010056724W WO 2011060369 A1 WO2011060369 A1 WO 2011060369A1
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Prior art keywords
acoustic wave
surface acoustic
suspension
wave transducer
analyte
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PCT/US2010/056724
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English (en)
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David R. Goodlett
Scott R. Heron
Jon Cooper
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Goodlett David R
Heron Scott R
Jon Cooper
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Application filed by Goodlett David R, Heron Scott R, Jon Cooper filed Critical Goodlett David R
Publication of WO2011060369A1 publication Critical patent/WO2011060369A1/fr
Priority to US13/296,793 priority Critical patent/US8415619B2/en
Priority to US13/858,594 priority patent/US8692192B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
    • H01J49/0431—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components for liquid samples
    • H01J49/0454—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components for liquid samples with means for vaporising using mechanical energy, e.g. by ultrasonic vibrations

Definitions

  • the present invention relates generally to mass spectrometry.
  • the present invention relates more particularly to methods and systems for use in mass spectrometric identification of a variety of analytes, including high molecular weight species such as proteins and low molecular weight compounds like peptides, glyco lipids and polyphenols.
  • Electrospray ionization is a conventional method for transferring non- volatile compounds such as peptides and proteins to the gas phase for mass spectrometric detection.
  • ESI is often used to couple real-time separation techiques (e.g., HPLC) with mass spectrometry.
  • ESI can be advantaged in that it can produce precursor ions with higher order charge states (e.g., [M+nH] n+ , where n>l) in order to provide more readily interpretable peptide tandem mass spectra, and thus allow peptide sequence to be assigned de novo or via a database search engine.
  • ESI is disadvantaged in that it requires a capillary or nozzle for ionization. Such structures can be difficult to repeatably reproduce; accordingly, device-to-device variation can be significant. In turn, the conditions necessary to get a "Taylor cone" jet-and-plume structure desirable for ESI can vary significantly across devices.
  • ESI can be a relatively high-energy ionization process, and can therefore cause an undesired level of parent ion decomposition.
  • MALDI Matrix-assisted laser desorption ionization
  • MALDI is another popular method transfer of peptides and proteins to the gas phase for mass spectrometry.
  • MALDI is a "softer" ionization technique, generating primarily [M+H] + ions.
  • MALDI is a pulsed technique that can allow separation to be decoupled from ionization. This decoupling can provide the opportunity to repeatedly re-examine a sample (e.g., to interrogate the evolution of a sample over time).
  • MALDI requires a matrix (often benzoic acid derivatives such as sinpainic acid), and that matrix provides contamination of the resulting mass spectrum at low m/z.
  • One aspect of the invention is a method for analyzing an analyte.
  • the method includes nebulizing a suspension of the analyte in a solvent with a surface acoustic wave transducer to provide nebulized suspension; and performing mass spectrometry on the nebulized suspension
  • Another aspect of the invention is an analytical system for analyzing an analyte provided as a suspension in a solvent.
  • the analytical system includes a mass spectrometer having an input; and a surface acoustic wave transducer operatively coupled to the mass spectrometer, such that when the surface acoustic wave transducer is used to nebulize the suspension to provide nebulized suspension, at least some of the nebulized suspension enters the input of the mass spectrometer.
  • a surface acoustic wave transducer can provide pulsed nebulization from the surface of a chip, allowing separation to be decoupled from analysis, as described above with respect to MALDI.
  • the resulting mass spectra are not contaminated with matrix ions at low m/z (i.e., ratio of mass to charge).
  • the surface acoustic wave-based methods described herein can provide "softer" ionization as compared to ESI, and therefore can result in relatively more parent ions (single and multiply-ionized), allowing for more useful mass spectral data for proteins and peptides.
  • the methods and systems of the present invention do not require a capillary or nozzle, and the corresponding Taylor cone jet-spray pattern, and therefore can be made repeatably device-to-device.
  • the methods can be coupled with lab-on-a-chip devices in order to provide chemical analysis after a separation, purification, or reaction performed thereon.
  • FIG. 1 is a schematic depticion of surface acoustic wave transduction.
  • FIG. 2 is a schematic view of an analytical system for analyzing an analyte via mass spectrometry according to one embodiment of the invention; and its use in performing a method for analyzing an analyte according to one embodiment of the invention;
  • FIG. 3 is a schematic top view and schematic cross-sectional view of a surface acoustic wave transducer according to one embodiment of the invention.
  • FIG. 4 is a schematic cross-sectional view of a surface acoustic wave transducer including a superstrate according to one embodiment of the invention
  • FIG. 5 is a schematic top view of a surface acoustic wave transducer having concentric electrodes
  • FIG. 6 is a schematic diagram of the electrode design of the surface acoustic wave transducer of Example 1;
  • FIG. 7 is a photograph of the surface acoustic wave transducer of Example 1.
  • FIG. 8 is a graph showing the nebulization onset powers measured in Example 1.
  • FIG. 9 is a graph showing the volume of liquid ejected vs. pulse width as measured in Example 1;
  • FIG. 10 is a set of photographs showing contact angle at the point of nebulization as determined in Example 1 ;
  • FIG. 11 is a set of graphs showing the dependence of nebulized droplet size on frequency and identity of liquid as determined in Example 1 ;
  • FIG. 12 is a picture of a surface acoustic wave transducer positioned at the inlet of a mass spectrometer.
  • FIG. 13 is a graph of ion abundance as a function of acquisition time for the experiments of Example 2.
  • FIG. 14 is a set of mass spectra for the experiments of Example 2.
  • FIG. 15 is a set of tandem mass spectra for the experiments of Example 2.
  • FIG. 16 is set of mass spectra for MALDI and ESI experiments on lipid A as described in Example 3;
  • FIG. 17 is a set of mass spectra for lipid A generated using surface acoustic wave nebulization, as described in Example 3;
  • FIG. 18 is the mass spectrum of FIG. 17 annotated with fragment analysis
  • FIG. 19 is a set of tandem mass spectra for lipid A, generated using surface acoustic wave nebulization, as described in Example 3;
  • FIG. 20 is the set of tandem mass spectra of FIG. 19, annotated with fragment analysis;
  • FIG. 21 is a pair of negative mode mass spectra of retinoic acid, comparing surface acoustic wave nebulization with ESI, as described in Example 4.
  • One embodiment of the invention is a method for analyzing an analyte.
  • the method includes nebulizing a suspension of the analyte in a solvent with a surface acoustic wave transducer; and performing mass spectrometry on the nebulized suspension.
  • the surface acoustic wave transducer can be used, for example, to transfer non- volatile peptides and proteins (as well as other analyztes, such as oligonucleotides and polymers) to the gas phase at atmospheric pressure.
  • Nebulization using surface acoustic waves can be conducted in a discontinuous or pulsed mode, similar to that used in MALDI, or in a continuous mode, as in ESI.
  • the nebulized plume can last, for example, on the order of minutes in continuous mode, and can produce multiply charged precursor ions with a charge state distribution shifted to higher m/z ratios compared to an identical sample produced by ESI.
  • the quality of precursor ion scans and tandem mass spectra of analyte can be consistent across plume lifetime.
  • the surface acoustic wave- generated spectra have substantially no such interference.
  • the surface acoustic wave methods and devices described herein can be performed without capillaries or nozzles extending from the surface of the surface acoustic wave device.
  • Surface acoustic wave technology is also amenable to an array-based format, in which multiple sample areas arrayed on a chip can be nebulized sequentially or simultaneously.
  • a surface acoustic wave is an acoustic wave travelling along the surface of a material exhibiting elasticity, with an amplitude that typically decays exponentially with depth into the substrate.
  • a surface acoustic wave device typically uses interdigitating electrodes on a substrate to convert an electrical signal to an acoustic wave, using the piezoelectric properties of the substrate.
  • Surface acoustic waves are used in microfluidic devices; owing to the mismatch of sound velocities between the surface acoustic wave substrate and the fluid, surface acoustic waves can be efficiently transferred into the fluid, to create significant inertial force and fluid velocities.
  • surface acoustic wave -based microfluidic techniques do not require pressure-driven pumps and their associated dead volumes. Moreover, unlike electrokinetics-based techniques, the sample need not be in contact with the electrodes to drive the sample flow.
  • Surface acoustic wave-based microfluidic techniques have been used to perform mixing within channels, heating, droplet movement and delivery to or from a microfluidic port.
  • surface acoustic wave nebulization has been used to generate small droplets (e.g., 5-10 nm diameter) for assisting with synthesis of polymeric
  • nanoparticles to nebulize protein samples for writing protein arrays, and to generate monodispserse aerosols and nanoparticles for drug delivery.
  • FIG. 1 is a schematic depiction of surface acoustic wave transduction, showing interdigitated electrodes (IDT) generating a surface acoustic wave (SAW) on a substrate.
  • IDT interdigitated electrodes
  • SAW surface acoustic wave
  • the energy is dissipated into the wetted drop as a series of surface waves, which cause the fluid to oscillate at high rates.
  • the inertia of the fluid becomes too great, causing liquid fractionation, resulting in emission of droplets on the order of femtoliters in volume in which droplets of fluid are created and emitted from the surface at a pitch of several microns.
  • the pitch is related to the wavelength of sound in the fluid, which is a function of viscosity and density.
  • the surface appears to "boil.”
  • two other processes are possible. At lower energies, the drop can simply move along the surface.
  • ejection of picoliter sized droplets can occur as a consequence of a high degree of localization of energy. Ejection is generally observed from a single location within the drop, rather than across the drop.
  • Analytical system 200 includes a mass spectrometer 210 having an input (here, capillary 212).
  • the inlet can be a so-called atmosphereic pressure ionization inlet, for example, as provided for use with Thermo, Bruker, Waters and Agilent mass spectrometers, among others.
  • a surface acoustic wave transducer 220 is operatively coupled to the mass spectrometer 210, so that when the surface acoustic wave transducer is used to nebulize the suspension, at least some of the nebulized suspension enters the input of the mass spectrometer. Accordingly, in an embodiment of a method according to the invention, a suspension 230 of the analyte in a solvent is provided to an active surface 222 of the surface acoustic wave transducer 220.
  • the surface acoustic wave tranducer 220 is activated (e.g., by creating an oscillating electrical potential between interdigitating electrodes, as described below), creating acoustic energy (as a surface acoustic wave) that nebulizes the suspension 230 into small droplets. Mass spectrometry is performed on the nebulized suspension 232 that enters the input of the mass spectrometer.
  • Surface acoustic wave transducer 320 includes a substrate 321, with two sets of interdigitating electrodes (326a and 328a; and 326b and 328b) formed on a surface 322 thereof. Between the sets of electrodes is an aperture 325.
  • the substrate can be formed, for example, from lithium niobate.
  • Other piezoelectric materials such as quartz, lead zirconate titanate, zinc oxide, lithium tantalate, and lanthanum gallium silicate, can also be used.
  • the interdigitating electrodes can have, for example, a pitch in the range of about 200 ⁇ to about 600 ⁇ , electrode widths in the range of about 20 ⁇ to about 150 ⁇ .
  • the aperture is in the range of about 1 mm to about 100 mm.
  • the person of skill in the art can modify the device attributes outside of these ranges in order to provide a surface acoustic wave transducer that can be driven to nebulize the suspension.
  • different electrode designs and aperture configurations can be used.
  • more or less than two sets of electrodes can be used.
  • the nebulization is performed continuously.
  • the nebulization is performed discontinuously, for example, in pulses or steps over time.
  • the nebulization/analysis steps can be repeated over the course of hours or even days, allowing a sample to be interrogated for evolution over time, as is conventional in MALDI techniques.
  • the data generated by the methods described herein are not contaminated with matrix ions at low m/z.
  • the nebulization can provide nebulized suspension having a variety of droplet sizes. As the person of skill in the art would appreciate, nebulization will result in a distribution of droplet sizes.
  • the average droplet size of the nebulized mode can be, for example, in the range of about 0.1 ⁇ to about 50 ⁇ , and in some embodiments, about 3 ⁇ to about 20 ⁇ .
  • the frequency of the surface acoustic wave can be used to control the droplet size, with higher frequencies resulting in smaller average droplet size. For example, Ju, J.Y., et al, Sensors and Actuators A: Physical, 2008, 145: p.
  • surface acoustic wave transducer can include a superstate disposed on the piezoelectric substrate.
  • One embodiment is shown in schematic cross- sectional view in FIG. 4.
  • Surface acoustic wave tranducer 420 includes piezoelectric substrate 421 (and electrodes 426, 428, with superstate 450 disposed thereon.
  • the superstate is shown as being roughly the same size as substrate.
  • the superstate can be larger, or smaller than the substrate.
  • the superstate can be part of a larger microfluidic device; for example, a channel can lead from a separation or reaction region of the device to the region that acts as the superstate of the transducer.
  • the superstate can be formed from a variety of materials, for example, from glass, silica, silicon, semiconductor materials, or polymer.
  • the superstate can be placed on the substrate, with a fluid layer (e.g., water) between the two for effective transfer of energy to the superstate.
  • a fluid layer e.g., water
  • the surface acoustic wave of the piezoelectric substrate will be coupled into the superstate, such that the suspension can be placed on the surface 452 of the superstate 450 and nebulized therefrom.
  • the superstate can provide a disposable or easily cleanable surface, so the more difficult-to-fabricate piezoelectric substrate/electrode structures can have a longer service life.
  • the superstate can be formed from relatively simple standard microfabrication methods, such as photolithography, etching, and microembossing. The person of skill in the art will recognize that other techniques can be used to form the transducer.
  • the surface of the transducer e.g., the surface of the superstate
  • the surface of the transducer can have surface features such as ridges, channels, or surface coatings (e.g., organic-containing) or patterning to guide the movement and activity of liquid thereon.
  • the surface of the superstate has an organically-modified silicate coating formed thereon.
  • the organically-modified silicate coating can be a monolayer, or a multilayer, and can be formed using standard silane chemistry.
  • the organically-modified silicate can be selected to provide a desired contact angle of the drop of suspension with the surface.
  • an organically modified silicate formed from trimethylchlorosilane and/or methyltrimethoxysilane can provide relatively large contact angles with aqueous solutions.
  • An organically modified silicate made with a highly fluorinated alkylsilane, such as perfluoro-lH,lH,2H,2H-octyltrichlorosilane can provide increased contact angles even when the suspension includes an organic solvent.
  • the nebulization of the suspension will depend on contact angle, so surface chemistry can be tuned to change the nebulization behavior.
  • a clean glass surface e.g., cleaned with strong base or strong oxidizing acid
  • the surface of the transducer (e.g., the surface of the superstate) has regions of different wettability.
  • Silane chemistry can be used to differently pattern the surface.
  • a clean glass or silicon superstrate can be photolithographically patterned, and treated with a desired chlorosilane in a solvent that does not dissolve the photoresist (e.g. hexanes).
  • the photoresist can be removed, and optionally the exposed area can be reacted with another silane.
  • Such patterning can, for example, form a wettable area for the suspension, surrounded by non-wettable areas, thus confining the drop of suspension, and therefore the nebulization to a defined area.
  • a hydrophilic surface region can be created on the surface of the transducer, surrounded by a hydrophobic surface region.
  • the hydrophilic region can be, for example, bare oxide.
  • the hydrophobic region can be formed from a silane as described above, for example, a long chain alkyl silane, or a highly fluorinated alkyl silane.
  • a plurality of wettable areas can be formed on the surface, for example, to provide for a plurality of areas from which to nebulizer a suspension.
  • the wettable areas can be aligned with other features of the device, for example, any channels or features that couple a microfluidic system to the transducer.
  • the nebulization of the suspension is from a substantially flat surface.
  • no additional capillaries, nozzles, channels or electrodes are necessary.
  • such embodiments do not suffer from the high surface area-to-volume ratios, and the adventitious material losses (e.g., non-specific adsorption of proteins and biofouling by lipids) associated therewith.
  • clogging of narrow nozzles or capillaries by materials such as lipids is not a concern when nebulizing from a substantially flat surface.
  • features such as channels can be used to deliver the suspension to the substantially flat surface for nebulization.
  • the surface of the transducer is not at an electrical potential substantially different from ground.
  • the capillary is at a high voltage, which can promote analyte oxidation and thus mask the ability to determine oxidation of analytes in vivo.
  • ESI can oxidize methionyl, tryptophanyl and tyrosyl residues, complicating peptide database searches by the addition of additional differential modifications, and confounding attempts to measure differences in protein quantities between samples.
  • Sample oxidation has also been widely observed for the DESI process. Accordingly, it can be desirable to maintain the surface of the transducer at a relatively low voltage (e.g., not substantially different from ground), to avoid oxidation.
  • a potential (e.g., greater than 10 V from ground, greater than 100 V from ground, or even greater than 1000 V from ground, e.g., 5 kV) is applied to the surface of the transducer.
  • the added voltage increases the charge that the liquid carries as it is nebulized. This increases the attraction between the vapor and the inlet of the mass spectrometer, pulling more of the vapor inside the instrument, thereby leading to better detection of the analyte.
  • This added potential can be applied, for example, by an electrode provided as part of the surface acoustic wave transducer (e.g., disposed at or underneath the surface from which the suspension is nebulized).
  • the mass spectrometry can be performed using a mass spectrometer.
  • Any suitable mass spectrometer for mass spectrometric analysis of the analyte can be used.
  • the mass spectrometer can be based on a sector field mass analyzer, a time of flight mass analyzer, a quadrupole mass analyzer, a quadrupole ion trap, a linear quadrupole ion trap, an orbitrap, or a Fourier transform ion cyclotron resonance mass analyzer.
  • a sector field mass analyzer a time of flight mass analyzer
  • a quadrupole mass analyzer a quadrupole ion trap
  • a linear quadrupole ion trap a linear quadrupole ion trap
  • an orbitrap or a Fourier transform ion cyclotron resonance mass analyzer.
  • other types of mass spectrometric systems can be used in practicing the methods and constructing the systems described herein.
  • the nebulized suspension is directed to the input of the mass spectrometer, for example, using a carrier gas, a stream of nebulized solvent, or a
  • the angle and/or distance of nebulization from the surface acoustic wave transducer is low enough that it is desirable to more actively convey the nebulized suspension to the input of the mass spectrometer in order to provide a relatively larger amount of analyte to the mass spectral analysis.
  • a source of carrier gas or a source of a stream of nebulized solvent is included in the system, configured to direct an nebulized suspension from the surface acoustic wave tranducer to the input of the mass spectrometer.
  • the nebulization process itself will provide sufficient nebulized suspension to the mass spectrometer.
  • the mass spectrometer can pull nebulized suspension into its input as a result of the imposed pull of the vacuum system and the electrical potential of the orifice.
  • An electrical field e.g., created by the potential of the orifice relative to ground
  • the use of concave, curved capillary inlets can be more efficient than flat-fronted designs for ion capture and transfer. Wu, S.
  • the concave aspect of the capillary can also be lined with non-conductive anti-static materials to help facilitate ion entry to the mass spectrometer. Hawkridge A.M. et al., Anal Chem. 2004 Jul 15;76(14):4118-22, which is hereby incorporated herein by reference in its entirety.
  • a shield or enclosure can be provided around the transducer in order to protect the nebulized suspension from being blown about by room air currents.
  • gas dynamics e.g., within an enclosure
  • a multiple capillary inlet can be used to provide increased gas load to the mass spectrometer.
  • the nebulized suspension can be emitted from the surface of the surface acoustic wave transducer as a somewhat nebulous plume.
  • Surface chemistry and phononic bandgap structures can be used to minimize the area of the surface from which the nebulized suspension is emitted, and to provide some directionality to the emission, in order to improve the capture of the by nebulized suspension by the inlet of the mass spectrometer. In certain embodiments, however, it can be desirable to provide additional focusing of the plume of nebulized suspension.
  • electrofocusing is used to improve the efficiency of the mass transfer from the nebulized suspension to the inlet of the mass spectrometer, for example, using an ion funnel.
  • An ion funnel is an electrodynamic radiofrequency ion guide, and is known in the art to more efficiently capture ions entering the mass spectrometer.
  • Certain embodiments of ion funnels include series of evenly-spaced stacked-ring electrodes. The diameters of the electrodes taper down to a relatively small exit aperture, which is coupled to the input of the mass spectrometer.
  • Ions are confined in the plane parallel to the funnel axis by the application of RF fields (e.g., in the range of 700 kHz - 1.4 MHz) applied through equal amplitude but opposite polarity on adjacent electrodes. Ions are moved through the device along the funnel axis from the wide end to the narrow end by co-application of a direct current field gradient. In use, the large acceptance aperture of the ion funnel can more efficiently capture the expanding plume of nebulized suspension, presenting them as a more focused collimated ion beam at the input of the mass spectrometer. Ion funnels are described in, for example, Shaffer, S.A. et al, Anal Chem.
  • no additional ionization technique need be used. As the solvent is stripped from the analyte droplet, the analyte becomes ionized. In other embodiments, however, an additional ionization technique is used to assist in ionization. For example, ionization of the nebulized suspension can be assisted using known techniques such as ESI, ACPI (corona discharge), DESI (desorption electrospray ionization), and LAESI (laser ablation electrospray ionization). Moreover, application of a voltage to the suspension on the transducer, as described above, can also provide additional assistance to ionization.
  • the surface acoustic wave electrodes are concentrically interdigitated. Propagation of a surface acoustic wave on a linear electrode can lead to inconsistent locations for nebulization, because the travelling wave can dislocate the drop. Yeo, L.Y. and J.R. Friend, Biomicrofluidics, 2009. 3(1): p. 12002, which is hereby incorporated herein by reference in its entirety. This feature can be harnessed to control droplet movement, but in many embodiments can be beyond the level of complexity desired for a simple sample analysis system. Focused surface acoustic wave devices, such as those described in Wu, T.T. et al, Journal of Physics D-Applied Physics, 2005.
  • FIG. 5 An example of such a device is shown in schematic top view in FIG. 5.
  • Surface acoustic wave transducer 520 includes a piezoelectric substrate 521, with two sets of interdigitating electrodes 526 and 528 formed thereon in a concentric circular pattern, defining aperture 525.
  • Such devices can help to keep the droplet centered (e.g., in the center of the "bullseye").
  • Such focused surface acoustic wave devices can have more power than devices based on linear electrodes, potentially making them more efficient at nebulization.
  • the electrodes are shown in a circular pattern in FIG. 5; other configurations can be used.
  • a linearally interdigitated electrode configuration is used, optionally with surface patterning (as described below) to provide a consistent location of drop nebulization.
  • the methods and systems described herein can provide relatively "soft" ionization of the analyte as compared to other techniques such as ESI.
  • the mass spectral analysis results in the detection of an [M+H] + or [M-H] " peak.
  • the methods described herein can provide significant amounts of singly protonated or deprotonated analyte, thereby yielding a significant and detectable [M+H] + or [M-H] " peak.
  • the [M+H] + or [M-H] " peak can be of, for example, at least 10% of the intensity of the [M+2H] + or [M- 2H] 2" peak.
  • the [M+H] + or [M-H] " peak is of at least 5%, or even of at least 10% of the intensity of the largest detected decomposition ion peak.
  • the base peak will be an [M+nH] n+ or an [M-nH] n" peak.
  • spectrometry settings e.g., inlet temperature
  • analytes can be analyzed using the methods and systems described herein.
  • the analyte is non-volatile.
  • the analyte can have molecular weight greater than about 500 Da, greater than about 1000 Da, or even greater than about 2000 Da. There is no general upper limit other than that imposed by the mass spectrometer. Accordingly, analytes having molecular weights up to about 100 kDa, up to about 500 kDa, up to about 1000 kDa and even up to about 5000 kDa can be analyzed using the methods and systems described herein.
  • the analyte has a molecular weight in the range of about 50 Da to about 500 Da.
  • the methods and systems described herein can be advantaged, in that they can provide soft ionization without matrix interference at low m/z.
  • the analyte is a biomolecule.
  • the analyte is a peptide or a protein.
  • peptides and proteins for analysis are often available in only very small amounts.
  • the methods and systems described herein can operate on such very small amounts with relatively little material loss on device surfaces to provide meaningful analytic data.
  • other analytes can be analyzed, such as metabolites, small organic molecules, oligonucleotides, polysaccharides, glycoproteins, lipids, carbohydrates, and other
  • the analyte can be from a biologic source, or in other embodiments can be from a non-biologic source (e.g., synthetic in nature).
  • the methods and systems described herein can also be useful for analyzing other types of analytes.
  • other organic materials such as polymers, oligomers, and small organic molecules can be analyzed using the methods and systems described herein.
  • Inorganic materials can also be analyzed using the methods and systems described herein.
  • the solvent has a boiling point less than about 150 °C, less than about 120 °C, or even less than about 105 °C.
  • the solvent can be, for example, water, a lower alcohol (e.g., methanol, ethanol, or a propanol), or a mixture thereof.
  • the analyte can be fully dissolved (i.e., to form a solution), or merely suspended, or a combination thereof (e.g., partially dissolved and partially suspended).
  • the analyte can be present in the suspension at a variety of concentrations. Notably, even low concentrations can be detected using the method and systems described herein. For example, in one embodiment, the analyte is present in the sample at a detectable concentration less than about 50 ⁇ .
  • an acid or a base can be included in the suspsension, for example to provide a greater abundance of ions for mass spectral analysis.
  • the suspension includes an acid.
  • the acid can be used to provide a greater abundance of positive ions (e.g., [M+Hf) for mass spectral analysis.
  • the acid is formic acid.
  • the acid is a hydrohalic acid (e.g., HC1), or a carboxylic acid such as acetic acid.
  • the acid can, for example, be provided at a concentration to yield a pH in the range of about 2 to about 5.
  • the acid is formic acid, added to the suspension at a concentration of about 0.1 wt%.
  • the mass spectrometer can be run in positive mode, as would be apparent to the person of skill in the art.
  • the suspension includes a base.
  • the base can be used to provide a greater abundance of negative ions (e.g., [M-H] " ) for mass spectral analysis.
  • the base can be, for example, ammonium hydroxide.
  • bases e.g., volatile bases such as amine bases
  • the base can, for example, be provided at a concentration to yield a pH in the range of about 5 to about 9.
  • the mass spectrometer can be run in negative mode, as would be apparent to the person of skill in the art.
  • the surface acoustic wave tranducer is operative ly coupled to a micro fluidic (e.g., "lab-on-a-chip") device.
  • the micro fluidic device can be used, for example, to perform a reaction, separation, and/or purification of the analyte, for example, before nebulization of the suspension.
  • the microfluidic device can be coupled to the surface acoustic wave transducer to perform other functions.
  • the surface acoustic wave transducer can be built on the same substrate as the microfluidic device, and merely couple thereto through one or more microfluidic channels.
  • the microfluidic device is disposed on top of the piezoelectric substrate, such that the region of the microfluidic device over the piezoelectric substrate forms a superstrate of the transducer.
  • microfluidic devices can be coupled to a surface acoustic wave transducer for mass spectrometric analysis.
  • a surface acoustic wave transducer for mass spectrometric analysis.
  • microfluidic device is a so-called EWOD (electrowetting on dielectric) or DMF (digital microfluidic) device.
  • EWOD electrowetting on dielectric
  • DMF digital microfluidic
  • a sample can be moved along the surface of the device using the property of electrocapillarity (the modification of surface tension by applying an electric field).
  • Other types of micro fiuidic devices that can be coupled to the surface acoustic wave transducer include capillary-based devices, thin layer chromatography, capillary electrophoresis, PCR devices, and microfluidic chemical reactors. Examples of microfluidic devices are generally described in Erickson, D. and Li, D., Analytica Chimica Acta 507 (2004) 11-26, which is hereby incorporated herein by reference in its entirety.
  • the device can provide for affinity capture and separation, for example as described in U.S. Patent no. 6,881,586, which is hereby incorporated herein by reference in its entirety.
  • Other devices can be coupled to the surface acoustic wave transducer.
  • a microwave device can be coupled to the surface acoustic wave transducer, for example, for sample preparation.
  • multiple surface acoustic wave transducers are arrayed together, for example, in a monolithic device. Each such tranducer can be used, for example, to nebulize a different sample.
  • Arrays of surface acoustic wave transducers can be used, for example, for multiplexing or interfacing with devices in which multiple samples are handled in parallel, such as microtiter plates and parallel microfluidic arrays.
  • the arrayed transducers can, for example, resemble MALDI plates in functionality, allowing for the spotting of a plurality of samples, with sequential analysis thereof.
  • the array of transducers can be provided using an array of slanted reflectors, as described in U.S. Patent no., 7,633,206, which is hereby incorporated herein by reference in its entirety.
  • Such devices can provide a plurality of individually addressable (by different frequencies) spots from which a suspension can be nebulized.
  • the slanted reflectors can be aligned with wettable areas defined by surface chemistry, as described above.
  • FIG. 6 is a schematic diagram of the electrode design of the transducer
  • FIG. 7 is a photograph of the transducer surface, showing two sets of interdigitating electrodes with an aperture disposed between them.
  • the device was built on a 128 Y-cut X-propagating 3" LiNb0 3 wafer diced into four segments of equal size (i.e., to make four devices), each with a 1.5" front edge.
  • Each device included 10 pairs of 100 ⁇ thick interdigitating electrodes on a 400 ⁇ pitch, with an about 10 mm square aperture.
  • the transducer was created using photolithography and lift-off techniques familiar to the person of skill in the art on the LiNb0 3 substrate.
  • SI 828 photoresist was first spun onto the wafer segment at 4000 rpm for 30 s, then patterned using UV exposure through a chrome mask for 6.5 s and developing in the appropriate developer for 40 s.
  • the interdigitating electrodes were produced by deposition of 20 nm Ti (as a bonding layer) followed by evaporation of Au. Lift-off was performed using acetone (2 h).
  • the surface acoustic wave transducer was used to nebulize different liquids, including water; 1 : 1 watenmethanol; and the GluFib solution, deposited on the surface of the device in its aperture in an amount of 1 ⁇ .
  • the transducer was driven at 12 MHz.
  • the pulse width was varied from 1 to 20 ms. The results are shown in FIG. 8. The power required for nebulization varied among the samples, with lowest power requirements observed at 20 ms pulses.
  • the onsets of nebulization were: -315 mW, 1 : 1 methanol: water solution; -400 mW, water; -800 mW, acidified GluFib solution.
  • the inventors surmise that the fact that water exhibited the lowest onset voltage, and therefore the greatest tendency to nebulize, is related to the surface energy of the drop.
  • FIG. 11 shows the results of these experiments for three different liquids: water; 10% aqueous glycerol; and 12 ⁇ GluFib in water.
  • the water exhibited an average nebulized droplet size of 9.4 ⁇ , with the average nebulized droplet size decreasing to 8.9 ⁇ and 5.2 ⁇ for 20 MHz and 30 MHz excitation frequencies, respectively.
  • the glycerol and GluFib solutions exhibited larger average nebulized droplet sizes, of 15.6 ⁇ and 16.4 ⁇ , respectively. In all three cases, other droplet size modes (i.e., with larger droplet sizes) were observed; these phenomena do not interfere with the observed mass spectra.
  • Mass spectra were acquired using a hybrid linear ion trap Fourier-transform ion cyclotron resonance mass spectrometer (LTQ-FT, Thermo Scientific).
  • LTQ-FT linear linear ion trap Fourier-transform ion cyclotron resonance mass spectrometer
  • samples were delivered via a fused silica capillary with a pulled tip at 1 ⁇ / ⁇ via a syringe pump.
  • the ESI voltage was set at 1.6 kV, with the voltage delivered via a liquid junction electrode as described in Yi, E.C., et al, Rapid Commun. Mass
  • the surface acoustic wave transducer of Example 1 was interfaced with the LTQ-FT mass spectrometer.
  • a picture of the experimental setup is provided as FIG. 12.
  • the transducer was positioned 1 cm below the heated capillary inlet of the mass spectrometer, with the center of the surface acoustic wave device being in line with the capillary inlet.
  • the inlet orifice was maintained at 100 V, and the heated capillary ion transfer tube maintained at 200 °C.
  • Surface acoustic wave nebulization was initiated as described above, with a 4.5 kV potential placed on the surface of the transducer.
  • the other instrument settings were as reported in Scherl, A., et al, J. Am. Soc. Mass
  • Detection of peptide ions was performed either across the full m/z range, or via selected ion monitoring of the expected precurson m/z values, as appropriate. A maximum ion trap time of 200 ms at 1 intervals was used for ESI and surface acoustic wave nebulization.
  • Mass spectra and fragment ion tandem mass spectra were generated from a 1 ⁇ ⁇ sample of 1 ⁇ angiotensin (i.e., 1 pmol angiotensin total) nebulized from the surface of the transducer.
  • FIG. 13 plots the ion abundance (i.e., as measured by total ion current) plotted as a function of acquisition time for surface acoustic wave nebulization and ESI. The surface acoustic wave-generated plume lasted about two minutes, and was drifted somewhat with room air current.
  • FIG. 14 provides mass spectra for the surface acoustic wave and ESI experiments. Both spectra were generated by averaging the 1.2 minutes of data shown in FIG. 13. Notably, the surface acoustic wave- generated spectrum produced a charge state distribuition with an [M+2H] 2+ base peak and a [M+H] + ion about 25% of the intensity of the base peak.
  • Lipid A endotoxin from Gram-negative bacteria was analyzed.
  • Lipid A is a glycolipid which typically (and problematically for structure determination) displays more monosaccharide modifications when measured by ESI than MALDI.
  • FIG. 16 shows example mass spectra (on different m/z scales) of Yersinia pestis Lipid A obtained by (A) MALDI- TOF and (B) ESI-LTQFT-ICR-MS. Notably, the same sample produces drastically different data.
  • lipid A extracts can clog ESI tips.
  • FIG. 17 is a set of mass spectra and the structure of Lipid A generated using surface acoustic wave transduction of a 50:50 methanol/chloroform suspension of Lipid A and a SYNAPT mass spectrometer.
  • the parent ion at m/z ⁇ 1979 g/mol has high
  • FIG. 18 provides additional analysis of the mass spectra with respect to various fragments.
  • the same Lipid A suspension was analyzed using surface acoustic wave nebulization in a Velos ion trap mass spectrometer (including an S-lense ion trap) in positive mode.
  • the precursor mass spectrum is not shown, but appeared similar to that of FIG. 14.
  • FIG. 19 presents three mass spectra of sequential fragments. To generate the top mass spectrum of FIG.

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Abstract

La présente invention concerne de façon générale la spectrométrie de masse. Plus particulièrement, la présente invention porte sur des procédés et des systèmes destinés à être utilisés dans l'identification par spectrométrie de masse d'une variété d'analytes, comprenant les espèces de masse moléculaire élevée telles que les protéines. Un mode de réalisation de l'invention est un procédé d'analyse d'un analyte. Le procédé consiste à nébuliser une suspension de l'analyte dans un solvant avec un transducteur d'ondes acoustiques de surface ; et à effectuer une spectrométrie de masse sur la suspension nébulisée. Le transducteur d'ondes acoustiques de surface peut être utilisé, par exemple, pour transférer des peptides non volatils et protéines non-volatiles (ainsi que d'autres analytes, tels que des oligonucléotides et des polymères) dans la phase gazeuse à pression atmosphérique. La nébulisation à l'aide d'ondes acoustiques de surface peut être conduite dans un mode discontinu ou pulsé, analogue à celui utilisé dans la désorption-ionisation laser assistée par matrice (MALDI), ou dans un mode continu, comme dans l'ionisation par électronébuliseur (ESI).
PCT/US2010/056724 2009-11-13 2010-11-15 Ions générés par un dispositif à ondes acoustiques de surface détectés par spectrométrie de masse WO2011060369A1 (fr)

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US9375690B2 (en) 2009-08-24 2016-06-28 The University Court Of The University Of Glasgow Fluidics apparatus and fluidics substrate
US9273339B2 (en) 2011-01-03 2016-03-01 University Of Maryland, Baltimore Methods for identifying bacteria
US9410873B2 (en) 2011-02-24 2016-08-09 The University Court Of The University Of Glasgow Fluidics apparatus for surface acoustic wave manipulation of fluid samples, use of fluidics apparatus and process for the manufacture of fluidics apparatus
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WO2013128933A1 (fr) 2012-03-01 2013-09-06 学校法人関西大学 Procédé d'ionisation, procédé de spectrométrie de masse, procédé d'extraction, et procédé de purification
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EP2912678A1 (fr) * 2012-10-25 2015-09-02 Micromass UK Limited Vibration piézoélectrique sur une structure d'ionisation à surface source d'ions pour la réduction de gouttelettes secondaires
GB2511643A (en) * 2013-03-05 2014-09-10 Micromass Ltd Charging plate for enhancing multiply charged ions by laser desportion
GB2511643B (en) * 2013-03-05 2016-12-21 Micromass Ltd Charging plate for enhancing multiply charged ions by laser desorption
US9721775B2 (en) 2013-03-05 2017-08-01 Micromass Uk Limited Charging plate for enhancing multiply charged ions by laser desorption
EP2779209A1 (fr) 2013-03-11 2014-09-17 Commissariat à l'Énergie Atomique et aux Énergies Alternatives Dispositif de determination de la masse d'une particule en suspension ou en solution dans un fluide
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US11311686B2 (en) 2014-11-11 2022-04-26 The University Court Of The University Of Glasgow Surface acoustic wave device for the nebulisation of therapeutic liquids
US11771846B2 (en) 2014-11-11 2023-10-03 The University Court Of The University Of Glasgow Nebulisation of liquids
GB2548071B (en) * 2015-12-18 2018-05-02 Thermo Fisher Scient Bremen Gmbh Liquid sample introduction system and method, for analytical plasma spectrometer
US10978282B2 (en) 2015-12-18 2021-04-13 Thermo Fisher Scientific (Bremen) Gmbh Liquid sample introduction system and method, for analytical plasma spectrometer
GB2548071A (en) * 2015-12-18 2017-09-13 Thermo Fisher Scient (Bremen) Gmbh Liquid sample introduction system and method, for analytical plasma spectrometer
WO2022019855A1 (fr) * 2020-07-24 2022-01-27 Ihsan Dogramaci Bilkent Universitesi Dispositif permettant d'obtenir la masse de nanoparticules, de virus et de protéines uniques en suspension ou dans une solution avec une efficacité de collecte élevée

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