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Laser ablation electrospray ionization

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Laser ablation electrospray ionization (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary electrospray ionization (ESI) process. The mid-IR laser is used to generate gas phase particles which are then ionized through interactions with charged droplets from the ESI source. LAESI was developed in Professor Akos Vertes lab by Peter Nemes in 2007 and it was marketed commercially by Protea Biosciences, Inc until 2017. Fiber-LAESI for single-cell analysis approach was developed by Bindesh Shrestha in Professor Vertes lab in 2009. LAESI is a novel ionization source for mass spectrometry (MS) that has been used to perform MS imaging of plants,[1][2][3] tissues,[4][5][6][7] cell pellets,[8] and even single cells.[9][10][11][12] In addition, LAESI has been used to analyze historic documents[13] and untreated biofluids such as urine and blood.[1] The technique of LAESI is performed at atmospheric pressure and therefore overcomes many of the obstacles of traditional MS techniques, including extensive and invasive sample preparation steps and the use of high vacuum. Because molecules and aerosols are ionized by interacting with an electrospray plume, LAESI's ionization mechanism is similar to SESI and EESI techniques.

Schematic representation of laser ablation electrospray ionization (LAESI)

LAESI can be used to perform MS analysis of many different classes of compounds ranging from small molecules, such as pharmaceuticals, saccharides,[1][2][3][9][10] lipids,[5][7] and metabolites[1][2][3][4][5][6][7][8][9][10] to larger biomolecules like peptides[1] and proteins.[1] LAESI has also been shown to have a quantitative dynamic range of 4 decades and a limit of detection (LOD) of 8 fmol with verapamil, a small pharmaceutical molecule.[1] The technique has a lateral resolution of <200 μm for imaging applications[7][14] and has been used for 3D imaging of plant tissues.[3] Additionally, in cell-by-cell LAESI imaging experiments single cells can be used as the pixels of the molecular image.[12] This LAESI application uses etched optical fibers to produce laser spot sizes of <50 μm to deliver the laser energy and has also been utilized in single cell analysis experiments.[9][10][11][12]

Principle of operation

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LAESI produces ions for MS analysis under normal atmospheric conditions for samples containing water.[15] The entire process can be divided into two steps.

Generation of analyte species

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When a mid-IR laser beam is applied to a target which contains a hydroxide group, the target will absorb energy from this laser beam leading to evaporation of moisture from the targeted area.[16] A small-scale explosion occurs in the target and a small portion of the sample is ablated into the gas phase by a short (5 ns), mid-IR (2,940 nm) laser pulse.[17][18] The plume expands until it collapses into the sample due to the pressure exerted by the atmosphere. At this point a jet of material is ejected from the sample surface.[17][19] As mid-IR has low energy most of the ejected particles from sample remain neutral.[16][20]

Reacting analyte species with charged solvent species

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An electrospray ionization (ESI) source is located above the sample for post-ablation ionization.[21] The jet of ablated material is intersected and ionized by a spray plume from the ESI source located above the sample. The ionized molecules are then swept into the mass spectrometer for analysis. Because an ESI source is used for ionization, the LAESI mass spectra are similar to traditional ESI spectra, which can exhibit multiply charged analyte peaks, and extend the effective mass range of detection to biomolecules >100,000 Da in size.[19][20]

Applications

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LAESI can be used to perform MS imaging experiments of diverse tissue samples, not only in three dimensions but also with respect to time. Similarly, LAESI can also be used for process monitoring applications because each individual analysis requires less than 2 seconds to perform. Because of the speed of a LAESI analysis, the technique is amenable to rapid, sensitive, and direct analysis of aqueous samples in 96- and 384-well microplates. These analyses can also be performed on liquid samples, such as biofluids, containing peptides, proteins, metabolites, and other biomarkers for clinical, diagnostic, and discovery workflows.[22] LAESI technology allows high throughput analysis of these sample types and the use of internal standards and calibration curves permit the absolute quantitation of targeted biomolecules.[23][22][20]

Advantages and limitations

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Advantages

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This technique needs very little or no sample preparation and it has high sensitivity.[22][15] This ionization technique does not need any external matrix. Therefore, the spatial resolution is not compromised by the presence of matrix crystal resulting in high spatial resolution.[20] This ionization technique can be carried out in natural and uneven biological surface.[23] Finally, as laser ablation and electronspray ionization work independently, they can be independently manipulated to achieve greater resolution.[20]

Limitations

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LAESI is a relatively new technique for those samples which contain water and are relatively stable. However, it has limitations for those samples which have a lower water content. For example, this technique does not ionize dry skin, nails, tooth and bone well; this is due to low water content in these samples.[16][22] Also, it needs a relatively large sampling area, compared to some other common ionization techniques.[20]

See also

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References

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  1. ^ a b c d e f g Nemes, Peter; Vertes, Akos (2007-09-27). "Laser Ablation Electrospray Ionization for Atmospheric Pressure, in Vivo, and Imaging Mass Spectrometry". Analytical Chemistry. 79 (21). American Chemical Society (ACS): 8098–8106. doi:10.1021/ac071181r. ISSN 0003-2700. PMID 17900146.
  2. ^ a b c Nemes, Peter; Barton, Alexis A.; Li, Yue; Vertes, Akos (2008-05-13). "Ambient Molecular Imaging and Depth Profiling of Live Tissue by Infrared Laser Ablation Electrospray Ionization Mass Spectrometry". Analytical Chemistry. 80 (12). American Chemical Society (ACS): 4575–4582. doi:10.1021/ac8004082. ISSN 0003-2700. PMID 18473485.
  3. ^ a b c d Nemes, Peter; Barton, Alexis A.; Vertes, Akos (2009-07-02). "Three-Dimensional Imaging of Metabolites in Tissues under Ambient Conditions by Laser Ablation Electrospray Ionization Mass Spectrometry". Analytical Chemistry. 81 (16). American Chemical Society (ACS): 6668–6675. doi:10.1021/ac900745e. ISSN 0003-2700.
  4. ^ a b Nemes, Peter; Vertes, Akos (2010-09-03). "Atmospheric-pressure Molecular Imaging of Biological Tissues and Biofilms by LAESI Mass Spectrometry". Journal of Visualized Experiments (43). MyJove Corporation: 1–4. doi:10.3791/2097. ISSN 1940-087X. PMC 3157867. PMID 20834223.
  5. ^ a b c Shrestha, Bindesh; Nemes, Peter; Nazarian, Javad; Hathout, Yetrib; Hoffman, Eric P.; Vertes, Akos (2010). "Direct analysis of lipids and small metabolites in mouse brain tissue by AP IR-MALDI and reactive LAESI mass spectrometry". The Analyst. 135 (4). Royal Society of Chemistry (RSC): 751–758. doi:10.1039/b922854c. ISSN 0003-2654. PMID 20349540.
  6. ^ a b Sripadi, Prabhakar; Nazarian, Javad; Hathout, Yetrib; Hoffman, Eric P.; Vertes, Akos (2008-12-14). "In vitro analysis of metabolites from the untreated tissue of Torpedo californica electric organ by mid-infrared laser ablation electrospray ionization mass spectrometry". Metabolomics. 5 (2). Springer Science and Business Media LLC: 263–276. doi:10.1007/s11306-008-0147-x. ISSN 1573-3882. S2CID 8286288.
  7. ^ a b c d Nemes, Peter; Woods, Amina S.; Vertes, Akos (2010-01-05). "Simultaneous Imaging of Small Metabolites and Lipids in Rat Brain Tissues at Atmospheric Pressure by Laser Ablation Electrospray Ionization Mass Spectrometry". Analytical Chemistry. 82 (3). American Chemical Society (ACS): 982–988. doi:10.1021/ac902245p. ISSN 0003-2700. PMC 2964874. PMID 20050678.
  8. ^ a b Sripadi, Prabhakar; Shrestha, Bindesh; Easley, Rebecca L.; Carpio, Lawrence; Kehn-Hall, Kylene; Chevalier, Sebastien; Mahieux, Renaud; Kashanchi, Fatah; Vertes, Akos (2010-09-07). Jacobson, Steven (ed.). "Direct Detection of Diverse Metabolic Changes in Virally Transformed and Tax-Expressing Cells by Mass Spectrometry". PLOS ONE. 5 (9). Public Library of Science (PLoS): e12590. doi:10.1371/journal.pone.0012590. ISSN 1932-6203. PMC 2935367. PMID 20830293.
  9. ^ a b c d Shrestha, Bindesh; Vertes, Akos (2010-09-04). "Direct Analysis of Single Cells by Mass Spectrometry at Atmospheric Pressure". Journal of Visualized Experiments (43). MyJove Corporation: 1–4. doi:10.3791/2144. ISSN 1940-087X. PMC 3157873. PMID 20834224.
  10. ^ a b c d Shrestha, Bindesh; Vertes, Akos (2009-09-17). "In Situ Metabolic Profiling of Single Cells by Laser Ablation Electrospray Ionization Mass Spectrometry". Analytical Chemistry. 81 (20). American Chemical Society (ACS): 8265–8271. doi:10.1021/ac901525g. ISSN 0003-2700.
  11. ^ a b Shrestha, Bindesh; Nemes, Peter; Vertes, Akos (2010-06-03). "Ablation and analysis of small cell populations and single cells by consecutive laser pulses". Applied Physics A. 101 (1). Springer Science and Business Media LLC: 121–126. doi:10.1007/s00339-010-5781-2. ISSN 0947-8396. S2CID 98617638.
  12. ^ a b c Shrestha, Bindesh; Patt, Joseph M.; Vertes, Akos (2011-03-09). "In Situ Cell-by-Cell Imaging and Analysis of Small Cell Populations by Mass Spectrometry". Analytical Chemistry. 83 (8). American Chemical Society (ACS): 2947–2955. doi:10.1021/ac102958x. ISSN 0003-2700. PMID 21388149.
  13. ^ Stephens, Catherine H.; Shrestha, Bindesh; Morris, Hannah R.; Bier, Mark E.; Whitmore, Paul M.; Vertes, Akos (2010). "Minimally invasive monitoring of cellulose degradation by desorption electrospray ionization and laser ablation electrospray ionization mass spectrometry". The Analyst. 135 (9). Royal Society of Chemistry (RSC): 2434–2444. doi:10.1039/c0an00155d. ISSN 0003-2654. PMID 20672159.
  14. ^ Nemes, Peter; Vertes, Akos (2010). "Laser Ablation Electrospray Ionization for Atmospheric Pressure Molecular Imaging Mass Spectrometry". Methods in Molecular Biology. Vol. 656. Totowa, NJ: Humana Press. pp. 159–171. doi:10.1007/978-1-60761-746-4_9. ISBN 978-1-60761-745-7. ISSN 1064-3745.
  15. ^ a b Bartels, Benjamin; Svatoš, Aleš (2015). "Spatially resolved in vivo plant metabolomics by laser ablation-based mass spectrometry imaging (MSI) techniques: LDI-MSI and LAESI". Frontiers in Plant Science. 6: 471. doi:10.3389/fpls.2015.00471. ISSN 1664-462X. PMC 4498035. PMID 26217345.
  16. ^ a b c Nemes, Peter; Vertes, Akos (2007-11-01). "Laser Ablation Electrospray Ionization for Atmospheric Pressure, in Vivo, and Imaging Mass Spectrometry". Analytical Chemistry. 79 (21): 8098–8106. doi:10.1021/ac071181r. ISSN 0003-2700. PMID 17900146.
  17. ^ a b Chen, Zhaoyang; Vertes, Akos (2008-03-25). "Early plume expansion in atmospheric pressure midinfrared laser ablation of water-rich targets". Physical Review E. 77 (3). American Physical Society (APS): 036316. doi:10.1103/physreve.77.036316. ISSN 1539-3755. PMID 18517520.
  18. ^ Chen, Zhaoyang; Bogaerts, Annemie; Vertes, Akos (2006-07-24). "Phase explosion in atmospheric pressure infrared laser ablation from water-rich targets". Applied Physics Letters. 89 (4). AIP Publishing: 041503. doi:10.1063/1.2243961. ISSN 0003-6951.
  19. ^ a b Apitz, I.; Vogel, A. (2005). "Material ejection in nanosecond Er:YAG laser ablation of water, liver, and skin". Applied Physics A. 81 (2). Springer Science and Business Media LLC: 329–338. doi:10.1007/s00339-005-3213-5. ISSN 0947-8396. S2CID 97063971.
  20. ^ a b c d e f Huang, Min-Zong; Cheng, Sy-Chi; Cho, Yi-Tzu; Shiea, Jentaie (2011). "Ambient ionization mass spectrometry: A tutorial". Analytica Chimica Acta. 702 (1): 1–15. doi:10.1016/j.aca.2011.06.017. PMID 21819855.
  21. ^ Vertes, Akos; Nemes, Peter; Shrestha, Bindesh; Barton, Alexis A.; Chen, Zhaoyang; Li, Yue (2008). "Molecular imaging by Mid-IR laser ablation mass spectrometry". Applied Physics A. 93 (4). Springer Science and Business Media LLC: 885–891. doi:10.1007/s00339-008-4750-5. ISSN 0947-8396. S2CID 97866908.
  22. ^ a b c d Kiss, András; Hopfgartner, Gérard (2016). "Laser-based methods for the analysis of low molecular weight compounds in biological matrices". Methods. 104: 142–153. doi:10.1016/j.ymeth.2016.04.017. PMID 27107904.
  23. ^ a b Román, Jessica K.; Walsh, Callee M.; Oh, Junho; Dana, Catherine E.; Hong, Sungmin; Jo, Kyoo D.; Alleyne, Marianne; Miljkovic, Nenad; Cropek, Donald M. (2018-03-01). "Spatially resolved chemical analysis of cicada wings using laser-ablation electrospray ionization (LAESI) imaging mass spectrometry (IMS)". Analytical and Bioanalytical Chemistry. 410 (7): 1911–1921. doi:10.1007/s00216-018-0855-7. ISSN 1618-2642. PMID 29380018. S2CID 3415847.
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