MALDI-TOF

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MALDI-TOF is a method of mass analysis of chemical compounds. The method combines the M atrix- A ssistierte L aser- D esorption- I onisierung (MALDI) with the flight analysis (engl. Time of Flight , TOF) released ions to mass spectrometry .

history

MALDI-TOF / TOF mass spectrometer from Bruker

The acronym MALDI, coined in 1985 by Michael Karas , Doris Bachmann and Franz Hillenkamp , means matrix-assisted laser desorption ionization. They found that the amino acid alanine could be ionized when the amino acid tryptophan was added. Because only tryptophan absorbs the energy of a pulse laser at 266 nm and helps to ionize the non-absorbing alanine. Koichi Tanaka's group made decisive progress when they mixed tiny cobalt particles (30 nm) into glycerine and used an inexpensive nitrogen laser (337 nm). With such a matrix-laser combination, large biomolecules such as carboxypeptidase A can be ionized. In 2002 Tanaka received a quarter of the Nobel Prize in Chemistry.

In the early 1990s, the first commercial instruments came onto the market, making MALDI accessible to broad application and further research.

functionality

Matrix-assisted laser desorption / ionization (MALDI)
schematic representation of a time-of-flight mass spectrometer with reflectron

MALDI is a three-step process:

  • The sample is provided with supporting matrix material and fixed on a carrier.
  • A pulsed laser beam releases molecules from the sample as hot gas; this process is called ablation or desorption .
  • The release or acceptance of protons converts the released molecules into ions.

Finally, the ions are accelerated in a mass spectrometer and their TOFs are recorded.

MALDI-TOF is used to analyze large molecules and (bio) polymers. The molecules of a sample are first ionized (MALDI) and then analyzed by mass spectroscopy according to their time of flight (TOF).

With MALDI, the analyte is ionized by laser bombardment over a matrix in which the actual analytes are embedded. For a more detailed explanation of this step, see Matrix-Assisted Laser Desorption / Ionization (MALDI). The resulting ions are accelerated in an electric field. Typical acceleration voltages for this are 10–30 kV. Because of the pulsed ion generation, a TOF analyzer ( time-of-flight mass spectrometer , sometimes with reflectron ) is ideal for mass analysis .

The time of flight ( ) of the ions depends on their mass ( ) and their charge number ( ) as follows:

An ion detector (often a secondary electron multiplier such as a microchannel plate ) converts the incoming ions into an electrical signal. The advantage of this measuring method is the fast analysis of a comparatively large mass range. It is noteworthy that the TOF analyzer does not have a fundamental mass limit for large masses, so that ions from m / z up to 1,000,000 have already been measured. The pseudomolecular ions [M + H] + , [M + Na] + or also [M + K] + appear as ionized species . The occurrence (or the relative intensities) of the different species depends strongly on the previous history of the sample and on the substance class itself.

Since membrane proteins or lipids are not water-soluble without surfactants and surfactants interfere with MALDI-TOF-MS, some cleavable surfactants are used. On the other hand, cleavable amphiphilic derivatives of α-cyano-4-hydroxycinnamic acid (CHCA), which have been coupled to decanol via formaldehyde , do not have to be removed since they can also be used as a matrix in the MALDI-TOF-MS. A matrix of α-cyano-4-hydroxycinnamic acid with the surfactant CTAB can also be used in MALDI-TOF-MS. There are matrix mixtures that are less sensitive to surfactants.

application

Mass spectrum of an SDS-PAGE gel after tryptic digestion

Apart from the matrix, MALDI-TOF is a marker-free method that does not require any dyes, antibodies or radioactive elements. Therefore it is available for a wide range of applications, not only for technical material control, but also for biological and medical issues.

Mass spectrum of Bacillus cereus ( ATCC 10876) presented in OpenChrom

In bacteriology , the technology can be used to identify the species. Measurements of isolated pure cultures are compared using reference spectra from a database. Compared to molecular biological methods such as 16S rRNA or ITS sequencing, the running costs are significantly lower, which is why the process is increasingly being used in food microbiology to increase product safety and industrial hygiene . For highly pathogenic microorganisms, the devices are set up in laboratories with the appropriate biological protection level and the cultures are safely inactivated beforehand.

The official food control in Germany is working in cooperation with trade laboratories and medical supply centers to create an exchange platform for spectrum libraries in order to promote scientific exchange. In addition to microorganisms, it is food chemists of CVUA Stuttgart succeeded also a method for the differentiation of mammalian - species develop to food fraud in the gastronomy reveal.

When diagnosing tumors with a microscope, a distinction must be made between malignant and normal cells. Based on the protein pattern, MALDI-TOF could indicate the aggressiveness of a tumor or its sensitivity to therapy. The method supports tumor typing and may contribute to objective grading. A colored image of the same tissue section is required for the morphological assignment of the MALDI image . The exact superposition of two pixel files is part of the routine in digital microscopy.

literature

  • Franz Hillenkamp, ​​M Karas. Mass spectrometry of peptides and proteins by matrix-assisted ultraviolet laser desorption / ionization. In: Methods Enzymol 193/1990: 280-295. doi: 10.1016 / 0076-6879 (90) 93420-P .
  • Franz Hillenkamp, ​​Anthony Tsarbopoulos, Michael L Gross. Focus on desorption ionization and macromolecular mass spectrometry. In: J Am Soc Mass Spectrom 19/2008: 1041-1044. doi: 10.1016 / j.jasms.2008.06.017 .

Web links

Individual evidence

  1. ↑ Michael Karas, Doris Bachmann, Franz Hillenkamp. Influence of the wavelength in high-irradiance ultraviolet laser desorption mass spectrometry of organic molecules. In: Analytical Chem 57/1985: 2935-2939. doi: 10.1021 / ac00291a042
  2. ↑ Koichi Tanaka, Y. Ido, S. Akita, Y. Yoshida, T. Yoshida: Detection of high mass molecules by laser desorption time-of-flight mass spectrometry. In: Proceedings of the Second Japan-China Joint Symposium on Mass Spectrometry 1987: 185-188.
  3. ↑ nobelprize.org: Koichi Tanaka - Facts , accessed on February 27, 2017.
  4. ↑ Michael Karas, U. Bahr. Laser desorption ionization mass spectrometry of large biomolecules. In: Trends Analyt Chem 9/1990: 321-325. doi: 10.1016 / 0165-9936 (90) 85065-F
  5. ↑ Michael Karas, U. Bahr. Laser desorption ionization mass spectrometry of bioorganic molecules. In: Methods Mol Biol 17/1993: 215-228. doi: 10.1385 / 0-89603-215-9: 215
  6. ↑ Michael Karas, Ralf Krüger: Ion formation in MALDI: The cluster ionization mechanism. In: Chem Rev 103/2003: 427-440. doi: 10.1021 / cr010376a .
  7. ↑ JL Norris, NA Porter, RM Caprioli: Mass spectrometry of intracellular and membrane proteins using cleavable detergents. In: Analytical chemistry. Volume 75, Number 23, December 2003, pp. 6642-6647. doi: 10.1021 / ac034802z . PMID 14640740 .
  8. ^ R. Gottardo, A. Chiarini, I. Dal Prà, C. Seri, C. Rimondo, G. Serpelloni, U. Armato, F. Tagliaro: Direct screening of herbal blends for new synthetic cannabinoids by MALDI-TOF MS. In: Journal of Mass Spectrometry Volume 47, Number 1, January 2012, pp. 141-146. doi: 10.1002 / jms.2036 . PMID 22282100 .
  9. ↑ L. Signor, E. Boeri Erba: Matrix-assisted laser desorption / ionization time of flight (MALDI-TOF) mass spectrometric analysis of intact proteins larger than 100 kDa. In: Journal of visualized experiments: JoVE. Number 79, 2013. doi: 10.3791 / 50635 . PMID 24056304 . PMC 3857990 (free full text).
  10. ↑ Fahad J Alharbi, Tarekegn Geberhiwot, Derralynn A Hughes, Douglas G Ward. A novel rapid MALDI-TOF-MS-based method for measuring urinary globotriaosylceramide in Fabry patients. In: J Am Soc Mass Spectrom 27/2016: 719-725. doi: 10.1007 / s13361-015-1318-4 .
  11. ↑ M. Pavlovic, K. Grünwald, V. Zeller-Péronnet, M. Maggipinto, I. Huber, R. Konrad, A. Berger, U. Messelhäußer, P. Zimmermann, S. Hörmansdorfer, A. Sing, U. Busch : Identification of bacteria with the MALDI Biotyper at the Bavarian State Office for Health and Food Safety. In: Healthcare. 73/2011, doi: 10.1055 / s-0031-1274482
  12. ↑ P Nenoff, M Erhard, JC Simon, J Herrmann, GK Muylowa, W Rataj, Yvonne grasses. MALDI-TOF mass spectrometry: A rapid method for the identification of dermatophyte species. In: Med Mycol 51/2013: 17-24. doi: 10.3109 / 13693786.2012.685186
  13. ↑ LABO online: MALDI-TOF-MS prevents expensive fruit juice bombs , May 1, 2012
  14. ↑ Peter Lasch, Herbert Nattermann, Marcel Erhard, Maren Stämmler, Roland Grunow: MALDI-TOF Mass Spectrometry Compatible Inactivation Method for Highly Pathogenic Microbial Cells and Spores . In: Analytical Chemistry . tape 80 , no. 6 , March 15, 2008, ISSN  0003-2700 , p. 2026-2034 , doi : 10.1021 / ac701822j .
  15. ↑ J. Rau, R. Sting (CVUA Stuttgart); T. Eisenberg (Landesbetrieb Hessisches Landeslabor Gießen): MALDI-UP - An open catalog for database entries by users for users on MALDI-TOF-MS-user-platform.ua-bw.de
  16. ↑ Jörg Rau: Differentiation of animal species in meat using MALDI-TOF-MS , CVUA Stuttgart
  17. ↑ Jörg Kriegsmann, Mark Kriegsmann, Rita Casadonte: MALDI TOF imaging mass spectrometry in clinical pathology: A valuable tool for cancer diagnostics (review). In: Int J Oncol 46/2015: 893-906. doi: 10.3892 / ijo.2014.2788 .
  18. ↑ H. Li, Z. Tang, H. Zhu, H. Ge, S. Cui, W. Jiang: Proteomic study of benign and malignant pleural effusion. In: Journal of cancer research and clinical oncology. Volume 142, Number 6, June 2016, pp. 1191-1200, doi : 10.1007 / s00432-016-2130-7 , PMID 26945985 .
  19. ↑ K. Jia, W. Li, F. Wang, H. Qu, Y. Qiao, L. Zhou, Y. Sun, Q. Ma, X. Zhao: Novel circulating peptide biomarkers for esophageal squamous cell carcinoma revealed by a magnetic bead-based MALDI-TOFMS assay. In: Oncotarget. Volume 7, number 17, April 2016, pp. 23569-23580, doi : 10.18632 / oncotarget.8123 , PMID 26993605 , PMC 5029648 (free full text).