Soft laser desorption (SLD) is laser desorption of large molecules that results in ionization without fragmentation. "Soft" in the context of ion formation means forming ions without breaking chemical bonds. "Hard" ionization is the formation of ions with the breaking of bonds and the formation of fragment ions.
Background
The term "soft laser desorption" has not been widely used by the mass spectrometry community, which in most cases uses matrix-assisted laser desorption/ionization (MALDI) to indicate soft laser desorption ionization that is aided by a separate matrix compound. The term soft laser desorption was used most notably by the Nobel Foundation in public information released in conjunction with the 2002 Nobel Prize in Chemistry.[1] Koichi Tanaka was awarded 1/4 of the prize for his use of a mixture of cobalt nanoparticles and glycerol in what he called the “ultra fine metal plus liquid matrix method” of laser desorption ionization. With this approach, he was able to demonstrate the soft ionization of proteins.[2] The MALDI technique was demonstrated (and the name coined) in 1985 by Michael Karas, Doris Bachmann, and Franz Hillenkamp,[3] but ionization of proteins by MALDI was not reported until 1988, immediately after Tanaka's results were reported.
Some have argued that Karas and Hillenkamp were more deserving of the Nobel Prize than Tanaka because their crystalline matrix method is much more widely used than Tanaka's liquid matrix.[4][5] Countering this argument is the fact that Tanaka was the first to use a 337 nm nitrogen laser while Karas and Hillenkamp were using a 266 nm Nd:YAG laser. The "modern" MALDI approach came into being several years after the first soft laser desorption of proteins was demonstrated.[6][7][8]
The term soft laser desorption is now used to refer to MALDI as well as "matrix free" methods for laser desorption ionization with minimal fragmentation.[9]
Variants
Graphite
The surface-assisted laser desorption/ionization (SALDI) approach uses a liquid plus graphite particle matrix.[10][11] A colloidal graphite matrix has been called "GALDI" for colloidal graphite-assisted laser desorption/ionization.[12]
Nanostructured surfaces
The desorption ionization on silicon (DIOS) approach is laser desorption/ionization of a sample deposited on a porous silicon surface.[13] Nanostructure-initiator mass spectrometry (NIMS) is a variant of DIOS that uses "initiator" molecules trapped in the nanostructures.[14] Although nanostructures are typically formed by etching, laser etching can also be used, for example as in laser-induced silicon microcolumn arrays (LISMA) for matrix-free mass spectrometry analysis.[15]
Nanowires
A commercial NALDI target
Silicon nanowires were initially developed as a DIOS-MS application.[16] This approach was later commercialized as Nanowire-assisted laser desorption/ionization (NALDI) uses a target consisting of nanowires made from metal oxides or nitrides.[17] NALDI targets are available from Bruker Daltonics (although they are marketed as "nanostructured" rather than "nanowire" targets).
Surface-enhanced laser desorption/ionization (SELDI)
Main article: surface-enhanced laser desorption/ionization
The surface-enhanced laser desorption/ionization (SELDI) variant is similar to MALDI, but uses a biochemical affinity target.[18][19] The technique known as surface-enhanced neat desorption (SEND)[18] is a related variant of MALDI with the matrix is covalently linked to the target surface. The SELDI technology was commercialized by Ciphergen Biosystems in 1997 as the ProteinChip system. It is now produced and marketed by Bio-Rad Laboratories.
Other methods
The technique known as laser induced acoustic desorption (LIAD) is transmission geometry LDI with a metal film target.[20][21]
References
"The Nobel Prize in Chemistry 2002". The Nobel Foundation. 9 October 2002. Retrieved 2013-01-31.
Tanaka, Koichi; Hiroaki Waki; Yutaka Ido; Satoshi Akita; Yoshikazu Yoshida; Tamio Yoshida; T. Matsuo (1988). "Protein and polymer analyses up to m/z 100 000 by laser ionization time-of-flight mass spectrometry". Rapid Communications in Mass Spectrometry. 2 (8): 151–153. Bibcode:1988RCMS....2..151T. doi:10.1002/rcm.1290020802.
Karas, M.; Bachmann, D.; Hillenkamp, F. (1985). "Influence of the Wavelength in High-Irradiance Ultraviolet Laser Desorption Mass Spectrometry of Organic Molecules". Anal. Chem. 57 (14): 2935–9. doi:10.1021/ac00291a042.
Spinney, Laura (December 11, 2002). "Nobel Prize controversy". The Scientist. Archived from the original on May 17, 2007. Retrieved 2007-08-29.
"ABC News Online: 2002 Nobel chemistry choice sparks protest". B.U. Bridge. Boston University. Week of 13 December 2002. Retrieved 2007-08-29. Check date values in: |date= (help)
Beavis RC, Chait BT (1989). "Matrix-assisted laser-desorption mass spectrometry using 355 nm radiation". Rapid Commun. Mass Spectrom. 3 (12): 436–9. Bibcode:1989RCMS....3..436B. doi:10.1002/rcm.1290031208. PMID 2520224.
Beavis RC, Chait BT (1989). "Cinnamic acid derivatives as matrices for ultraviolet laser desorption mass spectrometry of proteins". Rapid Commun. Mass Spectrom. 3 (12): 432–5. Bibcode:1989RCMS....3..432B. doi:10.1002/rcm.1290031207. PMID 2520223.
Strupat K, Karas M, Hillenkamp F; Karas; Hillenkamp (1991). "2,5-Dihidroxybenzoic acid: a new matrix for laser desorption-ionization mass spectrometry". Int. J. Mass Spectrom. Ion Process. 72 (111): 89–102. Bibcode:1991IJMSI.111...89S. doi:10.1016/0168-1176(91)85050-V.
Vertes, Akos (2007). "Soft Laser Desorption Ionization — Maldi, Dios and Nanostructures". Laser Ablation and its Applications. Springer Series in Optical Sciences. 129. pp. 505–528. doi:10.1007/978-0-387-30453-3_20. ISBN 978-0-387-30452-6.
Sunner, J.; Dratz, E.; Chen, Y.-C. (1995). "Graphite surface-assisted laser desorption/ionization time-of-flight mass spectrometry of peptides and proteins from liquid solutions". Anal. Chem. 67: 4335–42. doi:10.1021/ac00119a021. PMID 8633776.
Dale, Michael J.; Knochenmuss, Richard; Zenobi, Renato (1996). "Graphite/Liquid Mixed Matrices for Laser Desorption/Ionization Mass Spectrometry". Analytical Chemistry. 68 (19): 3321–9. doi:10.1021/ac960558i. PMID 21619267.
Cha, Sangwon; Yeung, Edward S. (2007). "Colloidal Graphite-Assisted Laser Desorption/Ionization Mass Spectrometry and MSnof Small Molecules. 1. Imaging of Cerebrosides Directly from Rat Brain Tissue". Analytical Chemistry. 79 (6): 2373–85. doi:10.1021/ac062251h. PMID 17288467.
Wei, J.; Buriak, J. M.; Siuzdak, G. (1999). "Desorption-ionization mass spectrometry on porous silicon". Nature. 399: 243–246. Bibcode:1999Natur.399..243W. doi:10.1038/20400. PMID 10353246.
Northen, Trent R.; Yanes, Oscar; Northen, Michael T.; Marrinucci, Dena; Uritboonthai, Winnie; Apon, Junefredo; Golledge, Stephen L.; Nordström, Anders; Siuzdak, Gary (2007). "Clathrate nanostructures for mass spectrometry". Nature. 449 (7165): 1033–6. Bibcode:2007Natur.449.1033N. doi:10.1038/nature06195. PMID 17960240.
Chen, Yong; Vertes, Akos (2006). "Adjustable Fragmentation in Laser Desorption/Ionization from Laser-Induced Silicon Microcolumn Arrays". Analytical Chemistry. 78 (16): 5835–44. doi:10.1021/ac060405n. PMID 16906730.
Go EP, Apon JV, Luo G, Saghatelian A, Daniels RH, Sahi V, Dubrow R, Cravatt BF, Vertes A, Siuzdak G (March 2005). "Desorption/ionization on silicon nanowires". Anal Chem. 77 (6): 1641–6. doi:10.1021/ac048460o. PMID 15762567.
Kang, Min-Jung; Pyun, Jae-Chul; Lee, Jung-Chul; Choi, Young-Jin; Park, Jae-Hwan; Park, Jae-Gwan; Lee, June-Gunn; Choi, Heon-Jin (2005). "Nanowire-assisted laser desorption and ionization mass spectrometry for quantitative analysis of small molecules". Rapid Communications in Mass Spectrometry. 19 (21): 3166–3170. Bibcode:2005RCMS...19.3166K. doi:10.1002/rcm.2187.
Hutchens, T. W.; Yip, T. T. (1993). "New desorption strategies for the mass spectrometric analysis of macromolecules". Rapid Commun. Mass Spectrom. 7: 576–580. doi:10.1002/rcm.1290070703.
Poon TC (2007). "Opportunities and limitations of SELDI-TOF-MS in biomedical research: practical advices". Expert Review of Proteomics. 4 (1): 51–65. doi:10.1586/14789450.4.1.51. PMID 17288515.
Golovlev, V. V.; Allman, S. L.; Garrett, W. R.; Taranenko, N. I.; Chen, C. H. (December 1997). "Laser-induced acoustic desorption". International Journal of Mass Spectrometry and Ion Processes. 169–170: 69–78. Bibcode:1997IJMSI.169...69G. doi:10.1016/S0168-1176(97)00209-7.
Somuramasami J, Kenttämaa HI (2007). "Evaluation of a Novel Approach for Peptide Sequencing: Laser-induced Acoustic Desorption Combined with Chemical Ionization and Collision-activated Dissociation in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer". J. Am. Soc. Mass Spectrom. 18 (3): 525–40. doi:10.1016/j.jasms.2006.10.009. PMC 1945181. PMID 17157527.
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