Soft laser desorption
Encyclopedia
Soft laser desorption 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 bond
s. "Hard" ionization is the formation of ions with the breaking of bonds and the formation of fragment ions.
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
. Koichi Tanaka
was awarded 1/4 of the prize for his use of a mixture of cobalt
nanoparticle
s 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. The MALDI technique was demonstrated (and the name coined) in 1985 by Michael Karas, Doris Bachmann, and Franz Hillenkamp, 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. 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.
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.
(SELDI) variant is similar to MALDI, but uses a biochemical affinity target. The technique known as surface-enhanced neat desorption (SEND) 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.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
desorption of large molecules that results in ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...
without fragmentation. "Soft" in the context of ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
formation means forming ions without breaking chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
s. "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 spectrometryMass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
community, which in most cases uses matrix-assisted laser desorption/ionization
Matrix-assisted laser desorption/ionization
Matrix-assisted laser desorption/ionization is a soft ionization technique used in mass spectrometry, allowing the analysis of biomolecules and large organic molecules , which tend to be fragile and fragment when ionized by more conventional ionization methods...
(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
Nobel Foundation
The Nobel Foundation is a private institution founded on 29 June 1900 to manage the finances and administration of the Nobel Prizes. The Foundation is based on the last will of Alfred Nobel, the inventor of dynamite....
in public information released in conjunction with the 2002 Nobel Prize in Chemistry
Nobel Prize in Chemistry
The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,...
. Koichi Tanaka
Koichi Tanaka
is a Japanese scientist who shared the Nobel Prize in Chemistry in 2002 for developing a novel method for mass spectrometric analyses of biological macromolecules with John Bennett Fenn and Kurt Wuthrich ....
was awarded 1/4 of the prize for his use of a mixture of cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
nanoparticle
Nanoparticle
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized...
s and glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
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. The MALDI technique was demonstrated (and the name coined) in 1985 by Michael Karas, Doris Bachmann, and Franz Hillenkamp, 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. Countering this argument is the fact that Tanaka was the first to use a 337 nm nitrogen laser
Nitrogen laser
A nitrogen laser is a gas laser operating in the ultraviolet range using molecular nitrogen as its gain medium, pumped by an electrical discharge....
while Karas and Hillenkamp were using a 266 nm Nd:YAG laser
Nd:YAG laser
Nd:YAG is a crystal that is used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet , since they are of similar size...
. The "modern" MALDI approach came into being several years after the first soft laser desorption of proteins was demonstrated.
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.
Graphite
The surface-assisted laser desorption/ionization (SALDI) approach uses a liquid plus graphite particle matrix. A colloidal graphite matrix has been called "GALDI" for colloidal graphite-assisted laser desorption/ionization.Nanostructured Surfaces
The desorption ionization on silicon (DIOS) approach is laser desorption/ionization of a sample deposited on a porous silicon surface. Nanostructure-initiator mass spectrometry (NIMS) is a variant of DIOS that uses "initiator" molecules trapped in the nanostructures. 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.Nanowires
Silicon nanowires were initially developed as a DIOS-MS application. This approach was later commericialized as Nanowire-assisted laser desorption/ionization (NALDI) uses a target consisting of nanowires made from metal oxides or nitrides. NALDI targets are available from Bruker Daltonics (although they are marketed as "nanostructured" rather than "nanowire" targets).Surface-enhanced laser desorption/ionization (SELDI)
The surface-enhanced laser desorption/ionizationSurface-enhanced laser desorption/ionization
Surface-enhanced laser desorption/ionization is an ionization method in mass spectrometry that is used for the analysis of protein mixtures. SELDI is typically used with time-of-flight mass spectrometers and is used to detect proteins in tissue samples, blood, urine, or other clinical samples...
(SELDI) variant is similar to MALDI, but uses a biochemical affinity target. The technique known as surface-enhanced neat desorption (SEND) 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
Bio-Rad
Bio-Rad Laboratories, Inc. , was founded in 1952 in Berkeley, California. The company was initially engaged in the development and production of specialty chemicals used in biochemical, pharmaceutical, and other life science research applications...
Laboratories.