science

Soft laser desorption

Soft laser desorption is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Soft laser desorption rather than just read about it. In short: 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…

Key takeaways

Soft laser desorption belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Soft laser desorption to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Soft laser desorption from memory before moving on to harder problems.

Reference excerpt

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. 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. 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.

Variants

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 commercialized 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/ionization (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.

Other methods The technique known as laser induced acoustic desorption (LIAD) is transmission geometry LDI with a metal film target.

References

External links The Nobel Prize in Chemistry 2002 – Information for the Public

Worked examples

Example 1 — a first encounter with Soft laser desorption

Start with the simplest possible case. Write down what Soft laser desorption claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Soft laser desorption before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Soft laser desorption ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Soft laser desorption

In research: Soft laser desorption appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Soft laser desorption in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Soft laser desorption is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ion source, Mass spectrometry, so understanding it makes those chapters shorter.
In everyday life: Look for Soft laser desorption outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Soft laser desorption in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Soft laser desorption means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Soft laser desorption out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Soft laser desorption in simple terms?

Why does Soft laser desorption matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Soft laser desorption?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Soft laser desorption.