Desorption/ionization on silicon

Soft laser desorption is a soft ionization technique which desorbs and ionizes molecules from surfaces with minimal fragmentation. This is useful for a broad range of small and large molecules and molecules that fragment easily. The first soft laser desorption techniques included matrix-assisted laser desorption/ionization (MALDI) nanoparticles in glycerol. In MALDI, the analyte is first mixed with a matrix solution. The matrix absorbs energy from the laser pulse and transfers it to the analyte, causing desorption and ionization of the sample. MALDI generates [M+H]⁺ ions.{{cite journal|last1=Karas|first1=Michael|last2=Krüger|first2=Ralf|title=Ion Formation in MALDI: The Cluster Ionization Mechanism|journal=Chemical Reviews|volume=103|issue=2|year=2003|pages=427–440|issn=0009-2665|doi=10.1021/cr010376a|pmid=12580637}}

DIOS was first reported by Gary Siuzdak, Jing Wei and Jillian M. Buriak in 1999. It was developed as a matrix-free alternative to MALDI for smaller molecules. Because MALDI uses a matrix, background ions are introduced due to ionization of the matrix. These ions reduce the usefulness of MALDI for small molecules. In contrast, DIOS uses a porous silicon surface to trap the analyte. This surface is not ionized by the laser, therefore creating minimal background ionization and thus allowing for the analysis of small molecules.{{cite journal|last1=Lewis|first1=Warren G.|last2=Shen|first2=Zhouxin|last3=Finn|first3=M.G.|authorlink4=Gary Siuzdak|last4=Siuzdak|first4=Gary|title=Desorption/ionization on silicon (DIOS) mass spectrometry: background and applications|journal=International Journal of Mass Spectrometry|volume=226|issue=1|year=2003|pages=107–116|issn=1387-3806|doi=10.1016/S1387-3806(02)00973-9|bibcode=2003IJMSp.226..107L}}{{cite journal|last1=Peterson|first1=Dominic S.|title=Matrix-free methods for laser desorption/ionization mass spectrometry|journal=Mass Spectrometry Reviews|volume=26|issue=1|year=2007|pages=19–34|issn=0277-7037|doi=10.1002/mas.20104|pmid=16967450|bibcode=2007MSRv...26...19P|url=https://zenodo.org/record/1229265}}

DIOS has been shown to be an ultra-sensitive means of generating and detecting molecules at the yoctomole level, both for DIOS{{Cite journal|last1=Trauger|first1=Sunia A.|last2=Go|first2=Eden P.|last3=Shen|first3=Zhouxin|last4=Apon|first4=Junefredo V.|last5=Compton|first5=Bruce J.|last6=Bouvier|first6=Edouard S. P.|last7=Finn|first7=M. G.|last8=Siuzdak|first8=Gary|date=2004-08-01|title=High Sensitivity and Analyte Capture with Desorption/Ionization Mass Spectrometry on Silylated Porous Silicon|url=https://doi.org/10.1021/ac049657j|journal=Analytical Chemistry|volume=76|issue=15|pages=4484–4489|doi=10.1021/ac049657j|pmid=15283591|issn=0003-2700}} nanostructured surfaces modified with fluorocarbons, and a subsequent related technology known as nanostructure-initiator mass spectrometry or nanostructure imaging mass spectrometry (NIMS).

DIOS has been shown to detect peptides, natural products, small organic molecules, and polymers with little fragmentation.{{cite journal|last1=Shen|first1=Zhouxin|last2=Thomas|first2=John J.|last3=Averbuj|first3=Claudia|last4=Broo|first4=Klas M.|last5=Engelhard|first5=Mark|last6=Crowell|first6=John E.|last7=Finn|first7=M. G.|last8=Siuzdak|first8=Gary|title=Porous Silicon as a Versatile Platform for Laser Desorption/Ionization Mass Spectrometry|journal=Analytical Chemistry|volume=73|issue=3|year=2001|pages=612–619|issn=0003-2700|doi=10.1021/ac000746f|pmid=11217770}}

DIOS can be used for proteomics. It has been reported as a useful method protein identification. Because it is matrix free, it can be used to identify smaller biomolecules than MALDI. In addition, it can be used to monitor reactions on a single surface through repeated MS analyses. Reaction monitoring can be used to screen enzyme inhibitors.{{cite journal|last1=Thomas|first1=J. J.|last2=Shen|first2=Z.|last3=Crowell|first3=J. E.|last4=Finn|first4=M. G.|last5=Siuzdak|first5=G.|title=Desorption/ionization on silicon (DIOS): A diverse mass spectrometry platform for protein characterization|journal=Proceedings of the National Academy of Sciences|volume=98|issue=9|year=2001|pages=4932–4937|issn=0027-8424|doi=10.1073/pnas.081069298|pmid=11296246|pmc=33141|bibcode=2001PNAS...98.4932T|doi-access=free}}

Atmospheric pressure DIOS was shown to be an effective tool for quantitative analysis of drugs with high proton affinity.{{cite journal|last1=Huikko|first1=K.|last2=Östman|first2=P.|last3=Sauber|first3=C.|last4=Mandel|first4=F.|last5=Grigoras|first5=K.|last6=Franssila|first6=S.|last7=Kotiaho|first7=T.|last8=Kostiainen|first8=R.|title=Feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry in analysis of drugs|journal=Rapid Communications in Mass Spectrometry|volume=17|issue=12|year=2003|pages=1339–1343|issn=0951-4198|doi=10.1002/rcm.1051|pmid=12811757|bibcode=2003RCMS...17.1339H}}

The use of DIOS to image small molecules has been demonstrated. Lin He and coworkers imaged small molecules on mouse liver cells. They also used marker molecules to image HEK 293 cancer cells.{{cite journal|last1=Liu|first1=Qiang|last2=Guo|first2=Zhong|last3=He|first3=Lin|title=Mass Spectrometry Imaging of Small Molecules Using Desorption/Ionization on Silicon|journal=Analytical Chemistry|volume=79|issue=10|year=2007|pages=3535–3541|issn=0003-2700|doi=10.1021/ac0611465|pmid=17428031}}

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