Surface-enhanced laser desorption/ionization
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Surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) is method of analyzing a complex mixture of proteins. Tang et al. provide a good review of the field. [1] SELDI-TOF-MS is most often used to measure proteins in tissue samples, blood, urine, or other clinical samples. Comparison of protein levels between patients with and without a disease can be used for biomarker discovery.[2][3]
SELDI-TOF-MS is similar to matrix-enhanced laser desorption/ionization (MALDI-TOF). They differ in how the matrix, or energy-absorbing molecule (EAM), is mixed with the protein sample. In MALDI, a protein or peptide sample is mixed with the matrix molecule in solution. Small amounts of the mixture are "spotted" on a surface and allowed to dry. The peptide sample and matrix co-crystallizes as the solvent evaporates. In SELDI the protein mixture is spotted on a surface modified with some chemical functionality. Some proteins in the sample bind to the surface, while the others are removed by washing. After washing the spotted sample, matrix (EAM) is applied to the surface and allowed to crystallize with the sample peptides. Binding to the SELDI surface acts as a chromatography step and the subset of proteins that bind to the surface are easier to analyze. Common surfaces include CM10 (weak-cation exchanger), H50 (hydrophobic surface, similar to C6-C12), IMAC30 (metal-binding surface), and Q10 (strong anion exchanger). Surfaces can also be functionalized with antibodies, other proteins, or DNA.
Samples spotted on a SELDI surface are analyzed using time-of-flight mass spectrometry. A laser ionizes peptides from crystals of the sample/matrix mixture. The ions are accelerated through an electric potential and down a flight tube. A detector measures ions as they reach the end of the tube. The mass-to-charge ratio of each ion can be determined from the length of the tube, the kinetic energy given to ions by the electric field, and the time taken to travel the length of the tube.
SELDI technology was developed by T. William Hutchens at Baylor College of Medicine in 1993 [4]. The technology was commercialized by Ciphergen Biosystems Inc. in 1997 as the ProteinChip system. It is now produced and marketed by Bio-Rad Laboratories.
[edit] References
- ^ Tang N, Tornatore P, Weinberger SR. "Current developments in SELDI affinity technology." Mass Spec Rev, 23(1):34-44 (2003).[1]
- ^ Li J, Zhang Z, Rosenzweig J, Wang YY, Chan DW. "Proteomics and Bioinformatics Approaches for Identification of Serum Biomarkers to Detect Breast Cancer." Clin Chem, 48:1296-1304 (2002). [2]
- ^ Wright Jr GL, et al. "ProteinChip surface enhanced laser desorption/ionization (SELDI) mass spectrometry: a novel protein biochip technology for detection of prostate cancer biomarkers in complex protein mixtures." Prostate Cancer Prostatic Dis, 2(5/6):264-276 (1999)
- ^ Hutchens TW and Yip TT. "New desorption strategies for the mass spectrometric analysis of macromolecules." Rapid Commun Mass Spectrom 7: 576-580 (1993). [3]
[edit] External Links
- Bio-Rad Laboratories ProteinChip SELDI System [4] describes the equipment, surfaces, and reagents for SELDI-TOF-MS.
- Ciphergen Biosystems [5] developed much of the original technology and now works on biomarker discovery for a range of diseases.
