Surface-enhanced laser desorption/ionization
|Related||Matrix-assisted laser desorption/ionization
Soft laser desorption
Surface-enhanced laser desorption/ionization (SELDI) 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. Comparison of protein levels between patients with and without a disease can be used for biomarker discovery.
How it works 
SELDI-TOF-MS is a variation of matrix-assisted laser desorption/ionization (MALDI) that uses a target modified to achieve biochemical affinity with the analyte compound. In MALDI, a protein or peptide sample is mixed with the matrix molecule in solution and small amounts of the mixture are deposited on a surface and allowed to dry. The sample and matrix co-crystallize as the solvent evaporates. In SELDI, the protein mixture is spotted on a surface modified with a chemical functionality. Some proteins in the sample bind to the surface, while the others are removed by washing. After washing the spotted sample, the matrix is applied to the surface and allowed to crystallize with the sample peptides. Binding to the SELDI surface acts as a separation step and the subset of proteins that bind to the surface are easier to analyze. Common surfaces include CM10 (weak-positive ion exchange), H50 (hydrophobic surface, similar to C6-C12 reverse phase chromatography), 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 typically 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. The technology was commercialized by Ciphergen Biosystems in 1997 as the ProteinChip system. It is now produced and marketed by Bio-Rad Laboratories.
See also 
- Tang N, Tornatore P, Weinberger SR (2004). "Current developments in SELDI affinity technology". Mass spectrometry reviews 23 (1): 34–44. doi:10.1002/mas.10066. PMID 14625891.
- Li J, Zhang Z, Rosenzweig J, Wang YY, Chan DW (2002). "Proteomics and bioinformatics approaches for identification of serum biomarkers to detect breast cancer". Clin. Chem. 48 (8): 1296–304. PMID 12142387.
- Jr GW, Cazares LH, Leung SM, Nasim S, Adam BL, Yip TT, Schellhammer PF, Gong L, Vlahou A (1999). "Proteinchip(R) 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 and Prostatic Diseases 2 (5/6): 264–276. doi:10.1038/sj.pcan.4500384. PMID 12497173.
- Hutchens TW and Yip TT. "New desorption strategies for the mass spectrometric analysis of macromolecules." Rapid Commun Mass Spectrom 7: 576-580 (1993).