SELDI desorption/ionization

Wright, G. L., Cazares, L. H., Leung, S.-M., Nasim, S., Adam, B.-L., Yip, T.-T., Schellhammer, P. F., Gong, L., and Vlahou, A. (2000). 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 and Prostatic Diseases 2, 264-276. 

The ProteinChip System from Ciphergen Biosystems uses patented SELDI (Surface-Enhanced Laser Desorption/Ionization) ProteinChip technology to rapidly perform the separation, detection, and analysis of proteins at the femtomole level directly from biological samples. ProteinChip Systems use ProteinChip Arrays which contain chemically (cationic, anionic, hydrophobic, hydrophilic, etc.) or biochemically (antibody, receptor, DNA, etc.) treated surfaces for specific interaction with proteins of interest. Selected washes create on-chip, high-resolution protein maps. This protein mass profile, or reten-tate map of the proteins bound to each of the ProteinChip Array surfaces, is quantitatively detected in minutes by the ProteinChip Reader. 

Diamond DL, Zhang Y, Gaiger A, et al. Use of ProteinChip array surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) to identify thymosin beta-4, a differentially secreted protein from lymphoblastoid cell lines. J. Am. Soc. Mass Spectrom. 2003 14 760-765. 

Also for MALDI, there is a special case worth mentioning. Surface-enhanced laser desorption/ionization (SELDI) is a technique that utilizes special sample plates [196, 197]. These have different modified surfaces, for example, hydrophobic, anionic, or antibody treated. Which type of surface to select depends on the application. After application of analyte the surface is washed according to a protocol leaving only the desired components on the target. Finally, a MALDI matrix is applied before analysis in the spectrometer. See Chapter 12 for an application example of SELDI. 

Surface enhanced laser desorption/ionization (SELDI) is a distinctive form of laser desorption ionization where the target plays an active role in the sample preparation procedure and ionization process [49]. Depending on the chemical or biochemical treatment, the SELDI surface acts as solid phase extraction or an affinity probe. Chromatographic surface is used for sample fractionation and purification of biological samples prior to direct analysis by laser desorption/ ionization. SELDI is mainly applied for protein profiling and in biomarker discovery by comparing protein profiles from control and patient groups. 

Mass spectrometers are used not only to detect the masses of proteins and peptides, but also to identify the proteins, to compare patterns of proteins and peptides, and to scan tissue sections for specific masses. MS is able to do this by giving the mass-to-charge ratio of an ionized species as well as its relative abundance. For biological sample analysis, mass spectrometers are connected to an ionizing source, which is usually matrix-assisted laser desorption ionization (MALDI) [14], surface-enhanced laser desorption/ioni-zation (SELDI, a modified form of MALDI) [15], or electrospray ionization [16]. These interfaces enable the transfer of the peptides or proteins from the solid or liquid phase, respectively, to the gas (vacuum) phase inside the mass spectrometer. Both MALDI and electrospray ionization can be connected to different types of mass analyzers, such as quadrupole, quadruple-ion-traps, time of flight (TOF), or hybrid instruments such as quadrupole-TOF or Fourier transform-ion cyclotron resonance. Each of these instruments can... 

FT-ICR-Fourier transform-ion cyclotron resonance. MALDI-matrix-assisted laser desorption ionization. SELDI-surface-enhanced laser desorption/ionization. 

Matrix-assisted laser desorption ionization (MALDI) and surface-enhanced laser desorption ionization (SELDI) have been used online with TOF-MS for protein differential profiles of intact or hydrolyzed biological matrices in proteomics. The potential use of affinity chips, grafted with specific Ab towards the drug compound for MALDI or SELDI, will bring sensitive and selective tools for macromolecules. Specific Ab towards either the intact protein or several signature peptides... 

Similar to SELDI-TOF MS profiling, magnetic RP beads and Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS have been used for salivary peptidome characterization under pathophysiological conditions, as, for example, in the evaluation of periodontal-orthodontic treatment (32). However, the information retrieved using these strategies is limited requiring complementary bottom-up approaches. 

FIGURE 7 Group B streptococcus infection-induced differential protein expression in nonhuman primate (A) and human (B) amniotic fluid samples by surface-enhanced laser desorption/ionization (SELDI-TOF MS) using normal-phase protein chip arrays. Spectrum from 2.5 to 15 kDa collected at 235 nm laser intensity. Detailed spectra show increased expression of the 3.5 and 10.8 kDa peaks between control and infected. Arrows indicate the unique peaks represented by polypeptides overexpressed in infection. 

The Bik glycoprotein has an isoelectric point (p/) of 2.1 and is composed of a peptide and two glycoconjugate portions [30]. The predicted peptide sequence of Bik is helpful to understanding protein function. The peptide has Kunitz-binding domains I and II attached to the N-terminal peptide tail [31-33] (Fig. 2). Protein mass spectrometry by surface-enhanced laser desorption ionization (SELDI) in combination with detection by Bik antibodies has demonstrated that substantial variation exists in the Bik molecule [13,14]. 

The wide application of newly developed advanced Surface MALDI MS methods, such as laser desorption ionization (LDI), surface-enhanced laser desorption ionization (SELDI), direct ionization on silicon surface (DIOS), etc. have two shortcomings. First, problems with MALDI-TOF MS sample preparation for nano-sized systems have not been completely worked out. Second, the reliability and reproducibility of experimental data concerning similar bio-active systems is lacking. Sometimes molecular, associative and fragment ions cannot, be observed in the MALDI mass spectra. We are currently working on overcoming these difficulties with some encouraging results.13,14... 

RC-MS stems from the observation that mass spectra of peptides and proteins can be generated by laser activation of chromatographic surfaces placed on MALDI targets. The product application of RC-MS, called surface-enhanced laser desorption ionization-time of fiight (SELDI-TOF), refers to a mass spectrometry method for measuring native proteins adsorbed (retained) on various chemical or biochemical surfaces (Figure 4.11). Although the concept of laser desorption of intact proteins is well established, it has been commercially exploited only recently as a means... 

The SELDI instrument is a laser desorption ionization mass spectrometer capable of ionizing proteins from an adsorptive surface, or biochip. The instrument has a customized carriage to feed biochips into what is essentially a MALDI instrument... 

On-probe purification using derivatized MALDI probe surfaces has been described to simplify the sample preparation process. Various developments in this field have allowed the introduction of new techniques such as the surface-enhanced laser desorption ionization (SELDI) [42], The surface of the probe plays an active role in binding the analyte by hydrophobic or electrostatic interactions, while contaminants are rinsed away. In the same way, this technique uses targets with covalently coupled antibodies directed against a protein, allowing its purification from biological samples as urine or plasma. Subsequent addition of a droplet of matrix solution allows MALDI analysis. 

Label-free optical techniqnes for detecting bound proteins on microarrays have been recently reviewed. The advantage of these methods over labeling methods is that the native form of the analyte is preserved. These methods include SPR, surface-enhanced laser desorption/ionization mass spectrometry (SELDI-MS), atomic force microscopy " and fiber-optic methods. 

SELDI Surface-enhanced laser desorption/ionization... 

Surface-enhanced laser/desorption ionization mass spectrometry Protein-Chip . See Tang, N., Tomatore, P, and Weinberger, S.R., Current developments in SELDI affinity technology. Mass Spectrom. Rev. 23a, 34-44,2004. 

SELDI-TOF surface enhanced laser desorption ionization time-of-fhght... 

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