Matrix-enhanced surface-assisted laser

Liu Q, Xiao Y, Pagan-Miranda C, Chiu Y, He L (2009) Metabolite imaging using matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS). J Am Soc Mass Spectrom 20 80-88. doi 10.1016/j.jasms.2008.09.011... 

Mass Spectrometry Imaging of Small Molecules Using Matrix-Enhanced Surface-Assisted Laser Desorptlon/lonizatlon Mass Spectrometry (ME-SALDI-MS)... 

The ionization methods reported for IMS included MALDI [41,76-80], Secondary Ion Mass Spectrometry (SIMS) [19, 81-86], Matrix-enhanced (ME)-SIMS [87, 88], Desorption Electrospray Ionization (DESI) [89-99], Nanostructure Initiator Mass Spectrometry (NIMS) [100-102], Atmospheric Pressure Infrared MALDI Mass Spectrometry (AP-IR-MALDI-MS) [103], Laser Ablation-inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) [104-106], Laser Desorption Postionization (LDPI) [107], Laser Ablation Electrospray Ionization Mass Spectrometry (LAESI) [108, 109], and Surface-assisted Laser Desorption/ioniza-tion Mass Spectrometry (SALDI) [110-112], Another method was called probe electrospray ionization (PESI) that was used for both liquid solution and the direct sampling on wet samples. 

The analysis for proteins present in plasma or a cell extract is a challenging task due to their complexity and the great difference between protein concentrations present in the sample. Simple mixtures of intact proteins can be analyzed by infusion with electrospray ionization and more complex ones by matrix assisted laser desorption ionization. MALDI is more suited for complex mixtures because for each protein an [M+H]+ signal is observed while for ESI multiply charged ions are observed. Surface enhanced laser desorption (SEEDI) is a technique for the screening of protein biomarkers based on the mass spectrometric analysis of intact proteins [49]. However in most cases for sensitivity reasons mass spec-... 

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... 

While ESI and APCI have been the most commonly used means for the separahon and mass analysis of biotransformahon products, matrix-assisted laser desorphon/ionization (MALDl) and related techniques, such as surface-enhanced laser desorphon/ionization (SELDI) [75] and direct ionizahon off silicon (DIOS) [76], hold promise for rapid screening of biotransformahon samples, and may one day replace much of the work now done by LC-MS for qualitahve studies. The advantage of these techniques over LC-MS is rapid sample analysis, and high-density sample formats that can be prepared robotically. 

Label-free methods use the intrinsic properties of proteins to report binding events on protein chips. Ciphergen ProteinChips can be incorporated directly into a matrix-assisted laser desorbtion/ionization (MALDI) source of a mass spectrometer, which can identify the proteins and provide quantitative analysis. The ionization of proteins bound to Protein-Chips is enhanced by the properties of the chip surface, leading to more uniform mass spectra than possible with standard MALDI mass spectrometric... 

The matrix-assisted effect refers to enhanced ionization efficiency of molecules that is observed when they are desorbed with another molecule in the mixture that acts as a primary chromophore as compared to their direct laser desorption ionization efficiency as a pure compound. Thus, in a matrix-assisted laser desorption/ionization (MALDI) experiment, one must always add the matrix to enhance the ionization efficiency of the analytes. Good matrices generally have high absorption coefficients for the laser wavelength of interest and are usually acidic to be able to donate a proton (positive ion mode) in the plume. It is also often desirable for a matrix to form large, flat crystals upon evaporation of solvent. This latter requirement is particularly true for time-of-flight mass analyzers because the resolving power is dependent on the flatness of the sample surface. 

---