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See detailMALDI In-Source Decay, from sequencing to imaging
Debois, Delphine ULg; Smargiasso, Nicolas ULg; Demeure, Kevin ULg et al

in Topics in Current Chemistry (2013), 331

MALDI is now a mature method allowing the identification and, more challenging, the quantification of biopolymers (proteins, nucleic acids, glycans…). MALDI spectra show mostly intact singly charged ions ... [more ▼]

MALDI is now a mature method allowing the identification and, more challenging, the quantification of biopolymers (proteins, nucleic acids, glycans…). MALDI spectra show mostly intact singly charged ions. To obtain fragments, the activation of singly charged precursors is necessary, but not efficient above 3.5 kDa thus making MALDI MS/MS difficult for large species. In-source decay (ISD) is a prompt fragmentation reaction that can be induced thermally or by radicals. As fragments are formed in the source, precursor ions cannot be selected; however, the technique is not limited by the mass of the analyzed compounds and pseudo MS/MS can be performed on intense fragments. The discovery of new matrices that enhance the ISD yield, combined with the high sensitivity of MALDI mass spectrometers, and software development, opens new perspectives. We first review the mechanisms involved in the ISD processes, then discuss ISD applications like top-down sequencing and post-translational modifications studies, and finally review MALDI-ISD tissue imaging applications. [less ▲]

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See detailNew Advances for In Situ Protein Identification by MALDI In-Source Decay FTMS Imaging
Calligaris, David ULg; Zimmerman, Tyler ULg; Debois, Delphine ULg et al

Poster (2012, April 18)

MALDI imaging mass spectrometry has proven to be effective for the discovery and the monitoring of disease-related proteins. With this technique a molecular analysis could be performed directly from ... [more ▼]

MALDI imaging mass spectrometry has proven to be effective for the discovery and the monitoring of disease-related proteins. With this technique a molecular analysis could be performed directly from tissue sections in the region of the diseased area. The use of in-source decay (ISD), allowing fast and reliable sequences assignments of proteins termini, has proven to be a crucial tool for proteins identification in solution and tissue slices. However, it is necessary to develop additional tools that allow unambiguous assignment of proteins sequences in complex tissue slices. The development of bioinformatic tools and the use of ultra-high mass resolution and high mass accuracy of Fourier transform ion-cyclotron (FTICR) mass spectrometry are ideal for this purpose. In this study, we show that FTICR mass spectrometry combined with data filtering with a software that subtracts matrix peaks aid protein identification. All measurements were carried out on a SolariX FTMS (9.4 Tesla) equipped with a Dual Source with a smartbeamTMII laser (Bruker Daltonics). Mouse brain tissue slices of 14 µm thickness were rinsed to obtain optimal sensitivity and high-quality ions. Before matrix application, a spot of myelin was deposited near mouse brain. 1,5-Diaminionaphtalene was sprayed using an ImagePrep (Bruker Daltonics). Results were interpreted using BioToolsTM 3.2 in combination with MascotTM (Matrix Science) for ISD spectra and FlexImagingTM 3.0 for MALDI-ISD imaging experiments. Matrix peaks were subtracted using an in-house written Java code that sequentially scans all peak lists from acquired spectra against the DAN mass list. Then, another Java code allows to create 2D ion images at selected m/z ratios. The studies were carried out by MALDI-ISD imaging to create interest on FTICR mass spectrometer for proteins identification in the field of biomarkers characterization. It is demonstrated that protein ISD leads to the same pattern of fragmentation observed during MALDI-TOF analyzes. Fragmentation generates cn- and zn-series ions of myelin in presence of DAN. The internal calibration of all the data provides a mass accuracy neighboring 2.5 ppm over the m/z range of interest (300-2500 Da) and a mass resolution of 70000 at m/z 400 Da. It allows the assignment of ISD fragments of proteins in the low mass range (m/z between 300 and 900) that is unambiguously validated by the “ISD signal” recorded from the spots of pure protein solution (myelin) near tissue slice. Moreover, the use of our software “cleans” MS imaging data by reducing/eliminating MALDI matrix peaks that are isobaric to an analyte peak. Novel aspect This study evidences the main input of FTICR mass spectrometer for pathologies diagnosis based on biomarkers localization and identification by MALDI-ISD imaging. [less ▲]

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See detailRaman spectroscopy and laser desorption mass spectrometry for minimal destructive forensic analysis of black and color inkjet printed documents
Heudt, Laetitia ULg; Debois, Delphine ULg; Zimmerman, Tyler ULg et al

in Forensic Science International (2012), 219

Inkjet ink analysis is the best way to discriminate between printed documents, or even though more difficult, to connect an inkjet printed document with a brand or model of printers. Raman spectroscopy ... [more ▼]

Inkjet ink analysis is the best way to discriminate between printed documents, or even though more difficult, to connect an inkjet printed document with a brand or model of printers. Raman spectroscopy and laser desorption mass spectrometry (LDMS) have been demonstrated as powerful tools for dyes and pigments analysis, which are ink components. The aim of this work is to evaluate the aforementioned techniques for inkjet inks analysis in terms of discriminating power, information quality, and nondestructive capability. So, we investigated 10 different inkjet ink cartridges (primary colors and black), 7 from the HP manufacturer and one each from Epson, Canon and Lexmark. This paper demonstrates the capabilities of three methods: Raman spectroscopy, LDMS and MALDI-MS. Raman spectroscopy, as it is preferable to try the nondestructive approach first, is successfully adapted to the analysis of color printed documents in most cases. For analysis of color inkjet inks by LDMS, we show that a MALDI matrix (9- aminoacridine, 9AA) is needed to desorb and to ionize dyes from most inkjet inks (except Epson inks). Therefore, a method was developed to apply the 9AA MALDI matrix directly onto the piece of paper while avoiding analyte spreading. The obtained mass spectra are very discriminating and lead to information about ink additives and paper compositions. Discrimination of black inkjet printed documents is more difficult because of the common use of carbon black as the principal pigment. We show for the first time the possibility to discriminate between two black-printed documents coming from different, as well as from the same, manufacturers. Mass spectra recorded from black inks in positive ion mode LDMS detect polyethylene glycol polymers which have characteristic mass distributions and end groups. Moreover, software has been developed for rapid and objective comparison of the low mass range of these positive mode LDMS spectra which have characteristic unknown peaks. [less ▲]

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See detailAn analytical pipeline for MALDI in-source decay mass spectrometry imaging
Zimmerman, Tyler ULg; Debois, Delphine ULg; Mazzucchelli, Gabriel ULg et al

in Analytical Chemistry (2011), 83(15), 6090-6097

In-source decay (ISD) fragmentation as combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry allows protein sequencing directly from mass spectra. Acquisition of MALDI-ISD ... [more ▼]

In-source decay (ISD) fragmentation as combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry allows protein sequencing directly from mass spectra. Acquisition of MALDI-ISD mass spectra from tissue samples is achieved using an appropriate MALDI matrix, such as 1,5-diaminonaphthalene (DAN). Recent efforts have focused on combining MALDI-ISD with mass spectrometry imaging (MSI) to provide simultaneous sequencing and localization of proteins over a thin tissue surface. Successfully coupling these approaches requires the development of new data analysis tools, but first, investigating the properties of MALDI-ISD as applied to mixtures of protein standards reveals a high sensitivity to the relative protein ionization efficiency. This finding translates to the protein mixtures found in tissues and is used to inform the development of an analytical pipeline for data analysis in MALDI-ISD MS imaging, including software to identify the most pertinent spectra, to sequence protein mixtures, and to generate ion images for comparison with tissue morphology. The ability to simultaneously identify and localize proteins is demonstrated by using the analytical pipeline on three tissue sections from porcine eye lens, resulting in localizations for crystallins and cytochrome c. The variety of protein identifications provided by MALDI-ISD-MSI between tissue sections creates a discovery tool, and the analytical pipeline makes this process more efficient. [less ▲]

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