Analysis of various organic and organometallic compounds using nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS)

Abstract

Nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS) has been developed recently as a matrix-free/surface-assisted alternative to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The NALDI surface of silicon nanowires is already very effective for the analysis of small to medium sized, polar organic molecules in positive ion mode. The current study examined this technology for the analysis of several nonpolar organic, organometallic, and ionic compounds in positive ion mode, as well as a fluorinated compound and various acids in negative ion mode. NALDI data are compared and contrasted with MALDI data for the same compounds, and the higher sensitivity of NALDI is highlighted by the successful characterization of two porphyrins for a sample amount of 10 amol per spot. (J Am Soc Mass Spectrom 2010, 21, 1256 -1259) © 2010 American Society for Mass Spectrometry T he established matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOFMS) technique of co-crystallizing an analyte with a radiation absorbing matrix is not optimal for the analysis of small molecules (Ͻ600 Da) due to high intensity matrix species that dominate the spectrum in the low mass range. The large choice of matrix compounds with varying properties also means that sample preparation is problematic and requires analyst expertise to achieve reproducible data. To address both of these problems, several research groups have investigated matrix-free or surface-assisted techniques, that is, the analyte does not require mixing and co-crystallization with any matrix compound. The aim is to produce an immobilized surface that mimics the matrix, but would give little or no background ions, while also removing the requirement for analyte/matrix mixing. Deposition of an analyte solution directly onto a surface would greatly simplify sample preparation.Tanaka's pioneering work with cobalt particles dispersed in glycerol [1] has been followed by studies of other metal and metal oxide particles [2], but these methods are better termed as using an 'inorganic matrix' rather than being surface-assisted. The first surface-assisted method to show promise was the use of graphite particles [3], which afforded successful characterization of several peptides. The development of desorptionionization on a random porous silicon surface (DIOS) [4], not only allowed surface-assisted analysis of peptides, but also afforded spectra of small organic molecules devoid of matrix species. A more ordered silicon nanocavity array has been fabricated using nanosphere lithography [5]. Matrix-free techniques were reviewed in detail in 2007 by Peterson [6]. The area has continued to develop, with several silicon-based variations, including unmodified silica [7], modified silica gels (mf-MELDI-MS) [8], silicon nitride nanoparticles [9], and chemically modified porous silicon [10].One variation that has given very encouraging results is desorption-ionization on silicon nanow...

Surface analysis of lipids by mass spectrometry: More than just imaging

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Laser desorption ionization mass spectrometry of protein tryptic digests on nanostructured silicon plates

“…For instance gold [14], iron [15], silver [16], platinum [17], cobalt [18], titanium [19] and other elements [20][21][22][23][24], alone or in combination, were investigated as inorganic matrices by several research groups worldwide. Moreover, disposable ready-to use LDI nanostructured surfaces can be purchased like Nano-Assisted Laser Desorption/Ionization (NALDI™) target plates, constituted by silylated silicon nanowires, which were recently developed for 'matrix-free' LDI analysis of small molecules [25]. In the search for an alternative method to conventional MALDI-MS peptide mass fingerprinting, various 'matrix-free' LDI analyses have been undertaken in the laboratory for peptide detection starting with commercially available inert materials, which were compared to the original method of Siuzdak on porous etched silicon (DIOS-chips).…”

Silver nanostructures in laser desorption/ionization mass spectrometry and mass spectrometry imaging

“…46 Active surfaces with silver nanostructures for LDI-MS MALDI has not been applied too often to detect low molecular weight (LMW) compounds, of MW < 600 Da, because common MALDI matrices are low molecular weight organic acids, producing a variety of matrix-related ions, causing interfering signals in the low-mass range. SALDI should be considered as a general term including nanostructure-dependent methods such as AuNPET, AgNPET, nanostructure-assisted laser desorption/ionization (NALDI), 49 nanoparticle-assisted desorption/ionization (nano-PALDI), or methods utilizing DIOS surfaces and others, 50 with the strict condition that the mentioned nanostructures are bound to the target surface prior to sample application. SALDI surfaces often contain organic, inorganic or metallic micro-or/and nanostructures.…”