Laser desorption ionization of small molecules assisted by tungsten oxide and rhenium oxide particles

Abstract

Inorganic metal oxides have shown potential as matrices for assisting in laser desorption ionization (LDI) with advantages over the aromatic acids typically used. Rhenium and tungsten oxides are an attractive option due to their high work functions and relative chemical inertness. In this work, it is shown that ReO3 and WO3, in microparticle (μP) powder forms, can efficiently ionize various types of small molecules and provide minimized background contamination at analyte concentrations below 1 ng/μL. This study shows that untreated inorganic WO3 and ReO3 particles are valid matrix options for detection of protonatable, radical, and precharged species under LDI. Qualitatively, the WO3 μP showed an improved detection of apigenin, sodiated glucose, and the precharged analyte choline, while the ReO3 μP allowed detection of protonated cocaine, quinuclidine, ametryn, and radical ions of polyaromatic hydrocarbons at detection levels as low as 50 pg/μL. For thermometer ion survival yield experiments, it was also shown that the ReO3 powder was significantly softer than CCA. Furthermore, it provided higher intensities of cocaine and polyaromatic hydrocarbons, at laser flux values equal to that used with CCA.

Molecular Imaging of Biological Samples on Nanophotonic Laser Desorption Ionization Platforms

“…[4,5] Among the established vacuum-based ionization methods,s econdary ion mass spectrometry (SIMS) [6] and matrixassisted laser desorption ionization (MALDI) [7][8][9] have been extensively applied for MSI, single cell, and subcellular analysis.I nm ost implementations,S IMS does not require am atrix and can achieve < 100 nm spatial resolution, how-ever it is known to induce ac onsiderable amount of fragmentation for large molecules.I nc ontrast, MALDI requires the addition of an organic matrix that can contribute to ion suppression and spectral interferences in the low mass range.E merging atmospheric-pressure MSI techniques, including desorption electrospray ionization (DESI) [10] and laser ablation electrospray ionization (LAESI) allow for direct tissue imaging with minimal sample preparation but typically provide limited spatial resolution. [12] Despite the large variety of these platforms (surface-assisted LDI (SALDI)), [13] carbon nanotubes, [14] porous alumina, [15] platinum nanoflowers, [16] diamond nanowires, [17] nanostructured gold thin film, [18] and zinc, tungsten, and rhenium oxide nanoparticles [19,20] ), only afew of them, for example,d esorption ionization on porous silicon (DIOS), [21,22] and nanostructure initiator mass spectrometry (NIMS) [23] have been broadly explored for MSI. [12] Despite the large variety of these platforms (surface-assisted LDI (SALDI)), [13] carbon nanotubes, [14] porous alumina, [15] platinum nanoflowers, [16] diamond nanowires, [17] nanostructured gold thin film, [18] and zinc, tungsten, and rhenium oxide nanoparticles [19,20] ), only afew of them, for example,d esorption ionization on porous silicon (DIOS), [21,22] and nanostructure initiator mass spectrometry (NIMS) [23] have been broadly explored for MSI.…”

“…[1,2] Targeted techniques,s uch as autoradiography and histological staining,require radioactive or fluorophore labeling resulting in al imited number of analytes that can be visualized in as ingle experiment. [12] Despite the large variety of these platforms (surface-assisted LDI (SALDI)), [13] carbon nanotubes, [14] porous alumina, [15] platinum nanoflowers, [16] diamond nanowires, [17] nanostructured gold thin film, [18] and zinc, tungsten, and rhenium oxide nanoparticles [19,20] ), only afew of them, for example,d esorption ionization on porous silicon (DIOS), [21,22] and nanostructure initiator mass spectrometry (NIMS) [23] have been broadly explored for MSI. [4,5] Among the established vacuum-based ionization methods,s econdary ion mass spectrometry (SIMS) [6] and matrixassisted laser desorption ionization (MALDI) [7][8][9] have been extensively applied for MSI, single cell, and subcellular analysis.I nm ost implementations,S IMS does not require am atrix and can achieve < 100 nm spatial resolution, how-ever it is known to induce ac onsiderable amount of fragmentation for large molecules.I nc ontrast, MALDI requires the addition of an organic matrix that can contribute to ion suppression and spectral interferences in the low mass range.E merging atmospheric-pressure MSI techniques, including desorption electrospray ionization (DESI) [10] and laser ablation electrospray ionization (LAESI) allow for direct tissue imaging with minimal sample preparation but typically provide limited spatial resolution.…”

“…[11] To overcome the challenges associated with matrix heterogeneity and interferences in the low m/z region, as ignificant number of matrix-free LDI techniques have been introduced. [12] Despite the large variety of these platforms (surface-assisted LDI (SALDI)), [13] carbon nanotubes, [14] porous alumina, [15] platinum nanoflowers, [16] diamond nanowires, [17] nanostructured gold thin film, [18] and zinc, tungsten, and rhenium oxide nanoparticles [19,20] ), only afew of them, for example,d esorption ionization on porous silicon (DIOS), [21,22] and nanostructure initiator mass spectrometry (NIMS) [23] have been broadly explored for MSI. In al imited number of applications,other matrix-free techniques,including LDI from laser engineered graphene paper, [24] carbonsubstrate-assisted LDI, [25] silica plate imprinting followed by LDI, [26] nanowire-assisted LDI (NALDI), [27] and SALDI, [28,29] were also explored for MSI.…”

The quest for improved reproducibility in MALDI mass spectrometry

“…Since the compounds chosen are usually very small (<100 Da), they eliminate the interference that is usually seen in the low mass range when using traditional MALDI matrices such as CHCA. Currently a range of compounds have been used as inorganic matrices including silica/ CHCA (Fleith et al, 2014), graphite (Sunner, Dratz, & Chen, 1995), -naphthylethylenediamine dihydrochlorid (NEDC) (Hou et al, 2014), sulfur (Kruegel, Pavlov, & Attygalle, 2013), titanium dioxide anatase (Castro et al, 2008), tungsten oxide (Bernier, Wysocki, & Dagan, 2015), mesoporous tungsten titanate (Shan et al, 2007), gold nano-particles (Marsico et al, 2015), and two dimensional graphene (Friesen et al, 2015).…”

Amorphous Conjugated Polymers as Efficient Dual‐Mode MALDI Matrices for Low‐Molecular‐Weight Analytes

“…A number of approaches were explored to avoid intense matrix signal generation by SOMs, e. g. matrix suppression effects, cyclodextrin‐supported 2,5‐DHB matrix, improved reactive functional groups, and chemical derivatization . Also, new classes of matrix systems were developed and successfully established, e. g. nanoparticles, ionic liquids, graphene, doped graphene, graphene oxides, graphite (GALDI‐MS), metal oxides, mostly targeting polar and non‐polar, biochemical LMWCs (e. g. amino acids, nucleosides, steroids, etc. ).…”