Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes

Abstract

Desorption/ionization on silicon (DIOS) mass spectra of model ionic dyes methylene blue (MB+Cl-) and methyl orange (Na+MO-) were studied using p+ type-derived porous silicon (PS) free layers. As-prepared PS (PS-H), the PS thermally oxidized at 300 degrees C (PS-OX), PS with chemically grafted cation-exchanging alkylsulfonic acid (PS-SO(3)H) and anion-exchanging propyl-octadecyldimethylammonium chloride (PS-ODMA+Cl-) groups was tested as ionization platforms. Two mechanisms of the methylene blue desorption/ionization were found: (1) the formation of [MB + H]+* ion due to the reduction/protonation of MB+, which is predominant for PS-H and PS-OX platforms and (2) direct thermal desorption of the MB+ cation, prevailing for PS-SO3H. The fragmentation of the cation is significantly suppressed in the latter case. The samples of PS-SO3H and PS-ODMA+ Cl- efficiently adsorb the dyes of the opposite charge from their solutions via the ion-exchange. Consequent DIOS MS studies allow to detect only low fragmented ions (MB+ and MO-, respectively), demonstrating the potential of the ion-exchange adsorption combined with DIOS MS for the analysis of ionic organic compounds in solutions.

A layer-by-layer assembled MoS2 thin film as an efficient platform for laser desorption/ionization mass spectrometry analysis of small molecules

“…38–40 As an example, AuNPs functionalized with perfluoroalkane thiol provided higher LDI-MS efficiency than citrate-stabilized AuNPs. 41 The surface of MoS 2 nanoflakes can be also modified with thiol derivatives through the coordination of thiol group to their defect sites or physisorption.…”

Monomer/dimer dependent modulation of reduction of the cationic dye methylene blue in negatively charged nanolayers as revealed by mass spectrometry

“…Reduction of various compounds including dyes, 22-26 MB 24,26 in particular, was observed under the condition of various mass spectrometric techniques: secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB), 22 laser desorption/ ionization (LDI) and matrix-assisted LDI (MALDI), 23,24 and electrospray ionization (ESI). [28][29][30][31][32] On this basis we have formulated a mass spectrometric approach to the observation of changes in reduction of dyes in dependence of experimental conditions, aimed at modeling and studying reduction and oxidation processes in nanostructures. 27 Moreover, mass spectrometry can also monitor the way how the interactions of dyes with their environment inuence the reduction rate.…”

“…Although FAB was one of the very rst mass spectrometric methods for analysis of biomolecules, it is now replaced by more efficient ESI 38 and MALDI, 39 while SIMS remains a powerful tool both in basic studies and industrial analysis of metals, dielectrics and nanomaterials. 31 This nanotextured material can be probed by LDI mass spectrometry; LDI involving silicon substrate (target) is referred to as desorption/ ionization on silicon (DIOS) or porous silicon. It is known that under FAB or lSIMS a bombarding particle excites a sample material to a depth of about 10 nm, 33,40 which correlates with an average thickness of the surfactants layer at the surface of a liquid matrix.…”

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

“…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 nanowires [11,12], grown from silane vapor, which has recently been commercialized as nanostructure-assisted laser desorption/ …”

“…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].…”