Laser-induced Desorption Ionization Research Articles

Unraveling a self-assembling mechanism of isomeric aminothiophenol on Ag dendrite by correlated SERS and matrix-free LDI-MS

Correlated spectroscopic analysis can provide complementary chemical insights that are often unattainable by either approach used in isolation. We distinguished the different self-assembling behavior of isomeric aminothiophenols (ATPs) on Ag dendrite by the correlation of surface-enhanced Raman spectroscopy and laser-induced desorption ionization mass spectrometry, demonstrating that steric effect impinged significantly upon surface molecular density and plasmon-driven catalytic reaction yield, which led to drastic variations in the resulting SERS spectra. The correlative measurement shows that ortho-substitute barely formed a self-assemble monolayer, relative to the para-isomer, which can form a close-packed self-assembled monolayer and perform a decent azo-coupling reaction. Comparison between normal and SERS spectra of ATP isomers supports the fact that additional disulfide- or hydrogen-bonding interactions are established in para-ATP solid crystal, but neither of ortho- nor meta-isomers. This work is expected to create a significant impact on the development of an orthogonally correlated spectroscopic tool in deciphering chemical insights and underlying reaction mechanism. Graphical abstract.

Ultra-high sensitivity detection of gold nanorods on a blotting membrane by laser induced desorption/ionization of gold ions

Laser induced desorption/ionization (LDI) of gold ions from gold nanoparticles was examined. The detection limit was estimated to be about 0.02 amol mm−2.

High-throughput discrimination of bacteria isolated fromAstacus astacusandA. leptodactylus

Bacterial diseases and pathogens of crayfish are common, widespread, and occasionally causing serious mortalities. In order to take rapid measures for correct treatment of crayfish diseases, the turnover time and accuracy in bacterial identification is an issue. Bacteria isolated from tissues of apparently healthy Astacus astacus and A. leptodactylus were identified by the commercial phenotypic tests (API 20E) and by the matrix assisted laser induced desorption ionization connected to the time of flight mass spectrometry (MALDI-TOF MS). For Gram-negative rods, API 20E resulted in fewer species identifications than MALDI-TOF MS (5.2% versus 52.61%). The most frequently identified genus from A. astacus and A. leptodactylus was Pseudomonas spp.: API 20E (47.82%) and MALDI-TOF MS (52.17%). Both systems identified 60.86% of total isolates identically to the genus. Hafnia alvei was the only isolate for which API 20E and MALDI-TOF MS had a concordant reading to the species. MALDI-TOF MS proved to be a powerful, low-cost, rapid tool in bacterial genus identification. This is the first report of a direct comparison between the two systems for the identification of bacteria in crayfish, and also the first report on using MALDI-TOF MS for discrimination of freshwater crayfish bacterial isolates.

Nanoporous GaN–Ag Composite Materials Prepared by Metal-Assisted Electroless Etching for Direct Laser Desorption-Ionization Mass Spectrometry

Three-dimensional nanoporous gallium nitride(PGaN) produced by metal-assisted electroless etching is chemically embedded with silver nanoparticles via electroless deposition, forming a metallized semiconductor membrane with large surface area and nanoscale metal features. A new application utilizing the unique chemical and morphological features of these composite nanostructures is described here, laser induced desorption-ionization(LDI) of biomolecules(e.g., cholesterol and nucleotides) for direct mass analysis, without use of additional organic matrix. Although PGaN itself is a poor matrix for direct LDI mass spectrometry, the combination of Ag and PGaN greatly improves ion signals relative to PGaN or Ag nanostructure surfaces alone. This behavior is attributed to the combination of strong UV absorption, enhanced surface area, and favorable thermal properties of PGaN. Importantly, Ag-PGaN is shown to facilitate the formation of Ag adduct ions in some cases, for example adenine, where adducts are not observed from either porous anodic aluminum membranes or surfaces presenting Ag nanoparticles in isolation. Nanopore-embedded Ag nanostructures serve a dual role: as cationization agents and to assist thermal desorption under UV laser irradiation. The results reported here suggest that the combination of Ag nanostructures embedded in PGaN has the capacity for high quality matrix-free LDI mass analysis.

Electrochemical Reactions and Ionization Processes

Electrochemical or photo-electrochemical reactions in both electrospray ionization and laser desorption ionization are discussed stressing the role of the electrode reaction in influencing the ionization process. In particular, upon application of a high voltage during electrospray ionization, the emitter includes a working electrode, where redox reactions are observed, such as electro-generation of benzoquinone and metal ions. In contrast, the target plate in laser-induced desorption ionization also acts as a photo-electrode, especially when modified with a mesoporous semiconductor. We illustrate here how these electrochemical reactions can be used for tagging purposes, and for oxidative or reductive dissociation reactions.

Surface assisted laser desorption–ionization mass spectrometry on patterned nanoporous silica thin films

We describe the preparation and use of patterned nanocomposite silica thin films deposited on silicon for laser desorption-ionization mass spectrometry (LDI-MS) without the use of conventional matrices. Ordered nanocomposite silica thin films deposited on silicon substrates were prepared by evaporation induced self-assembly using Brij56 as the surfactant template. The films were then exposed to masked deep-UV light to selectively remove the template to yield isolated regions of ordered nanoporous silica in a field of nanostructured silica. The nanoporous regions act as isolated “wells” that allow for the mass spectral characterization of analytes by laser induced desorption–ionization MS using a commercial MALDI-TOF instrument. We demonstrate the utility of these patterned films for the mass spectral analysis of small organic molecules, such as amino acids, peptides and siderophores. No consistent background signal from the films was observed at laser intensities typically used to desorb/ionize analytes. We also show that the films remain active for over a year when stored at ambient laboratory conditions. Because these patterned nanocomposite films are straightforward to produce, readily modifiable and stable at ambient laboratory conditions, they provide a potentially useful alternative to currently available films and substrates for matrix-free LDI-MS analysis of small molecules.

Laser Initiation Processes in Thermite Energetic Materials Using Laser Desorption Ionization Time-of-Flight Mass Spectrometry

The reactive processes that occur during the laser initiation of aluminum/iron(III) oxide metastable intermolecular composites (MIC) have been studied by laser-induced desorption ionization time-of...

Molecular Heterogeneity in Recombinant Erythropoietin Using Surface Enhanced Laser Induced Desorption Ionization (SELDI). Clinical Implications.

Several erythropoietin preparations (EPO) are used globally for anemia management. Repeated EPO use has been reportedly associated with thrombotic complications. Molecular profiles of these recombinant proteins vary widely, impacting their clinical profile. This may be due to cellular/receptor interactions and other modulatory properties. There are WHO and FDA regulatory guidelines regarding molecular profile; data on protein profiling is usually not provided by the manufacturers. Purpose of this investigation was to compare various clinically-used recombinant erythropoietin products Epogen (Amgen), Vintor (Emcure), Eprex (Janssen-CILAG) and Neo Recormon (Roche) utilizing protein chip array technology (Ciphergen, Fremont, CA). All products were analyzed using anionic SAX2 chips and molecular profile was obtained in the range of 0–150 KDa. Epogen and Vintor exhibited a main component at 32.4 KDa range with minor peaks at 13.5, 21.7 and 43.2 KDa. Intensity of the main component varied widely even within the 3 batches of Epogen. The Epogen preparations and Vintor brand contained albumin in different quantities. One batch of Epogen contained 4x higher amount of this material with a heterogeneous distribution. Epex and Neo Recormon did not have any albumin. One of the Epogen product also contained a component at 110.0 KDa. Glycosylation profiles of each of these preparations also differ. These data suggest that molecular heterogeneity exists within different recombinant erythropoietin preparations. Molecular heterogeneity among these preparations may be partly responsible for differential interactions within erythropoietin receptors on cells and anti-epo antibody generation. Protein chip array technology may be helpful in examining the protein components within different recombinant erythropoietins and may be helpful in establishing molecular profile guideline to minimize pharmacodynamic variance in erythropoietin preparations. Furthermore, molecular profiling of these recombinant proteins may be helpful in establishing the purity and homogeneity of these drugs.

On the mechanism of laser-induced desorption–ionization of organic compounds from etched silicon and carbon surfaces

The laser-induced desorption/ionization of organic compounds from etched carbon and silicon substrate surfaces was investigated. Two different etching procedures were used. Silicon surfaces were etched either by galvanostatic anodization to produce porous silicon or by a hyperthermal (∼5 eV) F-atom beam to produce nonporous silicon. Atomic force microscopy (AFM) images showed that both etching procedures yielded surfaces with sub-micrometer structures. Highly oriented pyrolytic graphite was etched with hyperthermal O atoms. A 337 nm ultraviolet (UV) laser and a 3.28 μm infrared (IR) laser were used for desorption. Analytes were deposited on the substrates either from the liquid or the gas phase. Mass spectra were obtained provided that three conditions were fulfilled. First, sufficient laser light had to be absorbed. When the IR laser was employed, a thin physisorbed solvent layer was required for sufficient laser light absorption to occur. Though the required fluence of IR and UV light differed by a factor of about 20, the calculated maximum surface temperatures were similar, about 1000 K. The second requirement was that the substrate had a “rough” surface. The third requirement, for the observation of protonated analytes, was that the aqueous pKa-value of the analyte be larger than about 4. These observations support the conclusion that the desorption–ionization mechanisms of analytes from porous and nonporous surfaces are very similar or essentially the same.

Penta(cyclopentadienyl)- η5-cyclopentadienylmanganesetricarbonyl: structure and laser-induced conversion to fullerenes

The title compound [Cp 5CpMn(CO) 3], 1, has been characterized by X-ray crystallography and shown by laser-induced desorption/ionization (LDI) to undergo dissociative coalescence to fullerene C 60 and other carbon clusters.

Comparison of two methods of UV laser-induced surface ionization

Two different methods of UV laser-induced desorption ionization are compared by measuring the dependence of each on the laser pulse repitition rate. At an aniline sample pressure of 2.3 × 10 -8 torr, the ionization signal obtained with a prism internal reflection geometry increases linearly with the time between laser pulses. In contrast, the signal obtained with light incident on the surface from the gas phase side is independent of the laser repetition rate, as in conventional gas phase ionization experiments. These observations, in conjunction with measurements of the time of flight peak distribution, enable us to ascertain the locations where ionization takes place in the two experiments. UV laser-induced surface ionization with prism internal reflection is found to be appropriate for studying adsorption/desorption kinetics in experiments where gas phase molecules are continuously adsorbing and desorbing from a metal surface.

A reflectron mass spectrometer with UV laser-induced surface ionization

A modified reflectron time-of-flight mass spectrometer is developed using UV laser-induced desorption ionization with prism internal reflection. Theoretical calculations indicate that mass resolution of over 10 6 is possible if a picosecond laser and appropriate electronics are available. By ionizing aniline ( m = 93 u) with a 2 ns pulsed UV laser, mass resolution of 11 000 has been experimentally achieved. Some of the advantages of this new mass spectrometer are discussed.