Laser Desorption Ionization Technique Research Articles

Matrix- and Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Methods for Urological Cancer Biomarker Discovery-Metabolomics and Lipidomics Approaches.

Urinary tract cancers, including those of the bladder, the kidneys, and the prostate, represent over 12% of all cancers, with significant global incidence and mortality rates. The continuous challenge that these cancers present necessitates the development of innovative diagnostic and prognostic methods, such as identifying specific biomarkers indicative of cancer. Biomarkers, which can be genes, proteins, metabolites, or lipids, are vital for various clinical purposes including early detection and prognosis. Mass spectrometry (MS), particularly soft ionization techniques such as electrospray ionization (ESI) and laser desorption/ionization (LDI), has emerged as a key tool in metabolic profiling for biomarker discovery, due to its high resolution, sensitivity, and ability to analyze complex biological samples. Among the LDI techniques, matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) should be mentioned. While MALDI methodology, which uses organic compounds as matrices, is effective for larger molecules, SALDI, based on the various types of nanoparticles and nanostructures, is preferred for smaller metabolites and lipids due to its reduced spectral interference. This study highlights the application of LDI techniques, along with mass spectrometry imaging (MSI), in identifying potential metabolic and lipid biomarkers for urological cancers, focusing on the most common bladder, kidney, and prostate cancers.

A combinatorial droplet microfluidic device integrated with mass spectrometry for enzyme screening.

Mass spectrometry (MS) enables detection of different chemical species with a very high specificity; however, it can be limited by its throughput. Integrating MS with microfluidics has a tremendous potential to improve throughput and accelerate biochemical research. In this work, we introduce Drop-NIMS, a combination of a passive droplet loading microfluidic device and a matrix-free MS laser desorption ionization technique called nanostructure-initiator mass spectrometry (NIMS). This platform combines different droplets at random to generate a combinatorial library of enzymatic reactions that are deposited directly on the NIMS surface without requiring additional sample handling. The enzyme reaction products are then detected with MS. Drop-NIMS was used to rapidly screen enzymatic reactions containing low (on the order of nL) volumes of glycoside reactants and glycoside hydrolase enzymes per reaction. MS "barcodes" (small compounds with unique masses) were added to the droplets to identify different combinations of substrates and enzymes created by the device. We assigned xylanase activities to several putative glycoside hydrolases, making them relevant to food and biofuel industrial applications. Overall, Drop-NIMS is simple to fabricate, assemble, and operate and it has potential to be used with many other small molecule metabolites.

Silver Nanostructured Substrates in LDI-MS of Low Molecular Weight Compounds.

Mass spectrometric techniques can provide data on the composition of a studied sample, utilizing both targeted and untargeted approaches to solve various research problems. Analysis of compounds in the low mass range has practical implications in many areas of research and industry. Laser desorption ionization techniques are utilized for the analysis of molecules in a low mass region using low sample volume, providing high sensitivity with low chemical background. The fabrication of substrates based on nanostructures to assist ionization with well-controlled morphology may improve LDI-MS efficiency for silver nanoparticles with plasmonic properties. In this work, we report an approach for the preparation of silver nanostructured substrates applied as laser desorption ionization (LDI) plates, using the chemical vapor deposition (CVD) technique. Depending on the mass of used CVD precursor, the approach allowed the synthesis of LDI plates with tunable sensitivity for various low molecular weight compounds in both ion-positive and ion-negative modes. Reduced chemical background and sensitivity to small biomolecules of various classes (fatty acids, amino acids and water-soluble metabolites) at nanomolar and picomolar detection levels for lipids such as triacylglycerols, phosphatidylethanolamines and lyso-phosphatidylcholines represent an emerging perspective for applications of LDI-MS plates for the collection of molecular profiles and targeted analysis of low molecular weight compounds for various purposes.

MASS SPECTROMETRY FOR A HOLISTIC VIEW OF NATURAL EXTRACTS OF PHYTOTHERAPEUTIC INTEREST.

In the study of natural products new strategies which favor a holistic approach, integrating the traditional reductionist methods usually employed, have been proposed. In this frame, the studies carried out by us in the last decade show that fingerprints, mainly obtained by electrospray ionization mass spectrometry (ESI-MS), lead to the characterization of natural extracts from different botanical species but also of phytotherapeutic products constituted by mixtures of extracts from different plants. Laser desorption ionization and matrix-assisted laser desorption ionization techniques were also employed and by the use of different matrices some complementary results were achieved. Results obtained by standard spectrophotometric and liquid chromatography methods were compared with those achieved by direct infusion of the extract in ESI-MS conditions, indicating an excellent agreement between the two approaches. The findings of these researches were considered in the frame of complex systems theory, investigating how relationships between a system's parts can give rise to its collective behaviors and how the system interacts and forms relationships with its environment. In this view, the peculiar pharmacological behavior of biologically active natural compounds can be justified by the occurrence of molecular interactions due to the high complexity of the natural matrix. Some of these interactions have been widely studied in the case of green tea extracts (GTEs) proving unequivocally the presence of caffeine/catechin complexes in GTE samples. The presence of bimolecular complexes has been observed also in the case of Ceylon tea and Mate extracts. These data indicate that the formation of complexes in natural extracts is a common behavior and their presence must be considered in the description of natural extracts and, consequently, in their biological activity. ©2020 John Wiley & Sons Ltd. Mass Spec Rev.

New Mass Spectrometric Approaches for the Quantitative Evaluation of Anticancer Drug Levels in Treated Patients.

Alternatively to the well-consolidated liquid chromatography coupled to tandem mass spectrometry approach used for the evaluation of anticancer drug concentrations in treated patients, new mass spectrometric methods have been proposed and tested recently. They exhibited faster analysis time and, at first sight, simpler instrumental approaches. However, results obtained by these methods require an in-depth evaluation, because of their strong dependence on the experimental set-up. In this short review, the quantification of irinotecan, sunitinib, and 6-α-hydroxy paclitaxel (the main metabolite of paclitaxel) by laser desorption ionization techniques (matrix-assisted laser desorption/ionization, nanostructure-assisted laser desorption/ionization, and surface-assisted laser desorption/ionization) is reported and discussed, showing the advantages but also the drawbacks of the methods. The matrix-assisted laser desorption/ionization approach led to the most reliable results, and the cross-validation for the quantitative analysis of irinotecan indicates that this method can be fruitfully used for therapeutic drug monitoring and pharmacokinetic studies. Another recently proposed technique, paper spray mass spectrometry, has been tested for the quantitative measurement of imatinib in plasma samples. Even if the approach is, at first sight, really simple, the parameterization of the analytical and instrumental aspects has required many efforts to reach satisfactory results. What it should be expected in the future is the evaluation of these methods, not only in scientific environments dedicated to instrument development, but also in clinical chemistry laboratories, to evaluate their effectiveness and to give new and valid tools for TDM and for other qualitative or quantitative measurements of biomedical interest.

Advances in mass spectrometry-based metabolomics for investigation of metabolites.

Metabolomics is the systematic study of all the metabolites present within a biological system, which consists of a mass of molecules, having a variety of physical and chemical properties and existing over an extensive dynamic range in biological samples. Diverse analytical techniques are needed to achieve higher coverage of metabolites. The application of mass spectrometry (MS) in metabolomics has increased exponentially since the discovery and development of electrospray ionization and matrix-assisted laser desorption ionization techniques. Significant advances have also occurred in separation-based MS techniques (gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, capillary electrophoresis-mass spectrometry, and ion mobility-mass spectrometry), as well as separation-free MS techniques (direct infusion-mass spectrometry, matrix-assisted laser desorption ionization-mass spectrometry, mass spectrometry imaging, and direct analysis in real time mass spectrometry) in the past decades. This review presents a brief overview of the recent advanced MS techniques and their latest applications in metabolomics. The software/websites for MS result analyses are also reviewed.

Detection of trace organics in Mars analog samples containing perchlorate by laser desorption/ionization mass spectrometry.

Evidence from recent Mars missions indicates the presence of perchlorate salts up to 1 wt % level in the near-surface materials. Mixed perchlorates and other oxychlorine species may complicate the detection of organic molecules in bulk martian samples when using pyrolysis techniques. To address this analytical challenge, we report here results of laboratory measurements with laser desorption mass spectrometry, including analyses performed on both commercial and Mars Organic Molecule Analyzer (MOMA) breadboard instruments. We demonstrate that the detection of nonvolatile organics in selected spiked mineral-matrix materials by laser desorption/ionization (LDI) mass spectrometry is not inhibited by the presence of up to 1 wt % perchlorate salt. The organics in the sample are not significantly degraded or combusted in the LDI process, and the parent molecular ion is retained in the mass spectrum. The LDI technique provides distinct potential benefits for the detection of organics in situ on the martian surface and has the potential to aid in the search for signs of life on Mars.

Effects of retinoic acid isomers on proteomic pattern in human breast cancer MCF-7 cell line

Retinoids, acting through their cognate nuclear receptors, are crucial transcriptional regulators of many cellular processes such as differentiation, development, apoptosis, carbohydrate and lipid metabolism, homeostasis, etc. The aim of this study was the exploration of molecular mechanisms in relation to therapy of human breast cancer. One of the efficient strategies is identification of biomarkers as important tools in early cancer diagnosis and advisable treatment. Retinoids have been regarded as important therapeutic agents for many types of cancers, including human breast cancer. The effects of all-trans retinoic acid and 9-cis retinoic acid or their combination on proteomic pattern in human MCF-7 breast cancer line were investigated. The total cell proteins were extracted utilizing a commercially Radio-Immunoprecipitation Assay (RIPA) buffer and separated on 1D sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D SDS-PAGE). The proteins were subsequently digested in-gel by trypsin and identified by matrix assisted laser desorption ionization technique with time of flight mass analyzer (MALDI-TOF/TOF). Our data offer novel information on the proteomic pattern of proteins evaluated after treatment of MCF-7 cells with retinoic acid isomers.

Ultraviolet photodegradation of tris(8-hydroxy-quinolinate) aluminum (Alq3) thin films studied by electron and laser stimulated desorption

Alq3 has been the reference material used widely in the fabrication and characterization of efficient OLEDs due to its good properties as electroluminescent and electron transporting layer. Although the inclusion of these devices in commercial displays and lighting devices represents many benefits, the knowledge about the progressive loss of performance and efficiency with time for such devices is still limited. Therefore, it is an incentive to understand the mechanisms of Alq3 degradation when it is subjected to the influence of various extrinsic factors such as UV radiation. In the present work the degradation processes of Alq3 thin films as a result of 254nm UV light irradiation are presented and discussed. The degradation products produced by the action of UV light were evaluated by time-of-flight mass spectrometry using electron stimulated ion desorption and laser desorption ionization techniques. Strong evidence for carboxylic acid formation after photodegradation was observed by the electron desorption technique.

An efficient route towards a new branched tetrahydrofurane δ-sugar amino acid from a pyrolysis product of cellulose

(1R,5S)-1-hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one, is a bicyclic lactone obtained in gram-scale by catalytic pyrolysis of the renewable source cellulose. Now it has been used as a chiral building block in the preparation of the new δ-sugar amino acid, (3R,5S)-5-(aminoethyl)-3-hydroxytetrahydrofurane-3-carboxylic acid, by an efficient synthesis in five steps with a 67% overall yield. The structure of this tetrahydrofurane amino acid, isolated in protonated form, was assigned by extensive mono- and bidimensional (1)H- and (13)C-NMR analysis and mass spectrometry, including measurements by electrospray and matrix-assisted laser desorption ionization techniques, the latter one for high-resolution experiments. This amino acid is an isoster of dipeptide glycine-alanine (H-Gly-Ala-OH), with a potential use in the access of new peptidomimetics with conformationally restricted structures due to the presence of tetrahydrofurane ring. As a preliminary study in order to disclose this effect, density functional theory calculation performed in water using polar continuum model was applied to the new amino acid and H-Gly-Ala-OH dipeptide, so that to evaluate and compare the relative torsional angles for the energy-minimized structures.

UV-Vis-NIR Laser Desorption/Ionization of Synthetic Polymers Assisted by Gold Nanospheres, Nanorods and Nanostars

The laser desorption/ionization (LDI) assisted by gold nanospheres, nanorods and nanostars has been investigated. Laser fluence thresholds for the appearance of cationized adducts of a polydispersed polyether standard (polyethylenglycol PEG600) have been determined at the near ultraviolet–visible–near infrared wavelengths delivered by a Nd:YAG laser (266, 355, 532, 1,064 nm). The results demonstrate the efficiency of surface plasmon excitation to assist laser desorption/ionizaton at laser wavelengths extending to the visible and near infrared, with advantages with respect to conventional LDI techniques using ultraviolet wavelengths. A close correlation is found between the optical absorbance of the nanoparticles and the LDI thresholds, although for the nanospheres plasmonic excitation in the visible appears to be more efficient than non-plasmonic excitation at shorter UV wavelengths. The recorded molecular weight distributions for the PEG600 standard show that the LDI process tends to be less efficient for the heavier components of the polymer mixture, presumably as a consequence of their stronger bonding to the nanoparticle substrate. The role of the coating agent of the nanoparticles in the observed LDI behavior is discussed.

Time-of-flight mass spectrometry of bioorganic molecules by laser ablation of silver thin film substrates and particles

A laser desorption/ionization (LDI) technique, which uses laser ablation of a thin silver film substrate under vacuum conditions to desorb and ionize bioorganic molecules, was developed for molecular mass and structural reactivity analysis in time-of-flight mass spectrometry (TOF-MS). After a sample overlayer is deposited by solvent evaporation on a thin silver film substrate, it is subjected to 355 or 532 nm Nd:YAG laser light by back-irradiation. Photoablation of the silver film substrate occurs with sufficient laser fluence, producing Agn+ (n=1–9) cluster cations which can react with the desorbed bioorganic molecules in the gas phase to form M+ or [M+H]+ and [M+Ag]+ ions for TOF-MS analysis. This LDI technique has been successfully applied to dithizone, benzo[e]pyrene, 1,4,8,11-tetraazocyclotetradecane, dicyclohexyl-18-crown-6, [5]-helicene dendrimer, gramicidin S, substance P and melittin. One advantage of this method over conventional LDI techniques is that the sample does not need to have appreciable spectral absorption at the laser wavelength. The use of silver in thin-film substrates affords analyte-dependent efficiencies that may serve for the direct and accurate mass analysis of specific groups of bioorganic molecules in sample mixtures. In a new sample preparation method, gramicidin S is added to a Tollen’s reagent mixture for direct impregnation on to silver particles during their formation and growth in the colloidal solution. These silver particles provide a silver matrix for the analyte molecules, which can enhance the LDI efficiency to produce greater [M+H]+ and [M+Ag]+ signals. © 1998 John Wiley & Sons, Ltd.

FORMATION OF ODD-NUMBERED FULLERENE-FRAGMENT IONS IN THE COALESCENCE REACTIONS OF FULLERENES

We found that the coalescence reactions of fullerenes occur more efficiently for chemical adduct compounds of C 60 than pristine C 60 by the laser-desorption ionization technique. Under specific conditions, not only the even-numbered daughter fullerenes by successive C 60 losses or captures appeared, but also odd-numbered carbon-cluster anions [Formula: see text](51≤N≤65) were detected in the chemical fusion processes. The result suggests a new way to open fullerene cages, and the possible mechanism involved is discussed.