Surface-assisted Laser Desorption/ionization Research Articles

Dual-Mechanism-Driven Strategy for High-Coverage Detection of Serum Lipids on a Novel SALDI-MS Target.

Serum lipid metabolites have been emerging as ideal biomarkers for disease diagnosis and prediction. In the current stage, nontargeted or targeted lipidomic research mainly relies on a liquid chromatography-mass spectrometry (LC-MS) platform, but future clinical applications need more robust and high-speed platforms. Surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) has shown excellent advantages in the high-speed analysis of lipid metabolites. However, the platform in the positive ion mode is more inclined to target a certain class of lipids, leading to the low coverage of lipid detection and limiting its practical translation to clinical applications. Herein, we proposed a dual-mechanism-driven strategy for high-coverage detection of serum lipids on a novel SALDI-MS target, which is a composite nanostructure comprising vertical silicon nanowires (VSiNWs) decorated with AuNPs and polydopamine (VSiNW-Au-PDA). The performance of laser desorption and ionization on the target can be enhanced by charge-driven desorption coupled with thermal-driven desorption. Simultaneous detection of 236 serum lipids (S/N ≥ 5) including neutral and polar lipids can be achieved in the positive ion mode. Among these, 107 lipid peaks were successfully identified. When combined with VSiNW-Au-PDA and VSiNW chips, 479 lipid peaks can be detected in serum samples in positive and negative ion modes, respectively. Based on the platform, serum samples from 57 hepatocellular carcinoma (HCC) patients and 76 healthy controls were analyzed. After data mining, 14 lipids containing different lipid types (TAG, CE, PC) were selected as potential lipidomic biomarkers. With the assistance of an artificial neural network, a diagnostic model with a sensitivity of 92.7% and a specificity of 96% was constructed for HCC diagnosis.

Imaging Metabolites in Agar‐Based Bacterial Co‐Cultures with Minimal Sample Preparation using a DIUTHAME Membrane in Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry**

AbstractWhile the imaging of bacteria, directly on agar‐based media, has been reported in matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI), such samples usually require laborious and time‐consuming preparation prior to analysis. Furthermore, the MALDI sample preparation may require desiccation, potentially causing sample deformation and/or degradation. Other issues may be associated with the use of a matrix in MALDI‐MSI. Here, we propose an alternative approach to image a co‐culture of Pseudomonas and Bacillus bacteria, grown on agar, in the positive and negative ionization modes, using surface‐assisted laser desorption/ionization (SALDI) MSI. A rapid and easy sample preparation was performed using a “desorption/ionization using through‐hole alumina membrane” (DIUTHAME) with a blotting method. The porous DIUTHAME membrane was used (1) for the transfer of the metabolites from the sample to the membrane, and (2) as assisting material in SALDI‐MSI. The advantages and limitations of this new sample preparation are discussed in this paper.

Single-Walled Carbon Nanohorns as Boosting Surface for the Analysis of Low-Molecular-Weight Compounds by SALDI-MS.

Limits of Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry (MS) in the study of small molecules are due to matrix-related interfering species in the low m/z range. Single-walled carbon nanohorns (SWCNH) were here evaluated as a specific surface for the rapid analysis of amino acids and lipids by Surface-Assisted Laser Desorption Ionization (SALDI). The method was optimized for detecting twenty amino acids, mainly present as cationized species, with the [M+K]+ response generally 2-time larger than the [M+Na]+ one. The [M+Na]+/[M+K]+ signals ratio was tentatively correlated with the molecular weight, dipole moment and binding affinity, to describe the amino acids’ coordination ability. The SWCNH-based surface was also tested for analyzing triglycerides in olive oil samples, showing promising results in determining the percentage composition of fatty acids without any sample treatment. Results indicated that SWCNH is a promising substrate for the SALDI-MS analysis of low molecular weight compounds with different polarities, enlarging the analytical platforms for MALDI applications.

Laser Desorption Ionization–Mass Spectrometry with Graphite Carbon Black Nanoparticles for Simultaneous Detection of Taste- and Odor-Active Compounds

There is no analytical system to directly and simultaneously detect taste- and odor-active compounds. Graphite carbon black (GCB) nanoparticles, a chemical adsorbent for a variety of compounds, including gaseous molecules, which consists of nanoparticles made from multilayered sheets of sp2-conjugated atomic carbon, have the characteristics required for a surface-assisted laser desorption ionization–mass spectrometry (SALDI-MS) material. Thus, in this study, GCB-LDI-MS was developed for the simultaneous detection of taste- and odor-active compounds. The proposed GCB-LDI-MS successfully detected volatile compounds, including ethyl esters, alcohols, fatty acids, and aldehydes with up to 16 carbons (maximum carbon number of the tested compounds), which could not be detected by conventional matrix-assisted-LDI-MS. Moreover, a series of taste-active compounds (e.g., amino acids and sugars) and various volatile compounds (e.g., ethyl esters, aldehydes, alcohols, fatty acids, and lactones) as a mixture in liquid samples were also detected by the present GCB-LDI-MS. Thus, the proposed simple and rapid detection technique can digitize the analysis of flavor compounds, which provides an analytical concept for flavor scanning to evaluate the palatability of food products.

Gold-TiO2@gallic acid nanospheres for enhanced surface-assisted laser desorption/ionization mass spectrometry imaging

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry imaging (MSI) can effectively reduce the matrix interference and ion suppression that occurred in traditional matrix-assisted laser desorption/ionization (MALDI) MSI. In this work, gold nanoparticles (AuNPs) modified TiO2 nanospheres were synthesized and modified with gallic acid (GA) to fabricate Au-TiO2@GA nanospheres (Au-TiO2@GA NSs). The SALDI substrate was prepared by coating the ITO glass slide with Au-TiO2@GA NSs using a gas-assisted electric sprayer. Compared with often-used MALDI matrices such as 2,5-dihydroxybenzoic acid (DHB), 2-mercaptobenzothiazole (MBT), 1,5-diaminonaphthalene (DAN), 2,5-dihydroxyacetophenone (DHA), and 9-aminoacridine (9-AA), the Au-TiO2@GA NSs provide higher detection sensitivity, lower background interference, dual-polarity detection and enhanced ionization efficiency of various endogenous molecules, particularly to the detection of neutral lipids. SALDI MSI could be straightforwardly performed on biological tissues thaw-mounted on the prepared substrate. The spatial distribution of various molecular species was unraveled in the mouse brain, kidney, and liver tissues. Not limited to animal tissues, Au-TiO2@GA NSs showed a more universal application to SALDI MSI of secondary metabolites in plant tissues. The spatial distribution of various natural products was mapped using SALDI MSI, such as parishins in Gastrodia elata tuber (Tianma) and glycoalkaloids in potato tuber. This work provides a high-efficient and high-compatible nanomaterial for SALDI MSI

Optimization of Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

In recent years, there has been a growing interest in the study of small molecules (e.g. metabolites, lipids, drugs) as they play important roles in various research areas, including biomedicine, biotechnology, environmental science and drug discovery. Mass spectrometry (MS) has become a predominant technology to analyze these low molecular weight compounds. However, the analysis of small molecules by the established matrix-assisted laser desorption/ionization (MALDI) MS technique can be difficult because of the interference generated by the matrix in the low m/z range. Therefore, new innovating ionization techniques that do not require an organic matrix have been developed. Among these alternatives is surface-assisted laser desorption/ionization (SALDI) MS, which relies on nanostructured surfaces to promote the desorption/ionization process. Yet, the implementation of this novel ionization technique introduces new challenges, which include the understanding of the fundamental mechanisms that govern the SALDI process, and the optimization of the experimental factors. In particular, the design and optimization of the assisting nanosubstrates are not straightforward, because of the wide range of available nanomaterials (in terms of chemical nature and morphology), characterized by different properties, which impact the performance of the SALDI MS experiments. Thus, it is essential to find a model to compare the capabilities of the SALDI nanosubstrates, in order to optimize their characteristics based on the same reference. In this context, thermometer ions have been used as reference compounds to test novel instrumentation, new methodologies, or to tune instruments. In this article, we review the study of thermometer ions in SALDI MS, which have enabled to rationalize the effect of the experimental factors (i.e. the nanosubstrate morphology and chemical nature, and the instrumental settings) on the performance of SALDI MS experiments. These studies allow the rational design of optimized nanosubstrates for advanced applications, such as SALDI MS imaging, which will be discussed at the end of this article.

Surface-Assisted Laser Desorption/Ionization Imaging Mass Spectrometry (SALDI-IMS)-Based Detection of Vinca Alkaloids Distribution in the Petal of Madagascar Periwinkle.

The surface-assisted laser desorption/ionization (SALDI) technique uses inorganic materials to aid desorption and ionization of molecules. SALDI is suitable for analyzing small molecules due to the absence of interfering signals in the low m/z range originating from the organic matrix. Imaging mass spectrometry (IMS) is a versatile imaging approach with high spatial resolution for analyzing various molecular species, but its application depends heavily on the ionization method. We have developed a functionalized titanium dioxide (TiO2) nanowire as a solid substrate for SALDI-MS detection of low-molecular-weight molecules. We apply this novel substrate for imprinting fragile specimens such as petals and further SALDI-IMS analysis. The TiO2 nanowire substrate is prepared from a commercial Ti plate by a hydrothermal process and subsequently chemically modified to improve the quality and selectivity of imprinting as well as the sensitivity of SALDI-IMS analysis. Here, the functionalized TiO2 nanowire substrate is applied to visualize the distribution of vinca alkaloids in the petal of Madagascar periwinkle (Catharanthus roseus).

Aptamer-Conjugated Graphene Oxide Based Surface Assisted Laser Desorption Ionization Mass Spectrometry for Selective Extraction and Detection of Aβ1-42

Aptamer-Conjugated Graphene Oxide Based Surface Assisted Laser Desorption Ionization Mass Spectrometry for Selective Extraction and Detection of Aβ1-42

Improvement in Ionization Efficiency Using Metal Oxide Nanoparticles in Laser Desorption/Ionization Mass Spectrometry of a Cancer Drug.

Mass spectrometry imaging (MSI) without labeling has the potential for faster screening in drug development. Matrix-assisted laser desorption/ionization (MALDI) is typically used, but it has a large matrix size and uneven drug distribution. Surface-assisted laser desorption/ionization (SALDI) using nanoparticles (NPs) may overcome these issues. Here, the influence of NPs, solvent ratio, and order of dropping of NPs on SALDI-MSI of protoporphyrin IX (PpIX), a cancer drug, are reported. A solution of PpIX in a 50% aqueous solution of 50% acetonitrile at a concentration of 10 μM was used. The NPs include ZnO, Fe3O4, and four types of TiO2. The NPs were fabricated by dissolving them on an aqueous 90% acetonitrile solution. Mass spectra were obtained with a time-of-flight mass spectrometer using a Nd:YAG laser at a 355-nm wavelength. The signal intensity using TiO2 at a 0.5 mg/mL concentration in 50% acetonitrile was increased by 1.6-fold compared to that without TiO2. Changing the solvent to 90% acetonitrile gave a uniform TiO2 distribution and a 9-fold increase in the signal intensity for PpIX. Among the four types of TiO2 with different particle sizes and crystal structures, TiO2 with a smaller particle size and a rutile crystal structure produced the highest signal intensity. Forming a layer on top of the PpIX also resulted in an increased signal intensity. Hence, SALDI using TiO2 provides effective ionization of the drug. In the future, we plan to investigate a spray method for the ionization of PpIX using TiO2 for the MSI of various drugs.

Microporous hydrogen-bond organic frameworks-based SALDI-TOF MS for simultaneous enrichment and high sensitivity detection of paraquat and chlormequat

This study proposes a surface-assisted laser desorption ionization time-of-flight mass spectrometry (SALDI-TOF MS) method using an ultrastable microporous hydrogen-bonded organic frameworks (MP-HOFs) for selective and sensitive analysis of two common organic pesticides: paraquat (PQ) and chlormequat (CQ) in real samples. MP-HOFs are formed by H-bonding self-assembly of co-planar π-conjugated large aromatic tectons with carboxylate groups. They can not only efficiently absorb and transfer laser energy, but also specifically capture and isolate target analytes from complicated systems. The proposed SALDI-TOF MS method exhibited high salt tolerance and low background. The selective enrichment performance of MP-HOFs was demonstrated by analyzing PQ and CQ in real samples. Simultaneous analysis results of PQ and CQ showed satisfactory reproducibility with relative standard deviations (RSDs) of 3.2–9.2% and 5.7–12.3% for spot-to-spot and sample-to-sample, good linearity (R2 > 0.99), and high sensitivity with a limit of detection of 0.001 and 0.05 ng mL−1, respectively. The detection limits of PQ and CQ test analytes were three and two orders of magnitude lower than those of non-enriched PQ and CQ, respectively. Furthermore, the possible ionization mechanism was discussed, and the presented approach was successfully applied for PQ and CQ detection in tap water, river water, and soil, confirming its potential in practical applications.

Detection of Acetaminophen and Its Glucuronide in Fingerprint by SALDI Mass Spectrometry Using Zeolite and Study of Time-Dependent Changes in Detected Ion Amount

The ingredients of an antipyretic (acetaminophen, AAP) and their metabolites excreted into fingerprint were detected by surface-assisted laser desorption ionization (SALDI) mass spectrometry using zeolite. In the fingerprint taken 4 h after AAP ingestion, not only AAP but also the glucuronic acid conjugate of AAP (GAAP), caffeine (Caf), ethenzamide (Eth), salicylamide (Sala; a metabolite of Eth), and urea were detected. Fingerprints were collected over time to determine how the amounts of AAP and its metabolite changed with time, and the time dependence of the peak intensities of protonated AAP and GAAP was measured. It was found that the increase of [GAAP+H]+ peak started later than that of [AAP+H]+ peak, reflecting the metabolism of AAP. Both AAP and GAAP reached maximum concentrations approximately 3 h after ingestion, and were excreted from the body with a half-life of approximately 3.3 h. In addition, fingerprint preservation was confirmed by optical microscopy, and fingerprint shape was retained even after laser irradiation of the fingerprint. Our method may be used in fingerprint analysis.

Development of efficient SALDI substrate based on Au–TiO2 nanohybrids for environmental and forensic detection of dyes and NSAIDs

Herein, a matrix-free approach is presented for comprehensive environmental and forensic analysis of dyes and nonsteroidal anti-inflammatory drugs (NSAIDs) using Au–TiO2 nanohybrids coupled with surface-assisted pulsed laser desorption ionization-mass spectrometry (SALDI-MS). The Au–TiO2 nanohybrids was prepared and characterized using inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), surface area measurements, ultraviolet–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). Initially, the optimal Au content was assessed using the survival yield (SY) method, confirming that 7.5% Au content on the TiO2 surface offered the highest ionization efficiency. Subsequently, environmental analyses of dyes and NSAIDs in water samples were performed, and sensitive detection of all analytes was achieved with limits of detection (LODs) ranging from 10.0 ng mL−1 to 10.0 fg mL−1 and good spot-to-spot reproducibility. Additionally, the effect of potential contaminants commonly found in environmental samples, such as salts, surfactants and pesticides was also considered. Despite signal intensity reduction at high concentrations of some salts, the target analytes were detected, while the presence of surfactants and pesticides did not cause significant signal intensity reduction. Additionally, dyed and undyed Tetoron fibers and the effect of adhesive tape were evaluated. Direct analysis of the dyed Tetoron fibers on the target plate, using the nanohybrids, enabled higher detection sensitivity of the dyes, in addition to adducts of polystyrene and cellulose, the main components of the fiber. Finally, NSAIDs in oral fluid were analyzed and sensitive detection of the analytes was observed using the nanohybrids with LODs and LOQs in the range of 0.1–10 ng mL−1 and 1–20 ng mL−1, respectively. The trueness of the exact mass was in the range of 0.64–6.2 ppm while the recovery of the spiked samples was in the range of 82.90–107.54%% indicating the efficiency of the Au–TiO2 nanohybrids as SALDI substrate. Thus, the Au–TiO2 nanohybrids hold considerable promise in terms of sensitivity, reproducibility, and LOD, and may significantly contribute to environmental and forensic identification.

A Polymer-Based Matrix for Effective SALDI Analysis of Lipids

Surface-assisted laser desorption/ionization (SALDI) has become an attractive branch of matrix-assisted laser desorption/ionization (MALDI) and has been successfully applied for the detection of small molecules due to the lack of the interference of matrix. Herein, the low-cost and highly accessible polyvinylidene fluoride (PVDF) was modified using a facile alkali treatment and investigated as a SALDI matrix. The modified PVDF has a strong optical absorption and can be applied as a dual-mode substrate for both SALDI MS and SALDI imaging analysis. Modified PVDF powder showed superior performance in SALDI MS analysis of lipids, with good reproducibility, high sensitivity, and low background interference, especially for triacylglycerols (TAGs) and fatty acids. Additionally, the lipids in raw and extracted serum were both successfully determined with modified PVDF powder. A modified PVDF membrane (m-PVDF-m) showed excellent ability in lipids imaging in tissues due to its flat surface, mass signal enhancement, and elimination of matrix coating. The distribution of several TAGs and cholesteryl esters on mouse kidney section was presented by SALDI imaging directly on m-PVDF-m. These results demonstrated that modified PVDF materials presented exciting opportunities as matrices for the first time in SALDI MS acquisition and SALDI imaging.

Silicon surface assisted laser desorption ionization mass spectrometry for quantitative analysis.

The approach to quantitative analysis by silicon Surface Assisted Laser Desorption Ionization Mass Spectrometry (Si-SALDI) is proposed. The approach is based on the new method for forming an active surface layer on a silicon substrate by exposing to laser radiation directly in the ion source of a mass spectrometer. The method can be used repeatedly on the same substrate, providing high reproducibility of its surface ionization properties and high ionization efficiency of organic compounds. Within the proposed approach, the methods of improvement of signal reproducibility are also considered, including continuous monitoring of the silicon surface ionization properties using a Knudsen effusion cell; scanning the surface of a silicon substrate with a laser beam; selecting the optimal value of laser fluence and using a reproducible sample introduction technique. It is demonstrated that this approach can be successfully applied to quantify clinically relevant concentrations of pharmaceutical drugs in extracts of blood.

Visualizing vinca alkaloids in the petal of Catharanthus roseus using functionalized titanium oxide nanowire substrate for surface-assisted laser desorption/ionization imaging mass spectrometry.

Imaging mass spectrometry (IMS) is a powerful technique that enables analysis of various molecular species at a high spatial resolution with low detection limits. In contrast to the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) approach, surface-assisted laser desorption/ionization (SALDI) can be more effective in the detection of small molecules due to the absence of interfering background signals in low m/z ranges. We developed a functionalized TiO2 nanowire as a solid substrate for IMS of low-molecular-weight species in plant tissues. We prepared TiO2 nanowires using an inexpensive modified hydrothermal process and subsequently functionalized them chemically with various silane analogs to overcome the problem of superhydrophilicity of the substrate. Chemical modification changed the selectivity of imprinting of samples deposited on the substrate surface and thus improved the detection limits. The substrate was applied to image distribution of the metabolites in very fragile specimens such as the petal of Catharanthus roseus. We observed that the metabolites are distributed heterogeneously in the petal, which is consistent with previous results reported for the C. roseus plant leaf and stem. The intermediates corresponding to the biosynthesis pathway of some vinca alkaloids were clearly shown in the petal. We also performed profiling of petals from five different cultivars of C. roseus plant. We verified the semi-quantitative capabilities of the imprinting/imaging approach by comparing results using the LC-MS analysis of the plant extracts. This suggested that the functionalized TiO2 nanowire substrate-based SALDI is a powerful technique complementary to MALDI-MS.

Application of Graphdiyne in Surface-Assisted Laser Desorption Ionization Mass Spectrometry.

Graphdiyne (GD) is a new kind of carbon nanomaterial which has carbon-carbon triple bonds to form a layered structure. Here, we report the application of GD as the matrix for small molecule analysis in laser desorption ionization mass spectrometry (LDI MS). The GD matrix displayed two advantages: little background in the low mass range and good molecular ion signal in negative ion mode for many small molecules, e.g., fatty acids, amino acids, peptides, and drugs can be obtained in negative ion mode. By comparing the signal intensity of tetraphenylborate and juglone with and without GD existing, it was found that GD can enhance both of the desorption efficiency and ionization efficiency in LDI. Through analysis of the serum samples from liver cancer patients and healthy people, the GD-assisted LDI MS results showed that fatty acids could be used as potential biomarkers for the early diagnosis of liver cancer.

Gas aggregated Ag NPs as a matrix for small molecules: a study on natural amino acids

The use of nanomaterials as a matrix for soft ionization mass spectrometry has been investigated and reported various times. Under certain conditions, measurements of samples containing small molecules enhanced by nanomaterials have better sensitivity compared with other methods. Nanoscaled Ag prepared by various methods was reported as a substrate for surface-assisted LDI MS. Higher desorption and (in some cases) charge transfer through adduct formation with silver ion was reported. But primary ionization mechanism was through attachment of proton or alkali ion. Our approach is to overcoat the sample by Ag nanoparticles (the so-called nanoparticle-assisted LDI MS or nanoPALDI MS). As nanoparticles having adsorption maxima close to the laser wavelength, we expect an improvement in desorption enhancement, release of silver ions and (as a result of latter) increased adduct formation of [analyte+Ag]+ ions. The nanoparticles are produced by gas aggregation under low-pressure, making the process homogeneous over relatively large areas, free from impurities, and absence of capping agent often presented in colloidal nanoparticles. This work reports the detection of natural amino acids with Ag nanoparticles as a matrix. We successfully detected all amino acids (as [analyte+Ag]+ ion), including in the mixtures of few amino acids. Moreover, a formation of other adducts, particularly [analyte+Ag3]+ and [analyte2+Ag]+ is reported. The differences in ion intensity ratios depending on amino acid types are discussed. The obtained results showed that laser ablation is more efficient for amino acids with hydrophobic, unique, and neutral side chains.

Porous TiO2 Film Immobilized with Gold Nanoparticles for Dual-Polarity SALDI MS Detection and Imaging.

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) has become an attractive complementary approach to matrix-assisted laser desorption/ionization (MALDI) MS. SALDI MS has great potential for the detection of small molecules because of the absence of applied matrix. In this work, a functionalized porous TiO2 film immobilized with gold nanoparticles (AuNPs-FPTDF) was prepared to enhance SALDI MS performance. The porous TiO2 films were prepared by the facile sol-gel method and chemically functionalized for dense loading of AuNPs. The prepared AuNPs-FPTDF showed superior performance in the detection and imaging of small molecules in dual-polarity modes, with high detection sensitivity in the low pmol range, good repeatability, and low background noise compared to common organic MALDI matrixes. Its usage efficiently enhanced SALDI MS detection of various small molecules, such as amino acids and neurotransmitters, fatty acids, saccharides, alkaloids, and flavonoids, as compared with α-cyano-4-hydroxycinnamic acid, 9-aminoacridine, and the three precursor substrates of AuNPs-FPTDF. In addition, the blood glucose level in rats was successfully determined from a linearity concentration range of 0.5-9 mM, as well as other biomarkers in rat serum with SALDI MS. More importantly, the spatial distribution of metabolites from the intact flowers of the medicinal plant Catharanthus roseus was explored by using the AuNPs-FPTDF as an imprint SALDI MS substrate in dual-polarity modes. These results demonstrate wide applications and superior performances of the AuNPs-FPTDF as a multifunctional SALDI surface with enhanced detection sensitivity and imaging capabilities.

Laser Desorption of Organic Compound Ions from a Silicon Surface Modified by Laser Irradiation

Laser desorption of organic compound ions from specially prepared surfaces is known as surface-assisted laser desorption/ionization (SALDI). In this work the properties of a SALDI ion emitter obtained by two-stage laser treatment of crystalline silicon surface have been investigated. The laser surface treatment leads to the formation of a layer with nanoscale objects—quantum dots (QDs) less than 10 nm in size, providing laser desorption of organic compound ions. A change in the desorbing laser wavelength from 351 to 263 nm at comparable laser-exposed spot sizes and fluences results in a sharp decrease in the formation efficiency for MH+ ions and appearance of ions M+ for the same analytes. The effect is apparently determined by the spectral properties of the quantum dots formed on the silicon surface under laser irradiation.

Rapid Fingerprinting of High-Molecular-Weight Polymers by Laser Desorption-Ionization Using Through-Hole Alumina Membrane High-Resolution Mass Spectrometry

Residual acid found in the desorption ionization using through-holes alumina membranes (DIUTHAME) induces a reproducible protonation/in-source dissociation of polymers made of ester, amide, or siloxane moieties during their surface-assisted laser desorption ionization (SALDI) mass analysis. Deposited on the DIUTHAME chips in solution (solvent-based) or in pure form by melting the polymer powder in situ (solvent-free), high-molecular-weight nylons, silicone, or functionalized celluloses among other polymers are instantly fingerprinted by laser DIUTHAME high-resolution mass spectrometry (MS) with specific patterns resembling their direct analysis in real-time (DART) single-stage or tandem mass spectra. Depending on the polymer, two main types of fingerprints are observed with either the protonated monomer or product ions revealing the nature of the repeating unit or its functionalization. This technique allows a rapid molecular analysis of industrial homopolymers regardless of their molecular weight and complementary to DART with simple or no sample preparation and also promisingly applicable for copolymers.