Surface-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry Research Articles

Novel magnetic single-layer nano-MXene as a highly effective adsorbent and new SALDI-TOF-MS matrix for enrichment and rapid determination of p-Phenylenediamine antioxidants in water

A novel magnetic single-layer nano-MXene (SNM@Fe3O4) was prepared for the first time with small size, high surface area, abundant active sites and excellent energy absorption/transfer capability. The combined experimental and theoretical investigation revealed SNM@Fe3O4 could be served as a highly effective adsorbent for enrichment and a new surface-assisted laser desorption/ionization-time of flight-mass spectrometry (SALDI-TOF-MS) matrix for rapid analysis of p-Phenylenediamine (PPD) antioxidants, a kind of emerging environmental contaminants, in actual water samples from North and South China. The SNM@Fe3O4-based SALDI-TOF-MS approach featured free matrix interference, acceptable linearity (R2 ≥ 0.97), high sensitivity (LOD at ng mL−1 level) and qualified precision (RSD ≤ 8.46 %) for the four PPDs’ detection. The corresponding determined pollution levels also revealed the widespread occurrence of PPDs in Chinese water system. Compared to previous works, SNM@Fe3O4-based method achieved reproducible and more rapid analysis of PPDs in water, demonstrating a considerable potential of our self-synthesized nanomaterial for sensitive analysis of low-concentration organic small-molecule compounds in complicated sample matrix.

Preparation and comparison of Fe3O4@graphene oxide nanoclusters for analysis of glimepiride in urine by surface-assisted laser desorption/ionization time-of-flight mass spectrometry.

Graphene oxide (GO) has the ability to absorb certain compounds, and it can be modified with functional groups for different purposes; for instance, iron oxide (IO) nanoparticles can be used to concentrate analyte by a magnet. Recently, many kinds of GO have been developed, such as single-layer GO (SLGO), two-to-four layers of GO (i.e., few-layer GO, FLGO2-4), and four-to-eight layers of GO (i.e., multi-layer GO, MLGO4-8). However, the abilities of these layered GO coated with IO nanoparticles have not been investigated. In this study, we conducted a novel analysis of glimepiride by using layered GO-coated magnetic clusters of IO nanoparticles that were synthesized through a simple and facile emulsion-solvent evaporation method. The methodology is based on (i) enrichment of glimepiride using the layered GO-coated magnetic clusters of IO nanoparticles (IO@SLGO, IO@FLGO2-4, and IO@MLGO4-8), and (ii) rapid determination using magnetic cluster-based surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOFMS). We found that IO@MLGO4-8, the magnetic cluster with the greatest number of GO layers, had the best limit of detection (28.6pmol/μL for glimepiride). The number of GO layers played a significant role in increasing the sensitivity of the SALDI-MS, indicating that the size of GO in the magnetic clusters contributed to the desorption/ionization efficiency. To the best of our knowledge, this is the first study to enrich glimepiride using magnetic clusters of different GO types and to show that the glimepiride in HLB purified urine adsorbed by magnetic clusters can be analyzed by SALDI-TOFMS.

Atmospheric Pressure Plasma-Treated Carbon Nanowalls’ Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (CNW-SALDI-MS)

Carbon nanowalls (CNWs), vertically standing highly crystallizing graphene sheets, were used in the application of a surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS). The CNW substrates solved the issues on interferences of matrix molecules and alkali metal addition ions in low-weight molecule detection. Before SALDI sample preparations, the hydrophobic CNW was treated by atmospheric pressure plasma for exposing hydrophilicity to the CNWs’ surface. Detection of water soluble amino acids, arginine, was demonstrated.

Analysis of paper foxing by newly available omics techniques

The aim of this study was to determine the cause of foxing on 19th century paper using omics methods, including metagenomics via high-throughput sequencing on the Illumina platform and metabolomics via high-resolution surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-ToF-MS) imaging using the gold nanoparticle-enhanced target (AuNPET) method. Metabolomic analysis as well as ninhydrin and amido black staining of paper samples showed the presence of proteinaceous substances in areas corresponding to foxing. Products of cellulose biodegradation and microbial metabolites, including yellow-coloured pigments (2-methyl-6-phytylquinol; delta-, gamma- and beta-tocopherols; 3-hydroxy-L-kynurenine) were detected. No difference in metal-ion content was seen between areas with and without foxing. Higher degrees of biodiversity were identified within foxing stains compared to foxing-free areas. Phoma sp. and Cladonia sp. moulds and Gluconobacter and Ralstonia bacteria were predominant in DNA samples obtained from foxing stains. The presence of these microbes has never previously been linked to the phenomenon of foxing. These studies indicate that foxing is a result of a combined effect of microbial action, paper-degradation by microbes, dye production, and chemical changes occurring in paper due to oxidation of cellulose metabolites.

Surface-assisted laser desorption-ionization mass spectrometry of oligosaccharides using magnesium oxide nanoparticles as a matrix

We describe the use of magnesium oxide nanoparticles (MgO-NPs) as a new matrix for the analysis of oligosaccharides (maltoheptaose, palatinose, D-panose, N-acetyllactosamine and β-gentiobiose) by surface-assisted laser desorption-ionization time-of-flight mass spectrometry (SALDI-MS). The use of MgO-NPs results in mass spectra without background noise and no fragmented ions in the low-mass region. The MgO-NPs were characterized by FT-IR, scanning electron microcopy, transmission electron microscopy which reveal that the particles are well dispersed in solution. The system allows the detection of the analytes at <20 nM concentrations, with limits of detection of 4.0, 5.5, 6.0, 10.0 and 7.0 nM, respectively. The calibration plots are linear (R 2 values between 0.9896 and 0.9985), and relative standard deviations are <10 %. We conclude that MgO-NPs-based SALDI-MS enables the efficient and sensitive analysis of oligosaccharides in the low-mass region.

Suitability of GaP nanoparticles as a surface-assisted laser desorption/ionization mass spectroscopy inorganic matrix and their soft ionization ability

Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) using GaP nanoparticles (NPs) prepared by a gas evaporation method was investigated on poly(ethylene glycol)s (PEGs). The mass spectra of PEG and survival yield measurements suggested that larger GaP NPs have a quite high soft ionization ability.

Detection of nitro-organic and peroxide explosives in latent fingermarks by DART- and SALDI-TOF-mass spectrometry

The ability of two mass spectrometric methods, surface-assisted laser desorption/ionization-time of flight-mass spectrometry (SALDI-TOF-MS) and direct analysis in real time (DART-MS), to detect the presence of seven common explosives (six nitro-organic- and one peroxide-type) in spiked latent fingermarks has been examined. It was found that each explosive could be detected with nanogram sensitivity for marks resulting from direct finger contact with a glass probe by DART-MS or onto stainless steel target plates using SALDI-TOF-MS for marks pre-dusted with one type of commercial black magnetic powder. These explosives also could be detected in latent marks lifted from six common surfaces (paper, plastic bag, metal drinks can, wood laminate, adhesive tape and white ceramic tile) whereas no explosive could be detected in equivalent pre-dusted marks on the surface of a commercial lifting tape by the DART-MS method due to high background interference from the tape material. The presence of TNT and Tetryl could be detected in pre-dusted latent fingermarks on a commercial lifting tape for up to 29 days sealed and stored under ambient conditions.

Doped silica nanoparticles for the detection of pharmaceutical terbinafine in latent fingerprints by mass spectrometry

A detailed study on terbinafine excretion in latent fingerprints of a patient prescribed with the medication was carried out for a period of 14 days. Latent fingerprints collected from the patient were dusted with a fingerprint developing agent consisting of magnetized carbon black doped silica nanoparticles and directly analyzed by surface assisted laser desorption ionization-time of flight-mass spectrometry (SALDI-TOF-MS). MS and MSMS spectra of the latent fingerprints confirmed the presence of terbinafine, with the parent ion at m/z 292 and the fragment ion at m/z 141. Coupled with imaging, a gradual increment in the amount of terbinafine detected on the latent fingerprints from day 0 to day 14 was observed. When compared against commonly used 2,5-dihydroxybenzoic acid (DHB), these nanoparticles were more effective as a matrix for MS analysis of terbinafine, recording improved signal-to-noise values. The results demonstrate the efficacy of this technique for the detection of exogenous pharmaceutical drugs in latent fingerprints, providing information pertaining to the donor which may prove useful in cases of smudged prints.

Sensing of Oligopeptides Using Alternatively-Deposited Gold Nanorods for Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

ABSTRACTGold nanorods (NRs) were fixed on an ITO plate and used for the Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SALDI-MS) of oligopeptides (angiotensin I). The SALDI-MS measurements had a high sensitivity to the angiotensin on the ITO plate on which isolated NRs were deposited. Angiotensin molecules in a very diluted solution (1 × 10-11 M) could be detected at m/z = 1297 with a good signal/noise ratio (S/N = 18). In contrast, alternatively deposited NR an ITO plate, which present broad surface plasmon bands, was found to be inactive for SALDI measurements.

One-pot synthesis of dopamine dithiocarbamate functionalized gold nanoparticles for quantitative analysis of small molecules and phosphopeptides in SALDI- and MALDI-MS

The sensitivity and efficiency of SALDI-MS or MALDI-MS is mainly dependent on the nature of matrix. A novel approach is proposed for one-pot synthesis of dopamine dithiocarbamate-functionalized gold nanoparticles (DDTC-Au NPs). Their application to quantification of small molecules by surface assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) and rapid identification of phosphopeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is investigated. The synthesized DDTC-Au NPs were characterized by UV-visible and FT-IR spectroscopy, H(1)NMR, SEM and TEM. DDTC-Au NPs offers marked improvement on analyte ionization and effectively suppressed the background noise which leads to clean mass spectra. We also demonstrated the use of DDTC-Au NPs as affinity probes for selective enrichment of phosphopeptides from the solutions of microwave tryptic digested casein proteins. Compared with a conventional matrix, DDTC-Au NPs exhibited a high desorption/ionization efficiency for accurate quantification of small molecules including amino acid (glutathione), drugs (desipramine and enrofloxacin) and peptides (valinomycin and gramicidin D) and successfully utilized as novel affinity probes for straightforward and rapid identification of phosphopeptides from casein proteins (α-, β-casein and nonfat milk), showing a great potentiality to the real-time analysis.

Sensing of oligopeptides using localized surface plasmon resonances combined with Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Gold nanorods were fixed on an ITO plate and used for the spectroscopic sensing and Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SALDI-MS) of oligopeptides (angiotensin I). The longitudinal surface plasmon bands of the gold nanorods responded to the 10(-10) M angiotensin solution that was cast on the ITO plate. The SALDI-MS measurements had an ultra-high sensitivity to the angiotensin on the ITO plate. A very small surface density (5 × 10(-19) mol cm(-2)) of angiotensin could be detected at m/z = 1297 with a good signal/noise ratio (S/N = 11). The ITO plate, which was modified with gold nanorods, was found to be effective in collecting angiotensin molecules adjacent to the gold nanorods, and the SALDI processes that were induced by the photoabsorption of the gold nanorods efficiently contributed to the desorption and ionization of the angiotensin.

Functionalized Nanoparticles and Nanostructured Surfaces for Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) using nanoparticles (NPs) and nanostructured surfaces as the LDI-assisting nanomaterials is a soft ionization technique that features minimal fragmentation of analytes. As compared to traditional matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) using organic matrices, SALDI-MS affords several advantages, such as the ability to detect small molecules (<500 Da), easy sample preparation, low-noise background, high salt tolerance, and fast data collection without the use of an organic matrix. The performance of SALDI has been further improved recently in terms of the detection sensitivity, detection mass range from the low- to the high-mass region, a soft LDI process, the detection of both polar and nonpolar compounds, the selective detection of analytes from a complex mixture using functionalized NPs, and various applications, including imaging mass spectrometry. This review summarizes recent developments pertaining to various NPs and nanostructured surfaces for SALDI-MS.

Screening Assay of Very Long Chain Fatty Acids in Human Plasma with Multiwalled Carbon Nanotube-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Peroxisomal disorders are characterized biochemically by elevated levels of very long chain fatty acids (VLCFAs) in serum. Herein, we describe a novel approach for quantification of VLCFAs in serum, namely, eicosanoic acid (C20:0), docosanoic acid (C22:0), tetracosanoic acid (C24:0), and hexacosanoic acid (C26:0). The methodology is based on (i) enrichment of VLCFA derivatives using multiwalled carbon nanotubes (MWCNTs); (ii) quantification using stable isotope-labeled internal standards; and (iii) direct detection using MWCNT-based surface-assisted laser desorption/ionization-time-of-flight mass spectrometry (SALDI-TOFMS). Four kinds of MWCNTs (Aldrich 636843, 636495, 636509, and 636819) of different lengths and diameters were tested using the developed technique. The data show that 636843, the MWCNT with the largest outer diameter (o.d.), the widest wall thickness, and shortest length, had the best limit of detection (0.5-1 microg/mL) We also found that there was no significant difference in enrichment efficiency of VLCFAs between the four MWCNTs, which suggests that the size of the MWCNT may contribute to desorption/ionization efficiency. To our knowledge, this is the first study to test the enrichment of VLCFAs using MWCNTs of different sizes. We have shown that the VLCFAs adsorbed by MWCNTs can be analyzed by SALDI-TOFMS. In addition, this method does not require liquid/gas chromatography separation, thereby allowing for high-throughput screening of VLCFAs in peroxisomal disorders.

SALDI-MS Signal Enhancement Using Oxidized Graphitized Carbon Black Nanoparticles

The signal intensity of low-molecular-weight compounds analyzed using surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) was significantly enhanced when oxidized graphitized carbon black (GCB) particles were used as the desorption/ionization surface. The surface of oxidized GCB contains more carboxylic acid groups than non-oxidized GCB. Carboxylic acid groups enhance the efficiency of the ionization process and the desorption of more hydrophobic compounds. A common pharmaceutical compound, propranolol, was successfully extracted from Baltic Sea blue mussels and quantified using oxidized GCB as the SALDI surface, whereas deuterated propranolol was used as the internal standard. The calibration curve showed a wide linear dynamic range of response (0.1-20 microg/mL) and good reproducibility (RSD < 10%). It was not possible to detect propranolol in Baltic Sea blue mussels when non-oxidized GCB was used as the SALDI surface.

Characterization of silver ions adsorbed on gold nanorods: surface analysis by using surface-assisted laser desorption/ionization time-of-flight mass spectrometry

Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-MS) indicated AgBr2-, which adsorbed on gold nanorod surfaces, was a key material to control the anisotropic growth of gold nanorods.

Comparison of ZnS Semiconductor Nanoparticles Capped with Various Functional Groups as the Matrix and Affinity Probes for Rapid Analysis of Cyclodextrins and Proteins in Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Zinc sulfide (ZnS) semiconductor nanoparticles (NPs) capped with a variety of functional groups including bare ZnS NPs, 3-mercaptopropanoic acid (ZnS-3-MPA), sodium citrate (ZnS-citrate), cysteamine (ZnS-Cys), and 2-mercaptoethane sulfonate (ZnS-2-MES) have been investigated as the matrix and affinity probes for analysis of alpha-, beta-, and gamma-cyclodextrins (CDs), ubiquitin, and insulin in biological samples by using surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS). Various parameters that would influence the ionization efficiency and sensitivity of these ZnS NPs in SALDI-TOF-MS were examined including the effect of capping agents, sample pH, ion abundance, and concentration of ZnS NPs. Among these ZnS NPs, our results have demonstrated that ZnS-3-MPA exhibited the highest efficiency toward CDs, ubiquitin, and insulin for high-sensitivity detection in SALDI-TOF-MS. The detection limits were 20-55 nM for CDs, 91 nM for ubiquitin, and 85 nM for insulin. The applicability of the present method is demonstrated by detection of ubiquitin-like proteins in oyster mushroom and also in the analysis of analytes in biological samples such as human urine and plasma. To our best knowledge, this is the first time semiconductor NPs were used as the matrix and affinity probes for high-sensitivity detection of organic and biomolecules in SALDI-TOF-MS. This approach exhibits the advantages of being simple, rapid, efficient, and straightforward for direct analysis of organic and biological samples in SALDI-TOF-MS without the need for time-consuming separation processes, tedious washing steps, or further laborious purification. In addition, it also can provide a sensitive and reliable quantitative assay for small- and large-molecule analysis with the detectable mass up to 8500 Da. We believe that this novel ZnS nanoprobe is simple, efficient, lower cost (compared with Au, Ag, and Pt NPs), fast, and with the potential for high-throughput analysis in SALDI-TOF-MS.

μ-Trap for the SALDI-MS Screening of Organic Compounds Prior to LC/MS Analysis

A procedure for rapidly screening and quantitatively analyzing organic molecules is presented, in which a miniaturized solid-phase extraction (SPE) cartridge containing 0.6 mg of graphitized carbon black (the GCB-mu-trap) is used for sample pretreatment. Then surface-assisted laser desorption ionization time-of-flight mass spectrometry (SALDI-TOF-MS) screening is followed by liquid chromatography/mass spectrometry (LC/MS) for robust quantitative analysis of samples containing analytes of interest. Liquid samples with volumes up to 100 mL were extracted using the GCB-mu-trap, and SALDI screening was performed by transferring a few particles of the GCB 4 sorbent from the mu-trap onto a stainless steel plate. Analytes were then simply ionized and desorbed by irradiating the GCB 4 particles without any further pretreatment. GCB 4 was found to be an excellent surface for the SALDI analysis of small molecules, providing spectra with very clean backgrounds. The small size of the cartridge (micropipet filter tip) results in enrichment of the analytes on a small surface area, affording low SALDI-TOF-MS detection limits. Furthermore, the removal of just a few particles from the mu-trap does not significantly affect the subsequent quantitative determination. This approach offers considerable reductions in analytical costs by eliminating unnecessary SPE-LC/MS analyses.