Surface-assisted Laser Desorption/ionization Research Articles

Surface assisted laser desorption/ionization mass spectrometry of lithium cationized lignans – A tool for rapid screening of plant extracts

Lignans are one of the most widespread classes of plant secondary metabolites possessing unique biological activities. The search for new sources of such compounds, their screening and identification in plant biomass is an urgent task, requiring the use of advanced analytical methods. In the present study, matrix-free surface assisted laser desorption/ionization (SALDI) mass spectrometry was proposed for its solution. The combination of carbon nanocoating sputtered on a target plate with lithium cationization allowed obtaining high-quality mass spectra of eight coniferous wood lignans with different bonds between aromatic units (secoisolariciresinol, matairesinol, 7-hydroxymatairesinol, nortrachelogenin, pinoresinol, guaiacylglycerol-β-guaiacyl ether, dehydrodihydrodiisoeugenol, and divanillin). Three types of fragmentation methods (post-source decay, high- and low-energy collision induced dissociation) for the first time were implemented on two types of MALDI instruments. Regardless of tandem mass spectrometry technique, lignans demonstrated the similar fragmentation patterns including the cleavage of bonds between aromatic units with the formation of mostly lithiated product ions. The low-energy collision induced dissociation in quadrupole ion trap provided the most informative tandem mass spectra and multi-stage fragmentation capabilities in structural studies. On this basis, an approach to rapid, high-throughput, and low-cost screening and tentative identification of lignans including isomeric compounds in plant biomass was developed and successfully tested on real samples of pine, fir, spruce, and larch knotwood extracts.

Isoporous Membrane Mediated Imprinting Mass Spectrometry Imaging for Spatially-Resolved Metabolomics and Rapid Histopathological Diagnosis.

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry imaging (MSI) holds great value in spatial metabolomics and tumor diagnosis. Tissue imprinting on the SALDI target can avoid laser-induced tissue ablation and simplifies the sample preparation. However, the tissue imprinting process always causes lateral diffusion of biomolecules, thereby losing the fidelity of metabolite distribution on tissue. Herein, a membrane-mediated imprinting mass spectrometry imaging (MMI-MSI) strategy is proposed using isoporous nuclepore track-etched membrane as a mediating imprinting layer to selectively transport metabolites through uniform and vertical pores onto silicon nanowires (SiNWs) array. Compared with conventional direct imprinting technique, MMI-MSI can not only exclude the adsorption of large biomolecules but also avoid the lateral diffusion of metabolites. The whole time for MMI-based sample preparation can be reduced to 2min, and the lipid peak number can increase from 46 to 113 in kidney tissue detection. Meanwhile, higher resolution of MSI can be achieved due to the confinement effect of the pore channel in the diffusion of metabolites. Based on MMI-MSI, the tumor margins of liver cancer can be clearly discriminated and their different subtypes can be precisely classified. This work demonstrates MMI-MSI is a rapid, highly sensitive, robust and high-resolution technique for spatially-resolved metabolomics and pathological diagnosis.

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.

Direct detection of dithiocarbamate fungicides by SALDI/MS using porous TiC ceramic powder as a substrate.

Dithiocarbamate fungicides (DTCs) have been widely used all over the world. Some of them show toxicities, such as growth toxicity and teratogenicity. Therefore, the analysis of DTCs in environments or crops is very significant. However, their direct and individual analysis was difficult, because most of them are metal complex compounds and have macromolecular properties and a low solubility in water or organic solvents. In the conventional analytical methods for DTCs, the total amount of DTCs was obtained by the quantification of the derivatives of the ligand or by measuring the carbon disulfide formed by the decomposition of the fungicides. Surface assisted laser desorption (SALDI)/MS can detect various compounds, such as metal complexes and macromolecules, present in a nanostructured substrate. The porous titanium carbide (TiC) ceramic powder shows adsorptive properties to various substances and can be used as a substrate for SALDI/MS. In this study, a method for the individual and direct detection of dithiocarbamate pesticides by SALDI/MS using porous TiC ceramics as a substrate has been developed. The dithiocarbamate fungicide was mixed with the porous TiC powder in a mortar, and the mixture was analyzed by SALDI/MS. The deprotonated ion of the ethylene-bis-dithiocarbamate complex, mancozeb or zineb, was detected in the negative ion mode. For the dimethyldithiocarbamate complexes, ferbam and ziram, the ion of the eliminated dithiocarbamate ligand was detected in the positive ion mode. Calibration curves by the present method for Manzeb showed good linearity by using an internal standard material. Based on these results, we concluded that this method is useful for the analysis of DTCs.

Efficient Analysis of Small Molecules via Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (LDI-TOF MS) Using Gold Nanoshells with Nanogaps.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a commonly used technique for analyzing large biomolecules. However, the utilization of organic matrices limits the small-molecule analysis because of the interferences in the low-mass region and the reproducibility issues. To overcome these limitations, a surface-assisted laser desorption/ionization (SALDI), which utilizes nanostructured metallic surfaces, has been developed. Herein, a novel approach for SALDI-MS was proposed using silica@gold core-shell hybrid materials with a nanogap-rich shell (SiO2@Au NGS), which is an emerging material due to its excellent heat-generating capabilities. The gold shell thickness was controlled by adjusting the concentration of gold precursor for the growth of gold nanoparticles. SALDI-MS measurements were performed on a layer formed by drop-casting a mixture of SiO2@Au NGS and analytes. At the optimized process, the gold shell thickness was observed to be 17.2 nm, which showed the highest absorbance. Based on the enhanced SALDI capability, SiO2@Au NGS was utilized to detect various small molecules, including amino acids, sugars, and flavonoids, and the ionization softness was confirmed with a survival yield upon fragmentation. The limits of detection, reproducibility, and salt tolerance of SiO2@Au NGS demonstrate its potential as an effective and reliable SALDI material for small-molecule analyses.

Serum lipidomic profiling for liver cancer screening using surface-assisted laser desorption ionization MS and machine learning

The liver is a major organ in metabolism, and alterations in serum lipids are associated with liver disorders. Here, a rapid, easy, and reliable screening technique based on lipidomic profiling was developed using machine learning and surface-assisted laser desorption ionization mass spectrometry (SALDI MS) for liver cancer diagnosis. A graphitized carbon matrix (GCM) was created for serum lipid profiling in SALDI MS and demonstrated a better performance for neutral lipids analysis than conventional organic matrices. The fingerprint of serum lipids, including triacylglycerols (TGs), diacylglycerols (DGs), cholesteryl esters (CEs), glycerophospholipids (GPs), and other components, could be directly obtained by GCM-assisted LDI MS without extraction. Five machine learning methods were applied to distinguish liver cancer (LC) patients from healthy controls (HC) and chronic hepatitis B (CHB) patients. The best diagnostic performance was attained by linear discriminant analysis (LDA), which has a confusion matrix accuracy of 98.3 %. The receiver operating characteristic (ROC) curve for liver cancer exhibited an area under the curve (AUC) of 0.99, indicating a high degree of prediction accuracy. One-way ANOVA analysis revealed that numerous TGs were down-regulated in LC group. The results demonstrated the viability of GCM-assisted LDI MS as a valuable diagnostic tool for liver cancer.

Imaging Analysis of Phosphatidylcholines and Diacylglycerols Using Surface-Assisted Laser Desorption/Ionization Mass Spectrometry with Metal Film Formed by Mist Chemical Vapor Deposition.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has been widely used for analyses of biomolecules and industrial materials. Surface-assisted laser desorption/ionization (SALDI) is studied to complement the ionization ability for the MALDI/MS. In this study, lab-made mist chemical vapor deposition (mist CVD) system was used to produce metal films as ionization assistance materials for SALDI/MS. The system could give Ag film from inexpensive silver trifluoroacetate solution rapidly and simply under atmospheric pressure. Phosphatidylcholines could be detected high sensitively and diacylglycerols (DAGs) could not be detected in MALDI/MS. In the SALDI/MS and the MS imaging with Ag film by mist CVD, both the phosphatidylcholines and the DAGs could be detected and the localized images. In the Ag film-SALDI/MS of lipids, not only Ag-adducted ions but also Na- and K-adducted ions were detected. The Ag film formed by the mist CVD to act as an ionization-assistance material and a cationization agent in SALDI would be useful in MS imaging of biological tissue sections.

Advances in thin layer chromatography coupled with mass spectrometry technology

Thin layer chromatography (TLC) is a very useful liquid chromatography approach. The simple device, convenient operation, versatility, high throughput capabilities, low cost, and simple sample pretreatments make it widely employed in various fields. In recent years, TLC-MS has become one of the most prominent trends for this technology as developments of modern analytical technology and comprehensive application of different approaches. With the development and upgrading of medicine, food, and scientific instrument industries, it is believed that TLC-MS technology should play a better role and obtain an opportunity for development. This study reviewed TLC-MS interface technologies (most of which are in recent 10 years) based on more than 150 studies and classified these TLC-MS technologies as three strategies. The first is indirect coupling using commercially available interface instruments. The second is TLC-in-site detection directly with special MS ion source devices like fast-atom-bombardment desorption ionization, matrix-assisted laser desorption ionization, surface-assisted laser desorption ionization, electrospray-assisted laser desorption ionization, laser-induced acoustic desorption/electrospray ionization, electrostatic-spray ionization, easy ambient sonic-spray ionization, desorption sonic spray ionization, ionization using "desorption/ionization resource", ionization using "molecular ionization-desorption analysis source", multiwavelength laser desorption ionization, ionization using flowing afterglow-atmospheric pressure glow discharge, ionization low-temperature plasma probe, desorption/ionization induced using neutral clusters, ionization using inductively coupled plasma and so on. These MS analyses are performed after TLC development, thus, the relative position of the chromatographic bands on TLCs is invariable, and this analysis can be regarded as static detection, though flexible travel stages or conveyor belts can be introduced to move TLC plates. The third strategy is to monitor TLC run using MS in real-time just as the monitor employed in HPLC, in which the chromatographic bands are still moving. This strategy is generally run on forced-flow TLC techniques and is less examined. The typical coupling technologies (especially appeared in recent ten years) are summarized and briefly described in this study. TLC-MS has greatly enhanced the research efficiency of bioactive substances for food and drugs due to the widespread usage of TLC-bioautography technology. Nowadays, the main bottleneck in the development of TLC-MS is the design and commercialization of "plug and play" components. The high-throughput and real-time monitoring TLC-MS technology with flexible scanning functions is also expected. Furthermore, the comparative studies of different kinds of desorbing-ionizing technologies are also application problems for further discussion.

Titania Nanosheet as a Matrix for Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Analysis and Imaging.

Surface-assisted laser desorption/ionization (SALDI) acts as a soft desorption/ionization technique, which has been widely recognized in small-molecule analysis owing to eliminating the requirement of the organic matrix. Herein, titania nanosheets (TiO2 NSs) were applied as novel substrates for simultaneous analysis and imaging of low-mass molecules and lipid species. A wide variety of representative analytes containing amino acids, bases, drugs, peptides, endogenous small molecules, and saccharide-spiked urine were examined by the TiO2 NS-assisted LDI mass spectrometry (MS). Compared with conventional organic matrices and substrates [Ag nanoparticles (NPs), Au NPs, carbon nanotubes, carbon NPs, CeO2 microparticles, and P25 TiO2], the TiO2 NS-assisted LDI MS method shows higher sensitivity and less spectral interference. Repeatability was evaluated with batch-to-batch relative standard deviations for 5-hydroxytryptophan, glucose-spiked urine, and glucose with addition of internal standard, which were 17.4, 14.9, and 2.8%, respectively. The TiO2 NS-assisted LDI MS method also allows the determination of blood glucose levels in mouse serum with a linear range of 0.5-10 mM. Owing to the nanoscale size and uniform deposition of the TiO2 NS matrix, spatial distributions of 16 endogenous small molecules and 16 lipid species from the horizontal section of the mouse brain tissue can be visualized at a 50 μm spatial resolution. These successful applications confirm that the TiO2-assisted LDI MS method has promising prospects in the field of life science.

UV-Absorbing Ligand Capped Gold Nanoparticles for the SALDI-MS Analysis of Small Molecules.

We report that modifying the surface of gold nanoparticles (Au NPs) with 2-mercaptopyridine-3-carboxylic acid (MPyCA) enhances surface-assisted laser desorption/ionization (SALDI) performance in the analysis of small molecules. The MPyCA ligand has a strong UV absorbance at the wavelengths of the typical MALDI laser at 337 nm, resulting in efficient thermal/energy transfer from the Au NPs to analytes during pulse-laser irradiation. In addition, the MPyCA ligand contains carboxylic acid and pyridine groups, providing affinity to various analytes through acid-base interactions. Irganox1010, glucose and meropenem were utilized as model analytes to evaluate SALDI performance because these molecules are generally ionized with difficulty by conventional MALDI-MS. Our results demonstrate that the MPyCA-Au NP based SALDI-MS could detect Irganox1010, glucose and meropenem with stronger ion peaks for these molecules compared to MALDI-MS using CHCA. The limit of detection (LOD) for meropenem was much lower in the case of SALDI (LOD=1 ng/mL) compared to MALDI (LOD=10 μg/mL).

Application of Iron Oxide Nanoparticles in the Surface-Assisted Laser Desorption and Ionization–Mass Spectrometry of Small-Molecule Compounds

Iron oxide nanoparticles were applied to the surface-assisted laser desorption and ionization–mass spectrometry (SALDI–MS) of small-molecule compounds, such as oligosaccharides, phytohormones, flavonoids, triglycerides, phospholipids, and amino acids. The spatial distribution of small-molecule compounds in soybean was further studied by using imaging mass spectrometry. After different preparation methods were compared, iron oxide nanoparticles calcined at 300 °C were selected. Results showed that in SALDI–MS analysis, iron oxide nanoparticles were characterized by good stability and low background noise. Analysis was performed in the positive ion mode at the laser energy of 70% with the average spectrum accumulated 30 times. The results showed that iron oxide nanoparticles had good repeatability and sensitivity in the analysis of the abovementioned small-molecule compounds. Four samples, namely, sucrose, abscisic acid, DL-aspartic acid, and 1,2-dipalmitoyl-sn-glycerol-3-phosphorylcholine, were analyzed via SALDI–MS. The spot-to-spot repeatability RSD was less than 2.8%, and the interpoint repeatability RSD was less than 5.2%. The linear correlation coefficient of the four samples was R2 > 0.993 within the concentration range of 0.05–1.0 mg/mL. On the basis of these results, the distribution of small-molecule components in soybean cotyledon, radicle, and germ was analyzed through SALDI–MSI.

Quantitative analysis capability of DIUTHAME mass spectrometry verified by acetylcholinesterase enzyme-catalyzed reaction assays.

Matrix-assisted laser desorption/ionization (MALDI) is advantageous for mass spectrometry applications where throughput is important. However, quantitative analysis is essentially problematic for MALDI-MS whose results depend on the intrinsically stochastic microcrystalline state of the matrix. High-throughput screening (HTS) of drug candidates is a typical example that requires high throughput. The application of MALDI-MS to HTS, which is quantitative analysis, imposes restrictions on designing an experimental system. Surface-assisted laser desorption/ionization (SALDI) methods, which do not depend on matrix crystal formation, are expected to be applied to quantitative analyses such as HTS. A recently developed one type of SALDI methods, desorption ionization using through hole alumina membrane (DIUTHAME), possesses a distinct feature that the surface microstructure effective for ionization is formed by through holes. In this study, the quantitative analysis capability of DIUTHAME was verified by applying DIUTHAME to enzyme-catalyzed reaction measurements, which are also used for HTS. Quantitative DIUTHAME-MS was conducted on various conditions of acetylcholinesterase-catalyzed reaction solutions containing cow milk as a substitute of biological media. Even for the enzyme-catalyzed reaction solutions containing complex additives that make the quantitative analysis extremely difficult, DIUTHAME based on the through hole structure enables quantitative measurements of the analytes by applying the reaction solutions to the back side of the laser exposed surface. In comparison with those obtained by MALDI-MS, the results obtained by DIUTHAME-MS showed less variability of data and delivered a better linearity of the Lineweaver-Burk plots and a more reasonable value of the Michaelis constant. Accordingly, it was demonstrated that DIUTHAME-MS possesses the quantitative analysis capability much better than that of MALDI-MS.

Mapping Molecular Signatures in Plant Leaves, Flowers, and Fruits by a TiO2 Nanotube-Based Plasmonic Chip for Imprint Mass Spectrometry Imaging

Mapping molecular signatures within a fragile leaf or flower of medicinal plants with mass spectrometry imaging (MSI) techniques is crucial in plant biology yet remains a great challenge due to the inability to slice such samples. Herein, we constructed a composite substrate, hydrophobic polydopamine-modified TiO2 nanotube coated with plasmonic gold nanoparticle (AuNP-hPDA-TDNT) and exploited its potential as a surface-assisted laser desorption/ionization (SALDI) substrate for imprinting/stamping MSI analysis. With the integrated advantages of satisfactory imprinting/stamping capability and enhanced ion production, this AuNP-hPDA-TDNT substrate-based SALDI-MSI exhibits remarkable performance in mapping tissue-specific distribution patterns of functional metabolites in medicinal plant (i.e., Catharanthus roseus, Ginkgo biloba, and Jatropha integerrima) leaves/flowers and fruits (i.e., strawberry and cherry tomato) regardless of tedious sample preparation. Collectively, we believe that this functionalized TiO2 nanotube substrate will expand the scope of SALDI-MSI in plant science, providing more biologically relevant insights into the functions and mechanisms of plant systems.

Peptide Mass Spectra from Micrometer-Thick Ice Films Produced with Femtosecond Pulses

We present a cryogenic mass spectrometry protocol with the capability to detect peptides in the attomole dilution range from ice films. Our approach employs femtosecond laser pulses and implements neither substrate modification nor proton donor agents in the aqueous solution, known to facilitate analyte detection in mass spectrometry. In a systematic study, we investigated the impact of temperature, substrate composition, and irradiation wavelength (513 and 1026 nm) on the bradykinin signal onset. Our findings show that substrate choice and irradiation wavelength have a minor impact on signal intensity once the preparation protocol is optimized. However, if the temperature is increased from −140 to 0 °C, which is accompanied by ice film thinning, a somehow complex picture of analyte desorption and ionization is recognizable, which has not been described in the literature yet. Under cryogenic conditions (−140 °C), obtaining a signal is only possible from isolated sweet spots across the film. If the thin ice film is between −100 and −70 °C of temperature, these sweet spots appear more frequently. Ice sublimation triggered by temperatures above −70 °C leads to an intense and robust signal onset that could be maintained for several hours. In addition to the above findings, we notice that a vibrant fragmentation pattern produced is strikingly similar with both wavelengths. Our findings suggest that while following an optimized protocol, femtosecond mass spectrometry has excellent potential to analyze small organic molecules and peptides with a mass range of up to 2.5 kDa in aqueous solution without any matrix, as employed in matrix-assisted laser desorption/ionization (MALDI) or any substrate surface modification, found in surface-assisted laser desorption/ionization (SALDI).

Aptamer-conjugated graphene oxide-based surface assisted laser desorption ionization mass spectrometry for selective extraction and detection of Aβ1-42 in an Alzheimer's disease SH-SY5 cell model.

The generation and accumulation of amyloid-beta peptide (Aβ1–42) in amyloid plaques are key characteristics of Alzheimer’s disease (AD); thus, specific detection of Aβ1–42 is essential for the diagnosis and treatment of AD. Herein, an aptamer-conjugated graphene oxide (Apt-GO) sensor was synthesized by π-π and hydrophobic interactions using thiol poly (ethylene glycol) amine (SH-PEG-NH2) as a spacer unit. Then, it was applied to selective capture of Aβ1–42, and the resulting complex was directly analyzed by surface-assisted laser desorption ionization mass spectrometry (SALDI-MS). The results revealed that the Apt-GO could enhance the detection specificity and reduce non-specific adsorption. This method was validated to be sensitive in detecting Aβ1–42 at a low level in human serum (ca. 0.1 μM) within a linear range from 0.1 to 10 μM. The immobilizing amount of aptamer on the GO was calculated to be 36.1 nmol/mg (RSD = 11.5%). In conclusion, this Apt-GO-based SALDI-MS method was sensitive and efficient in selective extraction and detection of Aβ1–42, which proved to be a good option for early AD diagnosis.

Isolation and Identification of Lactococcus lactis and Weissella cibaria Strains from Fermented Beetroot and an Investigation of Their Properties as Potential Starter Cultures and Probiotics.

The presence of certain microorganisms in dairy products or silage is highly desirable. Among them are probiotic strains of lactic acid bacteria (LAB), which show many beneficial features, including antimicrobial properties that support the development of beneficial microflora; in addition, owing to their biochemical activity, they influence the nutritional, dietary, and organoleptic properties of food products. Before being placed on the market, each strain requires separate testing to determine its probiotic properties and effectiveness. The aim of this study was to isolate LAB strains from a pickled beetroot sample that could be used in the dairy industry and with the potential to be considered as a probiotic in the future. Two strains identified using the MALDI technique were selected—Lactococcus lactis and Weissella cibaria. The optimal growth conditions of the strains were determined, and their proteolytic properties were assessed with the use of the o-PA reagent and spectrophotometry. The lipid profile was analyzed using the SALDI (surface-assisted laser desorption/ionization) technique and silver nanoparticles. High-performance liquid chromatography was used to assess the ability of the strains to synthesize beneficial metabolites, such as B vitamins (B2, B3, and B9) or lactic acid, and gas chromatography was used to analyze the substances responsible for organoleptic properties. Moreover, the ability to inhibit the growth of pathogenic strains was also tested in the selected strains. Both tested strains demonstrated the desired properties of starter cultures for future use in functional food production, showing that fermented plant products can serve as valuable potential probiotic sources.

Molecularly imprinted polymers based on magnetic metal-organic frameworks for surface-assisted laser desorption/ionization time-of-flight mass spectrometry analysis and simultaneous luteolin enrichment

UiO-66(NH2), a metal-organic framework, exhibits excellent UV absorption and energy transfer performance and can be used as a substrate for surface-assisted laser desorption/ionization (SALDI) analysis of small molecules. Molecularly imprinted polymers (MIPs) exhibit outstanding selectivity toward certain targets. The complexes of UiO-66(NH2) and MIPs can be applied as both an adsorbent and substrate for SALDI-time-of-flight mass spectrometry (SALDI-TOF MS) analysis of small molecules. Herein, magnetic UiO-66(NH2)-molecularly imprinted polymers (MUMIPs) were prepared for the selective enrichment and detection of luteolin via SALDI-TOF MS. The amino group on UiO-66(NH2) were used as functional monomer to prepare MIPs that interact with luteolin via hydrogen bonding. The surface functional monomer can effectively control the coating thickness of the MIPs to avoid embedding template molecules and enhance adsorption performance. In addition, Fe3O4 particles were introduced for rapid magnetic separation. The physicochemical properties of the MUMIPs were characterized via scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, vibrating sample magnetometry, Brunauer-Emmett-Teller analysis, and X-ray photoelectron spectroscopy. Adsorption experiments and selectivity studies indicated that MUMIPs exhibited good adsorption capacity, fast adsorption rates, and excellent luteolin selectivity. MUMIPs are efficient substrates for the SALDI analysis of luteolin and its structural analogs. In addition, the MUMIPs-SALDI-TOF MS method successfully detected luteolin in rat plasma and urine after administration of oral Chrysanthemum morifolium Ramat extracts. This method possessed high sensitivity with a limit of detection of 0.5 ng/mL. The traditional precipitation method combined with high-performance liquid chromatography-mass spectrometry was also used to analyze luteolin in biological samples. Compared with the traditional method, the novel MUMIP-SALDI-TOF MS method can more effectively detect the target compounds in complex samples. Ultimately, the MUMIP-SALDI-TOF MS method was applied to detect luteolin and its metabolites in rat liver after oral luteolin treatment. Three luteolin metabolites (apigenin, chrysoeriol, and diosmetin) were analyzed using the newly developed MUMIP-SALDI-TOF MS method.

Nanostructured Layer of Silver for Detection of Small Biomolecules in Surface-Assisted Laser Desorption Ionization Mass Spectrometry.

A facile approach for the synthesis of a silver nanostructured layer for application in surface-assisted laser desorption/ionization mass spectrometry of low-molecular-weight biomolecules was developed using electrochemical deposition. The deposition was carried out using the following silver salts: trifluoroacetate, acetate and nitrate, varying the voltage and time. The plate based on trifluoroacetate at 10 V for 15 min showed intense SALDI-MS responses for standards of various classes of compounds: fatty acids, cyclitols, saccharides and lipids at a concentration of 1 nmol/spot, with values of the signal-to-noise ratio ≥50. The values of the limit of detection were 0.71 µM for adonitol, 2.08 µM for glucose and 0.39 µM for palmitic acid per spot. SEM analysis of the plate showed anisotropic flower-like microstructures with nanostructures on their surface. The reduced chemical background in the low-mass region can probably be explained by the absence of stabilizers and reducing agents during the synthesis. The plate synthesized with the developed approach showed potential for future use in the analysis of low-molecular-weight compounds of biological relevance. The absence of the need for the utilization of sophisticated equipment and the synthesis time (10 min) may benefit large-scale applications of the layer for the detection of various types of small biomolecules.

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.