Combining Salt Doping and Matrix Sublimation for High Spatial Resolution MALDI Imaging Mass Spectrometry of Neutral Lipids

Diagnosis and prognosis prediction of gastric cancer by high-performance serum lipidome fingerprints

Early detection is warranted to improve prognosis of gastric cancer (GC) but remains challenging. Liquid biopsy combined with machine learning will provide new insights into diagnostic strategies of GC. Lipid metabolism reprogramming plays a crucial role in the initiation and development of tumors. Here, we integrated the lipidomics data of three cohorts (n = 944) to develop the lipid metabolic landscape of GC. We further constructed the serum lipid metabolic signature (SLMS) by machine learning, which showed great performance in distinguishing GC patients from healthy donors. Notably, the SLMS also held high efficacy in the diagnosis of early-stage GC. Besides, by performing unsupervised consensus clustering analysis on the lipid metabolic matrix of patients with GC, we generated the gastric cancer prognostic subtypes (GCPSs) with significantly different overall survival. Furthermore, the lipid metabolic disturbance in GC tissues was demonstrated by multi-omics analysis, which showed partially consistent with that in GC serums. Collectively, this study revealed an innovative strategy of liquid biopsy for the diagnosis of GC on the basis of the serum lipid metabolic fingerprints.

Expanding Spatial Metabolomics Coverage with Lithium-Doped Nanospray Desorption Electrospray Ionization Mass Spectrometry Imaging

Spatial metabolomics has emerged as a powerful tool capable of revealing metabolic gradients throughout complex heterogeneous tissues. While mass spectrometry imaging (MSI) technologies designed to generate spatial metabolomic data have improved significantly over time, metabolite coverage is still a significant limitation. It is possible to achieve deeper metabolite coverage by imaging in positive and negative polarities or imaging several serial sections with different targeted biomolecular classes. However, this significantly increases the number of tissue samples required for biological studies and reduces the capacity for larger sample cohorts. Herein, we introduce lithium-doped nanospray desorption electrospray ionization (nano-DESI) as a simple and robust method to increase spatial metabolomics coverage, which is achieved through enhancements to ionization efficiencies in positive ion mode for metabolites and lipids lacking basic moieties, and improved structurally diagnostic tandem mass spectra for [M + Li]+ adducts. Specifically, signal intensities were found to be enhanced by 10-1000× for 96 compounds including small molecule metabolites, fatty acids, neutral lipids (e.g., diacylglycerols, DAG), and phospholipids when lithium was added to the ESI solvent. In addition, proof-of-principle results reveal that lithium-doped nano-DESI MSI was able to comprehensively visualize metabolites and lipids in the prostaglandin (PG) biosynthetic pathway with PG isomeric resolution in an ovarian tumor section. These data show colocalization of fatty acid (FA) 20:4 containing DAGs, FA 20:4 monoacylglycerols (MAGs), and FA 20:4 with PGE2 and disparate localizations of PGD2. Overall, this study describes a simple and powerful approach to more comprehensively probe the spatial metabolome with MSI.

Thermal evaporation as sample preparation for silver-assisted laser desorption/ionization mass spectrometry imaging of cholesterol in amyloid tissues

Cholesterol plays an important biological role in the body, and its disruption in homeostasis and synthesis has been implicated in several diseases. Mapping the locations of cholesterol is crucial for gaining a better understanding of these conditions. Silver deposition has proven to be an effective method for analyzing cholesterol using mass spectrometry imaging (MSI). We optimized and evaluated thermal evaporation as an alternative deposition technique to sputtering for silver deposition in MSI of cholesterol. A silver layer with a thickness of 6 nm provided an optimal combination of cholesterol signal intensity and mass resolution. The deposition of an ultrathin nanofilm of silver enabled high-resolution MSI with a pixel size of 10 μm. We used this optimized method to visualize the distribution of cholesterol in the senile plaques in the brains of APP/PS1 mice, a model that resembles Alzheimer's disease pathology. We found that cholesterol was evenly distributed across the frontal cortex tissue, with no evidence of plaque-like accumulation. Additionally, we investigated the presence and distribution of cholesterol in myocardial sections of a human heart affected by wild-type ATTR amyloidosis. We identified the presence of cholesterol in areas with amyloid deposition, but complete colocalization was not observed.

Photocatalytic degradation-based ambient mass spectrometry imaging for enhancing detection coverage of poorly-ionizable lipidomes

Localization of lipidomes and tracking their spatial changes in tissues by mass spectrometry imaging (MSI) plays an important role in unveiling the mechanisms of living processes, diseases and therapeutic treatments. However, it is always challenging to achieve direct MSI of poorly-ionizable lipids, such as glycolipids and glycerolipids, due to the strong ion suppression and isobaric peaks interference from high-abundance phosphatidylcholines (PCs) in tissues. Here we developed a photocatalytic degradation-based ambient liquid extraction MSI method to largely enhance the detection coverage of poorly-ionizable lipids by rapid online removal of PCs in MSI. Phospholipids were found to be selectively photodegraded on TiO2 surface in acidic conditions in the presence of water under UV irradiation, while other poorly-ionizable lipids remained. Sulfate ion could largely improve the degradation efficiencies. Anatase nanoparticles-embedded TiO2 monolith was in-situ synthesized in the capillary of ambient liquid extraction system, and rapid online photodegradation of PCs was achieved during MSI with efficiency >80 %, largely reducing ion suppression. The pathway analysis showed that PC was oxidatively degraded starting from hydroxylation of C=C bonds. With intense UV irradiation, PCs were completely degraded into small molecules<200 Da without interference on the detection of endogenous lipids. With the new MSI method, detection coverage to cerebrosides, ceramides and diglycerides was enhanced by 2-9 times comparing with traditional MSI. Clearer localizations were observed for poorly-ionizable lipids via the new method than traditional method. Thus, this work provided a complementary MSI method for traditional MSI to address the issues on direct imaging of poorly ionizable lipids in ambient conditions.

Metabolic insights from mass spectrometry imaging of biofilms: A perspective from model microorganisms

Biofilms are dense aggregates of bacterial colonies embedded inside a self-produced polymeric matrix. Biofilms have received increasing attention in medical, industrial, and environmental settings due to their enhanced survival. Their characterization using microscopy techniques has revealed the presence of structural and cellular heterogeneity in many bacterial systems. However, these techniques provide limited chemical detail and lack information about the molecules important for bacterial communication and virulence. Mass spectrometry imaging (MSI) bridges the gap by generating spatial chemical information with unmatched chemical detail, making it an irreplaceable analytical platform in the multi-modal imaging of biofilms. In the last two decades, over 30 species of biofilm-forming bacteria have been studied using MSI in different environments. The literature conveys both analytical advancements and an improved understanding of the effects of environmental variables such as host surface characteristics, antibiotics, and other species of microorganisms on biofilms. This review summarizes the insights from frequently studied model microorganisms. We share a detailed list of organism-wide metabolites, commonly observed mass spectral adducts, culture conditions, strains of bacteria, substrate, broad problem definition, and details of the MS instrumentation, such as ionization sources and matrix, to facilitate future studies. We also compared the spatial characteristics of the secretome under different study designs to highlight changes because of various environmental influences. In addition, we highlight the current limitations of MSI in relation to biofilm characterization to enable cross-comparison between experiments. Overall, MSI has emerged to become an important approach for the spatial/chemical characterization of bacterial biofilms and its use will continue to grow as MSI becomes more accessible.

Advances in mass spectrometry imaging for spatial cancer metabolomics

Mass spectrometry (MS) has become a central technique in cancer research. The ability to analyze various types of biomolecules in complex biological matrices makes it well suited for understanding biochemical alterations associated with disease progression. Different biological samples, including serum, urine, saliva, and tissues have been successfully analyzed using mass spectrometry. In particular, spatial metabolomics using MS imaging (MSI) allows the direct visualization of metabolite distributions in tissues, thus enabling in-depth understanding of cancer-associated biochemical changes within specific structures. In recent years, MSI studies have been increasingly used to uncover metabolic reprogramming associated with cancer development, enabling the discovery of key biomarkers with potential for cancer diagnostics. In this review, we aim to cover the basic principles of MSI experiments for the nonspecialists, including fundamentals, the sample preparation process, the evolution of the mass spectrometry techniques used, and data analysis strategies. We also review MSI advances associated with cancer research in the last 5 years, including spatial lipidomics and glycomics, the adoption of three-dimensional and multimodal imaging MSI approaches, and the implementation of artificial intelligence/machine learning in MSI-based cancer studies. The adoption of MSI in clinical research and for single-cell metabolomics is also discussed. Spatially resolved studies on other small molecule metabolites such as amino acids, polyamines, and nucleotides/nucleosides will not be discussed in the context.

Spatial neurolipidomics-MALDI mass spectrometry imaging of lipids in brain pathologies

Given the complexity of nervous tissues, understanding neurochemical pathophysiology puts high demands on bioanalytical techniques with respect to specificity and sensitivity. Mass spectrometry imaging (MSI) has evolved to become an important, biochemical imaging technology for spatial biology in biological and translational research. The technique facilitates comprehensive, sensitive elucidation of the spatial distribution patterns of drugs, lipids, peptides, and small proteins in situ. Matrix-assisted laser desorption ionization (MALDI)-based MSI is the dominating modality due to its broad applicability and fair compromise of selectivity, sensitivity price, throughput, and ease of use. This is particularly relevant for the analysis of spatial lipid patterns, where no other comparable spatial profiling tools are available. Understanding spatial lipid biology in nervous tissue is therefore a key and emerging application area of MSI research. The aim of this review is to give a concise guide through the MSI workflow for lipid imaging in central nervous system (CNS) tissues and essential parameters to consider while developing and optimizing MSI assays. Further, this review provides a broad overview of key developments and applications of MALDI MSI-based spatial neurolipidomics to map lipid dynamics in neuronal structures, ultimately contributing to a better understanding of neurodegenerative disease pathology.

Sodium doping and trapped ion mobility spectrometry improve lipid detection for novel MALDI-MSI analysis of oats

Oat (Avena sativa L.) is an important cereal grain with a unique nutritional profile including a high proportion of lipids. Understanding lipid composition and distribution in oats is valuable for plant, food and nutritional research, and can be achieved using MALDI mass spectrometry imaging (MALDI-MSI). However, this approach presents several challenges for sample preparation (hardness of grains) and analysis (isobaric and isomeric properties of lipids). Here, oat sections were successfully mounted onto gelatin-coated indium tin oxide slides with minimal tearing. Poor detection of triacylglycerols was resolved by applying sodium chloride during mounting, increasing signal intensity. In combination with trapped ion mobility spectrometry (TIMS), lipid identification significantly improved, and we report the separation of several isobaric and isomeric lipids with visualisation of their "true" spatial distributions. This study describes a novel MALDI-TIMS-MSI analytical technique for oat lipids, which may be used to improve the discovery of biomarkers for grain quality.

Lewis Acidic Metal-Organic Framework Assisted Ambient Liquid Extraction Mass Spectrometry Imaging for Enhancing the Coverage of Poorly Ionizable Lipids in Brain Tissue

The spatial distribution of lipidomes in tissues is of great importance in studies of living processes, diseases, and therapies. Mass spectrometry imaging (MSI) has become a critical technique for spatial lipidomics. However, MSI of low-abundance or poorly ionizable lipids is still challenging because of the ion suppression from high-abundance lipids. Here, a metal-organic framework (MOF) Zr6O4(OH)4(1,3,5-Tris(4-carboxyphenyl) benzene)2(triflate)6(Zr6OTf-BTB) was prepared and used for selective on-tissue adsorption of phospholipids to reduce ion suppression from them to poorly ionizable lipids. The results show that Zr6OTf-BTB with strong Lewis acidic sites and a large specific surface area (647.9 m2·g-1) could selectively adsorb phospholipids under 1% FA-MeOH. Adsorption efficiencies of phospholipids are 88.4-144.9 times higher than those of other neutral lipids. Moreover, the adsorption capacity and the adsorption kinetic rate constant of the new material to phospholipids are higher than those of Zr6-BTB (242.72 vs 73.96 mg·g-1, 0.0442 vs 0.0220 g·mg-1·min-1). A Zr6OTf-BTB sheet was prepared by a lamination technique for on-tissue phospholipid adsorption from brain tissue. Then, the tissue section on the Zr6OTf-BTB sheet was directly imaged via ambient liquid extraction-MSI with 1% FA-MeOH as the sampling solvent. The results showed that phospholipids could be 100% removed directly on tissue, and the detection coverage of the Zr6OTf-BTB-enhanced MSI method to ceramides (Cers) and hexosylceramides (HexCers) was increased by 5-26 times compared with direct tissue MSI (26 vs 1 and 17 vs 3). The new method provides an efficient and convenient way to eliminate the ion suppression from phospholipids in MSI, largely improving the detection coverage of low-abundance and poorly ionizable lipids.

Pulled Flowprobe for Ambient Liquid Extraction-Based High Spatial Resolution Mass Spectrometry Imaging with Enhanced Sensitivity and Stability

Ambient liquid extraction techniques enable direct mass spectrometry imaging (MSI) under ambient conditions with minimal sample preparation. However, currently an integrated probe for ambient liquid extraction-based MSI with high spatial resolution, high sensitivity, and stability is still lacking. In this work, we developed a new integrated probe made of pulled coaxial capillaries, named pulled flowprobe, and compared it with the previously reported single-probe. Mass transfer kinetics in probes was first investigated. The extraction kinetic curves during probe sampling indicate a narrower and higher peak shape for the pulled flowprobe than single-probe. Computational fluid dynamics analysis reveals that in the pulled flowprobe flow velocities are lower in liquid microjunction and higher in the transferring channels, resulting in higher extraction efficiencies and reduced band diffusion compared with single-probe and other probes with a similar flow route. Results of ambient liquid extraction-based MSI of lipids in rat cerebrum show that signals of low-abundance lipids were 2-5 times higher via a pulled flowprobe than via a single-probe, and 26 more lipid species were detected on brain tissue via a pulled flowprobe than via a single-probe. The stability of MSI with the pulled flowprobe was found to be higher than that with single-probe (averaged relative standard deviation = 18% vs 80%) by imaging a lab-made uniform ink coating. Moreover, in the pulled flowprobe, no retraction of the inner capillary from outer capillary is optimal for both sensitivity and stability. The spatial resolution of the pulled flowprobe (30-40 μm) was measured to be higher than that of a comparable size single-probe by calculation with the "80-20" rule. Finally, the new pulled flowprobe was applied to high-resolution MSI of lipids in the hippocampus, and localization of several lipids to the specific cell layers in the hippocampus region was observed. Thus, this work provides an alternative easily fabricated sampling probe with enhanced sensitivity, stability, and spatial resolution, promoting the use of ambient liquid extraction-based MSI in biological and clinical research.

Matrix-assisted laser desorption/ionization mass spectrometry imaging sample preparation using wet-interface matrix deposition for lipid analysis

RATIONALE

Sample preparation is one of the most crucial steps for matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Scientists beginning their study with this technique may be overwhelmed by the variety of matrices, solvents, and concentrations; the methods of their applications; and the lack of widely available knowledge of the effect of these parameters on the results. Here we present in depth the aspects of matrix deposition, which will be helpful for the scientific community.

METHODS

In this study, we tested several MALDI matrices, such as 2,5-dihydroxybenzoic acid (DHB), norharmane, N-(1-naphthyl)ethylenediamine dihydrochloride (NEDC), and 9-aminoacridine (9AA), using the SunCollect system: wet-interface matrix deposition in the context of lipid analysis. We optimized the number of matrix layers and nozzle settings in terms of spectral intensity and the overall quality of the obtained ion maps.

RESULTS

Our research presents the effect of the number of matrix layers and nozzle settings on the results and allows for choosing the optimal parameters for the analyses. In positive ionization mode, DHB matrix could be chosen first. In the negative ionization mode, 1,5-diaminonaphthalene matrix produces a higher peak intensity in a lower mass range and seems to provide more information than 9AA. We recommend NEDC for particular processes such as glucose analysis. Compared to the remaining matrices, norharmane shows significant changes in the obtained ion maps.

CONCLUSIONS

Such a large amount of data allow us to observe an interesting conclusion: the obtained ion image for a particular ion could differ dramatically with a change in the matrix, the solvent composition, or even the number of matrix layers. This must be considered when interpreting the result, impelling us to compare the results obtained with different matrices with caution.

Analysis of tri-benzeneboronic esters of monosaccharides formed in aqueous solution by MALDI-TOF MS and DFT calculations

The affinity interactions between boronic acids and sugars have been successfully exploited in many fields, such as the sensing of saccharides, selective enrichment of glycoconjugates, and drug delivery. However, despite multiple techniques having been adopted to investigate the reaction of boronate affinity, the pathway of boronate esters formation under aqueous conditions remains controversial. We report a MALDI-MS approach to investigate the interactions between phenylboronic acid and monosaccharides in neutral aqueous solution by using polylevodopa as an innovative substrate instead of conventional matrix. A series of unusual tri-benzeneboronic esters were then revealed. The mass spectrometry data indicate that they bear a dibenzenepyroboronate cyclic ester moiety with seven-membered ring or eight-membered ring. With the aid of theoretical computations, their most likely geometrical structures are elucidated, and these tri-benzeneboronic esters are proposed to be formed via a boroxine binding monosaccharide pathway. This work provides more insight into the mechanism of boronate affinity interaction between boronic acid and sugars and proves the developed MALDI-MS approach is promising for studying interactions between small molecules.

Lipidomic Profiling of PFOA-Exposed Mouse Liver by Multi-Modal Mass Spectrometry Analysis

Perfluorooctanoic acid (PFOA) is a synthetic perfluorinated chemical classified as a persistent organic pollutant. PFOA has been linked to many toxic effects, including liver injury. Many studies report that PFOA exposure alters serum and hepatic lipid metabolism. However, lipidomic pathways altered by PFOA exposure are largely unknown and only a few lipid classes, mostly triacylglycerol (TG), are usually considered in lipid analysis. Here, we performed a global lipidomic analysis on the liver of PFOA-exposed (high-dose and short-duration) and control mice by combining three mass spectrometry (MS) techniques: liquid chromatography with tandem mass spectrometry (LC-MS/MS), matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Among all hepatic lipids identified by LC-MS/MS analysis, more than 350 were statistically impacted (increased or decreased levels) after PFOA exposure, as confirmed by multi-variate data analysis. The levels of many lipid species from different lipid classes, most notably phosphatidylethanolamine (PE), phosphatidylcholine (PC), and TG, were significantly altered. Subsequent lipidomic analysis highlights the pathways significantly impacted by PFOA exposure, with the glycerophospholipid metabolism being the most impacted, and the changes in the lipidome network, which connects all the lipid species together. MALDI-MSI displays the heterogeneous distribution of the affected lipids and PFOA, revealing different areas of lipid expression linked to PFOA localization. TOF-SIMS localizes PFOA at the cellular level, supporting MALDI-MSI results. This multi-modal MS analysis unveils the lipidomic impact of PFOA in the mouse liver after high-dose and short-term exposure and opens new opportunities in toxicology.

The influence of matrix concentration and solvent composition on the results of MALDI MSI, with the aid of wet-interface matrix deposition

Imaging mass spectrometry is a powerful technique for the molecular analysis of tissue sections. As in many analytical methods, sample preparation is one of the main and most important steps to obtain results of good quality. Usually, the matrix concentration and solvent composition in different studies are taken for granted without any further consideration. In our studies, we aimed to find how matrix concentration and a type of solvent influence the signal. Moreover, we also aimed to find the relationship between these parameters, how they influence the spectra, and how they influence obtained ion maps. In our experiments, we used SunCollect®, which is a commercially available wet-interface system for matrix deposition. We decided to choose two matrix concentrations (2,5-dihydroxybenzoic acid [DHB]: 15 and 25 mg/mL; 9-aminoacridine [9AA]: 7 and 5 mg/mL) and two different water solutions of solvents in two different percentages for the matrices (DHB: 50% and 70% of methanol [MeOH] and acetonitrile [ACN]; 9AA 70% and 50% of ethanol [EtOH] and MeOH). In the end, the influence of these parameters on obtained spectra and ion maps was assessed.

Direct introduction MALDI FTICR MS based on dried droplet deposition applied to non-targeted metabolomics on Pisum Sativum root exudates

Non-targeted metabolomic approaches based on direct introduction (DI) through a soft ionization source are nowadays used for large-scale analysis and wide cover-up of metabolites in complex matrices. When coupled with ultra-high-resolution Fourier-Transform ion cyclotron resonance (FTICR MS), DI is generally performed through electrospray (ESI), which, despite the great analytical throughput, can suffer of matrix effects due to residual salts or charge competitors. In alternative, matrix assisted laser desorption ionization (MALDI) coupled with FTICR MS offers relatively high salt tolerance but it is mainly used for imaging of small molecule within biological tissues. In this study, we report a systematic evaluation on the performance of direct introduction ESI and MALDI coupled with FTICR MS applied to the analysis of root exudates (RE), a complex mixture of metabolites released from plant root tips and containing a relatively high salt concentration. Classic dried droplet deposition followed by screening of best matrices and ratio allowed the selection of high ranked conditions for non-targeted metabolomics on RE. Optimization of MALDI parameters led to improved reproducibility and precision. A RE desalted sample was used for comparison on ionization efficiency of the two sources and ion enhancement at high salinity was highlighted in MALDI by spiking desalted solution with inorganic salts. Application of a true lyophilized RE sample exhibited the complementarity of the two sources and the ability of MALDI in the detection of undisclosed metabolites suffering of matrix effects in ESI mode.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Porous Graphitic Carbon-Based Imprint Mass Spectrometry Imaging with an Ambient Liquid Extraction Technique for Enhancing Coverage of Glycerolipids and Sphingolipids in Brain Tissue

Localization of lipidomes and tracking their spatial changes by mass spectrometry imaging (MSI) is critical for the mechanism studies on living process, disease, and therapeutic treatment. However, due to the strong ion suppression in complex biotissue, the imaging coverage for lipids with low polarity or low abundances, such as glycerolipids and sphingolipids, is usually limited. To address this issue, we utilized a porous graphitic carbon (PGC) material to imprint brain tissue sections for selective enrichment of neutral lipids with polar phospholipids removed. Then, the tissue imprint was scanned for desorption by the ambient liquid extraction MSI system. It was found that on the PGC surface, hydrophobic interaction dominates in protic solvents, and polar interaction dominates in aprotic solvents. Accordingly, methanol was selected as the spray solvent for tissue imprinting, and 75% acetonitrile-methanol was selected as the desorption solvent for the ambient liquid extraction MSI system. The results showed that glycerides had high recoveries after the imprinting-desorption process (recovery ∼ 70%) with phospholipids eliminated (recovery < 7%). To increase the transferring efficiencies of lipids from tissue onto PGC, electrospray was used for solvent application during imprinting, and the signals of diglycerides (DGs) in the imprint MSI of brain tissue increased by 2-3 times as compared to those via air spray. Finally, the new imprint MSI approach was applied to the imaging of the rat cerebellum and was compared with direct tissue MSI. The results showed that with imprint MSI, the coverage of DGs, sphingomyelins (SMs), and ceramides was enhanced by 4-5-fold (32 vs 6, 4 vs 1, and 5 vs 0). The ion images showed that with imprint MSI, higher signal intensities and clearer spatial distribution of DGs and SMs were obtained without interference from phosphatidylcholine signals compared with tissue MSI. This new method provides a complementary approach for traditional MSI to address the issues in imaging poorly ionizable or low-abundance lipids.

A Matrix Sublimation Device with an Integrated Solvent Nebulizer for MALDI-MSI

The current matrix deposition methods in MALDI-mass spectrometry imaging (MALDI-MSI) face technical problems related to the inhomogeneous distribution of crystals and the low analyte extraction and cocrystallization efficiency. In this work, an integrated matrix sublimation device with synchronous solvent nebulization was developed for MALDI-MSI. Droplets of solvents were directly introduced into the chamber of the sublimator by using a miniaturized ultrasonic nebulizer unit. The synchronous and asynchronous working modes of solvent nebulization and matrix sublimation were systematically investigated. Imaging of both protein and small metabolite distributions in mouse brain tissue sections was successfully performed using the developed matrix deposition device. The sensitivity and quality of the images were clearly improved in synchronous mode compared with those of the conventional spray and sublimation methods. These results demonstrate that the integrated device with both solvent nebulization and matrix sublimation is a useful tool in MALDI-MSI applications.

Metal-Assisted Laser Desorption Ionization Imaging Mass Spectrometry

Matrix-assisted laser desorption ionization (MALDI) remains the reference method to generate molecular images of proteins and lipids within thin tissue sections. However, traditional MALDI imaging mass spectrometry (IMS) suffers from low matrix homogeneity and high signal background in low mass range caused by matrix signals. To overcome these issues, alternative workflow and methods have been developed. Of these, metal-assisted laser desorption ionization (LDI) has become a reference technique to ionize low molecular weight compounds while allowing IMS at very high spatial resolutions with very low background signal in the low mass range. Silver and gold remain the two most used metals for the detection of neutral lipids including cholesterol, free fatty acids, and triglycerides. In this chapter, we demonstrate the potential of metal-assisted LDI IMS through the analysis of spinal cord and kidney thin tissue sections after silver and gold metal deposition. We also detail typical step-by-step workflows and discuss the strength of the methods.

Monolithic Gold Nanoparticles/Thiol-β-cyclodextrin-Functionalized TiO2 Nanowires for Enhanced SALDI MS Detection and Imaging of Natural Products

Surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) has been successfully applied in the analysis of various small molecules. In this work, gold nanoparticles/thiol-β-cyclodextrin-functionalized TiO₂ nanowires (AuNPs/SH-β-CD-TiO₂ NWs) were prepared to enhance the performance of SALDI MS and mass spectrometry imaging (MSI). A monolithic TiO₂ film was first grown on an indium tin oxide (ITO) glass slide via a modified sol-gel method and treated in an alkaline environment to form nanowires. TiO₂ NWs were chemically modified by SH-β-CD for immobilizing AuNPs densely and strongly. Compared with the conventional organic matrix 2,5-dihydroxybenzoic acid (DHB), the prepared AuNPs/SH-β-CD-TiO₂ NWs showed superior performances on detection sensitivity, repeatability, and analyte coverage. Analytes typically detectable with negative-ion matrix-assisted laser desorption/ionization (MALDI) MS could also be observed using AuNPs/SH-β-CD-TiO₂ NWs in the positive ion mode. Its successful usage efficiently enhanced the SALDI MS detection of various small molecules such as carbohydrates, fatty acids, and bile acids in the positive ion mode. The developed SALDI substrate was further used to characterize and discriminate the natural and in vitro cultured Calculus Bovis, as well as natural and artificial Moschus. Furthermore, the spatial distribution of several natural products in spearmint leaves and potato tubers was explored by tissue imprinting and deposition on the AuNPs/SH-β-CD-TiO₂ NW surface for SALDI MSI in dual-polarity mode, respectively. The wide application and satisfied detection sensitivity make AuNPs/SH-β-CD-TiO₂ NWs ideal for SALDI MS and MSI of various natural products.

Li+ and Na+ attachment to some dipeptides via LDI-TOF mass spectrometry: Fragmentation patterns

Laser desorption ionization-time of flight (LDI-TOF) mass spectrometry is used for studying the attachment of Na⁺ and Li⁺ ions to four dipeptides including phenylalanyl-alanine (Phe-Ala), tyrosyl-alanine (Tyr-Ala), L-Phenylalanyl-L-Phenylalanine (Phe-Phe), and alanyl-glutamine (Ala-Gln) dipeptides. The LiCl, NaOH, and NaF salts are used as the source of Li⁺ and Na⁺ ions in the LDI of the dipeptides. Our aim is the investigation of the difference between the fragmentation patterns of the selected dipeptides in the presence of Na⁺ and Li⁺ ions due to the laser radiation and providing information for the fragmentation of larger peptides in the same conditions. The characteristic peak, related to [dipeptide-H + 2Na]⁺ species, is observed in the mass spectrum of Phe-Ala and Tyr-Ala dipeptides in the presence of NaF, while the breaking of the peptide bond (OC-NH) occurs for the Phe-Phe in the presence of the aforementioned salts. The characteristic peak of Ala-Gln dipeptide ([(Ala-Gln)-H + 2Na]⁺) is observed in the absence of any salt. The mass spectra of the dipeptides, recorded in the presence of LiCl, are crowded compared to those recorded in the presence of NaF and NaOH showing the effect of the type of alkali salt on the dipeptide fragmentation. The theoretical calculations are employed to investigate the ability of the interaction sites of dipeptides for the attachment of one and two Na⁺ and determine the most stable structure of the [dipeptide-H + 2Na]⁺ species for each dipeptide.

Mass spectrometry-based lipid analysis and imaging

Mass spectrometry imaging (MSI) is a powerful tool for in situ mapping of analytes across a sample. With growing interest in lipid biochemistry, the ability to perform such mapping without antibodies has opened many opportunities for MSI and lipid analysis. Herein, we discuss the basics of MSI with particular emphasis on MALDI mass spectrometry and lipid analysis. A discussion of critical advancements as well as protocol details are provided to the reader. In addition, strategies for improving the detection of lipids, as well as applications in biomedical research, are presented.

Per-pixel absolute quantitation for mass spectrometry imaging of endogenous lipidomes by model prediction of mass transfer kinetics in single-probe-based ambient liquid extraction

With the development of mass spectrometry imaging (MSI), techniques providing quantitative information on the spatial distribution have attracted more attentions recent years. However, for MSI of endogenous compounds in bio-samples, the uncertainty of locally varied sampling efficiencies always hinders accurate absolute quantitation. Here single-probe was used for ambient liquid extraction MSI in rat cerebellum, and standards of phosphatidylcholines (PCs) and cerebrosides (CBs) were doped in extraction solvent. The extraction kinetic curves of endogenous lipids in the ambient liquid extraction during probe parking in single pixel of tissue were investigated. From the results, the extraction kinetic curves were varied between different lipid species in different brain regions, resulting in variations of extraction efficiencies between imaging pixels, and calibration with standards deposited in tissue could not compensate for the variations. In our approach, the theoretical kinetic model of ambient liquid extraction was established, and original concentrations of endogenous lipids in each pixel of tissue were predicted by fitting the experimental extraction kinetic curve in each imaging pixel to the model. The experimental data was demonstrated to be well fitted to the kinetic model with R² > 0.86, and only with 18-s extraction in each pixel, the original lipid concentrations were predicted accurately with relative errors <23%. With the new method, totally 157 lipids and small metabolites were imaged, and per-pixel quantitation was achieved for 19 PCs and 4 CBs. Compared with conventional quantitative MSI (q-MSI) method, the new q-MSI method had better reproducibility and wider linear range, and produced better contrast in the quantitative images of lipids in brain tissue with less hot spots and noises. The absolute quantitation results by the new method were verified by quantitative LC-MS method with Pearson'r > 0.9 and the slope of the linear fitting line of the correlation plot near 1.

Molecular Mapping of Neutral Lipids Using Silicon Nanopost Arrays and TIMS Imaging Mass Spectrometry

We demonstrate the utility of combining silicon nanopost arrays (NAPA) and trapped ion mobility imaging mass spectrometry (TIMS IMS) for high spatial resolution and specificity mapping of neutral lipid classes in tissue. Ionization of neutral lipid species such as triglycerides (TGs), cholestryl esters (CEs), and hexosylceramides (HexCers) from biological tissues has remained a challenge for imaging applications. NAPA, a matrix-free laser desorption ionization substrate, provides enhanced ionization efficiency for the above-mentioned neutral lipid species, providing complementary lipid coverage to matrix-assisted laser desorption ionization (MALDI). The combination of NAPA and TIMS IMS enables imaging of neutral lipid species at 20 μm spatial resolution while also increasing molecular coverage greater than 2-fold using gas-phase ion mobility separations. This is a significant improvement with respect to sensitivity, specificity, and spatial resolution compared to previously reported imaging studies using NAPA alone. Improved specificity for neutral lipid analysis using TIMS IMS was shown using rat kidney tissue to separate TGs, CEs, HexCers, and phospholipids into distinct ion mobility trendlines. Further, this technology allowed for the separation of isomeric species, including mobility resolved isomers of Cer(d42:2) (m/z 686.585) with distinct spatial localizations measured in rat kidney tissue section.

α-Cyano-4-hydroxycinnamic Acid and Tri-Potassium Citrate Salt Pre-Coated Silicon Nanopost Array Provides Enhanced Lipid Detection for High Spatial Resolution MALDI Imaging Mass Spectrometry

We have developed a pre-coated substrate for matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) that enables high spatial resolution mapping of both phospholipids and neutral lipid classes in positive ion mode as metal cation adducts. The MALDI substrates are constructed by depositing a layer of α-cyano-4-hydroxycinnamic acid (CHCA) and potassium salts onto silicon nanopost arrays (NAPA) prior to tissue mounting. The matrix/salt pre-coated NAPA substrate significantly enhances all detected lipid signals allowing lipids to be detected at lower laser energies than bare NAPA. The improved sensitivity at lower laser energy enabled ion images to be generated at 10 μm spatial resolution from rat retinal tissue. Optimization of matrix pre-coated NAPA consisted of testing lithium, sodium, and potassium salts along with various matrices to investigate the increased sensitivity toward lipids for MALDI IMS experiments. It was determined that pre-coating NAPA with CHCA and potassium salts before thaw-mounting of tissue resulted in a signal intensity increase of at least 5.8 ± 0.1-fold for phospholipids and 2.0 ± 0.1-fold for neutral lipids compared to bare NAPA. Pre-coating NAPA with matrix and salt also reduced the necessary laser power to achieve desorption/ionization by ∼35%. This reduced the effective diameter of the ablation area from 13 ± 2 μm down to 8 ± 1 μm, enabling high spatial resolution MALDI IMS. Using pre-coated NAPA with CHCA and potassium salts offers a MALDI IMS substrate with broad molecular coverage of lipids in a single polarity that eliminates the need for extensive sample preparation after sectioning.

[Mass spectrometry imaging technology and its application in breast cancer research]

乳腺癌是女性最常见的恶性肿瘤,其发病率在世界范围内呈现上升趋势,是威胁女性健康的重要疾病之一。随着现代医学技术的快速发展,早期有效的诊断和筛查方法能够改善乳腺癌患者生存率和提高其生活质量。由于乳腺癌肿瘤具有非常显著的异质性,这对于诊断和筛查带来了较大困难,亟须在肿瘤演进时间信息中,继续引入生物分子的空间信息,从而对其异质性、肿瘤微环境等进行准确的追踪。质谱成像技术,可在免标记的前提下利用离子质荷比的特性发现生物组织中的各种分子,并研究这些分子的时间和空间信息,对其进行准确的定性、定量和空间定位。目前,通过质谱成像技术可直接获取药物及其代谢物、内源性代谢物、脂质、多肽和蛋白质等在组织中的空间分布信息,为肿瘤分子分型诊断和确认以及相关抗肿瘤药物的筛选提供了新的思路和研究方向。该综述以乳腺癌相关的生物样品制备和研究进展为主要内容,从小分子样本、大分子样本、石蜡包埋样本、基质喷涂方式、常用离子源等方面阐述质谱成像中样本制备的重要性以及样品制备过程中存在的难点问题。同时,以细胞模型、动物模型和临床肿瘤标本为研究对象,汇总了质谱成像技术在乳腺癌方面的应用进展,并进行了展望,为开展癌症精准分型研究和药物药效的快速筛查提供了重要依据。

Imaging lipids in biological samples with surface-assisted laser desorption/ionization mass spectrometry: A concise review of the last decade

Knowing the spatial location of the lipid species present in biological samples is of paramount importance for the elucidation of pathological and physiological processes. In this context, mass spectrometry imaging (MSI) has emerged as a powerful technology allowing the visualization of the spatial distributions of biomolecules, including lipids, in complex biological samples. Among the different ionization methods available, the emerging surface-assisted laser desorption/ionization (SALDI) MSI offers unique capabilities for the study of lipids. This review describes the specific advantages of SALDI-MSI for lipid analysis, including the ability to perform analyses in both ionization modes with the same nanosubstrate, the detection of lipids characterized by low ionization efficiency in MALDI-MS, and the possibilities of surface modification to improve the detection of lipids. The complementarity of SALDI and MALDI-MSI is also discussed. Finally, this review presents data processing strategies applied in SALDI-MSI of lipids, as well as examples of applications of SALDI-MSI in biomedical lipidomics.

In-Depth Structural Characterization and Quantification of Cerebrosides and Glycosphingosines with Gas-Phase Ion Chemistry

Cerebrosides (n-HexCer) and glycosphingosines (n-HexSph) constitute two sphingolipid subclasses. Both are comprised of a monosaccharide headgroup (glucose or galactose in mammalian cells) linked via either an α- or β-glycosidic linkage to the sphingoid backbone (n = α or β, depending upon the nature of the linkage to the anomeric carbon of the sugar). Cerebrosides have an additional amide-bonded fatty acyl chain linked to the sphingoid backbone. While differentiating the multiple isomers (i.e. glucose vs galactose, α- vs β-linkage) is difficult, it is crucial for understanding their specific biological roles in health and disease states. Shotgun tandem mass spectrometry has been a powerful tool in both lipidomics and glycomics analysis but is often limited in its ability to distinguish isomeric species. This work describes a new strategy combining shotgun tandem mass spectrometry with gas-phase ion chemistry to achieve both differentiation and quantification of isomeric cerebrosides and glycosphingosines. Briefly, deprotonated cerebrosides, [n-HexCer-H]^-, or glycosphingosines, [n-HexSph-H]^-, are reacted with terpyridine (Terpy) magnesium complex dications, [Mg(Terpy)₂]²⁺, in the gas phase to produce a charge-inverted complex cation, [n-HexCer-H+MgTerpy]⁺ or [n-HexSph-H+MgTerpy]⁺. The collision-induced dissociation (CID) of the charge-inverted complex cations leads to significant spectral differences between the two groups of isomers, α-GalCer, β-GlcCer, and β-GalCer for cerebrosides and α-GlcSph, α-GalSph, β-GlcSph, and β-GalSph for glycosphingosines, which allows for isomer distinction. Moreover, we describe a quantification strategy with the normalized percent area extracted from selected diagnostic ions that quantify either three isomeric cerebroside or four isomeric glycosphingosine mixtures. The analytical performance was also evaluated in terms of accuracy, repeatability, and interday precision. Furthermore, CID of the product ions resulting from 443 Da loss from the charge-inverted complex cations ([n-HexCer-H+MgTerpy]⁺) has been performed and demonstrated for localization of the double-bond position on the amide-bonded monounsaturated fatty acyl chain in the cerebroside structure. The proposed strategy was successfully applied to the analysis of total cerebroside extracts from the porcine brain, providing in-depth structural information on cerebrosides from a biological mixture.

Mass spectrometry in the lipid study of cancer

Introduction: Cancer is a heterogeneous disease that exploits various metabolic pathways to meet the demand for increased energy and structural components. Lipids are biomolecules that play essential roles as high energy sources, mediators, and structural components of biological membranes. Accumulating evidence has established that altered lipid metabolism is a hallmark of cancer.Areas covered: Mass spectrometry (MS) is a label-free analytical tool that can simultaneously identify and quantify hundreds of analytes. To date, comprehensive lipid studies exclusively rely on this technique. Here, we reviewed the use of MS in the study of lipids in various cancers and discuss its instrumental limitations and challenges.Expert opinion: MS and MS imaging have significantly contributed to revealing altered lipid metabolism in a variety of cancers. Currently, a single MS approach cannot profile the entire lipidome because of its lack of sensitivity and specificity for all lipid classes. For the metabolic pathway investigation, lipid study requires the integration of MS with other molecular approaches. Future developments regarding the high spatial resolution, mass resolution, and sensitivity of MS instruments are warranted.

Analyzing Mass Spectrometry Imaging Data of 13C-Labeled Phospholipids in Camelina sativa and Thlaspi arvense (Pennycress) Embryos

The combination of ¹³C-isotopic labeling and mass spectrometry imaging (MSI) offers an approach to analyze metabolic flux in situ. However, combining isotopic labeling and MSI presents technical challenges ranging from sample preparation, label incorporation, data collection, and analysis. Isotopic labeling and MSI individually create large, complex data sets, and this is compounded when both methods are combined. Therefore, analyzing isotopically labeled MSI data requires streamlined procedures to support biologically meaningful interpretations. Using currently available software and techniques, here we describe a workflow to analyze ¹³C-labeled isotopologues of the membrane lipid and storage oil lipid intermediate―phosphatidylcholine (PC). Our results with embryos of the oilseed crops, Camelina sativa and Thlaspi arvense (pennycress), demonstrated greater ¹³C-isotopic labeling in the cotyledons of developing embryos compared with the embryonic axis. Greater isotopic enrichment in PC molecular species with more saturated and longer chain fatty acids suggest different flux patterns related to fatty acid desaturation and elongation pathways. The ability to evaluate MSI data of isotopically labeled plant embryos will facilitate the potential to investigate spatial aspects of metabolic flux in situ.

An optimized method for the detection and spatial distribution of aminoglycoside and vancomycin antibiotics in tissue sections by mass spectrometry imaging

Suboptimal antibiotic dosing has been identified as one of the key drivers in the development of multidrug-resistant (MDR) bacteria that have become a global health concern. Aminoglycosides and vancomycin are broad-spectrum antibiotics used to treat critically ill patients infected by a variety of MDR bacterial species. Resistance to these antibiotics is becoming more prevalent. In order to design proper antibiotic regimens that maximize efficacy and minimize the development of resistance, it is pivotal to obtain the in situ pharmacokinetic-pharmacodynamic profiles at the sites of infection. Mass spectrometry imaging (MSI) is the ideal technique to achieve this. Aminoglycosides, due to their structure, suffer from poor ionization efficiency. Additionally, ion suppression effects by endogenous molecules greatly inhibit the detection of aminoglycosides and vancomycin at therapeutic levels. In the current study, an optimized method was developed that enabled the detection of these antibiotics by MSI. Tissue spotting experiments demonstrated a 5-, 15-, 35-, and 54-fold increase in detection sensitivity in the washed samples for kanamycin, amikacin, streptomycin, and vancomycin, respectively. Tissue mimetic models were utilized to optimize the washing time and matrix additive concentration. These studies determined the improved limit of detection was 40 to 5 μg/g of tissue for vancomycin and streptomycin, and 40 to 10 μg/g of tissue for kanamycin and amikacin. The optimized protocol was applied to lung sections from mice dosed with therapeutic levels of kanamycin and vancomycin. The washing protocol enabled the first drug distribution investigations of aminoglycosides and vancomycin by MSI, paving the way for site-of-disease antibiotic penetration studies.

Multimodal chemical imaging of a single brain tissue section using ToF-SIMS, MALDI-ToF and immuno/histochemical staining

Cluster ion beam ToF-SIMS and/or MALDI-ToF mass spectrometry imaging (using 1,5-DAN matrix via sublimation) of a single coronal rat brain tissue section followed by classical- or immuno- histochemical staining faclilated a new multimodal chemical imaging workflow allowing complementary correlation of the lipid molecular ion images with the immuno/histological features within cerebellum region of the same brain tisue section.

Removal of optimal cutting temperature (O.C.T.) compound from embedded tissue for MALDI imaging of lipids

Matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) is a common molecular imaging modality used to characterise the abundance and spatial distribution of lipids in situ. There are several technical challenges predominantly involving sample pre-treatment and preparation which have complicated the analysis of clinical tissues by MALDI-MSI. Firstly, the common embedding of samples in optimal cutting temperature (O.C.T.), which contains high concentrations of polyethylene glycol (PEG) polymers, causes analyte signal suppression during mass spectrometry (MS) by competing for available ions during ionisation. This suppressive effect has constrained the application of MALDI-MSI for the molecular mapping of clinical tissues. Secondly, the complexity of the mass spectra is obtained by the formation of multiple adduct ions. The process of analyte ion formation during MALDI can generate multiple m/z peaks from a single lipid species due to the presence of alkali salts in tissues, resulting in the suppression of protonated adduct formation and the generation of multiple near isobaric ions which produce overlapping spatial distributions. Presented is a method to simultaneously remove O.C.T. and endogenous salts. This approach was applied to lipid imaging in order to prevent analyte suppression, simplify data interpretation, and improve sensitivity by promoting lipid protonation and reducing the formation of alkali adducts.

Complementary neuropeptide detection in crustacean brain by mass spectrometry imaging using formalin and alternative aqueous tissue washes

Neuropeptides are low abundance signaling molecules that modulate almost every physiological process, and dysregulation of neuropeptides is implicated in disease pathology. Mass spectrometry (MS) imaging is becoming increasingly useful for studying neuropeptides as new sample preparation methods for improving neuropeptide detection are developed. In particular, proper tissue washes prior to MS imaging have shown to be quick and effective strategies for increasing the number of detectable neuropeptides. Treating tissues with solvents could result in either gain or loss of detection of analytes, and characterization of these wash effects is important for studies targeting sub-classes of neuropeptides. In this communication, we apply aqueous tissue washes that contain sodium phosphate salts, including 10% neutral buffered formalin (NBF), on crustacean brain tissues. Our optimized method resulted in complementary identification of neuropeptides between washed and unwashed tissues, indicating that our wash protocol may be used to increase total neuropeptide identifications. Finally, we show that identical neuropeptides were detected between tissues treated with 10% NBF and an aqueous 1% w/v sodium phosphate solution (composition of 10% NBF without formaldehyde), suggesting that utilizing a salt solution wash affects neuropeptide detection and formaldehyde does not affect neuropeptide detection when our wash protocol is performed.

MALDI MSI Reveals the Spatial Distribution of Protein Markers in Tracheobronchial Lymph Nodes and Lung of Pigs after Respiratory Infection

Respiratory infections are a real threat for humans, and therefore the pig model is of interest for studies. As one of a case for studies, Actinobacillus pleuropneumoniae (APP) caused infections and still worries many pig breeders around the world. To better understand the influence of pathogenic effect of APP on a respiratory system-lungs and tracheobronchial lymph nodes (TBLN), we aimed to employ matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging (MALDI-TOF MSI). In this study, six pigs were intranasally infected by APP and two were used as non-infected control, and 48 cryosections have been obtained. MALDI-TOF MSI and immunohistochemistry (IHC) were used to study spatial distribution of infectious markers, especially interleukins, in cryosections of porcine tissues of lungs (necrotic area, marginal zone) and tracheobronchial lymph nodes (TBLN) from pigs infected by APP. CD163, interleukin 1β (IL‑1β) and a protegrin-4 precursor were successfully detected based on their tryptic fragments. CD163 and IL‑1β were confirmed also by IHC. The protegrin-4 precursor was identified by MALDI-TOF/TOF directly on the tissue cryosections. CD163, IL‑1β and protegrin‑4 precursor were all significantly (p < 0.001) more expressed in necrotic areas of lungs infected by APP than in marginal zone, TBLN and in control lungs.

Separation of Glycolipids/Sphingolipids from Glycerophospholipids on TiO2 Coating in Aprotic Solvent for Rapid Comprehensive Lipidomic Analysis with Liquid Microjunction Surface Sampling-Mass Spectrometry

In lipidomic analysis by direct mass spectrometry (MS), high abundance lipids with high ionizability (such as glycerophospholipids) would cause ion suppression to lipids with poor ionizability and low abundance (such as glycolipids, sphingolipids, or glycerides), which largely limits the detection coverage for lipidomics. In this work, TiO₂-based liquid microjunction surface sampling (LMJSS) coupled with MS was used for separation of glycerides, phospholipids and glycolipids/sphingolipids in biological samples and rapid analysis of lipids in different classes with high lipidome coverage. We found that, in nonaqueous aprotic solvents, lipids with a glycosyl or sphingosine group could be selectively separated from lipids with a phosphate group (selectivity >10) after being coenriched on TiO₂ by tuning the solvent composition. Accordingly, a selective multistep extraction method was developed by loading the biosamples on TiO₂ slides in neutral aprotic solvent, and sequentially eluting glycerides in pure acetonitrile, glycerophospholipids in 6% ammonia-94% acetonitrile (v/v) and glycolipids/sphingolipids in 5% formic acid-95% methanol (v/v) by LMJSS probe from TiO₂ slide. Each eluate from TiO₂ slide was directly delivered by LMJSS to MS for analysis. The total detection time with three desorption steps would be controlled in 3 min. The method performance for each lipid class was evaluated using lipid standards, including matrix effects (107-128%), RSDs (0.4-16%), linearity (0.98-0.99), detection limits (5-3000 ng/mL), the adsorption equilibrium constants (10²-10⁴) and adsorption capacity (1-38 μg/mm²) of TiO₂ coated slides to lipids. Finally, the TiO₂-based-LMJSS-MS method was applied to lipidomic analysis for blood plasma and brain tissue, and compared with direct infusion MS. Results showed that (2-5)-fold more sphingolipids/glycolipids and 40-50 more glycerophospholipids/glycerides were identified in both plasma and brain extract by the new method comparing with direct infusion MS method. Detected lipids were quantified with standard addition calibration method, and the absolute quantitation results measured by TiO₂-based-LMJSS-MS were verified with that by the traditional LC-MS method (correlation coefficient >0.98, slope of correlation line = 0.87-1.05).