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.

Distributions of CHN compounds in meteorites record organic syntheses in the early solar system

Carbonaceous meteorites contain diverse soluble organic compounds. These compounds formed in the early solar system from volatiles accreted on tiny dust particles. However, the difference in the organic synthesis on respective dust particles in the early solar system remains unclear. We found micrometer-scale heterogeneous distributions of diverse CHN_1-2 and CHN_1-2O compounds in two primitive meteorites: the Murchison and NWA 801, using a surface-assisted laser desorption/ionization system connected to a high mass resolution mass spectrometer. These compounds contained mutual relationships of ± H₂, ± CH₂, ± H₂O, and ± CH₂O and showed highly similar distributions, indicating that they are the products of series reactions. The heterogeneity was caused by the micro-scale difference in the abundance of these compounds and the extent of the series reactions, indicating that these compounds formed on respective dust particles before asteroid accretion. The results of the present study provide evidence of heterogeneous volatile compositions and the extent of organic reactions among the dust particles that formed carbonaceous asteroids. The compositions of diverse small organic compounds associated with respective dust particles in meteorites are useful to understand different histories of volatile evolution in the early solar system.

Perfluoroalkyl Group-Covered Organosilica Films for the Sensitive Detection of Sulfonylurea Herbicides in Laser Desorption/Ionization Mass Spectrometry

Simple and rapid screening of agrochemicals greatly contributes to food and environmental safety. Matrix-free laser desorption/ionization mass spectrometry (LDI-MS) is an effective tool for high-throughput analysis of low-molecular-weight compounds. In this study, we report a UV-laser-absorbing organosilica film for the sensitive detection of various sulfonylurea herbicides using LDI-MS. Organosilica films with fluoroalkyl groups on the organic part are fabricated, followed by additional modification of the silica moiety with a fluoroalkyl coupling agent to cover the film surface with hydrophobic fluoroalkyl groups. Nanoimprinting is conducted to impart nanostructures on the film surface to enhance the LDI performance. The fabricated nanostructured organosilica films accomplish sensitive detection of cyclosulfamuron and azimsulfuron at concentrations as low as 1 fmol μL^-1. The applicability of the nanostructured organosilica films is confirmed by the recovery of cyclosulfamuron and ethametsulfuron-methyl from pea sprouts (Pisum sativum) hydroponically grown in herbicide-spiked water at concentrations of 0.5 ppm.

Surface-assisted laser desorption/ionization mass spectrometry imaging: A review

In the last decades, surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has attracted increasing interest due to its unique capabilities, achievable through the nanostructured substrates used to promote the analyte desorption/ionization. While the most widely recognized asset of SALDI-MS is the untargeted analysis of small molecules, this technique also offers the possibility of targeted approaches. In particular, the implementation of SALDI-MS imaging (SALDI-MSI), which is the focus of this review, opens up new opportunities. After a brief discussion of the nomenclature and the fundamental mechanisms associated with this technique, which are still highly controversial, the analytical strategies to perform SALDI-MSI are extensively discussed. Emphasis is placed on the sample preparation but also on the selection of the nanosubstrate (in terms of chemical composition and morphology) as well as its functionalization possibilities for the selective analysis of specific compounds in targeted approaches. Subsequently, some selected applications of SALDI-MSI in various fields (i.e., biomedical, biological, environmental, and forensic) are presented. The strengths and the remaining limitations of SALDI-MSI are finally summarized in the conclusion and some perspectives of this technique, which has a bright future, are proposed in this section.

Tissue Imprinting on 2D Nanoflakes-Capped Silicon Nanowires for Lipidomic Mass Spectrometry Imaging and Cancer Diagnosis

Spatially resolved tissue lipidomics is essential for accurate intraoperative and postoperative cancer diagnosis by revealing molecular information in the tumor microenvironment. Matrix-free laser desorption ionization mass spectrometry imaging (LDI-MSI) is an emerging attractive technology for label-free visualization of metabolites distributions in biological specimens. However, the development of LDI-MSI technology that could conveniently and authentically reveal molecular distribution on tissue samples is still a challenge. Herein, we present a tissue imprinting technology by retaining tissue lipids on 2D nanoflakes-capped silicon nanowires (SiNWs) for further mass spectrometry imaging and cancer diagnosis. The 2D nanoflakes were prepared by liquid exfoliation of molybdenum disulfide (MoS₂) with nitrogen-doped graphene quantum dots (NGQDs), which serve as both intercalation agent and dispersant. The obtained NGQD@MoS₂ nanoflakes were then decorated on the tip of vertical SiNWs, forming a hybrid NGQD@MoS₂/SiNWs nanostructure, which display excellent lipid extraction ability, enhanced LDI efficiency and molecule imaging capability. The peak number and total ion intensity of different lipids species on animal lung tissues obtained by tissue imprinting LDI-MSI on NGQD@MoS₂/SiNWs were ∼4-5 times greater than those on SiNWs substrate. As a proof-of-concept demonstration, the NGQD@MoS₂/SiNWs nanostructure was further applied to visualize phospholipids on sliced non small cell lung cancer (NSCLC) tissue along with the adjacent normal tissue. On the basis of selected feature lipids and machine learning algorithm, a prediction model was constructed to discriminate NSCLC tissues from the adjacent normal tissues with an accuracy of 100% for the discovery cohort and 91.7% for the independent validation cohort.

Rapidity and Precision of Steroid Hormone Measurement

Steroids are present in all animals and plants, from mammals to prokaryotes. In the medical field, steroids are commonly classified as glucocorticoids, mineralocorticoids, and gonadal steroid hormones. Monitoring of hormones is useful in clinical and research fields for the assessment of physiological changes associated with aging, disease risk, and the diagnostic and therapeutic effects of various diseases. Since the discovery and isolation of steroid hormones, measurement methods for steroid hormones in biological samples have advanced substantially. Although immunoassays (IAs) are widely used in daily practice, mass spectrometry (MS)-based methods have been reported to be more specific. Steroid hormone measurement based on MS is desirable in clinical practice; however, there are several drawbacks, including the purchase and maintenance costs of the MS instrument and the need for specialized training of technicians. In this review, we discuss IA- and MS-based methods currently in use and briefly present the history of steroid hormone measurement. In addition, we describe recent advances in IA- and MS-based methods and future applications and considerations.

Mass spectrometry imaging for direct visualization of components in plants tissues

Mass spectrometry is considered the most informative technique for components identification and has been widely adopted in plant sciences. However, the spatial distribution of compounds in the plant, which is vital for the exploration of plant physiological mechanisms, is missed in MS analysis. In recent years, mass spectrometry imaging has brought a great breakthrough in plant analysis because it can determine both the molecular compositions and spatial distributions, which is conducive to understand functions and regulation pathways of specific components in plants. Mass spectrometry imaging analysis of plant tissue is toward high sensitivity, high spatial resolution, and even single-cell analysis. Despite many challenges and technical barriers, such as difficulties of sample pretreatment caused by morphological diversity of plant tissues, obstacles for high spatial resolution imaging, and so on, lots of researches have contributed to remarkable progress, including improvement in tissue preparation, matrix innovation, and ionization mode development. This review focuses on the advances of mass spectrometry imaging analysis of plants in the last 5 years, including commonly used ionization techniques, technical advances, and recent applications of mass spectrometry imaging in plants.

Silver spray deposition for AgLDI imaging MS of cholesterol and other olefins on thin tissue sections

Olefins such as cholesterol and unsaturated fatty acids play important biological roles. Silver-assisted laser desorption ionization (AgLDI) takes advantage of the strong affinity of silver to conjugate with double bonds to selectively ionize these molecules for imaging mass spectrometry (IMS) experiments. For IMS studies, two main approaches for silver deposition have been described in the literature: fine coating by silver sputtering and spray deposition of silver nanoparticles. While these approaches allow for extremely high resolution IMS experiments to be conducted, they are not readily available to all laboratories. Herein, we present a silver nitrate spray deposition approach as an alternative to silver sputtering and nanoparticle deposition for routine IMS analysis. The silver nitrate spray has the same level of specificity and sensitivity for olefins, particularly cholesterol, and has shown to be capable of IMS experiments down to 10-μm spatial resolution. Minimal sample preparation and the affordability of silver nitrate make this a convenient and accessible technique worth considering.

Detection and Quantification of 4-Methylimidazole in Cola by Matrix-assisted Laser Desorption Ionization Mass Spectrometry with Fe2O3 Nanoparticles on Zeolite

Food additives generally used in carbonated drinks, such as 4-methylimidazole (4MI), caffeine (Caf?), citric acid (CA), and aspartame (Apm), were measured by matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) using nanometer-sized particles of iron oxide (Fe₂O₃ NPs). The quantification of 4MI in Coca Cola (C-cola) was carried out. In order to improve the reproducibility of the peak intensities, Fe₂O₃ NPs loaded on ZSM5 zeolite were used as the matrix for quantification. By using 2-ethylimidazole (2EI) as the internal standard, the amount of 4MI in C-cola was determined to range from 88 to 65 μg/355 mL. The results agree with the published value (approx. 72 μg/355 mL). It was found that MALDI using Fe₂O₃ was applicable to the quantification of 4MI in C-cola.

High-Spatial Resolution Mass Spectrometry Imaging: Toward Single Cell Metabolomics in Plant Tissues

Mass spectrometry imaging (MSI) is a powerful tool that has advanced our understanding of complex biological processes by enabling unprecedented details of metabolic biology to be uncovered. Through the use of high-spatial resolution MSI, metabolite localizations can be obtained with high precision. Here we describe our recent progress to enhance the spatial resolution of matrix-assisted laser desorption/ionization (MALDI) MSI from ∼50 μm with the commercial configuration to ∼5 μm. Additionally, we describe our efforts to develop a 'multiplex MSI' data acquisition method to allow more chemical information to be obtained on a single tissue in a single instrument run, and the development of new matrices to improve the ionization efficiency for a variety of small molecule metabolites. In combination, these contributions, along with the efforts of others, will bring MSI experiments closer to achieving metabolomic scale.

MALDI IMS and Cancer Tissue Microarrays

Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) technology creates a link between the molecular assessment of numerous molecules and the morphological information about their special distribution. The application of MALDI IMS on formalin-fixed paraffin-embedded (FFPE) tissue microarrays (TMAs) is suitable for large-scale discovery analyses. Data acquired from FFPE TMA cancer samples in current research are very promising, and applications for routine diagnostics are under development. With the current rapid advances in both technology and applications, MALDI IMS technology is expected to enter into routine diagnostics soon. This chapter is intended to be comprehensive with respect to all aspects and considerations for the application of MALDI IMS on FFPE cancer TMAs with in-depth notes on technical aspects.

Recent advancements in matrix-assisted laser desorption/ionization mass spectrometry imaging

Matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a robust tool for spatially resolved analysis of biomolecules in situ. Recent advances in high ionization-efficiency MALDI matrices, new matrix deposition procedures, and the development of high spatial-resolution and high sensitivity MS instruments continue to drive new applications of MALDI-MSI, along with other MSI techniques, which allow us to visualize and determine the regio-specific and temporal changes in proteins, peptides, lipids, drug molecules, and metabolites within the tissues, cells and microorganisms. These provide researchers with a new route to the discovery of potential biomarkers of human disease and elucidation of the underlying biology of metabolic regulation, thus bringing our understanding of human health to a new level.