Predicting Fingerprint Age Based on Ozonolysis Kinetics of Unsaturated Triacylglycerol Degradation.

Answering the question, "How old is a fingerprint?", is a highly sought-after aim in forensic science. Despite several decades of studies to find an empirical correlation in fingerprint aging, there has been no reliable method so far. In this study, we attempt to determine the time since deposition (TSD) of aged fingerprints from the chemical profile captured within a matrix-assisted laser desorption/ionization mass spectrometry data set. Our approach is based on the chemical kinetics associated with the ambient ozonolysis of unsaturated triacylglycerols (TGs), a major component in fingerprint lipids. First, ozone concentration and ambient temperature were determined to be the major factors in the degradation of unsaturated TGs. A simple kinetics model is then developed to describe the decay of unsaturated TGs, dictated only by the temperature and ozone concentration. This model is then applied to the degradation of TGs in a mixture of TG standards and multiple individuals' fingerprints. The overall decay of unsaturated TGs follows the pseudo-first-order reaction kinetics, validating our hypothesis; however, there are significant person-to-person variations in the initial abundance of unsaturated TGs and the decay rate, hampering the accurate prediction of TSD unless they are corrected for each individual. Nevertheless, the model's applicability for ambient fingerprint aging data was successfully demonstrated.

Rapid and Automatic Annotation of Multiple On-Tissue Chemical Modifications in Mass Spectrometry Imaging with Metaspace.

On-tissue chemical derivatization is a valuable tool for expanding compound coverage in untargeted metabolomic studies with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Applying multiple derivatization agents in parallel increases metabolite coverage even further but results in large and more complex datasets that can be challenging to analyze. In this work, we present a pipeline to provide rigorous annotations for on-tissue derivatized MSI data using Metaspace. To test and validate the pipeline, maize roots were used as a model system to obtain MSI datasets after chemical derivatization with four different reagents, Girard's T and P for carbonyl groups, coniferyl aldehyde for primary amines, and 2-picolylamine for carboxylic acids. Using this pipeline helped us annotate 631 unique metabolites from the CornCyc/BraChem database compared to 256 in the underivatized dataset, yet, at the same time, shortening the processing time compared to manual processing and providing robust and systematic scoring and annotation. We have also developed a method to remove false derivatized annotations, which can clean 5-25% of false derivatized annotations from the derivatized data, depending on the reagent. Taken together, our pipeline facilitates the use of broadly targeted spatial metabolomics using multiple derivatization reagents.

Visualizing 13C-Labeled Metabolites in Maize Root Tips with Mass Spectrometry Imaging.

Tracing in vivo isotope-labeled metabolites has been used to study metabolic pathways or flux analysis. However, metabolic differences between the cells have been often ignored in these studies due to the limitation of solvent-based extraction. Here we demonstrate that the mass spectrometry imaging of in vivo isotope-labeled metabolites, referred to as MSIi, can provide important insights into metabolic dynamics with cellular resolution that may supplement the traditional metabolomics and flux analysis. Developing maize root tips are adopted as a model system for MSIi by supplementing 200 mM [U-13C]glucose in 0.1x Hoagland medium. MSIi data sets were acquired for longitudinal sections of newly grown maize root tips after growing 5 days in the medium. A total of 56 metabolite features were determined to have been 13C-labeled based on accurate mass and the number of carbon matching with the metabolite databases. Simple sugars and their derivatives were fully labeled, but some small metabolites were partially labeled with a significant amount of fully unlabeled metabolites still present, suggesting the recycling of "old" metabolites in the newly grown tissues. Some distinct localizations were found, including the low abundance of hexose and its derivatives in the meristem, the high abundance of amino acids in the meristem, and the localization to epidermal and endodermal cells for lipids and their intermediates. Fatty acids and lipids were slow in metabolic turnover and showed various isotopologue distributions with intermediate building blocks, which may provide flux information for their biosynthesis.

On-tissue chemical derivatization of volatile metabolites for matrix-assisted laser desorption/ionization mass spectrometry imaging.

Mass spectrometry imaging (MSI) of volatile metabolites is challenging, especially in matrix-assisted laser desorption/ionization (MALDI). Most MALDI ion sources operate in vacuum, which leads to the vaporization of volatile metabolites during analysis. In addition, tissue samples are often dried during sample preparation, leading to the loss of volatile metabolites even for other MSI techniques. On-tissue chemical derivatization can dramatically reduce the volatility of analytes. Herein, a derivatization method is proposed utilizing N,N,N-trimethyl-2-(piperazin-1-yl)ethan-1-aminium iodide to chemically modify short-chain fatty acids in chicken cecum, ileum, and jejunum tissue sections before sample preparation for MSI visualization.

Enhancing Metabolite Coverage for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging Through Multiple On-Tissue Chemical Derivatizations.

The ability to study and visualize metabolites on a cellular and sub-cellular level is important for gaining insights into biological pathways and metabolism of multicellular organisms. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a powerful analytical tool for metabolomics experiments due to its high sensitivity and small sampling size. The spatial resolution in MALDI-MSI is mainly limited by the number of molecules available in a small sampling size. When the sampling size is low enough to achieve cellular or subcellular spatial resolution, signal intensity is sacrificed making poorly ionized metabolites difficult to detect. To overcome this limitation, on-tissue chemical derivatization reactions have been used to enhance the desorption/ionization efficiency of selected classes of compounds by adding a functional group with a permanent positive charge or one that can be easily ionized. By utilizing several chemical derivatizations in parallel, metabolite coverage can be drastically improved. This chapter outlines methodology for sample preparation and data analysis for on-tissue chemical derivatization using various derivatization reagents.

On-tissue boronic acid derivatization for the analysis of vicinal diol metabolites in maize with MALDI-MS imaging.

Derivatization reactions are commonly used in mass spectrometry to improve analyte signals, specifically by enhancing the ionization efficiency of those compounds. Vicinal diols are one group of biologically important compounds that have been commonly derivatized using boronic acid. In this study, a boronic acid with a tertiary amine was adapted for the derivatization of vicinal diol metabolites in B73 maize tissue cross-sections for mass spectrometry imaging analysis. Using this method, dozens of vicinal diol metabolites were derivatized, effectively improving the signal of those metabolites. Many of these metabolites were tentatively assigned using high-resolution accurate mass measurements. In addition, reaction interference and cross-reactivity with various other functional groups were systematically studied to verify data interpretation.

Three-Dimensional Profiling of OLED by Laser Desorption Ionization-Mass Spectrometry Imaging.

Organic light emitting devices (OLEDs), especially in a screen display format, present unique and interesting substrates for laser desorption/ionization-mass spectrometry imaging (LDI-MSI) analysis. These devices contain many compounds that inherently absorb light energy and do not require an additional matrix to induce desorption and ionization. OLED screens have lateral features with dimensions that are tens of microns in magnitude and depth features that are tens to hundreds of nanometers thick. Monitoring the chemical composition of these features is essential, as contamination and degradation can impact device lifetime. This work demonstrates the capability of LDI-MSI to obtain lateral and partial depth resolved information on multicolored OLED displays and suggests the application to other mixed organic electronics with minimal sample preparation. This was realized when analyzing two different manufactured OLEDs, in an active-matrix display format, without the need to remove the cathode. By utilizing low laser energy and high lateral spatial resolution imaging (10 µm), depth profiling can be observed while maintaining laterally resolved information, resulting in a three-dimensional MSI approach that would complement existing OLED characterization methods.