Response Surface Methodology As a New Approach for Finding Optimal MALDI Matrix Spraying Parameters for Mass Spectrometry Imaging

Abstract

Supporting InformationThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jasms.9b00074.Step-by-step protocol and important notes for optimizing the HTX TM-spraying parameters using the RSM, containing (Table S1) coded and actual values of factors used in the experimental design, (Figure S1) organization of tissue biopsy sections on slides together with HTX TM-sprayer conditions used for each section, (Figure S2) example METASPACE webpage that shows the uploading process, (Figure S3) example METASPACE webpage that displays putative molecular annotations and corresponding ion images, and (Figure S4) examples of endogenous and off-tissue annotations by METASPACE (PDF)The authors declare no competing financial interest.

A reference tissue atlas for the human kidney

“…One advantage of the presented multiomics data integration strategy is the ability to infer how different classes of biomolecules may enable complex multicellular functions leading to potentially predictive biomarkers. Spatial metabolomics identifies N-Palmitoylsphingomyelin (SM d18:0/16:1) as a spatial correlate of glomerular kidney segments (correlation coefficient > 0.9; Figure 9A), as described previously (103,104). To identify the cell types involved in its synthesis, we screened all glomerular cell types for expression of genes involved in ceramide, sphingomyelin and sphingosine metabolism (105,106).…”

Matrix phase fractionation: Investigating the compromise between dynamic range of analyte extraction and spatial resolution in mass spectrometry imaging

“…In our experience, even with a properly calibrated instrument, the reliability of identifications from MS1 values is not confident enough without additional orthogonal validation. Previous studies have leveraged Fourier transform ion cyclotron resonance‐based mass spectrometry which exhibits the ultrahigh mass resolution necessary to provide accurate mass to <1 ppm 12 and hence accurate identifications. However, this was not possible for the present study.…”

“…In addition to improving the matrices themselves, a large body of work has focused on improving the mode of application. There have been several attempts to standardise and improve these methods, such as optimising and standardising spraying parameters to reduce delocalisation caused by oversaturation of carrier solvents 12 . Further studies have also characterised the physiochemical effects that are caused by utilisation of certain matrices, such as adducting of salt ions 13 and the physical effects that laser ablation/desorption have on the resulting ion plume 13 and sample substrate 14 .…”

Identifying the elephant

“…The method by which a MALDI matrix is applied can be just as important as which matrix is chosen. The more "wet" the method is, the greater the extraction of lipids from the tissue tends to be [119]. As such, spray-based methods have long been the workhorse for MALDI lipidomics, varying from hand-held sprayers modified from airbrushes to automated commercial sprayers [120].…”

“…In the case of analytes with lower proton affinities, the efficiency drops to as low as 1 in 100,000,000 [131,132]. An obvious consequence of this is a drive to improving ionization efficiency through new matrix application protocols [119,133,134], novel matrices [135][136][137][138], derivatization (covalently binding a charge to the analyte) [139][140][141][142][143], and post-ionization [144]. Matrix application, post-ionization, and matrix choice are significant factors in my quest to understand the lipidome.…”