Investigation of the Impact of Desorption Electrospray Ionization Sprayer Geometry on Its Performance in Imaging of Biological Tissue

Abstract

In this study, the impact of sprayer design and geometry on performance in desorption electrospray ionization mass spectrometry (DESI-MS) is assessed, as the sprayer is thought to be a major source of variability. Absolute intensity repeatability, spectral composition, and classification accuracy for biological tissues are considered. Marked differences in tissue analysis performance are seen between the commercially available and a lab-built sprayer. These are thought to be associated with the geometry of the solvent capillary and the resulting shape of the primary electrospray. Experiments with a sprayer with a fixed solvent capillary position show that capillary orientation has a crucial impact on tissue complex lipid signal and can lead to an almost complete loss of signal. Absolute intensity repeatability is compared for five lab-built sprayers using pork liver sections. Repeatability ranges from 1 to 224% for individual sprayers and peaks of different spectral abundance. Between sprayers, repeatability is 16%, 9%, 23%, and 34% for high, medium, low, and very low abundance peaks, respectively. To assess the impact of sprayer variability on tissue classification using multivariate statistical tools, nine human colorectal adenocarcinoma sections are analyzed with three lab-built sprayers, and classification accuracy for adenocarcinoma versus the surrounding stroma is assessed. It ranges from 80.7 to 94.5% between the three sprayers and is 86.5% overall. The presented results confirm that the sprayer setup needs to be closely controlled to obtain reliable data, and a new sprayer setup with a fixed solvent capillary geometry should be developed.

Optimized Mass Spectrometry Analysis Workflow with Polarimetric Guidance for ex vivo and in situ Sampling of Biological Tissues

“…Polarimetry-guided DESI-MS imaging (with histology validation) of a single tissue slice requires various technological improvements, including: (1) optimization of DESI-MS sprayer 26, 27 to provide gentle desorption which avoids tissue damage, while still providing sensitive detection with sufficient signal from the thinner tissue sections; (2) optimization of DESI-MS solvent conditions 28 to be compatible with post DESI-MS histology staining; (3) increased sensitivity of polarimetry detection to enable sufficient contrast using histology-compatible thin tissue sections; and (4) added functionality to the DESI-MS acquisition interface to allow co-registration of image coordinates for targeted collection of DESI-MS data. This work brings together these various improvements to enable improved targeted analysis of tissues using the polarimetry – DESI-MS tandem.…”

“…This MS method, where charged microdroplets of solvent incident on a thin tissue slice desorb and ionize small molecule lipids and metabolites, creates a unique MS profile for cancer typing and tumour subclass identification in a variety of cancers 1, 5, 6, 19, 24, 25 . Here we use a newly engineered DESI spray outlet 26, 27 that allows efficient and minimally destructive desorption ionization from thin tissue slices (e.g., 10 µm). The minimally destructive nature and reduced tissue thickness requirements allow subsequent histologic staining on the same MS-imaged tissue slice for detailed microscopy evaluation, provided suitable solvent compatible with post DESI-MS staining protocols is used 28 .…”

Lipidomics for translational skin research: A primer for the uninitiated

“…For each pixel with given x and y coordinates, a mass spectrum is recorded with information on m/z and ion abundance. By selecting an ion of interest and extracting the data for each pixel, a chemical map of the tissue can be built‐up, showing the distribution and abundance of that lipid molecular ion across the sample . This provides information on the different skin compartments in one image, revealing anatomical lipid distribution, as well as allowing semiquantitative comparison of lipid intensities between samples, and the MSI data can be coregistered with the same or a consecutive section that has undergone histochemical staining .…”

“…Unlike MALDI‐MSI, no matrix is required, so skin tissue simply requires sectioning prior to analysis. DESI‐MSI has proven capabilities in imaging of lipids across tissues, but until recently has lacked the spatial resolution to analyse intricate tissues such as skin, with typical pixel sizes around 100 μm …”

Electrospray Modifications for Advancing Mass Spectrometric Analysis

“…Some of the important parameters which determine the ion signals in DESI-MS are incident angle of spray, collection angle of secondary droplets, distance between sprayer and surface, composition and ow rate of spray solvent, and type of surface. 107) Over the years, DESI-MS has been applied in wide areas such as forensics, 106,108) biology, [109][110][111] chemistry, [112][113][114][115][116] imaging, 117,118) and cancer diagnostics. [119][120][121][122] Another related technique known as desorption sonic-spray ionization (DeSSI) 123) also uses the desorption phenomena like DESI.…”