Automated Platform for High-Resolution Tissue Imaging Using Nanospray Desorption Electrospray Ionization Mass Spectrometry

Abstract

An automated platform has been developed for acquisition and visualization of mass spectrometry imaging (MSI) data using nanospray desorption electrospray ionization (nano-DESI). The new system enables robust operation of the nano-DESI imaging source over many hours by precisely controlling the distance between the sample and the nano-DESI probe. This is achieved by mounting the sample holder onto an automated XYZ stage, defining the tilt of the sample plane, and recalculating the vertical position of the stage at each point. This approach is useful for imaging of relatively flat samples such as thin tissue sections. Custom software called MSI QuickView was developed for visualization of large data sets generated in imaging experiments. MSI QuickView enables fast visualization of the imaging data during data acquisition and detailed processing after the entire image is acquired. The performance of the system is demonstrated by imaging rat brain tissue sections. Low background noise enables simultaneous detection of lipids and metabolites in the tissue section. High-resolution mass analysis combined with tandem mass spectometry (MS/MS) experiments enabled identification of the observed species. In addition, the high dynamic range (>2000) of the technique allowed us to generate ion images of low-abundance isobaric lipids. A high-spatial resolution image was acquired over a small region of the tissue section revealing the distribution of an abundant brain metabolite, creatine, on the boundary between the white and gray matter. The observed distribution is consistent with the literature data obtained using magnetic resonance spectroscopy.

High Resolution Tissue Imaging Using the Single-probe Mass Spectrometry under Ambient Conditions

“…During MSI measurement, the sample was placed onto a motorized XYZ stage controlled by a custom designed LabVIEW software developed by the Laskin Group [27]. For rhodamine pattern MSI measurement, the scanning parameters were set to 2 μm/s rastering speed and 5 μm distance between lines.…”

“…High spatial resolution ambient MSI has generally been more difficult to achieve on complex biological samples such as tissue sections, which contains small surface unevenness (e.g., 1.5±0.6 μm variation [27]) that can introduce a greater degree of heterogeneity to data acquisition compared with flat surfaces. DESI MSI of biological samples are routinely made at a resolution of 200 μm [32,33], which is capable of giving informative analysis of large tissue sections but does not contain details that can be observed at higher spatial resolution.…”

Ambient Mass Spectrometry Imaging Using Direct Liquid Extraction Techniques

“…Nano-DESI has been used for sensitive localized analysis and imaging of complex molecules in biological and environmental samples. 60–62 The spatial resolution in nano-DESI MSI experiments is determined by the size of the capillaries that make up the probe, solvent flow rate, surface properties, and the ability to accurately control the distance between the sample and the probe. Nano-DESI MSI experiments have been performed with moderate spatial resolution of ~100–150 µm, 60,63,64 although a spatial resolution of better than 12 µm has been achieved using pulled capillaries.…”

Imaging Mass Spectrometric Analysis of Neurotransmitters

“…During IMS analysis, pre-selected positions create an array of points separated from each other at a determined distance and a mass spectrum is obtained at each spot. 6,7) With the development of automated instruments 8,9) and powerful so ware, 10,11) capable of rapidly acquiring and processing orderly yet massive imaging spectral data, it is now possible to simultaneously visualise innumerable individual biomolecules in tissue sections. 7,10) e identi cation and localisation of compounds such as neuropeptides, 12,13) neurotransmitters, 14) and small molecules 2) are especially important for the study of the brain, as it is a complex organ with a high spatial and somatotopic organisation.…”