Towards High-Resolution Tissue Imaging Using Nanospray Desorption Electrospray Ionization Mass Spectrometry Coupled to Shear Force Microscopy

Abstract

Constant mode ambient mass spectrometry imaging (MSI) of tissue sections with high lateral resolution of better than 10 μm was performed by combining shear force microscopy with nanospray desorption electrospray ionization (nano-DESI). Shear force microscopy enabled precise control of the distance between the sample and nano-DESI probe during MSI experiments and provided information on sample topography. Proof-of-concept experiments were performed using lung and brain tissue sections representing spongy and dense tissues, respectively. Topography images obtained using shear force microscopy were comparable to the results obtained using contact profilometry over the same region of the tissue section. Variations in tissue height were found to be dependent on the tissue type and were in the range of 0–5 μm for lung tissue and 0–3 μm for brain tissue sections. Ion images of phospholipids obtained in this study are in good agreement with literature data. Normalization of nano-DESI MSI images to the signal of the internal standard added to the extraction solvent allowed us to construct high-resolution ion images free of matrix effects.

High Spatial Resolution Imaging of Mouse Pancreatic Islets Using Nanospray Desorption Electrospray Ionization Mass Spectrometry

“…16 Similar to DESI, nanospray desorption electrospray ionization (nano-DESI) developed by our group enables analysis of biological samples with minimal sample pretreatment with high sensitivity and spatial resolution of better than 10 μm. 17–19 Moreover, addition of selected standards to the nano-DESI solvent may be used to compensate for signal variations caused by matrix effects and perform accurate quantification of lipids and metabolites in complex samples. 20–22 We recently introduced an approach for robust nano-DESI MSI with high spatial resolution by adding a shear force probe, which enables precise control of the distance between the sample and nano-DESI probe.…”

“…20–22 We recently introduced an approach for robust nano-DESI MSI with high spatial resolution by adding a shear force probe, which enables precise control of the distance between the sample and nano-DESI probe. 19,23 Herein, we used this approach for imaging of pancreatic islets with high spatial resolution.…”

“…In this study, we employ the recently developed constant-distance nano-DESI MSI approach 19,23 to obtain first insights into the localization of lipids and metabolites in both the pancreatic islets and surrounding exocrine tissue. This approach enables molecular imaging of individual pancreatic islets with a lateral resolution of ~11 μm.…”

In situ mass spectrometry analysis of intact proteins and protein complexes from biological substrates

“…Nano-DESI ( Figure 1B) is a continuous flow-based technique that has been reported for high spatial resolution (<20 μm) surface sampling of biological samples [49]. Nano-DESI may be automated, and requires no substantial sample preparation; however, the best performance of the nano-DESI probe has been shown to require technical skill and supplementary apparatus and there is currently no commercial implementation [50].…”

Ambient ionisation mass spectrometry for in situ analysis of intact proteins

“…The basic nanoDESI set‐up cannot achieve such precise control on samples of variable height, and thus, the size of the liquid bridge needs to be increased to absorb the differences without leading to loss of signal either through collision of the apparatus with the sample or loss of contact between the sample and the liquid bridge; the spot diameter could thus increase to approximately 1 mm for very rough samples such as bacterial colonies . This limitation was recently overcome by the integration of a shear force probe alongside the nanoDESI probe . Thus, the topography of the sample can be measured and fed back to the control interface of the apparatus during a raster scan across the sample surface, allowing for the continuous adjustment of the probe positioning to maintain optimum distance from the sample.…”