High-Spatial-Resolution Multimodal Imaging by Tapping-Mode Scanning Probe Electrospray Ionization with Feedback Control

Abstract

Direct extraction and ionization techniques using minute amounts of solvent can be employed for the rapid analysis of chemical components in a sample without any sample preparation steps. This type of approach is important for mass spectrometry imaging of samples with multiple chemical components that have different spatial distributions (i.e., biological tissues). To improve the spatial resolution of such imaging, it is necessary to reduce the solvent volume for extraction and deliver it to the sample surface. This report describes a feedback control system applied to tapping-mode scanning probe electrospray ionization. By combining the measurement technique of capillary probe vibration with the dynamic distance control system between the probe and the sample, the vibration amplitude of the probe is maintained while the probe scans over uneven samples. This method allows simultaneous high-resolution imaging of molecular distribution, surface topography, and amplitude/phase changes in the probe vibration. Such multimodal imaging is demonstrated on rhodamine B thin films in microwells and on a mouse brain tissue section. This technique can generally be applied to examine the multidimensional molecular distribution and the surface profiles of various objects.

Mass Spectrometry Imaging

“…In this article, we will focus on imaging using probe electrospray ionization (PESI) 30 ) and desorption electrospray ionization (DESI). 31 ) The schematic diagram of each ion source is shown in Fig. 17 .…”

“…As for PESI, the scanning probe electrospray ionization (SPESI) ion source has recently been introduced. 31 )…”

High-Throughput Mass Spectrometry Imaging with Dynamic Sparse Sampling

“…Current developments in this field focus on enhancing the spatial resolution, throughput, and molecular coverage. − For example, with a specially focused laser beam and postionization, the pixel size has been reduced to ∼1 μm. − Meanwhile, the spatial resolution of liquid extraction-based imaging has been improved from ∼100 μm to better than 10 μm. , Several strategies have been used to improve the molecular coverage. For example, ion mobility spectrometry has been coupled with MSI to separate ions based on their structures and charge states, which increases the depth of coverage and enables the differentiation of isobaric ions in the gas phase. − In addition, isomer-selective imaging of unsaturated lipids has been achieved by combining chemical derivatization with tandem mass spectrometry of the products. − Although these developments substantially enhance the analytical performance of MSI, they often increase the total acquisition time by either sampling more positions to increase the spatial resolution or increasing the per-pixel acquisition time for obtaining a broader molecular coverage.…”

Simultaneous spatial, conformational, and mass analysis of intact proteins and protein assemblies by nano-DESI travelling wave ion mobility mass spectrometry imaging

“…6 µm and laser desorption/ionization droplet delivery (LDIDD) has achieved up to ~3 µm for imaging of small molecules. 26,27 In situ native mass spectrometry remains challenging because of factors including ion suppression and low analyte concentration limiting the numbers of proteins that can be detected. Nevertheless, we have demonstrated LESA and nano-DESI MSI of folded proteins and protein complexes in tissue [1][2][3] and Sharon and coworkers have analyzed protein complexes from crude cell lysates.…”