Automatic z-Axis Correction Improves Mass Spectrometry Imaging of Uneven Surfaces

Mass spectrometry imaging (MSI) has revolutionized the field of molecular analysis, allowing researchers to visualize the spatial distribution of molecules in complex samples. However, most MSI experiments are limited to flat and uniformly thick samples, posing challenges when analyzing textured or uneven surfaces. Addressing this limitation, a team led by David C. Muddiman from North Carolina State University has developed an innovative method that automatically corrects for height differences on uneven surfaces during MSI experiments. The research was published in the Journal of the American Society for Mass Spectrometry (1).

3D rendering of a black ball with an uneven surface on a white background. The ball glows and looks like a virus, a dangerous microorganism. Abstract illustration for medical compositions. | Image Credit: © Станислав Чуб - stock. adobe.com

The researchers integrated a chromatic confocal sensor into the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) system. This sensor enabled the real-time measurement of the sample surface height at the location of each analytical scan. By incorporating this height profile information, the z-axis position of the sample was dynamically adjusted during MSI data acquisition, compensating for the unevenness of the surface.

To validate the effectiveness of this approach, the team tested it on two challenging samples: a tilted mouse liver section and an unsectioned Prilosec tablet, both exhibiting quasi-homogeneity and height differences of approximately 250 μm. When performing MSI with automatic z-axis correction, consistent ablated spot sizes and shapes were observed, allowing for the accurate measurement of ion spatial distribution across the mouse liver section and Prilosec tablet.

Conversely, when no z-axis correction was applied, irregular spots with reduced signals and high variability were observed, hindering the accurate assessment of molecular distribution. This highlighted the importance of the automatic z-axis correction method in achieving reliable and reproducible MSI results on uneven surfaces.

The development of this automatic z-axis correction method for MSI opens up new possibilities for analyzing samples with complex surface topographies. By enabling precise adjustments during data acquisition, researchers can now obtain high-resolution molecular images even from samples that were previously challenging to analyze. This advancement in MSI technology holds promise for various fields, including biomedical research, pharmaceutical development, and environmental analysis, where samples with uneven surfaces are common.

The work represents a significant step forward in expanding the capabilities of mass spectrometry imaging, providing researchers with a powerful tool to explore the spatial distribution of molecules in diverse samples with uneven surfaces.

Reference

(1) Xi, Y.; Knizner, K. T.; Garrard, K. P.; Muddiman, D. C. Automatic z-Axis Correction for IR-MALDESI Mass Spectrometry Imaging of Uneven Surfaces. J. Am. Soc. Mass Spectrom. 2023. DOI: https://doi.org/10.1021/jasms.3c00151