FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States.
AbbVie Inc., North Chicago, Illinois 60064, United States.
J Am Soc Mass Spectrom. 2024 Aug 7;35(8):1959-1968. doi: 10.1021/jasms.4c00219. Epub 2024 Jul 10.
Mass spectrometry imaging (MSI) has become a significant tool for measuring chemical species in biological tissues, where much of the impact of these platforms lies in their capability to report the spatial distribution of analytes for correlation to sample morphology. As a result, enhancement of spatial resolution has become a frontier of innovation in the field, and necessary developments are dependent on the ionization source. More particularly, laser-based imaging sources may require modifications to the optical train or alternative sampling techniques. These challenges are heightened for systems with infrared (IR) lasers, as their operating wavelength generates spot sizes that are inherently larger than their ultraviolet counterparts. Recently, the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) source has shown the utility of a diffractive optical element (DOE) to produce square ablation patterns, termed top-hat IR-MALDESI. If the DOE optic is combined with oversampling methods, smaller ablation volumes can be sampled to render higher spatial resolution imaging experiments. Further, this approach enables reproducible spot sizes and ablation volumes for better comparison between scans. Herein, we investigate the utility of oversampling with top-hat IR-MALDESI to enhance the spatial resolution of measured lipids localized within the head of sectioned zebrafish tissue. Four different spatial resolutions were evaluated for data quality (e.g., mass measurement accuracy, spectral accuracy) and quantity of annotations. Other experimental parameters to consider for high spatial resolution imaging are also discussed. Ultimately, 20 μm spatial resolution was achieved in this work and supports feasibility for use in future IR-MALDESI studies.
质谱成像（MSI）已成为测量生物组织中化学物质的重要工具，这些平台的主要优势在于其能够报告分析物的空间分布，以与样品形态相关联。因此，提高空间分辨率已成为该领域的创新前沿，而必要的发展取决于离子源。更具体地说，基于激光的成像源可能需要对光路进行修改或采用替代采样技术。对于具有红外（IR）激光器的系统，这些挑战更加严峻，因为其工作波长产生的光斑尺寸本身比紫外光对应物大。最近，红外基质辅助激光解吸电喷雾电离（IR-MALDESI）源已显示出衍射光学元件（DOE）的实用性，可产生称为平顶 IR-MALDESI 的方形烧蚀图案。如果将 DOE 光学器件与过采样方法结合使用，则可以采样更小的烧蚀体积，以实现更高的空间分辨率成像实验。此外，这种方法可以实现可重复的光斑尺寸和烧蚀体积，以便更好地比较扫描结果。在此，我们研究了过采样平顶 IR-MALDESI 在增强局部化在斑马鱼组织头部的测量脂质的空间分辨率方面的应用。为了评估数据质量（例如，质量测量精度、光谱精度）和注释数量，评估了四种不同的空间分辨率。还讨论了用于高空间分辨率成像的其他实验参数。最终，在这项工作中实现了 20 μm 的空间分辨率，支持在未来的 IR-MALDESI 研究中使用。
