Nazari Milad, Bokhart Mark T, Muddiman David C
W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University.
W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University;
J Vis Exp. 2016 Mar 24(109):e53942. doi: 10.3791/53942.
Ambient ionization sources for mass spectrometry (MS) have been the subject of much interest in the past decade. Matrix-assisted laser desorption electrospray ionization (MALDESI) is an example of such methods, where features of matrix-assisted laser desorption/ionization (MALDI) (e.g., pulsed nature of desorption) and electrospray ionization (ESI) (e.g., soft-ionization) are combined. One of the major advantages of MALDESI is its inherent versatility. In MALDESI experiments, an ultraviolet (UV) or infrared (IR) laser can be used to resonantly excite an endogenous or exogenous matrix. The choice of matrix is not analyte dependent, and depends solely on the laser wavelength used for excitation. In IR-MALDESI experiments, a thin layer of ice is deposited on the sample surface as an energy-absorbing matrix. The IR-MALDESI source geometry has been optimized using statistical design of experiments (DOE) for analysis of liquid samples as well as biological tissue specimens. Furthermore, a robust IR-MALDESI imaging source has been developed, where a tunable mid-IR laser is synchronized with a computer controlled XY translational stage and a high resolving power mass spectrometer. A custom graphical user interface (GUI) allows user selection of the repetition rate of the laser, number of shots per voxel, step-size of the sample stage, and the delay between the desorption and scan events for the source. IR-MALDESI has been used in variety of applications such as forensic analysis of fibers and dyes and MSI of biological tissue sections. Distribution of different analytes ranging from endogenous metabolites to exogenous xenobiotics within tissue sections can be measured and quantified using this technique. The protocol presented in this manuscript describes major steps necessary for IR-MALDESI MSI of whole-body tissue sections.
过去十年间，质谱分析（MS）的常压电离源备受关注。基质辅助激光解吸电喷雾电离（MALDESI）就是这类方法的一个例子，它结合了基质辅助激光解吸/电离（MALDI）（如解吸的脉冲特性）和电喷雾电离（ESI）（如软电离）的特点。MALDESI的主要优势之一在于其固有的通用性。在MALDESI实验中，紫外（UV）或红外（IR）激光可用于共振激发内源性或外源性基质。基质的选择不依赖于分析物，仅取决于用于激发的激光波长。在红外MALDESI实验中，在样品表面沉积一层薄冰作为能量吸收基质。红外MALDESI源的几何结构已通过实验设计（DOE）进行了优化，用于分析液体样品以及生物组织标本。此外，还开发了一种强大的红外MALDESI成像源；在该成像源中，可调谐中红外激光与计算机控制的XY平移台和高分辨质谱仪同步。一个定制的图形用户界面（GUI）允许用户选择激光的重复频率、每个体素的激光脉冲数、样品台的步长以及源解吸与扫描事件之间的延迟。红外MALDESI已用于多种应用，如纤维和染料的法医分析以及生物组织切片的质谱成像（MSI）。使用该技术可以测量和量化从内源性代谢物到外源性异生物质等不同分析物在组织切片中的分布。本手稿中介绍的方案描述了全身组织切片的红外MALDESI MSI所需的主要步骤。
