Mass spectrometry imaging under ambient conditions

Abstract

Mass spectrometry imaging (MSI) has emerged as an important tool in the last decade and it is beginning to show potential to provide new information in many fields owing to its unique ability to acquire molecularly specific images and to provide multiplexed information, without the need for labeling or staining. In MSI, the chemical identity of molecules present on a surface is investigated as a function of spatial distribution. In addition to now standard methods involving MSI in vacuum, recently developed ambient ionization techniques allow MSI to be performed under atmospheric pressure on untreated samples outside the mass spectrometer. Here we review recent developments and applications of MSI emphasizing the ambient ionization techniques of desorption electrospray ionization (DESI), laser ablation electrospray ionization (LAESI), probe electrospray ionization (PESI), desorption atmospheric pressure photoionization (DAPPI), femtosecond laser desorption ionization (fs-LDI), laser electrospray mass spectrometry (LEMS), infrared laser ablation metastable-induced chemical ionization (IR-LAMICI), liquid microjunction surface sampling probe mass spectrometry (LMJ-SSP MS), nanospray desorption electrospray ionization (nano-DESI), and plasma sources such as the low temperature plasma (LTP) probe and laser ablation coupled to flowing atmospheric-pressure afterglow (LA-FAPA). Included are discussions of some of the features of ambient MSI including the ability to implement chemical reactions with the goal of providing high abundance ions characteristic of specific compounds of interest and the use of tandem mass spectrometry to either map the distribution of targeted molecules with high specificity or to provide additional MS information in the structural identification of compounds. We also describe the role of bioinformatics in acquiring and interpreting the chemical and spatial information obtained through MSI, especially in biological applications for tissue diagnostic purposes. Finally, we discuss the challenges in ambient MSI and include perspectives on the future of the field.

Applications of the Single-probe: Mass Spectrometry Imaging and Single Cell Analysis under Ambient Conditions

“…The major advantage of ambient MSI over non-ambient methods is that sample preparation is kept at a minimum with no need for a vacuum sampling environment, which allows the sample to be analyzed in a near native state 8 . One of the major hurdles for most other ambient MSI technique has been a lack of spatial resolution 1 .…”

“…Ambient techniques such as desorption electrospray ionization (DESI) MS 5 , laser ablation electrospray ionization (LAESI) MS 6 , and nano-DESI MS 7 are capable of MSI of samples with little to no prior preparation under the ambient environment, which is able to produce MS images that potentially reflect the sample in its most native state. However, most of these techniques generally lack the high spatial resolution and detection sensitivity compared with the non-ambient techniques, with experiments typically conducted at around 150 μm per pixel 8 .…”

Mass Spectrometry in Cosmetic Science: Advanced Ionization Techniques for Detecting Trace Molecules in or on Human Skin

“…In addition to providing fast pro ling with minimal or no sample pretreatment, DESI has already been used as a MSI method in a variety of applications. 13) To date, applications of MSI to skin samples have mostly used time-of-ight secondary-ion mass spectroscopy (TOF-SIMS) and matrix-assisted laser desorption-ionization MSI (MALDI-MSI), presumably because of the broader interests in applications that provide high spatial resolution. [19][20][21] In fact, TOF-SIMS has been used for MSI analysis with submicron resolution, whereas, due primarily to the intrinsic characteristics of the ionization method used, the targets are limited to low-molecular-weight compounds.…”

“…and skin constituents (proteins, lipids, amino acids, minerals, etc.). In addition to conventional analytical methods, such as LC-MS, LC-MS/MS, GC-MS, GC-MS/MS, for bulk-sample analysis, two-dimensional (2D) desorption electrospray ionization 12,13) MS imaging (DESI MSI) and zero-volt paperspray ionization MS (zvPSI-MS) 14,15) have been introduced to obtain highspatial-resolution molecular distributions and rapid pro le information, respectively, with minimal sample pretreatment. As described in more detail in the following sections, 2D-DESI MSI, in conjunction with the tape-stripping stratum-corneum sampling technique, 16,17) and zvPSI-MS are tools that promise to accelerate progress in the eld of cosmetic science.…”

Mass Spectrometric Imaging Using Laser Ablation and Solvent Capture by Aspiration (LASCA)

“…A variety of ambient mass spectrometric imaging (MSI) methods [1], in particular laser ablation (LA) based techniques, such as matrix-assisted laser desorption ionization (MALDI) [2], electrospray-assisted laser desorption/ ionization (ELDI) [3], laser ablation electrospray ionization (LAESI) [4,5], and matrix-assisted laser desorption electrospray ionization (MALDESI) [6,7], have been developed in the past decade and applied to diverse biological systems. Although LA/MSI methods offer excellent control of sampled volumes, their possible limitations are low analyte collection and detection efficiencies.…”