Nonresonant, femtosecond laser vaporization and electrospray post-ionization mass spectrometry as a tool for biological tissue imaging

Abstract

An ambient mass spectrometry imaging (MSI) source is demonstrated with both high spatial and mass resolution that enables measurement of the compositional heterogeneity within a biological tissue sample. The source is based on nonresonant, femtosecond laser electrospray mass spectrometry (LEMS) coupled to a quadrupole time-of-flight (QTOF) mass analyzer. No matrix deposition and minimal sample preparation is necessary for the source. The laser, translation stage, and mass spectrometer are synchronized and controlled using a customized user interface. Single or multiple laser shots may be applied to each pixel. A scanning rate of 2.0s per pixel is achieved. Measurement of a patterned ink film indicates the potential of LEMS for ambient imaging with a lateral resolution of ∼60μm. Metabolites including sugar, anthocyanins and other small metabolites were successfully mapped from plant samples without oversampling using a spot size of 60×70μm(2). Molecular identification of the detected analytes from the tissue was enabled by accurate mass measurement in conjunction with tandem mass spectrometry. Statistical analysis, non-negative matrix factorization and principle component analysis, were applied to the imaging data to extract regions with distinct and/or correlated spectral profiles.

Mass Spectrometry Imaging: A Review of Emerging Advancements and Future Insights

“…Even with all the ionization methods available, researchers are still developing new methodology, such as laser electrospray ionization. 26 Each ionization method has its own advantages and disadvantages, ranging from the molecules that can be analyzed to the spatial resolution achievable, the latter to be discussed further in this review. Finally, after proper preparation and ionization, the instrument itself (e.g., mass analyzer) is important to consider before determining a proper sample handling workflow.…”

Laser Desorption/Ablation Postionization Mass Spectrometry: Recent Progress in Bioanalytical Applications

“…The feasibility of LEMS in MSI analysis has also been demonstrated. Proof‐of‐concept experiments on metabolic profiling of Impatiens flower tissues were performed using the precision of LEMS with lateral resolution smaller than 100 μm (Shi, Archer, & Levis, 2016a). Figure 15 demonstrates the MSI results of an Impatiens flower leaf, which clearly illustrates the distribution of small metabolites over the sample surface.…”

“…( f ) Overlay of the m / z 303.05 ion distribution map and the optical image. Reprinted from Shi, Archer, & Levis (2016a). [Color figure can be viewed at wileyonlinelibrary.com]…”

Review and perspectives on the applications of mass spectrometry imaging under ambient conditions

“…scripts localized volatile and semi‐volatile compounds more rapidly in cross cuts of chili fruit ( C. annuum ) . LEMS‐MS imaging of fresh pink and red New Guinea Impatiens flower petal and leaf was visualized by mapping sugars, anthrocyanins and other plant metabolites using a non‐resonant, femtosecond laser with improved resolution (a spot size of 60 μm × 70 μm) . In a later study, LEMS‐MS was investigated using low‐energy, femtosecond‐duration laser vaporization at wavelengths of 800 and 1042 nm followed by nanospray post‐ionization.…”

“…LEMS-MS imaging of fresh pink and red NewGuinea Impatiens flower petal and leaf was visualized by mapping sugars, anthrocyanins and other plant metabolites using a non-resonant, femtosecond laser with improved resolution (a spot size of 60 μm × 70 μm) 128. In a later study, LEMS-MS was investigated using low-energy, femtosecond-duration laser vaporization at wavelengths of 800 and 1042 nm followed by nanospray post-ionization.Low-energy (<50 μJ), fiber-based 1042 nm LEMS (F-LEMS) was capable of interrogating molecular species originating from fresh flower petal and leaf samples using 435 fs, 10 Hz bursts of 20 pulses from a ytterbium-doped fiber laser and revealed similar results to high energy (75-1120 μJ), 45 fs, 800 nm Ti:sapphire-based LEMS (Ti:sapphire-LEMS) measurements.…”