Infrared matrix-assisted laser desorption electrospray ionization mass spectrometry imaging analysis of biospecimens

Abstract

Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging (MSI) is a technique well suited for analysis of biological specimens. This tutorial review focuses on recent advancements and applications of IR-MALDESI MSI to better understand key biological questions. Through optimization of user-defined source parameters, comprehensive and quantitative MSI data can be obtained for a variety of analytes. The effect of an ice matrix layer is well defined in the context of desorption dynamics and resulting ion abundance. Optimized parameters and careful control of conditions affords quantitative MSI data which provides valuable information for targeted, label-free drug distribution studies and untargeted metabolomic datasets. Challenges and limitations of MSI using IR-MALDESI are addressed in the context of the bioimaging field.

Figure 1

Schematic of IR-MALDESI source. The sample is placed on a Peltier cooled X-Y translational stage where an exogenous ice matrix layer may be formed. A 2.94 μm laser is used to desorb material from the sample. The desorption plume interacts with an orthogonal electrospray plume where analytes partition into the charged droplets and ionization occurs in an ESI-like manner.

Figure 2

Influence of ice as a matrix for a 2940 nm IR laser. Targeted analysis of three antiretroviral (ARV) drugs in tissue from tissue with and without ice matrix. Ice matrix increased the frequency of detection and the average ion abundance for all three analytes of interest. Reproduced from Ref with permission from Springer.

Figure 3

Comparison of MALDI and IR-MALDESI MSI analysis of serial sections from a lapatinib dosed liver. A,F) optical images of the analysed tissue, B,G) image of tissue with matrix applied C,H) lapatinib D,I) heme b E,J) colocalization of lapatinib (blue) and heme b (red) in a single MS image. Reproduced from Ref. with permission from Elsevier.

Figure 4

Summary of a quantitative MSI experiment using IR-MALDESI. A) Emtricitabine (FTC) was quantified in a cervical tissue model system using a B) stable isotope labeled (SIL) calibration curve on the same tissue. C) MSI calibration curve showed good linearity and D) summary of calculated FTC in the model tissue. Reproduced from Ref. with permission from Springer.

Figure 5

MSI of efavirenz and CD3+ IHC imaging of A) colon B) ileum C) inguinal lymph node D) cerebellum E) spleen. Reproduced from Ref. with permission from American Society for Microbiology. Copywrite 2015.

Figure 6

IR-MALDESI analysis of ARVs in hair. A) EFV distribution before and after H₂O₂ sample preparation for the normalization of drug incorporation to melanin content. MSI images show that incorporated EFV does not delocalize during sample preparation B) Normalization of EFV to monomeric eumelanin unit potential for broad application of IR-MALDESI MSI analysis to hair analysis of drug incorporation. Reprinted with permission from Ref. . Copywrite 2016 American Chemical Society.

Figure 7

Control (left) and cancer (right) ovarian tissue was analysed using IR-MALDESI MSI. The two tissue types showed significant changes in lipid and metabolite profiles especially in maturing follicles (dashed line) and within cancerous regions (solid line). Reproduced from Ref. with permission from The Royal Society of Chemistry