Ambient Mass Spectrometry Imaging with Picosecond Infrared Laser Ablation Electrospray Ionization (PIR-LAESI)

Abstract

A picosecond infrared laser (PIRL) is capable of cutting through biological tissues in the absence of significant thermal damage. As such, PIRL is a standalone surgical scalpel with the added bonus of minimal postoperative scar tissue formation. In this work, a tandem of PIRL ablation with electrospray ionization (PIR-LAESI) mass spectrometry is demonstrated and characterized for tissue molecular imaging, with a limit of detection in the range of 100 nM for reserpine or better than 5 nM for verapamil in aqueous solution. We characterized PIRL crater size using agar films containing Rhodamine. PIR-LAESI offers a 20-30 μm vertical resolution (∼3 μm removal per pulse) and a lateral resolution of ∼100 μm. We were able to detect 25 fmol of Rhodamine in agar ablation experiments. PIR-LAESI was used to map the distribution of endogenous methoxykaempferol glucoronide in zebra plant (Aphelandra squarrosa) leaves producing a localization map that is corroborated by the literature. PIR-LAESI was further used to image the distribution inside mouse kidneys of gadoteridol, an exogenous magnetic resonance contrast agent intravenously injected. Parallel mass spectrometry imaging (MSI) using desorption electrospray ionization (DESI) and matrix assisted laser desorption ionization (MALDI) were performed to corroborate PIR-LAESI images of the exogenous agent. We further show that PIR-LAESI is capable of desorption ionization of proteins as well as phospholipids. This comparative study illustrates that PIR-LAESI is an ion source for ambient mass spectrometry applications. As such, a future PIRL scalpel combined with secondary ionization such as ESI and mass spectrometry has the potential to provide molecular feedback to guide PIRL surgery.

Optimized Mass Spectrometry Analysis Workflow with Polarimetric Guidance for ex vivo and in situ Sampling of Biological Tissues

“…DESI-MS analysis cannot be easily performed on thick or uneven tissue. Therefore, we developed a hand-held laser ablation device based on Picosecond InfraRed Laser (PIRL) technology that we’ve demonstrated to be a suitable MS desorption source when coupled to a post ionization method 31 . PIRL ablation, shown to provide rapid extraction of molecules from tissue 45 , including molecules already in solvated ionic state such as phospholipids and fatty acids, was coupled to a home-made soft thermal ionization interface capable of desolvating ionized tissue materials.…”

“…However, estimating from typical speed of movement we anticipate a depth of 300 μm. Characterization of open beam PIRL laser ablation using a controlled imaging setup with translation stages is presented in 29 .…”

“…The second workflow moves beyond thin tissue sections and explores the use of ‘reflection mode’ polarimetry combined with a novel, hand held MS point sampling probe utilizing Picosecond InfraRed Laser (PIRL) 29 ablation for tissue profiling with MS through guided point sampling. This workflow is used to examine the surface of thick tissue ex viv o, and extends the pioneering works of the Takats group in rapid tissue profiling with surgical aerosols produced with diathermy, lasers and ultrasonic aspiration methods 2, 12–14 .…”

“…The polarimetry-guided PIRL-MS examination thus does not substantially alter the examined tissue, an important practical consideration for clinical translation to thick tissues in situ and potentially in vivo . PIRL has been previously used by our group in biological tissue imaging after coupling to post ablation Electrospray ionization (PIR-LAESI) 31 . Laser Ablation Electrospray Ionization (LAESI) using nanosecond mid infrared laser radiation is an emerging ambient ion source being investigated for biological tissue imaging 32 .…”

Imaging mass spectrometry identifies prognostic ganglioside species in rodent intracranial transplants of glioma and medulloblastoma

“…The acquisition of the images was performed as previously described [17, 27, 28]. A time-of-flight tandem mass spectrometer (SCIEX TOF/TOFTM 5800 System; SCIEX, Vaughan, ON) was used to acquire the images.…”