The Era of Next-Generation Mass Spectrometry Imaging

With MALDI imaging recently surpassing the 30^th anniversary milepost, mass spectrometry imaging technologies have continued to surge ahead.

New products have emerged from concepts that once seemed limited in practicality and scope. Technologies from areas beyond typical mass spec fields have converged to add strength to imaging platforms. This MS Imaging sector of the industry has now passed beyond the mainstream and has entered the era of next-generation mass spectrometry imaging technologies.

Mass spectrometry imaging capabilities

Next-generation sequencing (NGS) is the familiar term used to describe the pass-through from DNA and RNA sequencing modes of the past, to deep-sequencing and massively parallel methods of the present and future. With leaps in technology has come the ability to sequencing entire genomes with high fidelity, sequence large arrays and libraries for screening applications, and the ability to peer into the genetic underpinnings of single cells.

Those concepts share similarities with emerging mass spec imaging (MSI) capabilities:

• MSI offers non-targeted methods for interrogating cells, tissues, and other specimens. This objective approach can produce significant insight into complex processes such as metabolism, cell death, disease, and many others.

• MSI has the capability to perform both unlabelled and labelled analysis of a diverse array of molecules (lipids, peptides, proteins, glycans) using a single sample and experiment.

• Coupled with spatial distribution analysis, MSI has the potential to produce entire maps of tissue samples and deduce chemical details at the single cell level.

Next-generation mass spec imaging applications

New MSI capabilities have been showcased throughout the field, including the recent ASMS Asilomar Conference — Mass Spectrometry Imaging: New Developments and Applications.

• A presentation on Multi-Modal Mass Spectrometry Imaging of Tumors shed light on the challenges and successes of using multi-scale multi-omics approaches towards better understanding of cancer development and growth.

• A presentation on Maximizing the Chemical Information from Biological Tissue Sections with MSI highlighted the convergence of techniques such as capillary electrophoresis, nano-DESI and other sampling approaches for MSI analysis from a wider array of sample types and experimental scales.

• Another interesting presentation shone light on MSI and single cell multi-omics approaches for measuring peptides, metabolites, and transcripts from the same discrete tissues and cells.

• Yet another presentation documented use of MSI approaches on three-dimensional cell cultures and organoids.

• Technologies such as infrared resonance spectroscopy and FT-ICR MS are being explored to extend the boundaries of current MSI territory.

• Entire systems, as shown through comprehensive mapping of neurotransmitter networks by MALDI imaging, now appear within reach of the MSI research domain.

New mass spec imaging instrumentation

New instruments and solutions are broadening the scope of next-generation imaging capabilties.

A pioneer in MALDI imaging, Bruker has developed a portfolio of analytical platforms to expand into new territory and applications.

• The MALDI guided SpatialOMx platform brings multi-omics abilities to mass spec imaging instrumentation. The recently released timsTOF flex incorporates combined electrospray and MALDI capabilities through a switchable dual source configuration.

• Other components specific to the timsTOF Pro and the previous MALDI flex instruments provides label-free high spatial resolution imaging along with high sensitivity molecular characterization. 

• These features allow label-free spatial mapping in concert with metabolomic, lipidomic, and proteomic analysis. 

• Applications may include: in-depth tumor profiling, biomarker discovery and validation, interactome mapping, all on native or disease tissue samples.

SimulTOF Systems offers a series of MALDI TOF platforms for advanced imaging applications. Based on an extensive history of scientific and technical expertise, the instruments are designed to offer a range of power and insight into whole tissue samples – from the sub-cellular molecular to single-cell level to whole organ slice mapping.

• SimulTOF One linear mass spectrometer provides high-speed molecular imaging of proteins. The website states: 500 pixels/sec with 10 m spatial resolution; up to 2 million pixels acquired, saved, and analyzed at 10 mm spatial resolution; 1 cm tissue analyzed in 35 min.

• SimulTOF Two is a linear bipolar MALDI-TOF which provides molecular imaging of large and small molecules in both positive and negative ion modes. Applications include comprehensive molecular mapping of cells and cell populations in tissues.

• SimulTOF Three is a linear-reflector MALDI-TOF which provides high-speed molecular imaging of both small and large molecules. The reflecting analyzer provides superior mass resolving power and accuracy for small molecules, peptides, nucleotides; with resolving power 50,000 and 1 ppm mass accuracy. Although not yet available, the instrument should allow ultra-high resolution for detailed molecular identification and mapping applications.

Waters offers the MALDI SYNAPT G2-Si mass spectrometry system as a high-resolution discovery platform for imaging, biological research, and chemical materials characterization.

Key features that enable high-performance, high-definition imaging workflows include:

• A 2.5kHz laser with selectable spot size for optimizing sensitivity and speed of imaging analysis.

• Orthogonal setup of the MALDI source and TOF analyzer, ensuring high-accuracy and resolution is achieved in both MS and MS/MS modes across the entire mass range.

• Statistical tools integrated with imaging data analysis to allow high-confidence results; flexibility to use several direct analysis sources (ASAP, DESI, DART, LAESI, and LDTD) for a greater range of biomolecule detection and mapping.

• Access to UPLC-MS/MS performance on the same platform as MALDI.

The evolving age of molecular microscopy

On the horizon of these new technologies is the broader landscape of molecular microscopy. This concept builds upon many of the strengths of the conventional microscopy field, while providing the means to visualize multiple depths of detail, from the molecular to whole tissue slices, on a unified platform with switchable interrogation tools.

Updated October 2021