Mass cytometry enables high-dimensional, single-cell analysis of cell type and state. In mass cytometry, rare earth metals are used as reporters on antibodies. Analysis of metal abundances using the mass cytometer allows determination of marker expression in individual cells. Mass cytometry has previously been applied only to cell suspensions. To gain spatial information, we have coupled immunohistochemical and immunocytochemical methods with high-resolution laser ablation to CyTOF mass cytometry. This approach enables the simultaneous imaging of 32 proteins and protein modifications at subcellular resolution; with the availability of additional isotopes, measurement of over 100 markers will be possible. We applied imaging mass cytometry to human breast cancer samples, allowing delineation of cell subpopulations and cell-cell interactions and highlighting tumor heterogeneity. Imaging mass cytometry complements existing imaging approaches. It will enable basic studies of tissue heterogeneity and function and support the transition of medicine toward individualized molecularly targeted diagnosis and therapies.

Single-cell, spatially resolved ‘omics analysis of tissues is poised to transform biomedical research and clinical practice. We have developed an open-source, computational multiplex image cytometry analysis toolbox (miCAT) to enable interactive, quantitative, and comprehensive exploration of individual cell phenotypes, cell-to-cell interactions, microenvironments, and morphological structures within intact tissues. We highlight the unique abilities of miCAT by analysis of highly multiplexed mass cytometry images of human breast cancer tissues.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was utilized for spatially resolved bioimaging of the distribution of silver and gold nanoparticles in individual fibroblast cells upon different incubation experiments. High spatial resolution was achieved by optimization of scan speed, ablation frequency, and laser energy. Nanoparticles are visualized with respect to cellular substructures and are found to accumulate in the perinuclear region with increasing incubation time. On the basis of matrix-matched calibration, we developed a method for quantification of the number of metal nanoparticles at the single-cell level. The results provide insight into nanoparticle/cell interactions and have implications for the development of analytical methods in tissue diagnostics and therapeutics.

In recent years, chemical imaging was prognosticated to become one of the key analytical applications for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). However, moderate spatial resolution and the associated measurement time required for a larger sampling area, have restricted this versatile, high sensitivity technique from being routinely used in two-dimensional chemical imaging. This work describes the development and investigation of a low dispersion sample chamber (tube cell), which allows improvement of the imaging capabilities by reduction of the single LA shot duration to 30 ms (full width at 1% maximum). The new tube cell is based on a constant laminar flow and a well-controlled delivery of the laser-ablated aerosol into the transport system, leading to minimized tailing of the aerosol washout and helping to separate the signals even at repetition rates as high as 20-30 Hz. To demonstrate the improved imaging capabilities, microstructured metallic thin film patterns were analyzed at a spatial resolution of a few micrometers. The LA-ICP-MS results obtained were comparable to Synchrotron-based micro-X-ray fluorescence (SR-microXRF). The suitability of the newly designed cell for multielement acquisitions was demonstrated using a simultaneous ICP-Mattauch-Herzog-MS. Finally, the novel laser ablation cell was applied to image the distribution of a metal-tagged biomarker in a thin section of breast cancer tissue. This application demonstrates that the technique is able to produce subcellular (~1 μm) spatial resolution, which is crucial for morphological assessment in cancer diagnostics.