Quantitative Single-Cell Multielemental Analysis Using Metal-Loaded Microparticles: toward a Universal Quantification...

The use of lanthanide-tagged antibodies enables multiplexed biomarker monitoring in individual cells by mass cytometry. Here, we show the design and application of a quantitative workflow that enables multiple-element determination in single-cell events using multielement barcoded polystyrene beads and mass cytometry. By online mixing of the cell suspension with the beads, transient events of both entities can be discriminated in the time-of-flight-mass spectrometry (TOF-MS). The element-specific content of the beads is used as a single-point calibration standard to assess the concentration of the same element used as a tag on labeled cells. Using this approach, the quantification of Lu in lymphocytic leukemia cells (MEC-I) labeled with a Lu-tagged anti-CD20 antibody is demonstrated. Moreover, multielemental analysis is shown by obtaining a polynomial model that relates the instrumental response for bead events to the m/z of the multiple elements and isotopes, enabling quantification of elements not included in the beads. This provides a general workflow for all lanthanides potentially used as tags and is tested in A2780 ovarian cancer cells labeled with Nd-tagged antitransferrin receptor 1 antibody and an Ir DNA intercalator. Excellent agreement with external calibrations is shown, highlighting enhanced quantitative capabilities of high-dimensional single-cell MS, applicable also to single-cell ICP-MS using TOF analyzers.