Multiplexed Ion Beam Imaging Readout of Single-Cell Immunoblotting

• Published in: Analytical chemistry (Washington) Vol. 93; no. 24; pp. 8517 - 8525
• Main Authors: Lomeli, Gabriela, Bosse, Marc, Bendall, Sean C, Angelo, Michael, Herr, Amy E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 22.06.2021
• Subjects: Analytical chemistry; Antibodies; Brain cancer; Chemistry; Confocal microscopy; Fluorescence; gels; Glioblastoma; Glioblastoma cells; Imaging techniques; Immobilization; Immunoblotting; Ion beams; Ions; Mass Spectrometry; Mass spectroscopy; Medical imaging; Multiplexing; Polyacrylamide; Proteins; Scientific imaging; Signal to noise ratio; Single-Cell Analysis; Single-cell protein; Spectroscopy
• ISSN: 0003-2700; 1520-6882; 1520-6882
• DOI: 10.1021/acs.analchem.1c01050

Improvements in single-cell protein analysis are required to study the cell-to-cell variation inherent to diseases, including cancer. Single-cell immunoblotting (scIB) offers proteoform detection specificity, but often relies on fluorescence-based readout and is therefore limited in multiplexing capability. Among rising multiplexed imaging methods is multiplexed ion beam imaging by time-of-flight (MIBI-TOF), a mass spectrometry imaging technology. MIBI-TOF employs metal-tagged antibodies that do not suffer from spectral overlap to the same degree as fluorophore-tagged antibodies. We report for the first-time MIBI-TOF of single-cell immunoblotting (scIB-MIBI-TOF). The scIB assay subjects single-cell lysate to protein immunoblotting on a microscale device consisting of a 50- to 75-μm thick hydrated polyacrylamide (PA) gel matrix for protein immobilization prior to in-gel immunoprobing. We confirm antibody–protein binding in the PA gel with indirect fluorescence readout of metal-tagged antibodies. Since MIBI-TOF is a layer-by-layer imaging technique, and our protein target is immobilized within a 3D PA gel layer, we characterize the protein distribution throughout the PA gel depth by fluorescence confocal microscopy and confirm that the highest signal-to-noise ratio is achieved by imaging the entirety of the PA gel depth. Accordingly, we report the required MIBI-TOF ion dose strength needed to image varying PA gel depths. Lastly, by imaging ∼42% of PA gel depth with MIBI-TOF, we detect two isoelectrically separated TurboGFP (tGFP) proteoforms from individual glioblastoma cells, demonstrating that highly multiplexed mass spectrometry-based readout is compatible with scIB.