Single-Cell ICP−MS Quantification of Intracellular Chromium and Cell-Surface TNFR2 for Assessing Cr(III/VI)-Induced Lung Epithelial Injury and COPD-Relevant Responses

An integrated platform combining droplet microfluidics, lanthanide labeling, and inductively coupled plasma mass spectrometry (ICP−MS) was proposed to quantify intracellular heavy metal and cell-surface protein at single-cell resolution. The workflow performs parallel measurements on homologous single-cell subsets to establish statistical correlations between metal accumulation and functional protein responses. Using tumor necrosis factor receptor 2 (TNFR2) as a model protein, we investigated the effects of atmospheric particulate matter-associated heavy metals on human lung epithelial cells (BEAS-2B). Several heavy metals trigger TNFR2 upregulation, with Cr(VI) exerting the most pronounced effect. The Cr(VI)-induced increase in TNFR2 expression was associated with elevated TNF-α release, higher intracellular ROS, and reduced SOD activity but did not correlate directly with intracellular Cr accumulation, likely due to distinct cellular uptake mechanisms between Cr(III) and Cr(VI). High-concentration Cr(III) exposure, however, led to intracellular Cr enrichment and provoked inflammatory responses. Integration of differential gene expression, TNF-α release, and TNFR2 expression support TNFR2 as a potential indicator of metal-induced oxidative stress, epithelial injury, and COPD-relevant inflammatory responses. This single-cell dual-parameter approach provides a new strategy for linking metal uptake to functional protein responses in environmental toxicology.