Quantitative elemental bioimaging: an antibody-based double-labelling method to quantify the cell-specific distribution of silver nanoparticles in lung tissue sections

Silver nanoparticles (Ag-NP) are contained in many consumer products although their uptake especially by respiration bears potential risks for human health. Quantitative data about the systemic distribution of Ag-NP at the cellular level is strongly required to better understand the mode of action and to create meaningful in vitro models. In this paper we present a novel approach to identify cells in tissue sections by mass spectrometry imaging. Starting with a specific antibody bound to a cell marker protein we employed a double labelling strategy: a conventional secondary fluorescent antibody staining is followed by a labelling with a colloidal gold-coupled antibody directed against the same primary antibody. This allows identification of, e.g. , regions of interest with conventional fluorescence microscopy and, thereafter, to detect identified cells by elemental mass spectrometry. The strategy circumvents the necessity to allocate mass-based signals to microscopic images. Unlike cost-intensive lanthanide-labelling the method is applicable to monoclonal and polyclonal primary antibodies. With this approach we confirmed the uptake of silver nanoparticles in alveolar macrophages and alveolar septal structures. The LA-ICP-MS image shows an overlay of the m / z 197 signal of colloidal gold labelled macrophages (green) and the m / z 107 signal of silver nanoparticles (red) in lung tissue, with colocations of Au and Ag in yellow colour.