Digital holographic microscopy overcomes the limitations of in vitro nanomaterial cytotoxicity testing

The cytotoxic potential of nanomaterials is commonly evaluated by different cellular endpoints as reactive oxygen species formation, cell viability or cell death. Usually these parameters are determined by intensity based optical readouts that are often influenced by nanomaterial-based interferences. Here we present Digital Holographic Microscopy (DHM) as a multimodal optical method, which overcomes the limitations of conventional in vitro assays based on color or fluorescence read outs. Using cell viability WST8- and cell death LDH-assay we investigated the toxic effects of two representative silver nanomaterials. Therefore, we used a matrix of four cell lines representing different organ functions. Compared to conventional toxicity assays DHM allows time resolved proliferation monitoring which is free of assay system interactions. Also, information about time-dependent mechanisms can be obtained. Additionally, we have analyzed single macrophages for refractive index, cell volume and dry mass after the incubation to cytotoxic silver spheres. The refractive index decreased dose dependent, while cell volume and dry mass stayed constant. We therefore suggest the evaluation of these parameters in cytotoxicity assessment for further evaluation of their relevance under the applied conditions. This demonstrates DHM as valuable label-free tool for nanomaterial toxicity analysis.