Quantitative Evaluation of the Cellular Uptake of Nanodiamonds by Monocytes and Macrophages

Nanodiamonds (NDs) with NV- defect centers are great probes for bionanotechnology applications, with potential to act as biomarkers for cell differentiation. To explore this concept, uptake of NDs (~120nm) by THP-1 monocytes and monocyte-derived M0-macrophages is studied. The time course analysis of ND uptake by monocytes confirms differing ND-cell interactions and a positive time-dependence. No effect on cell viability, proliferation and differentiation potential into macrophages is observed, while cells saturated with NDs, unload the NDs completely by 25 cell divisions and subsequently take up a second dose effectively. ND uptake variations by THP-1 cells at early exposure-times indicate differing phagocytic capability. The cell fraction that exhibits relatively enhanced ND uptake is associated to a macrophage phenotype which derives from spontaneous monocyte differentiation. In accordance, chemical-differentiation of the THP-1 cells into M0-macrophages triggers increased and homogeneous ND uptake, depleting the fraction of cells that were non-responsive to NDs. These observations verify that ND uptake allows for distinction between the two cell subtypes based on phagocytic capacity. Overall, NDs demonstrate effective cell labeling of monocytes and macrophages, and are promising candidates for tracking biological processes that involve cell differentiation.