Aims: The use of engineered metal-containing nanoparticles (NP) as drug carriers is an area of intense research. Despite the focus on targeting within the field, the approaches that are used to examine cellular NP uptake and biodistribution remain relatively crude. The use of mass cytometry has many potential advantages over the standard fluorescence or radiotracer-based techniques; therefore we have assessed the technology for use in quantifying NP uptake in vitro.
Methods: Branched polyethylene imine (bPEI), polyethylene glycol (PEG) and citrate stabilized silver nanoparticles (AgNP) of diameter 10, 30 and 60 nm were synthesized. AgNP were incubated with Jurkat cells for 24 h at 37°C, and non-internalized AgNP were removed in duplicate aliquots by chemical etching. The concentration of natural abundance Ag in individual cells was determined using the dual count values of cell-associated 107Ag and its transmission efficiency in a fluid-phase Ag standard. Mass cytometry data was compared to conventional inductively-coupled plasma mass-spectrometry (ICP-MS) on digested cell suspensions.
Results: Cell-associated Ag was readily resolved in Jurkat cells by mass cytometry and the use of a fluid-phase standard enabled determination of Ag concentrations within individual cells with a dynamic range of ~3 orders of magnitude (~1-1000 fg/cell). Single cell data correlated with ICP-MS data on bulk populations. Finally, the ability to chemically etch surface-associated AgNP enabled true uptake to be determined.
Conclusions: Mass cytometry is a reliable tool for quantifying NP uptake at the single cell level. Future studies should focus on investigating NP uptake in complex biological systems.