Mass Cytometry Enabling Absolute and Fast Quantification of Silver Nanoparticle Uptake at the Single Cell Level

In
the last decades, significant efforts have been made to investigate
possible cytotoxic effects of metallic nanoparticles (NPs). Methodologies
enabling precise information regarding uptake and intracellular distribution
of NPs at the single cell level remain to be established. Mass cytometry
(MC) has been developed for high-dimensional single cell analyses
and is a promising tool to quantify NP–cell interactions. Here,
we aim to establish a new MC-based quantification procedure to receive
absolute numbers of NPs per single cell by using a calibration that
considers the specific transmission efficiency (TE) of suspended NPs.
The current MC-quantification strategy accept TE values of complementary
metal solutions. In this study, we demonstrate the different transmission
behavior of 50 nm silver NPs (AgNP) and silver nitrate solution. We
have used identical AgNPs for calibration as for in vitro-differentiated macrophages (THP-1 cell line) in a time- and dose-dependent
manner. Our quantification relies on silver intensities measuring
AgNPs in the same detection mode as the cells. Results were comparable
with the TE quantification strategy using AgNPs but differed when
using ionic silver. Furthermore, intact and digested cell aliquots
were measured to investigate the impact of MC sample processing on
the amount of AgNPs/cell. Taken together, we have provided a MC-specific
calibration procedure to precisely calculate absolute numbers of NPs
per single cell. Combined with its unique feature of multiplexing
up to 50 parameters, MC provides much more information on the single
cell level than single cell-inductively coupled plasma mass spectrometry
(SC-ICPMS) and, therefore, offers new opportunities in nanotoxicology.