Single-Cell Isotope Dilution Analysis with LA-ICP-MS: A New Approach for Quantification of Nanoparticles in Single Cells.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method for the analysis of metal nanoparticles (NPs) in single cells. However, two main obstacles, low analytical throughput and lack of commercial reference materials, need to be overcome. In this work, we demonstrated the principles of a new approach termed "single-cell isotope dilution analysis" (SCIDA) to remove the two obstacles. For a proof of concept, macrophage cells were chosen as a model to study the uptake of silver NPs (AgNPs) at a single-cell level. Single cells exposed to AgNPs were placed in an array by a microfluidic technique; each cell in the array was precisely dispensed with a known picoliter droplet of an enriched isotope solution with a commercial inkjet printer; accurate quantification of AgNPs in single cells was done by using isotope dilution LA-ICP-MS. The average Ag mass of 1100 single cells, 396 ± 219 fg Ag per cell, was in good accord with the average of the population of cells determined by solution ICP-MS analysis. The detection limit was 0.2 fg Ag per cell. The SCIDA approach is expected to be widely applied for the study of cell-NP interactions and biological effects of NPs at the single-cell level.