Single-Particle Tracking and Trajectory Analysis of Fluorescent Nanodiamonds in Cell-Free Environment and Live Cells.

Diamond magnetometry can provide new insights on the production of free radicals inside live cells due to its high sensitivity and spatial resolution. However, the measurements often lack intracellular context for the recorded signal. In this paper, the possible use of single-particle tracking and trajectory analysis of fluorescent nanodiamonds (FNDs) to bridge that gap is explored. It starts with simulating a set of different possible scenarios of a particle's movement, reflecting different modes of motion, degrees of confinement, as well as shapes and sizes of that confinement. Then, the insights from the analysis of the simulated trajectories are applied to describe the movement of FNDs in glycerol solutions. It is shown that the measurements are in good agreement with the previously reported findings and that trajectory analysis yields meaningful results, when FNDs are tracked in a simple environment. Then the much more complex situation of FNDs moving inside a live cell is focused. The behavior of the particles after different incubation times is analyzed, and the possible intracellular localization of FNDs is deducted from their trajectories. Finally, this approach is combined with long-term magnetometry methods to obtain maps of the spin relaxation dynamics (or T1) in live cells, as FNDs move through the cytosol.