High-throughput approach to measure number of nanoparticles associated with cells: size dependence and kinetic parameters

Understanding how nanoparticle properties influence uptake by cells is highly important for developing nanomedicine design principles. For this, quantitative studies where actual numbers of cell-associated particles are determined are highly relevant. However, many techniques able to measure particle numbers suffer from low-throughput or place requirements on the types of nanoparticles that can be measured. Here we show the usage of flow cytometry to measure numbers of cell-associated nanoparticles for particles ranging in size from 100-500 nm, and extend this range to 40-500 nm by separate calibration. For the 100 nm particles, we corroborate the numbers by direct, low-throughput, counting using fluorescence microscopy. Applying flow cytometry we subsequently investigated the effect of particle size on the number of cell-associated particles for various timespans up to 5 h and found only a minor effect of size between 40, 100, and 200 nm particles. Next, we measured the kinetic rate constants describing the adsorption, desorption, and internalization for the 100 nm particles specifically. In general, we found values in accordance with previous literature. We foresee the future usage of the methodology applied here to investigate the kinetics of nanoparticle cellular uptake for a variety of particle types. Using calibrated flow cytometry, we measured the actual numbers of nanoparticles associated with cells for 40-200 nm polystyrene particles. Next, we fitted a kinetic model to obtain the adsorption, desorption and internalization rate constants.