Metal nanoparticles are increasingly used in cosmetics, food packaging, textiles, toothpaste, and other ubiquitous products. Yet, their impact on our environment, food, and health is largely unknown because measuring nanoparticles in environmental and biological systems is very difficult. Similarly, measuring the uptake of metal-containing drugs by cells to develop smart therapeutics targeting tumors is also difficult because it requires analysis of numerous individual cells to assess the selectivity of the drug uptake by diseased cells versus healthy cells.