Nanoparticles are omnipresent in our environment: Viruses in ambient air, proteins in the body, as building blocks of new materials for electronics, or in surface coatings. Visualizing these smallest particles is a problem: They are so small that they can hardly be seen under an optical microscope. Researchers have now developed a sensor that not only detects nanoparticles, but also determines their condition and tracks their movements in space.