A fridge magnet attracts a paperclip: we can feel that field with our hands. Now shrink that field by a billion times. Atoms inside our bodies emit such weak signals, and they are very hard to catch.

Scientists built the sensor from special molecules that themselves behave like tiny magnets. They placed these molecules in a droplet the size of a bacterium — about one millionth of a millimeter. The problem is that the magnets interfere with each other, like musicians playing out of sync. The researchers came up with a "conductor"—a sequence of radio pulses that makes all the molecules oscillate in rhythm. Thanks to this, the signal lasted as long as 400 microseconds — thousands of times longer than before.

With this tool, scientists picked up a signal from a few dozen atoms nearby. The sensor can be attached directly to the molecule under study, like gluing a microphone to a guitar string. This opens the way to observing the workings of proteins and drugs at the level of individual atoms.

So tiny magnets in a droplet have become ears capable of hearing the whisper of atoms.