A drop of blood is a bustling city in miniature. Thousands of different molecules scurry through it, each leaving its own trace. But peering directly into this city is hard: the streets are tangled, and there are so many inhabitants that counting them all individually is out of the question.

Scientists have found a way to listen to the whole city at once, without singling out its residents. They push blood plasma through a pore the size of a single molecule. As a molecule squeezes through the pore, it momentarily changes the electric current, like a passerby brushing against a subway turnstile. By recording these fluctuations, the device captures a 'fingerprint' of the entire plasma.

Then a program trained on thousands of such recordings takes over. It compares the fingerprint of a healthy person with that of a sick one and delivers a verdict: whether a disease is present, and if so, which one. Everything happens quickly, and the procedure itself is simple — no lengthy preparation or purification of the plasma is needed.

This approach is reminiscent of an experienced doctor who diagnoses a patient at a glance, without waiting for dozens of test results. Only here, the 'glance' is the electrical noise from thousands of molecules, and the 'experience' is a clever program.

The method promises to become cheap and accessible. It could be used in ordinary clinics, not just in research labs. And then a drop of blood will reveal a person's health in a minute, like a good storyteller who doesn't drag out the suspense.