Junhong Chen

A handful of lead sulfide nanocrystals coated with charged molecules spontaneously assembles into a perfect crystalline lattice. Each nanocrystal is like a brick just a few nanometers across, while the charged molecules on its surface act as the mortar.

In a hospital, blood from a finger prick usually goes to the lab, and the result comes back the next day. The new method promises to cut that wait to a few minutes. Instead of catching light reflected off a sample, it reads the electrical voltage that arises at the boundary between two media, like the faint tingle you feel when you touch a battery with wet fingers.

Every carbon atom in a molecule carries a passport — the energy with which its deepest electrons sit in their orbitals. This energy is sensitive to neighbors: add an oxygen nearby or a double bond, and the number in the passport changes. Chemists have long measured such energies with X-rays, but calculating each new molecule takes hours of machine time.