A pinch of diamond dust dropped into a glass of liquid acts like hundreds of tiny magnetic compasses. When molecules with unpaired electrons, known as paramagnetic, appear nearby, the needles of these compasses start to quiver. From that quiver, you can tell what the molecule is and how much of it is there.

Previously, such measurements were slow: diamond particles were interrogated one by one with laser pulses, and each answer took minutes. In the new work, the team built a setup where thousands of diamond grains are probed simultaneously, and the signal is read by a fast detector — an avalanche photodiode that works like a highly sensitive eye. Electronics on a programmable chip (FPGA) instantly sum up the responses from all particles.

Now chemists can watch reactions involving paramagnetic particles almost live. If the technique is improved, processes shorter than a second, such as how proteins in a cell exchange electrons, will become visible.