Magnetic fields are all around us, from the compass in your phone to the MRI machine at the hospital. To measure them with high precision, you need special materials that respond to the slightest changes in the field. One such material is molecular crystals, where electron spins, think of them as tiny tops, can hold their state for a long time.
Scientists took crystals of pentacene mixed with p-terphenyl and tested how well they work as sensors. Thin films showed a sensitivity spread of about 7.6%, while microcrystals came in at just 1.3%. What's more, microcrystals didn't lose sensitivity even at their very edge. A nanocrystal smaller than a micrometer kept a coherence time of 1.09 microseconds and a contrast of 25%—almost as good as a large crystal.
It's like comparing watchmakers: one crafts a watch that's off by a minute, another by a second. Microcrystals turned out to be those precise watchmakers, not losing a beat even at the edge of their dial. Such sensors could be used to measure magnetic fields in living cells or to check material quality.
Pentacene is an organic molecule made of five benzene rings that glows blue under ultraviolet light. It was used in the first organic transistors.
In the series "Star Trek," tricorders scan the environment with miniature sensors — molecular sensors could be a first step toward such technology.