When doctors need to deliver precise doses of medicine on a strict schedule, they often administer it intravenously. Intravenous drug delivery methods need to carefully control the flow of medicine into a patient. Knowing the medicine’s flow rate—or the volume of fluid flowing into the patient each second or minute—is crucial to delivering the right amount of medicine at the right time.

Surprisingly, the correct amount is sometimes not very much at all. Imagine a 1 L bottle divided up into a billion parts. One of those parts is a nanoliter.

Doctors may only need a handful of nanoliters of fluid to flow each minute.

Fluid flowing at the rate of one nanoliter per minute, in the words of NIST biomedical engineer and specialist in ultratiny technology Greg Cooksey, is like “draining a can of Coke through a hair if it were a straw, over about 700 years.”

Cooksey works to improve how we measure these super-slow flow rates. Currently, the devices we use to measure flow rate, called “flowmeters,” can be slow, fickle, or imprecise when used on nanoliter-per-minute flows.

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