The National Institute of Standards and Technology (NIST) has filed a provisional patent application for a microflow measurement system, about the size of a nickel, that can track the movement of extremely tiny amounts of liquids–as small as nanoliters (nL, billionth of a liter) per minute. If water were flowing at that rate from a 1-liter bottle of water, it would take about 200 years to drain.
The invention is designed to fill an urgent need in the rapidly expanding field of microfluidics, in which precisely measuring tiny flow rates is critical. For example, some medical drug-delivery pumps dispense as little as tens of nL per minute into the bloodstream. For comparison, a single drop of water contains 50,000 nL. Clinical diagnostics, chemical research, cell sorting and counting, and continuous-flow micromanufacturing–essentially tiny factories that work nonstop to make small quantities of liquids–also increasingly require accurate measurements of similarly minuscule volumes.
But current state-of-the-art devices used to measure flow on that scale have one or more operational limitations. “Some require calibration, others use complex imaging systems and microscopes; some take data over many minutes, and therefore, can’t track dynamic changes, and some are not traceable to the International System of Units,” said inventor Greg Cooksey, a biomedical engineer in NIST’s Physical Measurement Laboratory.
His optical microflow measurement system, fabricated at NIST’s Center for Nanoscale Science and Technology, avoids those complications. It monitors the speed of fluorescent molecules in liquid as they travel down a channel about the width of a human hair, measuring the time interval between the molecules’ responses to two separate laser pulses.