Going with the Microflow

There are still plenty of uses for the time-honored syringe, as every kid who goes to the doctor knows. But many modern drugs are administered in almost unimaginably tiny liquid volumes – in the range of nanoliters (nL, billionths of a liter) per minute. At 10 nL/min, it would take over three days to dispense a single drop. If water were flowing at that rate from a 1-liter bottle, it would take about 200 years to drain.

Accurate dose monitoring is essential. Yet current state-of-the-art devices used to measure flow on that scale have one or more operational limitations. So, a PML scientist invented a microflow meter that uses lasers and fluorescence of molecules to track the speed of liquid moving through a channel the width of a human hair.

It measures the time elapsed between when a molecule is hit by one laser beam and when it emits light after getting hit by another laser beam downstream.

The whole system of tubes, lasers, and detectors is about the size of a nickel, doesn’t need calibration, is traceable to the International System of Units, and provides continuous data on a time scale of milliseconds.

NIST has filed a provisional patent application for the system, which can be of direct benefit to makers and operators of medical drug-delivery pumps. In addition, clinical diagnostics, chemical research, biological 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.

For them, the microflow meter could be a real shot in the arm.