Extracting Ions From A Single Drop of Blood

The device enabled researchers to quickly measure two physiologically important ions in blood samples from volunteers.

Analyzing blood for ions, such as electrolytes or basic nutrients like iron, currently requires drawing several milliliters of blood and removing large molecules and cells via methods like centrifugation. But Kei Toda of Kumamoto University, in Japan, and his colleagues devised a method that needs little blood and eliminates the separation step, all with a device only about 3 cm2.

The scientists place a drop of human blood into a sample well, below which lies a dialysis membrane that keeps out large molecules and cells and another membrane that allows either positively or negatively charged ions to pass through. They apply an electric field for a minute, drawing ions of that charge through the membranes into water on the other side, which they then analyze using ion chromatography-mass spectrometry for ions of interest.

The team used the method to measure levels of iodide, an important nutrient for thyroid hormone development, in blood drops collected from 16 volunteers. The levels tracked what would be expected: Volunteers who reported eating iodide-rich miso soup with seaweed carried more than 10-µg/L iodide in their blood, while others carried 3–8 µg/L. The team also measured thiocyanate—a smoking biomarker—and found it was four times as concentrated in the blood of smokers as in nonsmokers. Because it requires less blood, the new method could allow for more frequent measurements and thus better characterization of how these ions fluctuate in the blood over a day or after particular exposures. Next, the researchers seek to create miniaturized devices to pair with the extraction device for analyzing the extracted ions.