The microneedle patch for modern sensors was developed by American researchers from the Sandia National Laboratories and the University of New Mexico. Microneedles are a few hairsbreadths wide and can sip the clear fluid between cells in the middle layer of skin.  The intercellular fluid, resembling blood plasma and located just below the surface of the skin, contains a variety of biomarkers, including potassium, sodium, and proteins, which are associated with both normal body function and certain diseases. Microneedles continuously sample interstitial fluid to track physiological conditions.

The new 'patch' contains microneedles, which can collect a relatively large amount of intercellular fluid for laboratory analysis. In addition, such a patch can serve as a basis for integrating sensors into it, for direct detection of biomarkers. According to Ronen Polsky, a Sandia materials scientist who leads the design of the microneedle sensor, this is the first way to extract large volumes of pure interstitial fluid for further study. Each microneedle in the patch is connected to a tiny tube where the intercellular fluid is collected. With the help of such tubes, about 2 microliters of intercellular fluid can be collected within 30 minutes and transferred to a laboratory test facility. Since the needles are painless and minimally invasive, they could be left in for hours or even a whole day without irritation, allowing constant monitoring.

In order to obtain large enough volumes of this liquid, the researchers tested needles of different length on people with different skin thicknesses. At the same time, scientists tried to take into account the comfort of using such an 'instrument' to make the patch as painless and convenient for future patients as possible. The result is a device capable of collecting more intercellular fluid than using other methods, and also making it almost painless, especially after the patch is fixed to the skin. A continual sampling of important biomarkers in this interstitial fluid could help monitor and diagnose many diseases and disorders. These markers include electrolytes, salts such as potassium and sodium that get out of balance during dehydration; glucose, a sugar that diabetics need to monitor constantly; and lactate, a potential marker of physical exhaustion or life-threatening sepsis.

For many applications the researchers envision, the biomarker sensors would be on the very tip of the microneedle to allow continual detection of the conditions inside the body. Future studies will use larger needle arrays to increase sample volume. For other applications, such as early cancer detection, collecting the interstitial fluid may take longer than a standard blood draw, but could provide different clues. The researchers are interested in business partners to help integrate the microneedle sensors into a self-contained device. The ultimate goal of commercialization or a partnership with industry would be to get the technology to the market in a way that benefits the public. The technology gained funds from Sandia’s Laboratory Directed Research and Development program and the U.S. Defense Threat Reduction Agency.