Painless Microneedle System Helps Monitor Drug Levels

The patch contains an integrated, hollow microneedle-optofluidic biosensor with needle-like projections less than half a millimeter long, which extract extremely small volumes--less than one nanoliter--of interstitial fluid (ISF).

The inner lumen of the microneedle is functionalized to be used as a micro-reactor during sample collection, trapping and binding target drug candidates during extraction, without the requirement of a sample transfer. An optofluidic device is integrated within the microneedle to rapidly quantify drug analytes with high sensitivity, using a straightforward absorbance scheme. In a clinical study, the antibiotic vancomycin was detected using ISF volumes that ranged between 50–100 μL. The study was published on July 6, 2106, in Scientific Reports.

“The microneedles resemble hollow cones and are less than half a millimeter in length; they are designed to puncture only the outer layer of skin, which acts as a protective barrier, but not the epidermis or dermis, which comprise nerves, blood vessels, and active immune cells,” said senior author Victor Cadarso, PhD, of PSI. “The combination of knowhow from UBC and PSI, bringing together microneedles, microfluidics, optics, and biotechnology, allowed us to create a device capable of both collecting the fluid and performing the analysis.”

ISF surrounds all tissue cells. It is advantageous in biosensing applications, since it does not contain any particulates such as red blood cells or platelets, and contains at least 5–10 times less protein than blood serum. But only extremely low volumes are found in human skin, making the process of ISF extraction rather difficult.

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