A microneedle device for rapid dermal interstitial fluid sampling

Dermal interstitial fluid (ISF) offers a promising alternative to invasive
blood tests and opportunities for novel skin diagnostics. Progress in both
the understanding and adoption of ISF tests is hindered by sampling
challenges, including lengthy collection times, non-negligible failure
rates, variable collection volumes, and inconsistent bioanalyte levels.
The causes of many of these issues are not well understood. We demonstrate
a microneedle device that is several times faster than state-of-the-art,
collecting an average of 15.5 mg of ISF in 5 minutes in humans with a
near-zero failure rate. This improvement was achieved by designing the
spatial pressure gradient driving ISF flow. The influence of penetration
depth, collection time, pressure, and age on ISF collection was
elucidated, with Darcy's law explaining multiple observations. A
data-driven acceptance criterion of <1% blood contamination for ISF
is proposed. The device and findings presented will empower researchers to
better conduct robust studies in the development of ISF diagnostics.