Publication: Microneedle Patch for Painless Intradermal Collection of Interstitial Fluid Enabling Multianalyte Measurement of Small Molecules, SARS-CoV-2 Antibodies, and Protein Profiling

Federico Ribet, et al., published this article in Advanced Healthcare Materials that presents a "cost-effective and compact single-microneedle-based device designed to painlessly collect precisely 1.1 µL of dermal ISF within minutes".  Just in that sentence there are a lot of things to consider:

1. single microneedle
2. painless
3. 1.1 µL 
4. interstitial fluid

The single microneedle drives the latter three - i.e., the microneedle is unlikely to hit a nerve, therefore painless, the microneedle cannot draw large volumes, hence 1.1 µL, and lastly the microneedle is unlikely to penetrate a capillary to draw blood, thus interstitial fluid is obtained. The use of interstitial fluid is interesting as any drug or biomarker molecules measured would be those which were able to cross the capillary boundaries and most likely represent free drug.  For those who have dealt with the whole free vs bound drug discussion and which is more appropriate to pharmacological models, I'll leave it to you to comment on the value of interstitial fluid concentrations. 

Regarding the volume, so many technologies are able to measure picomolar and femtomolar amounts, that this device has some potential for clinical study use, post-marketing therapeutic drug monitoring, as well as some clinical lab applications. 

Not noted is that the sample is absorbed into a paper storage component and stored dry.  A blue powder is used within the paper to identify when the volume hits the demarcated visualization volume window so that the device can be removed from the skin. The accuracy of the volume may be a hindrance when considering use by "free-range" humans, but there will be situations where the overall simplicity and cost would override any analytical variability.

The article includes a number of good graphics and pictures of the device, as well as skin penetration.  Using caffeine as a test compound, 5 dosed and one placebo subject had samples drawn using the device and concurrent 10uL capillary blood DBS samples drawn.  Reasonably good relationship exists between the two measures by LC-MS/MS.  They also presented data on a number of proteins, as well as antibodies to SARS Cov-2 spike protein. 

If interested, please read the article and come back and comment here.