fig1

Figure 1. Biomarker sensing strategies in the human body. (A) Overall anatomical structure of the skin; (B) The capillary interface consists of a single layer of endothelial cells and inter-endothelial junctions, regulating the exchange of metabolites between blood and ISF. Sampling strategies for blood (C-F) and ISF (G-J); (C) Schematic of a commercial blood glucose meter; (D) Single-needle lancet method for blood extraction; (E) Penetration schematic of a microscale needle array; (F) Conceptual illustration of ampule based blood collection from exuded droplets; (G) Solid MNA patch for minimally invasive ISF extraction; (H) Porous and surface-functionalized MN patch; (I) Hollow MN utilizing capillary action for ISF uptake; (J) Hydrogel-based MN patch for passive ISF absorption. ISF: Interstitial fluid; MN: microneedle.