Bridging Blood and Skin: Biomarker Profiling in Dermal Interstitial Fluid (dISF) for Minimally Invasive Diagnostics

Understanding the biochemical relationship between serum and dermal interstitial fluid (dISF) is critical for advancing minimally invasive diagnostics with wearables and point of care devices focusing on most relevant biomarkers accessible in the ISF. This work compares the composition of dISF and serum using Xsensio's microneedle-based collector, which yields an average of 3.4 μL/h. In the first study, total protein content, human serum albumin (HSA), and immunoglobulin G (IgG) are quantified in twelve volunteers. A second study is dedicated to screening 50 inflammation-related protein biomarkers across twenty volunteers. The results demonstrate that dISF closely resembles serum in its major protein constituents but at reduced concentrations (e.g., 57% for total protein). Strong correlations are observed between dISF and serum for CRP and SAA (R2>0.87), primarily driven by a subject with pathological levels, demonstrating the ability of dISF to reflect systemic inflammation. This study originally reports NT-proBNP detection at comparable levels in both fluids, suggesting that dISF could serve as a reliable proxy for blood NT-proBNP in the non-invasive diagnosis of cardiac failure. Cytokine profiling reveals 36 detectable cytokines, including several unique to dISF. Notably, interleukin concentrations are found to be highly similar between the two fluids. These experimental findings support dISF as a promising diagnostic medium for monitoring both localized and systemic biomarkers in clinical applications.