A transdermal and/or intradermal diagnostic device comprising a combined hollow microneedle interstitial fluid (IF) extraction device and a detector can monitor biomarkers in-situ. For example, electrode transducers with optimally arrayed and designed microneedles can be combined with a suitable pumping method to determine biomarker levels in human subjects under intense physical exertion to monitor metabolic stress and fatigue. The device can perform real-time, in-situ measurements of lactate in human subjects. Monitoring of other biomarkers is straightforward.
