Oxygen Detection in Dermal Interstitial Fluid with Microneedles Based on Platinum Nanoparticles

Herein, we have developed a microneedle-based oxygen sensor wearable patch (O₂ MN) designed for real-time, minimally invasive detection of dermal ISF oxygen levels. This work pioneers the use of platinum nanoparticles as the sensing element for oxygen detection within a microneedle platform, enabling high electrochemical sensitivity at a mild applied potential. The wearable patch integrates the nanoparticle-based microneedle as the working electrode and a Ag/AgCl ink-modified microneedle as the counter/reference electrode, operating at an applied potential of -0.3 V to detect a wide range of oxygen (10-254 μM) with high sensitivity (-0.51 nA μM^-1) and a rapid response time (9 s). The analytical assessment revealed excellent performance, including high reversibility (RSD = 3.4%), repeatability (RSD = 5.2%), medium-term stability (1.9% deviation over 90 min), acceptable reproducibility (6.6%), and mechanical reliability during skin insertion. Notably, to the best of our knowledge, this study represents the first comprehensive evaluation of the performance of an oxygen microneedle sensor, including systematic in vitro, on-body, and in vivo experiments. The sensor's accuracy was validated with a Pearson correlation coefficient of 0.99 for in vitro tests, and on-body oxygen measurements in euthanized rats highlighted the reliability of the O₂ MN patch for dermal ISF oxygen detection. In vivo studies further revealed a strong positive correlation (Pearson correlation coefficient = 0.83) between dermal ISF and blood oxygen levels, underscoring the O₂ MN patch's potential for biomedical applications through real-time, minimally invasive monitoring.