in vivo Monitoring with micro-implantable hypoxia sensor based on tissue acidosis.

Hypoxia is a common medical problem, sometimes difficult to detect and caused by different situations. Control of hypoxia is of great medical importance and early detection is essential to prevent life threatening complications. However, the few current methods are invasive, expensive, and risky. Thus, the development of reliable and accurate sensors for the continuous monitoring of hypoxia is of vital importance for clinical monitoring. Herein, we report an implantable sensor to address these needs. The developed device is a low-cost, miniaturised implantable electrochemical sensor for monitoring hypoxia in tissue by means of pH detection. This technology is based on protonation/deprotonation of polypyrrole conductive polymer. The sensor was optimized in vitro and tested in vivo intramuscularly and ex vivo in blood in adult rabbits with respiration-induced hypoxia and correlated with the standard device ePOCTM. The sensor demonstrated excellent sensitivity and reproducibility; 46.4 ± 0.4 mV/pH in the pH range of 4-9 and the selectivity coefficient exhibited low interference activity in vitro. The device was linear (R2 = 0.925) with a low dispersion of the values (n = 11) with a cut-off of 7.1 for hypoxia in vivo and ex vivo. Statistics with one-way ANOVA (α = 0.05), shows statistical differences between hypoxia and normoxia states and the good performance of the pH sensor, which demonstrated good agreement with the standard device. The sensor was stable and functional after 18 months. The excellent results demonstrated the feasibility of the sensors in real-time monitoring of intramuscular tissue and blood for medical applications.

Micro-needle implantable electrochemical oxygen sensor: ex-vivo and in-vivo studies.

Oxygen is vital for energy metabolism in mammals and the variability of the concentration is considered a clinical alert for a wide range of metabolic malfunctions in medicine. In this article, we describe the development and application of a micro-needle implantable platinum-based electrochemical sensor for measuring partial pressure of oxygen in intramuscular tissue (in-vivo) and vascular blood (ex-vivo). The Pt-Nafion® sensor was characterized morphological and electrochemically showing a higher sensitivity of -2.496 nA/mmHg (-1.495 nA/µM) when comparing with its bare counterpart. Our sensor was able to discriminate states with different oxygen partial pressures (pO2) for ex-vivo (blood) following the same trend of the commercial gas analyzer used as standard. For in-vivo (intramuscular) experiments, since there is not a gold standard for measuring pO2 in tissue, it was not possible to correlate the obtained currents with the pO2 in tissue. However, our sensor was able to detect clear statistical differences of O2 between hyperoxia and hypoxia states in tissue.