Monitoring of Oocyte/Embryo Respiration Using Electrochemical-Based Oxygen Sensors

Current commercially available instruments for monitoring mitochondrial respiration are incapable of single cell measurements. Therefore, we developed a three-electrode, Clark-type biosensor suitable for mitochondrial respirometry in single oocytes and embryos. The biosensor was embedded in a PMMA (polymethyl methacrylate) micro-chamber to allow investigation of single oocytes/embryos immersed in up to 100 μL of respiration buffer. The micro-chamber was completely sealed to avoid oxygen exchange between the inside of the chamber and the atmosphere, while being maintained at a temperature of 38.5 ̊C to preserve cell viability. Using amperometry, the oxygen consumption of cells inside the micro-chamber was measured as a change in output current and converted to femto-mol (fmol) oxygen consumed per second based on calibrations with known buffer oxygen concentrations. The sensor measured basal cell respiration supported by endogenous substrates, respiration associated with proton leak induced by inhibition of the adenosine triphosphate (ATP) synthase (complex V) with oligomycin, and the maximal noncoupled respiratory capacity revealed by Carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) titration. Some potential applications of this oxygen sensor system include evaluating effects of metabolic therapies on oocyte bioenergetics, and monitoring mitochondrial function throughout oocyte maturation and blastocyst development to predict embryo viability to compliment assisted reproductive technologies.