Oxygen consumption of single bovine embryos probed by scanning electrochemical microscopy

Oxygen consumption of individual bovine embryos was noninvasively quantifie d by scanning electrochemical microscopy (SECM). A probe microelectrode was used to scan near a single embryo surface in a culture medium to monitor t he oxygen reduction current at 37 degreesC, under a water-saturated atmosph ere of 5% CO2 and 95% air. The oxygen concentration profiles near the embry os were in good agreement with the theoretical spherical diffusion. When an embryo reached the stage of a morula with a 74-mum radius on day 6 after i n Nitro fertilization, the oxygen concentration difference (DeltaC) between the bulk solution and the morula surface was 6.90 +/- 1.35 muM. The oxygen consumption rate (F) of the single morula was estimated to be (1.40 +/- 0. 27) x 10(-14) Mol s(-1). After the SECM measurement, the embryo was continu ously cultured for another 2 days and grew to the stage of a blastocyst wit h a 100-mum radius. For the blastocyst, the DeltaC values for the inner cel l mass side and the trophoblast side were 16.40 +/- 1.83 and 9.14 +/- 1.68 muM, respectively. The oxygen consumption rate of the blastocyst was found to be in the range of (2.50 +/- 0.46) x 10(-14) Mol S-1 < F < (4.49 +/- 0.5 0) x 10(-14) Mol s(-1). We have carried out SECM measurements for 19 embryo s, and the results were compared in detail with these from an optical micro scopic observation. The DeltaC values for the morulae on day 6 after in vit ro fertilization were strongly related to the morphological embryo quality. The morulae showing a larger DeltaC value developed into blastocysts of a larger size, and the DeltaC value after the subsequent 2 days of cultivatio n was found to be increased.