Bioluminescence imaging (BLI) of cumulus oocyte complexes (COCs). A BLI of COCs matured in the presence of 0 nM (Control), 0.1 nM (QD0.1−), and 1 nM (QD1−) QD-BRET and 1 nM QD-BRET conjugated with anti-plasminogen antibody (QD1+). All samples were mixed with coelenterazine, the luciferase substrate, before BLI. The quantification of total signals (photons/s) is summarized in B. Imaging of each experimental replicate a included well without COCs, but filled with comparable volume of PBS as in the experimental groups to allow the evaluation of the PBS autofluorescence contribution to the results. Data are mean ± SEM of four independent replicates. Columns with different letters are significantly different (P < 0.05; ANOVA 1).