Confocal fluorescence imaging of QD-BRET labeled spermatozoa. Spermatozoa were labeled with 0 nM (control) and 1 nM plasminogen-conjugated (QD1+) or non-conjugated (QD1−) QD-BRET nanoparticles. The control group was used for fluorescence imaging settings and was designated as the negative control group. These settings were used to capture the fluorescence emission (upper panel). Both fluorescence and visible light signals are overlaid in the bottom panel. Scale bar 10 µm.