Application of quantum dot nanoparticles for potential non-invasive bio-imaging of mammalian spermatozoa

<p>Abstract</p> <p>Background</p> <p>Various obstacles are encountered by mammalian spermatozoa during their journey through the female genital tract, and only few or none will reach the site of fertilization. Currently, there are limited technical approaches for non-invasive investigation of spermatozoa migration after insemination. As the knowledge surrounding sperm behavior throughout the female genital tract still remains elusive, the recent development of self-illuminating quantum dot nanoparticles may present a potential means for real-time <it>in vitro</it> and <it>in vivo</it> monitoring of spermatozoa.</p> <p>Results</p> <p>Here, we show the ability of boar spermatozoa to harmlessly interact and incorporate bioluminescent resonance energy transfer-conjugated quantum dot (BRET-QD) nanoparticles. The confocal microscope revealed <it>in situ</it> fluorescence of BRET-QD in the entire spermatozoon, while the ultra-structural analysis using the transmission electron microscope indicated BRET-QD localization on the sperm plasma membrane and intracellular compartment. In controlled-<it>in vitro</it> assays, bioluminescent imaging demonstrated that spermatozoa incubated with BRET-QD and luciferase substrate (coelenterazine) emit light (photons/sec) above the background, which confirmed the <it>in situ</it> fluorescence imaging. Most importantly, sperm motility, viability, and fertilizing potential were not affected by the BRET-QD incorporation when used at an appropriated ratio.</p> <p>Conclusions</p> <p>Our results demonstrate that pig spermatozoa can incorporate BRET-QD nanoparticles without affecting their motility and capacity to interact with the oocyte when used at an appropriated balance. We anticipate that our study will enable in-depth exploration of the male components of <it>in vivo</it> migration, fertilization, and embryonic development at the molecular level using this novel approach.</p>