Fertilization of bovine oocytes induced solely with combined laser microbeam and optical tweezers

Purpose: Our purpose was to show that fertilization of oocytes can be obtained solely by laser light-mediated manipulation of gametes. Method: A small channel was drilled into the zona pellucida of bovine oocytes using an ultraviolet (UV)-laser microbeam. Highly diluted cattle sperm were not able to fertilize the laser drilled oocytes. Results: Fertilization was achieved only when three to five cattle sperm were trapped with optical tweezers and inserted directly through the laser drilled hole into the perivitelline space. After 20 hr 3 of 79 (3.8%) oocytes revealed two pronuclei and a sperm tail within their cytoplasm. Cattle sperm are difficult to catch. Therefore, the gametes had to remain for about 20 min in room atmosphere, which might be the reason for the low fertilization results. Conclusions: The results indicate that a combined UV-laser microbeam and optical tweezers trap can be used successfully for ''noncontact'' microinsemination procedures.