Hi, I was using costar 3516 6-well plate to culture HEK293T and reached the confluency 80-90%. Then I mix 1ug plasmid DNA with 2.5uL Plus reagent in 500uL DMEM. 10uL lipofectamine LTX reagent with 5oouL DMEM. I added the plasmid mixture into lipo mixture and incubate for 25min. Before transfection, I wash the cell once with fresh DMEM and then added transfection mixture. Right after that, the cells at the center of wells get detached and create an empty hole. I don't know how this comes. I do all the washing steps gently (dropwise). How does this happen? how can I improve?