I am interested in producing videos of growing and dividing bacterial cells. The problem, as I see it, it to keep the cells still and well-oxygenated without them drying out.

I have tried using a large drop of nutrient agar on a slide, covering with a coverslip and making observations as close as possible to the edge of the coverslip in order to maximise gaseous exchange. Unfortunately, the sample drifts out of focus in a few tens of seconds, which makes a time-lapse series impracticable. I imagine the problem is that the agar is slowly drying and contracting.

Does anybody know any tricks to tackly this problem?