Why does placing gram iodine at the edge of a coverslip do to motile organism?

Placing gram iodine at the edge of a coverslip creates a concentration gradient that can affect motile organisms, such as bacteria or protozoa. The iodine acts as a staining agent, which can immobilize or kill these organisms due to its toxicity, thereby hindering their movement. Additionally, the osmotic changes induced by the iodine solution may cause stress, affecting their motility further. As a result, this technique is often used to observe and study these organisms under a microscope.