Are there ferrofluids that work under water? Salt water?

Answer 1

I'd have to say yes, because I have read about cases where doctors have used ferrofluids to help seal off aneurysms. They inject the ferrofluids into the body far from the site of the aneurysm, then use magnetic probes to manipulate the ferrofluids until they are blocking the aneurysm from inside. Then, they can cauterize the aneurysm without cauterizing the entire blood vessel, because the ferrofluid is being held in place magnetically. Since blood is mostly water and contains dissolved salts, I'd say those ferrofluids would be able to work in salt water, too. I saw this in Popular Science magazine, but it was an old issue, from many years ago. I can't say any closer than that.

20 NOV 06, 2219 hrs, GMT.