quantum mechanics - Which is the biggest object which can interfere with itself?

I've heard that scientist proof that viruses of the Tobacco mosaic virus could interfere with themselves. I'm referring to quantum interference-- the same as photons. Unfortunately, I couldn't find any material on this problem on the Internet , so I don't know if it's true. Viruses have a width between 20nm and 1000nm, so they should be applied to mesoscopic physics, where that phenomenon is possible.

Is there proof that some species of virus can interfere with themselves?

If not, which is the biggest object where we may observe that interference?

Answer

http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.html
Above is a reference with interference of 6 nm molecules achieved

Here is a proposal to use much larger molecules in space:
http://arxiv.org/abs/1201.4756
Here is a proposal to use larger molecules in an optical interfereometer:
http://arxiv.org/abs/1103.4081