30 BC-640 AD: Ancient Romans create drinking cups that change colour under different lighting because the glass contains nanoparticles of gold and silver. The colour change suggests nanoparticles behave differently than their macro counterparts, but it is a discovery that wouldn't be recognized for about 2,000 years.
• A timeline of developments that have contributed to the science of nanotechnology
They could have added those reports of Greco-Roman hair-dye making unknowing use of similar technology in hair dye (the story was kicking around a couple of years ago):
• Ancient Hair Dye Harnessed Nanotechnology (Scientific American)
• Ancient Dye but Cutting-edge Science (CNRS)
• Ancient hair dye used nanotechnology (ABC)