What are your nanobots gonna do for entertainment?
According to the text, the strings on this guitar are actual and pluckable, although they would hardly make a noise if something managed to pluck them. Made from silicon crystals. The strings, they say, are 50 nanometers wide; for comparison, the diameter of a human hair is about 200 micrometers, or 200,000 nanometers. The whole guitar is about the size of a human blood cell.
Found
here amongst a gallery of other instruments, almost all of which would make an IotD candidate (but won't be, so enjoy).