The smallest nanotube brushes have bristles with an average diameter of 30 nm, which means that they are more than a thousand times smaller than current commercial brushes. The brushes have been created by researchers of Rensselaer Polytechnic Institute of Troy, New York (Dr. Pulickel M. Ajayan), and the University of Hawaii, Manoa, Honolulu (Mr. Vinod P. Veedu, Dr. Anyuan Cao and Dr. Mehrdad N. Ghasemi-Nejhad).

The nanotube brushes have multiple functions and have been tested in a variety of tasks that range from cleaning microscopic surfaces to serving as electrical contact.

From the BBC:
The bristles’ secret is carbon nanotubes, tiny straw-like molecules just 30 billionth of a metre across. They are incredibly tough and yet flexible enough that they will yield when pushed from the side. The multifunctional brushes can be used for sweeping up nano-dust, painting microstructures and even cleaning up pollutants in water.
The group of lead scientists Pulickel Ajayan has previously shown how carbon nanotubes can be grown controllably, and the team has now used the trick to make nanobrushes shaped like toothbrushes, bottle brushes and cotton-buds.