NANOTECHNOLOGY—TECHNOLOGY ON A MOLECULAR SCALE - Chemistry: Notable Research and Discoveries - page 47

by attaching a tiny plastic bead to one strand of a double helix and an-
choring the other strand to a firm surface. By using a laser beam, the ex-
perimenters made precise measurements of the movement of the bead,
observing the forces imposed by helicase enzymes. The report of this
research, “Single-Molecule Studies Reveal Dynamics of DNA Unwind-
ing by the Ring-Shaped T7 Helicase,” was published in 2007 in Cell.
Scientists study protein motors because they are biologically inter-
esting but also because they offer insights into mini-motors. Molecular
machinery such as nanorobots or nanobots—tiny robots—is a major
goal of nanotechnology, and it would have tremendous applications in
a lot of fields, especially in medicine. Some researchers are trying to
adapt protein motors to perform additional jobs, while other research-
ers simply use these tiny motors for inspiration. Ever since the 1966 film
Fantastic Voyage, in which scientists shrank a team of specialists and a
submarine and injected them into the body of a patient, people have
been fascinated with potential treatments that would be made possible
by tiny machines.
Alex Zettl and his colleagues at the University of California, Berke-
ley, have been active in this field. In 2005, Zettl and his team built an
oscillator that is one of the smallest electric motors in the world. The
motor works by driving some of the atoms of a tiny drop of liquid metal
over to an adjacent and smaller drop. An electric current powers this
movement. The most interesting phase of the operation occurs during
the rebound, as the atoms return to the original source. This phase hap-
pens because of a molecular force known as surface tension.
Forces in the nanoworld can appear strange because they do not
exist in the same proportion as forces in the macroscopic world. Gravi-
tational forces are insignificant to molecules because this force is weak
unless large masses are involved. Electrical interactions, as in the elec-
tric current driving the atomic movement in Zettl's motor, are tremen-
dously more important than gravity on this scale.
Interactions such as surface tension also become more influential at
smaller scales. Surface tension is due to attractions between molecules,
such as electrical charges and hydrogen bonds, which cause them to
bunch together and resist separation. For example, such forces create a
“tension” on the surface of water because the molecules stick together,
and this force is strong enough to let a bug known as the water strider
walk on water. In Zettl's motor, the smaller drop grows until it reaches