nanotechnology
nano
bits
Tiny Tinkertoys
At the end of the
day, nanotechnology researchers want to build stuff. But building things
at the nanoscale with the same ease that we construct them at the human
scale has proven elusive. The techniques are often quite cumbersome. Now
a team of scientists at the University of Michigan in Ann Arbor say they
have developed a faster, more effective way to produce certain nanoscale
structures, using strands of DNA as struts.
Bioengineers working with structures such as nanoparticles believe they
show great promise in fighting certain diseases. A nanoparticle, for instance,
could be engineered to target cancer cells, enter a diseased cell, and
kill it. But making a particle with the right properties is a challenge.
For example, researchers can attach various molecules on the tips of spiky
polymers known as dendrimers; like the blades on a Swiss Army knife, each
molecule performs a different function. Actually making a useful particle
of that sort is a painstaking process that may take weeks or months to
accomplish.
 |
| Two dendrimers, joined by a DNA splice. |
James R. Baker, a professor of nanotechnology at Michigan, and his colleagues
have developed a new technique for building dendrimers. The team built
two different kinds of dendrimer particles—one for targeting a
cancer cell, the other containing a fluorescent dye useful in imaging—each
with strands of DNA bound to their tendrils. DNA strands naturally bind
to other strands in a very specific fashion. When placed together in a
solution, the corresponding DNA strands glommed onto each other, resulting
in a dumbbell-shape particle that could find and tag cancer cells.
The hope is to create a tool chest of single-purpose nanoparticles that
can be combined in a mix-and-match fashion. Such nanoparticles could be
designed to deliver specific drugs directly to diseased cells.
Lotus Alone
The
lotus leaf is famous for its sheen: Even in the muddiest water, its leaves
look clean. Now engineers at Ohio State University in Columbus have borrowed
the secret of the lotus to design a surface that could lead to self-cleaning
glass or virtually frictionless machine parts.
From a distance the lotus leaf may appear shiny and smooth, but scientists
have long known that its surface is covered with microscopic bumps packed
close together. Drops of water stand up on the tips of the bumps and roll
off effortlessly. Bharat Bhushan, a mechanical engineer at Ohio State,
realized that the same kind of texture could be used to reduce friction
on other surfaces.
 |
| The bumps that make the lotus slick. |
Micromachines, for instance, can't be lubricated the way human-scale
machines can, so keeping moving parts from running against one another
and sticking has been a major concern. Bhushan and a colleague first developed
methods for measuring friction between moving micromachine parts in 2001
and have been looking for strategies to reduce this friction ever since.
Bhushan believes that the lotus-effect surface holds great promise. He
and his colleagues have created a computer model that calculates the best
surface pattern for different material and applications. Manufacturers
could incorporate the right surface pattern in their machine part design.
The surface could also be applied to making glass with microscale bumps
that would automatically shed water, reducing the need for cleaning.
Beyond Nanoscopes
People still marvel
at scanning electron micrographs of bugs and blood cells. But for researchers
at Oak Ridge National Laboratory in Tennessee such objects might as well
be as big as an elephant. A team there recently set a new record for imaging
very small objects—0.06 nanometer.
Atoms are somewhat bigger than that, about 0.1 nanometer.
The feat was performed thanks to an image-enhancing technology known as
aberration correction. Aberrations are artifacts introduced to images
because of imperfections in a lens. Such aberrations can keep cameras
from achieving their potential resolution.
 |
| Pretty silicon atoms, all in a row. |
Instead, aberration correction uses image analysis algorithms and advanced
computing hardware to remove imperfections that can crop up at the limits
of resolution. To test the process, the team, led by materials scientist
Stephen Pennycook, made an image of a silicon crystal using a 300-kilovolt
scanning transmission electron microscope. The corrected image clearly
showed not only the individual atoms but also the 0.078 nanometer space
between the atoms in the crystal.
The researchers hope that such images will help nanotechnologists better
understand the properties and behavior of material at the nanoscale.
Hollow Victory
Physicists have
been intrigued by high-frequency sound waves for years. Some believe the
energy released from acoustic cavitation—the formation, growth,
and implosion of small gas bubbles in a liquid blasted with sound—generates
a high enough temperature and pressure to touch off nuclear fusion. Now
researchers at the University of Illinois at Urbana-Champaign have discovered
another use: making hollow nanospheres and nanocrystals.
 |
| A nanosphere that has been crushed to form a hollow crystal. |
The hollow nanospheres were created by chemist Ken Suslick and his colleagues
at Illinois. They blasted molybdenum disulfide or molybdenum oxide with
high-intensity ultrasound to make minute particles, which then bound themselves
to the surface of a microscopic silica sphere. The molybdenum was heated
to form a smooth coating, and then the silica was dissolved with hydrofluoric
acid, leaving behind a hollow shell.
Because they provide more surface area than solid spheres, hollow nanospheres
made from catalysts such as molybdenum disulfide could one day be used
to scrub sulfur-bearing molecules from gasoline or diesel fuel. Hollow
spheres made from other material might find a role in delivering drugs
to specific parts of the body.
This section was written by Editor Jeffrey Winters.