This Sunday the programme takes us on a magical mystery tour of the
atomic realm. Specifically, it discusses an important emerging technology,
called nanotechnology, that aims to improve our ability to work at this
scale (nanos is the Greek word for dwarf).

According to Equinox, the emergence of nanotechnology could spell the
‘end of the industrial age as we have known it for 200 years. In its place
will arise a new technology where we can grow everything in tanks, molecule
by molecule.’ To reinforce the point we see a chemical plant operator pouring
several kinds of goo into a large vat, and pulling out a pristine new top-of-the-range
vacuum cleaner.

The programme essentially concentrates on the vision of one of the messiahs
of nano-technology, Eric Drexler of Stanford University in California.

Drexler believes that nanotechnology will enable us to build robots
smaller than viruses. He illustrates how these tiny robots could be used
to construct products by adding liquids, powders and solids into a coffee
jug. These components represent the robots, their fuel and the set of instructions
they follow. ‘We can now make almost anything,’ he says.

Drexler then builds up the tension as you wonder what he will pull out
of the coffee jug; another vacuum cleaner, a satellite broadcasting company,
some coffee, what could it be? The promised ‘almost anything’ turns out
to be a spoon.

But what is nanotechnology and how can it be used to make wondrous products,
such as spoons? Well, unfortunately, the programme does not say. Like many
of Channel 4’s programmes, Little by Little seems to be made by post-psychedelic
air heads for people who need to have something to talk about.

The programme makers seem to have asked a number of researchers to talk
about nanotechnology and elegantly stitched their ideas and analogies together
with beautiful images. The content flits from one ‘amazing notion’ to another
with hardly any time to get a ‘gee whizz’ in. Apart from a confused ramble
through the history of microscopy and catalysis, scant mention is made of
the current developments in the field, nor of the fact that Japan has targeted
the technology as one of the strategic areas that it plans to exploit in
the future.

Some of the futuristic ideas contained in nanotechnology are exciting,
but so are the current developments. Science programmes should look to the
future to see how technologies will change our lives, but the intelligent
general viewer is likely to be turned off rather than stimulated by programmes
whose contents are rooted firmly in the clouds.

Attila Pavlath, from the US Department of Agriculture Research Service
in Albany, California, has found a way to keep sliced fruit and vegetables
fresh for up to three days by covering them with an edible coating based
on milk.

Although farmers use coatings to increase the lifetime of their produce,
until now no one has found a way of preserving fruit and vegetables that
have been cut or peeled. The problem researchers face is to develop a coating
that will stick onto a moist surface and prevent oxygen passing in and water
passing out.

Most fruit and vegetables give off carbon dioxide after they have been
picked. Unless the coating enables the carbon dioxide to pass through it,
the taste of the food will change. The coating also has to be edible and
– perhaps the most difficult condition to meet – acceptable to the US Food
and Drug Administration (FDA).

Pavlath took milk as a starting point because the proteins in it make
a very good film. Protein films form an inadequate barrier against water
and oxygen, so Pavlath had to modify them by adding enzymes to the milk.

These enzymes ‘tie’ the proteins together. Pavlath used the technique
to weave proteins together, so forming a mesh fine enough to reduce the
amount of oxygen and water molecules crossing the barrier.

The films could also be used to modify produce and, according to Pavleth,
add ‘exciting new flavours or colourings to standard fare’.

One possibility, he suggests, is to ‘jazz up’ sliced pears, by protecting
them with a protein coating flavoured with natural red cherries. The coatings
could also be used to keep fillings in pies and pizzas from soaking the
crust, says Pavlath.

Although the barrier keeps cut fruit and vegetables fresh for several
days, food companies are unlikely to use Pavlath’s coating unless it can
preserve food for several weeks, because of the amount of time it takes
to distribute food to supermarkets.

Pavlath believes that he will be able to make his coating more effective
by making the molecular mesh even finer. The problem, however, is not trivial,
because if the mesh is too fine then the film will become rigid and prone
to crack, allowing the food to decay.

Pavlath is trying to find a solution by adding various compounds to
his milk coating, although, because the coating has to be edible, his choice
is restricted.

‘Trying to overcome the technical problems and satisfying the FDA is
like dancing on a tightrope,’ says Pavlath. ‘I am sure it can be done, but
it is a matter of time, perhaps two years.’

Until now, no one has been able to prove or disprove this hypothesis,
despite the fact that scientists have had electron microscopes powerful
enough to capture images of DNA at the molecular level for many years. The
main disadvantage with electron microscopy is that, researchers have first
to coat samples with metal in order to form an image. This process kills
any living samples and destroys much of the fine detail.

A technique developed in the early 1980s, known as scanning tunnelling
microscopy (STM), overcame the need to coat samples. But, until recently,
scientists could view only samples that they had previously dried.

However, water is an essential part of many molecules, such as DNA;
without it, they collapse into a distorted relic of their hydrated form.
Stuart Lindsay of Arizona State University, in Tempe, and his colleagues
have now adapted the technique of STM to produce the first pictures of DNA
in water. The pictures show kinks in the DNA double helix.

According to Lindsay, the technique will enable researchers to study
the way in which the environment affects the shape of the DNA. ‘We have
found that DNA in natural conditions can bend, wiggle and kink in remarkable
ways,’ says Lindsay.

However, when he synthesised DNA that had simple variations in the sequence
of bases in the laboratory, he found that it had no kinks or wiggles, unlike
natural DNA. Lindsay claims that this observation provides firm evidence
for the fact that the kinks and wiggles demarcate active regions of DNA.

Lindsay has found that these structural features can form or disappear
as the DNA makes contact with other molecules for transcription. This finding
indicates that a simple physical mechanism may regulate the expression of
genes.

One of the most dramatic features is a kinked structure in the nucleosome,
the basic unit of a chromosome, which consists of a stretch of DNA coiled
round a core of histone proteins. A fraction of the fragments shows two
sharp kinks. At these kinks, the double helix changes direction at an angle
of 98Degree . This angle agrees precisely with the model originally proposed
by Crick and Klug.

Lindsay claims that the scanning tunnelling microscope will be useful
in unravelling how genes are controlled.

‘We can gain an insight into the nature of biological processes at the
molecular level by studying the way that the DNA’s shape changes with base
sequence and the way interactions modify these changes,’ he says.

Samuel Stupp of the University of Illinois at Urbana-Campaign claimed
that these pictures show that the behaviour of the two polymers is ‘drastically
affected’ by their detailed chemical structures, more so than chemists had
previously believed.

Liquid crystals are relatively large regions of molecules which point
in the same direction, and so have a structure analagous to ordinary crystals.

Liquid crystals are best known for their use in displays in which an
electric field darkens parts of the display, to produce numbers, letters
or patterns, by rotating some of the molecules away from the direction of
their neighbours.

However, the molecules used in displays are small and have few other
uses. Chemists and physicists are now turning to more versatile liquid crystals,
known as liquid-crystal polymers. LCPs are already used in new engineering
materials, such as Kevlar, which are as light as fibreglass and as strong
as steel.

Polymers only form liquid crystals if their chains are stiff, like rigid
rods. Rigid molecules align because this is the most stable arrangement
for them thermodynamically. The stiffer the polymer, the better its propertes
as a liquid crystal. Until now, scientists thought that the length of rigid
chains was the main factor determining their stiffness. Stupp and his colleagues
have shown that more subtle factors also influence the chain’s stiffness.
These factors can affect the properties of the material even more than the
length of the chain.

Stupp and his students, Jeff Moore, Phil Martin and John Wu made two
polymers that were identical, apart from the fact that one had a periodic
chain while the other had a random chain.

According to established theory, both polymers should have very similar
properties because the average length of their chains was identical.

However, when Stupp melted the crystals, the polymer with the random
structure melted out of its liquid-crystal phase gradually, while the change
in the polymer with a periodic chain was more sudden.

According to Stupp, the result clearly demonstrates that the arrangement
of units in the chain is at least as important as its length in determining
the properties of the liquid crystal. The results also suggest that the
chains in the random structure have many values of stiffness (Macromolecules,
vol 21, p 1222).

Stupp claims that this variability in the degree of rigidity of long,
stiff polymers could be used to separate molecules that are biologically
interesting. ‘A mixture of proteins of polynucleotides is analogous to the
random system,’ he says. ‘It may be possible, therefore, to use the polyflexibility
of these molecules to separate polymeric chemical sequences in the mixtures
of proteins or genes that occur in nature or in biotechnological systems.’

The discovery raises some interesting new questions about fundamental
physics – not only of liquid-crystal polymers, but of all polymers. Stupp
says: ‘We noticed this effect in liquid crystals because their phase changes
are visible. The same subtle processes could occur in all polymers.’ Stupp
believes that, as chemists gain a better understanding of this phenomenon,
they will be able to fine-tune the properties of polymers.

‘The fact that the random material changed smoothly from its liquid-crystal
phase to a non-liquid-crystal phase implies that polymers with chains arranged
randomly have not just one value for chain stiffness but thousands or even
millions,’ says Stupp. ‘If you could ‘clone’ each of these chains, you could
in principle have a million different materials with a million slightly
different properties.’

Telecommunications companies currently use components known as waveguides
to direct and switch light in optical circuits. However, waveguides are
expensive because they need to be made to very precise standards. Heino
Finkelmann, a researcher at the University of Freiburg in West Germany,
has devised a way to make waveguides as simply and as cheaply as record
companies press records.

Waveguides channel light in integrated circuits in the same way that
a pipe directs water. They consist of a narrow trough, about the width of
a wavelength of visible light. Light travels along a waveguide by bouncing
off the sides of the trough at an angle. Physicists control this angle by
adjusting the refractive index of the material in the trough. One way of
doing this is to lay thin films of material in the trough, a process which
requires great precision and can only be done in clean surroundings.

Finkelmann stumbled across a simpler way of making waveguides while
developing a new class of liquid crystals with strange, rubber-like properties.
He was working with a type of such crystals known as side-chain liquid crystals.
These materials consist of rigid molecules attached to a long, flexible
chain of atoms. Finkelmann wove these molecules into a three-dimensional
lattice which had similar properties to rubber. In an electric field, the
rigid molecules in the rubber-like structure rotate as they do in the liquid
crystals used to make the displays of digital watches. However, Finkelmann
found that, unlike ordinary liquid crystals, the rigid molecules will also
rotate when he deforms the rubber. These rotated molecules react to light
in a different way from their unrotated neighbours. He realised that it
would therefore be possible to introduce local changes to the refractive
index of the material, simply by pressing it.

Finkelmann announced at the meeting that he had succeeded in doing this.
He is working with German companies to develop commercial devices that would
exploit the new rubbery crystals.

One of the problems with developing integrated circuits that exploit
the movement of photons of light, rather than electrons, is that they require
different types of materials to guide the light and then to process it.
This will make it difficult to manufacture optoelectronic components on
a commercial scale as the technology matures. The strength of electronic
integrated circuits is that manufacturers can use silicon both to carry
electronic signals and to process them. However, because of Finkelmann’s
‘rubber’ liquid crystals, materials scientists may now have found the optical
equivalent of silicon.

The development is a stroke of luck for materials scientists who are
trying to develop optoelectronic components. By sheer coincidence, researchers
are trying to develop polymers similar to these liquid crystals to change
the frequency of light within integrated circuits, using an effect known
as harmonic generation. By exploiting this effect, researchers hope to be
able to develop optical ‘transistors’. The development of such transistors
will, in turn, pave the way for a new generation of optical components that
will make present-day technology seem as outdated as valve technology.

Finkelmann believes that chemists will soon develop liquid crystals
capable of harmonic generation. Once they succeed in doing this, they will
be able to make wires to guide light and components to manipulate it out
of the same material.

Their results show that patterns of localised magnetic fields in bismuth
and thallium superconductors imply that the materials will still possess
a significant amount of resistance, even at temperatures well below their
critical temperature (Tc) – the temperatures are also known as the transition
temperature, at which they become superconducting.

For every superconductor, there is a critical current as well as a critical
temperature. If the current flowing through the material exceeds this amount,
superconductivity vanishes, even at temperatures below Tc. Another property
of superconductors is that varying the current usually has no effect on
the material’s resistance. Bishop’s work suggests that there will always
be a slight resistance while the material is superconducting and that this
resistance increases with temperature.

Two years ago, when researchers first discovered superconductivity at
90 kelvin, they thought that they might be able to find a superconducting
material that would work at room temperature. Work on new materials was
hopeful at first, but no one has achieved a critical temperature above 125
K. This latest announcement by Bishop comes as a further blow to those who
hoped to have room-temperature superconductors.

Magnetic fields cannot normally penetrate a superconductor. ÐÓ°ÉÔ­´´s
classify all high-temperature superconductors as type II. These, unlike
type-I superconductors, do not completely exclude any magnetic field in
the vicinity of the material. The magnetic field begins to penetrate the
type-II superconductors when the field strength exceeds a certain value,
known as the lower critical field.

In type II superconductors, at low temperatures the materials ‘freeze’
the lines of magnetic flux which stops them from moving and hindering superconductivity.
However, Bishop and his colleagues, Peter Gammel and Lynn Schneemeyer, discovered
that the magnetic flux lines break away in bismuth and thallium compounds,
the most promising superconducting materials to date, as the temperature
rises above a few tens of Kelvin. The movement of the flux lines dissipates
a small amount of energy in the superconductors, creating resistance.

Although initial reactions to the results were gloomy, physicists at
the meeting thought that the work was a significant step forward in understanding
how these new superconducting materials work. Bishop himself was optimistic
about the long-term significance of his work. ‘We are not engineers trying
to make coils. Our job is to find out about the basic physics of these materials,’
he said.

Alex Malozemoff, of IBM’s research centre at Yorktown Heights, New York,
said that the priority for physicists is to overcome the problem. ‘Things
look bad in terms of using bulk materials in some high-current applications,
but if we can think of ways to overcome the flux transport problem then
we may be able to improve the properties of these materials.’

David Nelson, a theoretical physicist at Harvard University in Cambridge,
Massachusetts, has already carried out calculations that show that the problem
may not be insoluble. His work shows that flux lines penetrating the superconductors
could entangle, and become rigid ‘like cold spaghetti,’ he says. ‘In this
rigid state you could pin down all the flux lines by pinning down one.’