Category: General

I’m optimistic in general about the prospects of solar energy; as should be well known, the total amount of energy arriving at the earth from the sun is orders of magnitude more than is needed to supply all our energy needs. The problem currently is reducing the price and hugely scaling up the production areas of photovoltaics. But, as I live in the not notoriously sunny country of Britain, someone will always want to make some sarcastic comment about how we’d be better off trying to harvest energy from rain rather than sun here. So I was pleased to see, in the midst of a commentary from Philip Ball on the general concept of scavenging energy from the environment, a reference to generating energy from falling raindrops.

The research, described in an article in physorg.com: Rain power: harvesting energy from the sky, was done by Thomas Jager, Romain Guigon, Jean-Jacques Chaillout, and Ghislain Despesse, from Minatec in Grenoble. The original work is described in two articles in the journal Smart Materials and Structures, Harvesting raindrop energy: theory and Harvesting raindrop energy: experimental study (subscription required for full article). The basic idea is very simple; it uses a piezoelectric material, which generates a voltage across its faces when it is deformed, to convert the energy imparted on the impact of a raindrop onto a surface into a pulse of electrical current. The material chosen is a polymer called poly(vinylidene fluoride), which is already extensively exploited for its piezoelectric properties in applications such as microphones and loudspeakers.

So, should we abandon plans to coat our roofs with solar cells and instead invest in rain-energy harvesting panels? It’s worth doing a back of an envelope sum. The article claims that a typical raindrop’s velocity is about 3 m/s. Taking Sheffield’s average annual rainfall of about 80 cm, we can estimate the total kinetic energy of the rain landing on a square meter in a year as 3600 J, corresponding to a power per unit area of about 3 milliwatts. This isn’t very impressive; even at these dismal northern latitudes the sun supplies about 100 W per square meter, averaged over the year. So, even accounting for the fact that PVDF is likely to be a lot cheaper than any photovoltaic material in prospect, and energy conversion efficiencies might be higher, its difficult to see any circumstances in which it would make sense to try and collect rainwater energy rather than sunlight.

From the poem “They” by R.S. Thomas:

The new explorers don’t go
anywhere and what they discover
we can’t see. But they change our lives.

They interpret absence
as presence, measuring it by the movement
of its neighbours. Their world is

an immense place: deep down is as distant
as far out, but arrived at
in no time. These are the new

linguists, exchanging across closed
borders the currency of their symbols….

All the best for the New Year to all my readers.

My book, Soft Machines: nanotechnology and life, has now been released in the UK as a paperback, with a price of £9.99. It should be available in the USA early in the new year. It’s available from from Amazon UK here, and can be preordered from from Amazon USA here.

Having an opportunity to make corrections, I re-read the book in the summer. One very embarrassing numerical error needed correcting, and anything to do with the dimensions of semiconductor processes needed to be updated to account for four more years of Moore’s law. But in general I think what I wrote has stood the test of time pretty well.

I’m on my way back from India, where I’ve been at the conference Bangalore Nano 07. The enthusiasm for nanotechnology in India has been well publicised; it’s traditional to bracket the country with China as two rising science powers that see nano as an area in which they can compete on equal terms with the USA, Europe and Japan. So it was great to get an opportunity to see for myself something of what’s going on.

I’ll just mention a couple of highlights from the conference itself. Prof Ramgopal Rao from the Indian Institute of Technology Bombay described a very nice looking project to make an inexpensive point of care system for cardiac diagnostics. He began with the gloomy thought that soon more than half the cases of cardiac disease in the world will be India. If acute myocardial infarction can be detected early enough a heart attack can be prevented, but this currently needs expensive and time consuming tests. The need, then, is for a simple test that’s cheap and reliable enough to be done in a doctor’s office or clinic.

To do this one needs to integrate a microfluidic system to handle the blood sample, a sensor array to detect the appropriate biochemical markers, and a box of electronics to analyse the results. The sensor array and fluid handling system needs to be disposable, and to cost no more than a few hundred rupees (i.e. a couple of dollars), while the box should only cost a few thousand rupees, even though the protocols for diagnosis need to be quite sophisticated and robust. Rao is aiming for a working prototype very soon; the biosensor is based on a cantilever which bends when the marker binds to a bound antibody. He uses a polymer photoresist to make the cantilever, with an embedded poly-silicon piezo-resistor to measure the deflection (this isn’t trivial at all, as the change in resistance amounts to about 10 parts per million).

Another nice talk was from Prof T. Pradeep, a surface chemist from the Indian Institute of Technology Madras. He described a water filter incorporating gold and silver nanoparticles mounted on a substrate of alumina, which is particularly effective at removing halogenated organic compounds such as pesticide residues. This is already marketed, with the filter cartridge costing about a few hundred rupees. He also mentioned a kit that can test for such pesticide residues with a detection limit of around 25 parts per billion.

The closing talk was given by Prof CNR Rao, and consisted of reflections on the future of nanotechnology. His opinions are worth paying attention to, if for no other reason than that he is undoubtedly the most powerful and influential scientist in India, and his views will shape the way nanotechnology is pursued there. What follows are my notes on his talk, tidied up but not verbatim.

Rao is a materials chemist, and he started by observing that now we can make pretty much any material in any form. But the question is, how can we use them, how can we assemble them and integrate them into devices? This is the biggest gap – we need products, devices and machines from nano-objects, and this is still probably at least 10 years, maybe 15 years, away. But we shouldn’t worry just about products and devices – nanotechnology is a new type of science, which will dissolve barriers between physics and chemistry and biology and bring in engineering. As an example – many people have made molecular motors. But… can they be connected together to do something? This sort of thing needs combinations of molecular science and nanoscience. Soft matter is another area with many good people and interesting work, including some in Bangalore. But there’s still a gap in applying them, what about active gels? Similarly, we see big successes in sensors, imaging but there’s much left to do. As an example of one very big challenge, many people suffer in Bangalore and everywhere else from dementia; we know this is related to the nanoscale phenomenon of peptide aggregation, but we need to understand why it happens and how to stop it. Drug delivery and tissue engineering are other examples where nanotechnology can make a real impact on human suffering. If one wants a role model, Robert Langer is a great example of someone who has produced many new results in tissue engineering and drug delivery, many graduate students and many companies; science in India should be done like this. We must remove the barriers and bureaucracy to give more freedom to scientists and engineers. At the moment, public servants like academics, cannot get involved in private enterprise, and this must change. Nanotechnology doesn’t take much money – it’s the archetypal knowledge based industry, and as such it should lead to much more linkage between industry and academia.

Tomorrow I am going to Birmingham to take part in a citizens’ jury on the use of nanotechnology in consumer products, run by the consumer organisation Which? They are running a feature on nanotechnology in consumer products in the New Year, and in advance of this they asked me, and a number of other people, a number of questions. Here are my answers.

How are nanomaterials created?

A wide variety of ways. A key distinction to make is between engineered nanoparticles and self-assembled nanostructures. Engineered nanoparticles are hard, covalently bonded clusters of atoms which, fundamentally, can be made in two ways. You can break down bigger particles by milling them, or you can make the particles by a chemical reaction which precipitates them, either from solution or from a vapour (a bit like making smoke with very fine particles). Examples of engineered nanoparticles are the nanoscale titanium dioxide particles used for some sunscreens, and the fullerenes, forms of carbon nanoparticles that can be thought of as well-bred soot. Because nanoparticles have such a huge surface area relative to their mass, it’s often very important to control the properties of their surfaces (if for no other reason than that most nanoparticles have a very strong tendency to want to stick together, thus stopping being nanoparticles and losing the properties you were presumably interested in them having in the first place). So, it would be very common to make the nanoparticle with an outer coating of molecules that might make it less chemically reactive.

Self-assembly, on the other hand, is a process by which rather soft and mutable nano-structures are formed by particular types of molecules sticking together in small clusters. The classic example of this is soap. Soap molecules have a tail that is repelled from water, and a head that is soluble in water. In a dilute solution in water they make the best of these conflicting tendencies by arranging themselves in clusters of maybe 50 or so molecules, with the headgroups on the outside and the tails shielded from the water in the middle. These nanoparticles are called micelles. Biology relies extensively on self-assembly to construct the nanostructures that all living organisms are made of, including ourselves. For this reason, most food is naturally nanostructured. For example, in milk protein molecules called caseins form self-assembled nanoparticles, and traditional operations like cheese-making involve making these nanoparticles stick together to make something more solid. Of course, we don’t call cooking nanotechnology, because we don’t intentionally manipulate the nanostructure of the foods, even if this is what happens without us knowing about it, but, armed with modern techniques for studying the nanoscale structure of matter, people are increasingly seeking to make artificial nanostructures for applications in food and health. An example of an artificial self-assembled nanostructure that’s becoming important in medicine is the liposome (small ones are sometimes called nanosomes) – here one has soap-like molecules that arrange themselves into sheets exactly two molecules thick (a common material would be the phospholipid lecithin, obtained from soya beans, that is currently widely used as a food emulsifier, for example being an important ingredient of chocolate. If one can arrange the sheet to fold round onto itself you get a micro- or nano- scale bag that you can fill with molecules that you want to protect from the environment (or vice versa).

Can you tell us about the existing and expected applications of developments in nanotechnology in the areas of food and health (including medical applications)?

In food applications, the line separating conventional food processing to change the structure and properties of food and nanotechnology is rather blurred. For example, it was reported that an ice cream company was using nanotechnology to make low fat ice cream; this probably involved a manipulation of the size of the natural fat particles in the ice cream. This really isn’t very different from conventional food processing, the only difference being that modern instrumentation makes it possible for the food scientists involved to see what they are doing to the nanoscale structure. This sort of activity will, I’m sure, increase in the future, driven largely by the perceived market demand for more satisfying low fat food.

One area that is very important in health, and may become important in food, is the idea of wrapping up and delivering particular types of molecules. In medicine, some drugs, particularly the anti-cancer drugs used in chemotherapy, are actually quite toxic and lead to serious side-effects. If the molecules could be wrapped up and only released at the point at which they were needed – the tumour, in the case of an anticancer drug, then the side effects would be much reduced and the drug would be much more effective. This is beginning to happen, with drugs being wrapped up in liposomes for delivery. Another way in which nanotechnology can help in medicine is for drugs which can’t easily be dissolved, and thus can’t be easily introduced into the body. These can be prepared as nanoparticles, in which form the molecules can be absorbed by the body (a new anti-breast-cancer drug – Abraxane – is in this category). In food, in the future additives which are believed to be good for the health (so-called nutriceuticals) may be added to food in this way.

Other applications in health are in fast diagnostic tests. The idea here is that, instead of a GP having to send off a patient’s blood sample for a test to detect certain bacteria or biochemical abnormalities, and having to wait a week or so for the result to come back, nanotechnology would make possible a simple and reliable test that could be done on the spot. Looking further ahead, it’s possible to imagine a device that automatically tested for some abnormality, and then if it detected it automatically released a drug to correct it (for example, a diabetic might have a device implanted under their skin that automatically tested blood sugar levels and released the right amount of insulin in response).

Another area that is in tissue engineering – the growing of artificial tissues and organs to replace those damaged by disease or injury. Here it’s important to have a “scaffold” on which to grow human cells (ideally the patient’s own cells) in a way that they make a working organ. Currently growing replacement skin for burn victims is an a fairly advanced state of development.

Are manufacturers required to disclose the presence of nanomaterials on their labelling?

Currently, no.

What are the risks or concerns about using manufactured nanomaterials in health or food products?

There are concerns that some engineered nanoparticles might be more toxic than the same chemical material present in larger particles, both because the increased surface area might make them more reactive, and because they might be able to penetrate into tissues and cells more easily than larger particles.

Are some nanomaterials more risky than others?

This is very likely. Engineered nanoparticles, made from covalently bonded inorganic materials, seem the most likely to cause concern, but even among these it is important to consider each type of nanoparticle individually. Moreover, it may well be that the dangers posed by nanoparticles might be altered by the surface coatings they are given.

Are some applications of nanotechnology more risky than others?

Yes. In my opinion the biggest risk is in the use of engineered nanoparticles in situations in which they could be ingested or breathed in. The control of naturally occurring nanostructure in foods, the use of self-assembled objects like liposomes, and the kind of nanotechnology that is likely to be used in diagnostic devices, should present few if any risks.

In your opinion, should consumers be concerned about the use of manufactured nanomaterials in health or food products?

Somewhat, but not very. The key dangers come from the potential use of engineered nanoparticles without adequate information about their toxicity. In principle food additive regulations don’t generally discriminate by size. For example, a material like titanium dioxide, that is a permitted food additive (E171), could be used in a nanoscale form without additional testing. In principle it is possible to specify permitted size ranges for particles – this is done for microcrystalline cellulose – so this measure should be extended to other materials that could be used in the form of engineered nanoparticles on the basis of testing that discriminates between particles of different sizes.

If any, what protections need to be put in place?

The government should act on the recommendations of the March 2007 report by the Council of Science and Technology

The BBC World Service program World Business Review devoted yesterday’s program to nanotechnology, with a half-hour discussion between me, Michio Kaku and Peter Kearns from the OECD. I haven’t managed to bring myself to listen to it yet, and as it’s difficult to get a very accurate impression of a radio program while you are recording it I’ll make no comment about it. You can listen to it through the internet from this link (this will work until next Saturday).

New Scientist magazine carries a nice article this week about the difficulties of propelling things on the micro- and nano- scales. The online version of the article, by Michelle Knott, is called Fantastic Voyage: travel in the nanoworld (subscription required); we’re asked to “prepare to dive into the nanoworld, where water turns to treacle and molecules the size of cannonballs hurl past from every direction.”

The article refers to our work demonstrating self-motile colloid particles, which I described earlier this year here – Nanoscale swimmers. Also mentioned is the work from Tom Mallouk and Ayusman Sen at Penn State; very recently this team demonstrated an artificial system that shows chemotaxis; that is, it swims in the direction of increasing fuel concentration, just as some bacteria can swim towards food.

The web version of the story has a title that, inevitably, refers back to the classic film Fantastic Voyage, with its archetypal nanobot and magnificent period special effects, in which the nanoscale environment inside a blood vessel looks uncannily like the inside of a lava lamp. The title of the print version, though, Das (nano) Boot, references instead Wolfgang Peterson’s magnificently gloomy and claustrophobic film about a German submarine crew in the second world war – as Knott concludes, riding in nanoscale submarines is going to be a bumpy business.