Radical nanotechnology — dreams and nightmares

Nanotechnology represents an important interface between 'big world' science and technology, and molecular structures. Radical nanotechnology envisages the possibilities of a mature technology that allows us to exercise control with engineering precision down to the atomic level.

A number of possible routes to enhance our ability to manipulate matter at the molecular, and even the atomic level, are currently being explored:

Bio-nanotechnology

Perhaps the biggest breakthrough of nanotechnology to date is in showing us quite how competent nature is at this scale, working with soft materials like proteins in aqueous solutions. These are not the sorts of materials that engineers are familiar with, but cellular machinery offers a glimpse as to what is possible.

Nature offers us an extremely competent nano-scale toolbox, with control over the design and construction of proteins. These molecules can self-assemble into a wide range of shapes and devices, from rotary engines to ion pumps.

Left: Existing cellular machinery driven by biochemicals such as ATP can serve as templates for new nanotech devices.
Acknowledgement: Professor J.B.C.Findlay and Dr M.A.Harrison, Biochemistry and Molecular Biology, University of Leeds.

In a process that might be termed 'biokleptic' nanotechnology, a number of scientists are working to include these devices into nano-scale devices, and/or using DNA synthesis methods to build them.

Biokleptic nanotechnology is restricted to working with proteins, which have a restricted operating environment. There is, however, a wide range of other 'soft materials' - such as polymers. Biomimetic nanotechnology, therefore, is the study of how devices that mimic biological systems can be made using these rather more familiar materials.

A problem that some have seen with nanotechnology is that of making enough nano-devices to be useful. Certainly positioning each atom using an AFM would be laborious in the extreme! One of the big dreams of nanotechnology is, therefore, a replicator capable of generating copies and useful products. This is, after all, exactly what a living cell does...

What is the possibility of a nano-machine running amuck, and converting the whole world into replicas of itself - a fine grey goo?

Synthetic life: Currently molecular biologists are working on creating 'stripped down' organisms, with the minimum coding required to allow them to reproduce. The hope is that these might serve as nano factory units, into which code for doing whatever we want might be installed.

Converting the world to grey goo: What is the possibility of a nano-machine running amuck, and converting the whole world into replicas of itself - a fine grey goo? Any such goo-bot will have pretty strong competition from very well entrenched organisms, with several billion years evolutionary experience at deterring just such attacks. We think it is more likely that, like H.G. Wells' Martians in the book The War of the Worlds, our goo-bot would make a tasty snack for the first passing bacterium!

Health and nanotechnology

The first medicine that specifically mentions nanotechnology in its patent has recently been licensed in the USA for treatment of patients with breast cancer. It is based on combining an active anti-cancer drug with nano-sized particles of the protein albumin. The nanoparticle acts as an inert carrier for the drug in place of a solvent that was having unpleasant side effects.

In general, anti-cancer drugs work by killing cancerous cells; unfortunately they are not as picky as to which cells they kill as we would like, and this results in a range of unpleasant side effects which limits the dosages that can be given, and may result in treatment having to be stopped before the cancer has been killed. An important focus of a lot of research into nano-medicine is therefore to make drug delivery systems smart enough to recognise cancer cells and deliver their active payload just to them.

Above right: Scientists at Sheffield have been making polymer particles that can carry peptides and other molecules into cells. Here fluorescent polymer particles show up blue against the red-stained cellular material. (Image courtesy Steve Rimmer.)

At present we are a long way away from nanobot surgeons that can travel through blood vessels, repairing damage and excising malignancies at the cellular level.

The likely effect of nano-toxins is difficult to quantify; we don't in general expect materials to become toxic simply because they have been prepared as a nano-particle formulation. Powders, however, have lots of surface compared to their volume, and this can increase the reactivity and toxicity of some materials. This could be compounded in certain environments by the smaller particle size being able to penetrate further into the lungs.

Common sources of nano-particulates in the environment are hydrocarbon combustion (engine emissions) and gas to particulate reactions in the atmosphere (aerosol formation). There is certainly some evidence that urban environments with higher levels of engine emissions and other aerosols are associated with increased prevalence of diseases.

Molecular nanotechnology (MNT)

Combining components with different properties at the nano-scale allows us to make a new class of 'metamaterials'.

One area that is receiving considerable attention is the possibility of software control over the assembly of molecules. This is already possible with DNA and protein synthesisers, and there is a small range of chemical linkers that can be used in combination with other monomer units (i.e. not amino acids or nucleic acids).

Combining components with different properties at the nano-scale allows us to make a new class of 'metamaterials'. At this scale an electron experiences a combination of the properties of all of the components, potentially allowing us to manufacture materials with very unusual properties. GMR devices are an example of metamaterials which are in widespread use. Being able to do this sort of thing with individual molecules, however, will result in a blurring of the distinction between materials and devices.

Hard nano-engineering: Based on what nature can do with soft materials, can something similar be done with the steel, glass, ceramics and silicon that engineers currently prefer? To realise this dream, we will need nano-machinery capable of handling a wide range of substrates. It is worth bearing in mind that there is biological machinery for working with metals, ceramics and silica (see Nature's Nanotechnologists ), but it will be hard work to adapt this to making motorcars, computers or aeroplanes...

Above right: A hypothetical nano-fabricator would be able to build a wide range of objects - given the software blueprint - from simple feedstocks.

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