Miniaturisation has become a familiar aspect of modern technology: every year, laptops get thinner, mobile phones get smaller, and computers get faster as more and more components can be accommodated on their chips. The emergence of nanoscience as a scientific discipline has been driven by the relentless quest by the electronic device industry over the past four decades for ever-faster chips. The importance of miniaturisation is not just in the fact that smaller devices can be packed more closely together, however: when objects become very small indeed, they sometimes acquire entirely new properties that larger objects formed from the same materials do not normally exhibit. Catalysts have been used for over a century to accelerate chemical reactions, and many catalysts consist of metal particles supported on ceramics. For several decades, catalytic converters in car exhausts have used metallic nanoparticles – particles a few billionths of a metre in size – to clean the exhaust gas because the catalytic activity has been found to be dramatically increased by the small size of the active metal. When semiconductors are formed into structures of the same size, they acquire entirely new optical properties purely as a consequence of their small size – for example, they glow brightly when stimulated by electrical current, and the colour of the light emitted is determined by the size of the particle (and can thus be controlled with high precision). These phenomena are referred to as low-dimensional ones: they are new, unexpected phenomena that result only from the small size of the active objects.
There is a very important sense in which biological objects may also be said to be low-dimensional. Cells are tiny objects that are driven by processes that involve small numbers of molecules. The chromatophore vesicle from R. sphaeroides, shown on the right, is barely any larger than the gate length in a commercial transistor, and yet it contains within it an entire biochemical pathway, that captures solar energy with astonishing efficiency. Biologists have recognised that single molecules are quite different from large groups of molecules, and there has therefore been a lot of interest in studying them, because they may help us to understand much better how larger systems work. However, there are no established tools for building systems of interacting single molecules, what might be called “low-dimensional systems”. New tools are required to achieve this, and the goal of our programme is be to develop them. We wish to build a synthetic low-dimensional system, which will incorporate biological molecules and synthetic models for them, that replicates the photosynthetic pathway of a bacterium. Photosynthesis is the basis for all life on earth, so it has fundamental importance. However, there are other important motivations for studying the marvellously efficient processes by which biological organisms collect sunlight and use it to live, grow and reproduce. The current concerns about shortage of fossil fuels, and the problems associated with the carbon dioxide produced by burning them, make solar energy a highly attractive solution to many pressing problems. At a fundamental level, biological systems work quite differently from electronic devices: they are driven by complex signals, they are fuzzy and probabilistic, where microsystems are based on binary logic and are deterministic. The construction of a functioning low-dimensional system that replicates a cellular pathway will require the adoption, in a man-made structure, of these very different design principles. If we can achieve this it may yield important new insights into how similar principles could be applied to other technologies.