Building a Lego castle in the dark with boxing gloves
Life is an interplay of molecular machines, like repair enzymes patrolling our DNA powered by sunlight and molecular walkers moving along peptide strands. Similar molecular machines now emerge from laboratories. Chemist Rainer Herges on Molecular Nanotechnology – the highly topical research area was honoured with a Nobel Prize last year and is explored in the Collaborative Research Center »Function by Switching«.
Motorised paramecium: artistic view with artificial cilia. Cilia were the first strategy towards directed motion in nature emerging more than two billion years ago. The molecules shown were prepared by Tobias Tellkamp in the group of Professor Herges. Foto: Herges
Increasing efficiency by miniaturization is not restricted to microelectronics. Modern projectors include more than two million tiny switchable mirrors illuminating TV and cinema screens. Upon further shrinking of these devices, we reach the size of molecules. Consequently, the ultimate limits of miniaturization are molecular switches and machines.
Already ten years ago, in July 2007, molecular nanosciences started at Kiel University with the collaborative research center CRC 677 »Function by Switching.« About a hundred scientists from chemistry, physics, material sciences and pharmaceutical chemistry are collaborating to design, to build, and to investigate molecular machines. Chemists prepare the molecules, physicists put them on surfaces and investigate them with ultra-high resolution microscopy, and material scientists include them in composite materials.
A number of impressive advancements have been made. The integration density of our functional molecules is more than two orders of magnitude higher than in the latest generation of Intel processors, probably higher than anything achievable with the current lithography techniques used in microchip industry. Smaller is better, however, besides increasing speed and efficiency, we think that molecular engineering will open up completely new and fascinating applications.
Unlike microelectronics, molecular switches and machines are compat ible with biochemistry in size and function. Life on earth is a delicate interplay of molecular machines. There are enzymes incessantly patrolling our DNA, autonomously repairing mismatches, there are molecular walkers moving cargo on protein strands, there are pumps, triggers, valves, practically every engineering device we know from our macroscopic world. Artificial machines can directly communicate and interact with the chemistry of living organisms.
One of our projects, aiming at the design of photoswitchable drugs, might illustrate the basic idea. Drugs are usually taken orally, or are injected. They spread over most parts of the body, and often cause side effects in healthy tissue. Switchable drugs would be administered in an inactive state, and activated exclusively at the site of illness. After a while they would return to the inactive state, and thus avoid contamination of waste water. Our first prototypes already demonstrate the proof of principle.
In another project, we built machinetype molecules that measure temperatures and make them visible in a 3D-thermogramm in magnetic resonance tomography. This could be useful in search of inflammation and tumours, which are higher in temperature than the surrounding tissue. In a more distant future, one can also imag ine hybrids of biological and artificial units. Controlled motion in nature is realised by hair-like protrusions performing whip-like motions (e.g. cilia in our respiratory tract). We synthesized artificial cilia that are driven by light, which could actively drive cells or vesicles.
Compared to the industrial revolution in the 19th century, the development of molecular machines is at the very beginning. It is difficult to predict which applications will arise from research. The engineers at the beginning of the 19th century who experimented with the first atavistic electro motors could not envision that cars, washing machines or industrial robots would be driven by their devices. We are now on the verge of a new molecular technology.
The author is Professor for Organic Chemistry and chairman of the CRC 677 at Kiel University.
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