'Frankly, some researchers didn't think what we were doing was possible,' says Dr Keith Firman, on the completion of the Sixth Framework Programme (FP6) Mol-Switch project that he coordinates. 'However, we got our molecular switch to work,' he told IST Results.

The project has not just worked, but has succeeded under intense scrutiny and scepticism from experts in associated fields, such as biotechnology and biophysics. The project itself is rather difficult to conceptualise: a 'nano-actuator' device so small that it could be used to move specific DNA fragments, and allow individual DNA sequencing. The project's aim was to produce an individual molecular 'nano-switch'.

Six partners, the University of Portsmouth, UK; the National Physical Laboratory, UK; ENS/CNRS, France; TUDelft, the Netherlands; the University of Parma, Italy and the Institute of Microbiology in Prague, the Czech Republic, developed the nano-device over three years.

It was decided beforehand that the project would be considered a success if it could demonstrate the activity, efficiency and stability of the switch, its effectiveness at DNA sequencing, and its commercial potential.

The experimental part of the project had two phases - firstly, to use a biological motor to produce a nanoactuator (or simply a device) which would pull a magnetic bead towards a surface. The movement of the bead would generate a tiny, but detectable, electrical current.

Secondly, the biological motor should pull fluorescently-labelled DNA towards a fluorescently-labelled version of the motor. This will result in 'Fluorescent Resonant Energy Transfer' (FRET), which can give accurate measurements of the DNA sequencing, and therefore the switch's accuracy.

DNA sequencing is what the Human Genome project was set up to decode in the human body. DNA has four 'bases' within it. These bases are all proteins, identified by the letters A, C, G and T. Different gene sequences are simply lists of A, C, G and T in different combinations.

The researchers used a type of molecular motor known as a 'Restriction-Modification enzyme'. This molecular motor attaches itself only to specific sequences of A, C, G and T. 'This binding is very specific, a motor will bind only with its corresponding bases, so you can control exactly where the motor is placed on the vertical DNA strand,' said Dr Firman.

The DNA strand is held upright by a magnetic field, pulling a magnetic marker at the end of the DNA strand. The molecular motor sits somewhere below the magnetic marker at a specific position, and does not move. When the molecular engine is started, when fed biological fuel ATP, it pulls the DNA strand, stopping when it reaches the magnetic marker.

Why does this matter, and what use is this? Most simply, this nano-switch enables one form of energy to be transferred to another for a useful purpose, and in a controlled fashion. 'The light switch, the button that makes a retractable pen, all these are actuators, and by developing a molecular switch we've created a tiny actuator that could be used in an equally vast number of applications,' says Dr Firman.

The result is quite literally a building-block for the nano-world, and as the imaginations of researchers grow, so will useful applications of the switch. 'It could be used as a communicator between the biological and silicon worlds. I could see it providing an interface between muscle and external devices, through its use of ATP, in human implants. Such an application is still 20 or 30 years away,' says Dr Firman 'It's very exciting and right now we're applying for a patent for the basic concepts.'

One unintended by-product of this research is in DNA sequencing. If the DNA strand is marked with fluorescence, then 'Knowing the speed of the motor, which is quite reliable and steady at any specific temperature, we could locate the position of the DNA-based Fluor [molecule] relative to the binding site of the motor,' says Dr Firman. 'More work needs to be done. However, the concept is sound and we now have enough evidence to indicate that this could be used to sequence single-nucleotide polymorphisms (SNPs) that cause genetic disorders.'

The next step is to turn this idea into a marketable product. 'We're applying for a new project under the [European Union's] New and Emerging Science and Technology (NEST) scheme and, if that's successful, we will be able to develop a commercial product for biosensing,' says Dr Firman.

For further information see
http://www.nanonet.org.uk/molswitch/default.asp