However, another driving force behind this project is that magnets are used in a large number of applications, world-wide, and their global market is actually larger than that for semiconductors. In addition, there is a strong demand to produce smaller and smaller magnets for this market. This research is pushing the development of magnetic particles toward the area of Nanotechnology. There is a great deal of interest in single molecule magnets and a powerful interest in making such material bio-compatible for use in medical applications (Aubin et al., 2001; Boskovic et al., 2001; Gatteschi, 2001) .

Many different technologies have been described that could be applied to the problems associated with single-molecule DNA sequencing (many of which are reviewed in Journal of Nanotechnology Volume 86, Issue 3). The techniques generally fall into three types – those based on degradation of labelled DNA and detection and identification of the degradation products (e.g. Dörre et al., 2001) , those that make use of arrays and DNA hybridisation (reviewed in (Meldrum, 2000) and those that use direct detection of labelled DNA in double-stranded DNA (as described here). All these techniques depend upon the use of highly sensitive detection systems such as confocal multi element systems and the manipulation of the DNA with microstructures (Dörre et al., 2001) .

The major problem associated with non-degradative techniques is ensuring that the detection system is sufficiently sensitive to distinguish suitably labelled bases that are separated by only 0.32nm. An ideal situation would be direct reading of the bases using a derivatised cantilever tip from an AFM, but this is an extremely demanding technology to develop. Incorporation of tagged bases as they are synthesised is another approach (Figure). Recognition of the time sequence of base additions is achieved by detecting fluorescence from appropriately labeled nucleotide analogs as they are incorporated into the growing nucleic acid strand.
However, more likely the bases will be labelled with a fluorophore and their position read using fluorescence resonance energy transfer (FRET), which detect photons from two closely located (<10nm) fluorophores. By suitable positioning of one fluorophore, within a detection device such as an evanescent-wave epifluorescence microscope, movement of the DNA past this first fluorophore will produce FRET signals for each labelled base. However, it is unlikely that labelling of every base will be possible, or reliable. A more realistic system will require random labelling of the DNA and the use of parallel systems to read several randomly labelled DNA molecules. Such a system will require an accurate means for detecting and determining the rate of movement of the DNA past the detector independent of the frequency of the FRET signals (a weakness of the system described by US Genomics).

The DNA-based motors, and the associated nano-actuator, we describe in this project provide many advantages for the development of such a system including re-setting after translocation (allowing increased accuracy of reading labelled bases by re-reading), defined positioning of translocation start-points, a simple system for ‘stretching’ the DNA before and after the re-setting process and finally a mechanism (based on the use of magnetic beads) for independently determining the rate of movement of the translocating DNA. We will also use this project to investigate techniques for improving detection of the labelled bases such as FRET between a fluorescently labelled AFM tip and a fluorescently labelled DNA molecule.