ERC Stories - Diving into the world of the very small
Imagine a circular swimming pool with a diving board at its rim. Now imagine that this 'swimming pool' is the round end of an optical fibre and the ‘diving board’ is thinner than a human hair. This is what Dr Iannuzzi makes: it is called a 'fibre-top cantilever' and it has the potential to transform many different areas of research. Fibre-tops The project arose from Dr Iannuzzi's experiments in fundamental physics, trying to measure forces due to quantum effects, such as the 'Casimir Effect'. The usual apparatus shines a laser beam on to a tiny cantilever. The force to be measured will bend the cantilever and, by measuring this bend through deflection of the light, you can measure the force. 'Commercial instruments were causing spurious effects, however,' explains Dr Iannuzzi. 'The focus of the laser was too wide and the light missing the lever would cause problems in the very sensitive, small-scale measurements we were trying to make. In trying to avoid these problems, the researcher hit on the answer: 'Why not fabricate the cantilever on to the end of an optical fibre?' The team used the same optical fibres as in telecommunications — a 0.1mm-diameter glass fibre, transmitting a 0.01mm light beam within it. The laser light shines precisely on to the cantilever and is reflected back into the fibre so that interference between the emitted and returning light indicates the amount of movement. Thanks to an ERC Starting Grant 2007, ‘we have been able to bring this technology to maturity and patented a fabrication method,' Dr Iannuzzi explains. ‘We can fabricate micro-machined devices on glass fibres using the same techniques as for silicon-based MEMS,' he continues. Applications include atomic-force microscopy (AFM): a sharp tip on the cantilever can be pressed to a surface and moved 'like the stylus of a record player'. By recording the location and bend of the 'stylus' you can build up an image of the surface with a resolution of nanometres — better than is possible using optical microscopes. Normally, this equipment is bulky, expensive and requires complex alignment of mechanical and optical parts, 'but with fibre-top technology there is no need for alignment,' says Dr Iannuzzi. Even if the sensor is more expensive to make, this leads to cheaper and smaller microscopes. 'We have already built a table-top model and they could even be hand-held,' he says. Since the cantilever is at the end of a long optical fibre, it is suited for use in harsher environments, with electronics kept at a safe distance. It can also be used in small, narrow spaces: 'The dream is that we could eventually use it in applications such as minimally invasive surgery.' Start-ups and spin-offs With the help of a new ERC Proof of Concept Grant, the team now want to show that this process can be scaled up to volume production. 'This would be a tremendous result for our research group and for Optics11, our start-up company to commercialise fibre-top technology.' The new design even has some advantages the team had not anticipated. 'We can also fabricate a shorter cantilever so the very tip is exactly aligned with the light beam,' explains Dr Iannuzzi. 'We could measure the position of the cantilever with one colour while shining a light on the same point of the sample in another colour.' The light beam could generate fluorescence in the materials being studied, collecting chemical data from the same point that is being scanned. The fibre-top cantilever also seems capable of greater sensitivity and precision than existing techniques. 'We can even detect stiffness and whether a surface is hard or soft,' Dr Iannuzzi says. So researchers could examine the physical properties of biological cells, detecting the stiffness of the cell wall - which can be an indicator of health or illness. These biophysics applications could result in greater understanding of the fundamental properties of cells, which in turn could lead to both medical and surgical applications. - Source: Dr Davide Iannuzzi - Project coordinator: VU University Amsterdam, Netherlands - Project title: Fiber-top micromachined devices: ideas on the tip of a fiber - Project acronym: Ftmems - Dr Davide Iannuzzi’s website - FP7 funding programme (ERC call): Starting Grant 2007 & Proof of Concept 2011 - EC funding: EUR 1.8 million - Project duration: five years glossary AFM – atomic force microscopy: a very high-resolution type of scanning probe microscopy which achieves a much higher resolution than optical microscopes by using a physical probe instead of light casimir Effect: a force, explained through quantum theory which, for example, can produce an attraction or repulsion between two uncharged plates placed very close together. cantilever: an overhanging beam, or lever, supported at only one end. fluorescence: the emission of light, or luminescence, by materials that have absorbed energy from light or some other form of electromagnetic radiation. MEMS – microelectromechanical systems: very small, electronically controlled mechanical devices. They are usually fabricated using deposition techniques in the same way as semiconductor microchips. optical fibre: flexible, transparent fibres made of glass and used in telecommunications because they can transmit light between the two ends of the fibre