Super sensors made of metamaterials

August 28, 2012, Nr. 60

From fuel cells to tests for diabetics

Metamaterials are mostly associated with optical cloaks, which for example make military equipment invisible. The innovative artificial structures comprising nanometre small metal particles, however, can also be used for sensors, which can detect hydrogen in the environment of fuel cells or glucose in diabetics. However, up to now the area of application of these metamaterials has been limited due to their slight size. Prof. Harald Giessen and his scientists from the 4th Institute of Physics at the University of Stuttgart and Prof. Paul V. Braun from the University of Illinois/USA now wish to take the plunge from the laboratory towards the application and manufacturing of metamaterials of high quality on a scale of square centimetres.

At present large scale structures are still written layer for layer with a laser or an electron ray, which takes hours and is expensive. ”At present optical metamaterials are limited to laboratory samples of sizes under one square millimetre. We wish to overcome these limits, which have stood in the way of the practical use of metamaterials up to now.“ This is how Prof. Harald Giessen describes the aim of the project that goes by the title of ”large-scale three-dimensional metamaterials for optical and sensor applications”, which is to lead metamaterials beyond basic research to the world of applications. The project is being funded by the Baden-Württemberg Foundation in the framework of the programme “Top International Research“ with a sum of 500,000 Euros.

For a more effective manufacturing of metamaterials the scientists test very different approaches, including a non-electrical process of metal separation, which can be realised using relatively simple equipment and without a clean room. Other paths are phase plates holography as well as the functionalising of surfaces with the help of laser beams, which are directed at the structures at a certain angle. Simple, partly still two-dimensional structures can already be manufactured using these approaches. Yet three-dimensional “chiral” structures would be of particular interest for sensors, which turn spirals immediately to the right and left. The Stuttgart physicists and the team working for the material scientist from Illinois complement each other excellently in this respect. ”Stuttgart brings strengths to the optic, Paul Braun the chemistry“, is how Giessen sums it up in a nutshell. The first applications the scientists are aiming for are very innovative nano-structured optical building elements with an active surface of at least one square centimeter, which chemists for example can use in order to research the spatial structure of new medicaments. Moreover, the researchers are developing optical sensor concepts for various chemicals, i.e. for example a detector to measure hydrogen, which is of great interest to energy research, among other things.

Relief for diabetic patients
Already at the threshold of the practical test is an innovative, optical glucose sensor with which diabetic patients can ascertain the sugar level in their blood through the tear fluid without pricking themselves. This project is being conducted by the Stuttgart physicist together with Prof. Cristina Tarin from the Institute for System Dynamics at the University in the framework of the Interuniversity Centre for Medical Technologies Stuttgart-Tübingen. A contact lens acts as a measuring instrument on which a hydrogel layer with minute nanostructures made of gold is attached; the measured values are read with an infrared laser beam. The aim now is to increase the life cycle of the contact lenses, up to now limited to around five days, and to reduce the manufacturing costs to a level that also makes this so beneficial innovation affordable for the patients. For this purpose the researchers are continuing to develop hydrogel on the one hand, in which the gold particles are embedded. Another, longer term promising approach would be to attach chiral nanostructures directly onto a large surface of the contact lens so that the hydrogel would be superfluous.

Your contact person :
Prof. Harald Giessen, University of Stuttgart, 4th Institute of Physics
tel. 0711/685-65111, email: giessen@physik.uni-stuttgart.de

 

Three-dimensional photonic crystal made of silver with chiral structure. The minute wire elements are only 100 nanometres wide. Photo: University of Stuttgart, 4th Institute of Physics.
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