BIOTECHNOLOGY 15
surface with specific ‘molecular traps’ that bind the chosen target molecules. Once bound, the target molecules would change the colours that the device absorbs and scatters, alerting the sensor to their presence.
The team’s next step is to test whether the pair of nanostructures can detect chosen substances in lab experiments. Professor Maier concludes: “This study is a
beautiful example of how concepts from different areas of physics fertilise each other.” Meanwhile, the German Federal Ministry of Education and Research (BMBF) has just approved a joint project under leadership of Forschungszentrum Dresden-Rossendorf (FZD) and in collaboration with the University of Rostock, Proaqua in Mainz and the Helmholtz Centre for Environmental Research (UFZ). The project is part of the Bionic Innovations for
Sustainable Products and Technologies (BIONA) research programme. It will use the natural nanostructures of bacterial coat proteins to fix aptamers onto sensor surfaces in a controlled manner. The UFZ is to develop aptamers that are capable
of detecting certain organic substances, such as undesirable pharmaceutical residues, that enter the environment through wastewater (Fig. 1). The term aptamer means something like “fitting
pieces” (from the Latin word aptus, meaning to fit, and the Greek word meros, meaning piece). Aptamers consist of nucleic acids and have a 3D structure that enables them to identify and bind certain target molecules. These binding abilities allow, for instance, tracing, detecting and measuring certain substances. Hence their potential as biosensors. The challenge is to identify the right aptamer for a particular target molecule. Such target molecules can be very complex structures, like whole cells or organisms, or tiny molecules consisting of just a few atoms. This selection method is called systematic evolution of
ligands by exponential enrichment (SELEX). Scientists at the UFZ’s biosensor laboratory have
developed two different modifications of the SELEX method. One of these is known as FluMag SELEX. The ‘Flu’ stands for fluorescence and refers to the fact that a fluorescence molecule is added to the nucleic acids during the SELEX procedure to make them visible. In this manner the molecules can always be found again and researchers can measure the enrichment of those which exhibit best binding and detecting abilities to the given target. The ‘Mag’ refers to magnetic beads. These are dust-mote-sized magnetic beads onto which the scientists stick the even smaller target molecules to make them more manageable
Novel naval assays]
Naval Research Laboratory scientists in the US are also partnering with industry to develop a sensor system for biomolecules that could make a significant contribution to a variety of fields such as healthcare, veterinary
Fig. 2. BARC has the potential to detect 64 different target analytes.
diagnostics, food safety, environmental testing, and national security. NRL has developed a highly sensitive, portable biosensor system called the compact bead array sensor system (cBASS). This innovative instrument utilises a special integrated sensor chip, called the Bead ARray Counter (BARC), which contains an embedded array of giant magnetoresistive sensors. With 64 200 µm diameter sensors on the chip, BARC has the potential to detect 64 different target analytes (Fig. 2). The technology has already been licensed to Seahawk
Biosystems Corporation in Rockville, Maryland, for further development in veterinary diagnostic, clinical diagnostic, and environmental applications. Researchers at NRL began working on the
magnetoelectronic biosensor concept more than a decade ago, under the leadership of Richard Colton and former NRL researcher David Baselt.
Baselt used a quantum-mechanical effect called giant
magnetoresistance (GMR). In simplistic terms, GMR materials are magnetic field-dependent resistors - their resistance changes when subjected to an externally applied magnetic field. GMR devices are typically constructed of alternating magnetic and non-magnetic metal thin-film multilayers that are only nanometers in thickness.
Baselt looked specifically at a type of GMR called multilayer GMR in which the resistance of two thin
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