(Nanowerk News) An interdisciplinary research team from Bochum, Duisburg and Zurich has developed a new approach to building modular optical sensors capable of detecting viruses and bacteria. For this purpose, the researchers used fluorescent carbon nanotubes with a new type of DNA anchor that acts as a molecular grip. The anchor structures can be used to conjugate biological recognition units such as aptamers antibodies to nanotubes. The recognition unit can then interact with bacterial or viral molecules onto the nanotubes. This interaction affects the fluorescence of the nanotubes and increases or decreases their brightness.
A team consisting of Professors Sebastian Kruss, Justus Metternich and four colleagues from Ruhr Bochum University, the Fraunhofer Institute for Microelectronic Circuits and Systems and ETH Zurich report their findings at Journal of the American Chemical Society (“Near Infrared Neon Biosensor Based on Covalent DNA Anchors”).
Direct adjustment of the carbon nanotube biosensor
The team used a tubular nanosensor made of carbon and less than one nanometer in diameter. When exposed to visible light, carbon nanotubes emit light in the near-infrared range. Near-infrared light is invisible to the human eye. However, it is very suitable for optical applications, because the signal level of others in this range is greatly reduced. In previous studies, Sebastian Kruss’ team has demonstrated how nanotube fluorescence can be manipulated to detect vital biomolecules. Now, researchers are looking for ways to adapt carbon sensors for use with different target molecules directly.
The key to success was a DNA structure with a so-called guanine quantum defect. This involves connecting DNA bases to the nanotubes to create defects in the crystal structure of the nanotubes. As a result, the fluorescence of the nanotubes changes at the quantum level. In addition, defects act as molecular handles that allow for the introduction of detection units, which can be matched to their respective target molecules for the purpose of identifying specific viral or bacterial proteins.
“By attaching the detection units to DNA anchors, the assembly of such a sensor resembles a system of building blocks – except that the individual parts are 100,000 times smaller than a human hair,” explains Sebastian Kruss. The sensors identify different bacterial and viral targets
The group showcased a new sensor concept using the SARS CoV-2 spike protein as an example. For this purpose, the researchers used aptamers, which bind to the spike protein of SARS CoV-2. “Aptamers are folded strands of DNA or RNA. Because of their structure, they can selectively bind to proteins,” explained Justus Metternich. “In the next step, one can transfer the concept to an antibody or other unit of detection.”
The fluorescent sensor shows the presence of the SARS-CoV-2 protein with a high degree of reliability. The selectivity of sensors with quantum guanine defects is higher than the selectivity of sensors without the defect. In addition, sensors with guanine quantum defects are more stable in solution.
“This is an advantage if you think about measurements beyond simple aqueous solutions. For diagnostic applications, we have to measure in complex environments for example with cells, in blood or within the organism itself,” said Sebastian Kruss, who heads the Functional Interfaces and Biosystems Group at Ruhr University Bochum and is a member of the Ruhr Explores Solvation Cluster of Excellence (RESOLV) and the International Graduate School of Neuroscience.