A team of researchers from Bochum, Duisburg, and Zurich has developed a new approach to creating modular optical sensors capable of detecting viruses and bacteria. The researchers utilized fluorescent carbon nanotubes with unique DNA anchors that act as molecular handles. These anchors can be used to attach biological recognition units, such as antibodies or aptamers, to the nanotubes. The attached recognition units can then interact with viral or bacterial molecules, affecting the fluorescence of the nanotubes and altering their brightness.
A team consisting of Professor Sebastian Kruss, Justus Metternich, and four co-workers from Ruhr University Bochum (Germany), the Fraunhofer Institute for Microelectronic Circuits and Systems, and the ETH Zurich published their findings in the Journal of the American Chemical Society, which was published online on 27 June 2023.
Straightforward customization of carbon nanotube biosensors
The team utilized tubular nanosensors made of carbon with a diameter of less than one nanometer. When exposed to visible light, these carbon nanotubes emit light in the near-infrared range. While not visible to the human eye, near-infrared light is ideal for optical applications due to its minimal interference from other signals. Previous studies by Sebastian Kruss’ team demonstrated how the fluorescence of nanotubes can be manipulated to detect vital biomolecules. Now, the researchers sought a way to customize the carbon sensors for different target molecules in a simple manner.
The key to their success was the use of DNA structures with guanine quantum defects. By attaching DNA bases to the nanotubes, a defect in the crystal structure was created, resulting in a change in the nanotubes’ fluorescence at the quantum level. Additionally, this defect acted as a handle for introducing detection units that could be tailored to specific target molecules, such as viral or bacterial proteins. “Through the attachment of the detection unit to the 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,” explained Sebastian Kruss.
Sensor identifies various bacterial and viral targets
The group demonstrated the new sensor concept using the SARS CoV-2 spike protein as an example. They used aptamers, which are folded DNA or RNA strands that selectively bind to proteins, to target the spike protein. “In the future, we could apply this concept to antibodies or other detection units,” added Justus Metternich.
The fluorescent sensors reliably detected the presence of the SARS-CoV-2 protein. Sensors with guanine quantum defects exhibited higher selectivity compared to sensors without such defects. Furthermore, sensors with guanine quantum defects demonstrated greater stability in solution. “This is advantageous when considering measurements in complex environments, such as cells, blood, or organisms themselves, for diagnostic applications,” said Sebastian Kruss, who leads 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.