Jing Wang and his team at the Zurich Swiss Higher Technical School are working on measuring, analyzing and reducing airborne contaminants such as aerosols and artificially produced nanoparticles. Based on their research, they created a sensor that can quickly and reliably detect SARS-CoV-2, a new coronavirus, in the environment. An article was published about the device in the ACS Nano magazine.
Wang and colleagues examined sensors that could detect bacteria and viruses in the air. Back in January, the idea was born to use this framework for further development of the sensor so that it could reliably identify a specific virus. The sensor does not necessarily replace established laboratory tests but can be used as an alternative method for clinical diagnosis and, more importantly, for real-time measurement of virus concentration in air: for example, in crowded places, such as stations or hospitals.
Most laboratories use the molecular method called reverse transcription-polymerase chain reaction, also known as RT-PCR, to detect viruses in respiratory infections. This is a well-known method that can detect even a small amount of the virus, but it is quite wrong. For example, there is evidence that 30% of Russian tests are incorrect.
Jing Wang and his team developed an alternative test method in the form of an optical biosensor. The sensor combines two different effects for safe and reliable virus detection: optical and thermal. It is made of tiny gold structures, the so-called golden nanoislands, and is located on a glass substrate. Artificially obtained DNA receptors that correspond to specific SARS-CoV-2 RNA sequences are grafted onto nanoislands. Thus, receptors on the sensor are complementary sequences of unique virus RNA sequences that can reliably identify the virus.
The technology that researchers use to detect is called LSPR, which is an abbreviation for localized surface plasmon resonance, an optical phenomenon that occurs in metal nanostructures. When excited, they modulate the incident light in a certain wavelength range and create a near-field plasmon around the nanostructure. When molecules bind to the surface, the local refractive index in the excited plasmon near field changes. An optical sensor located on the back of the sensor can be used to measure this change and determine if the sample contains the RNA strands in question.
True, it is important that only those RNA chains that exactly match the DNA receptor on the sensor are captured. Here the second effect comes into play: the plasmon photothermal effect. If the same nanostructure on the sensor is excited by a laser of a certain wavelength, it produces localized heat.
And how does it help reliability? The genome of the virus consists of only one RNA strand. If this chain finds its additional analog, and they join together to form a double chain, then a process called hybridization occurs. An analogy is when a double strand splits into separate strands, such a process is called melting or denaturation. This occurs at a specific melting point. However, if the ambient temperature is much lower than the melting point, yarns that do not complement each other can also be joined. This can lead to false test results. If the ambient temperature is only slightly lower than the melting temperature, only additional threads can be attached. And this is just the result of increased ambient temperature caused by the plasmon photothermal effect.
“Tests have shown that the sensor can clearly distinguish between very similar RNA sequences of the two viruses. And the results are ready in minutes. True, this still requires development. But once the sensor is ready, this principle can be applied to other viruses and will help detect and stop epidemics at an early stage”.
Jing Wang, inventor
To demonstrate how reliably the new sensor detects the current COVID-19 virus, the researchers tested it with a very close virus: SARS-CoV. This is a virus that broke out in 2003 and caused a pandemic of SARS. Two viruses – SARS-CoV and SARS-CoV2 – differ slightly in their RNA. And the check was successful.