A biosensor is created that detects a coronavirus in the air.

Wang and his colleagues explored sensors that could detect bacteria and viruses in the air. Back in January

the idea was born to use this basis forfurther development of the sensor so that it can reliably identify a specific virus. The sensor will not necessarily replace established laboratory tests, but can be used as an alternative method for clinical diagnosis and, more importantly, to measure the concentration of the virus in the air in real time: for example, in crowded places such as train stations or hospitals.

In most laboratories for virus detectionfor respiratory infections, a molecular method is used called the reverse transcription polymerase chain reaction, which is also known as RT-PCR. 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 alternativetest 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.

Technology that researchers use todetection, called LSPR, 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 chains are capturedRNAs that exactly match the DNA receptor on the sensor. 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 analogue, and they join together to form a double chain, then a process called hybridization occurs. An analogue 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 clearlydistinguish between very similar RNA sequences of 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 help detect and stop epidemics at an early stage."

Jing Wang, inventor

To demonstrate how reliable the newthe 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.