Aerosols are less than 100 microns in diameter and can be inhaled directly into the lungs and are one of the important ways of transmission of the new crown pneumonia virus. In the new crown pneumonia epidemic in Guangzhou last year, aerosol transmission occurred, but at that time, an effective means of testing for the new crown virus for aerosols had not yet appeared.
Researchers from Tsinghua University, Peking University, Institute of Pathogenic Biology of the Chinese Academy of Medical Sciences, Changping Laboratory and other scientific researchers have carried out emergency research and jointly developed a public space bioaerosol new coronavirus monitoring system, which has been successfully applied in the Beijing Winter Olympic Test Match. The system is capable of collecting and detecting bioaerosols present in the air with up to 10 times the sensitivity of conventional methods.
Realize fully automatic integrated detection
In order to solve the problem of aerosol detection, in October 2020, under the deployment of the Beijing Municipal Party Committee and Municipal Government and the direct leadership of the Beijing Municipal Science and Technology Commission, Liu Peng, a researcher at the Department of Biomedical Engineering of Tsinghua University School of Medicine, joined hands with Changping Laboratory, Peking University and other units to successfully complete scientific research after 8 months of efforts.
Liu Peng introduced that the bioaerosol new coronavirus monitoring system for public space is divided into two parts: the portable bioaerosol sampler as a front-end collection device will work in the place where testing is required to carry out air sample sampling; the automated fully integrated high-sensitivity virus nucleic acid detection system is set up in the laboratory to analyze the collected samples and generate test reports.
Previously, the aerosol collector has been successfully developed by Professor Yao Maosheng of Peking University, and then has been improved and upgraded many times to make it more portable and easy to use. Open the bioaerosol sampler, and in the middle is a specially designed cavity in which the inhaled air forms a "vortex". After the instrument is started, at a flow rate of more than 400 liters per minute, the air cyclone is directed into the reagent-filled detection tube.
"Pure air will bounce off the solution, but the aerosols, dust and other substances contained in the air will be collected. Like a grain of sand entering the water, it will quickly sink to the bottom. Li Xinyue, a doctoral student at peking university's school of the environment, introduced that the design can separate gas and aerosol, so that aerosols are enriched in the sampling tube. At the same time, the collection reagent can inactivate the virus and ensure that the collected virus samples are no longer contagious.
At the detection end, Liu Peng led the team to tackle the problem for more than half a year, and a tape-sized nucleic acid capture and in situ amplification detection chip was developed. The chip adopts a fully enclosed design, and after the sample is collected, the nucleic acid capture and in situ amplification filter membrane can capture more than 80% of the viral nucleic acid from 1 ml of sample. Subsequently, the experimenter only needs to neatly insert the chip into the molecular diagnosis and control integrated machine, and the instrument can automatically amplify and analyze the nucleic acid, directly generating the detection results, without manual participation in the whole process.
The sensitivity is increased by an order of magnitude
"It's much more difficult to test air than traditional methods like throat swabs." Liu Peng said that because the virus content in the air is much lower than the content in the human body, and the new crown virus is an RNA virus, the stability is poor, and the air is always flowing, if it is delayed for too long, it will lose the significance of detection, which requires that sample collection must be efficient and the detection must be sensitive."
In April 2021, Liu Peng and his team entered Ditan Hospital with the aerosol nucleic acid detection system to carry out field collection of new coronavirus samples and actually verify the system. Liu Peng's team collected the patient's nasopharyngeal swab, saliva, exhaled gas and aerosol samples from the ward, and divided the samples into two, and carried out aerosol testing and routine testing at the same time. The results showed that the two detection methods were highly consistent, and the detection rate of the aerosol system was three times that of the existing PCR system.
Liu Peng said that the aerosol nucleic acid detection system can achieve a sensitivity of 20 copies per milliliter, while conventional methods require 200 to 500 copies per milliliter to detect, "it can be said that the detection sensitivity is an order of magnitude higher than the existing technology." At the same time, this system does not "pick" the strain, when conducting amplification detection, Liu Peng chose a conservative sequence that the new crown virus will not mutate, even the latest mutation of the Olmikron strain, it also can not escape the detection of the system.
Each collector works on site for 30 minutes to collect aerosol particles within 12 cubic meters, and then after 45 minutes of automated integrated detection, the detection conclusion can be drawn. From the beginning of sampling to the feedback of the final results to the epidemic prevention department, the whole process will not exceed 4 hours.
It will soon land in the Winter Olympic venues
Before it was officially put into use, the aerosol nucleic acid detection system was verified by experts to confirm that the virus collected through the aerosol would be rapidly inactivated in the collection tube to ensure the safety of the subsequent detection process.
Since October 2021, the system has been tested and verified in five Winter Olympic venues and main media centers, and 348 samples have been taken at the Winter Olympic Test Games. Liu Peng said that if a weak positive or positive sample is found in the test, the laboratory will immediately communicate with the epidemic prevention department and start a series of epidemic prevention processes such as environmental disinfection and personnel testing and tracking as soon as possible.
According to the plan, the project team will arrange aerosol collectors in multiple venues of the Winter Olympic Games and set up temporary testing stations to provide comprehensive aerosol new coronavirus testing guarantee for the Winter Olympics.
"Our technical application is equivalent to a link in the epidemic prevention system of the event, which plays a role in supplementing and early warning." Liu Peng said that the epidemic prevention system includes a series of monitoring methods such as daily prevention and control, sampling and testing, and environmental disinfection, and air environmental testing is part of the overall epidemic prevention system. If there is an abnormality in the test, the laboratory will communicate with the epidemic prevention department in time and take a series of follow-up measures.
Liu Peng said that carrying out new crown virus monitoring is bound to be a long-term process, and he looks forward to the system being able to land in crowded places such as hospitals, stations and airports in the future to find clues to the epidemic in a timely manner.