Aerosols with a diameter of less than 100 microns and a transmission distance of more than 1 meter can be inhaled directly into the lungs, which is one of the important ways of transmission of the new crown pneumonia virus.
In order to monitor the aerosols in the air, researchers from Tsinghua University, Peking University, the Institute of Pathogenic Biology of the Chinese Academy of Medical Sciences, and the Changping Laboratory carried out emergency research and jointly developed a public space bioaerosol new coronavirus monitoring system. At present, a number of sample collectors have been "posted" in many venues of the Winter Olympic Games.
Compared with conventional methods, the sensitivity of the monitoring system is an order of magnitude higher. Recently, the reporter came to the bioaerosol testing laboratory of Beijing Zhongguancun Life Science Park to reveal how such a sensitive device works.
Collect aerosol particles from confined space for 30 min
Aerosol refers to a system of tiny particles suspended in the air for a long time, generally below 100 microns in diameter, and fog and haze are aerosols. Aerosols whose components include microorganisms such as viruses, bacteria, fungi, pollen, animal and plant-derived proteins, etc., are called "bioaerosols".
According to Liu Peng, a researcher at the School of Medicine of Tsinghua University, aerosol particles will be transmitted to the air with people's breathing and sneezing, and their transmission distance is more than 1 meter, which can be directly inhaled into the lungs, which is one of the important ways of transmission of the new crown virus.
Compared to doing nucleic acid testing for people, it is not easy to do "nucleic acid testing" for air. "Because the aerosol sample size is large, the viral load in the air is relatively low, far lower than that directly sampled from the human throat, and at the same time, the viral RNA stability is poor, which requires our collection method to be efficient and the detection method to be very sensitive." Liu Peng said.
At the bioaerosol testing laboratory located in Beijing's Zhongguancun Life Science Park, the reporter met with the bioaerosol new coronavirus nucleic acid monitoring system, which is composed of two parts: a portable aerosol collector and an integrated high-sensitivity new coronavirus nucleic acid detector.
Developed by the team of Professor Mao Sheng of the School of the Environment of Peking University, the aerosol collector is small and lightweight, suitable for use in small confined spaces such as warm-up rooms and referee rooms, and can collect aerosol particles within 12 cubic meters within 30 minutes and collect them into the sampling tube.
The acquisition tube is fixed to the collector. Beijing News reporter Tao Ran photographed
Li Bao, a graduate student at Tsinghua University School of Medicine, put on gloves and fixed the collection tube to the collector and demonstrated the process to reporters. In the middle of the bioaerosol sampler is a specially designed cavity in which the air sucked in by the air inlet forms a gas "vortex". After the instrument is started, the air cyclone is directed into the collection tube at a flow rate of more than 400 liters per minute, and particles such as aerosols in the air are thrown into the collection tube.
The collection tube is filled with 4 ml of virus inactivation solution, and once the aerosol contains virus, it will be inactivated to ensure the safety of sampling and subsequent testing personnel.
Virus detection sensitivity is 10 times that of conventional methods
After the collection is completed, it is the turn of the "integrated highly sensitive new coronavirus nucleic acid detector" to appear.
Li Bao used a pipette to remove 1 ml of liquid from the collection tube with only about 2 ml of solution left after concentration and transferred it into the sample tube. "The remaining 1 ml of liquid is retained for sample retention, and once positive, it can be retested." The sample tube is loaded into the chip cassette and fully enclosed into the detector for detection.
On January 18, at the Beijing Institute of Life Sciences, staff put a chip cartridge into a testing instrument. Beijing News reporter Tao Ran photographed
The card box is smaller than the palm of the hand, but it contains a dry kun. The liquid flows through the general thickness of the "hair strand" under the cassette and flows into the nucleic acid capture membrane independently developed by Liu Peng's team at Tsinghua University, which enriches the nucleic acids together and the remaining solution flows into the waste liquid pool. The first step from cracking to capture of nucleic acids is complete.
In the second step, the cleaning solution will also flow from the runner to clean the impurities and membranes in the sample. Next, the reaction reagent flows to the position of the membrane and amplifies the nucleic acid locally in situ. Read by the fluorescence detector, the final data is displayed directly on the screen, generating the inspection results.
"Although the curve of the negative sample will fluctuate slightly, it is basically flat, while the curve of the positive sample will rise in an S-shape, which is obviously distinguished from the negative sample." Li Bao said.
All of these steps take only 45 minutes and do not require human involvement. Eight chip cassettes can be installed in the detector to detect 8 samples at the same time to improve the detection efficiency.
The detector uses a microfluidic control platform combined with new nucleic acid extraction and amplification technology to make the detection sensitivity of the new crown virus reach 20 copies/ml, which is 10 times more sensitive than conventional methods.
What is the concept of 20 copies per milliliter? For example, Liu Peng explained that the new crown virus test will collect a throat swab and check the concentration of the virus in the solution of the test tube. Detection using conventional real-time PCR methods requires 200-500 viruses per milliliter to detect. Using an aerosol virus detector, the sensitivity reached 20 viruses per milliliter, 10 times that of conventional methods, an order of magnitude higher.
Chip cartridge, the far right of the cassette is the sample tube. Beijing News reporter Tao Ran photographed
Completed emergency research and development in 8 months
The monitoring system was difficult to develop, but the process took only 8 months.
In October 2020, researchers from Tsinghua University, Peking University, the Institute of Pathogenic Biology of the Chinese Academy of Medical Sciences, and the Changping Laboratory carried out emergency research and jointly developed a public space bioaerosol new coronavirus monitoring system.
Li Bao still remembers those "very hard" days. "It is normal for me and my brother Li Shanglin to do experiments at 1 or 2 a.m., and Teacher Liu Peng hardly rests on weekends and holidays. As soon as there is a data result, we often discuss it in the middle of the night. ”
In April 2021, the system entered the actual verification. Liu Peng's team took the aerosol new coronavirus monitoring system into Ditan Hospital to carry out field collection of new coronavirus samples. They took nasopharyngeal swabs, saliva, exhaled gases, and aerosol samples from the ward and performed aerosol testing and routine testing simultaneously. Clinical test validation results from more than 100 samples showed that the system-positive detection rate was three times the detection rate of existing real-time PCR systems.
In order to promote the application of this technology in the Beijing Winter Olympics, the Beijing Municipal Science and Technology Commission organized experts to demonstrate the technology. The R&D team conducted experimental verification in the P3 laboratory according to expert opinions, and proved the safety of aerosol collection.
It is used for epidemic prevention in Winter Olympic events to play an early warning role
Before the official "induction" of the Winter Olympics, the system has already shown its skills in the ice making period and the Winter Olympic testing activities.
Since October 2021, the system has been tested and applied in venues such as the Capital Gymnasium, Wukesong Ice Center, National Speed Skating Hall, "Water Cube", National Stadium and Main Media Center. According to Liu Peng, in order to ensure biosecurity, the team adopted the mode of negative pressure tent and biosafety cabinet, taking into account timeliness and safety. As of early December 2021, a total of 348 aerosol specimens had been tested, demonstrating the feasibility of aerosol testing.
During the Winter Olympics, it is expected that more than 100 sample collectors will be "posted" in multiple venues of the Winter Olympics, and multiple detectors will be set up at temporary testing stations. From sampling to sample transportation to detecting results, the entire process will take no more than 4 hours.
"The application of our technology is equivalent to a link in the entire epidemic prevention system, which plays a role in supplementing and early warning." Liu Peng introduced 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.
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Up to now, more than 200 technologies have been tested and used in the Winter Olympic scenarios, and more than 70 have been confirmed to be applied during the games, of which more than 20 are highly representative in terms of technological advancement and application display.
At present, the new crown pneumonia epidemic has not been completely contained in the world, and scientific epidemic prevention has become an important prerequisite for the successful operation of this Winter Olympic Games. Through organizing scientific and technological epidemic prevention technology research, expert demonstration, on-site testing and other forms, we have promoted the application of a number of technical achievements in body temperature monitoring, environmental disinfection, pathogen detection and other links, effectively played the role of science and technology in supporting the prevention and control of the epidemic at the Beijing Winter Olympics, and fully guaranteed the safety of the event. ——Yang Pengyu, head of the Winter Olympic special class of the Beijing Municipal Science and Technology Commission and the Zhongguancun Management Committee
Beijing News reporter Zhang Lu photojournalist Tao Ran
Edited by Zhu Lihua Zhang Lei Proofreader Yang Xuli