For EBC collection, sterile water (DNA and RNA free) was first added into the collection base of the device up to a depth of 5 mm as observed in Figure 2 . And then, the device base together with the cover was placed in an ultralow temperature (270uC) refrigerator (Thermo Fisher Scientific Co. Marietta, OH) to form a layer of ice. Following this step, a sterile hydrophobic parafilm measured as 8064060.3 (mm)(length6width6thickness) was placed onto the surface of the ice suited in the collection base. To collect EBC samples, a disposable sterile straw with a diameter of 5 mm (16 cm long) is inserted through the exhaled breath inlet shown in Figure 2 , with its end 2 mm above the hydrophobic parafilm. The human subjects are then advised to mouth-breathe without wearing a nose clip through the exhaled breath inlet shown in Figure 2 toward the hydrophobic film for a selected time (1-4 min). Due to the low temperature and hydrophobic nature of the parafilm surface, exhaled breath quickly condenses into tiny liquid droplets on the hydrophobic surface. Assuming an average breathing rate of 12 L/min for an adult, the particle speed from the exhaled breath would be around 10 m/s given the size of the straw (5 mm in diameter). Therefore, during the exhaled breath collection, the bacteria or virus particles would impact onto the hydrophobic surface at a speed of 10 m/s. In addition to condensing used for other EBC collection procedures, the method developed here also rely on the impaction to collect the bacterial and viral particles. Given such a speed, there might be possible particle bounce problems, however the bacterial or viral particles in the exhaled breath usually come with water droplets, which thus minimizes the potential particle bounce problem.