Disinfection knowledge series

Physical disinfection factor – plasma

In the material world, we are familiar with solid, liquid and gas, however, there is also a mysterious form of matter – plasma, which is called the fourth state of matter. Today, let us walk into the wonderful world of plasma and explore its unique application in disinfection.

Plasma is mainly composed of charged positive particles and negative particles (including positive ions, negative ions, electrons, free radicals and various active groups). Since the number of positive ions and negative ions (electrons) is equal, the whole is electrically neutral. It is widely present in the universe, and more than 99% of matter exists in the plasma state. Because of its unique properties that are different from the three states of solid, liquid and gas, such as electromagnetic properties, it has important applications in many fields.

In the field of disinfection, plasma, as a physical disinfection factor, plays a role that cannot be underestimated. Among them, low-temperature plasma has become the main force in disinfection applications due to its relatively mild conditions. It can be further divided into low-pressure plasma and atmospheric pressure plasma.

Low-pressure plasma is usually produced under vacuum. According to the discharge method, it can be divided into direct current glow discharge (DC) plasma and radio frequency glow discharge (RF) plasma. The low-pressure gas is excited by a higher voltage, and the electrons in the tube collide with neutral particles under the action of the electric field and ionize, resulting in a glow discharge phenomenon, and then forming a glow discharge plasma. This plasma has a higher voltage but a lower current. DC glow discharge plasma relies on a DC power supply, while RF glow discharge plasma is driven by a high-frequency AC power supply, the latter of which has a higher working gas pressure and a lower voltage. In the disinfection of some precision instruments with strict environmental requirements, low-pressure plasma can efficiently kill bacteria, viruses and other microorganisms without damaging the instruments.

Normal-pressure plasma can be generated under atmospheric pressure, has a lower molecular free path, makes the collision of active component molecules more frequent, and its temperature is slightly higher than that of low-pressure plasma. It mainly includes dielectric barrier discharge (DBD) plasma and cold plasma jet. Dielectric barrier discharge plasma requires an AC power supply because there is an insulating dielectric between its electrodes. When the potential between the plates is large enough, the gas is broken down to form a uniformly distributed plasma. Cold plasma jet generates plasma by passing high-frequency AC current between open plates, and transports the plasma to the working area with the help of high-speed flowing working gas. In places such as hospital wards and operating rooms that require continuous disinfection, normal-pressure plasma can dynamically disinfect the air and the surface of objects to effectively prevent cross-infection.

Plasma, the magical fourth state of matter, is shining in the field of disinfection with its unique physical and chemical properties, protecting our lives and health. With the continuous advancement of science and technology, it is believed that plasma disinfection technology will be more widely used and developed.