Plasma sterilisation device kills MRSA
Researchers have demonstrated a prototype device for hospital disinfection, which uses plasma sterilisation to kill bacteria, including MRSA. The device works by creating a plasma that produces chemicals in the air that kill bacteria without causing skin irritations.
Plasma disinfection is said to decrease the standard scrubbing-up time for hospital staff to a few seconds rather than the current several minutes for hand washing or scrubbing. It also has the potential to provide a more thorough disinfection through its ‘molecular’ rather than fluid application.
The team, led by Professor Gregor Morfill of the Max Planck Institute in Germany, says that an exposure to the plasma of only 12 seconds reduces the incidence of bacteria, viruses, and fungi on hands by a factor of a million, compared with the several minutes hospital staff can take to wash using traditional soap and water.
Writing in the New Journal of Physics, the researchers say plasma sterilisation of equipment is already used to disinfect surgical instruments. As it works at the atomic/molecular level it is able to reach all surfaces, including the interior of hollow needle injections and other regions not accessible to fluid disinfectants. A more recent development is biocompatible low-temperature atmospheric pressure plasmas, which can be of use for in vivo applications.
Most plasma sterilisation developments employ one form or other of ‘plasma jets’ or ‘dielectric barrier discharges’. The former are generally too small for large area sterilisation (such as hands) while the latter require the close proximity (of the order of millimetres) of the skin to the plasma device — the skin is in fact the second (grounded) electrode.
The prototype device is specifically designed for large area disinfection and has a total electrode area of 200cm2 and can be scaled up or down to the required size. Two electrodes are placed with a separation of 4cm.
The ‘sandwich electrode’ consists of three parts: a 1mm thick copper sheet electrode, a 1mm Teflon plate and a stainless steel mesh electrode. The wire diameter of the mesh electrode is 0.5mm. The plasma is produced in the squares between the wires of the mesh electrode. The sinusoidal high voltage is applied to the copper electrode and the mesh electrode is grounded.
The researchers describe the operation of this electrode as barrier corona discharge. Tests have shown that insulating the grounded mesh electrode does not significantly alter the performance.
In summary, the plasma dispenser is equipped with a robust, low-power electrode, which is easy to manufacture at a reasonable cost. It operates in air at (essentially) room temperature.