Removal of biofilms using carbon dioxide aerosols

The formation of biofilm (bacterial film) has been serious concerns in a wide variety of applications, because it is involved in many human and device-associated infections. We present a novel method of effectively and rapidly removing Escherichia coli (XL1-blue) biofilm from a silicon chip, using carbon dioxide aerosols. The aerosols were generated by adiabatic expansion of a high-pressure CO2 gas through a nozzle and they were applied to biofilms that had been grown for 24 h on silicon chips. We measured the percentage area cover of the bacteria from the scanning electron micrographs taken before and after applying the aerosols. The decrease in the percentage area cover, caused by the aerosols, was measured as several parameters such as the distance between the nozzle and the chip, the angle of the nozzle axis relative to the horizontal, CO2 stagnation pressure, rinsing solution, the aerosol exposure time, and drying time were varied. Nearly 100% of the biofilms were removed within 90 s whether the chip surfaces were very humid (no-drying) or dry (7 h-drying) immediately before applying the aerosols. This method has potential application to cleaning of a wide variety of bio-contaminated surfaces.