Fast, intensive, and targeted treatment: understanding “green” disinfection using visible light and its applications.

Identifying the most “antimicrobial” wavelengths and understanding the type of cellular damage caused by high-power light treatment at these wavelengths were the main challenges of the GreenDeconta project.

The first experiments consisted of searching for wavelengths in the visible spectrum that had the most lethal effect on microorganisms. These experiments identified wavelengths associated with blue light as the most effective. Based on these results, a reactor consisting of two series of LEDs emitting at wavelengths of 385 nm and 405 nm was developed. A specific LED arrangement made it possible to generate a high light output of 5000 W/m² per wavelength. The impact of air humidity on the inactivation of microorganisms was also evaluated by placing the reactor in a climate chamber with controlled humidity.  After characterizing the inactivation efficiency of high-power blue light in terms of time and energy consumed, the cellular mechanisms of inactivation were investigated. Photo-oxidation is the central mechanism of photodynamic inactivation described to date in the literature. However, the use of high light intensity could induce additional damage. Microscopy and flow cytometry were used to characterize the intracellular generation of reactive oxygen species (ROS) and membrane permeabilization. The model yeast S. cerevisiae and certain mutants were used to identify cellular responses and enzymatic systems involved in resistance to light treatment. The potential of high-power treatment on an industrial scale was evaluated in the laboratory by treating surface materials (contaminated with S. cerevisiae) or finished products (apples infected with P. digitatum spores).