Biocides are compounds widely used in industry to increase the life span of products as diverse as medicines, cosmetics and paints. The most commonly-used biocides to date are organic molecules that unfortunately are not problem-free. For example, parabens are considered endocrine disruptors and isothiazolinones are allergenic. One solution to these concerns is to consider mineral biocides based on metal ions such as copper and silver, whose effects are known and have been used for a long time, for example copper in agriculture. But the major issue with these biocides is their very low biodegradability. Therefore, the question arises as to how to obtain tailored biocides that can release the necessary dose of metal ions while avoiding the undesirable release of toxic ions into the environment?

The envisioned solution consists of using metallic nanoparticles fixed on a support allowing both easy and safe use, while allowing a progressive availability of these ions. It is indeed necessary to avoid the release of the nanoparticles which tend to aggregate and whose toxic and ecotoxic effects are still poorly known. It is in this context that researchers from IRIG, in collaboration with researchers from INRAE in Nantes, have developed hybrid biocides composed of silver nanoparticles fixed on a biodegradable support made of cellulose nanocrystals.
In a first phase, the mechanisms of synthesis and anchoring of silver nanoparticles on cellulose were studied ^[1]. Different hybrid biocides were then developed, varying in the proportion of silver attached, as well as in the size and shape of the nanoparticles grafted onto the cellulose nanocrystals. These constructs were tested for their biocidal performances as well as for their possible toxic effects on mammalian cells ^[2]. The researchers showed that the most effective configurations were obtained for small nanoparticles (about 10 nm). The minimum effective concentrations to achieve sustained biocidal effects were determined and found to be lower than those described in the literature. Finally, these hybrid biocides were tested in an application involving paints, in collaboration with ALLIOS, a French industrial company, and researchers from LITEN at CEA-Grenoble. Compared to organic biocides, which are only effective in liquid paint, these new biocides were found to be effective at conferring a sustained biocidal effect on the dry paint film ^[3].

This work opens the way to the realization of tailored biocides, i.e. depending on their use. In addition to adjusting parameters such as the amount of silver fixed, the size and shape of the nanoparticles, it will be possible to modify the cellulose support in order to finely modulate the release of the biocidal metal ion. These tailored biocides will thus link optimal efficiency and economy of metallic atoms for minimized toxic and ecotoxic effects.