Chitosan/calcium nanoparticles as advanced antimicrobial coating for paper documents

Preservation of paper-based historical artifacts against deterioration due to the presence of bacteria and fungi colonies has been one of the major issues for the importance of protecting the cultural heritage of humankind. Advances in nanotechnology have enabled the implementation of nanomaterials for this purpose. In this work, calcium/chitosan nanoparticles (Ca/CS NPs) were prepared and well-characterized to investigate their potential as a novel approach for preserving paper-based documents. Following the fundamental characterizations, it was found that Ca/CS NPs are spherical nanoparticles with ~65 nm average size and homogenous dispersion (PdI: 0.2). Besides, minimum inhibition concentration results revealed that Ca/CS NPs show a superior antimicrobial effect against specific bacteria and fungi strains commonly found on paper documents compared to the effect of bare chitosan nanoparticles (CS NPs). After the deposition of Ca/CS NPs onto the paper the pH level was increased and stabilized, and only a limited amount of microbial colony formation was observed for up to 20 days. Moreover, molecular docking analysis provided a better insight into the antibacterial and antifungal activities of these nanoparticles. The antimicrobial activity of CS NPs and Ca/CS NPs was investigated through their interactions with E. coli DNA gyrase B and C. albicans dihydrofolate reductase. The binding modes and all possible interactions of active sites were confirmed by in silico molecular docking method. Collectively, our findings revealed that the formulated Ca/CS NPs are promising candidates for preserving paper documents.