2023 IMEKO TC-4 International Conference on Metrology for Archaeology and Cultural Heritage Rome, Italy, October 19-21, 2023 Long-lasting methods to prevent biodeterioration of stone monuments: new silica nanosystem coupled to natural biocide Flavia Bartoli 1 , Zohreh Hosseini 2 , Alma Kumbaric 2 , Giulia Caneva 2,3 1 Institute of Heritage Science (CNR-ISPC), National Research Council of Italy, Area della Ricerca di Roma 1, Montelibretti, Via Salaria Km 29,300, 00015 Rome, Italy, flavia.bartoli@cnr.it 2 University of Roma Tre, Viale G. Marconi 446, 00149 Rome, Italy, seyedhzohreh.hosseini@uniroma3.it, alma.kumbaric@uniroma3.it 3 National Biodiversity Future Center (NBFC), Università di Palermo, Piazza Marina 61, I‐90133 Palermo, Italy, giulia.caneva@uniroma3.it Abstract - Nanotechnology, specifically nanocompounds, shows promise due to their potential to reduce biocide quantities, operational times, and restoration costs. This study investigates the biodeterioration of stone materials and explores green, eco-sustainable alternatives to traditional biocides. In the context of the SUPERARE and GRAL projects, we assessed the long-term efficacy of two biocides, 2- mercaptobenzothiazole (MBT) and zosteric sodium salt (ZOS), applied via silica-nanosystems on various lithotypes. After three years, results reveal minimal recolonization by fungal and non-photosynthetic organisms, with MBT proving more effective than ZOS. Further analysis will determine if colonizing microorganisms cause physical or chemical damage. This research highlights the potential of green nanotechnology in stone conservation. I. INTRODUCTION The phenomenon of biodeterioration of stone materials is particularly relevant when the environmental conditions, the supply of nutrients, and the edaphic conditions (bioreceptivity) favor biological growth [1-3]. Different treatment methods, such as UV, laser cleaning, microwaves, and heat shock treatments (HSTs) [4-7], as well as several biocidal substances have been used in combination with prevention strategies. Considering the risk to human health and the environment, the use of traditional biocides to reduce biodeterioration phenomena is increasingly discouraged and, in the current national and international context, research for the conservation of cultural heritage is mainly focused to identify techniques that are as "green and eco- sustainable" as possible. The use of natural active compounds coupled to this nanotechnology seems a good way to pursue an eco-friendly, sustainable, and safe approach for the conservation of cultural heritage, reducing the amount of the bioactive compound and obtaining a satisfactory, long-lasting, antifouling action [8- 10]. The literature reports the synthesis of different nanocontainers and loading techniques [10,11]. However, nanosystems based on mesoporous silica materials, applied in a multifunctional coating, as a controlled release biocide system over time, are reported only in a few cases [11-12]. In previous works, two different silica-based nanocontainers (Ns), namely a core-shell nanocapsule (NC) and a mesoporous nanoparticle (MNP), have been synthesized and characterized [13-14]. Previous preliminary in vitro cultures exposed to the nanopar- ticles showed a high antifouling activity associated with a slight biocidal activity against photosynthesizing microorganisms [12]. However, the efficiency of these Ns in the release control of the engaged biocides and the improvement of biocide efficiency, allowing a reduction in the quantities of biocide required, have not been sufficiently addressed. In addition to the selection of non-hazardous biocides for humans and the environment, we are focusing on the development of nanotechnologies, since the application of a "nanocompound" would allow shorter operating times as well as greatly reduced quantities of biocides, with the obvious advantage for the environment and the health of operators. At the same time, these technologies would also make it possible to reduce the costs of restoration operations thanks to prolonged control over time. The search for multifunctional products, therefore, represents an innovative approach capable of making significant improvements to restoration techniques. The present work, developed within the SUPERARE (SUPER - particelle per Rivestimenti Autopulenti e Antivegetativi a Rilascio lEnto) and then GRAL (GReen And Long-lasting stone conservation products) projects granted by the Lazio Region within the 2020 Research Groups Project, dealt with the problem of biological colonization of the Aurelian walls by testing in situ the efficacy of two biocides: (2- 593