Formulation of Mesoporous Silica Nanoparticles for Controlled Release of Antimicrobials for Stone Preventive Conservation

Abstract

The biotic deterioration of artifacts of archaeological and artistic interest mostly relies on the action of microorganisms capable of thriving under the most disparate environmental conditions. Thus, to attenuate biodeterioration phenomena, biocides can be used by the restorers to prevent or slow down the microbial growth. However, several factors such as biocide half-life, its wash-out because of environmental conditions, and its limited time of action make necessary its application repeatedly, leading to negative economic implications. Sound and successful treatments are represented by controlled release systems (CRSs) based on porous materials. Here, we report on the design and development of a CRS system based on mesoporous silica nanoparticles (MSNs), as a carrier, and loaded with a biocide. MSNs, with a diameter of 55 nm and cylindrical pores of ca. 3-8 nm arranged as parallel arrays concerning the NP diameter, and with 422 m 2 /g of specific surface area were synthesized by the sol-gel method assisted by oil in water emulsion. Biocide loading and release were carried out in water and monitored by UV-Vis Spectroscopy; in addition, microbiological assay was performed using as control the MCM-41 mesoporous silica loaded with the same biocide. The role of specific supramolecular interaction in regulating the release is discussed. Further, we demonstrated that this innovative formulation was useful in inhibiting the in vitro growth of Kocuria rhizophila, an environmental Gram-positive bacterial strain. Besides, the CRS here prepared reduced the bacterial biomass contaminating a real case study (i.e., stone derived from the Santa Margherita cave located in Sicily, Italy), after several months of treatment thus opening for innovative treatments of deteriorated stone artifacts.

Biodeterioration of Salón de Reinos, Museo Nacional del Prado, Madrid, Spain

“…One of the biocides most used by restorers and conservators in Italy [56][57][58] and also tested in Spain [59,60] is Preventol RI 80, based on a quaternary ammonium salt. It is active against a wide variety of bacteria, fungi, algae, and lichens on stones and building materials [57,59,[61][62][63]. Nevertheless, quaternary ammonium salts have shown, in a few cases, to be unsuitable, such as in subterranean environments (caves with rock art paintings) with high and constant relative humidity (above 90%) [64,65].…”

Advanced Materials in Cultural Heritage Conservation

“…These particles, synthesized by a sol-gel method assisted by o / w emulsion, have been loaded with Preventol RI-80, a commercial biocide, and then applied over degraded stone fragments. The biocide included in the mesoporous particles is then released over the surface in a gradual and controlled way, inhibiting bacterial growth over time [ 97 ]. Incorporation of engineered Ag/SiO 2 nanoparticles in organically modified silica-based surface treatments was demonstrated to be an effective strategy to obtain anti-fouling coatings, thanks to the formation of a nano-roughness which leads to superhydrophobic behavior [ 98 , 99 ].…”

Ionic Systems and Nanomaterials as Antiseptic and Disinfectant Agents for Surface Applications: A Review

“…Presentato et al [54] developed a controlled release system (CRS) based on mesoporous silica nanoparticles (MSNs) loaded with a biocide for the preservation and conservation of archeologically interesting stone. To achieve this, the team prepared the MSNs by an emulsion-condensation method, which consists in the hydrolysis of alkoxysilanes followed by a reaction of poly-condensation of the resulting silanol molecules around a CTAB surfactant template.…”