Cationic silicone based paper impregnation agent for the protection of historical paper against fungal growth. Detection and quantification of fungi using micro-invasive fluorescence microscopy and non-invasive FTIR spectroscopy

Abstract

• Paper impregnation with 10 % ATP for an effective protection of historical paper against mould development. • 3D surface topography showed no adverse effects of ATP on paper support. • Portable “on the spot” non-invasive FTIR spectroscopy in reflection mode is an effective method for a rapid and highly sensitive detection of mould biofilms. Even though contamination of historical paper by moulds causes aesthetic, physical, and biochemical biodeterioration, dissolving cellulose fibers and inks, the currently applied physical and chemical disinfection methods are either extremely dangerous to human health (ethylene oxide), may harm the underlying support material, or their efficiency is dependent on fungal species, many of which may resist. Therefore, our aim was to test a new paper impregnation agent, aminopropyl-terminated polydimethylsiloxane (ATP), in regards to its biological potency, ease of handling and support material safety. According to the Gelest Inc. (Morrisville, PA 19067) safety data sheet DMS-A31, ATP in solution causes eye irritation, but in dry from is relatively safe. Our biofouling experiments with four cellulase-active fungal strains, originally isolated from historical books, were conducted directly on impregnated and aged paper at verifying concentrations of ATP and at a relative humidity of 95 %. Fungal biofilm development was quantified using micro-invasive fluorescence microscopy and after incubation non-invasive FTIR spectroscopy was also employed. 3D surface topography scan results showed that ATP impregnation at a concentration of 30 % does not harm the visible structural characteristics of the tested paper and no alterations in surface roughness parameters were observed and is therefore safe for the supporting material. At least a 10 % paper impregnation was needed for an effective suppression of fungal biofilm development and tolerance to lower concentrations was species dependent, with Penicillium canescens ZIM-9717 tolerating 1 % of ATP and Aspergillus niger ZIM-9721 tolerating 1 % and 5 % of ATP. Lastly, we have shown that portable “on the spot” non-invasive FTIR spectroscopy in reflection mode can be effectively used for a rapid but highly sensitive detection and monitoring of mould biofilms on paper support materials. This is important, because sampling and fluorescence dye staining in fluorescence microscopy, will harm the integrity of cultural heritage books and documents. Therefore, non-invasive FTIR spectroscopy can provide for an initial overview or insight into the microbiological condition of library and paper materials.