## 2 Sampling Techniques  
With respect to cultural heritage, conservation science focuses mainly on protection and maintenance of physical or \"tangible\" cultural heritage such as artworks, architecture, monuments, and museum collections. The code of ethics in the conservation of cultural heritage outlines that the conservation-restoration of any given physical or \"tangible\" heritage is to only do the minimum required for preservation [45]. Thus, a detailed diagnostic analysis of the current status of a cultural heritage object by a non-invasive/non-destructive technique is a prerequisite to avoiding unnecessary or potential damage and to keeping the amount of handling to a minimum. Before the advent of the specialized instruments used for conservation studies, visual inspections were the only non-invasive inspection method available in the field of heritage conservation to examine for visual detectable signs of damage, decay, or deterioration. Because of the methodological limitations of visual inspection,the earliest conservation studies could not yield the detailed quantitative information on deterioration processes and mechanisms, and always led to inconclusive results [46; 47]. Microorganisms were not previously considered in this field. Currently, a number of generic or specialized research techniques have begun to be applied to heritage conservation studies to provide the powerful means to analyze the current state of an object for preservation or to detect any products of deterioration and decay that ought to be removed or cleaned. On the collection of samples involved in heritage conservation studies, the dogma which outlines the best practice for conservators and scientists alike for scientific analysis is \"non-invasive and non-destructive method for bio-molecular and chemical analysis that requires very small quantities of sample from inconspicuous locations on artworks and objects\" [48]. As the requirement for sampling techniques has suggested, any analytical techniques to be used must be highly sensitive, requiring minimum amounts of sample or none at all. Because of this, conservation microbiologists need to maintain a close communication with conservators, curators, and heritage authorities and work closely on research projects to determine the most appropriate sampling schemes and the proposed measurements prior to carry out the sampling. A significant proportion of the cultural heritage relics and physical objects that suffer varying levels of biodeterioration caused by microorganisms have been rescued by salvage archaeology effort. Under non-ideal preservation and storage conditions, artifacts that have always been in storage such as archives, books, documents and paintings, and their constituent materials, both organic and inorganic, can provide a suitable surface or substratum for colonization by different types of microorganisms to form biofilm [30; 38; 49; 50]. Microorganisms grow on the surface of artifacts mainly in clusters or aggregates called microbial biofilms, that have the potential to cause adverse reactions chemically or biochemically with cultural heritage objects [30; 31; 36]. A microbial biofilm is a collection of microbial cells and extracellular polymer substances (EPSs) together adhering onto a solid substratum surface (Figure 1). They are ubiquitous and play an important role in ecosystems. Numerous studies have confirmed that biofilms are not simple microbial assemblages, but have well-defined spatial distribution characteristics and microbial community composition and structures to assist in their ecological functions [33; 51]. Spatial microbial distribution has been reported in some environmental biofilms, especially in aquatic ecosystems [52; 53; 54]. Microorganisms communicate via chemical cues prior to and during the biofilm formation. A stratified bacterial structural organization exhibited in biofilms has been reported on the limestone of historical monuments at a Mayan site [55], and on sandstone of Angkor temples with both spatial and temporal dynamics [33; 56].