Since the first scanning electron microscope was commercialized in the early 1960s, its applications have ranged from the analysis of biological materials to elemental mapping. For architectural purposes, several different SEM techniques have been used to maintain the quality of building materials.
Early Findings of Water-Damaged Materials
In 1997, an Applied and Environmental Microbiology paper discussed one of the earliest applications of scanning electron microscopic analysis of building materials to detect the presence of water damage and microorganisms. In this study, the researchers utilized light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyze materials taken from water-damaged sites.
In terms of microbiological analysis, seven different samples of indoor building materials were analyzed for the presence of different microbial biomarkers, endotoxin, -D-glucan and stratoxin. Of these samples included gypsum liners that were taken from the interior walls and ceilings of a single building. When examined by SEM, the researchers were able to visualize the unique morphologies associated with hyphae, conidiophores and conidia that were colonizing on the surface of the gypsum liner. Through close examination of these characteristics, the researchers determined the aforementioned microorganism features to be indicative of the Stachybotyrs family; however, further examination by TEM indicated the presence of other bacteria species as well.
It is important to note that, in addition to the microscopic analyses that was performed on these samples, the researchers in this study also utilized several microbiological analysis tools to confirm the identity of these different microorganisms. These techniques included genomic DNA extraction, polymerase chain reaction (PCR)-mediated amplification of the DNA extractions and purification of PCR products. Cytotoxicity assays were also performed to assess the toxicity of these microorganisms to the sampled indoor building materials.
Preserving Built Cultural Heritage
More recently, researchers have utilized various scanning microscopy techniques to protect the cultural heritage associated with different historical structures. Of these scanning microscopy techniques that is most commonly used for this purpose includes SEM coupled with energy-dispersive X-ray spectroscopy (EDX), as well as TEM and atomic force microscopy (AFM).
SEM-EDX allows users to investigate the precise chemical, morphological and microstructural composition that comprises the microstructure of a material’s surface. For example, SEM-EDX has already been successful in assessing the environmental impact experienced by historical buildings as a result of pollution, salt crystallization and biological deterioration.
As compared to standard SEM, SEM-EDX can achieve a nanoscale resolution, which thereby provides researchers with a heightened precision level when gathering details on a building materials’ components. Some of the other advantages associated with the use of SEM-EDX for building material analysis include:
- Nondestructive treatment of specimens
- Little sample preparation required
- Easily adjusted magnification
- Qualitative and quantitative analysis
When applied for the analysis of cultural heritage building materials, TEM is useful in providing precise morphological information, as well as details on the material’s chemical composition when TEM is coupled with EDX. In fact, TEM has proven to be particularly useful when researchers are interested in evaluating the nanostructures present in historical building materials. Researchers in this area will also commonly utilize TEM while developing novel nanomaterials that will be used to preserve historical structures.
AFM has also emerged as a useful scanning microscopy technique for this purpose; however, its use is often limited in cultural heritage samples as a result of the rough surfaces typically associated with these types of building materials.
References and Further Reading
- Bacteria, Molds, and Toxins in Water-Damaged Building Materials - Andersson, M. A., Nikulin, M., Koljalg, U., Andersson, M. C., Rainey, F., Reijula, K., et al. (1997). Applied and Environmental Microbiology; 387-393.
- Scanning Microscopy Techniques as an Assessment Tool of Materials and Interventions for the Protection of Built Cultural Heritage - Moropoulou, A., Zendri, E., Ortiz, P., Delegou, E. T., Ntoutsi, I., Balliana, E., et al. (2019). Scanning. DOI: 10.1155/2019/5376214.