Currently, about 400 such compounds and about 350 species of fungi are known to produce them [12; 15]. The intensity of mVOC production is influenced by environmental factors such as fungal species composition, substrate and nutrient availability, and thermo-humidity conditions (air temperature and relative humidity) [16; 17]. It should be noted that the mVOCs produced by fungi can be transformed into other compounds, making their detection much more difficult. For example, alcohols are easily oxidized to aldehydes and then to carboxylic acids, whereas ketones can be transformed into aldehydes through chemical transformations [18], which can contribute to hindering the detection of the presence of mVOCs in the air and thus interfere with the effectiveness of assessing the degree of infestation of buildings by using chemical methods. When assessing the degree of infestation of buildings, it is important to determine the concentration of fungal spores in infested buildings. This concentration is expressed in (CFU (colony-forming units)). Its permissible value in residential buildings is 50 CFU/m\({}^{3}\) for mold fungi and 150 CFU/m\({}^{3}\) for mixed fungi (mold and non-mold)--excluding pathogens. In contrast, according to the PN-EN 13098:2007 standard currently in force in Poland, the permissible number of indoor CFU should be less than 500 CFU/m\({}^{3}\). Fungal colonies of the _Cladosporium_ and _Alternaria_ genera are allowed at 300 CFU/m\({}^{3}\), while the presence of _Aspergillus fumigatus_ and _Stachybotrys chartarum_ is not allowed to any extent [19]. According to [PERSON] and [PERSON] [20], the dominant genera in buildings are _Aspergillus versicolor_, _Penicillium chrysogenum_, and _Cladosporium cladosporoides_. It should be noted that infested buildings can exceed as much as 1000 CFU/m\({}^{3}\), and there have been values as high as 67,000 CFU/m\({}^{3}\) in particularly infested areas [21], reaching up to 260,000 CFU/m\({}^{3}\) in the carpets and bedding of infested rooms [22]. The presence of fungi can be determined using numerous techniques. As a method for the fast detection of fungal presence in buildings, it appears that e-nose devices have a significant application potential. The e-nose was successfully used to find fungi in archives and libraries [23]. E-nose devices may additionally be applied to assess the threat of mold in equipment and buildings. Literature data indicate that an array of 16 MOS (metal oxide semiconductor) sensors used indoors was sufficient to identify and classify five fungi species at a quality level of approximately 96%. Additionally, five mold-emitted microbial volatile compounds (MVOCs) were identified [24]. Two e-noses were used in other studies to detect the presence of fungi: Moses II and Kamina. The former produced more precise results. It was not possible to distinguish between species, despite the application of a sophisticated valuation model. According to [PERSON]'s research [25], using 12 MOS sensors, one of four mold species could be identified with an estimation accuracy of 80-85%, bred under laboratory conditions on the following materials: particleboard, plasterboard, oriented strand board (OSB), and wallpaper. The functional elements of e-noses are the arrays that consist of many various sensors [26; 27; 28]. This hinders signal interpretation that is multidimensional and requires advanced techniques of analysis [29; 30; 31; 32]. The MOS sensor array is made up of thin-film metal oxide semiconductor materials. In the case of the applied sensor array, this is tin dioxide (SnO\({}_{2}\)) [26; 29]. When the sensor is exposed to the sample, specific mVOCs and VOCs present in the air become adsorbed onto the surface of the sensing material [33]. Different gases will have different affinities to the sensor material, leading to varying degrees of adsorption [34]. The presence of adsorbed gases on the surface of the metal oxide semiconductor material causes a change in the electrical resistance of the material [35].