Surface enhanced Raman spectroscopy and cultural heritage biodeterioration: Fungi identification in earthen architecture from Paraíba Valley (São Paulo, Brazil)

In this work, Surface Enhanced Raman Spectroscopy (SERS) was employed in the taxonomic identification of fungi found in biofilms formed on earthen architecture walls (adobe, wattle and daub, and rammed earth) of historical buildings in the region known as Paraíba Valley (or São Paulo Historical Valley), which are representative of the first phase of the Brazilian coffee cycle (1820-1880). Very few studies are reported in the literature where SERS-based techniques are used in fungi identification, most of them focused on clinical diagnosis. In the present investigation, pure colonies isolated from biofilms on earthen walls previously identified by classic taxonomy and molecular biology were selected. The genera were Trichoderma, Cladosporium, Aspergillus, Neurospora, Fusarium and Penicillium. The fungi were cultured on solid potato dextrose agar, extracted with ethyl acetate and the extracts were applied on dried Au nanoparticles. The SERS spectra exhibited bands in the 600-1800 cm−1 region which are characteristic of each genus, except Penicillium, as revealed by PCA statistical analysis. This work reports the use of a facile to prepare SERS-active substrate in the identification of microbial communities on earthen architecture walls and is the first step of an investigation aiming at the fast identification of fungi species from biofilms formed on earthen architecture buildings without the need of isolating the pure cultures.