Spectroscopic analysis of mushrooms by surface-enhanced Raman scattering (SERS)

Abstract

Background Mushrooms have always been considered an important source of food and biologically active compounds with several medicinal properties. In recent years, different methods were used to study the quality and chemical composition of mushrooms. Among these, Fourier transform infrared (FT-IR) and FT-Raman spectroscopy techniques have been successfully applied to identify different mushroom species. However, the structural biomolecule components existing in the mycelium or in the fruiting bodies may produce strong fluorescence emission that overlaps the Raman radiation, thus avoiding their analyses by Raman. SERS spectroscopy is a powerful technique which uses metal nanoparticles (NPs) to enhance the Raman signal of molecules adsorbed on the NPs surface. In addition, SERS is able to quench the macromolecule florescence. In this work, we have employed silver nanoparticles in order to get mushroom fingerprints based on SERS as quick procedure to analyze and identify different chemical compounds from the fruiting bodies of six edible and/or medicinal mushrooms: Lentinula edodes, Ganoderma lucidum, Pleurotus cornucopiae, Pleurotus ostreatus, Tuber aestivum and Tuber magnatum. Results SERS analyses performed directly on fruiting body fragments produced characteristic spectra for each species. One group of mushrooms (L. edodes, G. lucidum, T. aestivum and T. magnatum) was dominated by the bands of nucleic acids; and the other one (P. cornucopiae and P. ostreatus), by the bands of pigments such as melanins; carotenoids; azafilones; polyketides; and flavonoids located in the cell wall. Additionally, bands corresponding to cell wall polysaccharides, particularly chitosan and 1,3-β D-glucan, were identified in the extracts of P. cornucopiae, P. ostreatus and L. edodes. No signal of cell wall polysaccharides was found in G. lucidum extract. Raman mapping of the analyzed samples was useful in tracking the spatial distribution of the marker bands. Moreover, the principal component analysis (PCA) carried out on the acquired SERS spectra, allows to discriminate the analyzed mushroom species. Conclusions The SERS technique has the ability to generate a strong Raman signal from mushroom fruiting bodies using Ag-NPs deposited directly on intact, untreated mushroom tissues. Using this methodology, commonly applied laboratory time-consuming methods can be avoided or bypassed as well as analysis time can be reduced. Graphical Abstract

Sustainable Management of Anaerobic Digestate: From Biogas Plant to Full-Scale Cultivation of Pleurotus ostreatus

“…This compound was ubiquitously found in plants and animals, and it is specifically very abundant in P. ostreatus [66]. This amino acid molecule was also detected in a previous work made by us on different mushrooms and displayed a high SERS activity, as also revealed by the Raman study in an analysis done on biological materials [30,67,68]. The characteristic band at 486 cm −1 can serve to identify it from other biomolecules that may occur in the same biological matrix.…”

“…Actually, these methods have been successfully proven for the study of organic material as well as for biological tissues [26][27][28]. Specifically, SERS is a highly sensitive vibrational technique that, thanks to the use of nanostructured metals (Au and Ag), permits a better and more rapid detection of trace amounts of molecules, including some typical fungal compounds, as previously reported by Fornasaro et al (2021) and Puliga et al (2022) [29][30][31][32]. The efficiency of SERS is based on the interaction between the incident light and the metal nanostructures resulting in the so-called localized surface plasmon resonance effect.…”

“…An interesting method that can be used to better understand the molecular structure of the fruiting bodies is SERS spectroscopy. This technique allows better intercept of some vibrational signals, thus enhancing the identification of chemical compounds [30]. The resulting SERS spectra are dominated by the bands attributed to the amino acid ergothioneine [29].…”

“…The extraction of polysaccharides from the fruiting bodies was carried out as described by Puliga et al (2022) [30]. Briefly, the powder was immersed in an 85% ethanol solution and treated overnight.…”

“…The wet portions were next deposited on a microscope slide glass and coated with 5 µL of a concentrated Ag-NPs suspension. This last was previously obtained by centrifugation of 500 µL and successive redispersion to 10% of the initial volume, as described by Puliga et al (2022) [30]. Prior to SERS analyses, the resulting samples were dried at room temperature.…”