Graphene-Based and Surface-Enhanced Raman Spectroscopy for Monitoring the Physio-Chemical Response of Thermophilic Bacterial Spores to Low Temperatures Exposure

• Published in: Sensors
• Main Authors: Carlo Camerlingo, Giuseppe Di Meo, Maria Lepore, Mikhail Lisitskiy, Annarita Poli, Marianna Portaccio, Ida Romano, Paola Di Donato
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2020
• Subjects: thermophilic bacteria; spore germination; SERS; graphene-based pH-meter; Chemical technology; TP1-1185; Antarc*; Antarctica
• Online Access: https://doi.org/10.3390/s20154150; https://doaj.org/article/596c84ff1d894e7195eac7f2a0224132

Monitoring the spore life cycle is one of the main issues in several fields including environmental control, sustainable ecosystems, food security, and healthcare systems. In this framework, the study of the living organism resistance to extreme conditions like those mimicking space environments is particularly interesting. The assessment of the local change of the pH level can be extremely useful for this purpose. An optical physiometer method based on the Raman response of the graphene, which is able to locally sense pH of a fluid on a micrometric scale, has been recently proposed. Due to the presence of <math display="inline"> <semantics> <mi>π</mi> </semantics> </math> -bonds at the surface, the electronic doping of graphene is determined by the external conditions and can be electrochemically controlled or altered by the contact with an acid or alkaline fluid. The doping level affects the vibrational energies of the graphene that can be monitored by conventional Raman spectroscopy. In addition, Surface-Enhanced Raman Spectroscopy (SERS) can give direct information on the biochemical changes occurring in spore components. In this work, we propose the joint use of Graphene-Based Raman Spectroscopy (GbRS) and SERS for the monitoring of the response of spores to exposure to low temperatures down to 100 K. The spores of the thermophilic bacterium Parageobacillus thermantarcticus isolated from an active volcano of Antarctica (Mt. Melbourne) were investigated. These spores are particularly resistant to several stressing stimuli and able to adapt to extreme conditions like low temperatures, UV irradiation, and <math display="inline"> <semantics> <mi>γ</mi> </semantics> </math> -rays exposure. The results obtained showed that the joint use of GbRS and SERS represents a valuable tool for monitoring the physio-chemical response of bacterial spores upon exposure to stressing stimuli.