Biological activity of selected lichens and lichen-based Ag nanoparticles prepared by a green solid-state mechanochemical approach.

Affiliation

Goga M(1), Baláž M(2), Daneu N(3), Elečko J(4), Tkáčiková Ľ(5), Marcinčinová M(6), Bačkor M(6).
Author information:
(1)Department of Botany, Institute of Biology and Ecology, Faculty of Science, Pavol Jozef Šafárik University, Mánesova 23, 04167 Košice, Slovakia; Core Facility Cell Imaging and Ultrastructure Research, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria. Electronic address: [Email]
(2)Department of Mechanochemistry, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Košice, Slovakia.
(3)Advanced Materials Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
(4)Department of Organic Chemistry, Institute of Chemistry, University of Pavol Jozef Šafárik, Košice, Slovakia.
(5)Department of Microbiology and Immunology, University of Veterinary Medicine and Pharmacy, Komenského 73, 041 81 Košice, Slovakia.
(6)Department of Botany, Institute of Biology and Ecology, Faculty of Science, Pavol Jozef Šafárik University, Mánesova 23, 04167 Košice, Slovakia.

Abstract

Lichens dispose a wide spectrum of bioactive compounds known as secondary metabolites. Their biological effects like antioxidant and antibacterial activities are widely studied. Green synthesis of silver nanoparticles (AgNPs) is a method where the compounds/substances present in plants are used for reduction of AgNO3instead of toxic chemicals. However, this methodology is usually a two-step process (extract preparation step and the synthesis step) performed under the elevated temperatures nad in the case of lichens, the redicing compounds are insoluble in water. These disadvantages can be overcome by a solid-state mechanochemical synthesis applied in the present study. As microorganisms are becoming more resistant to commercial antibiotics, AgNPs prepared in an environmentally friendly way represent an interesting alternative. In the present study, we compared the processing of lichen material of Pseudevernia furfuracea and Lobaria pulmonaria for extraction as well as for synthesis of AgNPs, and tested the antibacterial and antioxidant activity of the extracts. Both selected lichen species could be successfully used as reducing agents to produce AgNPs. Six different bacterial strains were tested for antibacterial activity of AgNPs-containing products and it was highly effective on all strains. However, the antioxidant activity of lichen extracts showed the lowest effect even if AgNPs are present which positively correlated with the content of total phenols and flavonoids. Both phenols and flavonoids are natural antioxidants and react with silver nitrate. Due to this fact, we observed a decrease of total phenols, total flavonoids as well as antioxidant activity when processing of lichen extracts with silver nitrate was used. We demonstrated that the formation of AgNPs increased the antibacterial activity but on the other hand reduced the antioxidant activity. Thus, antibacterial and antioxidant effects have to be treated differentially.