Nanobiophotonics: Effect of carbon nanoparticles on the optical and spectroscopic properties of Cichorium intybus leaves

Abstract

The effect of different types of nanoparticles on plants has been of great interest in recent years. Within this general context, the specific purpose of the present work was to study the interaction between carbon nanoparticles and the photosynthetic electron chain, to determine whether they induced a beneficial or toxic effect on the primary steps of photosynthesis. Two types of nanoparticles were synthesized and physicochemically characterized: nanocarbon black (nano-CB) and graphene quantum dots (GQD). They were sprayed over Cichorium intybus leaves and their effect on the photosynthetic chain was studied using chlorophyll-a fluorescence analysis. Nano-CB was prepared by an acid exfoliation method from commercial carbon black, whereas GQD were obtained by pyrolysis of L-glutamic acid. The nanoparticulate systems displayed luminescent properties and the fluorescence quantum yield for GQD resulted about six times higher than the value for nano-CB. Both kind of nanoparticles presented similar effects on the plant leaves, but the action of GQD was more pronounced. They induced an evident decrease in the content of photosynthetic pigments, a reduced xanthophyll cycle and a lower ability to dissipate excess energy by non-photochemical quenching. Changes in the concentration ratios Chlorophyll a/b and Chlorophylls/Carotenoids were similar to those previously found for shaded leaves but could not be assigned to shading effects in this case. The results of this work suggested a particular deleterious action on the performance of photosystem I (PSI). The phytotoxicity of the tested carbon nanoparticles on Cichorium intybus, at the level of the primary photosynthesis stages was, thus, demonstrated.