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Fig. 1 | Journal of Nanobiotechnology

Fig. 1

From: Non-invasive continuous monitoring of pro-oxidant effects of engineered nanoparticles on aquatic microorganisms

Fig. 1

Reprinted with permission from (Nanotoxicology 2014; 8: 605–630). Copyright (2014)

Mechanisms of ROS generation by engineered nanomaterials via intracellular chemical reactivity (left hand side) or via physical interactions with subcellular compartments (right hand side). ENPs generate ROS by direct and indirect chemical reactions. Direct reactions involve the photoexcitation of O2, which yields singlet oxygen (1O2) and superoxide (O ·−2 ). Indirect chemical reactions involve reactions between leached ENP constituents (e.g. metal ions, organic compounds) that engage in redox cycling that yields superoxide (O ·−2 ) and hydrogen peroxide (H2O2) or in hydroxyl radical (OH·) producing Fenton and Haber–Weiss reactions. ROS yielding interactions encompass the interference with electron transfer chains in chloroplasts, peroxisomes, mitochondria and the endoplasmatic reticulum. Furthermore, interactions of ENPs and mitochondria or the endoplasmatic reticulum can also cause a loss of organelle membrane integrity that triggers the release of Ca2+ ions from interior stores, which may activate ROS generating Ca2+/calmodulin-dependent enzymes, i.e. certain nitrogen monoxide synthase isoforms that produce NO·. Interactions with NADPH oxidase (NOX) complexes in the cell membrane yield O ·−2 [29]. Illustration adapted from Unfried, Albrecht [29], not to proportion.

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