Effect of galvanotaxic graphene oxide on chloroplast activity: Interaction quantified with Biolayer-Interferometry coupled confocal microscopy Sandeep Sharma a , Bandana Sahu a , Subramanian Srinivasan b , Manish Singh a , Jayamurugan Govindasamy a , Vijayakumar Shanmugam a, * a Institute of Nano Science and Technology, Habitat Centre, Phase- 10, Sector- 64, Mohali, Punjab,160062, India b Department of NMR, Indian Institute of Technology Madras, Chennai, 600036, India article info Article history: Received 16 November 2019 Received in revised form 2 February 2020 Accepted 17 February 2020 Available online 18 February 2020 abstract The knowledge on the effect of graphene oxide (GO) on plants are limited to germination, growth, and toxicity. Since, chloroplast generates sugar by the reduction of CO 2 with the optical stimulation through a series of electron transport chain and GO being the 2D material with electron transport property, it is reasonable to check their interaction. Here, the effect of GO without and with amine conjugation (AGO) having opposite charges were allowed to interact with chloroplast. The uptake is documented by using biolayer interferometry coupled with confocal imaging. The ex vivo chloroplast activity with GO and AGO has been tested and found that the GO treatment shows 1.3 times more activity than control. In contrast, AGO function as efficient electron conductor and cause imbalance in the redox beyond the capacity of the antioxidant rich chloroplast solute. Finally, in vivo toxicity has been evaluated in the spinach plants, which highlights the chance of AGO application as herbicide to remove any unwanted plants. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Carbon-based materials, have shown potential applications in the diverse fields like energy [1], transparent electronics [2], catalysis [3], water treatment [4], sensing [5], drug delivery [6], externally triggered delivery [7], multidrug carrier [8], gene de- livery [9], cell imaging [10], tissue engineering [11], bactericidal [12], pesticide application [13], and fruit preservation [14]. Various properties of carbon nanomaterial’s like high surface area, electron transport [15], defects [16], and surface reactivity raised the con- cerns in the environment [17 , 18]. In this regards, the effect of carbon nanotubes on plant health has been studied [19,20]. Multi-walled (MWCNT) and single-wall carbon nanotubes (SWCNT) were found to increase the photosynthesis rate in chloroplast by sup- plementing the electrons transfer [21]. As the redox biomolecules in the chloroplast cater only <15% capacity of the photosynthetic apparatus [22]. In case of GO-a 2D material which lacks curvature, behaves differently with the ions, molecules and biomacromolecules [23]. The GO has shown beneficial effects in wheat [24], tomato [25], maize [26] and faba bean [27]; also, GO was found to increase the plant health under abiotic stress like salinity stress [28]. Further, GO was found to activate the hydration of seeds, and lead to the increase in physiological response [24,27]. To the best of our knowledge, the interaction of GO with chloroplast has not been reported, which is the primary activity centre for plant photosynthesis. Nanoparticles (NPs) interactions with biological entities, cellular uptake, and their toxicity need to be considered [29]. The chloroplast have high antioxidant content viz., ascorbic acid and glutathione compared to other plant organelles [30], which makes more relevance in the toxicity point to test GO’s interaction. In nanoscale, properties like size, charge, polarity, and surface functionalities are the key determinant of biological interaction. It was found that carboxylated MWCNT significantly increased the biomass in tomato as compared to unfunctionalized MWCNT [31]. On the other hand, the amino groups on GO surface was reported to increase its affinity to the bacterial cell wall [32,33]. This curiosity to understand the effect of GO based 2D materials on chloroplast, motivated us to synthesize and compare the effect of negatively charged GO and positively charged amine functionalized * Corresponding author. E-mail addresses: psvijayakumar@inst.ac.in, vijayakumarshanmugham@gmail. com (V. Shanmugam). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon https://doi.org/10.1016/j.carbon.2020.02.054 0008-6223/© 2020 Elsevier Ltd. All rights reserved. Carbon 162 (2020) 147e156