Graphitic nanomaterials such as graphene layers (G) and single-wall carbon nanotubes (SWCNT) are potential candidates in a large number of biomedical applications. However, little is known about the effects of these nanomaterials on biological systems. Here we show that the shape of these materials is directly related to their induced cellular toxicity. Both G and SWCNT induce cytotoxic effects, and these effects are concentration- and shape-dependent. Interestingly, at low concentrations, G induced stronger metabolic activity than SWCNT, a trend that reversed at higher concentrations. Lactate dehydrogenase levels were found to be significantly higher for SWCNT as compared to the G samples. Moreover, reactive oxygen species were generated in a concentration- and time-dependent manner after exposure to G, indicating an oxidative stress mechanism. Furthermore, time-dependent caspase 3 activation after exposure to G (10 microg/mL) shows evidence of apoptosis. Altogether these studies suggest different biological activities of the graphitic nanomaterials, with the shape playing a primary role.

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Carbon nanotubes (CNTs) were found to penetrate tomato seeds and affect their germination and growth rates. The germination was found to be dramatically higher for seeds that germinated on medium containing CNTs (10-40 mug/mL) compared to control. Analytical methods indicated that the CNTs are able to penetrate the thick seed coat and support water uptake inside seeds, a process which can affect seed germination and growth of tomato seedlings.

Understanding the nature of interactions between engineered nanomaterials and plants is crucial in comprehending the impact of nanotechnology on the environment and agriculture with a focus on toxicity concerns, plant disease treatment, and genetic engineering. To date, little progress has been made in studying nanoparticle-plant interactions at single nanoparticle and genetic levels. Here, we introduce an advanced platform integrating genetic, Raman, photothermal, and photoacoustic methods. Using this approach, we discovered that multiwall carbon nanotubes induce previously unknown changes in gene expression in tomato leaves and roots, particularly, up-regulation of the stress-related genes, including those induced by pathogens and the water-channel LeAqp2 gene. A nano-bubble amplified photothermal/photoacoustic imaging, spectroscopy, and burning technique demonstrated the detection of multiwall carbon nanotubes in roots, leaves, and fruits down to the single nanoparticle and cell level. Thus, our integrated platform allows the study of nanoparticles' impact on plants with higher sensitivity and specificity, compared to existing assays. (2) is one of the most intensely studied areas in nanotechnology. Nanoscale materials have been shown to be uptaken by tumor cells (3), bacteria (4), plant cells (5), and animal tissues (6). In particular, carbon nanotubes (CNTs) with their unique structural and dimensional properties have been intensively studied for drug and gene delivery, tissue engineering, and other biomedical applications (7-9). It has also been shown that carbon nanotubes have the ability to penetrate plant cells (5) and induce phytotoxicity at high doses (10). We have demonstrated that single-wall CNTs at relatively low doses can penetrate even thick seed coats, stimulate germination, and activate enhanced growth of tomato plants (11). However, a thorough understanding of the effects induced by the nano-sized engineered materials on plant physiology at the molecular level is still lacking. In addition, the methods used for detecting such nanostructures in plant tissues are not well established and most of them are time consuming and labor intensive. Moreover, existing nanoparticle detection techniques usually decompose and destroy samples to prove the presence of nanomaterials; as a result, the same plant samples cannot be assessed for genomic/proteomic analysis. For example, the detection of magnetic nanoparticles in pumpkin plants by vibrating sample magnetometer requires drying and digestion of tissue samples with HNO 3 (12). Transmission electron microscopy (TEM) has been used to monitor the uptake and transportation of CNTs in rice (13), but it has few quantitative capabilities and may result in false positive interpretation because of considerable similarity in TEM images of CNTs and natural plant structures. Consequently, the analysis has to be combined with spectroscopic studies for the exact identification and assessment of the CNTs in the host plant tissue, and this requires the total destruct...

Carbon nanotubes have shown promise as regulators of seed germination and plant growth. Here, we demonstrate that multiwalled carbon nanotubes (MWCNTs) have the ability to enhance the growth of tobacco cell culture (55-64% increase over control) in a wide range of concentrations (5-500 μg/mL). Activated carbon (AC) stimulated cell growth (16% increase) only at low concentrations (5 μg/mL) while dramatically inhibited the cellular growth at higher concentrations (100-500 μg/mL). We found a correlation between the activation of cells growth exposed to MWCNTs and the upregulation of genes involved in cell division/cell wall formation and water transport. The expression of the tobacco aquaporin (NtPIP1) gene, as well as production of the NtPIP1 protein, significantly increased in cells exposed to MWCNTs compared to control cells or those exposed to AC. The expression of marker genes for cell division (CycB) and cell wall extension (NtLRX1) was also up-regulated in cells exposed to MWCNTs compared to control cells or those exposed to activated carbon only.