Berkeley researchers injected a solution of carbon nanotubes loaded with DNA coding for green fluorescent protein into the leaves of various plant species, from tobacco to cotton, resulting in strong GFP protein expression throughout the leaf without integrating into the plant genome.
She immediately saw how to flip this around to deliver genes into plants. Current methods are cumbersome and can be low-yield. Eager to give it a try, Landry and her colleagues wrapped the gene for green fluorescent protein GFP around a nanotube and injected it into an organic arugula leaf purchased from a local Whole Foods Market.
The effect lasted only a few days, however, probably because the proteins get recycled, and the DNA slowly degrades. When we look in the microscope seven to 10 days later, the expression is gone, the fluorescence is gone. Her plan is to package DNA into a single-stranded plasmid that is then attached to a carbon nanotube.
Within two or three days after diffusing into the cell, both the Cas9 protein and CRISPR guide RNA would be expressed, allowing them to link up to form a ribonucleoprotein complex that edits the genome, permanently. She has not found any toxic effects from the nanotube. Relationships between three components plant, carbon nanomaterial and growth medium as a complex system determining effects of nanomaterial influence of plant development.
Similar to other classes of nanomaterials, uptake into seeds and seedlings [ ], plant growth stimulation [ , ] at low concentrations e. A very detailed investigation of oxidative stress, induced by different concentrations of graphene oxide in faba bean V. Additionally, indirect toxicity of GO has been reported in wheat T. Mechanical damage of the cell wall and plasma membrane caused by the graphene oxide sheets, contributed to increased As uptake, which led to toxicity and further changes in metabolism.
Similarly, mechanical damages of cell wall and other organelles chloroplasts due to GO treatments as well as enhanced formation of ROS have been detected in algal cells [ , ]. Thus, the published data suggest that the main mechanisms of graphene toxicity are based on i mechanical damage of cells and tissues caused by the sharp edges of graphene sheets and ii formation of ROS which in small doses can also induce hormetic effects.
Many authors emphasize that in studies on nanomaterial toxicity, specific methodological considerations should be taken into account. Very often these studies have been criticized for the use of unrealistically high concentrations of the applied carbon-based nanomaterials. By analyzing the available literature on carbon nanomaterial-plant interactions, it can be concluded that the concentration of applied fullerenes, nanotubes, graphene and their derivatives is highly variable, ranging from the lowest applied concentration of 0.
Considering each group of nanomaterials separately, it turns out that fullerenes were tested in a concentration range between 0. The real concentrations of carbon-based nanomaterials in different environmental compartments are yet unknown but modeled release rates of carbon-based nanomaterials into soils for EU are higher for CNTs 1. However, certain management strategies such as sludge soil applications can dramatically increase these values CNTs: These estimates provide important basic information concerning the range of potentially expected inputs, although the long-term behavior and persistence of CNMs in various environmental compartments still remains to be determined.
At least some studies demonstrate the environmental transformations of CNMs including soil sorption and microbial degradation [ , — ] which can finally reduce the real CNM bioavailability. For ecotoxicological studies, it is recommended to use an appropriate range of CNM concentrations with respect to the study objectives.
However, the experimental concentrations of CNMs used to investigate potential consequences of CNM release as environmental contaminations ppb range , in many cases largely exceed the levels arising from model calculations ppt range. On the other hand, in studies aiming at the development of agricultural or biotechnological CNM applications, substantially higher concentrations frequently need to be investigated according to the envisaged product design. Therefore, a clear definition of study objectives is essential to obtain valuable results.
Another important methodological issue is the availability of reliable techniques for CNMs detection in plant tissues. Qualitative methods of CNM detection in plant samples comprise light microscopy, transmission and scanning electron microscopy TEM and SEM able to detect carbon nanotubes, fullerenes and graphene particles in plant samples.
A significantly higher resolution can be obtained using TEM, which has been used for detection of graphene oxide in the tissues of wheat T. Challenges related to TEM comprise low contrast between CNMs and plant tissue structures [ , ], a complicated sample preparation and the need for analysis of large numbers of samples.
Use of fluorescent labels attached to CNTs can significantly improve the feasibility of microscopic techniques [ ]. However, this type of chemical CNT functionalization can also lead to alterations of their physicochemical properties associated with altered effects on plants [ ].
Scanning electron microscopy is another technique to visualize CNMs: it has been used to detect graphene sheets at the root surface of red spinach A. Visualization of CNMs at the surface or inside plant tissues can provide important information on interactions of CNMs with plant cells and cell structures, internalization mechanisms of CNMs, and transport and distribution of CNMs within the plant, with particular importance for the development of vehicle systems.
Alternative technique to identify the presence of carbon nanotubes in plant samples is Raman spectroscopy. In contrast to TEM, this method does not produce false negative results, but it cannot provide detailed information on intracellular CNM location.
Therefore, both techniques are frequently used for complementary analyses. A combination of Raman spectroscopy and TEM was employed for detection of CNTs in tomato Solanum lycopersicum [ ], wheat Triticum aestivum [ ] and red spinach Amaranthus tricolor [ ] seedlings and in tobacco Nicotiana tabacum cell cultures [ ].
A promising novel approach for detection of MWCNTs in plant tissues is based on a combination of photothermal and photoacoustic mapping developed by Khodakovskaya et al.
The method has demonstrated high sensitivity, and the obtained results were confirmed by optical imaging. In another study, infra-red IR spectroscopy was used for detection of fullerols in bitter melon [ ], since fullerols exhibit specific infra-red absorption features. Despite numerous examples of evidence for the uptake of carbon nanomaterials into plant organs, only limited information exists concerning the quantities of CNMs taken up by plants.
However, in the recent past significant progress has been made in the development of techniques for CNMs quantification; fullerene C60 has been quantified in zucchini C. In a study with wheat T. The high discrepancy between the externally applied amount of CNTs and the fraction really taken up by the plants, as well as typical features of carbon nanomaterials, such as agglomeration or sedimentation in suspensions and surface adsorption to solid substrates, which can vary considerably depending on the composition of the incubation media [ ], demonstrate that the simple indication of application concentrations is easy to use but only of little informative value with respect to the real effective dosage.
Moreover, frequently pristine nanomaterials are used in test systems to investigate their interactions with living organisms. This scenario hardly reflects realistic natural conditions, since depending on the composition of the incubation medium, carbon nanomaterials can undergo significant conformational changes e.
To define realistic application conditions, much more information is required concerning the behavior of the various types of nanomaterials in soils and planting substrates. For comparative analyses, the development of standardized test systems would be urgently needed. It has been also recommended to pay more attention to selected controls [ ] by also including positive controls in addition to the commonly used negative controls, as well as other carbon activated carbon and non-carbon contaminants in CNTs controls that will eliminate any possible artifacts.
Nanotechnology develops rapidly and promises innovations in many fields of science and technology. Nanomaterials, including carbon-based nanomaterials, are ready to be produced on a large, industrial scale for a wide range of application fields including the environmental and agricultural sectors.
However, a surprisingly limited body of information exists concerning the real concentrations and behavior of these materials in natural environments and their interactions with living organisms as a prerequisite for safety evaluations.
This is further complicated by the wide range of nanomaterials with different properties and by conformational changes of carbon nanomaterials during interactions with the various constituents of different incubation media e. Apart from these limitations however, at least some principal properties of carbon nanomaterials, relevant for their interactions with plants have been identified:. Most carbon nanomaterials can be taken up by plants.
This is frequently associated also with internal translocation;. Induction of oxidative stress by formation of ROS seems to be a major common mechanism of phytotoxicity induced by carbon nanomaterials, while beneficial effects are probably based on hormesis, which is frequently observed during exposure to toxic agents at sub-toxic levels e.
Chemical functionalization or conformational agglomeration modifications of carbon nanomaterials can significantly influence their toxicity potential;. In many studies of CNM phytotoxicity tested dosages significantly exceed the expected environmental concentrations. As a major challenge for the future, a more comprehensive and systematic survey of the key factors important for interactions of the various carbon nanomaterials with living organisms and the environment will be important for both risk evaluation and the characterization of potential applications.
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Smart microcapsules encapsulating reconfigurable carbon nanotube cores. Adv Funct Mater. Multifunctional and recollectable carbon nanotube ponytails for water purification. Nanocomposites combining semiconductor materials with metal NPs bring additional benefits to plasmonic photocatalysis 6 — 9. The contact potential difference between metal NPs and a semiconductor can separate photogenerated electrons and holes 6 — 9 , thereby reducing electron-hole pair diffusion lengths and leading to more efficient photogenerated charge separation and transfer, which in turn enhances photocatalytic activity 2 — 5.
Here, we show an increase in probability and efficiency of both chemical reactions and SERS detection through electro-optical synergy, using a microfabricated chip design in air rather than electrochemical 2 — 4. This is achieved through the use of a plasmonic-semiconductor system based on aligned diphenylalanine peptide nanotube FF-PNTs wide band gap semiconductors 10 — Diphenylalanine FF , a peptide consisting of a naturally occurring amino acid phenylalanine, can self-assemble into micro and nanosized tubular structures 10 — They can be used in applications requiring the use of a wide bandgap semiconductor 10 — FF-PNTs have been reported to have high thermal and chemical stability 10 — 15 in addition to piezoelectric 16 , 17 and pyroelectric 15 properties.
We show experimentally and theoretically that applying a longitudinal electric field allows the FF-PNT density of states to be tuned from a semiconductor to a metal, enabling effective charge transfer from the nanotube to the metal nanoparticles.
This results in an enhancement in the state density of hot electrons 18 — The effect is optimized through the physical alignment of the FF-PNTs, since the inherent electric dipoles of the FF-PNTs are then aligned and maximally responsive to the applied longitudinal electric field a cooperative effect.
We demonstrate that this optoelectrical device enhances photocatalytic conversion for model oxidation reactions exemplified here by p-aminothiophenol PATP oxidized to p-nitrothiophenol PNTP , and 2-aminophenol 2-AMP oxidized to 2-nitrophenol 2-NIP , exploiting the facile field-activated trans-template charge transfer. We also demonstrate that this same approach can be used to enhance the strength of Raman scattering from molecules with small Raman cross-sections for example glucose and DNA-based molecules, establishing the potential of our template design for sensitive detection and analytics.
This approach is versatile and can be applied to a range of plasmonic metal nanoparticle and semiconductor combinations.
The template comprises microfabricated gold electrodes on an Si substrate, with a 0. Experiments are undertaken in a dry environment not electrochemical. Scanning electron microscopy SEM images Fig. An external electric field is produced by applying a voltage across the electrodes. These results further demonstrate the feasibility of using FF-PNTs in electronic devices, and provide a platform to explore the influence on SERS of an applied electric field.
Substrate fabrication and characterization. The electric field is generated by applying a voltage across the gold nanoelectrodes see Methods. The inset to Fig. We also find that the yield of the oxidized product PNTP increases with an AC voltage applied in addition to the offset bias, allowing to optimize reaction conditions.
Reactant and product can be interconverted by switching on and off the field over many cycles with no apparent degradation , Fig. AC electric field, showing manipulation of the product yield achieved by utilizing an electric field with a voltage of 10 V and an offset DC bias of mV conditions that yield PNTP vs.
Photoexciting the nanotubes directly increases the photocatalytic reaction processes, as well as the SERS signal intensity Supplementary Fig. The resulting SERS spectra show no changes in the band positions with applied external electric field, although intensity fluctuations were observed Supplementary Fig.
Previous studies suggest that an external electric field can additionally enhance the localized electric field produced by Ag NP as the electrons are disturbed from their equilibrium positions, resulting in Raman intensity fluctuations 18 — Another possible reason for the appearance of fluctuations in FF-PNT spectra is that the oscillating electric field may induce synchronous FF-PNT molecular vibrations for high voltage and offset bias that can change their dipole moment 16 , 17 , 29 , Raman control studies of a probe molecules on FF-PNTs in the absence of Ag NPs show a modest increase in signal intensity possibly indicating partial charge redistribution , but no changes in band positions, establishing the need for the LSPRs from the Ag NPs for oxidation reactions.
We also performed extensive tests to establish the high stability of the template. We note that following the addition of the probe molecule, these structural characteristics remain unaltered. These effects where reproducible for different metal nanoparticle sizes. Finally, we explored the effect of NP size Supplementary Fig. Therefore, in the present work we use 60 nm NPs, which produce significant hot-electron yield while retaining good SERS sensitivity.
The plasmonic photocatalytic pathway without an external electric field may result from the formation of hot electrons following the excitation of the Ag NPs LSPR by the Raman excitation laser.
This can result in downshifts in the vibrational modes that are sensitive to this resonance structure. The frequency shifts can be understood as resulting from the strong interaction between the adsorbate molecule and substrate.
Similar behavior of such interaction between PATP and a substrate, as well as the downshifts in the vibrations was previously reported when using TiO 2 with metal NPs 24 — To better understand the mechanism for template-mediated photocatalysis of PATP oxidation, and for optimization of the template for future rational design, we turn now to the theory of NT-NP-molecule charge transport.
Photoexcitation of the Ag NPs produces hot electrons; the wavelength of the incident radiation is tuned so the excitation energy of these hot electrons matches the HOMO—LUMO gap of the attached target molecule, thereby promoting an oxidation reaction. However, this process alone cannot be catalytically sustained without replenishing the lost electrons from the Ag NPs. The choice of substrate for the Ag NPs is therefore critical to the design of an effective template for photocatalysis.
While a metallic substrate is an ideal source for NP charge replacement, the plasmonic properties of the NP would be drastically changed and any hot electrons produced would be quickly lost to the thermal conduction electron reservoir.
An insulating substrate preserves the photoexcitation-oxidation mechanism, but obviously hinders template charge redistribution. In principle, however, semiconductors allow for a separation of time scales for the NP-molecule oxidation reaction, and the substrate-NP charge equilibration.
We argue that the optimal setup involves careful matching of the substrate semiconductor band-gap to the metallic NP band-width. On one hand, we aim to preserve an efficient NP-molecule plasmon-driven oxidation, while on the other hand allowing for a catalytic cycle through subsequent redistribution of charge across the semiconductor and NPs. Low-energy non-excited electrons of the semiconductor substrate transferred to the metallic NPs quickly relax.
In general, a small finite conduction band overlap and weak coupling is required. However, as was shown in Fig. As shown below, this is due to a field-induced coupling of low-energy electrons in the FF-PNT with the Ag NPs, opening a channel for facile charge transport across the template. The in-situ controllability of the product yield using a tunable electric field has obvious practical utility, and also opens the possibility to suppress unwanted side-reactions.
In the following, we develop a theory of charge transport across the template, to substantiate the general principles discussed above. Our philosophy here is not to undertake a realistic simulation of the full system. Even if exact first-principles calculations for such a system was possible, the significant structural and chemical complexity of the FF-PNT alone obfuscates the underlying mechanisms, largely limiting use to a case-by-case basis.
Rather, we seek to develop the simplest possible quantum-mechanical model that encapsulates the vital physics of the constituents, which can then be solved exactly by quantum many-body techniques to understand in detail the key ingredients for template-enhanced plasmonic catalysis.
Figure 4 outlines schematically the justification for our reduced model. FF units Fig. Our reduced model of the FF-PNT e is highly simplified, consisting of a single infinite 1d quantum tight-binding chain with alternating couplings. The NT Hamiltonian in second-quantized notation reads,. Electron interactions 33 are neglected.
The effect of an aligned static electric field is taken into account via a potential gradient in the last term of Eq. The NT model is a semiconductor at zero field, as required, with a spectral gap of 4.
The gapped NT local density of states see Methods is shown in Fig. Figure 5b—d show spectral weight redistribution into the gap when an electric field is applied. Schematic formulation of reduced theoretical model.
Theoretical results obtained from reduced model. No electric field is applied in a ; it is a perfect semiconductor with spectral gap 4. Spectral weight redistribution upon increasing field strength first yields conducting, then insulating, behavior.
Inset: qualitatively similar behavior for a more realistic model of the FF-PNT taking into account the six-fold macrocycle FF unit cell and inter-layer hydrogen bonding. The NPs are large enough to be metallic, but their finite size is a critical feature that must be retained in the model to understand change transfer across it from NT to molecule.
Despite its simplicity, we show below that this quantum model describes the physics controlling the functionality of the template. A high conductance indicates facile charge transport across the template, which is necessary for its catalytic function in oxidation reactions.
We do not simulate the plasmonic physics directly per se, but focus instead on the charge redistribution following photoexcitation, encoded in the conductance. In the following we are interested in temperatures T t. It shows a series of conductance resonances as the field is tuned, indicating that there are specific values of the field strength that strongly enhance catalytic activity of the template. To understand the experimental results in Fig.
Also, note that the experimental SERS intensity results from the combined scattering from target molecules on all NPs. Accounting for this in the theoretical modeling, we assume a NP is coupled to each NT unit cell and calculate the total conductance from the NT to the molecules Methods.
The result is shown in Fig. To confirm this, we also implemented a more realistic model of the FF-PNT, taking into account the stacked layers of six-fold macrocycles Fig. We again emphasize that the reduced quantum model is designed to capture the essential physics of the problem, not to provide quantitative agreement with experiment.
Our theoretical results do demonstrate that spectral weight redistribution in the FF-PNT induced by an applied electric field does activate a facile charge-transport channel across the template, which in turn we argue is responsible for enhanced catalytic function for oxidation reactions of target molecules.
The local heat generated from metal NPs due to LSPR excitation during laser illumination can enhance photocatalytic activity FF-PNTs are known to have piezo and pyroelectric characteristics that can be affected by temperature 10 , 11 , 15 — 17 , Materials provided by American Institute of Physics. Note: Content may be edited for style and length.
Science News. Electrolyte-gated carbon nanotube field-effect transistor-based biosensors: Principles and applications. ScienceDaily, 21 December American Institute of Physics.
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