Carbon dots as light converter for plant photosynthesis: Augmenting light coverage and quantum yield effect

Unlocking the potential of carbon dots in agriculture using data-driven approaches

The utilization of carbon dots (CDs) in agriculture to enhance plant growth has gained significant attention, but the data remains fractionated. Systematically integrating existing data is needed to identify the factors driving the interactions between CDs and plants and strategically guide future research. Articles reporting on CDs and their effects on plants were searched based on inclusion and exclusion criteria, resulting in the collection of 71 articles comprising a total of 2564 data points. The meta-analysis reveals that the soil and foliar application of red-emitting bio-derived CDs at a low concentration (<10 ppm) leads to the most beneficial effects on plant growth. Random forest and gradient boosting algorithms revealed that the size and dose of CDs were important factors in predicting plant responses across multiple aspects (CDs properties, plant properties, environmental factors, and experimental conditions). Specifically, smaller sizes are more favorable to growth indicators (GI) below 6 nm, nutrient and quality (NuQ) at 3-6 nm, photosynthesis (PSN) below 7 nm, and antioxidant responses (AR) below 5 nm. Overall, our analysis of existing data suggests that CDs applications can significantly improve plant responses (GI, NuQ, PSN, and AR) by 10-39 %. To unlock the full potential of CDs, customized synthesis techniques should be employed to meet the specific requirements of different crops and climate condition. For example, we recommend the synthesis of small CDs (<7 nm) with emission peak values falling within the range of 405-475 and 610-670 nm to enhance plant growth. The global prediction of plant responses to CDs application in future scenarios have shown significant improvements ranging from 17 to 58 %, suggesting that CDs have widespread applicability. This novel understanding of the impact of CDs on plant response provides valuable insights for optimizing the application of these nanomaterials in agriculture.

Single-Step Low-Temperature Synthesis of Carbon Dots for Advanced Multiparametric Bioimaging Probe Applications

Carbon dots (CDs) have recently emerged in biomedical and agricultural domains, mainly for their probe applications in developing efficient sensors. However, the existing high-temperature approaches limit the industrial level scaling up to further translate them into different products by mass-scale fabrication of CDs. To address this, we have attempted to lower the synthesis temperature to 140 °C and synthesized different CDs using different organic acids and their combinations in a one-step approach (quantum yield 3.6% to 16.5%; average size 3 to 5 nm). Further, sensing applications of CDs have been explored in three different biological models, mainly Danio rerio (zebrafish) embryos, bacterial strains, and the Lactuca sativa (lettuce) plant. The 72 h exposure of D. rerio embryos to 0.5 and 1 mg/mL concentrations of CDs exhibited significant uptake without mortality, a 100% hatching rate, and nonsignificant alterations in heart rate. Bacterial bioimaging experiments revealed CD compatibility with Gram-positive (Bacillus subtilis) and Gram-negative (Serratia marcescens) strains without bactericidal effects. Furthermore, CDs demonstrated effective conduction and fluorescence within the vascular system of lettuce plants, indicating their potential as in vivo probes for plant tissues. The single-step low-temperature CD synthesis approach with efficient structural and optical properties enables the process as industrially viable to up-scale the technology readiness level. The bioimaging of CDs in different biological models indicates the possibility of developing a CD probe for diverse biosensing roles in diseases, metabolism, microbial contamination sensing, and more.

Non-toxic orange carbon dots stimulate photosynthesis and CO2 assimilation in hydroponically cultivated green beans (Phaseolus vulgaris)

Continuous increasing leaf photosynthesis may enhance plant yield. As an evolutionary property, plants use less photosynthetic capacity than is theoretically possible. Plant nanobionics is a bioengineering field that improves plant functions using nanoparticles. We applied orange carbon dots (o-CDs) onto the foliage of green beans (Phaseolus vulgaris ) grown in hydroponics to improve their photosynthetic performance and CO2 assimilation. Photosynthesis parameters, photosynthetic pigments content, total phenolic content (TPC) and antioxidative activity (TAA) were measured. Results show that photosynthetic pigments remained unchanged, while photosynthesis was improved. Both o-CDs concentrations decreased TPC and TAA. The light response curve showed higher CO2 assimilation at both o-CDs concentrations, particularly at lower light intensity. Correlation analysis confirmed increased CO2 binding and assimilation at 1mg L-1 . This study demonstrated the potential of using o-CDs as a safe biostimulator through photosynthesis increase and CO2 assimilation without toxic effects on plants. This may stimulate yield increase that paves the way for their agricultural application.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Enhanced photosynthetic efficiency by nitrogen-doped carbon dots via plastoquinone-involved electron transfer in apple

Artificially enhancing photosynthesis is critical for improving crop yields and fruit qualities. Nanomaterials have demonstrated great potential to enhance photosynthetic efficiency; however, the mechanisms underlying their effects are poorly understood. This study revealed that the electron transfer pathway participated in nitrogen-doped carbon dots (N-CDs)-induced photosynthetic efficiency enhancement (24.29%), resulting in the improvements of apple fruit qualities (soluble sugar content: 11.43%) in the orchard. We also found that N-CDs alleviated mterf5 mutant-modulated photosystem II (PSII) defects, but not psa3 mutant-modulated photosystem I (PSI) defects, suggesting that the N-CDs-targeting sites were located between PSII and PSI. Measurements of chlorophyll fluorescence parameters suggested that plastoquinone (PQ), the mobile electron carrier in the photosynthesis electron transfer chain (PETC), was the photosynthesis component that N-CDs targeted. In vitro experiments demonstrated that plastoquinone-9 (PQ-9) could accept electrons from light-excited N-CDs to produce the reduced plastoquinone 9 (PQH2-9). These findings suggested that N-CDs, as electron donors, offer a PQ-9-involved complement of PETC to improve photosynthesis and thereby fruit quality. Our study uncovered a mechanism by which nanomaterials enhanced plant photosynthesis and provided some insights that will be useful in the design of efficient nanomaterials for agricultural/horticultural applications.

Transfer, transportation, and adsorption of UV-B by Mg-N co doped carbon quantum dots: Response of growth indicators, antioxidant effect and mechanism explanation

Mg and N co-doped carbon quantum dots (Mg-N-CQDs) were synthesized and applied to alleviate oxygen toxicity by UV-B radiation and enhance antioxidative responses to wheat seedlings. It showed that Mg-N-CQDs pre-treatment attenuated the UV-B stress effects in a dose-dependent manner, as indicated by enhancing the characteristics of seed germination and early seedling growth parameters. Meanwhile, Mg-N-CQDs can be applied in plant nutrient solutions with nitrogen, phosphorus, potassium, and other fertilizers to promote the growth of seedlings. Furthermore, efficient antioxidant systems, chlorophyll content, and stability of fluorescence intensity were activated by Mg-N-CQDs pre-treatment, which effectively increased the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and eliminate the contents of malondialdehyde (MDA) and hydrogen peroxide, and the production rate of superoxide anion radical in the roots and germs, thereby preventing oxidative damage from UV-B stress. Notably, Mg-N-CQDs pre-treatment significantly increased the expression of related genes to improve the antioxidant capacity of roots and germs, resulting in an increased level of ATPS, CS, and GS. The mechanism study indicated that amino and hydroxyl groups and Mg, N modified CQDs could broaden the light absorption range of CQDs and improve the ability to convert blue light and ultraviolet rays to visible light, which was the main reason why Mg-N-CQDs could relieve wheat seedlings from ultraviolet stress. Therefore, Mg-N-CQDs could serve as a regulator to reduce the damage of UV-B, laying the foundation for their application in environmental protection and agricultural production.

Next generation chemical priming: with a little help from our nanocarrier friends

Plants are exposed to multiple threats linked to climate change which can cause critical yield losses. Therefore, designing novel crop management tools is crucial. Chemical priming has recently emerged as an effective technology for improving tolerance to stress factors. Several compounds such as phytohormones, reactive species, and synthetic chimeras have been identified as promising priming agents. Following remarkable developments in nanotechnology, several unique nanocarriers (NCs) have been engineered that can act as smart delivery systems. These provide an eco-friendly, next-generation method for chemical priming, leading to increased efficiency and reduced overall chemical usage. We review novel engineered NCs (NENCs) as vehicles for chemical agents in advanced priming strategies, and address challenges and opportunities to be met towards achieving sustainable agriculture.

Structural Features of Carbon Dots and Their Agricultural Potential

Carbon dots (CDs) have drawn attention due to their enticing physical, chemical, and surface properties. Besides, good conductivity, low toxicity, environmental friendliness, simple synthetic routes, and comparable optical properties are advantageous features of CDs. Further, recently, CDs have been explored for biological systems, including plants. Among biological systems, only plants form the basis for sustainability and life on Earth. In this Review, we reviewed suitable properties and applications of CDs, such as promoting the growth of agricultural plants, disease resistance, stress tolerance, and target transportation. Summing up the available studies, we believe that the applications of CDs are yet to be explored significantly for innovation and technology-based agriculture.

Application of Nanomaterials in the Production of Biomolecules in Microalgae: A Review

Nanomaterials (NMs) are becoming more commonly used in microalgal biotechnology to empower the production of algal biomass and valuable metabolites, such as lipids, proteins, and exopolysaccharides. It provides an effective and promising supplement to the existing algal biotechnology. In this review, the potential for NMs to enhance microalgal growth by improving photosynthetic utilization efficiency and removing reactive oxygen species is first summarized. Then, their positive roles in accumulation, bioactivity modification, and extraction of valuable microalgal metabolites are presented. After the application of NMs in microalgae cultivation, the extracted metabolites, particularly exopolysaccharides, contain trace amounts of NM residues, and thus, the impact of these residues on the functional properties of the metabolites is also evaluated. Finally, the methods for removing NM residues from the extracted metabolites are summarized. This review provides insights into the application of nanotechnology for sustainable production of valuable metabolites in microalgae and will contribute useful information for ongoing and future practice.

Machine-learning analysis to predict the fluorescence quantum yield of carbon quantum dots in biochar

Biochar nanoparticles have recently attracted attention, owing to their environmental behavior and ecological effects. However, biochar has not been shown to contain carbon quantum dots (< 10 nm) with unique photovoltaic properties. Therefore, this study utilized several characterization techniques to demonstrate the generation of carbon quantum dots in biochar produced from 10 types of farm waste. The generated carbon quantum dots had a quasi-spherical morphology and high-resolution lattice stripes with lattice spacings of 0.20-0.23 nm. Moreover, they contained functional groups with good hydrophilic properties, such as amino and hydroxyl groups, and elemental O, C, and N on the surface. A crucial determinant of the photoluminescence properties of carbon quantum dots is their fluorescence quantum yield. Therefore, the relationship between the biochar preparation parameters and the fluorescence quantum yield was investigated using six machine learning analytical models based on 480 samples. Among the models, the gradient-boosting decision-tree regression model exhibited the best predictive performance (R2 > 0.9, RMSE <0.02, and MAPE <3), and was used for the analysis of feature importance; compared to the properties of the raw material, the production parameters had a greater effect on the fluorescence quantum yield. Additionally, four key features were identified: pyrolysis temperature, residence time, N content, and C/N ratio, which were independent of farm waste type. These features can be used to accurately predict the fluorescence quantum yield of carbon quantum dots in biochar. The relative error range between the predicted and the experimental value of fluorescence quantum yield is 0.00-4.60 %. Thus, the prediction model has the potential to predict the fluorescence quantum yield of carbon quantum dots in other types of farm waste biochar, and provides fundamental information for the study of biochar nanoparticles.

Boosting Plant Photosynthesis with Carbon Dots: A Critical Review of Performance and Prospects

Artificially augmented photosynthesis in nano-bionic plants requires tunable nano-antenna structures with physiochemical and optoelectronic properties, as well as unique light conversion capabilities. The use of nanomaterials to promote light capture across photosystems, primarily by carbon dots, has shown promising results in enhancing photosynthesis through tunable uptake, translocation, and biocompatibility. Carbon dots possess the ability to perform both down and up-light conversions, making them effective light promoters for harnessing solar energy beyond visible light wavelengths.This review presents and discusses the recent progress in fabrication, chemistry, and morphology, as well as other properties such as photoluminescence and energy conversion efficiency of nano-antennas based on carbon dots. The performance of artificially boosted photosynthesis is discussed and then correlated with the conversion properties of carbon dots and how they are applied to plant models. The challenges related to the nanomaterial delivery and the performance evaluation practices in modified photosystems, consideration of the reliability of this approach, and the potential avenues for performance improvements through other types of nano-antennas based on alternative nanomaterials are also critically evaluated. It is anticipated that this review will stimulate more high-quality research in plant nano-bionics and provide avenues to enhance photosynthesis for future agricultural applications.

Physiological Functions of Carbon Dots and Their Applications in Agriculture: A Review

Carbon dots are carbon-based nanoparticles, which have the characteristics of a simple preparation process, photoluminescence, biocompatibility, an adjustable surface function, water solubility, and low-level toxicity. They are widely used in biological applications, such as imaging, biosensing, photocatalysis, and molecular transfer. They have also aroused great interest among researchers in agriculture, and there has been significant progress in improving crop growth and production. This review presents the physiological functions of carbon dots for crop growth and development, photosynthesis, water and nutrient absorption, and abiotic stress resistance and their applications in improving the ecological environment and agriculture as biosensors, and future application prospects and research directions of carbon dots in agriculture.

Preparation of N-doped carbon dots and application to enhanced photosynthesis

Regulation of photosynthesis rates is one of the key ways to increase crop yields. Carbon dots (CDs), which are low-toxity and biocompatible optical nanomaterials, can be easily prepared and are ideal for improving photosynthesis efficiency. In this study, nitrogen-doped CDs (CNDs) with a fluorescent quantum yield of 0.36 were synthesized via a one-step hydrothermal method. These CNDs can convert a part of ultraviolet light in solar energy to blue light (emission peak at 410 nm) that can be utilized in photosynthesis and that overlaps with the optical absorption spectrum of chloroplasts in the blue light zone. Consequently, chloroplasts can pick up photons excited by the CNDs and transfer them to the photosynthetic system in the form of electrons, thereby accelerating the photoelectron transport rate. These behaviors can reduce ultraviolet light stress on wheat seedlings and improve the efficiency of electron capture and transfer from chloroplasts through optical energy conversion. As a result, various photosynthetic indices and biomass of wheat seedlings are improved. Cytotoxicity experiments have showed that CNDs within a certain concentration range almost do not affect cell survival.

Optical Properties of Carbon Dots Synthesized by the Hydrothermal Method

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200-300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420-565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups.

Nitrogen-doped carbon dots enhanced seedling growth and salt tolerance with distinct requirements of excitation light

Numerous nanomaterials with optical properties have demonstrated excellent capacities to enhance plant growth and stress tolerance. However, the corresponding mechanisms have only been partially characterized, especially the excitation-light dependencies of different actions. Here, nitrogen-doped carbon dots (N-CDs) were developed to explore the excitation-light dependence in N-CD-induced growth enhancement and salt tolerance. Compared to the control, N-CDs induced significant enhancements in Arabidopsis thaliana growth under excitation light, including fresh/dry weight of shoot (21.07% and 16.87%), chlorophyll content (9.17%), soluble sugar content (23.41%), leaf area (28.68%), total root length (34.07%) and root tip number (46.69%). In the absence of excitation light, N-CD-treated seedlings exhibited little differences in these parameters, except the enhancements in root length (24.51%) and root tip number (10.24%). On the other hand, N-CD-treatment could improve seedling salt tolerance with or without excitation light. Under salt stress (150 mM NaCl), in the presence of excitation light, the N-CDs treatment significantly increased shoot/root fresh weight and chlorophyll content by 43.29%, 50.66% and 22.59%, and reduced malondialdehyde (MDA) content and relative conductivity by 17.59% and 32.58% compared to the control group. In the absence of excitation light, significant enhancements in shoot/root fresh weight (34.22%, 32.60%) and chlorophyll content (10.45%), and obvious decreases in MDA content (28.84%) and relative conductivity (16.13%) were also found. These results indicated that N-CDs only induced growth enhancement under excitation light, but they improved salt tolerance with and without excitation light, suggesting that the two effects occurred via distinct signaling pathways. This study revealed the excitation-light dependencies of nanomaterial-involved agriculture applications, providing insight into designing more efficient nanomaterials in the future.

Sensibility, multiple tolerance and degradation capacity of forest species to sequential contamination of herbicides in groundwaters

Herbicides have already reported environmental contamination in several countries with intense agricultural activity. The transport of these molecules due to leaching and surface runoff has frequently caused contamination of rivers, groundwater and soil in non-agricultural areas. Thereby, we propose to investigate the sensitivity and phytoremediation capacity of 5 native Cerrado species to sequential exposure to 2,4-D, atrazine, diuron and hexazinone. We hypothesized that species have different sensitivity levels to sequential exposure to these herbicides absorbed from contaminated simulated groundwater model. The objectives of this work were: i) to determine the sensitivity of native cerrado species by sequential exposure to 2,4-D, atrazine, diuron and hexazinone via contaminated simulated groundwater model; ii) to evaluate the presence and degradation capacity of these herbicides in the soil and water leached by tolerant species. Some species showed high phytoremediation potential for groundwater already contaminated with 2,4-D, atrazine, diuron and hexazinone. S. macranthera and C. antiphilitica are tolerant and reduce the concentration of herbicides in simulated groundwater model. Among these species, C. antiphilitica reduces the concentration of all herbicides, suggesting greater adaptability to compose decontamination strategies in areas close to agricultural systems that use 2,4-D herbicides, atrazine, diuron and hexazinone. Also, our results show that herbicides can act as a selection factor for Cerrado forest species, however, two species can mitigate the effects of contamination due to their ability to degrade herbicides.

Pyridinic Nitrogen Doped Carbon Dots Supply Electrons to Improve Photosynthesis and Extracellular Electron Transfer of Chlorella pyrenoidosa

Optimizing photosynthesis is imperative for providing energy and organics for all life on the earth. Here, carbon dots doped with pyridinic nitrogen (named lev-CDs) are synthesized by the one-pot hydrothermal method, and the structure-function relationship between functional groups on lev-CDs and photosynthesis of Chlorella pyrenoidosa (C. pyrenoidosa) is proposed. Pyridinic nitrogen plays a key role in the positive effect on photosynthesis caused by lev-CDs. In detail, lev-CDs act as electron donors to supply photo-induced electrons to P680⁺ and QA⁺ , causing electron transfer from lev-CDs to the photosynthetic electron transport chain in the photosystems. In return, the recombination efficiency of electron-hole pairs on lev-CDs decreases. As a result, the electron transfer rate in the electron transport chain, the activity of photosystem II, and the Calvin cycle are enhanced. Moreover, the electron transfer rate between C. pyrenoidosa and external circumstances enhanced by lev-CDs is about 50%, and electrons exported from C. pyrenoidosa can be used to reduce iron(III). This study is of great significance for engineering nanomaterials to improve photosynthesis.

Effects of plastic-derived carbon dots on germination and growth of pea (Pisum sativum) via seed nano-priming

Seed nano-priming is a promising technology employed in the agronomic field to promote seed germination and plant growth. However, the effects of carbon dots (CDs) on plant development via seed nano-priming remain unclear. In the present study, CDs synthesized from non-biodegradable plastic wastes were adopted as a nano-priming agent for pea (Pisum sativum) seed treatment. The results demonstrated positive effects of seed priming at all CD concentrations (0.25-2 mg/mL), including accelerated seed germination rate, increased shoot and root elongation, biomass accumulation, and root moisture level compared to the control groups. Surface erosion of seed coat was observed after CD priming, which effectively promoted seed imbibition capability. CD penetration, internalization, and translocation were confirmed using transmission electron microscopy. Furthermore, the CD-plant interaction significantly enhanced seed antioxidant enzyme activity, as well as augmented root vigor, chlorophyll content, and carbohydrate content. These findings exhibit great potential of waste-derived CDs as nano-priming agents for seed germination and seedling development in a cost-effective and sustainable manner.

ZnO quantum dots outperform nanoscale and bulk particles for enhancing tomato (Solanum lycopersicum) growth and nutritional values

Tomato (Solanum lycopersicum) seedlings were exposed by foliar or root applications to Zn in different nanoscale and non-nanoscale forms (40 mg Zn/L) under hydroponic conditions for 15 days. Under foliar exposure, ZnO QDs significantly promoted tomato growth, while ZnO NPs and BPs had lower impacts. ZnO QDs increased fresh weight and plant height by 42.02 % and 21.10 % relative to the untreated controls, respectively. The ionic control (ZnSO₄·7H₂O, 176.6 mg/L) decreased fresh weight by 39.31 %. ZnO QDs also significantly increased the Chla/Chlb ratio, as well as carotenoids and protein content by 7.70 %, 8.90 % and 26.33 %, respectively, over the untreated controls, suggesting improvement in seedling photosynthetic performance. Antioxidant enzyme (POD, PPO and PAL) activities in ZnO QDs treated shoots were significantly decreased by 31.1 %, 17.8 % and 48.3 %, respectively, indicating no overt oxidative damage from exposure. Importantly, the translocation factor of Zn (TF_Zn) in the foliar exposure of the ZnO QDs treatment was 73.2 %, 97.1 % and 276.9 % greater than the NPs, BPs, and ionic controls, respectively. Overall, these findings clearly demonstrate that foliar spray of nanoscale nutrients at the appropriate concentration and size can significantly increase crop growth and be a sustainable approach to nano-enabled agriculture.

Carbon dots promoted soybean photosynthesis and amino acid biosynthesis under drought stress: Reactive oxygen species scavenging and nitrogen metabolism

With global warming and water scarcity, improving the drought tolerance and quality of crops is critical for food security and human health. Here, foliar application of carbon dots (CDs, 5 mg·L^-1) could scavenge reactive oxygen species accumulation in soybean leaves under drought stress, thereby enhancing photosynthesis and carbohydrate transport. Moreover, CDs stimulated root secretion (e.g., amino acids, organic acids, and auxins) and recruited beneficial microorganisms (e.g., Actinobacteria, Ascomycota, Acidobacteria and Glomeromycota), which facilitate nitrogen (N) activation in the soil. Meanwhile, the expression of GmNRT, GmAMT, and GmAQP genes were up-regulated, indicating enhanced N and water uptake. The results demonstrated that CDs could promote nitrogen metabolism and enhance amino acid biosynthesis. Particularly, the N content in soybean shoots and roots increased significantly by 13.2 % and 30.5 %, respectively. The amino acids content in soybean shoots and roots increased by 257.5 % and 57.5 %, respectively. Consequently, soybean yields increased significantly by 21.5 %, and the protein content in soybean kernels improved by 3.7 %. Therefore, foliar application of CDs can support sustainable nano-enabled agriculture to combat climate change.

Enhancing the light reactions of photosynthesis: Strategies, controversies, and perspectives

Photosynthesis is central to life on Earth, employing sunlight, water, and carbon dioxide to produce chemical energy and oxygen. It is generally accepted that boosting its efficiency offers one promising way to increase crop yields under agronomically realistic conditions. Since the components, structure, and regulatory mechanisms of the light reactions of photosynthesis are well understood, concepts for enhancing the process have been suggested and partially tested. These approaches vary in complexity, from targeting single components to comprehensive redesign of the whole process on the scales from single cells or tissues to whole canopies. Attempts to enhance light utilization per leaf, by decreasing pigmentation, increasing levels of photosynthetic proteins, prolonging the lifespan of the photosynthetic machinery, or massive reconfiguration of the photosynthetic machinery and the incorporation of nanomaterials, are discussed in this review first. Secondly, strategies intended to optimize the acclimation of photosynthesis to changes in the environment are presented, including redesigning mechanisms to dissipate excess excitation energy (e.g., non-photochemical quenching) or reduction power (e.g., flavodiiron proteins). Moreover, schemes for improving acclimation, inspired by natural or laboratory-induced adaptation, are introduced. However, all these endeavors are still in an early exploratory phase and/or have not resulted in the desired outcome, largely because photosynthesis is embedded within large networks of closely interacting cellular and metabolic processes, which can vary among species and even cultivars. This explains why integrated, systems-wide approaches are required to achieve the breakthroughs required for effectively increasing crop yields.

Nanobionics-Driven Synthesis of Molybdenum Oxide Nanosheets with Tunable Plasmonic Resonances in Visible Light Regions

Nanobionics-driven synthesis offers a process of designing and synthesizing functional materials on a nanoscale based on the structures and functions of biological systems. An approach such as this is environmentally friendly and sustainable, providing a viable option for synthesizing functional nanomaterials for catalysis and nanoelectronic components. In this work, we present a facile and green nanobionics approach to synthesize plasmonic H_xMoO₃ by interacting chloroplasts extracted from spinach with two-dimensional (2D) MoO₃ nanoflakes. The generated plasmon resonances can be modulated in the visible wavelength ranges, and the efficiency to form the plasmonic materials is enhanced by 90% within 45 min of light excitation compared to reactions without chloroplast involvement. Such a characteristic is ascribed to the interfacial carrier dynamics between the two entities in the reactions, in which highly doped metal oxides with quasi-metallic properties can be formed to generate optical absorptions in the visible light region. The green synthesized plasmonic materials show high photocatalytic activities without the coupling of semiconductors, providing a promising nanoelectronics unit, based on the nanobionics-driven synthesized plasmonic materials.

Inhibition of UV-B stress in lettuce through enzyme-like Scutellaria baicalensis carbon dots

Oxidative stress in plants caused by UV-B stress has always been a great challenge to the yield of agricultural products. Carbon dots (CDs) with enzyme-like activity have been developed, and inhibiting oxidative stress in animals has been achieved, but little is known about abiotic stress resistance in plants, especially UV-B stress. In this study, CDs were synthesized from Scutellaria baicalensis via a hydrothermal method. The ability of CDs to scavenge reactive oxygen species (ROS) in vivo and in vitro and to enhance antioxidant resistance in vivo was evaluated. The results show that CDs promoted the nutrient assimilation ability of lettuce seedlings and protected the plants from UV-B stress by increasing the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX). Moreover, the antioxidant metabolism of plants can be activated by CDs and the expression levels of aquaporin (AQP) genes PIP1 and PIP2 are also up-regulated. These results facilitate the design and fabrication of CDs to meet the challenge of abiotic stress in food production.

Sustainable agronomic response of carbon quantum dots on Allium sativum: Translocation, physiological responses and alternations in chromosomal aberrations

The revolutionary growth in the usage of carbon quantum dots (CQDs) in different areas have ultimately directed their discharge in the environment and further augmented the exposure of agricultural crops to these released particles. Therefore, the aim of current study is to evaluate the uptake, translocation and phytotoxicity of blue emissive CQDs on Allium sativum plant. The genotoxicity and cytotoxicity assessment of CQDs towards Allium sativum roots was estimated as function of three different concentrations. Considering the role of CQDs in promoting seed germination at 50 ppm concentration, a greenhouse experiment was performed to evaluate their effect on plant growth. Systematic investigations have shown the translocation of CQDs and their physiological response in terms of increased shoot length wherein P-CQDs exhibited more accumulation into Allium sativum parts. Our investigations unfold the opportunity to utilize Aegle marmelos fruit derived CQDs as a growth regulator in variety of other food plants.

Glycine assists in efficient synthesis of herbal carbon dots with enhanced yield and performance

As a special type of biomass, herbal medicine often contains a variety of biologically active substances, and taking it as a carbon source, it is expected to produce various types of biologically functional carbon dots (CDs). However, there are few reports in this field, especially in achieving enhanced performance of CDs by improving the utilization efficiency of active substances in medicinal materials. In this work, by adding glycine as an auxiliary agent in the preparation of CDs from herbal medicine (Exocarpium Citri Grandis), the carboxyl and amino groups of the adjuvant provided more reactive sites, which greatly improved the yield of CDs (about 6 times). More importantly, the antioxidant and biological activities of herbal CDs were also improved. By controlling the functional groups of adjuvants, the effects of carboxyl and amino groups in adjuvants on the synthesis of herbal CDs were compared. The results reveal that both carboxyl and amino groups can react with the substances in the carbon source, and the influence of amino groups was greater. After adding glycine, the size of the CDs became larger, resulting from the more abundant functional groups on the carbon skeleton, which was the main reason for the improved performance of the CDs. Finally, the biological activity experiment demonstrated that CDs derived from Exocarpium Citri Grandis and glycine could greatly enhance the vitality of cells and activate immune cells, which are expected to be applied in the field of cell reproduction and biological immunity. The method proposed in this work provides a potential strategy for high-yield preparation of CDs from biomass.

Carbon Dots Improve Nitrogen Bioavailability to Promote the Growth and Nutritional Quality of Soybeans under Drought Stress

The inefficient utilization of nitrogen (N) in soil and drought stress seriously threatens agricultural and food production. Herein, soil application of carbon dots (CDs, 5 mg kg^-1) promoted the growth and nutritional quality of soybeans by improving N bioavailability, which was beneficial to alleviate the economic losses caused by drought stress. Soil application of CDs enhanced the N-fixing ability of nodules, regulated rhizosphere processes, and ultimately enhanced N and water uptake in soybeans under drought stress. Compared to control (drought stress), the application of CDs under drought stress enhanced soybean nitrogenase activity by 8.6% and increased N content in soybean shoots and roots by 18.5% and 14.8%, respectively. CDs in soil promoted the secretion of root exudates (e.g., organic acids, fatty acids, and polyketides) and regulated beneficial microbial communities (e.g., Proteobacteria, Acidobacteria, Gemmatimonadetes, and Actinobacteria), thus enhancing the N release from soil. Besides, compared to control, the expression of GmNRT, GmAMT, GmLB, and GmAQP genes in roots were upregulated by 1.2-, 1.8-, 2.7-, and 2.3-fold respectively, implying enhanced N transport and water uptake. Furthermore, the proteins, fatty acids, and amino acids in soybean grains were improved by 3.4%, 6.9%, and 17.3%, respectively, as a result of improved N bioavailability. Therefore, CD-enabled agriculture is promising for improving the drought tolerance and quality of soybeans, which is of significance for food security in facing the crisis of global climate change.

Targeted Carbon Nanostructures for Chemical and Gene Delivery to Plant Chloroplasts

Nanotechnology approaches for improving the delivery efficiency of chemicals and molecular cargoes in plants through plant biorecognition mechanisms remain relatively unexplored. We developed targeted carbon-based nanomaterials as tools for precise chemical delivery (carbon dots, CDs) and gene delivery platforms (single-walled carbon nanotubes, SWCNTs) to chloroplasts, key organelles involved in efforts to improve plant photosynthesis, assimilation of nutrients, and delivery of agrochemicals. A biorecognition approach of coating the nanomaterials with a rationally designed chloroplast targeting peptide improved the delivery of CDs with molecular baskets (TP-β-CD) for delivery of agrochemicals and of plasmid DNA coated SWCNT (TP-pATV1-SWCNT) from 47% to 70% and from 39% to 57% of chloroplasts in leaves, respectively. Plants treated with TP-β-CD (20 mg/L) and TP-pATV1-SWCNT (2 mg/L) had a low percentage of dead cells, 6% and 8%, respectively, similar to controls without nanoparticles, and no permanent cell and chloroplast membrane damage after 5 days of exposure. However, targeted nanomaterials transiently increased leaf H₂O₂ (0.3225 μmol gFW^-1) above control plant levels (0.03441 μmol gFW^-1) but within the normal range reported in land plants. The increase in leaf H₂O₂ levels was associated with oxidative damage in whole plant cell DNA, a transient effect on chloroplast DNA, and a decrease in leaf chlorophyll content (-17%) and carbon assimilation rates at saturation light levels (-32%) with no impact on photosystem II quantum yield. This work provides targeted delivery approaches for carbon-based nanomaterials mediated by biorecognition and a comprehensive understanding of their impact on plant cell and molecular biology for engineering safer and efficient agrochemical and biomolecule delivery tools.

Carbon quantum dots: An environmentally friendly and valued approach to sludge disposal

Sewage sludge, produced daily and inherent to urban development, presents problems of disposal that are still challenging today. Its disposal still offers palliative solutions, where the final destination is generally in landfills or, restrictively, to use in agriculture. The synthesis of carbon quantum dots (CQDs) from sewage sludge is a better alternative to use the stock of organic material present in the sludge. The present work aims to produce Carbon quantum dots (CQDs) using principles of green chemistry and to use an alternative raw material intrinsic stock of carbon present in sewage sludge, making its final disposal more sustainable. The material obtained has a core structure mainly composed of sp² carbon and nitrogen. The surface functional groups containing sulfur, nitrogen, and oxygen of CQDs were investigated using FTIR and TG/DSC coupled FTIR techniques. The CQDs showed a luminescence decay time equivalent to fluorescent compounds and with satisfying quantum yield since no passive/oxidizing agent or material purification process was used. The photoluminescence spectroscopy analysis showed that the CDQs excitation λ_max was at 360 nm and caused a λ_max emission at 437 nm (CQDs^a) and 430 nm (CQDs^b). The CQDs obtained showed sizes of 9.69 ± 2.64 nm (CQDs^a) and 10.92 ± 2.69 nm (CQDs^b). In vitro experiments demonstrated the uptake of CQDs by the endothelial cell line EAhy 926 and their nontoxicity. However, the production of CQDs can be used for the sustainable disposal of sewage sludge.

Calcium-Mobilizing Properties of Salvia miltiorrhiza-Derived Carbon Dots Confer Enhanced Environmental Adaptability in Plants

Biomass-derived carbon dots (CDs) are promising nanotools for agricultural applications and function as a reactive oxygen species (ROS) scavenger to alleviate plant oxidative stress under adverse environments. Nevertheless, plants need ROS burst to fully activate Ca²⁺-regulated defensive signaling pathway. The underlying mechanism of CDs to improve plant environmental adaptability without ROS is largely unknown. Here, Salvia miltiorrhiza-derived CDs triggered ROS-independent Ca²⁺ mobilization in plant roots. Mechanistic investigation attributed this function mainly to the hydroxyl and carboxyl groups on CDs. CDs-triggered Ca²⁺ mobilization was found to be dependent on the production of cyclic nucleotides and cyclic nucleotide-gated ion channels. Lectin receptor kinases were verified as essential for this Ca²⁺ mobilization. CDs hydroponic application promoted Ca²⁺ signaling and plant environmental adaptability under salinity and nutrient-deficient conditions. All these findings uncover that CDs have a Ca²⁺-mobilizing property and thus can be used as a simultaneous Ca²⁺ signaling amplifier and ROS scavenger for crop improvement.

Foliar carbon dot amendment modulates carbohydrate metabolism, rhizospheric properties and drought tolerance in maize seedling

Improving maize drought tolerance is of great importance for scaling up production due to food security and population growth. Carbon dots (CDs) were synthesized by hydrothermal method with citric acid and ethylenediamine as carbon sources. Then, CDs (5 ml, 5 mg‧L^-1) were sprayed on 25th day-old maize (Zea mays L., drought-stress, 35% soil moisture) for seven consecutive days (spraying ultra-pure water as control), after which the physiological parameters and rhizospheric properties of maize under drought were evaluated. Foliar sprayed CDs (5 mg‧L^-1) could increase root exudates (e.g., succinic acid (14.5 folds), pyruvic acid (10.0 folds), and betaine (11.8 folds)), and modify microbial community. Particularly, the relative abundance of Pseudomonas, Sphingomonas, Nitrospira, and Conocybe were significantly increased by 344.4%, 233.3%, 126.2%, and 122.6%, respectively. The altered microbial abundance could improve soil available nitrogen and phosphorus by 33.5% and 16.8%, respectively, and increase plant water uptake by 37.2%. The change of exudate synthesis and microbial abundance could be driven by the significantly increased in net photosynthesis rate by 122.9%, and carbohydrate content by 35.4% in shoots and 113.6% in roots, respectively upon foliar application of CDs. Meanwhile, fresh weight of shoots and roots were increased by 62.1% and 50.6%, and dry weight of shoots and roots were increased by 29.2% and 37.5%, respectively. These results demonstrated that foliar application of CDs could improve the rhizosphere environment to enhance maize drought tolerance and even growth. Therefore, foliar application of CDs would be a promising strategy for sustainable nano-agriculture in response to drought stress.

Carbon-Based Nanomaterials for Sustainable Agriculture: Their Application as Light Converters, Nanosensors, and Delivery Tools

Nano-enabled agriculture is now receiving increasing attentions. Among the used nanomaterials, carbon-based nanomaterials are good candidates for sustainable agriculture. Previous review papers about the role of carbon-based nanomaterials in agriculture are either focused on one type of carbon-based nanomaterial or lack systematic discussion of the potential wide applications in agriculture. In this review, different types of carbon-based nanomaterials and their applications in light converters, nanosensors, and delivery tools in agriculture are summarized. Possible knowledge gaps are discussed. Overall, this review helps to better understand the role and the potential of carbon-based nanomaterials for nano-enabled agriculture.

Plant Bioelectronics and Biohybrids: The Growing Contribution of Organic Electronic and Carbon-Based Materials

Life in our planet is highly dependent on plants as they are the primary source of food, regulators of the atmosphere, and providers of a variety of materials. In this work, we review the progress on bioelectronic devices for plants and biohybrid systems based on plants, therefore discussing advancements that view plants either from a biological or a technological perspective, respectively. We give an overview on wearable and implantable bioelectronic devices for monitoring and modulating plant physiology that can be used as tools in basic plant science or find application in agriculture. Furthermore, we discuss plant-wearable devices for monitoring a plant's microenvironment that will enable optimization of growth conditions. The review then covers plant biohybrid systems where plants are an integral part of devices or are converted to devices upon functionalization with smart materials, including self-organized electronics, plant nanobionics, and energy applications. The review focuses on advancements based on organic electronic and carbon-based materials and discusses opportunities, challenges, as well as future steps.

Nitrogen-Doped Carbon Dots Increased Light Conversion and Electron Supply to Improve the Corn Photosystem and Yield

Fluorescent carbon dots (CDs) have been reported as an artificial antenna to amplify the harvesting ability of light and enhance photosynthesis in plants. However, the main mechanism of this promotive effect and contributions of CDs' structure are unclear. Herein, CDs and nitrogen (N)-doped CDs (N-CDs) with blue fluorescence were synthesized, and they could promote photosynthesis and growth of corn at an application concentration of 50 mg·L^-1 or lower, compared to the control. Foliar application of N-CDs (5 mg·L^-1) on corn could increase the net photosynthesis rate (21.51%), carbohydrate content (66.43% in roots and 42.03% in shoots), fresh weight (24.03% in roots and 34.56% in shoots), and dry weight (72.30% in roots and 55.75% in shoots), which were much higher than those of CDs. Principal component analysis and density functional theory calculation demonstrated that, compared with undoped CDs, N doping enhanced the light conversion and electron supply via altering the structure of CDs, making N-CDs effective light conversion materials and electron donors to promote the photoelectron transfer rate. Furthermore, foliar application of N-CDs could increase the yield and 1000-grain weight by 24.50 and 15.03%, respectively. Therefore, the application of N-CDs could be a promising approach for increasing agricultural production.

Fluorescent carbon-dots enhance light harvesting and photosynthesis by overexpressing PsbP and PsiK genes

BACKGROUND

Fluorescent carbon-dots (CDs) with multifaceted advantages have provided hope for improvement of crop growth. Near infrared (NIR) CDs would be more competitive and promising than short-wavelength emissive CDs, which are not directly utilized by chloroplast. The molecular targets and underlying mechanism of these stimulative effects are rarely mentioned.

RESULTS

NIR-CDs with good mono-dispersity and hydrophily were easily prepared by a one-step microwave-assisted carbonization manner, which showed obvious UV absorptive and far-red emissive properties. The chloroplast-CDs complexes could accelerate the electron transfer from photosystem II (PS II) to photosystem I (PS I). NIR-CDs exhibited a concentration-dependent promotion effect on N. benthamiana growth by strengthening photosynthesis. We firstly demonstrated that potential mechanisms behind the photosynthesis-stimulating activity might be related to up-regulated expression of the photosynthesis and chloroplast synthesis related genes, among which PsbP and PsiK genes are the key regulators.

CONCLUSION

These results illustrated that NIR-CDs showed great potential in the applications to increase crop yields through ultraviolet light harvesting and elevated photosynthesis efficiency. This work would provide a theoretical basis for the understanding and applications of the luminescent nanomaterials (not limited to CDs) in the sunlight conversion-related sustainable agriculture.