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Increasing the production of renewable energy will be critical to achieving global sustainability goals in the coming decades. Biofuels derived from microalgae have great potential to contribute to this production. However, cultivating algae with sufficient neutral lipid content, while maintaining high growth rates, is a continual challenge in making algal-derived biofuels a reality. Previous work has shown that exposure to polymer-functionalized carbon dots can increase the lipid content of the microalgaeRaphidocelis subcapitata. This study investigates this finding, aiming to determine the mechanisms underlying this effect and if altering nanoparticle surface charge mediates the mechanism of action of the carbon dots used. Carbon dots with both negative and positive surface charges were added to microalgal cultures, and the impacts of this exposure were analyzed using high-content imaging, growth measurements, and chlorophyll content measurements. Results indicate that positively charged carbon dots induce a nano-specific increase in lipid content but also cause decreases in growth. Additionally, the mechanism of action of each nanoparticle was examined by conducting a morphological comparison to treatments with known mechanisms of action. This analysis showed that negatively charged carbon dots cause similar impacts toR. subcapitataas nitrogen deprivation. Nitrogen deprivation is known to increase lipid content in microalgae. The findings of this study suggest that carbon dots may have surface charge dependent effects on the lipid metabolism ofR. subcapitata. Future work should consider the use of carbon dots with varied surface charge densities for enhancing algae biofuel production in bioreactors. 

Global food security is a pressing issue in our society. Maintaining food security in coming years will require improving crop yield, as well as increased resiliency to abiotic and biotic stress. Nanoscale materials have increasingly been proposed as a tool which could be used to meet these challenges. However, much research is needed to optimize nanoparticle design and crop application for this to become a reality. In this study, we investigated the impact of polymer-functionalized carbon dots on tomatoes (Solanum lycopersicum L.). Tomato seeds were vacuum infiltrated with carbon dots and then grown for 3 weeks before collection of phenotypic and transcriptomic data. No changes to fresh biomass or chlorophyll content were observed, indicating that these particles can be applied without overt harm to the plant at early growth stages. In addition, changes in gene expression suggest that polymer-functionalized carbon dots can initiate the expression of biochemical pathways associated with a pathogen resistance response in tomato plants. Specifically, genes involved in ethylene signaling, ethylene production, and camalexin synthesis were upregulated. These findings suggest that seed priming with carbon dots may improve plant tolerance to biotic stress by modulating ethylene signaling pathways. Carbon dots could also be loaded with nutrients or other agrochemicals to create a multifunctional platform. Future work should focus on understanding the mechanisms by which nanoparticles can modulate ethylene signaling, enabling use of this knowledge to develop sustainable and effective nanoparticles for agricultural applications. 

Nitrogen fertilizer delivery inefficiencies limit crop productivity and contribute to environmental pollution. Herein, we developed Zn- and Fe-doped hydroxyapatite nanomaterials (ZnHAU, FeHAU) loaded with urea (∼26% N) through hydrogen bonding and metal-ligand interactions. The nanomaterials attach to the leaf epidermal cuticle and localize in the apoplast of leaf epidermal cells, triggering a slow N release at acidic conditions (pH 5.8) that promote wheat (Triticum aestivum) growth and increased N uptake compared to conventional urea fertilizers. ZnHAU and FeHAU exhibited prolonged N release compared to urea in model plant apoplast fluid pH in vitro (up to 2 days) and in leaf membranes in plants (up to 10 days) with a high N retention (32% to 53%) under simulated high rainfall events (50 mm). Foliar N delivery doses of up to 4% as ZnHAU and FeHAU did not induce toxicity in plant cells. The foliar-applied ZnHAU and FeHAU enhanced fresh and dry biomass by ∼214% and ∼161%, and N uptake by ∼108% compared to foliar-applied urea under low soil N conditions in greenhouse experiments. Controlled N release by leaf-attached nanomaterials improves N delivery and use efficiency in crop plants, creating nanofertilizers with reduced environmental impact. 

Dynamic optical modulation in response to stimuli provides exciting opportunities for designing novel sensing, actuating, and authentication devices. Here, we demonstrate that the reversible swelling and deswelling of crosslinked polymer colloidal spheres in response to pH and temperature changes can be utilized to drive the assembly and disassembly of the embedded gold nanoparticles (AuNPs), inducing their plasmonic coupling and decoupling and, correspondingly, color changes. The multi‐responsive colloids are created by depositing a monolayer of AuNPs on the surface of resorcinol‐formaldehyde (RF) nanospheres, then overcoating them with an additional RF layer, followed by a seeded growth process to enlarge the AuNPs and reduce their interparticle separation to induce significant plasmonic coupling. This configuration facilitates dynamic modulation of plasmonic coupling through the reversible swelling/deswelling of the polymer spheres in response to pH and temperature changes. The rapid and repeatable transitions between coupled and decoupled plasmonic states of AuNPs enable reversible color switching when the polymer spheres are in colloidal form or embedded in hydrogel substrates. Furthermore, leveraging the photothermal effect and stimuli‐responsive plasmonic coupling of the embedded AuNPs enables the construction of hybrid hydrogel films featuring switchable anticounterfeiting patterns, showcasing the versatility and potential of this multi‐stimuli‐responsive plasmonic system. 

Surface charge is a key characteristic of nanoparticles which has great potential to impact the interactions of nanoparticles and biological systems. Understanding the role charge plays in these interactions is key to determining the ecological risks of nanoparticle exposure and informing sustainable nanoparticle design. In this study, the model freshwater algae Raphidocelis subcapitata was exposed to carbon dots (CDs) functionalized with polymers to have positive, negative, or neutral surface charges to examine the impact of nanoparticle surface charge on nano-algae interactions. Traditional toxicological endpoints of survival and growth inhibition were measured. Additionally, morphological impacts on whole cells, individual organelles, and cellular components were quantified using high-content fluorescence microscopy, demonstrating one of the first uses of high-content imaging in microalgae. Results indicate that PEI functionalized, positively charged CDs are most toxic to green algae (EC50 42.306 μg/L), but that CDs with negative charge induce sublethal impacts on algae. PEI-CD toxicity is hypothesized to be related to electrostatic interactions between CDs and the algal cell wall, which lead to significant cell aggregation. Interestingly, morphological data suggests that exposure to both positively and negatively charged CDs leads to increased neutral lipid droplet formation, a possible indicator of nutrient stress. Further investigation of the mechanisms underlying impacts of nanoparticle surface charge on algae biology can lead to more sustainable nanoparticle design and environmental protections. 

Abstract Delivery of proteins in plant cells can facilitate the design of desired functions by modulation of biological processes and plant traits but is currently limited by narrow host range, tissue damage, and poor scalability. Physical barriers in plants, including cell walls and membranes, limit protein delivery to desired plant tissues. Herein, a cationic high aspect ratio polymeric nanocarriers (PNCs) platform is developed to enable efficient protein delivery to plants. The cationic nature of PNCs binds proteins through electrostatic. The ability to precisely design PNCs’ size and aspect ratio allowed us to find a cutoff of ≈14 nm in the cell wall, below which cationic PNCs can autonomously overcome the barrier and carry their cargo into plant cells. To exploit these findings, a reduction‐oxidation sensitive green fluorescent protein (roGFP) is deployed as a stress sensor protein cargo in a model plantNicotiana benthamianaand common crop plants, including tomato and maize. In vivo imaging of PNC‐roGFP enabled optical monitoring of plant response to wounding, biotic, and heat stressors. These results show that PNCs can be precisely designed below the size exclusion limit of cell walls to overcome current limitations in protein delivery to plants and facilitate species‐independent plant engineering. 

Abstract Current practices for delivering agrochemicals are inefficient, with only a fraction reaching the intended targets in plants. The surfaces of nanocarriers are functionalized with sucrose, enabling rapid and efficient foliar delivery into the plant phloem, a vascular tissue that transports sugars, signaling molecules, and agrochemicals through the whole plant. The chemical affinity of sucrose molecules to sugar membrane transporters on the phloem cells enhances the uptake of sucrose‐coated quantum dots (sucQD) and biocompatible carbon dots with β‐cyclodextrin molecular baskets (suc‐β‐CD) that can carry a wide range of agrochemicals. The QD and CD fluorescence emission properties allowed detection and monitoring of rapid translocation (<40 min) in the vasculature of wheat leaves by confocal and epifluorescence microscopy. The suc‐β‐CDs more than doubled the delivery of chemical cargoes into the leaf vascular tissue. Inductively coupled plasma mass spectrometry (ICP‐MS) analysis showed that the fraction of sucQDs loaded into the phloem and transported to roots is over 6.8 times higher than unmodified QDs. The sucrose coating of nanoparticles approach enables unprecedented targeted delivery to roots with ≈70% of phloem‐loaded nanoparticles delivered to roots. The use of plant biorecognition molecules mediated delivery provides an efficient approach for guiding nanocarriers containing agrochemicals to the plant vasculature and whole plants.