Towards realizing nano-enabled precision delivery in plants.

Nanocarriers (NCs) that can precisely deliver active agents, nutrients and genetic materials into plants will make crop agriculture more resilient to climate change and sustainable. As a research field, nano-agriculture is still developing, with significant scientific and societal barriers to overcome. In this Review, we argue that lessons can be learned from mammalian nanomedicine. In particular, it may be possible to enhance efficiency and efficacy by improving our understanding of how NC properties affect their interactions with plant surfaces and biomolecules, and their ability to carry and deliver cargo to specific locations. New tools are required to rapidly assess NC-plant interactions and to explore and verify the range of viable targeting approaches in plants. Elucidating these interactions can lead to the creation of computer-generated in silico models (digital twins) to predict the impact of different NC and plant properties, biological responses, and environmental conditions on the efficiency and efficacy of nanotechnology approaches. Finally, we highlight the need for nano-agriculture researchers and social scientists to converge in order to develop sustainable, safe and socially acceptable NCs.

Anticancer Effects of α-Pinene in AGS Gastric Cancer Cells.

Gastric cancer is the fifth most common cancer globally and the third leading cause of cancer-related mortality. Existing treatment strategies for gastric cancer often present numerous side effects. Consequently, recent studies have shifted toward devising new treatments grounded in safer natural substances. α-Pinene, a natural terpene found in the essential oils of various plants, such as Lavender angustifolia and Satureja myrtifolia, displays antioxidant, antibiotic, and anticancer properties. Yet, its impact on gastric cancer remains unexplored. This research assessed the effects of α-pinene in vitro using a human gastric adenocarcinoma cell-line (AGS) human gastric cancer cells and in vivo via a xenograft mouse model. The survival rate of AGS cells treated with α-pinene was notably lower than that of the control group, as revealed by the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide assay. This decline in cell viability was linked to apoptosis, as verified by 4',6-diamidino-2-phenylindole and annexin V/propidium iodide staining. The α-pinene-treated group exhibited elevated cleaved-poly (ADP-ribose) polymerase and B cell lymphoma 2 (Bcl-2)-associated X (Bax) levels and reduced Bcl-2 levels compared with the control levels. Moreover, α-pinene triggered the activation of extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 within the mitogen-activated protein kinase (MAPK) pathway. In the xenograft mouse model, α-pinene induced apoptosis through the MAPK pathway, devoid of toxicity. These findings position α-pinene as a promising natural therapeutic for gastric cancer.

Kaempferol induces apoptosis through the MAPK pathway and regulates JNK-mediated autophagy in MC-3 cells.

This study sought to determine the anticancer effect of kaempferol, a glycone-type flavonoid glycoside with various pharmacological benefits, on human oral cancer MC-3 cells. In vitro studies comprised a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, annexin V and propidium iodide staining, western blotting analysis, and acridine orange staining, while the in vivo studies entailed a xenograft model, hematoxylin and eosin staining, and TdT-mediated dUTP-biotin nick end labelling. In vitro, kaempferol reduced the rate of survival of MC-3 cells, mediated intrinsic apoptosis, increased the number of acidic vesicular organelles, and altered the expression of autophagy-related proteins. Further, treatment with the autophagy inhibitors revealed that the induced autophagy had a cytoprotective effect on apoptosis in kaempferol-treated MC-3 cells. Kaempferol also decreased the expression of phosphorylated extracellular signal-regulated kinase and increased that of phosphorylated c-Jun N-terminal kinase (p-JNK) and phosphorylated p38 kinase in MC-3 cells, suggesting the occurrence of mitogen-activated protein kinase-mediated apoptosis and JNK-mediated autophagy. In vivo, kaempferol reduced tumor growth inducing apoptosis and autophagy. These results showed that kaempferol has the potential use as an adjunctive agent in treating oral cancer.

Targeted Delivery of Sucrose-Coated Nanocarriers with Chemical Cargoes to the Plant Vasculature Enhances Long-Distance Translocation.

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 ß-cyclodextrin molecular baskets (suc-ß-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-ß-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.

Electrostatics Control Nanoparticle Interactions with Model and Native Cell Walls of Plants and Algae.

A lack of mechanistic understanding of nanomaterial interactions with plants and algae cell walls limits the advancement of nanotechnology-based tools for sustainable agriculture. We systematically investigated the influence of nanoparticle charge on the interactions with model cell wall surfaces built with cellulose or pectin and performed a comparative analysis with native cell walls of Arabidopsis plants and green algae (Choleochaete). The high affinity of positively charged carbon dots (CDs) (46.0 ± 3.3 mV, 4.3 ± 1.5 nm) to both model and native cell walls was dominated by the strong ionic bonding between the surface amine groups of CDs and the carboxyl groups of pectin. In contrast, these CDs formed weaker hydrogen bonding with the hydroxyl groups of cellulose model surfaces. The CDs of similar size with negative (-46.2 ± 1.1 mV, 6.6 ± 3.8 nm) or neutral (-8.6 ± 1.3 mV, 4.3 ± 1.9 nm) ζ-potentials exhibited negligible interactions with cell walls. Real-time monitoring of CD interactions with model pectin cell walls indicated higher absorption efficiency (3.4 ± 1.3 10-9) and acoustic mass density (313.3 ± 63.3 ng cm-2) for the positively charged CDs than negative and neutral counterparts (p < 0.001 and p < 0.01, respectively). The surface charge density of the positively charged CDs significantly enhanced these electrostatic interactions with cell walls, pointing to approaches to control nanoparticle binding to plant biosurfaces. Ca2+-induced cross-linking of pectin affected the initial absorption efficiency of the positively charged CD on cell wall surfaces (∼3.75 times lower) but not the accumulation of the nanoparticles on cell wall surfaces. This study developed model biosurfaces for elucidating fundamental interactions of nanomaterials with cell walls, a main barrier for nanomaterial translocation in plants and algae in the environment, and for the advancement of nanoenabled agriculture with a reduced environmental impact.

Piperlongumine induces apoptosis via the MAPK pathway and ERK­mediated autophagy in human melanoma cells.

Piperlongumine (PL) is an amide alkaloid with diverse pharmacological effects against cancer, bronchitis and asthma; however, research on its efficacy against melanoma is lacking. The present study investigated the anticancer effects of PL on A375SM and A375P human melanoma cells. PL decreased the survival rate of A375SM and A375P cells, as shown by MTT assay, increase of apoptotic cells by DAPI staining. And PL induced apoptosis by decreasing the expression of the anti­apoptotic protein Bcl­2 and increasing that of the pro­apoptotic proteins cleaved­PARP and Bax. PL also induced apoptosis in A375SM and A375P cells via the MAPK pathway, increasing expression of the MAPK pathway proteins, phosphorylated­(p­ERK), p­JNK p­p38. These proteins were confirmed by western blot. In addition, A375SM and A375P cells treated with PL showed an increased number of acidic vesicular organelles by acridine orange staining. Also, autophagy induced by the expression of 1A/1B­light chain 3, Beclin 1and mTOR was investigated through western blot. When PL was applied following treatment with autophagy inhibitors 3­methyladenine and hydroxychloroquine, autophagy exhibited a cytoprotective effect against apoptosis in MTT assay. Pretreatment of A375P cells with the ERK inhibitor PD98059 and the JNK inhibitor SP600125 followed by treatment with PL confirmed that apoptosis and autophagy were mediated via the MAPK/ERK pathway by western blot. In summary, the present study provided empirical evidence supporting the anticancer effects of PL on human melanoma cells and indicated the potential of PL as a treatment for melanoma.

Piperlongumine induces apoptosis and autophagy via the PI3K/Akt/mTOR pathway in KB human cervical cancer cells.

Natural products are continuously being researched to develop safe and effective treatment options for cervical cancer, the fourth most common cancer in women. Piperlongumine (PL), an amide alkaloid mainly present in long pepper, exhibits neuroprotective and anti-cancer properties. However, the specific effect of PL in cervical cancer and the relationship between the anti-cancer pathway and autophagy remain unclear. Therefore, we aimed to investigate PL-induced apoptosis in KB human cervical cancer cells and the relationship between apoptosis and autophagy therein. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and wound-healing assays showed that PL treatment suppressed KB cell viability and proliferation. Apoptosis was identified through 4',6-diamidino-2-phenylindole and annexin V-propidium iodide staining, increased cleaved-poly (ADP-ribose) polymerase and Bcl-2 associated X levels, and decreased B cell lymphoma 2 levels. Acridine orange staining and increased microtubule-associated protein 1A/1B-light chain 3-II and Beclin-1 levels confirmed autophagy. We determined that KB cell-related autophagy exerted cytoprotective effects using the autophagy inhibitors 3-methyladenine and hydroxychloroquine. PL treatment promoted apoptosis by inhibiting the phosphatidylinositol-3-kinase (PI3K)/protein kinase B/mammalian target of rapamycin pathway in KB cells; inhibiting the pathway using PI3K inhibitors increased autophagy. We suggest that PL is a potential natural anticancer agent for cervical cancer treatment.

Piperlongumine Induces Apoptosis and Cytoprotective Autophagy via the MAPK Signaling Pathway in Human Oral Cancer Cells.

Oral cancer is a malignant tumor that primarily affects areas such as the lips, tongue, buccal mucosa, salivary gland, and gingiva and has a very high malignancy. Piperlongumine (PL), isolated from long pepper (Piper longum L.), is a natural alkaloid with pharmacological effects, such as anti-inflammatory and anti-atherosclerotic effects. The effect and mechanism of PL in oral cancer cell lines has not been explored. Therefore, this study aimed to investigate the mechanism of anticancer effects of PL in the human oral cancer cell lines MC-3 and HSC-4 in vitro. This study demonstrated that PL inhibits cell proliferation by inducing apoptosis and autophagy in human oral cancer cell lines, which was confirmed by the levels of apoptosis- and autophagy-related proteins through Western blotting. Moreover, the pharmacological blockade of autophagy activation by hydroxychloroquine (HCQ), an autophagy inhibitor, significantly improved PL-induced apoptosis in MC-3 cells, suggesting a cytoprotective effect. In addition, activation of the mitogen-activated protein kinase (MAPK) signaling pathway contributed to PL-induced apoptosis. Collectively, the study suggested that combining an autophagy inhibitor with PL treatment can exert effective anticancer properties in oral cancer cells by inducing apoptosis and cytoprotective autophagy via the JNK-mediated MAPK pathway.

Piperine Induces Apoptosis and Autophagy in HSC-3 Human Oral Cancer Cells by Regulating PI3K Signaling Pathway.

Currently, therapies for treating oral cancer have various side effects; therefore, research on treatment methods employing natural substances is being conducted. This study aimed to investigate piperine-induced apoptosis and autophagy in HSC-3 human oral cancer cells and their effects on tumor growth in vivo. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay demonstrated that piperine reduced the viability of HSC-3 cells and 4',6-diamidino-2-phenylindole staining, annexin-V/propidium iodide staining, and analysis of apoptosis-related protein expression confirmed that piperine induces apoptosis in HSC-3 cells. Additionally, piperine-induced autophagy was confirmed by the observation of increased acidic vesicular organelles and autophagy marker proteins, demonstrating that autophagy in HSC-3 cells induces apoptosis. Mechanistically, piperine induced apoptosis and autophagy by inhibiting the phosphatidylinositol-3-kinase (PI3K)/protein kinase B/mammalian target of rapamycin pathway in HSC-3 cells. We also confirmed that piperine inhibits oral cancer tumor growth in vivo via antitumor effects related to apoptosis and PI3K signaling pathway inhibition. Therefore, we suggest that piperine can be considered a natural anticancer agent for human oral cancer.

Chrysin Induces Apoptosis via the MAPK Pathway and Regulates ERK/mTOR-Mediated Autophagy in MC-3 Cells.

Chrysin is a flavonoid found abundantly in substances, such as honey and phytochemicals, and is known to exhibit anticancer effects against various cancer cells. Nevertheless, the anticancer effect of chrysin against oral cancer has not yet been verified. Furthermore, the mechanism underlying autophagy is yet to be clearly elucidated. Thus, this study investigated chrysin-mediated apoptosis and autophagy in human mucoepidermoid carcinoma (MC-3) cells. The change in MC-3 cell viability was examined using a 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide cell viability assay, as well as 40,6-diamidino-2-phenylindole, annexin V, and propidium iodide staining. Western blotting was used to analyze the proteins related to apoptosis and the mitogen-activated protein kinase (MAPK) pathway. In addition, the presence or absence of autophagy and changes in the expression of related proteins were investigated using acridine orange staining and Western blot. The results suggested that chrysin induced apoptosis and autophagy in MC-3 oral cancer cells via the MAPK/extracellular signal-regulated kinase pathway. Moreover, the induced autophagy exerted a cytoprotective effect against apoptosis. Thus, the further reduced cell viability due to autophagy as well as apoptosis induction highlight therapeutic potential of chrysin for oral cancer.

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-ß-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-ß-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.

Chrysin Induces Apoptosis and Autophagy in Human Melanoma Cells via the mTOR/S6K Pathway.

Chrysin is known to exert anti-inflammatory, antioxidant, and anticancer effects. The aim of this study was to investigate the anticancer effects of chrysin in the human melanoma cells A375SM and A375P. The results obtained demonstrated successful inhibition of the viability of these cells by inducing apoptosis and autophagy. This was confirmed by the level of apoptosis-related proteins: Bax and cleaved poly (ADP-ribose) polymerase both increased, and Bcl-2 decreased. Moreover, levels of LC3 and Beclin 1, both autophagy-related proteins, increased in chrysin-treated cells. Autophagic vacuoles and acidic vesicular organelles were observed in both cell lines treated with chrysin. Both cell lines showed different tendencies during chrysin-induced autophagy inhibition, indicating that autophagy has different effects depending on the cell type. In A375SM, the early autophagy inhibitor 3-methyladenine (3-MA) was unaffected; however, cell viability decreased when treated with the late autophagy inhibitor hydroxychloroquine (HCQ). In contrast, HCQ was unaffected in A375P; however, cell viability increased when treated with 3-MA. Chrysin also decreased the phosphorylation of mTOR/S6K pathway proteins, indicating that this pathway is involved in chrysin-induced apoptosis and autophagy for A375SM and A375P. However, studies to elucidate the mechanisms of autophagy and the action of chrysin in vivo are still needed.

Subacute Oral Toxicity Evaluation of Expanded-Polystyrene-Fed Tenebrio molitor Larvae (Yellow Mealworm) Powder in Sprague-Dawley Rats.

Tenebrio molitor larvae, as known as edible insects, has advantages of being rich in protein, and has been recognized as a suitable alternate protein source for broiler and pig feed. Moreover, given their ability to biodegrade polystyrene, a major pollutant, Tenebrio molitor larvae has been proposed as an innovative solution to environmental problems. In the present study, we investigated the toxicity of Tenebrio molitor larvae powder (TMlp) ingested with expanded-polystyrene (W/ eps) through in vitro and in vivo experiments. The objective of this study was to determine whether TMlp W/ eps can be applied as livestock alternative protein source. For in vitro experiments, cytotoxicity test was performed to investigate the effects of TMlp-extract on the viability of estrogen-dependent MCF-7 cells. The possibility of estrogen response was investigated in two groups: Expanded-polystyrene-fed (W/ eps) TMlp group and without expanded-polystyrene-fed (W/o eps) TMlp group. For in vivo experiments, The male Sprague-Dawley rats were divided based on the dosage of TMlp administered and oral administration was performed to every day for 5 weeks. A toxicological assessments were performed, which included clinical signs, food consumption, body and organ weights, hematology, serum chemistry, and hematoxylin and eosin staining of liver and kidney. There were no specific adverse effect of TMlp W/ eps-related findings under the experimental conditions of this study, but further studies on both sexes and animal species differences should be investigated. In conclusion, TMlp W/ eps was considered non-toxic and observed to be applicable as an alternative protein source for livestock feed.

Star Polymers with Designed Reactive Oxygen Species Scavenging and Agent Delivery Functionality Promote Plant Stress Tolerance.

Plant abiotic stress induces reactive oxygen species (ROS) accumulation in leaves that can decrease photosynthetic performance and crop yield. Materials that scavenge ROS and simultaneously provide nutrients in vivo are needed to manage this stress. Here, we incorporated both ROS scavenging and ROS triggered agent release functionality into an ∼20 nm ROS responsive star polymer (RSP) poly(acrylic acid)-block-poly((2-(methylsulfinyl)ethyl acrylate)-co-(2-(methylthio)ethyl acrylate)) (PAA-b-P(MSEA-co-MTEA)) that alleviated plant stress by simultaneous ROS scavenging and nutrient agent release. Hyperspectral imaging indicates that all of the RSP penetrates through the tomato leaf epidermis, and 32.7% of the applied RSP associates with chloroplasts in mesophyll. RSP scavenged up to 10 µmol mg-1 ROS in vitro and suppressed ROS in vivo in stressed tomato (Solanum lycopersicum) leaves. Reaction of the RSP with H2O2in vitro enhanced the release of nutrient agent (Mg2+) from star polymers. Foliar applied RSP increased photosynthesis in plants under heat and light stress compared to untreated controls, enhancing the carbon assimilation, quantum yield of CO2 assimilation, Rubisco carboxylation rate, and photosystem II quantum yield. Mg loaded RSP improved photosynthesis in Mg deficient plants, mainly by promoting Rubisco activity. These results indicate the potential of ROS scavenging nanocarriers like RSP to alleviate abiotic stress in crop plants, allowing crop plants to be more resilient to heat stress, and potentially other climate change induced abiotic stressors.

Transition-Metal Dichalcogenide Artificial Antibodies with Multivalent Polymeric Recognition Phases for Rapid Detection and Inactivation of Pathogens.

Antibodies are recognition molecules that can bind to diverse targets ranging from pathogens to small analytes with high binding affinity and specificity, making them widely employed for sensing and therapy. However, antibodies have limitations of low stability, long production time, short shelf life, and high cost. Here, we report a facile approach for the design of luminescent artificial antibodies with nonbiological polymeric recognition phases for the sensitive detection, rapid identification, and effective inactivation of pathogenic bacteria. Transition-metal dichalcogenide (TMD) nanosheets with a neutral dextran phase at the interfaces selectively recognized S. aureus, whereas the nanosheets bearing a carboxymethylated dextran phase selectively recognized E. coli O157:H7 with high binding affinity. The bacterial binding sites recognized by the artificial antibodies were thoroughly identified by experiments and molecular dynamics simulations, revealing the significance of their multivalent interactions with the bacterial membrane components for selective recognition. The luminescent WS2 artificial antibodies could rapidly detect the bacteria at a single copy from human serum without any purification and amplification. Moreover, the MoSe2 artificial antibodies selectively killed the pathogenic bacteria in the wounds of infected mice under light irradiation, leading to effective wound healing. This work demonstrates the potential of TMD artificial antibodies as an alternative to antibodies for sensing and therapy.

Peptide-mediated Targeting of Nanoparticles with Chemical Cargoes to Chloroplasts in Arabidopsis Plants.

Plant nanobiotechnology is a flourishing field that uses nanomaterials to study and engineer plant function. Applications of nanotechnology in plants have great potential as tools for improving crop yield, tolerance to disease and environmental stress, agrochemical delivery of pesticides and fertilizers, and genetic modification and transformation of crop plants. Previous studies have used nanomaterials functionalized with chemicals, including biocompatible polymers with charged, neutral, or hydrophobic functional groups, to improve nanomaterial uptake and localization in plant cells. Recently, the use of biorecognition motifs such as peptides has been demonstrated to enable the targeted delivery of nanoparticles in plants ( Santana et al., 2020 ). Herein, we describe a bio-protocol to target nanoparticles with chemical cargoes to chloroplasts in plant leaves and assess targeting efficiency using advanced analytical tools, including confocal microscopy and elemental analysis. We also describe the use of isothermal titration calorimetry to determine the affinity of nanomaterials for their chemical cargoes. Nanotechnology-based methods for targeted delivery guided by conserved plant molecular recognition mechanisms will provide more robust plant bioengineering tools across diverse plant species. Graphic abstract: Targeted delivery of nanomaterials with chemical cargoes to chloroplasts enabled by plant biorecognition.

Multivalent Nanosheet Antibody Mimics for Selective Microbial Recognition and Inactivation.

Antibodies are widely used as recognition elements in sensing and therapy, but they suffer from poor stability, long discovery time, and high cost. Herein, a facile approach to create antibody mimics with flexible recognition phases and luminescent rigid scaffolds for the selective recognition, detection, and inactivation of pathogenic bacteria is reported. Tripeptides with a nitriloacetate-Cu group are spontaneously assembled on transition metal dichalcogenide (TMD) nanosheets via coordination bonding, providing a diversity of TMD-tripeptide assembly (TPA) antibody mimics. TMD-TPA antibody mimics can selectively recognize various pathogenic bacteria with nanomolar affinities. The bacterial binding sites for TMD-TPA are identified by experiments and molecular dynamics simulations, revealing that the dynamic and multivalent interactions of artificial antibodies play a crucial role for their recognition selectivity and affinity. The artificial antibodies allow the rapid and selective detection of pathogenic bacteria at single copy in human serum and urine, and their effective inactivation for therapy of infected mice. This work demonstrates the potential of TMD-TPA antibody mimics as an alternative to natural antibodies for sensing and therapy.

Modulation of oligonucleotide-binding dynamics on WS2 nanosheet interfaces for detection of Alzheimer's disease biomarkers.

Non-covalent adsorption and desorption of oligonucleotides on two-dimensional nanosheets are widely employed to design nanobiosensors for the rapid optical detection of targets. A precise control over the weak interactions between nanosheet interfaces and oligonucleotides is crucial for a high-sensing performance. Herein, the interface of ultrathin WS2 nanosheets used as a fluorescence quencher was engineered by four different dextran polymers in an aqueous solution to control the adsorption kinetics and thermodynamics of the DNA probe. The WS2 nanosheets, functionalized by the carboxyl group-bearing dextran (CM-dex-WS2) or the trimethylammonium-modified dextran (TMA-dex-WS2), exhibited 3.6-fold faster adsorption rates of the fluorescein-labeled DNA probe (FAM-DNA), which led to the effective fluorescence quenching of FAM, compared to the nanosheets functionalized with pristine dextran (dex-WS2) or the hydrophobic phenoxy groups-bearing dextran (PhO-dex-WS2). Isothermal titration calorimetry measurements showed that the adsorption strength of FAM-DNA for CM-dex-WS2 was one order of magnitude greater than its hybridization energy for a target microRNA (miR-29a) that is well-known as an Alzheimer's disease (AD) biomarker, leading to the unfavorable desorption of the DNA probe from the surface. In contrast, TMA-dex-WS2 exhibited the proper adsorption strength of FAM-DNA, which was lower than its hybridization energy for miR-29a, leading to its favorable desorption from the nanosheet surface along with the noticeable restoration of the quenched fluorescence after its hybridization with miR-29a. Finally, the interface modulation of WS2 nanosheets allowed the selective and sensitive recognition of miR-29a against non-complementary RNA and single base-mismatched RNA in human serum via increases in target-specific fluorescence.

Monitoring Plant Health with Near-Infrared Fluorescent H2O2 Nanosensors.

Near-infrared (nIR) fluorescent single-walled carbon nanotubes (SWCNTs) were designed and interfaced with leaves of Arabidopsis thaliana plants to report hydrogen peroxide (H2O2), a key signaling molecule associated with the onset of plant stress. The sensor nIR fluorescence response (>900 nm) is quenched by H2O2 with selectivity against other stress-associated signaling molecules and within the plant physiological range (10-100 H2O2 µM). In vivo remote nIR imaging of H2O2 sensors enabled optical monitoring of plant health in response to stresses including UV-B light (-11%), high light (-6%), and a pathogen-related peptide (flg22) (-10%), but not mechanical leaf wounding (<3%). The sensor's high biocompatibility was reflected on similar leaf cell death (<5%) and photosynthetic rates to controls without SWCNT. These optical nanosensors report early signs of stress and will improve our understanding of plant stress communication, provide novel tools for precision agriculture, and optimize the use of agrochemicals in the environment.

Tuning the response selectivity of graphene oxide fluorescence by organometallic complexation for neurotransmitter detection.

It is of great interest to design nanomaterial biosensors that can selectively detect target molecules without the use of fragile and expensive antibodies. Here, we report a chemical approach to modulate the response selectivity of graphene oxide (GO) fluorescence for neurotransmitters, in order to design an optical biosensor for the selective detection of dopamine without using antibodies. To this end, GO was functionalized with six different amino acids, followed by the immobilization of seven metal ions, resulting in the production of forty-two different GO nanohybrids (denoted GO-AA-MI derivatives). The fluorescence response of GO-AA-MI derivatives to dopamine, norepinephrine, and epinephrine was modulated by varying the type of amino acids and metal ions introduced. Tyrosine-modified GO with Fe2+ ions (GO-Y-Fe) exhibited selective quenching of its fluorescence in the presence of dopamine whereas lysine-modified GO with Au3+ ions (GO-K-Au) showed a selective increase in fluorescence upon addition of norepinephrine. The GO-Y-Fe sensor developed was able to differentiate dopamine from similar structures of norepinephrine and epinephrine, as well as abundant interferents such as ascorbic acid and uric acid, without the use of antibodies. In addition, the GO-Y-Fe sensor successfully detected dopamine secreted from living neuron cells in a rapid and simple manner.