Single-layer Graphene Oxide Research Articles

Single-layer graphene oxide nanosheets induce proliferation and Osteogenesis of single-cell hBMSCs encapsulated in Alginate Microgels

Microfluidics cell encapsulation offers a way to mimic a 3D microenvironment that supports cell growth and proliferation, while also protecting cells from environmental stress. This technique has found extensive applications in tissue engineering and cell therapies. Several studies have demonstrated the advantages of graphene oxide (GO) as an osteogenic inducer; however, the significance of GO on stem cell fate in the single-cell state is still unclear. Here, a microfluidics-based approach is developed for continuous encapsulation of mesenchymal stem cells (MSCs) at the single-cell level using alginate microgels. So, single-layer graphene oxide (slGO) nanosheet is used to be encapsulated inside the alginate droplets. The results of AFM and SEM show that slGO can increase the roughness and reduce the stiffness of alginate hydrogels. The Young’s modulus of the alginate and alginate-slGO was obtained as 1414 kPa and 985.9 kPa, respectively. Live/dead assay and fluorescence microscopy images illustrate that slGO can maintain the viability and proliferation of microencapsulated hBMSCs. The obtained results show that slGO increases the mineralization of the encapsulated hBMSCs, so that microgels containing hBMSCs gradually became opaque during 21 days of culture. RT-qPCR results indicate that the expression of OCN, Runx2, and ALP in the alginate-slGO microgels is significantly higher than in the alginate microgels. The expression of OCN and Runx2 in the alginate-slGO microgels is 4.27 and 5.87-fold higher than in the alginate microgels, respectively. It can be concluded that low doses of slGO nanosheets have the potential to be utilized in the development of tissue engineering and bone regeneration. This finding offers a new method for creating injectable tissue transplants that are minimally invasive.

Construction of fluorescent aptasensor based on graphene oxide for the detection of metronidazole in food

Aiming at the detection of metronidazole (MNZ) residues in food, a high sensitivity fluorescent aptasensor was designed, which carboxyfluorescein (FAM)-labeled nucleic acid aptamer (FAM-MNZ) as the core probe and graphene oxide (GO) as an efficient fluorescence quencher. The principle is that GO adsorbs the aptamer onto the surface, causing short-range contact between the fluorescent group of the aptamer and GO. Due to its sp2 hybridized domains, GO undergoes fluorescence resonance energy transfer (FRET). Thus, the fluorescence is quenched. When MNZ is added, it preferentially forms a stable complex with the aptamer without FRET. Under optimized conditions, milk samples can be accurately detected with a detection limit of 0.033 μM. In addition, molecular docking, lumo electron orbital simulations, and experimental methods were used to explore the effect of different average radial sizes of single-layer GO on sensing performance. It is shown that GO with a larger average size makes it easy for aptamers to be regularly arranged on its surface. This also provides a basis for electron transfer, resulting in higher fluorescence quenching ability through the FRET mechanism. Therefore, the constructed fluorescent aptamer sensor has a significant application value in food detection.

Regulating the microstructure and hydrophilicity of cellulose nanofibers using taurine and the application in humidity sensor and actuator

Exploring the interrelationships between microstructure, hydrophilicity, humidity response, and material stability through molecular structure design and low-cost preparation, and manufacturing sensing and driving materials with a perfect balance between structures and properties is crucial for biomimetic robots and intelligent devices. Herein, inspired by the capillary phenomenon, the cellulose nanofiber (CNF) was grafted by using taurine to form the “micro cilia” microstructure on its surface (CNF-TAU). By controlling the cilia density and symmetry, the hydrophilicity of the materials was adjusted, and the water was allowed to quickly separate from the inside of the materials, which led to improving the humidity sensitivity and stability of materials. Concretely, compared with CNF, the puncture load, tearing strength, and elongation at break of the CNF-TAU-1.0 were improved by 11.95 times, 2.16 times, and 15.6 %, respectively, and excellent tensile strength was presented. Moreover, the hydrophilicity of CNF-TAU was first weakened and then enhanced with TAU content increasing. At last, the CNF-TAU-1.0 (WCA 55.43°) was selected and blended with single-layer graphene oxide (GO) to prepare CNF-TAU/GO composite films by vacuum filtration. The results indicated that the composite film had excellent mechanical (room and high humidity), humidity responsiveness, and humidity gradient-driven properties. In detail, the CNF-TAU/GO-10 % composite film had the generated stable induced voltage (68.4 mV), the fast response/recovery time (0.3 s/0.9 s), the large max. bending angle (178.4°), and the drive cycle stability (1000 cycles). Moreover, the composite film could be applied to produce biomimetic soft robots, such as human fingers and butterfly-shaped robots.

Strong flexible conductive hydrogel based on adaptive temperature and humidity characteristics

The development of conductive hydrogels has attracted great attention due to their broad applications. In this work, based on a dual-network structure, a highly flexible and adaptive conductive hydrogel has been developed, using the catalytic polymerization method, which also obtains Poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT: PSS). Upon environmental warming, the double-network-structured hydrogel featuring a LiBr solution (LiBr@PAM-SA) undergoes a gradual water loss. However, significant moisture depletion occurs only when the temperature reaches 180 °C. Notably, compared to hydrogels devoid of a LiBr solution that experiences dehydration at 120 °C, LiBr@PAM-SA hydrogels manifest a superior capacity for adapting to varying environmental temperatures. Furthermore, this hydrogel maintains 90% of its inherent conductivity after undergoing 1000 cycles of stretching and compression. Upon incorporating 1 wt% PEDOT: PSS, the conductive hydrogel (LiBr@PAM-SA) displays the smallest volume resistivity of 0.022 Ω-cm and the highest volume conductivity of 44.665 µS/cm, in comparison to the hydrogels of single-layer graphene oxide (SLGO) and AgNWs. Additionally, its light transmittance and hydrogel quality improve in environments with lower temperatures or higher humidity. Finally, this conductive hydrogel might show great potential in varied fields of dynamic environment monitoring, intelligent conductive transmission, and intelligent sensing identification.

Evaluating the Impact of Sonication Process on Graphene Oxide Structural Properties

Graphene oxide (GO) is one of the members of carbon-based nanomaterials and can be featured as graphene structure decorated with various oxygenated functional groups. Recently, various methods have been found for producing carbon-based nanomaterials with enhanced efficiency in several applications. The chemical process involves oxidizing graphite to GO using a powerful oxidizing chemical. Hummers method is one of the most known and versatile method for the production of GO nanomaterials because of its ease of application, parameter controllability and high yield. This process enables graphite oxidation and exfoliation into single- or multi-layered GO sheets. Exfoliation, the separation of graphene or graphitic layers, is a critical process in GO synthesis. Since exfoliation separates multilayered graphite oxide flakes or particles, it forms single layer GO by forcing oxidizing agents or solvent molecules between layers. The sonication process can exfoliate the oxidized layers, resulting in the formation of GO structure when the exfoliated layers consist of only one or a few layers of carbon atoms. Therefore, sonication procedure is among the key parameters of Hummers method that influences the characteristics of GO-based nanomaterials. In this study, the impact of sonication duration time and power parameters on morphological and structural characteristics of GO development was examined. For this purpose, characterization studies were performed by using Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and Raman spectroscopy analysis. The findings revealed that the increase in sonication power and time led to an increase in defects in the resulting GO structure.

Enhancing Radiosensitization of Non-Small Cell Lung Cancer with Graphene Oxide@AgPt Nanocomposites: A Bioinformatics Study

In this study, we employed bioinformatics techniques to investigate the radiosensitization mechanisms of graphene oxide (GO) and silver-platinum (AgPt) nanocomposites (NCs) on microRNAs (miRNAs) in non-small cell lung cancer (NSCLC). The GO@AgPt nanocomposites were synthesized through a hydrothermal method involving graphene oxide. Characterization and structural analysis were performed using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Our experimental model was A549 cells, categorized into three groups: the blank group, control group, and GO@AgPt group. The blank group remained untreated, while the control group was exposed to 4Gy X-ray irradiation. The GO@AgPt group received 15 μg/mL GO@AgPt for 4 hours before exposure to 4Gy X-ray irradiation. Cellular RNA was extracted from each group, and a transcriptome sequencing library was constructed. Subsequent analysis identified differential genes, followed by gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway assessments. Our results revealed the uniform attachment of AgPt spherical nanoparticles (NPs) with an approximate diameter of 10 nm to the GO surface. The GO@AgPt nanocomposites comprised four single-layer GO sheets, each approximately 4 nm in thickness, with the Ag peak area being about six times that of the Pt peak area. A total of 197 miRNAs exhibited differential expression between the GO@AgPt and control groups, with 94 up-regulated and 103 down-regulatedmiRNAs. These miRNAs were associated with biological processes such as positive regulation of gene expression, cell surface interactions, and growth factor binding. Furthermore, they were implicated in various pathways, including microRNAs in cancer, fatty acid metabolism, human T-cell leukemia virus 1 infection, FoxO signaling, and alcoholic liver disease. Our findings demonstrate that GO@AgPt nanocomposites enhance the radio-sensitization effect in NSCLC, with 197 differentialmiRNAs participating in the process.

On-Site Fluorescent Detection of Sepsis-Inducing Bacteria using a Graphene-Oxide CRISPR-Cas12a (GO-CRISPR) System.

Sepsis is an extremely dangerous medical condition that emanates from the body's response to a pre-existing infection. Early detection of sepsis-inducing bacterial infections can greatly enhance the treatment process and potentially prevent the onset of sepsis. However, current point-of-care (POC) sensors are often complex and costly or lack the ideal sensitivity for effective bacterial detection. Therefore, it is crucial to develop rapid and sensitive biosensors for the on-site detection of sepsis-inducing bacteria. Herein, we developed a graphene oxide CRISPR-Cas12a (GO-CRISPR) biosensor for the detection of sepsis-inducing bacteria in human serum. In this strategy, single-stranded (ssDNA) FAM probes were quenched with single-layer graphene oxide (GO). Target-activated Cas12a trans-cleavage was utilized for the degradation of the ssDNA probes, detaching the short ssDNA probes from GO and recovering the fluorescent signals. Under optimal conditions, we employed our GO-CRISPR system for the detection of Salmonella Typhimurium (S. Typhimurium) with a detection sensitivity of as low as 3 × 103 CFU/mL in human serum, as well as a good detection specificity toward other competing bacteria. In addition, the GO-CRISPR biosensor exhibited excellent sensitivity to the detection of S. Typhimurium in spiked human serum. The GO-CRISPR system offers superior rapidity for the detection of sepsis-inducing bacteria and has the potential to enhance the early detection of bacterial infections in resource-limited settings, expediting the response for patients at risk of sepsis.

Quantifying defects in graphene oxide structures

Oxidation of graphite and subsequent exfoliation leads to single layer graphene oxide (GO). One of the key structural features of GO is the presence of different kinds of defects that dictates their various physical and chemical properties. Molecular dynamics simulations with ReaxFF force fields have been widely used to generate realistic models of GO. In these simulations, the extent and distribution of the defects are varied by changing the initial oxygen (O)/carbon (C) ratio while the defect density is often measured by the total number of non-graphitic carbon (non-gC) atoms. Our calculations suggest that this parameter overestimates the defect densities at low O/C ratio. Herein, we employ the relative area of the defects as an alternative metric to gauge the defect density. Being exclusive to the defects and sensitive to the structural irregularities, this metric works well at both low and high defect densities. In another example, we consider the reduction of GO to reduced graphene oxide (rGO) for different O/C ratios, where the decrease in the number of non-gC atoms is associated with the formation of comparatively larger defects. Hence, it is unclear whether the extent of reduction in the defect density (if at all) should vary monotonically with the O/C ratio. The defect area, unlike the count of the non-gC atoms, mirrors this ambiguity and the change with respect to O/C ratio is not strictly monotonic. Additionally, we also investigate the dependence of the defect distribution and defect area on the size of the simulation cell.

Establishing Exceptional Durability in Ultralow-Temperature Organic-Sodium Batteries via Stabilized Multiphase Conversions.

Operation of rechargeable batteries at ultralow temperature is a significant practical problem because of poor kinetics of the electrode. Here, we report for the first time stabilized multiphase conversions for fast kinetics and long-term durability in ultralow-temperature, organic-sodium batteries. We establish that disodium rhodizonate organic electrode in conjunction with single-layer graphene oxide obviates consumption of organic radical intermediates, and demonstrate as a result that the newly designed organic electrode exhibits excellent electrochemical performance of a highly significant capacity of 130 mAh g-1 at -50 °C. We evidence that the full-cell configuration coupled with Prussian blue analogues exhibits exceptional cycling stability of >7000 cycles at -40 °C while maintaining a discharge capacity of 101 mAh g-1 at a high current density 300 mA g-1. We show this is among the best reported ultralow-temperature performance for nonaqueous batteries, and importantly, the pouch cell exhibits a continuous power supply despite conditions of -50 °C. This work sheds light on the distinct energy storage characteristics of organic electrode and opens up new avenues for the development of reliable and sustainable ultralow-temperature batteries.

Rapid-response humidity sensors based on ultra-thin films stacked with single-layer graphene oxide

Monitoring and control of humidity is important for industry, agriculture and human activities. Currently, it is achallengeto develop highly sensitive humidity sensors with both the response time and recovery time less than 1 s.Therefore, it isdifficult to dynamically monitor rapid changes in humidity. Here, we report a resistive humidity sensor based on an ultrathin graphene oxide (GO) film, which is formed by stacked single-layered GO. Both the response and recovery time of the sensor is less than 1 s in the range of 10 %–95 % relative humidity (RH). The shortest response and recovery time of the reported GO-based resistive humidity sensor can be 0.33 s at 10 % RH, indicating the fastest response and recovery property to date. Moreover, the sensor is sensitive, and it can accurately detect the distance between the sensor and the human finger as well as the strength of the human breath. The simple preparation, microscale structure, and extremely fast response make the GO-based sensor a new alternative for integrated humidity sensors with real-time monitoring functions.

Facile Synthesis of Mesoporous Nanohybrid Two-Dimensional Layered Ni-Cr-S and Reduced Graphene Oxide for High-Performance Hybrid Supercapacitors.

This study describes the single-step synthesis of a mesoporous layered nickel-chromium-sulfide (NCS) and its hybridization with single-layered graphene oxide (GO) using a facile, inexpensive chemical method. The conductive GO plays a critical role in improving the physicochemical and electrochemical properties of hybridized NCS/reduced GO (NCSG) materials. The optimized mesoporous nanohybrid NCSG is obtained when hybridized with 20% GO, and this material exhibits a very high specific surface area of 685.84 m2/g compared to 149.37 m2/g for bare NCS, and the pore diameters are 15.81 and 13.85 nm, respectively. The three-fold superior specific capacity of this optimal NCSG (1932 C/g) is demonstrated over NCS (676 C/g) at a current density of 2 A/g. A fabricated hybrid supercapacitor (HSC) reveals a maximum specific capacity of 224 C/g at a 5 A/g current density. The HSC reached an outstanding energy density of 105 Wh/kg with a maximum power density of 11,250 W/kg. A 4% decrement was observed during the cyclic stability study of the HSC over 5000 successive charge-discharge cycles at a 10 A/g current density. These results suggest that the prepared nanohybrid NCSG is an excellent cathode material for gaining a high energy density in an HSC.

A sensitive single-layered graphene oxide-based sensor for electrochemical sensing of phosphate anion

In recent years, the electrochemical determination of phosphate anion in aqueous solution has attracted widespread interest because of its potential to address the environmental, economic and health concerns associated with phosphate management protocol. Herein, we report a direct electrochemical approach to identify phosphates using a special architecture of single-layered graphene oxide (SLGO) with abundant oxygen-containing surface functional groups. The electrochemical adsorption of phosphate onto SLGO was confirmed by X-ray photoelectron spectroscopy (XPS), and the formation of covalent bonds between phosphorus and carbon atoms occurred through the partial conversion of C-O covalent bonds to C-O semi-ionic bonds, which was beneficial to the electrochemical performances of phosphate at SLGO. The electrochemical adsorption of phosphates at other carbon nanomaterials modified glassy carbon electrodes (GCE) and bare GCE was also carried out. Further characterization by XPS, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) revealed the electrochemical mechanism of SLGO/GCE toward phosphates. Under the optimized conditions, the concentration of phosphate was linearly related to the peak current in the range of 10.0–100.0 μM with limit of detection (LOD) of 2.0 μM (S/N = 3). More importantly, SLGO/GCE could be further extended to the quantitative detection of phosphate in industrial wastewater and human serum with acceptable recoveries (95.09–103.48%). This research could provide an effective method for the detection of trace phosphates in environmental media as well as physiological media.

Falling-Leaves Stacking Aggregation of Two-Dimensional Macromolecular Graphene Oxide in Solution.

Understanding the dynamical behaviors of two-dimensional (2D) macromolecules is of fundamental importance for the precise modulation of their assembled structures and material performances. However, considerably less is known about how discrete macromolecular sheets aggregate into extended macroscopic assemblies in solutions. The absence of a quantitative description of the assembly process limits the precise structural control of assemblies. Here, we investigated the aggregation thermodynamic transition and kinetic behavior of 2D macromolecules in the model of single layer graphene oxide (GO). Combining Flory-Huggins theory with experimental observations, we unveiled the critical thermodynamic transition of GO to correlate with the solvent property. We proposed a theoretical falling-leaf model to quantitatively describe the kinetic aggregation process of 2D GO sheets. Experimental analysis validated the theoretical prediction that the thickness of GO aggregates has a power law relation with the poor solvent content. Our work provides a fundamental understanding of phase separation of 2D macromolecules and offers an insight into modulating the aggregated structures of their assembled materials.

Facile recyclable process of high-quality single layer graphene oxide via waste graphite anode scrap

Here we report a facile reusable method for graphene oxide (GO) from the oxidation of waste graphite anode scrap (WGAS), which was synthesized by Couette–Taylor flow reactor. The toroidal motion of fluids generated by the mechanical and structural specificity of the reactor increased the intercalation rate and oxidation efficiency of the WGAS, resulting in high production yield (95 ± 1%) of GO within 90 min reaction time. In addition, the as-synthesized GO nanosheets were extensively characterized using a variety of techniques, which allowed the identification of two-dimensional monolayers (∼1.3 nm) and successfully functionalized high-quality graphene oxides. Our approach of the high-efficiency oxidation and exfoliation of recycled GO with WGAS may find potential application in numerous industrial fields, such as catalysis and electrodes in energy conversion and storage systems, and conductive materials in electronic devices.

Environment-adaptable PAM/CMC semi-IPN hydrogels microspheres with high latent heat achieved through dual locking water strategy

Polyacrylamide (PAM) hydrogel is easy to prepare and has been widely used in industrial and biomedical fields. But its mechanical properties and environmental adaptability are very poor. In this work, by introducing carboxymethyl cellulose (CMC) into the PAM crosslink network, a semi-interpenetrating (semi-IPN) network structure was constructed to improve the mechanical properties of PAM hydrogels. PAM/CMC hydrogel microspheres (HMPs) with semi-IPN structure were successfully prepared by in-situ precipitation droplet crosslinking polymerization (PDIC). On this basis, a double locking water strategy was proposed and achieved: firstly, lithium chloride (LiCl) was introduced into PAM/CMC hydrogel to retain the internal water; secondly, the PAM/CMC HMPs were coated with single layer graphene oxide (GO) to restrain the loss of free water on the HMPs surfaces. The morphology, the state of water in HMPs, the compression performance, phase transition behavior and heat transfer performance of the GO coated PAM/CMC/LiCl HMPs (GO@HMPs) were further studied. The experimental results showed that the CMC could effectively improve the compression performance of PAM HMPs, and the PAM/CMC HMPs had also good compression recovery performance. The anti-dehydration performance of PAM/CMC HMPs was effectively improved by the double locking water strategy. The latent heat of GO@HMPs was higher than that of the current commercial phase change microsphere materials. The GO@HMPs had excellent heat absorption ability and were expected to be used in infrared stealth and thermal camouflage fields.

Poly(2-hydroxyethyl methacrylate) hydrogels containing graphene-based materials for blood-contact applications: from soft inert to strong degradable material.

Degradable biomaterials for blood-contacting devices (BCDs) are associated with weak mechanical properties, high molecular weight of the degradation products and poor hemocompatibility. Herein, the inert and biocompatible FDA approved poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel was turned into a degradable material by incorporation of different amounts of a hydrolytically labile crosslinking agent, pentaerythritol tetrakis(3-mercaptopropionate). In situ addition of 1wt.% of oxidized graphene-based materials (GBMs) with different lateral sizes/thicknesses (single-layer graphene oxide, and oxidized forms of few-layer graphene materials) was performed to enhance the mechanical properties of hydrogels. An ultimate tensile strength increases up to 0.2 MPa (293% higher than degradable pHEMA) was obtained using oxidized few-layer graphene with 5 μm lateral size. Moreover, the incorporation of GBMs has demonstrated to simultaneously tune the degradation time, which ranged from 2 to 4 months. Notably, these features were achieved keeping not only the intrinsic properties of inert pHEMA regarding water uptake, wettability and cytocompatibility (short and long term), but also the non-fouling behavior towards human cells, platelets and bacteria. This new pHEMA hydrogel with degradation and biomechanical performance tuned by GBMs, can therefore be envisioned for different applications in tissue engineering, particularly for BCDs where non-fouling character is essential. STATEMENT OF SIGNIFICANCE: Suitable mechanical properties, low molecular weight of the degradation products and hemocompatibility are key features in degradable blood contacting devices (BCDs), and pave the way for significant improvement in the field. In here, a hydrogel with outstanding anti-adhesiveness (pHEMA) provides hemocompatibility, the presence of a degradable crosslinker provides degradability, and incorporation of graphene oxide reestablishes its strength, allowing tuning of both degradation and mechanical properties. Notably, these hydrogels simultaneously provide suitable water uptake, wettability, cytocompatibility (short and long term), no acute inflammatory response, and non-fouling behavior towards endothelial cells, platelets and bacteria. Such results highlight the potential of these hydrogels to be envisioned for applications in tissue engineered BCDs, namely as small diameter vascular grafts.

Tuning Structural Defects on a Nominal Single-Layered Graphene Oxide Membrane for Selective Separation of Biomolecules.

Two-dimensional (2D) materials provide a great opportunity for fabricating ideal membranes with ultrathin thickness for high-throughput separation. Graphene oxide (GO), owing to its hydrophilicity and functionality, has been extensively studied for membrane applications. However, fabrication of single-layered GO-based membranes utilizing structural defects for molecular permeation is still a great challenge. Optimization of the deposition methodology of GO flakes could offer a potential solution for fabricating desired nominal single-layered (NSL) membranes that can offer a dominant and controllable flow through structural defects of GO. In this study, a sequential coating methodology was adopted for depositing a NSL GO membrane, which is expected to have no or minimum stacking of GO flakes and thus ensure GO's structural defects as the major transport pathway. We have demonstrated effective rejection of different model proteins (bovine serum albumin (BSA), lysozyme, and immunoglobulin G (IgG)) by tuning the structural defect size via oxygen plasma etching. By generating appropriate structural defects, similar-sized proteins (myoglobin and lysozyme; molecular weight ratio (MWR): ∼1.14) were effectively separated with a separation factor of ∼6 and purity of 92%. These findings may provide new opportunities of using GO flakes for fabricating NSL membranes with tunable pores for applications in the biotechnology industry.

High-velocity transverse impact of monolayer graphene oxide by a molecular dynamics study

2D materials have attracted tremendous attention recently due to their unique characteristic under extreme loading conditions such as impact. Owing to its exceptional mechanical properties and low cost of processing, graphene oxide (GO), which is a 2D amorphous material, has been widely utilized as a nanocomposite building block under such loading conditions. To date, extensive researches have been conducted to unravel the chemistry-dependent mechanical properties of GO. Nonetheless, high-velocity impact characterization of single-layer GO received less attention. Therefore, the aforementioned problem is investigated using ReaxFF molecular dynamics simulations in this work. Accordingly, the penetration-resistance of single-layer GO with different oxidation levels under nano-projectile impact is assessed. It is found that (a) as oxidation level increases the onset of complete perforation velocity decreases, (b) penetration-resistance is influenced by hydroxyl-to-epoxide ratio for a fixed oxidation level, and (c) spatial distribution of oxygen functional groups alters the perforation-resistance of a monolayer for the same oxidation level. The findings of this study may provide some insights into the design of surface coatings and novel protective barriers in which GO is used as reinforcement nanofillers.

The nitrate uptake and growth of wheat were more inhibited under single-layer graphene oxide stress compared to multi-layer graphene oxide

Although the phytotoxicity of graphene-based materials has been investigated extensively, the effects of different graphene-based materials on nutrient uptake in plants remain unclear. Here, we analyzed the differences in phytotoxicity between single-layer graphene oxide (sGO) and multi-layer graphene oxide (mGO) by analyzing the growth status and nitrate (NO3–) accumulation in wheat plants at 0, 100, 200, 400, and 800 mg L−1 graphene oxide supply. Both sGO and mGO displayed concentration-dependent inhibitory effects on biomass, root length, number of lateral roots, and nitrogen (N) nutrient status. Treatment with 400 mg L−1 sGO caused 0.9-, 1.3-, and 1-fold higher reductions in NO3–-N, assimilated N, and total N concentrations in roots, respectively, than mGO treatment. Analysis of root oxidative stress and in situ NO3– uptake revealed that sGO caused more significant damage to the root tip and a lower NO3– net influx rate than mGO. In addition, the expression of NO3– transporter (NRT) genes in roots, including NRT1.5, NRT2.1, NRT2.2, NRT2.3, and NRT2.4, under sGO treatment were lower than those under mGO treatment. Overall, sGO treatment induced a more severe inhibitory effect on root growth and NO3– uptake and accumulation than mGO treatment, accompanied by significant suppression of the expression of NRTs in sGO-treated roots. This study provides a physiological and molecular basis for studying the phytotoxic effects of various sizes of graphene oxide.

Composite PVK/SLGO As Matrix for MALDI-TOF MS Detection of Small Molecules in Dual-Ion Mode.

Currently, most matrices developed for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) for small-molecule detection are only suitable for the positive or negative ion mode and not the dual-ion mode, except for carbon-based nanomaterials. The lone-pair electrons on the N atom in poly n-vinylcarbazole (PVK) can serve as a Lewis base with strong electron-donation effects, which is favorable for negative ion mode detection. The surface of single-layer graphene oxide (SLGO) contains many oxygen atoms in carboxyl and hydroxyl groups that act as Lewis acids and thereby provides favorable protonation sites for positive ion mode detection. In this study, composite PVK/SLGO was prepared by combining the advantages of amorphous PVK and SLGO. PVK/SLGO was tested as a novel matrix for positive- and negative-ion-mode MALDI-TOF MS for the analysis of amino acids, nucleic acid bases, environmental endocrine disruptors, antibiotics, and various small molecules. PVK/SLGO was compared with PVK, SLGO, and commercially available matrices of 9-aminoacridine (9-AA) and α-cyano-4-hydroxycinnamic acid (CHCA). The PVK/SLGO matrix was demonstrated to be suitable for the positive and negative ion modes, exhibiting high signal intensity and detection sensitivity without background interference. The limits of detection of the aforementioned molecules ranged from 0.1 to 0.0001 and 0.01 to 0.0001 mg/mL in the positive and negative ion modes, respectively. The quantitative determination of enrofloxacin in milk was realized using an internal standard method with a linear range of 0.0001-0.1 mg/mL (R 2 = 0.9991). Furthermore, the PVK/SLGO matrix exhibited high salt tolerance (up to 1000 mmol/L) and stability over 28 consecutive days. Studies regarding its ionization mechanism revealed that the good performance originates from the combined materials acting synergistically. This study provides a foundation for developing bimodal composite matrices and further expands the scope of PVK/SLGO applications.