Monodispersed and spherical silver nanoparticles/graphene nanocomposites from gamma-ray assisted in-situ synthesis for nitrite electrochemical sensing

Carbon Nanomaterials-Based Novel Hybrid Platforms for Electrochemical Sensor Applications in Drug Analysis

Nowadays, the rapid improvements in the medical and pharmaceutical fields increase the diversity and use of drugs. However, problems such as the use of multiple or combined drugs in the treatment of diseases and insensible use of over-the-counter drugs have caused concerns about the side-effect profiles and therapeutic ranges of drugs and environmental contamination and pollution problems due to pharmaceuticals waste. Therefore, the analysis of drugs in various media such as biological, pharmaceutical, and environmental samples is an important topic of discussion. Electrochemical methods are advantageous for sensor applications due to their easy application, low cost, versatility, high sensitivity, and environmentally-friendliness. Carbon nanomaterials such as diamond-like carbon thin films, carbon nanotubes, carbon nanofibers, graphene oxide, and nanodiamonds are used to enhance the performance of the electrochemical sensors with catalytic effects. To further improve this effect, it is aimed to create hybrid platforms by using different carbon nanomaterials together or with materials such as conductive polymers and ionic liquids. In this review, the most used carbon nanoforms will be evaluated in terms of electrochemical characterizations and physicochemical properties. Furthermore, the effect of hybrid platforms developed in the most recent studies on electrochemical sensors will be examined and evaluated in terms of drug analysis studies in the last five years.

Technical Evaluation of a Paper-Based Electrochemical Strip to Measure Nitrite Ions in the Forensic Field

Nitrite is a compound used as a food additive for its preservative action and coloring capability, as well as an industrial agent for its antifreezing action and for preventing corrosion, and it is also used as a pharmaceutical in cyanide detoxification therapy. However, even recently, because of its high toxicity, it has been used as a murder and suicidal agent due to its affordability and ready availability. In this technical report, we describe an electrochemical paper-based device for selectively determining nitrite in complex biofluids, such as blood, cadaveric blood, vitreous humor, serum, plasma, and urine. The approach was validated in terms of the linearity of response, selectivity, and sensitivity, and the accuracy of the determination was verified by comparing the results with a chromatographic instrumental method. A linear response was observed in the micromolar range; the sensitivity of the method expressed as the limit of detection was 0.4 μM in buffer measurements. The simplicity of use, the portability of the device, and the performance shown make the approach suitable for detecting nitrite in complex biofluids, including contexts of forensic interest, such as murders or suicides in which nitrite is used as a toxic agent. Limits of detection of ca. 1, 2, 4, 5, 3, and 4 μM were obtained in vitreous humor, urine, serum and plasma, blood, and cadaveric blood, also highlighting a satisfactory accuracy comprised between 91 and 112%.

A simple nanocomposite photocatalyst HT-rGO/TiO2 for deoxynivalenol degradation in liquid food

A simple nanocomposite photocatalyst HT-rGO/TiO₂ for deoxynivalenol (DON) degradation was synthesized by hydrothermal method to maintain the quality of cereal grains and byproducts. The characterization of HT-rGO/TiO₂ was analyzed by XRD, FTIR, Raman spectroscopy, and XPS. Moreover, according to UV-vis DRS analysis, HT-rGO/TiO₂ had a smaller band gap, indicating a wider response range to light and a higher utilized rate of quantum photons. Additionally, the results of LC-MS showed that the hydroxyl group at the C3 position, and the unsaturated bond between C9 and C10, and the epoxy group at C12 and C13 positions of DON molecule were destroyed step by step by photocatalytic degradation. These groups have active effects on the DON toxicity, which means it is successful to degrade DON in liquid-food by HT-rGO/TiO₂ photocatalyst.

Using an ionomer as a size regulator in γ-radiation induced synthesis of Ag nanocatalysts for oxygen reduction reaction in alkaline solution

Ag nanoparticles (Ag NPs) are among the most promising candidates to replace Pt as the catalyst for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). However, synthesizing size-controlled Ag NPs with efficient catalytic performance is still challenging. Herein, uniform Ag NPs are produced through a γ-radiation induced synthesis route in aqueous solutions, using the ionomer PTPipQ100 as both an efficient size regulator in the synthesis and a conductor of hydroxide ions during the ORR process. The origin of the size control is mainly attributed to the affinity of the ionomer to metallic silver. The resulting Ag NPs covered with ionomer layers can be applied as model catalysts for ORR. The nanoparticles that were prepared using 320 ppm ionomer in the reaction solution turned out to be coated with a ∼ 1 nm thick ionomer layer and exhibited superior ORR activity as compared to other Ag NPs of similar size studied here. The improved electrocatalytic performance can be attributed to the optimal ionomer coverage that enables fast oxygen diffusion, as well as interactions at the Ag-ionomer interface which promote the desorption of OH intermediates from the Ag surface. This work demonstrates the advantage of using an ionomer as the capping agent to produce efficient ORR catalysts.

The Role of Silver Nanoparticles in Electrochemical Sensors for Aquatic Environmental Analysis

With rapidly increasing environmental pollution, there is an urgent need for the development of fast, low-cost, and effective sensing devices for the detection of various organic and inorganic substances. Silver nanoparticles (AgNPs) are well known for their superior optoelectronic and physicochemical properties, and have, therefore, attracted a great deal of interest in the sensor arena. The introduction of AgNPs onto the surface of two-dimensional (2D) structures, incorporation into conductive polymers, or within three-dimensional (3D) nanohybrid architectures is a common strategy to fabricate novel platforms with improved chemical and physical properties for analyte sensing. In the first section of this review, the main wet chemical reduction approaches for the successful synthesis of functional AgNPs for electrochemical sensing applications are discussed. Then, a brief section on the sensing principles of voltammetric and amperometric sensors is given. The current utilization of silver nanoparticles and silver-based composite nanomaterials for the fabrication of voltammetric and amperometric sensors as novel platforms for the detection of environmental pollutants in water matrices is summarized. Finally, the current challenges and future directions for the nanosilver-based electrochemical sensing of environmental pollutants are outlined.

The impact of silver nanoclay functionalisation on optical and electrochemical properties

Three different fractions of nanoclay (nanomer 1.44P) were functionalised with Ag forming silver nanoclay composites (Ag/nanomer 1.44P). The optical and electrochemical properties of the functionalised nanoclay were studied. Optical, morphology, and electrochemical techniques were used for the characterisation of the synthesised Ag/nanomer 1.44P nanocly composites. The presence and the absence of functional groups observed in the FTIR spectrum of Ag/nanomer 1.44P, compared with those found in the spectra of silver and pure nanomer 1.44P prove that a reaction occurred, thus a successful functionalisation of nanomer 1.44P nanoclay with silver. The XRD data of all composites showed four diffraction peaks within the silver spectrum range, with the intensity of silver decreasing with increasing concentration of nanomer 1.44P. SEM represented well-dispersed particles of different shapes with average particle sizes of 2.5, 27.5, and 5 nm with the enhanced concentration of nanomer 1.44P nanoclay. The decrease in diffusion coefficient values from 4.26 × 10^-10, 2.50 × 10^-13 , 1.40 × 10^-13 cm² s^-1 and electron transfer rates of 1.50 × 10^-5, 3.94 × 10^-7, 2.86 × 10^-7 cm s^-1 are respectively proportional to an increase in nanomer 1.44P concentration depicting changes in nanocomposites sizes.

A Novel Highly Sensitive Electrochemical Nitrite Sensor Based on a AuNPs/CS/Ti3C2 Nanocomposite

Nitrite is common inorganic poison, which widely exists in various water bodies and seriously endangers human health. Therefore, it is very necessary to develop a fast and online method for the detection of nitrite. In this paper, we prepared an electrochemical sensor for highly sensitive and selective detection of nitrite, based on AuNPs/CS/MXene nanocomposite. The characterization of the nanocomposite was demonstrated by scanning electron microscopy (SEM), a transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the fabricated electrode showed good performance with the linear range of 0.5–335.5 μM and 335.5–3355 μM, the limit of detection is 69 nM, and the sensitivity is 517.8 and 403.2 μA mM⁻¹ cm⁻². The fabricated sensors also show good anti-interference ability, repeatability, and stability, and have the potential for application in real samples.

Reduce and concentrate graphene quantum dot size via scissors: vacancy, pentagon-heptagon and interstitial defects in graphite by gamma rays

Graphene quantum dots (GQDs) with ultrafine particle size and centralized distribution have advantages of small size, narrow size distribution and large specific surface area, which make it be better applied in bioimaging, drug delivery and so on. In our research, we used graphite irradiated byγ-rays to successfully prepare GQDs with ultrafine particle size, narrow size distribution and high quantum yields through solvothermal method. Vacancy defects, pentagon-heptagon defects and interstitial defects were introduced to graphite structure after irradiation, which caused the abundance and concentrated distribution of defects. The defects generated by irradiation could damage the lattice structure of graphite to make it easy for introduction of C-O-C inside graphite sheets. The oxygen-containing functional groups in graphene oxide (GO) increased and centrally distributed after irradiation in graphite, especially for C-O-C group, which were beneficial for cutting of GO and grafting of functional groups in GQDs. Therefore, average size of GQDs was successfully reduced to 1.43 nm and concentrated to 0.6-2.4 nm. After irradiation in graphite, the content of carbonyl and C-N in GQDs had a promotion, which suppressed non-radiative recombination and upgraded the quantum yields to 13.9%.

Efficient and Recyclable Heterogeneous Catalyst Based on PdNPs Stabilized on a Green-Synthesized Graphene-like Nanomaterial: Effect of Surface Functionalization

This work reports for the first time a straightforward and efficient approach to covalent surface functionalization of a sustainable graphene-like nanomaterial with abundant carboxylic acid groups. This approach results in an efficient and robust chelatant platform for anchoring highly dispersed ultrasmall palladium particles with excellent catalytic activity in the reduction of both cationic (methylene blue, MB) and anionic (eosin-Y, Eo-Y) toxic organic dyes. The large-specific-surface-area (S_BET = 266.94 m²/g) graphene-like nanomaterial (GHN) was prepared through a green and cost-effective pyrolysis process from saccharose using layered bentonite clay as a template. To introduce a high density of carboxylic acid functions, GHN was first doubly functionalized by successive grafting reaction using two different strategies: (i) in the first case, GHN was first grafted by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and then bifunctionalized by chemical grafting of tris(4-hydroxyphenyl)methane triglycidyl ether (TGE). In the second case, the grafting order of the two molecules has been reversed. GHN-GPTMS-TGE provided the highest number of grafted reactive epoxy groups, and it was selected for further functionalization with carboxylic acid functions via a ring-opening reaction through a two-step hydrolysis (H₂SO₄)/oxidation (KMnO₄) approach. The GHN nanomaterial bearing carboxylic acid groups was then treated with sodium hydroxide to produce a deprotonated carboxylic acid-rich platform. Finally, due to a high density of accessible chelatant carboxylic acid groups, GHN-COO^- binds strongly a great amount of Pd²⁺ ions to form stable complexes which after reduction by NaBH₄ leads to highly dispersed, densely anchored, and uniformly distributed nanoscale Pd particles (d ∼ 4.5 nm) on the surface of the functionalized GHN. The GHN-COO^-@PdNPs nanohybrid proved to be highly efficient for dye reduction by NaBH₄ in aqueous solution at room temperature. Moreover, because of the high stability of the as-prepared graphene-like supported PdNPs, it exhibited very good reusability and could be recycled up to eight times without any significant loss in activity.

Photo-induced green synthesis of bimetallic Ag/Pd nanoparticles decorated reduced graphene oxide/nitrogen-doped graphene quantum dots nanocomposite as an amperometric sensor for nitrite detection

The present study introduces a novel nanocomposite based on reduced graphene oxide, nitrogen-doped graphene quantum dots, and palladium and silver nanoparticles (rGO/NGQD/AgPd) as an electrocatalyst toward nitrite oxidation reaction. Metal nanoparticles were prepared via a green one-pot photochemical reduction procedure utilizing UV light and NGQD simultaneously as a reducing and directing agent. Formation of the nanocomposite was thoroughly demonstrated by the FT-IR, XRD, Raman, XPS, FE-SEM, and TEM characterization tests. Various electrochemical tests evaluated the efficiency of the prepared sensing platform on the surface of a gold working electrode. Sensitivity and limit of detection (LOD) were calculated to be 0.854 μA.μM^-1.cm^-2 and 0.052 μM, respectively, from the chronoamperometry data. Finally, the proposed sensor was successfully applied for the determination of nitrite ions in river and mineral water samples as natural water sources.

Rapid one-pot synthesis of PAM-GO-Ag nanocomposite hydrogel by gamma-ray irradiation for remediation of environment pollutants and pathogen inactivation

Designing a cost-effective, high potential and recyclable catalyst remains a challenge. In the present work, a monolithic PAM-GO-Ag hydrogel is prepared by a facile, eco-friendly method using gamma-ray irradiation. The formation of GO-Ag composite by gamma radiation is also investigated and it is authenticated by XRD, FTIR, Raman, XPS and TEM analysis. The PAM-GO-Ag hydrogel exhibits excellent catalytic activity to different catalysant like methylene blue, Rhodamine-B, and pharmaceutical compound ciprofloxacin. The high catalyst carrying capacity and rapid electron shuttling ability of GO plays a significant role in the high performance of PAM-GO-Ag hydrogel. The PAM-GO-Ag hydrogel also exhibits excellent antibacterial activity. The damaged cell membrane, protein leakage, and increased ROS level contribute to the antibacterial activity of PAM-GO-Ag. The monolithic structure of PAM-GO-Ag hydrogel makes it easy to handle, recover, and reuse for several runs without significant loss of catalytic and antibacterial activity. All these results showed the possible application of PAM-GO-Ag hydrogel as a promising catalyst for the reduction of different pollutants and antibacterial agents on a large scale with good reusability.

Carbon nitride/positive carbon black anchoring PtNPs assembled byγ-rays as ORR catalyst with excellent stability

Electrocatalytic performance of low-cost graphitic carbon nitride (CN) is greatly limited by its limited conductivity and small specific surface area. Herein, a simple and cost-effective idea to produce novel nanocomposite is constructed by the CN and cetyl trimethyl ammonium bromide functionalized carbon black (CB) anchored platinum nanoparticles as highly efficient oxygen reduction catalysts based on gamma irradiation. The assembled carbon nitride/positive carbon black anchoring PtNPs (Pt/CN₂-CB⁺₁) catalyst exhibits significantly improved specific surface area, high graphitization, and uniformly dispersed ultra-small platinum nanoparticles. For the oxygen reduction reaction (ORR) performance, the catalyst shows more positive onset-potential (0.93 V versus RHE) and larger diffusion limiting current density (5.65 mA cm^-2) compared with benchmark Pt/C catalysts in alkaline medium. Moreover, the Pt/CN₂-CB⁺₁catalyst exhibits a small Tafel slope (92 mV dec^-1). Besides, the catalyst was demonstrated the remarkable methanol tolerance and good long-term stability under working conditions. This work provides a new and effectiveγ-rays irradiation for synthesizing the carbon nitride catalysts for energy conversion and storage applications.

Fabricating Antibacterial and Antioxidant Electrospun Hydrophilic Polyacrylonitrile Nanofibers Loaded with AgNPs by Lignin-Induced In-Situ Method

Concerning the environmental hazards owing to the chemical-based synthesis of silver nanoparticles (AgNPs), this study aimed to investigate the possibility of synthesizing AgNPs on the surface of polyacrylonitrile (PAN) nanofibers utilizing biomacromolecule lignin. SEM observations revealed that the average diameters of the produced nanofibers were slightly increased from ~512 nm to ~673 nm due to several factors like-swellings that happened during the salt treatment process, surface-bound lignin, and the presence of AgNPs. The presence of AgNPs was validated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The amount of synthesized AgNPs on PAN nanofibers was found to be dependent on both precursor silver salt and reductant lignin concentration. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectra confirm the presence of lignin on PAN nanofibers. Although the X-ray diffraction pattern did not show any AgNPs band, the reduced intensity of the stabilized PAN characteristics bands at 2θ = 17.28° and 29.38° demonstrated some misalignment of PAN polymeric chains. The water contact angle (WCA) of hydrophobic PAN nanofibers was reduced from 112.6 ± 4.16° to 21.4 ± 5.03° for the maximum AgNPs coated specimen. The prepared membranes exhibited low thermal stability and good swelling capacity up to 20.1 ± 0.92 g/g and 18.05 ± 0.68 g/g in distilled water and 0.9 wt% NaCl solution, respectively. Coated lignin imparts antioxidant activity up to 78.37 ± 0.12% at 12 h of incubation. The resultant nanofibrous membranes showed a proportional increase in antibacterial efficacy with the rise in AgNPs loading against both Gram-positive S. aureus and Gram-negative E. coli bacterial strains by disc diffusion test (AATCC 147-1998). Halos for maximum AgNPs loading was calculated to 18.89 ± 0.15 mm for S. aureus and 21.38 ± 0.17 mm for E. coli. An initial burst release of silver elements within 24 h was observed in the inductively coupled plasma-atomic emission spectrometry (ICP-AES) test, and the release amounts were proportionally expansive with the increase in Ag contents. Our results demonstrated that such types of composite nanofibers have a strong potential to be used in biomedicine.

An ultra-sensitive and selective AChE based colorimetric detection of malathion using silver nanoparticle-graphene oxide (Ag-GO) nanocomposite

Herein, we propose rapid, precise acetylcholinesterase (AChE) inhibition-based sensing strategy for malathion detection in the presence of Ag-GO and acetylthiocholine (ATCh). The biosensing method was developed with a nanocomposite of citrate stabilized AgNPs anchored on the GO sheets (Ag-GO). The physical and chemical properties of the prepared Ag-GO composite were analyzed with various characterization techniques, including XRD, FT-IR, XPS, UV-Visible spectroscopy, and HR-TEM. The positively charged thiocholine (TCh) produced by enzyme hydrolysis triggers the AgNPs aggregation on GO sheets, which ultimately decreases the intensity of the corresponding SPR absorption peak. While the addition of malathion into the sensing system hindered the AChE activity and limited the TCh production, and thus inhibits the decrease in the SPR band intensity. The designed sensing system displayed linearity in the broad range of malathion concentrations (0.01 pM-1000 pM) with a limit of detection and the limit of quantification values of 0.01 pM, and 0.035 pM, respectively. The application of the designed biosensing system was extended to determine the malathion in actual samples namely, tap water, agricultural runoff water, lake water, and grape extract, which resulted in almost 100% recovery rates in all the spiked samples.

Interface design of carbon filler/polymer composites for electromagnetic interference shielding

The main three methods of interface design for carbon/polymer composites for different carbon materials.

Constructing Conductive Channels between Platinum Nanoparticles and Graphitic Carbon Nitride by Gamma Irradiation for an Enhanced Oxygen Reduction Reaction

Electrocatalytic performance of low-cost graphitic carbon nitride (g-C₃N₄) is greatly limited by its conductivity. In this work, an innovative method, gamma irradiation technology, was used to efficiently synthesize g-C₃N₄/Pt nanoparticle (CN/Pt) nanocomposites, which can construct conductive channels between the nanostructure g-C₃N₄ and supported platinum nanoparticles (PtNPs). Then, the as-prepared CN/Pt nanocomposites were applied in the oxygen reduction reaction (ORR) as an electrocatalyst, which shows a small Tafel slope and the fast four-electron transfer path in the ORR. The oxygen reduction performance over the CN/Pt nanocomposite is much superior to that of the commercial Pt/C and mostly reported in g-C₃N₄-based electrodes. Experimental results have confirmed the fast charge transfer between PtNPs and g-C₃N₄ through a metal-support interaction, and using gamma irradiation technique to disperse PtNPs on g-C₃N₄ proves to be an effective strategy to enhance the catalytic performance of g-C₃N₄ in ORR. Therefore, gamma irradiation may possess great potential for preparing CN/Pt nanocomposites as a highly efficient ORR catalyst.

Gold nanoparticles decorated bimetallic CuNi-based hollow nanoarchitecture for the enhancement of electrochemical sensing performance of nitrite

Gold nanoparticles (AuNPs) decorated bimetallic CuNi-based hollow nanoarchitecture (CNHN) are reported for the first time as a nonenzymatic sensor for the quantification of nitrite in neutral solution . The CNHN was prepared via a convenient calcining routine using the bimetallic CuNi-MOFs as a coprecursor. The unique chemical structure of hollow CNHN with high specific surface area and abundant terminal amino groups effectively avoid the aggregation of AuNPs and facilitate the subsequent adsorption of nitrite. The Au/CNHN exhibited high electrocatalytic activity towards nitrite oxidation due to the synergetic catalytic effect of AuNPs and CNHN. Chronoamperometric detection of nitrite at the Au/CNHN/GCE achieved a lower linear calibration range of 0.05 to 1.15 mM, with an LOD of 0.017 μM compared with previous reports. The proposed method obtained satisfactory recoveries for nitrite determination in practical applications, which was verified by UV-Vis spectrophotometry. The prepared sensor based on Au/CNHN featured favorable selectivity and stability, which provides a promising approach for real sample analysis. Graphical abstract.

Mechanistic Insight into the Limiting Factors of Graphene-Based Environmental Sensors

Graphene has demonstrated great promise for technological use, yet control over material growth and understanding of how material imperfections affect the performance of devices are challenges that hamper the development of applications. In this work, we reveal new insight into the connections between the performance of the graphene devices as environmental sensors and the microscopic details of the interactions at the sensing surface. We monitor changes in the resistance of the chemical-vapor deposition grown graphene devices as exposed to different concentrations of ethanol. We perform thermal surface treatments after the devices are fabricated, use scanning probe microscopy to visualize their effects down to nanometer scale and correlate them with the measured performance of the device as an ethanol sensor. Our observations are compared to theoretical calculations of charge transfers between molecules and the graphene surface. We find that, although often overlooked, the surface cleanliness after device fabrication is responsible for the device performance and reliability. These results further our understanding of the mechanisms of sensing in graphene-based environmental sensors and pave the way to optimizing such devices, especially for their miniaturization, as with decreasing size of the active zone the potential role of contaminants will rise.

Silver Nanomaterials for Wound Dressing Applications

Silver nanoparticles (AgNPs) have recently become very attractive for the scientific community due to their broad spectrum of applications in the biomedical field. The main advantages of AgNPs include a simple method of synthesis, a simple way to change their morphology and high surface area to volume ratio. Much research has been carried out over the years to evaluate their possible effectivity against microbial organisms. The most important factors which influence the effectivity of AgNPs against microorganisms are the method of their preparation and the type of application. When incorporated into fabric wound dressings and other textiles, AgNPs have shown significant antibacterial activity against both Gram-positive and Gram-negative bacteria and inhibited biofilm formation. In this review, the different routes of synthesizing AgNPs with controlled size and geometry including chemical, green, irradiation and thermal synthesis, as well as the different types of application of AgNPs for wound dressings such as membrane immobilization, topical application, preparation of nanofibers and hydrogels, and the mechanism behind their antimicrobial activity, have been discussed elaborately.

Effects of silver-graphene oxide on seed germination and early growth of crop species

Due to its excellent material properties, silver-graphene oxide (Ag-GO) is being studied for diverse applications, such as antimicrobial agents, catalysts and absorbents. Such use of Ag-GO may lead to its release into terrestrial ecosystems, but little is known about the impact of Ag-GO on plants. In the present study, we determined the effects of Ag-GO on seed germination and early growth of crop species by analyzing the germination rate, growth of roots and shoots, hydrogen peroxide (H₂O₂) accumulation, and the uptake of Ag in alfalfa, radish and cucumber treated with 0.2–1.6 mg mL⁻¹ of Ag-GO. Ag-GO treatment increased the shoot growth of radish at 0.2–1.6 mg mL⁻¹ but decreased that of cucumber at 0.8 mg mL⁻¹. In addition, Ag-GO enhanced the root elongation of radish at 0.2 mg mL⁻¹ but inhibited that of alfalfa at 0.2, 0.8 and 1.6 mg mL⁻¹. Ag-GO treatment induced H₂O₂ production in alfalfa, radish and cucumber in a concentration-dependent manner. Larger amounts of Ag accumulated in the seedlings as the concentration of Ag-GO increased, and such accumulation suggests that Ag may be transferred to higher trophic levels when plants are exposed to Ag-GO in ecosystems. Our study can, thus, serve as an important basis for setting guidelines for the release of nanomaterials into the environment.

Application of Graphene-Based Materials for Detection of Nitrate and Nitrite in Water-A Review

Nitrite and nitrate are widely found in various water environments but the potential toxicity of nitrite and nitrate poses a great threat to human health. Recently, many methods have been developed to detect nitrate and nitrite in water. One of them is to use graphene-based materials. Graphene is a two-dimensional carbon nano-material with sp² hybrid orbital, which has a large surface area and excellent conductivity and electron transfer ability. It is widely used for modifying electrodes for electrochemical sensors. Graphene based electrochemical sensors have the advantages of being low cost, effective and efficient for nitrite and nitrate detection. This paper reviews the application of graphene-based nanomaterials for electrochemical detection of nitrate and nitrite in water. The properties and advantages of the electrodes were modified by graphene, graphene oxide and reduced graphene oxide nanocomposite in the development of nitrite sensors are discussed in detail. Based on the review, the paper summarizes the working conditions and performance of different sensors, including working potential, pH, detection range, detection limit, sensitivity, reproducibility, repeatability and long-term stability. Furthermore, the challenges and suggestions for future research on the application of graphene-based nanocomposite electrochemical sensors for nitrite detection are also highlighted.

Microstructure evolution of sandwich graphite oxide/interlayer-embedded Au nanoparticles induced from γ-rays for carcinoembryonic antigen biosensor

With the capability of inducing small particle sizes of supported metal in graphite oxide (GO), the γ-ray irradiation method applied for preparing graphite oxide-gold (GO-Au) nanocomposites as electrochemical immunosensors has attracted specific attention recently. To study the accurate factors influencing the precise morphology and final performance of the prepared composites in the γ-irradiation system, we proposed a facile method to investigate the evolution of the GO structure, size and dispersion of Au nanoparticles (AuNPs) produced with the addition of isopropyl alcohol to the system. The GO-Au nanocomposites were characterized by Fourier transform infrared spectroscopy, x-ray diffraction spectra, Raman spectra, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. These nanocomposites with sandwich morphology exhibited an excellent immunosensor performance with a low detection limit of 15.8 pg ml^-1 (S/N = 3) and a wide linear range from 1 to 40 ng ml^-1 for detecting carcinoembryonic antigens. The enhanced biosensing performance is attributed to the synergistic effect of γ-irradiation and the precise structure of GO, which endows the smaller size and more uniform distribution of AuNPs on the GO as well as the good signal amplification capability. Furthermore, adopting the γ-irradiation method and use of GO as a precursor is propitious for application in large-scale production because of its high-efficiency and high-yielding characteristics.

Synthesis of a Carbonaceous Two-Dimensional Material

Despite tremendous accomplishments achieved in 2D materials, little progress has been made in carbonaceous 2D materials beyond graphene and graphene oxide. Here, we report a 2D material of carbonaceous nanoplates (CANP). The bottom-up synthesis of CANP is green, separation-free, and massive. The nanoplates are 2 to 3 monolayers thick with an average interlayer spacing of 0.57 nm. The synthesis involves viscosity-aided two-dimensional growth of fragmented glucose derivatives and leads to the complete conversion of glucose to the 2D nanoplates. Application tests demonstrate the usefulness of the affordable 2D material.