Nanocomposites of size-controlled gold nanoparticles and graphene oxide: formation and applications in SERS and catalysis

Facile Cu-MOF-derived Co3O4 mesoporous-structure as a cooperative catalyst for the reduction nitroarenes and dyes

The present study describes the environmentally friendly and cost-effective synthesis of magnetic, mesoporous structure-Co3O4 nanoparticles (m-Co3O4) utilizing almond peel as a biotemplate. This straightforward method yields a material with high surface area, as confirmed by various characterization techniques. Subsequently, the utilization of m-Co3O4, graphene oxide (GO), Cu(II)acetate (Cu), and asparagine enabled the successful synthesis of a novel magnetic MOF, namely GO-Cu-ASP-m-Co3O4 MOF. This catalyst revealed remarkable stability that could be easily recovered using a magnet for consecutive use without any significant decline in activity for eight cycles in nitro compound reduction and organic dye degradation reactions. Consequently, GO-Cu-ASP-m-Co3O4 MOF holds immense potential as a catalyst for reduction reactions, particularly in the production of valuable amines with high industrial value, as well as for the elimination of toxic-water pollutants such as organic dyes.

Electrocatalytic quantification of quinol in cosmetic samples using Co-doped graphitic carbon nitride @biomolecule assisted electrochemically reduced graphene nanosheets

A bio-nanocomposite "Co-doped-g-C3N4@ biomolecule assisted electrochemically reduced graphene nanosheets (Co-g-C3N4@GNbme)" was prepared by electrochemical exfoliation of GO from graphite anode in the presence of amino acid 'l-cysteine' followed by its association with Co-g-C3N4. The preparation of material has been confirmed by characterizations with FTIR, XRD, XPS and Raman spectroscopy. The morphology was investigated with TEM and SEM. Further, Co-g-C3N4@GNbme modified GC electrode was utilized for detecting and quantifying the 'Quinol' (a skin lightning agent) in cosmetic samples electrochemically. Quinol is a fundamental constituent utilized in various industries such as pharmaceuticals, oil refineries, textiles, and dyes. In the realm of cosmetics, it is utilized as a skin-lightning agent to inhibit the production of melanin in the skin. However, prolonged use of this component often results in allergic reactions among individuals. Furthermore, the effluents discharged from its manufacturing units pose a significant threat to the environment and human health due to its slow degradation. The detection limit was calculated to be 2.4 nM (S/N = 3).

Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

Precision Covalent Chemistry for Fine-Size Tuning of Sandwiched Nanoparticles between Graphene Nanoplatelets

The covalent functionalization of graphene for enhancing their stability, improving their electrical or optical properties, or creating hybrid structures has continued to attract extensive attention; however, a fine control of nanoparticle (NP) size between graphene layers via covalent-bridging chemistry has not yet been explored. Herein, precision covalent chemistry-assisted sandwiching of ultrasmall gold nanoparticles (US-AuNP) between graphene layers is described for the first time. Covalently interconnected graphene (CIG) nanoscaffolds with a preadjusted finely tuned graphene layer-layer distance facilitated the formation of sandwiched US-AuNPs (∼1.94 ± 0.20 nm, 422 AuNPs). The elemental composition analysis by X-ray photoelectron spectroscopy displayed an aniline group addition per ∼55 graphene carbon atoms. It provided information on covalent interconnection via amidic linkages, while Raman spectroscopy offered evidence of covalent surface functionalization and the number of graphene layers (≤2-3 layers). High-resolution transmission electron microscopy images indicated a layer-layer distance of 2.04 nm, and low-angle X-ray diffraction peaks (2θ at 24.8 and 12.5°) supported a layer-layer distance increase compared to the characteristic (002) reflection (2θ at 26.5°). Combining covalent bridging with NP synthesis may provide precise control over the metal/metal oxide NP size and arrangement between 2D layered materials, unlocking new possibilities for advanced applications in energy storage, electrochemical shielding, and membranes.

A robust SERS calibration using a pseudo-internal intensity reference

Surface-enhanced Raman scattering (SERS) with high molecular sensitivity and specificity is a powerful nondestructive analytical tool. Since its discovery, SERS measurements have suffered from the vulnerability of calibration curve, which makes quantification analysis a great challenge. In this work, we report a robust calibration method by introducing a referenced measurement as the intensity standard. This intensity reference not only has the advantages of the internal standard method such as reflecting the SERS substrate enhancement, but also avoids the introduction of competing adsorption between target molecules and the internal standard. Based on the normalized calibration curve, the magnitude of the R6G concentration can be well evaluated from 10^-7 M to 10^-12 M. Furthermore, we demonstrate that this pseudo-internal standard method can also work well using a different type of molecule as the reference. This SERS calibration method would be beneficial for the development of quantitative SERS analysis.

Biomass-assisted fabrication of rGO-AuNPs as surface-enhanced Raman scattering substrates for in-situ monitoring methylene blue degradation

Reduced graphene oxide-gold nanoparticles nanocomposites (rGO-AuNPs) with high surface-enhanced Raman scattering (SERS) activity was created by biomass-assisted green synthesis with Lilium casa blanca petals biomass for the first time, and its application for methylene blue (MB) degradation was explored through in-situ monitoring. Lilium casa blanca petals biomass was used as a reducing agent to reduce GO and chloroauric acid successively when carrying out rGO-AuNPs in-situ synthesis while it also acted as a capping agent. The produced rGO had oxygen-containing functional groups which had an outstanding performance in enhancing the SERS effect. Characterization results confirmed that the AuNPs were grafted onto the rGO sheet, and the mechanism study showed that total flavonoids in Lilium casa blanca petals biomass were the main biological compounds involved in the reduction. rGO-AuNPs had a high Raman enhancement factor (EF) which could reach 3.88 × 10⁷. The synthesized nanocomposite also had a good catalytic activity that could be employed as catalyst in MB degradation, and it could complete degradation within 15min. The reaction rate increased linearly with the amount of rGO-AuNPs, and the degradation could be in-situ monitored both by UV and SERS.

Biosynthesis of Gold and Silver Nanoparticles Using Phytochemical Compounds

Gold and silver nanoparticles are nanoparticles that have been widely used in various fields and have shown good benefits. The method of nanoparticle biosynthesis utilizing plant extracts, also known as green synthesis, has become a promising method considering the advantages it has compared to other synthesis methods. This review aims to give an overview of the phytochemical compounds in plants used in the synthesis of gold and silver nanoparticles, the nanoparticle properties produced using plant extracts based on the concentration and structure of phytochemical compounds, and their applications. Phytochemical compounds play an important role as reducing agents and stabilizers in the stages of the synthesis of nanoparticles. Polyphenol compounds, reducing sugars, and proteins are the main phytochemical compounds that are responsible for the synthesis of gold and silver nanoparticles. The concentration of phytochemical compounds affects the physical properties, stability, and activity of nanoparticles. This is important to know to be able to overcome limitations in controlling the physical properties of the nanoparticles produced. Based on structure, the phytochemical compounds that have ortho-substituted hydroxyl result in a smaller size and well-defined shape, which can lead to greater activity and stability. Furthermore, the optimal condition of the biosynthesis process is required to gain a successful reaction that includes setting the metal ion concentration, temperature, reaction time, and pH.

An improved surface enhanced Raman spectroscopic method using a paper-based grape skin-gold nanoparticles/graphene oxide substrate for detection of rhodamine 6G in water and food

Organic toxins are persistent chemicals of global concern capable of accumulating in environment and food. Surface enhanced Raman spectroscopy (SERS) is a promising technique that facilitates onsite detection of organic toxins. However, the fabrication of a SERS substrate is complicated and difficult to provide flexibility, fastness and cost-effectiveness. This study aims to develop a paper-based SERS method using grape skin-gold nanoparticles/graphene oxide (GE-AuNPs/GO) as SERS substrate and evaluate its efficiency with rhodamine 6G (Rh6G) as a model organic toxin and a real water and food contaminant. GE-AuNPs synthesized by green method using grape skin waste extract and GE-AuNPs/GO showed a surface plasmon resonance at 536 and 539 nm, particle size 18.6 and 19.5 nm, and zeta potential -44.6 and -59.7 mV, respectively. Paper-based SERS substrates were prepared by coating a hydrophobic thin-film of 30% polydimethylsiloxane solution in hexane on Whatman no. 1 filter paper, followed by drop-casting GE-AuNPs or GE-AuNPs/GO and drying. The SERS signals of Rh6G showed an enhancement factor of 5.8 × 10⁴ for GE-AuNPs and 1.92 × 10⁹ for GE-AuNPs/GO, implying that a combination of electromagnetic surface plasmon, charge transfer and molecular resonances may be responsible for a higher enhancement of signal by the latter. A low detection limit of 7.33 × 10^-11 M in the linear range of 10^-11-10^-5 M was obtained for GE-AuNPs/GO, while the relative standard deviation of repeatability and reproducibility was 9.6 and 12.6%, respectively. Paper-based GE-AuNPs/GO SERS substrate was highly stable as <20% loss in efficiency was shown over a 60-day storage period. Application to real samples showed a high recovery of Rh6G from tap water (93.9-100.8%) as well as food samples such as red chilli powder (91.0-95.4%), red glutinous rice ball (96.6-98.3%) and tomato ketchup (98.9-102.3%) after QuEChERS extraction. Collectively, the developed paper-based GE-AuNPs/GO can be a potential substrate for sensitive onsite detection of rhodamine 6G by SERS method.

Advances in analysis of pharmaceuticals by using graphene-based sensors

Safe and effective use of drugs relies on proper pharmaceutical analysis. Graphene has been extensively used to construct sensors for this purpose. Over the years, a large variety of pharmaceutical sensors have been developed from graphene or its derivatives. This articles reviews the current status of sensor development from graphene and its derivatives, and discusses the use of graphene-based sensors in pharmaceutical analysis. It is hoped that this article cannot only offer a snapshot of recent advances in the fabrication and use of graphene-based sensors, but can also provide insights into future engineering and optimization of the sensors for effective pharmaceutical analysis.

Graphene Oxide-Coated Metal–Insulator–Metal SERS Substrates for Trace Melamine Detection

Surface-enhanced Raman spectroscopy (SERS) has long been an ultrasensitive technique for trace molecule detection. However, the development of a sensitive, stable, and reproducible SERS substrate is still a challenge for practical applications. Here, we demonstrate a cost-effective, centimeter-sized, and highly reproducible SERS substrate using the nanosphere lithography technique. It consists of a hexagonally packed Ag metasurface on a SiO₂/Au/Si substrate. A seconds-lasting etching process of a self-assembled nanosphere mask manipulates the geometry of the deposited Ag metasurface on the SiO₂/Au/Si substrate, which attains the wavelength matching between the optical absorbance of the Ag/SiO₂/Au/Si substrate and the excitation laser wavelength as well as the enhancement of Raman signals. By spin-coating a thin layer of graphene oxide on the substrate, a SERS performance with 1.1 × 10⁵ analytical enhancement factor and a limit of detection of 10⁻⁹ M for melamine is achieved. Experimental results reveal that our proposed strategy could provide a promising platform for SERS-based rapid trace detection in food safety control and environmental monitoring.

Highly sensitive near-infrared SERS nanoprobes for in vivo imaging using gold-assembled silica nanoparticles with controllable nanogaps

BACKGROUND

To take advantages, such as multiplex capacity, non-photobleaching property, and high sensitivity, of surface-enhanced Raman scattering (SERS)-based in vivo imaging, development of highly enhanced SERS nanoprobes in near-infrared (NIR) region is needed. A well-controlled morphology and biocompatibility are essential features of NIR SERS nanoprobes. Gold (Au)-assembled nanostructures with controllable nanogaps with highly enhanced SERS signals within multiple hotspots could be a breakthrough.

RESULTS

Au-assembled silica (SiO2) nanoparticles (NPs) (SiO2@Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO2@Au@Au NPs using six different sizes of Au NPs (SiO2@Au@Au50-SiO2@Au@Au500) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO2 surface could be controlled from 4.16 to 0.98 nm by adjusting the concentration of Au precursor (hence increasing Au NP sizes), which resulted in the formation of effective SERS hotspots. SiO2@Au@Au500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 106 under 785-nm photoexcitation. SiO2@Au@Au500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO2@Au@Au500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice.

CONCLUSIONS

SiO2@Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region.

Advances in Graphene/Inorganic Nanoparticle Composites for Catalytic Applications

Graphene-based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen-doped graphene are excellent support materials due to their high surface area, their extended π-system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine-tune the surface composition for desired functionalities enhances the versatility of graphene-based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large-scale synthesis of graphene-based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies.

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles

Janus nanoparticles (JNPs) feature heterogeneous compositions, bringing opportunities in technological and medical applications. We introduce a theoretical approach based on nonequilibrium molecular dynamics simulations and heat transfer continuum theory to investigate the temperature fields generated around heated spherical JNPs covering a wide range of particle sizes, from a few nm to 100 nm. We assess the performance of these nanoparticles to generate anisotropic heating at the nanoscale. We demonstrate that the contrasting interfacial thermal conductances of the fluid-material interfaces arising from the heterogeneous composition of the JNPs can be exploited to control the thermal fields around the nanoparticle, leading to a temperature difference between both sides of the nanoparticle (temperature contrast) that is significant for particles comprising regions with disparate hydrophilicity. We illustrate this idea using coarse-grained and atomistic models of gold nanoparticles with hydrophobic and hydrophilic coatings, in water. Furthermore, we introduce a continuum model to predict the temperature contrast as a function of the interfacial thermal conductance and nanoparticle size. We further show that, unlike homogeneous nanoparticles, the interfacial fluid temperature depends on the interfacial thermal conductance of Janus nanoparticles.

Improving the efficiency of n-Si/PEDOT:PSS hybrid solar cells by incorporating AuNP-decorated graphene oxide as a nanoadditive for conductive polymers

A gold nanoparticle-decorated graphene oxide (GO-AuNP) hybrid material was prepared by using the chemical reduction method. The obtained results showed that the AuNPs of about of 15 nm are well bound on the surface of GO. The GO-AuNP hybrid material was used for transparent conductive film (TCF) and organic/inorganic hybrid solar cells. The TCF based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) containing GO-AuNPs was fabricated at room temperature. The obtained results show that the TCF containing 0.5 wt% GO-AuNPs has a high transmittance of 69.7% at 550 nm, a low sheet resistance of 50.5 Ω □⁻¹ and a conductivity that increased to 3960 S cm⁻¹, which is three times higher than those of the PEDOT:PSS and PEDOT:PSS/GO film. The power conversion efficiency (PCE) of the n-Si/PEDOT:PSS hybrid solar cell containing GO-AuNPs was 8.39% and is higher than pristine PEDOT:PSS (5.81%) and PEDOT:PSS/GO (7.58%). This is a result of the increased electrical conductivity and localized surface plasmon resonance of the PEDOT:PSS coating layer containing the GO-AuNP hybrid material.

A GO-AuNP hybrid material was successfully prepared and used for improving the performance of the optoelectronics devices.

Preparation and surface-enhanced Raman scattering properties of GO/Ag/Ta2O5 composite substrates

The composite substrate composed of precious metal, semiconductor and graphene has not only high sensitivity and uniform Raman signal but also stable chemical properties, which is one of the important topics in the field of surface-enhanced Raman scattering (SERS). In this paper, a sandwich SERS substrate based on tantalum oxide (Ta₂O₅) is designed and fabricated. The substrate has high sensitivity, stable performance and high quantification capability. The composite substrate can achieve a high sensitivity Raman detection of crystal violet (CV) with a detection limit of 10^-11 M and an enhancement factor of 1.5 × 10⁹. This is the result of the synergistic effect of electromagnetic enhancement and chemical enhancement, in which the chemical enhancement is the cooperative charge transfer in the system composed of probe molecules, silver nanoparticles (AgNPs) and Ta₂O₅, and the electromagnetic enhancement comes from the strong local surface plasmon resonance between the adjacent AgNPs. After exposing the composite substrate to the air for one month, the Raman signal did not weaken, indicating that the performance of the composite substrate is stable. In addition, there is an excellent linear relationship between the intensity of Raman characteristic peak and the concentration of probe molecules, which proves that the composite substrate has high quantification capability. In practical application, the composite SERS substrate can be used to detect harmful malachite green quickly and sensitively and has a broad application prospect in the field of food safety and chemical analysis.

In Situ SERS Monitoring of the Plasmon-Driven Catalytic Reaction by Using Single Ag@Au Nanowires as Substrates

Single nanowires (NWs), as a kind of new surface-enhanced Raman scattering (SERS) substrates, have received extensive concern owing to their distinctive properties and distinct advantages. In this contribution, single Ag nanowires (AgNWs) and single Au-coated AgNWs (Ag@AuNWs) were fabricated by the laser-assisted pulling method and the galvanic replacement reaction, respectively. The prepared single Ag@AuNWs show both high SERS activity and catalytic activity through in situ monitoring and assessing the plasmon-driven surface-catalytic reaction of 4-nitrothiophenol (4-NTP) dimerizing to 4,4'-dimercaptoazobenzene and the reduction reaction of 4-NTP to para-aminothiophenol, respectively. It was found that the intensity of the Raman peak was affected greatly by the laser power, and the Raman peak could still be observed at 0.05% power under mild conditions (633 nm wavelength) in this single nanowire system. From the Raman spectrum, the SERS enhancement factor (EF) of 5.4 × 10⁴ can be obtained, and the EF value of 1.3 × 10⁹ can be reached at optimal conditions. Results have shown that single Ag@AuNWs can be utilized as a good platform for SERS applications with high sensitivity, stability, and reproducibility, which will benefit SERS-based research at the single entity level.

Functionalized Graphene Platforms for Anticancer Drug Delivery

Two-dimensional nanomaterials are emerging as promising candidates for a wide range of biomedical applications including tissue engineering, biosensing, pathogen incapacitation, wound healing, and gene and drug delivery. Graphene, due to its high surface area, photothermal property, high loading capacity, and efficient cellular uptake, is at the forefront of these materials and plays a key role in this multidisciplinary research field. Poor water dispersibility and low functionality of graphene, however, hamper its hybridization into new nanostructures for future nanomedicine. Functionalization of graphene, either by covalent or non-covalent methods, is the most useful strategy to improve its dispersion in water and functionality as well as processability into new materials and devices. In this review, recent advances in functionalization of graphene derivatives by different (macro)molecules for future biomedical applications are reported and explained. In particular, hydrophilic functionalization of graphene and graphene oxide (GO) to improve their water dispersibility and physicochemical properties is discussed. We have focused on the anticancer drug delivery of polyfunctional graphene sheets.

Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10^-7 M was detected with enhancement factor of 82 × 10⁴. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.

DNA/Nano based advanced genetic detection tools for authentication of species: Strategies, prospects and limitations

Authentication, detection and quantification of ingredients, and adulterants in food, meat, and meat products are of high importance these days. The conventional techniques for the detection of meat species based on lipid, protein and DNA biomarkers are facing challenges due to the poor selectivity, sensitivity and unsuitability for processed food products or complex food matrices. On the other hand, DNA based molecular techniques and nanoparticle based DNA biosensing strategies are gathering huge attention from the scientific communities, researchers and are considered as one of the best alternatives to the conventional strategies. Though nucleic acid based molecular techniques such as PCR and DNA sequencing are getting greater successes in species detection, they are still facing problems from its point-of-care applications. In this context, nanoparticle based DNA biosensors have gathered successes in some extent but not to a satisfactory stage to mark with. In recent years, many articles have been published in the area of progressive nucleic acid-based technologies, however there are very few review articles on DNA nanobiosensors in food science and technology. In this review, we present the fundamentals of DNA based molecular techniques such as PCR, DNA sequencing and their applications in food science. Moreover, the in-depth discussions of different DNA biosensing strategies or more specifically electrochemical and optical DNA nanobiosensors are presented. In addition, the significance of DNA nanobiosensors over other advanced detection technologies is discussed, focusing on the deficiencies, advantages as well as current challenges to ameliorate with the direction for future development.

Facile fabricating of rGO and Au/rGO nanocomposites using Brassica oleracea var. gongylodes biomass for non-invasive approach in cancer therapy

In this study, we report a facile green-synthesis route for the fabrication of reduced graphene oxide (rGO) using biomass of Brassica oleracea var. gongylodes (B. oleracea). In addition, we have attempted to provide a green synthesis approach to prepare Gold nanoparticles (Au NPs) on the surface of rGO by using stem extract of B. oleracea. The synthesized Au/rGO nanocomposite was evaluated using UV-visible and FTIR spectroscopy, XRD, Raman, FE-SEM, EDX, AFM and DLS techniques. The obtained results demonstrated that the synthesized Au NPs on the surface of rGO was spherical with sizes ranging about 12-18 nm. The Au/rGO NC was, also, developed as photo-synthesizer system for the photothermal therapy (PTT) of MCF7 breast cancer cells. The near-infrared (NIR) photothermal properties of Au/rGO NCs was evaluated using a continuous laser at 808 nm with power densities of 1 W.cm-2. Their photothermal efficacy on MCF7 breast cancer cells after optimizing the proper concentration of the NCs were evaluated by MTT assay, Cell cycle and DAPI staining. In addition, the potential of the synthesized Au/rGO NCs on reactive oxygen species generating and antioxidant activity were assessed by DPPH. Au/rGO NCs possess high capacity to light-to-heat conversion for absorption in range NIR light, and it is able to therapeutic effects on MCF7 cells at a low concentration. The maximum amount of cell death is 40.12% which was observed in treatment groups that received a combination of Au/rGO NCs and laser irradiation. The results demonstrate that the nanomaterials synthesized by green approach lead to efficient destruction of cancer cell and might thus serve as an excellent theranostic agent in Photothermal therapy applications.

Three-dimensional porous SERS powder for sensitive liquid and gas detections fabricated by engineering dense "hot spots" on silica aerogel

A three-dimensional porous SERS powder material, Ag nanoparticles-engineered-silica aerogel, was developed. Utilizing an in situ chemical reduction strategy, Ag nanoparticles were densely assembled on porous aerogel structures, thus forming three-dimensional "hot spots" distribution with intrinsic large specific surface area and high porosity. These features can effectively enrich the analytes on the metal surface and provide huge near field enhancement. Highly sensitive and homogeneous SERS detections were achieved not only on the conventional liquid analytes but also on gas with the enhancement factor up to ∼10⁸ and relative standard deviation as small as ∼13%. Robust calibration curves were obtained from the SERS data, which demonstrates the potential for the quantification analysis. Moreover, the powder shows extraordinary SERS stability than the conventional Ag nanostructures, which makes long term storage and convenient usage feasible. With all of these advantages, the porous SERS powder material can be extended to on-site SERS "nose" applications such as liquid and gas detections for chemical analysis, environmental monitoring, and anti-terrorism.

Surfactant-free synthesis of copper nanoparticles and gas phase integration in CNT-composite materials

Copper nanoparticles (Cu-NPs) represent a viable low-cost alternative to replace bulk copper or other more expensive NPs (e.g. gold or silver) in various applications such as electronics for electrical contact materials or high conductivity materials. This study deals with the synthesis of well dispersed Cu-NPs by using an Ar + H₂ microplasma using a solid copper precursor. The morphological analysis is carried out by electron microscopy showing particles with a mean diameter of 8 nm. Crystallinity and chemical analyses were also carried out by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. In the second step, the Cu-NPs were successfully deposited onto porous carbon nanotube ribbons; surface coverage and the penetration depth of the Cu-NPs inside the CNT ribbon structure were investigated as these can be beneficial for a number of applications. The oxidation state of the Cu-NPs was also studied in detail under different conditions.

Graphene Oxide/Silver Nanocomposites as Antifouling Coating on Sensor Housing Materials

These days, sensors are widely used in a variety of underwater sites like marine monitoring, fish-farming and water quality monitoring. However, to achieve reliable sensor data from long-term monitoring in aqueous solution, several challenges still need to be solved. Biofilm formation both on sensor housings and membranes is among one of the most serious challenges, which strongly influences the sensor responds and the validity of the results. To prevent biofilm growth, a series of graphene oxide (GO)/silver nanoparticles (Ag NPs) nanocomposites (GOA) have been developed and coated on sensor housing materials, e.g. polypropylene. The antifouling property of the GOA nanocomposite has been demonstrated by antifouling tests using Halomonas. Pacifica (Baumann et al.) Dobson and Franzmann (ATCC® 27122) (H. Pacifica) and a mixture of marine algae. The antifouling property of GOA composites has been proved to be closely related to the dispersibility of Ag NP. The overall work might provide valuable insight into developing antifouling materials for sensors in general.

A Review of Graphene-Based Surface Plasmon Resonance and Surface-Enhanced Raman Scattering Biosensors: Current Status and Future Prospects

The surface plasmon resonance (SPR) biosensor has become a powerful analytical tool for investigating biomolecular interactions. There are several methods to excite surface plasmon, such as coupling with prisms, fiber optics, grating, nanoparticles, etc. The challenge in developing this type of biosensor is to increase its sensitivity. In relation to this, graphene is one of the materials that is widely studied because of its unique properties. In several studies, this material has been proven theoretically and experimentally to increase the sensitivity of SPR. This paper discusses the current development of a graphene-based SPR biosensor for various excitation methods. The discussion begins with a discussion regarding the properties of graphene in general and its use in biosensors. Simulation and experimental results of several excitation methods are presented. Furthermore, the discussion regarding the SPR biosensor is expanded by providing a review regarding graphene-based Surface-Enhanced Raman Scattering (SERS) biosensor to provide an overview of the development of materials in the biosensor in the future.

Fabrication of graphene oxide and sliver nanoparticle hybrids for fluorescence quenching of DNA labeled by methylene blue

Since graphene oxide‑silver nanoparticles (GO-AgNPs) have special affinities to DNA, it become increasingly important in fields of biological analysis in which GO-AgNPs nanocomposites universally functioned as a quencher. In this paper, GO-AgNPs nanocomposites with different GO to AgNPs ratios were synthesized as a fluorescence quencher to interact with DNA labeled by methylene blue (MB). The results showed that the fluorescence intensity of DNA-MB system decreased with the increasing of GO-AgNPs nanocomposites concentration. The quenching phenomenon of DNA-MB by AgNPs and GO was not a simple additive effect but a synergistic effect. The quenching efficiency of synthesized GO-AgNPs nanocomposites with different ratios (1:1, 1:3, 1:5, 1:10) increased with the decrease of GO/Ag ratio. Thermodynamic analysis was employed to investigate the interaction of GO-AgNPs and DNA-MB, it can be concluded that the intermolecular force between GO-AgNPs and DNA-MB was hydrogen bonding. Our works will provide important theoretical and experimental bases for fluorescence sensing of DNA.

Langmuir films of low-dimensional nanomaterials

A large number of low-dimensional nanomaterials having different shapes and being dispersible in solvents open a fundamental question if there is a universal deposition technique for the monolayer formation. A monolayer formation of various nanomaterials at the air-water interface, also known as a Langmuir film, is a well-established technique even for the large group of the recently developed low-dimensional nanomaterials. In this review, we cover the monolayer formation of the zero-dimensional, one-dimensional and two-dimensional nanomaterials. Thanks to the formation of a Langmuir layer at the thermodynamic equilibrium, by using a suitable nanomaterial dispersion and subphase, the monolayers can be formed from all kinds of materials, ranging from the graphene oxide to the semiconducting quantum dots. In this review, we will discuss the basic requirements for the successful formation of monolayers and summarize the recent scientific advances in the field of Langmuir films.

Iron oxide/gold nanoparticles-decorated reduced graphene oxide nanohybrid as the thermo-radiotherapy agent

The main focus of the current study is the fabrication of a multifunctional nanohybrid based on graphene oxide (GO)/iron oxide/gold nanoparticles (NPs) as the combinatorial cancer treatment agent. Gold and iron oxide NPs formed on the GONPs via the in situ synthesis approach. The characterisations showed that gold and iron oxide NPs formed onto the GO. Cell toxicity assessment revealed that the fabricated nanohybrid exhibited negligible toxicity against MCF-7 cells in low doses (<50 ppm). Temperature measurement showed a time and dose-dependent heat elevation under the interaction of the nanohybrid with the radio frequency (RF) wave. The highest temperature was recorded using 200 ppm concentration nanohybrid during 40 min exposure. The combinatorial treatments demonstrated that the maximum cell death (average of 53%) was induced with the combination of the nanohybrid with RF waves and radiotherapy (RT). The mechanistic study using the flow cytometry technique illustrated that early apoptosis was the main underlying cell death. Moreover, the dose enhancement factor of 1.63 and 2.63 were obtained from RT and RF, respectively. To sum up, the authors' findings indicated that the prepared nanohybrid could be considered as multifunctional and combinatorial cancer therapy agents.

Hyaluronic Acid-Modified Au-Ag Alloy Nanoparticles for Radiation/Nanozyme/Ag+ Multimodal Synergistically Enhanced Cancer Therapy

Gold nanoparticles (AuNPs) have been widely documented as tumor radiosensitizers via enhanced energy deposition of ionizing radiation. However, the sensitization efficiency of AuNPs is still far from satisfactory owing to the irradiation on nontarget tissues and the tumor radio-resistance. To address these issues, we report herein the rational design and development of hyaluronic acid-modified Au-Ag alloy nanoparticles (Au-Ag@HA NPs) with effective tumor radiosensitization by receptor mediated tumor targeting as well as microenvironment-activated hydroxyl radicals (•OH) generation. In our work, Au-Ag@HA NPs were synthesized by the coreduction of HAuCl₄ and AgNO₃ in the presence of trisodium citrate, followed by surface modification of HA to the Au-Ag alloy NPs. HA modification affords the alloy NPs with specific targeting to 4T1 breast cancer cells overexpressing CD44 receptor, while the introduction of Ag atom imparts the alloy NPs with superior multienzyme-like activities to the monometallic AuNPs for efficient tumor catalytic therapy. More importantly, the ionizing radiation and peroxidase-like activity of Au-Ag@HA NPs boost the production of •OH and the release of toxic Ag⁺ in the tumor sites, thereby leading to effective tumor therapeutic outcome. This work provides a promising treatment paradigm for radiation/nanozyme/Ag⁺ combined therapy against cancer and will advance the design and development of multifunctional nanoplatforms for synergetically enhanced tumor therapy.

Effective disposal of methylene blue using green immobilized silver nanoparticles on graphene oxide and reduced graphene oxide sheets through one-pot synthesis

This study reveals the feasibility of exploring highly efficient, cost-effective, and stable green adsorbents for the treatment of contaminated water. Here silver nanoparticles (AgNPs) were immobilized onto nanosheets of graphene oxide (GO) through in situ reduction process using green tea aqueous extract. GO reduction to reduced graphene oxide (rGO) and AgNPs decoration on rGO also occurred simultaneously. The impacts of the extract concentration, contact time, and temperature on the synthesis process have been investigated. The synthesized nanocomposites were examined by XRD, FTIR, Raman, SEM, TEM, and TGA. The GO nanosheets were decorated by AgNPs with a crystalline structure and an average particle size of 25 ± 3 nm. The temperature and the extract concentration were considerably affecting the type of the resulting nanocomposites. The GO/Ag nanocomposites were formed at room temperature (27 °C) using different extract concentration (2-18% (v/v)), while the rGO/Ag nanocomposite was formed only at a higher temperature (95 °C) with higher extract concentration (18%). The methylene blue (MB) dye was picked as a water pollutant to explore the adsorption ability of the nanocomposites. The adsorption behavior of the GO/Ag nanocomposites was examined under diverse factors (MB concentration, adsorbent dosage, pH, and contact time) to achieve optimization. The adsorption data concurs with Langmuir isotherm giving maximum adsorption up to 633 mg g^-1. Adsorption kinetics demonstrate good pseudo-second-order compliance. Spontaneous and endothermic nature of adsorption was affirmed via thermodynamic parameters. The nanocomposites could be utilized as eco-friendly and reliable adsorbents in wastewater treatment, as a result of their exceptional productivity and reusing potential.

A universal growth strategy for DNA-programmed quantum dots on graphene oxide surfaces

The emerging materials of semiconductor quantum dots/graphene oxide (QDs/GO) hybrid composites have recently attracted intensive attention in materials science and technology due to their potential applications in electronic and photonic devices. Here, a simple and universal strategy to produce DNA-programmed semiconductor quantum dots/graphene oxide (QDs/GO) hybrid composites with controllable sizes, shapes, compositions, and surface properties is reported. This proof-of-concept work successfully demonstrates the use of sulfhydryl modified single-stranded DNA (S-ssDNA) as a 'universal glue' which can adsorb onto GO easily and provide the growth sites to synthesize CdS QDs, CdSe QDs, CdTe QDs and CdTeSe QDs with distinctive sizes, shapes and properties. Also, adapting this method, other graphene oxide-based hybrid materials which are easily synthesized in aqueous solution, including oxides, core-shell structure QDs and metal nanocrystals, would be possible. This method provided a universal strategy for the synthesis and functional realization of graphene -based nanomaterials.

Silver-nanoparticles/graphene hybrids for effective enrichment and sensitive SERS detection of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widespread and dangerous group of pollutants existing in the environment. Trace detection of PAHs is essential and important. Surface-enhanced Raman scattering (SERS) is a powerful analytical tool for ultrasensitive chemical analysis. However, the direct detection of PAHs by SERS is difficult due to poor affinity of PAHs to metal surfaces. In this work, we present a SERS platform based on the Ag-nanoparticles/graphene hybrid for the direct detection of PAHs with graphene as PAHs assemblies. The target PAHs are captured by the graphene through π-π electronic stacking, and brought close to the hot spots generated by dense Ag-nanoparticles decorated on the graphene. Sensitive detection of PAHs has been realized using this SERS substrate without further surface modification. The limit of detection for the three typical PAHs including pyrene, anthracene and phenanthrene was as low as 0.73 ppb, 1.1 ppb and 0.57 ppb, respectively. Our results indicate that the immobilization of PAHs on graphene is a process that can be applied in the design of sensitive sensors for these aromatic pollutants. This functional SERS sensor shows a great potential application in food safety inspection and environment pollutants monitoring.

Spontaneous Growth of 3D Silver Mesoflowers on Poly(4-vinylpyridine) Brushes-Grafted-Graphene Oxide Films and Facile Creation of Nanoporosities over their Surface

Fabricating three-dimensional (3D) hierarchical noble-metal particles by spontaneous redox reactions between graphene and noble-metal salts still remains a great challenge. Herein, the fact that graphene oxide (GO) itself acts as both a platform for grafting polymer brushes and a reducing agent to reduce [Ag(NH₃ )₂ ]⁺ ions is taken advantages of. 3D flower-like Ag mesoparticles (Ag mesoflowers, Ag MFs) with tunable size and shapes can spontaneous grow on poly(4-vinylpyridine) brushes-grafted-graphene oxide (P4VP-g-GO) films in Ag(NH₃ )₂ OH solution without the use of any additional reducing agent. The residual Ag(NH₃ )₂ OH on 3D Ag MFs surface can be further reduced by NaBH₄ , causing abundant nanoporosities over the entire Ag MFs. The resulting Ag nanoporous MFs (Ag NMFs) with larger surface-to-volume ratio and higher nanoscale roughness exhibit ultrasensitivity in surface-enhanced Raman spectroscopy (SERS) detection, and the detection limit for 4-aminothiophenol is as low as 10^-13  m.

Theoretical study of methane adsorption and C─H bond activation over Fe-embedded graphene: Effect of external electric field

The effect of an external electric field (EF) on the methane adsorption and its activation on iron-embedded graphene (Fe-GPs) are investigated by using the M06-L density functional method. The EF is applied in the perpendicular direction to the graphene in the range of -0.015 to +0.015 a.u. with the interval of 0.005 a.u. The effects of EF on the adsorption, transition state and product complexes of the methane activation reaction are revealed. The binding energies of methane on Fe site in Fe-GPs are increased from -12.9 to -15.3, -18.1 and -21.5 kcal/mol for the negative EF of -0.005, -0.010 and -0.015, respectively. By applying positive EF, the activation barriers for methane activation are reduced in range of 3-8 kcal/mol (around 12-31%) and the reaction energies are more exothermic. The positive EF kinetically favors the reaction compared to the system without EF. The adsorption and activation of methane on Fe-GPs can be easily tuned by adjusting the external electric field for various applications. © 2019 Wiley Periodicals, Inc.

Microplasma assisted synthesis of gold nanoparticle/graphene oxide nanocomposites and their potential application in SERS sensing

This is the first study on the deployment of direct current atmospheric pressure microplasma technique for the single step synthesis of gold nanoparticle/graphene oxide (AuNP/GO) nanocomposites. The nanocomposites were characterized using ultraviolet-visible spectroscopy (UV-vis), x-ray diffraction and x-ray photoelectron spectroscopy and their formation mechanisms have been discussed in detail. Our AuNP/GO nanocomposites are highly biocompatible and have demonstrated surface enhanced Raman scattering (SERS) properties as compared to pure AuNPs and pure GO. Their potential as SERS substrate has been further demonstrated using probe molecules (methylene blue) at different concentrations.

Voltammetric measurements of neurotransmitter-acetylcholine through metallic nanoparticles embedded 2-D material

The most generally spread neurotransmitter acetylcholine (Ach) is used as a chemical messenger assisting in conveying signals transversely through the nerve synapse. Herein, two enzymes acetylcholinesterase and choline oxidase were covalently immobilized over the gold nanoparticles (Au_NPs) embedded graphene oxide (GO; 2D carbon material) nanocomposite modified ITO coated glass plate. The synergetic and unique properties of Au_NPs and GO present in nanocomposite are used to detect the ultra-small concentration of analyte, Ach. The prepared nanocomposites were characterized using different techniques i.e. TEM, XRD, SEM, FTIR, UV-Vis and Raman Spectroscopy. All the electrochemical measurements were performed using 3 electrodes integrated electrochemical system by introducing Ach through varying its concentration from 100 pM to 1000 nM. Cyclic voltammetry curves for different concentrations of Ach indicate the facile charge transfer process over the working electrode. Square wave voltammetry curves indicate the good sensing measurements of the modified electrode at the fixed potential. The limit of detection was found to be as low as 100 pM. In addition to these, selectivity of the electrode towards Ach molecule was confirmed by measuring the response towards other interfering agents. Besides this, the present nano interface is capable of detecting Ach in biological fluid such as serum.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

Two dimensional carbon based nanocomposites as multimodal therapeutic and diagnostic platform: A biomedical and toxicological perspective

Graphene based nanocomposites have revolutionized cancer treatment, diagnosis and imaging owing to its good compatibility, elegant flexibility, high surface area, low mass density along with excellent combined additive effect of graphene with other nanomaterials. This review inculcates the type of graphene based nanocomposites and their fabrication techniques to improve its properties as photothermal and theranostic platform. With decades' efforts, many significant breakthroughs in the method of synthesis and characterization in addition to various functionalization options of graphene based nanocomposite have paved a solid foundation for their potential applications in the cancer therapy. This work intends to provide a thorough, up-to-date holistic discussion on correlation of breakthroughs with their biomedical applications and illustrate how to utilize these breakthroughs to address long-standing challenges in the clinical translation of nanomedicines. This review also emphasizes on graphene based nanocomposites based toxicity concerns pertaining to delivery platforms.