Preparation of bimetallic nanoparticles using a facile green synthesis method and their application

Developmental toxicity, biochemical and biomarker in the zebrafish (Danio rerio) embryo exposed to biosynthesized cadmium oxide nanoparticles

Cadmium oxide nanoparticles (CdO-NPs) play an important role in health applications due to their antibacterial properties. However, ecotoxicological investigations of these NPs and their adverse effects on aquatic organisms are necessary to protect the environment. Zebrafish is widely used as a model organism to explore toxic effects at multiple levels of integration. Hence, the objective of this work was to pursue possible harmful impacts of CdO -NPs that have been produced through biosynthesis, utilizing extract from the lily plant Gloriosa superba leaves, on the growth and biochemical changes in zebrafish (Danio rerio) embryos and larvae. UV, SEM, TEM, FTIR, EDAX, DLS, and ZETA-potential techniques were employed to examine the structure and morphology of the biosynthesized CdO-NPs. The identification of bioactive chemicals from the leaf extract of G. superba was conducted using GC-MS. To study the in vivo toxicity of CdO-NPs, zebrafish embryos and larvae were treated with two different concentrations of G. superba leave extract (0.5 and 1.0 mg/mL) at 96 h after fertilization (hpf). Bended tail, pericardial edema, shortened yolk sac extension, scoliosis, and damaged eyes were observed in the CdO-NPs treated groups. In addition, there was a considerable decrease in the levels of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferases (GST), and lipid peroxidation (LPO). The CdO-NPs treated groups showed significant alterations in biochemical markers, including protein levels, glucose levels, and acetylcholinesterase (AChE) activity. Overall, our findings indicated that CdO-NPs induced a dose-dependent toxicity in zebrafish embryos. The investigated parameters serve as reliable biomarkers for the surveillance of CdO-NPs in aquatic ecosystems and their impact on living animals.

Au@Ag nanoparticles: an analytical tool to study the effect of tyrosine on dopamine levels

The neurotransmitter dopamine (DA) plays important roles in the human body, including regulatory functions, movement, memory and motivational control. The direct intake of DA is impossible as it cannot cross the blood-brain barrier (BBB) efficiently. Notably, l-tyrosine works as a precursor of DA in the human brain. Herein, we report an analytical method that strongly supports the hypothesis that the intake of tyrosine (Tyr)-rich food enhances DA levels. For this analysis, citrate-coated gold-core silver-shell nanoparticles (Au@Ag NPs) were synthesized. The interaction of DA with the Au@Ag NPs was investigated using multiple spectroscopic techniques, and different thermodynamic parameters were evaluated to assign the binding mechanism. Real sample analysis with Tyr-rich food was also conducted to study the effect of Tyr on DA levels. Analytical studies were performed to verify the outcomes of the present work. The limit of detection of the Au@Ag NPs-DA system for Tyr was found to be 1.64 mM. This study can contribute to development in the fields of medicine and pharmaceuticals, particularly in regard to neuromedicine. One of the major advantages of this investigation is that it will fuel research interest in the supplementation of neurotransmitters and help categorize Tyr as a dietary precursor of dopamine.

Fast synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms via galvanic replacement for efficient 4-nitrophenol reduction

We report the synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms (BTNPs) using a galvanic replacement method. Based on ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) analyses, the structure of Cu/Ag BTNPs was characterized. The prepared Cu/Ag BTNPs exhibited excellent catalytic activity and good cycling stability for the reduction of 4-nitrophenol (4-NP) due to the synergistic effect between Cu and Ag elements. The kinetic rate constant (k) and turnover frequency (TOF) values reached 331 × 10-3 s-1 and 500 × 10-3 s-1, respectively, which were higher than those of previously reported Cu, Ag, Au, Cu/Ag or Cu/Au-based catalysts. We hope that the development of promising routes for high-quality BTNPs can broaden their applications in catalysis and environmental sustainability.

Harnessing the potential of bimetallic nanoparticles: Exploring a novel approach to address antimicrobial resistance

The growing global importance of antimicrobial resistance (AMR) in public health has prompted the creation of innovative approaches to combating the issue. In this study, the promising potential of bimetallic nanoparticles (BMNPs) was investigated as a novel weapon against AMR. This research begins by elaborating on the gravity of the AMR problem, outlining its scope in terms of the effects on healthcare systems, and stressing the urgent need for novel solutions. Because of their unusual features and wide range of potential uses, bimetallic nanoparticles (BMNPs), which are tiny particles consisting of two different metal elements, have attracted a lot of interest in numerous fields. This review article provides a comprehensive analysis of the composition, structural characteristics, and several synthesis processes employed in the production of BMNPs. Additionally, it delves into the unique properties and synergistic effects that set BMNPs apart from other materials. This review also focuses on the various antimicrobial activities shown by bimetallic nanoparticles, such as the rupturing of microbial cell membranes, the production of reactive oxygen species (ROS), and the regulation of biofilm formation. An extensive review of in vitro studies confirms the remarkable antibacterial activity of BMNPs against a variety of pathogens and sheds light on the dose-response relationship. The efficacy and safety of BMNPs in practical applications are assessed in this study. It also delves into the synergistic effects of BMNPs with traditional antimicrobial drugs and their ability to overcome multidrug resistance, providing mechanistic insight into these phenomena. Wound healing, infection prevention, and antimicrobial coatings on medical equipment are only some of the clinical applications of BMNPs that are examined, along with the difficulties and possible rewards of clinical translation. This review covers nanoparticle-based antibacterial regulation and emerging uses. The essay concludes with prospects for hybrid systems, site-specific targeting, and nanoparticle-mediated gene and drug delivery. In summary, bimetallic nanoparticles have surfaced as a potential solution, offering the public a more promising and healthier future.

Light-Driven Catalytic Activity of Green-Synthesized SnO2/WO3-x Hetero-nanostructures

This work reports an environmentally friendly and economically feasible green synthesis of monometallic oxides (SnO₂ and WO₃) and their corresponding mixed metal oxide (SnO₂/WO_3-x) nanostructures from the aqueous Psidium guajava leaf extract for light-driven catalytic degradation of a major industrial contaminant, methylene blue (MB). P. guajava is a rich source of polyphenols that acts as a bio-reductant as well as a capping agent in the synthesis of nanostructures. The chemical composition and redox behavior of the green extract were investigated by liquid chromatography-mass spectrometry and cyclic voltammetry, respectively. Results acquired by X-ray diffraction and Fourier transform infrared spectroscopy confirm the successful formation of crystalline monometallic oxides (SnO₂ and WO₃) and bimetallic SnO₂/WO_3-x hetero-nanostructures capped with polyphenols. The structural and morphological aspects of the synthesized nanostructures were analyzed by transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Photocatalytic activity of the synthesized monometallic and hetero-nanostructures was investigated for the degradation of MB dye under UV light irradiation. Results indicate a higher photocatalytic degradation efficiency for mixed metal oxide nanostructures (93.5%) as compared to pristine monometallic oxides SnO₂ (35.7%) and WO₃ (74.5%). The hetero-metal oxide nanostructures prove to be better photocatalysts with reusability up to 3 cycles without any loss in degradation efficiency or stability. The enhanced photocatalytic efficiency is attributed to a synergistic effect in the hetero-nanostructures, efficient charge transportation, extended light absorption, and increased adsorption of dye due to the enlarged specific surface area.

Boosting the Catalytic Performance of AuAg Alloyed Nanoparticles Grafted on MoS2 Nanoflowers through NIR-Induced Light-to-Thermal Energy Conversion

MoS₂ nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS₂ NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0-2.5 nm) was possible through the decomposition of organometallic complexes [Au₂Ag₂(C₆F₅)₄(OEt₂)₂]_n and [Au(C₆F₅)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1-4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS₂ NFs component. The AuAg-MoS₂ nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS₂ nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field-Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy.

Recyclable Cu-Ag bimetallic nanocatalyst for radical scavenging, dyes removal and antimicrobial applications

An ecofriendly and cost effective green method has been used for the synthesis of recyclable, high functional nanoparticles. Bimetallic nanoparticles (BmNPs), Cu-Ag, have been synthesized using beetroot extract as reducing and capping agent. Formation of BmNPs was initially confirmed by UV-visible analysis, having distinct peaks of Ag at 429 nm and Cu at 628 nm. FTIR analysis also confirmed the association of bioactive phytochemicals with Cu-Ag nanoparticles. Crystallinity and morphology of BmNPs was determined through X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS) and energy dispersion X-ray spectroscopy (EDAX). The size of spherical shape Cu-Ag BmNPs was found to be 75.58 nm and EDAX studies confirmed the percent elemental composition of Cu and Ag in synthesized nanocatalyst. Results of different analysis provided supported evidences regarding the formation of BmNPs. Catalytic potential of BmNPs was tested for the degradation of rhodamine B (Rh-B), methylene blue (MB) and methyl orange (MO) dyes. Cu-Ag BmNPs exhibited outstanding catalytic activity for the degradation of selected organic dyes and percent degradation was recorded more than 90% for each dye. In addition, antiradical property of BmNPs was tested employing DPPH^● and ABTS^●+ assays and it was found to be promising. Synthesized BmNPs also exhibited strong antimicrobial activity against Salmonella typhimurium and Bacillus subtilis. Recyclability of nanoparticles was also evaluated and recovery from dye degradation reaction mixture was successfully achieved. The recovered nanoparticles exhibited same catalytic potential for the degradation of Rh-B. The objective of the current study was to synthesize BmNPs Cu-Ag employing a cost effective green method having promising catalytic, antiradical and antimicrobial potential. Further, BmNPs were reused after recovery from catalytic reactions, proving that BmNPs can be recycled having the same efficiency as that of a freshly prepared Cu-Ag BmNPs.

Fabrication of Bimetallic Cu-Ag Nanoparticle-Decorated Poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) and Its Enhanced Catalytic Activity for the Reduction of 4-Nitrophenol

We reported a study on the preparation of bimetallic Ag-Cu nanoparticles (NPs) impregnated on PZS poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) nanotubes via a facile and efficient reduction method. Herein, PZS nanotubes consisting of enriched hydroxyl groups are fabricated through an in situ template method, and then, fluctuating the amount ratios of Cu and Ag precursors, bimetallic NPs can be fabricated on readily prepared PZS nanotubes using NaBH4 as a reductant, which results in a series of bimetallic catalysts having tunable catalytic activity. The characterization investigations of scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy results show that Ag-Cu bimetallic NPs are well-dispersed, ultrasmall in size, and well-anchored on the surface of PZS nanotubes. In addition, to examine the catalytic activity and reusability of these nanocomposites, reduction of 4-nitrophenol to 4-aminophenol is utilized as a prototype reaction. The optimized Ag-Cu NPs with a copper ratio of 0.3% are well-stabilized by the organic-inorganic poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) nanotubes. The obtained results show that bimetallic NPs have remarkably higher catalytic ability than that of their monometallic counterparts with maximum catalytic activity. These results are even better than those of noble metal-based bimetallic catalysts and pave the avenue to utilize the polyphosphazene polymer as a substrate material for highly effective bimetallic catalysts.

State of the Art on Green Route Synthesis of Gold/Silver Bimetallic Nanoparticles

Recently, bimetallic nanoparticles (BMNPs) blending the properties of two metals in one nanostructured system have generated enormous interest due to their potential applications in various fields including biosensing, imaging, nanomedicine, and catalysis. BMNPs have been developed later with respect to the monometallic nanoparticles (MNPs) and their physicochemical and biological properties have not yet been comprehensively explored. The manuscript aims at collecting the main design criteria used to synthetize BMNPs focusing on green route synthesis. The influence of experimental parameters such as temperature, time, reagent concentrations, capping agents on the particle growth and colloidal stability are examined. Finally, an overview of their nanotechnological applications and biological profile are presented.

Reduction of 4-nitrophenol using green-fabricated metal nanoparticles

Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research. This review focuses on the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The mechanisms for the formation of these nanoparticles and the catalytic reduction of 4-NP are discussed. Furthermore, the parameters that need to be considered in the catalytic efficiency calculations and perspectives for future studies are also discussed.

Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research.

Bimetallic nanocomposite (Ag-Au, Ag-Pd, Au-Pd) synthesis using gum kondagogu a natural biopolymer and their catalytic potentials in the degradation of 4-nitrophenol

Bimetallic nanoparticles (BNPs) constitute two different metal elements and exhibit relatively superior mechanistic and catalytic efficacies owing to their synergistic functions over monometallic nanoparticles. In the present study various bimetallic Ag-Au, Ag-Pd, Au-Pd nanoparticles were synthesized using a natural biopolymer gum kondagogu (GK) as a reducing and capping agent, by a simple and cost-effective method. The synthesized BNPs when characterized using UV-vis spectroscopy revealed a specific surface plasmon resonance band (SPR) of each nanocomposite. The average particle size of Ag-Au, Ag-Pd, and Au-Pd BNPs was found to be 23 ± 10.3, 21 ± 7.6, and 23 ± 9.4 nm respectively based on transmission electron microscopy analysis. Surface morphology and functional groups on the gum matrix of GK-BNPs were analyzed by XRD and FT-IR respectively. The bimetallic nanocomposites were evaluated for their catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol in the presence of NaBH₄. The kinetic studies performed, depicted rate constants for Ag-Au, Ag-Pd, and Au-PdNPs as 0.31, 0.39, and 0.28 min^-1 respectively. The catalytic efficiencies of three bimetallic nanocomposites were of the following order Ag-Pd > Ag-Au > Au-Pd. This study establishes the catalytic potentials of the three different bimetallic nanocomposites in the reduction of 4-NP an environmental pollutant, and the impact of their synergistic property.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Controllable Synthesis of Bimetallic Nanostructures Using Biogenic Reagents: A Green Perspective

Bimetallic nanostructures are emerging as a significant class of metal nanomaterials due to their exceptional properties that are useful in various areas of science and technology. When used for catalysis and sensing applications, bimetallic nanostructures have been noted to exhibit better performance relative to their monometallic counterparts owing to synergistic effects. Furthermore, their dual metal composition and configuration can be modulated to achieve optimal activity for the desired functions. However, as with other nanostructured metals, bimetallic nanostructures are usually prepared through wet chemical routes that involve the use of harsh reducing agents and hazardous stabilizing agents. In response to intensifying concerns over the toxicity of chemicals used in nanomaterial synthesis, the scientific community has increasingly turned its attention toward environmentally and biologically compatible reagents that can enable green and sustainable nanofabrication processes. This article aims to provide an evaluation of the green synthetic methods of constructing bimetallic nanostructures, with emphasis on the use of biogenic resources (e.g., plant extracts, DNA, proteins) as safe and practical reagents. Special attention is devoted to biogenic synthetic protocols that demonstrate controllable nanoscale features, such as size, composition, morphology, and configuration. The potential use of these biogenically prepared bimetallic nanostructures as catalysts and sensors is also discussed. It is hoped that this article will serve as a valuable reference on bimetallic nanostructures and will help fuel new ideas for the development of more eco-friendly strategies for the controllable synthesis of various types of nanostructured bimetallic systems.

Synthesis, Properties, and Biological Applications of Metallic Alloy Nanoparticles

Metallic alloy nanoparticles are synthesized by combining two or more different metals. Bimetallic or trimetallic nanoparticles are considered more effective than monometallic nanoparticles because of their synergistic characteristics. In this review, we outline the structure, synthesis method, properties, and biological applications of metallic alloy nanoparticles based on their plasmonic, catalytic, and magnetic characteristics.

Facile green synthesis of Ag-Cu decorated ZnO nanocomposite for effective removal of toxic organic compounds and an efficient detection of nitrite ions

A facile and eco-friendly green synthesis of silver-copper@zinc oxide (Ag-Cu@ZnO) nanocomposite using Acacia caesia flower extract and their application on catalytic reduction of toxic compounds and electrochemical sensing of nitrite ions are reported. The phytochemicals present in the extract were utilized for the Ag-Cu metal nanoparticles synthesis and also enhanced the binding capability between ZnO and Ag-Cu NPs. The synthesized nanocomposites were characterized by XRD, UV-Vis spectroscopy, Raman spectra, FTIR, SEM, TEM, EDX, XPS and ICP-AES for the formation of Ag-Cu NPs on ZnO. The Ag-Cu@ZnO nanocomposite showed better catalytic efficiency as compared to monometallic nanoparticles for 4-nitrophenol to 4-aminophenol conversion and Rhodamine B and Congo red dye degradation with 99% efficiency up to four cycles. The Ag-Cu@ZnO modified GC electrode showed enhanced catalytic activity towards nitrite oxidation, and it exhibited better performance compared to the other nanocomposites. An appreciable detection limit (17 μM) was achieved with excellent sensitivity for nitrite detection. The sensor was highly selective even in a many-fold higher concentration of co-existing interfering compounds. The good catalytic and electrochemical sensing is mainly ascribed due to the synergistic effect of Ag-Cu on the ZnO in the Ag-Cu@ZnO nanocomposite materials.

Controllable Synthesis of Surface Pt-Rich Bimetallic AuPt Nanocatalysts for Selective Hydrogenation Reactions

Bimetallic nanocatalysts, with efficient and controllable catalytic performance, have a promising application in chemical production. In this study, surface Pt-rich bimetallic AuPt nanoparticles with different Pt/Au ratios were prepared and tested in selective hydrogenation reactions of substituted nitroaromatics. Au nanoparticles were first prepared with n-butyllithium as a rapid reducer, which were further used as seeds in the slow growth process of Pt atoms. Because of the employed sequential reduction method and the following atom diffusion, surface Pt-rich bimetallic AuPt nanoparticles were obtained. Compared with the uniform AuPt alloy nanocatalysts synthesized by the co-reduction method with n-butyllithium as the reducer and monometallic Pt nanocatalysts, the obtained surface Pt-rich AuPt bimetallic nanocatalysts presented an enhanced catalytic selectivity or activity. The performance enhancement is assigned to the optimized Au/Pt interaction in the surface Pt-rich bimetallic nanostructures. This work demonstrates that the optimization of the stoichiometry and construction of bimetallic materials is a feasible method to synthesize controllable and efficient nanocatalysts.

Engineering Lignin Stabilized Bimetallic Nanocomplexes: Structure, Mechanistic Elucidation, Antioxidant, and Antimicrobial Potential

Lignin, being a natural antioxidant and antimicrobial underutilized biopolymer derived mainly from agro-waste, is a material of great interest. In this study, lignin was chosen as a matrix to synthesize silver-gold bimetallic and monometallic nanocomplexes to explore the synergistic antioxidant and antimicrobial properties of the lignin stabilized nanoagents. The synthesis of the nanocomplexes was carried out using a one pot method, utilizing lignin as the sole source for reducing, capping, and stabilizing the nanoagents. Further, characterization studies were performed to determine the exact structure of the nanocomplexes. The developed nanocomplexes were found to possess substantial phenolic and flavonoid contents, which contributed to their high antioxidant activity. Further, the antioxidant and antimicrobial activity of the lignin-bimetallic and monometallic nanocomplexes was evaluated and compared with pristine lignin. Moreover, the mechanism behind the antimicrobial activity of the nanocomplexes was elucidated through various methods, namely, reactive oxygen generation, nucleic acid leakage, and DNA cleavage studies. The obtained results were greatly supported by scanning electron microscopy, transmission electron microscopy, and live-dead cell imaging techniques. This study is a contribution in converting waste to value added functional nanomaterials for potential antioxidant and antimicrobial applications.

Biogenic synthesis of biopolymer-based Ag-Au bimetallic nanoparticle constructs and their anti-proliferative assessment

This study reports an eco-friendly-based method for the preparation of biopolymer Ag-Au nanoparticles (NPs) by using gum kondagogu (GK; Cochlospermum gossypium), as both reducing and protecting agent. The formation of GK-(Ag-Au) NPs was confirmed by UV-absorption, fourier transformed infrared (FTIR), atomic force microscopy (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The GK-(Ag-Au) NPs were of 1-12 nm in size. The anti-proliferative activity of nanoparticle constructs was assessed by MTT assay, confocal microscopy, flow cytometry and quantitative real-time polymerase chain reaction (PCR) techniques. Expression studies revealed up-regulation of p53, caspase-3, caspase-9, peroxisome proliferator-activated receptors (PPAR) PPARa and PPARb, genes and down-regulation of Bcl-2 and Bcl-x(K) genes, in B16F10 cells treated with GK-(Ag-Au) NPs confirming the anti-proliferative properties of the nanoparticles.

Starch-mediated synthesis of mono- and bimetallic silver/gold nanoparticles as antimicrobial and anticancer agents

BACKGROUND AND AIM

Bimetallic silver/gold nanosystems are expected to significantly improve therapeutic efficacy compared to their monometallic counterparts by maintaining the general biocompatibility of gold nanoparticles (AuNPs) while, at the same time, decreasing the relatively high toxicity of silver nanoparticles (AgNPs) toward healthy human cells. Thus, the aim of this research was to establish a highly reproducible one-pot green synthesis of colloidal AuNPs and bimetallic Ag/Au alloy nanoparticles (NPs; Ag/AuNPs) using starch as reducing and capping agent.

METHODS

The optical properties, high reproducibility, stability and particle size distribution of the colloidal NPs were analyzed by ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and ζ-potential. The presence of starch as capping agent was determined by Fourier transform infrared (FT-IR) spectroscopy. The structural properties were studied by X-ray diffraction (XRD). Transmission electron microscopy (TEM) imaging was done to determine the morphology and size of the nanostructures. The chemical composition of the nanomaterials was determined by energy-dispersive X-ray spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS) analysis. To further study the biomedical applications of the synthesized nanostructures, antibacterial studies against multidrug-resistant (MDR) Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) were conducted. In addition, the NPs were added to the growth media of human dermal fibroblast (HDF) and human melanoma cells to show their cytocompatibility and cytotoxicity, respectively, over a 3-day experiment.

RESULTS

UV-visible spectroscopy confirmed the highly reproducible green synthesis of colloidal AuNPs and Ag/AuNPs. The NPs showed a face-centered cubic crystal structure and an icosahedral shape with mean particle sizes of 28.5 and 9.7 nm for AuNPs and Ag/AuNPs, respectively. The antibacterial studies of the NPs against antibiotic-resistant bacterial strains presented a dose-dependent antimicrobial behavior. Furthermore, the NPs showed cytocompat-ibility towards HDF, but a dose-dependent anticancer effect was found when human melanoma cells were grown in presence of different NP concentrations for 72 hours.

CONCLUSION

In this study, mono- and bimetallic NPs were synthesized for the first time using a highly reproducible, environmentally friendly, cost-effective and quick method and were successfully characterized and tested for several anti-infection and anticancer biomedical applications.

Mild Synthesis of Copper Nanoparticles with Enhanced Oxidative Stability and Their Application in Antibacterial Films

Copper nanoparticles possess unique physical and chemical properties; however, their application is often restricted, owing to their tendency to oxidize. In this work, we prepared copper nanoparticles with enhanced oxidative stability via a simple and low-cost method, where a modified starch was used as an environmentally friendly reducing agent and biocompatible polyethylenimine was used as a stabilizer. The prepared copper nanoparticles could be stored in air for at least 6 months without any oxidation in a dried state. Interestingly, our synthesis could even be performed at room temperature with a longer reaction time. We used various characterization methods to study the reaction mechanism. The prepared copper nanoparticles were further uniformly doped into an agar film, and this composite showed excellent bacterial killing efficiency, owing to the antibacterial properties of the copper nanoparticles. Our composite film shows potential for various clinical applications, such as wound dressing materials.

Catalytic activity, structure and stability of proteinase K in the presence of biosynthesized CuO nanoparticles

Here, CuO nanoparticles were synthesized using Sambucus nigra (elderberry) fruit extract. Further, the binding of proteinase K, as a model enzyme with green synthesized nanoparticles was investigated. The results demonstrated that the structural changes in enzyme were induced by the binding of nanoparticles. These changes were accompanied by the decrease in the Michaelis-Menten constant at 298 K. This means that the enzyme affinity for the substrate was increased. Thermodynamic parameters of protein stability and protein-ligand binding were estimated from the spectroscopic measurements at 298-333 K. Depending on the temperature, CuO nanoparticles showed a dual effect on the thermodynamic stability and binding affinity of enzyme. Nanoparticles increase the stability of the native state of enzyme at room temperature. On the other hand, nanoparticles stabilize the unfolded state of enzyme at 310-333 K. An overall favorable Gibbs energy change was observed for the binding process at 298-333 K. The enzyme-nanoparticle binding is enthalpically driven at room temperature. It was concluded that hydrogen bonding plays a key role in the interaction of enzyme with nanoparticles at 298-310 K. At higher temperatures, the protein-ligand binding is entropically driven. This means that hydrophobic association plays a major role in the proteinase K-CuO binding at 310-333 K.

Synthesis of Bimetallic Gold-Silver (Au-Ag) Nanoparticles for the Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol

Bimetallic gold-silver nanoparticles as unique catalysts were prepared using seed colloidal techniques. The catalytic capabilities of the nanoparticles were ascertained in the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. Our results clearly showed that the rate of 4-NP reduction to 4-AP increased with a corresponding decrease in the diameter of the bimetallic NPs. The Au-Ag nanoparticles prepared with 5.0 mL Au seed volume indicated higher reduction activity, which was approximately 1.2 times higher than that of 2.0 mL Au seed volume in the reductive conversion of 4-NP to 4-AP. However, the monometallic NPs showed relatively less catalytic activity in the reductive conversion of 4-NP to 4-AP compared to bimetallic Au-Ag nanoparticles. Our studies also reinforced the improved catalytic properties of the bimetallic Au-Ag nanoparticles structure with a direct impact of the size or diameter and relative composition of the bimetallic catalytic nanoparticles.

Metallic nanoparticle synthesised by biological route: safer candidate for diverse applications

Biological synthesis of nanoparticles (NPs) involves greater prospect; however, a detailed review is required for ecofriendly, faster and stable NP formulation in large scale for different commercial applications. The present article highlighted recent updates on biological route of single and bimetallic NP synthesis wherein the chemical reducing agents are eliminated and biological entities are utilised to convert metal ions to NPs. Application of the biological reducing agents ranging from bacteria to fungi and even natural plant extracts have emerged as eco-friendly and cost-effective routes for the synthesis of metal nanomaterials. Potential applications of such NPs, a wide range of analytical techniques used for characterisation and factors influencing the synthesis of NPs are focused. Further, elucidation of the mechanisms associated with the NP formation using microorganisms, as well as plant-based materials are analysed which would be helpful for wide range of readers in the field of NP research for future selection and commercial implementation.

Starch-metal complexes and metal compounds

Recently, metal derivatives of starch evoked considerable interest. Such metal derivatives can take a form of starch compounds bearing metal atoms and metal carrying moieties either covalently bound or complexed. Starch metal complexes may have a character of either Werner, inclusion, sorption or capillary complexes. In this publication, preparation, structure, properties and numerous current and potential applications of those compounds as well as benefits resulting from the application and formation of the complexes are presented. © 2017 Society of Chemical Industry.

Co-Ag alloy protected by nitrogen doped carbon as highly efficient and chemoselective catalysts for the hydrogenation of halogenated nitrobenzenes

The design of lower-cost alternative heterogeneous catalysts for the hydrogenation of halogenated nitrobenzenes using green method to synthesize the corresponding anilines is highly desirable. In this study, Ag was incorporated into the Co-MOFs during the growing process (Co-Ag(n)-MOFs), and then followed the carbothermal reduction process without any additional procedures, we synthesized a series of Co-Ag(n)@NCs. The self-supported catalysts exhibited excellent and stable catalytic performances for the chemoselective hydrogenation of halogenated nitrobenzenes without obvious dehalogenation. The Co-Ag bimetallic alloy nanoparticles were well-dispersed and protected from aggregation and leaching by the porous nitrogen doped carbon. Besides, either hydrazine hydrate (N₂H₄·H₂O, generating byproducts N₂ and H₂O) or H₂ could be used as green reducing agent with excellent selectivity towards synthesizing the corresponding anilines. And when the Co/Ag content ratio was approximate 1:1, the Co-Ag(1:1)@NC showed the best catalytic performance. Moreover, the Co-Ag(1:1)@NC could be efficiently recovered by using an external magnetic force and reused without obvious decrease of catalytic activity. Thus, such highly efficient, inexpensive, stable and magnetically recyclable catalysts could show great potentials in practical applications for many important reactions.

Ligand free green plasma-in-liquid synthesis of Au/Ag alloy nanoparticles

Au/Ag alloy nanoparticles were successfully prepared by a microwave-induced plasma in liquid process without any organic protecting or reducing agents.

Synthesis of a bimetallic conducting nano-hybrid composite of Au–Pt@PEDOT exhibiting fluorescence

One pot novel synthesis of ternary nanocomposite Au–Pt@PEDOT was accomplished using green solvent.