Au Bimetallic Nanoparticles Research Articles

Biosynthesis of bimetallic Au-Ag nanoparticles using Abrus precatorius seed Extract: Analysis of photocatalytic, cytotoxic, and antibacterial activities

The present investigation aims to examine the bio-route preparation of gold-silver bimetallic nanoparticles using an aqueous seed extract of the Abrus precatorius plant. The bio-synthesized gold-silver bimetallic nanoparticles (AP-Au-Ag NPs) were characterized by various spectroscopic techniques. The surface plasmon resonance (SPR) peak at 555 nm for Au, 433 nm for Ag, and 546 nm for the Au-Ag alloy indicates that bimetallic NPs have been formed. FTIR data provided evidence of functional groups such as OH, CO, and NH2 (proteins, flavonoids, and carbohydrates). When making a bimetallic Au-Ag alloy, carbohydrates are useful as a capping agent and proteins as a reducing agent. The AP-Au-Ag NPs’ stability was assessed by looking at their negative zeta potential value of −21.5 mV. The spherical-shaped crystalline alloy AP-Au-Ag NPs was produced with an average particle size of 10 nm. The TEM images verified the presence of polydispersity in the AP-Au-Ag NPs. The synthesized alloy nanoparticles have a potential cytotoxic effect against MCF-7 cancer cell lines with an IC50 value of 25 ± 1.5 μg/mL and the AP-Au-Ag NPs were found to be a good antibacterial agent against gram-positive and gram-negative bacteria. During visible light photocatalysis, ciprofloxacin was not removed after 60 min of exposure when employing materials made of a pure monometallic nanoparticle. However, the use of bi-metallic nanoparticles made of gold and silver resulted in the breakdown of over 90% of the ciprofloxacin into minerals. The produced bi-metallic nanoparticles, composed of Au-Ag showed exceptional catalytic efficiency. The gold-silver alloyed nanoparticles showed the most promise and efficiency when compared to others.

Eco-Friendly Synthesis, Characterization, and Biomedical Applications of Biosynthesized Bimetallic Silver-Gold Nanoparticles by Culture Supernatant of Aspergillus niger.

Green synthesis of bimetallic nanoparticles of noble metals is highly desirable in nanomedicine because of their potential use as anticoagulant, thrombolytic and anticancer agents. In this study, it was discovered that the filamentous fungus Aspergillus niger proved effective in producing bimetallic Ag-Au nanoparticles. A. niger culture supernatant was able to produce Ag-AuNPs by reducing the solution of chloroauric acid/silver nitrate (1.0:1.0 mM) within 2 min at 100 °C and pH 8. Experimental Ag-AuNP detection was performed by visually observing the color change to reddish brown. The produced nanoparticles displayed maximal absorbance at 530 nm in UV-vis spectroscopy. According to transmission electron microscopy, most of the nanoparticles were spherical, with a mean diameter of 8-10 nm. The biosynthesis of Ag-AuNPs by A. niger was confirmed by Fourier transform infrared spectroscopy, X-ray diffraction and energy dispersive X-ray analytical techniques. Its zeta potential was discovered to be -34.01 mV. The biosynthesized Ag-AuNPs exhibited effective thrombolytic and antiplatelet aggregation actions by totally preventing and dissolving the blood clot which was verified by microscopic examination, amelioration of blood coagulation assays, and carrageenan-induced tail thrombosis model. The findings verified the effectiveness of biosynthesized Ag-AuNPs as a powerful antitumor agent against HepG2 and A549 cell lines with IC50 values of 15.57 and 27.07 μg/mL, respectively. Crystal violet assay validated the cytopathic effects of Ag-AuNPs on A549 and HepG2 cell lines. Therefore, the produced Ag-AuNPs from A. niger are a promising candidate in the management of thrombosis.

Electrochemical Detection of Dopamine: Use of Covalently Bonded Ag (Silver) - Au (Gold) Bimetallic Nanoparticles

Dopamine (DA) is a crucial neurotransmitter that is generated by dopaminergic neurons in the central nervous system. We have produced and studied aspartic acid-capped gold nanoparticles and thioctic acid-capped silver nanoparticles, and we have covalently linked them via EDC-NHS coupling. The heightened stability and reproducibility of the Ag-Au-Nafion modified glassy carbon electrode (GCE) allowed for the sensitive and accurate detection of dopamine in PBS buffer at pH 6. The electrode modification approach’s selectivity and sensitivity as well as the possible interference of other compounds present in complicated biological samples, require more study. The creation of more precise and sensitive electrochemical sensors for dopamine detection is aided by this discovery, which has broad implications for medical diagnostics.

Bimetallic nanoparticles with sulfated galactan eliminate Vibrio parahaemolyticus in shrimp Penaeus vannamei

Bimetallic (Au/Ag) nanoparticles (BNPs) have shown enhanced antibacterial activity compared to their monometallic counterparts. Sulfated galactans (SG) are a naturally occurring polymer commonly found in red seaweed Gracilaria fisheri. They are biocompatible and biodegradable and environmentally friendly. In this study, we utilized SG in combination with BNPs to develop composite materials that potentially enhance antibacterial activity against shrimp pathogens Vibrio parahaemolyticus and Vibrio harveyi, compared to BNPs or SG alone. BNPs were coated with sulfated galactan (SGBNPs) and characterized using UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, zeta potential, and transmission electron microscopy (TEM). UV–vis spectroscopy analysis revealed that the surface plasmon peaks of BNPs and SGBNPs appeared at 530 nm and 532 nm, respectively. Zeta potential measurements showed that SGBNPs had a negative charge of −32.4 mV, while the BNPs solution had a positive charge of 38.7 mV. TEM images demonstrated the spherical morphology of both BNPs and SGBNPs with narrow size distributions (3–10 nm). Analysis of the FTIR spectra indicated that SG maintained its backbone structure in SGBNPs, but some functional groups were altered. Notably, SGBNPs showed superior antimicrobial and antibiofilm activities against V. parahaemolyticus and V. harveyi compared to SG and BNPs. Furthermore, treatment with SGBNPs significantly down-regulated the expression of virulence-related genes (toxR, cpsQ, and mfpA) for V. parahaemolyticus 3HP compared to the respective control, bacteria treated with BNPs or SG. Diets supplemented with SGBNPs, BNPs, or SG showed no detrimental impact on the growth of shrimp Penaeus vannamei. Shrimp fed with SGBNPs-supplemented feed showed significantly higher survival rates than those fed with BNPs-supplemented feed when infected with 3HP after being on the supplemented feed for seven days and a subsequent number of fifteen days. These findings collectively demonstrate the benefit of using SG capped Au–Ag BNPs as an antibacterial agent for the prevention and control of Vibrio sp. Infection in shrimp while reducing the risk of environmental contamination.

Ultrasound-electrochemistry assisted liquid-phase co-exfoliation of phosphorene decorated by Au-Ag bimetallic nanoparticles as nanozyme for smartphone-based portable sensing of 4-nitrophenol.

The stability of black phosphorene (BP) and its preparation and modification for developing and applying devices have become a hot topic in the interdisciplinary field. We propose ultrasound-electrochemistry co-assisted liquid-phase exfoliation as an eco-friendly one-step method to prepare gold-silver bimetallic nanoparticles (Au-AgNPs)-decorated BP nanozyme for smartphone-based portable sensing of 4-nitrophenol (4-NP) in different water sources. The structure, morphology, composition, and properties of Au-AgNPs-BP nanozyme are characterized by multiple instrumental analyses. Bimetallic salts are induced to efficiently occupy oxidative sites of BP to form highly stable Au-AgNPs-BP nanozyme and guarantee the integrity of the lamellar BP. The electrochemistry shortens the exfoliation time of the BP nanosheet and contributes to the loading efficiency of bimetallic nanoparticles on the BP nanosheet. Au-AgNPs-BP-modified screen-printed carbon electrode coupled with palm-sized smartphone-controlled wireless electrochemical analyzer as a portable wireless intelligent sensing platform was applied to the determination of 4-NP in a linear range of 0.6-10 μM with a limit of detection of 63 nM. It enables on-site determination of 4-NP content in lake water, river water, and irrigation ditch water. This work will provide a reference for an eco-friendly one-step preparation of bimetallic nanoparticle-decorated graphene-like materials as nanozymes and their smartphone-based portable sensing application outdoors.

Ag-Au bimetallic nanoparticle-based electrochemical sensing platform for quantification of B-type natriuretic peptide

A highly responsive and specific electrochemical biosensor utilizing Ag-Au bimetallic nanoparticles was engineered for the measurement of B-type natriuretic peptide (BNP), serving as an indicator for heart failure. The sensor was fabricated by modifying a glassy carbon electrode with Ag-Au bimetallic nanoparticles (average diameter: 20 ± 3 nm) and immobilizing anti-BNP antibodies. The sensor exhibited a wide linear range (0.0001–100 ng/mL), low limit of detection (0.03 pg/mL), and excellent specificity towards BNP, with minimal interference from other proteins (< 5 %). The practicality of the sensor was demonstrated by analyzing spiked serum samples, with recoveries ranging from 96.4 % to 103.5 % and relative standard deviations less than 4.5 %. The superior analytical property of the sensor is due to the synergistic effect of Ag and Au in enhancing electron transfer and antigen-antibody binding. The suggested biosensor holds significant promise for the early detection and monitoring of heart failure in medical environments.

Recyclable Ag-Au bimetallic nanoparticles supported on acid functionalized multi walled carbon nanotubes for effective catalytic applications

In the present investigation, in situ green reduction approach is used to uniformly decorate the Ag-Au bimetallic nanoparticles (BNPs) on the surface of acid functionalised multi-walled carbon nanotubes (MWCNTs). The adsorbed Terminalia catappa aqueous leaf extract biopolymers on the surface of MWCNTs can increase the in situ reduction of Ag, Au ions to Ag-Au BNPs and stabilise them which can operate as a capper/stabiliser and reductant agent. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy - energy dispersive x-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FT-IR) and UV–visible spectroscopy techniques were employed to examine the structures, morphologies, composition, chemical bonds and optical properties of the functionalised MWCNTs and the nanohybrid. The results revealed that the spherical T.C-Ag-Au bimetallic nanoparticle with average size 12.4 nm was uniformly distributed on the surface of modified MWCNTs. Finally, evaluation of the catalytic activity of the T.C-Ag-Au BNPs decorated MWCNTs exhibited excellent catalytic performance for completing the reduction of 4-Nitrophenol (4-NP) and degradation of alizarin red (AR) dye at ambient temperature with a great rate constant and the degradation efficiency of 98.7% and 96.4%, respectively. The order of reaction, rate constant, half-life and mechanism of catalytic activity of the T.C-Ag-Au BNPs@COOH-MWCNTs nanohybrid were calculated using the Langmuir–Hinshelwood model. The catalyst can be retained and reapplied eight times without affecting its catalytic performance. The interaction between T.C-Ag-Au BNPs and MWCNTs has a synergistic effect, which is accountable for the enhanced catalytic activity.

Research on the application of WO3 gas sensor based on noble metals modification in cable fire detection

In the monitoring of cable fire, it is of great significance to be able to conduct early fire warning, which requires that sensors have high sensitivity to the cable vapors at low temperatures. In this study, WO3 thick films modified with Au, Pd, and Pt single or bimetallic nanoparticles were fabricated via magnetron sputtering. Gas sensors utilizing these materials exhibited significant response to the low-temperature vapor emitted by YJV22 and YJY23 cables. Among them, Pd/WO3-20 demonstrated a response value of 20 to the vapor of 81[Formula: see text]C YJV22 cables, marking a remarkable 6.3-fold increase compared to pure WO3, and the response time was 13 s. Similarly, Pt/WO3-10 exhibited a response value of 11.11 to the vapor of 104[Formula: see text]C YJY23 cables, representing a 6.9-fold enhancement over pure WO3 with a response time of 12 s. The heating temperature of cables remains below their critical threshold, indicating that it is in the early stages of cable fires, the findings hold significant implications for early warning systems designed to detect cable fires promptly.

Flow field-flow fractionation and single particle inductively coupled plasma mass spectrometry as a powerful tool for tracking and understanding the sensing mechanism of Ag–Au bimetallic nanoparticles toward cobalt ions

BackgroundAg–Au bimetallic nanoparticles (BNPs), synthesized by using citrate reduction of Ag and Au ions, were used as sensor for detection of Co2+. In order to optimize sensing performance, it is necessary to control the particle size and size distribution of the original Ag–Au BNPs. Therefore, analytical methods based on the use of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and flow-field flow fractionation (FlFFF)-ICP-MS were developed to track the signal of Ag and Au in bimetallic nanoparticles at each step of the procedure: BNP synthesis, aggregation and sensing in order to understand the sensing mechanism. To better understand colorimetric sensing of Co2+ using Ag–Au BNPs, various solution mixtures were analyzed by using SP-ICP-MS and FlFFF-ICP-MS. ResultsSP-ICP-MS provided the information on the core size, size distribution and particle number concentration, as well as the heterogeneity of the particles synthesized by using various citrate concentrations and metal ratios. FlFFF-ICP-MS offered the information on hydrodynamic size as well as the signal intensity ratio of Ag and Au in BNPs and for the understanding of the aggregation of BNPs arising from the [Co(II)(en)3]2+ complex surrounding the surface of the BNPs. Under optimum sensing condition, the use of SP-ICP-MS for BNPs assisted detection of Co2+ improved the sensitivity of Co2+ determination by 20-fold in comparison with the conventional spectrophotometric analysis. SignificanceThe information obtained from SP-ICP-MS and FlFFF-ICP-MS can be combinedly used to understand sensing mechanism and to select the best condition for synthesis of BNPs used as sensor. This study illustrates the usefulness of SP-ICP-MS and FlFFF-ICP-MS in the nanoparticle-based sensor development research area.

Ionic Liquid-Assisted Thermal Evaporation of Bimetallic Ag-Au Nanoparticle Films as a Highly Reproducible SERS Substrate for Sensitive Nanoplastic Detection in Complex Environments.

Nanoplastic particles are emerging as an important class of environmental pollutants in the atmosphere that have adverse effects on our ecosystems and human health. While many methods have been developed to quantitatively detect nanoplastics; however, sensitive detection at low concentrations in a complex environment remains elusive. Herein, we demonstrate a greener method to fabricate a surface-enhanced Raman spectroscopy (SERS) substrate consisting of self-assembled plasmonic Ag-Au bimetallic nanoparticle (NP) films for quantitative SERS detection of nanoplastics in complex media. The self-assembly of Ag-Au bimetallic NPs was achieved through thermal evaporation onto a vapor-phase compatible ionic liquid based on deep eutectic solvent over the growth substrate. The finite-difference time-domain simulation revealed that the localized field enhancement is strong in the gaps, which generate uniform SERS "hotspots" in the obtained substrate. Benefiting from highly accessible SERS "hotspots" at the gaps, the SERS substrate exhibits excellent sensitivity for detecting crystal violet with a limit of detection (LOD) as low as 10-14 M and excellent reproducibility (RSD of 5.8%). The SERS substrate is capable of detecting PET nanoplastics with LOD as low as 1 μg/mL and about 100 μg/mL in real samples such as tap water, lake water, diluted milk, and wine. Moreover, we also validated the feasibility of the designed SERS substrate for the practical detection of PET nanoplastics collected from commercial drinking water bottles, and it showed great potential applications for sensitive detection in actual environments.

The effect of electrode composition on bimetallic AgAu nanoparticles produced by spark ablation

A flexible way to generate bimetallic nanoparticles with high control of their composition is to use spark ablation of alloyed electrodes. It has been generally accepted and stated that particles produced using spark ablation of alloyed electrodes obtain the same chemical composition as the electrodes. However, we identify a lack of studies fully supporting the connection between electrode and particle composition, presented in a small literature survey. The aim of the study is, hence, to explore the validity of the statement by analysing the relation between alloyed electrodes and their resulting particle composition using three sets of AgAu electrodes containing Au and 25, 50, and 75 atomic % Ag, respectively. The resulting composition is thoroughly investigated using both single particle (scanning- and transmission electron microscopy) and ensemble particle techniques (inductive coupled plasma-mass spectroscopy, x-ray photoelectron spectroscopy, x-ray fluorescence, and optical measurements of surface plasmon resonance. We also investigate how sample size (e.g., the number of particles analysed) affects the reliability of the resulting sample mean. For single-particle measurements of a sample with a compositional standard deviation of a few atomic percentage points, a sample size of 20 particles is a good benchmark for obtaining reliable results of the sample mean. Furthermore, this article aims to challenge the practice in which the composition of nanoparticles is measured, presented, and interpreted, to improve and facilitate future research related to this topic. From the results of this study, it could be concluded that for the investigated Ag–Au material system, the particles obtained a composition very similar to the alloyed AgAu electrodes.

Ag Surface Segregation in Sub-10-nm Bimetallic AuAg Nanoparticles Quantified by STEM-EDS and Machine Learning: Implications for Fine-Tuning Physicochemical Properties for Plasmonics and Catalysis Applications

Ag Surface Segregation in Sub-10-nm Bimetallic AuAg Nanoparticles Quantified by STEM-EDS and Machine Learning: Implications for Fine-Tuning Physicochemical Properties for Plasmonics and Catalysis Applications

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.

Enhancing the Extinction Efficiency and Plasmonic Response of Bimetallic Nanoparticles of Au-Ag in Robust Thin Film Sensing Platforms

The extinction efficiency of noble metal nanoparticles (NPs), namely gold (Au) and silver (Ag), are dependent on their size and surrounding dielectric. Exploiting the Localized Surface Plasmon Resonance (LSPR) phenomenon, the composition and structure of the NPs might be tailored to achieve a configuration that optimizes their response (sensitivity) to environmental changes. This can be done by preparing a bimetallic system, benefiting from the chemical stability of Au NPs and the higher scattering efficiency of Ag NPs. To enhance the LSPR sensing robustness, incorporating solid supports in the form of nanocomposite thin films is a suitable alternative. In this context, the NPs composed of gold (Au), silver (Ag), and their mixture in bimetallic Au-Ag NPs, were grown in a titanium dioxide (TiO2) matrix using reactive DC magnetron sputtering. Thermal treatment at different temperatures (up to 700 °C) tuned the LSPR response of the films and, consequently, their sensitivity. Notably, the bimetallic film with Au/Ag atomic ratio 1 exhibited the highest refractive index sensitivity (RIS), with a value of 181 nm/RIU, almost one order of magnitude higher than monometallic Au-TiO2. The nanostructural analysis revealed a wide NP size distribution of bimetallic NPs with an average size of 31 nm, covering about 20% of the overall surface area. These findings underscore the significant potential of bimetallic film systems, namely AuAg-TiO2, in LSPR sensing enhancement.

Catalytic and anti-cancer properties of platinum, gold, silver, and bimetallic Au-Ag nanoparticles synthesized by Bacillus sp. bacteria

Metallic nanoparticles play a significant role in the catalysis of chemical processes, besides, bimetallic nanoparticles with abundant active sites can reduce metallic nanoparticles toxicity in addition to increasing their catalytic performances. In this work, the platinum, gold, and silver nanoparticles are bio-synthesized using a native bacterium (GFCr-4). Also, the Au-Ag and Au@Ag bimetallic nanoparticles with alloy and core-shell structures, respectively, are biologically synthesized. To improve the synthesis, the effects of various factors like pH, temperature, electron donor, and ionic liquids were investigated. The as-synthesized nanoparticles were characterized with different techniques. The microscope images and dynamic light scattering (DLS) analysis confirm the uniform distribution of as-synthesized nanoparticles with average sizes of 25, 30, 47, 77, and 86 nm obtained for Ag, Au, Pt, Au-Ag alloy, and Au@Ag core-shell, respectively. The catalytic performances of as-synthesized nanoparticles were investigated. The Au-Ag alloy nanoparticles exhibit better catalytic performance than the as-synthesized metallic Au nanoparticles, according to the Gewald reaction. According to the photocatalytic study, the yield can be increased by up to 92% by using PtNPs in the presence of a green LED. Additionally, for the first time, PtNPs were utilized as an effective catalyst in a peroxyoxalate chemiluminescence (POCL) system in the presence of nuclear fast red (NFR) as a novel fluorophore. In addition, the results of the MTT (3-[4,5-dimethylthiazol-2-yl]−2,5 diphenyl tetrazolium bromide) assay revealed that the synthesized eco-friendly nanoparticles have a low effect on the lethality of 3T3 normal cells whereas MCF-7 cancer cells were inhibited up to 77.3% after treatment by PtNPs nanoparticles.

Pyto-Architechture of Ag, Au and Ag–Au bi-metallic nanoparticles using waste orange peel extract for enable carcinogenic Congo red dye degradation

Ecologically inspired to develop silver, gold and silver/gold bimetallic nanoparticles from discarded orange peel extract. The plant-derived compounds included in discarded orange peel extract have been accountable for the development of Ag, Au and Ag–Au bimetallic nanoparticles, that might be used in the biosynthetic process. The qualitative assessment of developed silver, gold and silver/gold bimetallic nanoparticles has been performed by UV–visible, XRD pattern, FT IR analysis, TEM/HRTEM, EDX and BET isotherm analysis. In this investigation, the photocatalytic effect of developed silver, gold and silver/gold bimetallic nanoparticles on Congo red dye breakdown efficiency was achieved at 96%, 94%, and 99.2%, respectively. Due to prolonged electron-hole recombination process was investigated using UV irradiation and reused for up to 5 consecutive runs without significant loss of photocatalytic activity. Moreover, silver, gold, and silver/gold bimetallic nanoparticles manufactured in an environmentally benign manner could potentially contribute to the ecological cleanup.

Fabrication of Au-Ag Bimetallic Nanoparticles Using Pulsed Laser Ablation for Medical Applications: A Review.

In recent years, the synthesis of Au-Ag bimetallic nanoparticles has garnered immense attention due to their potential applications in diverse fields, particularly in the realm of medicine and healthcare. The development of efficient synthesis methods is crucial in harnessing their unique properties for medical applications. Among the synthesis methods, pulsed laser ablation in a liquid environment has emerged as a robust and versatile method for precisely tailoring the synthesis of bimetallic nanoparticles. This manuscript provides an overview of the fundamentals of the pulsed laser ablation in a liquid method, elucidating the critical factors involved. It comprehensively explores the pivotal factors influencing Au-Ag bimetallic nanoparticle synthesis, delving into the material composition, laser parameters, and environmental conditions. Furthermore, this review highlights the promising strides made in antibacterial, photothermal, and diagnostic applications. Despite the remarkable progress, the manuscript also outlines the existing limitations and challenges in this advanced synthesis technique. By providing a thorough examination of the current state of research, this review aims to pave the way for future innovations in the field, driving the development of novel, safe, and effective medical technologies based on Au-Ag bimetallic nanoparticles.

Electrosynthesis of Nanocomposites of Catalytic Active Pd–Cu and Pd–Au Bimetallic Nanoparticles with Poly(N-vinylpyrrolidone) and Nanocellulose

Electrosynthesis of Nanocomposites of Catalytic Active Pd–Cu and Pd–Au Bimetallic Nanoparticles with Poly(N-vinylpyrrolidone) and Nanocellulose

Capping Layer Determined Self-assembly of Au-Ag Bimetallic Janus Nanoparticles at An Oil/Water Interface by Molecular Dynamics Simulations.

Bimetallic Janus nanoparticles (BJNPs) have gained more attention due to their unique catalytic and optical properties. The self-assembly of BJNPs is expected as an effective way to fabricate metamaterials suitable for different potential applications. However, the self-assembly dynamic process of BJNPs, which is key to achieving a controllable synthesis, is limited in both experimental and theoretical investigations. Herein, all-atom molecular dynamics (MD) simulations were employed to investigate the self-assembly process of 1-dodecanethiol (DDT)-decorated Au-Ag BJNPs at an oil-water interface. We demonstrate that DDT's van der Waals (vdW) interaction dominates the self-assembly process. BJNPs form close-packed structures at both fast and slow evaporation rates. Au-Ag BJNPs exhibit relatively larger rotations at a low evaporation rate than those at a high evaporation rate, suggesting that the evaporation rate influences the orientation of the Au-Ag BJNPs. BJNPs tend to orient their electric dipole moments toward the external electric field, according to the ab initio MD simulation results. Based on the energy comparison and model analysis, it is found that the parallel array is more stable than the antiparallel one for the Au-Ag BJNP arrays. The dipole-dipole interaction difference between the parallel and antiparallel BJNP arrays obtained according to dipole moment obtained from ab initio calculation is qualitatively consistent with that obtained from MD simulations, indicating that the dipole plays a decisive role in determining the orientation of the BJNP array. This work uncovers the self-assembly dynamic process of BJNPs, paving the way for future applications.

Facile green synthesis of highly stable, water dispersible carbohydrate conjugated Ag, Au and Ag-Au biocompatible nanoparticles: Catalytic and antimicrobial activity

Highly stable carbohydrate conjugated silver, gold and bimetallic silver-gold alloy biocompatible and nearly monodisperse nanoparticles (NPs) have been synthesized through bio-reduction of aqueous solution of corresponding metal salt precursors mediated by aqueous extracts of a high altitude lichen, Lobaria retigera. The biomolecule accountable for the reduction, stabilization and capping of the metal nanoparticles is identified to be carbohydrates. The as-synthesized carbohydrate conjugated nanoparticles have excellent dispersibilty in water, phosphate, phosphate-buffered saline, and serum media. The resulting nanoparticles were completely stable for several months in water. The nanoparticles were characterized using UV–visible spectroscopy, TEM, EDX, FT-IR, powder XRD, DLS and CV study. Though mostly spherical in shapes, occasionally truncated triangular and rod shapes were also noted. The average particle sizes of Ag, Au and Ag-Au alloy nanoparticles as determined from TEM analysis are 14.5 nm, 11.7 nm and 16.3 nm, respectively. Cyclic voltammetry pointed to a relatively high electrode potential barrier for the synthesized nanomaterials. The prepared Ag, Au and Ag-Au alloy nanoparticles served as efficient catalysts for the degradation of hazardous pollutant dye, methyl orange (MO) with rate constat of 0.1496 min−1, 0.1049 min−1, and 0.1882 min−1. The bimetallic Ag-Au nanoparticles exhibited the most accelerated reduction with 90.6% degradation efficiency. The reduction kinetics for the reactions followed a pseudo-first order, kAu < kAg< kAu-Ag. The Ag and Ag-Au alloy NPs showed pronounced antimicrobial activity towards selected bacterial strains while AuNPs lacked any such activity.