Surface Of Ag Nanoparticles Research Articles

Fluorescent properties of chitosan-stabilized bisdemethoxycurcumin-silver nanoparticles: Synthesis and characterization

The extraction and modification of naturally-occurring compounds are widely performed due to their valuable medicinal and physical properties. Herin, we reported the extraction of bis-demethoxycurcumin from Ragbrai turmeric root. The isolated derivative was characterized by X-ray diffraction, IR, and NMR spectroscopy. Also, the green synthesis of bis-demethoxycurcumin chitosan silver BDMC-Ag-Ch nanoparticles is illustrated. These nanoparticles are identified by atomic force microscopy AFM and exhibit average particle size ∼ 53.41 nm The crystalline structure was confirmed by XRD analysis, which showed distinct peaks corresponding to silver oxide nanoparticles and Zeta power measurements revealed stable dispersion of the nanoparticles, indicating a good chitosan coating on the surface of bis-demethoxycurcumin Ag nanoparticles. The absorption bands at 240 and 405 nm are due to oxygen atom (n → π*) and aromatic (π → π*) transitions in curcumin and Chitosan molecules. The photoluminescence (PL) study of synthesized BDMC-Ag-Ch nanoparticles demonstrated an existence of two emission excited states in light-emitting, namely local excited (LE) and intramolecular charge transfer (ICT) emission states, due to the aromatic conjugation system within BDMC units and intra charge transfer between the silver ion and organic part.

Surface‐enhanced Raman scattering of Cis‐(dicyanomethylene) squarate ion on a silver substrate

AbstractThere has been increasing interest in the use of squaraines with different physicochemical properties. However, their applications in nanoplasmonics are limited. For that, detailed information on the interactions of squaraines with plasmonic nanostructures is required. In this work, we have studied the adsorption of the squaraine cis‐dicyanomethylene squarate (CDSQ) on the surface of Ag nanoparticles (AgNP). We have combined normal Raman, surface‐enhanced Raman scattering (SERS), and DFT calculations to get insights into the configuration of its adsorption. DFT calculations have been carried out using simplified models of different adsorption geometries for comparison with the results of the SERS experiments. A comparison between the relative intensities of the normal Raman and SERS spectra indicates that CDSQ is adsorbed perpendicular to the AgNP surface. The predicted spectra suggest that CDSQ is chemically adsorbed on the silver surface through one of its N atoms.

Facile Synthesis of Ultra-Small Silver Nanoparticles Stabilized on Carbon Nanospheres for the Etherification of Silanes.

The dehydrocoupling reaction between alcohols and hydrosilanes is considered to be one of the most atom-economical ways to produce Si-O coupling compounds because its byproduct is only hydrogen (H2), which make it extremely environmentally friendly. In past decades, various kinds of homogeneous catalysts for the dehydrocoupling of alcohols and hydrosilanes, such as transition metal complexes, alkaline earth metals, alkali metals, and noble metal complexes, have been reported for their good activity and selectivity. Nevertheless, the practical applications of these catalysts still remain unsatisfactory, which is mainly restricted by environmental impact and non-reusability. A facile and recyclable heterogeneous catalyst, ultra-small Ag nanoparticles supported on porous carbon (Ag/C) for the etherification of silanes, has been developed. It has high catalytic activity for the Si-O coupling reaction, and the apparent activation energy of the reaction is about 30 kJ/mol. The ultra-small Ag nanoparticles dispersed in the catalyst through the carrier C have an enrichment effect on all reactants, which makes the reactants reach the adsorption saturation state on the surface of Ag nanoparticles, thus accelerating the coupling reaction process and verifying that the kinetics of the reaction of the catalyst indicate a zero-grade reaction.

Green Synthesis and Antimicrobial Study on Jujube Seed Extract Functionalized Ag Nanoparticles

AbstractGreen synthesis of Ag nanoparticles (AgNPs) by using the plant extract is a very important strategy to gain efficient antimicrobial agents with strong antimicrobial activity and low toxicity. In this study, jujube seed extract (JSE) is utilized to green synthesis of AgNPs by both hydrothermal process and solution‐based approaches. UV–vis absorption spectroscopy and infrared spectroscopy (FTIR) spectra confirm that jujube seed extract functionalized Ag nanoparticles are formed by both approaches and jujube seed extract covered on the surface of Ag nanoparticles. Transmission electron microscopy (TEM) images indicate that the JSE‐AgNPs are spherical with the average diameter of 17.7 and 14.2 nm for the hydrothermal process and solution‐based approaches, respectively. X‐ray diffraction (XRD) results indicate that the JSE‐AgNPs prepared by both approaches have face‐centered cubic crystal structure. The antimicrobial activity test reveals that minimum inhibitory concentrations (MIC) of JSE‐AgNPs by the solution‐based method are 62.5, 125, and 62.5 µg mL−1 against Escherichia coli, Staphylococcus aureus, and Candida albicans, respectively. These results imply that the JSE‐AgNPs have potential to be developed as efficient antimicrobial agents.

Highly sensitive “off-on” sensor based on MXene and magnetic microspheres for simultaneous detection of lung cancer biomarkers - Neuron specific enolase and carcinoembryonic antigen

In this work, a highly sensitive lung cancer biomarkers detection probe was developed based on Ag and MXene co-functionalized magnetic microspheres. By using carboxyl magnetic microspheres as carrier, MXene was coated repeatedly by Poly (allylamine hydrochloride) (PAH) as interlayer adhesive, and silver particles grown on the surface of MXene in situ can efficiently improve the sensitivity of the probe. The detection of neuron specific enolase (NSE) is mainly through the formation of a specific complex between NSE antigen and antibody, and the release of antibody labeled with amino carbon quantum dots (CQDs) from the surface of Ag nanoparticles (AgNPs), so that the fluorescence is restored and "OFF-ON" is formed. The biosensor exhibits excellently wide linear range (0.0001–1500 ng/mL) and the limit of detection (LOD) is up to 0.03 pg/mL, which is superior to most tumor marker probes based on fluorescence mechanism. Furthermore, we constructed dual detection strategy for NSE and carcinoembryonic antigen (CEA) simultaneously.

Synthesis, characterization, and performance evaluation of polyamide‐Ag@SiO2 Raman substrate

At present, Ag nanoparticles have been widely used as Raman substrates, but their easy oxidation and aggregation have limited practical applications. In order to address the above problems, firstly, tetraethyl orthosilicate as a precursor was applied to synthesis silver coated with silica dioxide nanoparticles (Ag@SiO2). As a result, the surface of Ag nanoparticles is uniformly coated with a thin layer of SiO2 in order to solve the easy oxidation problem without adversely affecting their surface‐enhanced Raman scattering (SERS) performance. Furthermore, Ag@SiO2 nanoparticles were electrostatically deposited onto polyamide (PA) films to form a two‐dimensional PA‐Ag@SiO2 film substrate, thus resolving nanoparticle agglomeration issues and further improving the repeatability of the entire system. As can been from the SERS detection results obtained from the probe molecules and pollutants, the Raman signal on the PA‐Ag@SiO2 thin film substrate has a good degree of sensitivity, stability, and repeatability.

Rapid preparation of sintered Ag nanoparticles pastes for high-power electronic packaging

This study developed a low-temperature pressureless sintered Ag nanoparticles (AgNPs) paste with high thermal conductivity (TC), which can be produced on a large scale through rapid pre-treatment. Commercially available unmodified AgNPs were coated with polyvinylpyrrolidone (PVP), and subsequently, citric acid (CA) was used to remove the native oxide layer from the AgNPs surface and improve sintering activity. Compared to the treatment strategy of CA activation followed by PVP coating, applying PVP coating prior to CA activation could prevent their spontaneous bonding that will significantly promote the formation of large grains and strong sintering necks, reducing the interface scattering and leading to an ultra-high TC (≥200 W/mK), thereby meeting the packaging requirements of high-power electronic applications.

Multiplex Assays of MicroRNAs by Using Single Particle Electrochemical Collision in a Single Run.

It is important to quantify multiple biomarkers in a single run due to the advantages of precious samples and diagnostic accuracy. Based on the distinguishability of two types of current signals from single particle electrochemical collision (SPEC), step-type current transients produced by Pt nanoparticles (PtNPs) catalyzed hydrazine oxidation and peak-type current transients produced by Ag nanoparticles (AgNPs) oxidation, a kind of multiplex immunoassay of target microRNAs (miRNA-21 and Let-7a) have been established during SPEC in a single run. When the single-stranded DNA (ssDNA1) that was perfectly complementary to miRNA-21 was coupled to the surface of PtNPs, the SPEC of PtNPs electrocatalysis was inhibited and the step-type current transients disappeared, while the single-stranded DNA (ssDNA2) that was perfectly complementary to Let-7a was coupled to the surface of AgNPs, the SPEC of AgNPs oxidation was inhibited, and the peak-type current transients disappeared, thus the signals were in the "off" state at this time. After that, miRNA-21 and Let-7a were added into solution, complementary base pairing disrupted the weak DNA-NP interaction and restored the electrocatalysis of PtNPs and the electrooxidation of AgNPs, and the step-type current signals and peak-type current signals were in the "on" state. Moreover, the frequencies from two different recovered signals (PtNPs catalysis and AgNPs oxidation) corresponded to the amount of added miRNA-21 and Let-7a, thus a multiplex immunoassay method for dual quantification of miRNA-21 and Let-7a in a single run was established.

Boosting electrochemical CO2 reduction to CO over interfacial hydroxide-metal catalysts

Interface engineering is demonstrated to lead to significant improvement in the catalytic performance for electrochemical CO2 reduction reactions (CO2RR). In this work, we demonstrate a heterogeneous In(OH)3-Ag interface catalyst in which the appropriate In(OH)3 clusters modified on metal Ag nanoparticles surface greatly improves the CO selectivity in CO2RR, realizing a CO faradaic efficiency (FECO) of 93% at − 0.7 V vs. RHE. The performance enhancement is attributed to the preferentially CO2 adsorption and activation by the In(OH)3-Ag interface sites. In situ Raman spectroscopy reveals that the formation of In(OH)3-Ag interface sites is significantly favorable for the generation of key *CO2− intermediate at low overpotential. Further theoretical calculation confirms that the In(OH)3-Ag interface could enhance the adsorption of *COOH species on catalyst by means of tailoring the surface properties and electronic structures. This work shows that hydroxide-metal interface engineering is a promising pathway to regulate the activity for selective CO2RR properties.

Designing of surface chemical enhanced Raman AgCu and AuCu clusters: Density functional theory

Designing of surface-enhanced Raman material with low cost and high enhancement ability become animportant research direction in the field of surface-enhanced Raman scattering. In this paper, the density functional theory calculations were utilized to investigated the Raman performances of stabled CuAg and CuAu clusters for 4-NBT probe molecule. Some suitable alloying designs in atomic level were found to reduce cost and enhance Raman signal of noble nanoparticles, such as, a small quantity introduction of Cu element into the tip of Ag nanoparticle surface and the core–shell structure. The designed Cu2Ag2, Cu1Ag12, Cu1Au12, Cu3Ag10, Cu3Au10, Cu14Ag9, Cu4Au9, Cu9Au4 and Cu10Au3 clusters exhibited enhanced Raman diffraction peak intensity beyond 11.0% compared to the 4-NBT molecule on the Ag4, Ag13 and Au13 clusters. This strategy could be applied to designing noble metal based surface-enhanced Raman materials with low cost and high enhancement ability by adjusting the atom site in atomic level.

Ultra-sensitive, rapid detection of dried bloodstains by surface enhanced Raman scattering on Ag substrates

A simple water extraction and transfer procedure is found to result in reproducible and highly sensitive 785 nm excited SERS spectra of 24 h dried bloodstains on Ag nanoparticle substrates. This protocol allows confirmatory detection and identification of dried stains of blood that have been diluted by up to 105 in water on Ag substrates. While previous SERS results demonstrated similar performance on Au substrates when a 50% acetic acid extraction and transfer procedure was used, the water/Ag methodology avoids any potential DNA damage when the sample size is extremely small (≤∼1 μL) due to low pH exposure. The water only procedure is not effective on Au SERS substrates. This metal substrate difference results from the efficient red blood cell lysis and hemoglobin denaturation effects of the Ag nanoparticle surfaces as compare to that of Au nanoparticles. Consequently, the 50% acetic acid exposure is required for the acquisition of 785 nm SERS spectra of dried bloodstains on Au substrates.

A comprehensive DFT study of the stabilization of methyl-mercury over Ag nanoparticles

The surface structure of Nanoparticles (NPs) gives distinct interfacial chemical characteristics to individual facets, and it can control the capacity of MeHg adsorption at these interfaces. Here we propose a theoretical model based on the actual properties of the Ag NPs and perform a comparative study on the MeHg adsorption properties of different surfaces ((1 1 1), (1 1 0), (1 0 0), and (2 1 1)) based on the first-principles theoretical study. It is found that each surface of the NPs has a strong affinity (greater than 2 eV) for MeHg despite differences in surface structure. To better understand the electron interaction of adsorbed MeHg with each surface of Ag NPs, the electronic charge density difference, the partial density of states (PDOS), and the Bader charge were investigated. Furthermore, the energy barrier of MeHg diffusion on the facets of Ag NPs was calculated. The difficulty of MeHg diffusion on various facets of Ag NPs is follow the trend of (1 0 0) > (1 1 0) > (2 1 1) > (1 1 1). In virtue of its superior diffusivity and high affinity for MeHg, the prospect of Ag NPs application in MeHg removal in liquids is highly promising. This work could provide a new strategy to applied metal NPs as a scavenger material for MeHg in liquid conditions.

Origin of Superlinear Power Dependence of Reaction Rates in Plasmon-Driven Photocatalysis: A Case Study of Reductive Nitrothiophenol Coupling Reactions

The superlinear dependence of the reaction rate on the power of the excitation light, which may arise from both thermal and nonthermal effects, has been a hallmark of plasmon-driven photocatalysis on nanostructured metal surfaces. However, it remains challenging to distinguish and quantify the thermal and nonthermal effects because even slight uncertainties in measuring the local temperatures at the active surface sites may lead to significant errors in assessing thermal and nonthermal contributions to the overall reaction rates. Here we employ surface-enhanced Raman scattering as a surface-sensitive in situ spectroscopic tool to correlate detailed kinetic features of plasmon-mediated molecular transformations to the local temperatures at the active sites on photocatalyst surfaces. Our spectroscopic results clearly reveal that the superlinearity in the power dependence of the reaction rate observed in a plasmon-driven model reaction, specifically the reductive coupling of para-nitrothiophenol adsorbates on Ag nanoparticle surfaces, originates essentially from photothermal heating rather than nonthermal plasmonic effects.

Metal–Adsorbate Interactions Modulate Plasmonic Reactivity of Chemisorbed Nitrophenyl Derivatives

Energetic hot electrons generated upon nonradiative decay of localized plasmons in metallic nanostructures can be effectively harnessed to catalyze photochemical transformations of molecular adsorbates through unique reaction pathways. When designing metal–adsorbate hybrid systems for hot electron-driven photocatalysis, both the intrinsic plasmonic properties of metallic photocatalysts and the chemical nature of metal–adsorbate interactions should be taken into careful considerations. In this work, we show that the reactivity of nitrophenyl derivative adsorbates on Ag nanoparticle surfaces toward plasmon-driven reductive coupling reactions is intimately tied to the bonding nature of molecular chemisorption. We focus on the comparative studies of three representative nitrophenyl derivatives, specifically para-nitrothiophenol, para-nitrophenylacetylene, and para-nitrophenylisocyanide, which covalently interact with the Ag photocatalysts using chemically distinct surface-anchoring groups. Taking full advantage of the unique time-resolving and molecular fingerprinting capabilities offered by surface-enhanced Raman spectroscopy, we have been able to precisely correlate the chemical nature of metal–adsorbate interactions to the kinetic characteristics of molecular transformations under a broad range of reaction conditions. Although the kinetic features of the coupling reactions change substantially upon variation of the excitation wavelength, the light illumination power, and the pH of the reaction medium, we have consistently observed that the plasmonic reactivity of the nitrophenyl derivative adsorbates drops drastically, as reflected by significant decrease in both reaction rates and yields, when the bonding modes dominating the metal–adsorbate interactions are switched from σ-donation to π-back-donation.

Green Biosynthesis of Silver Nanoparticles Using Vaccinium oxycoccos (Cranberry) Extract and Evaluation of Their Biomedical Potential

Eco-friendly preparation of metallic nanoparticles (NPs) is a greatly evolving field of scientific research. These types of NPs have gained substantial recognition from scientists, including chemists, chemical biologists and technologists, who have successfully exploited them for the fabrication of a variety of advanced nanodevices. Herein, silver (Ag) NPs were synthesized by a green approach using the aqueous extract of Vaccinium oxycoccos (cranberry), which not only reduced the silver ions but also stabilized the surface of the resultant Ag NPs. The formation of Ag NPs is confirmed by different analytical techniques, including powder X-ray diffraction, UV analysis, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR). The UV analysis of the aqueous solution of the reaction mixture demonstrated an absorption band at ~450 nm, which is the typical peak of Ag NPs, leading to the confirmation of product formation. While the XRD confirmed the crystallinity of the sample and the formation of a face-centered cubic (fcc) structure, on the other hand, TEM revealed the presence of spherical NPs with an approximate size range between 5–30 nm. Furthermore, the as-obtained Ag NPs were subjected to thorough investigations to explore the biomedical potential of the sample. In this case, the Ag NPs demonstrated considerable antioxidant and antifungal properties towards various pathogens. In addition, Ag NPs also showed substantial inhibition of spore germination.

Surface plasmon coupling effects on the behaviors of radiative and non-radiative recombination in an InGaN/GaN quantum well

Although surface plasmon (SP) coupling has been widely used for enhancing the emission efficiency of an InGaN/GaN quantum well (QW) structure, the interplay of the carrier transport behavior in the QW with SP coupling, which is a crucial mechanism controlling the SP-coupling induced QW emission enhancement, is still an issue not well explored yet. To understand the effects of SP coupling on the radiative and non-radiative recombination behaviors of carriers in a QW structure, the temperature-dependent time-resolved photoluminescence spectroscopies of two QW samples of different indium contents with surface Ag nanoparticles are studied. A two-single-exponential model is used for calibrating their radiative and non-radiative decay times. The SP coupling process, which transfers carrier energy from a QW into the SP resonance mode for effective radiation and increases the effective radiative recombination rate, produces energy-dependent carrier depletion and, hence, disturbs the quasi-equilibrium condition of carrier distribution. In this situation, a strong carrier transport process occurs targeting a new quasi-equilibrium condition that enhances non-radiative recombination and, hence, reduces the benefit of using the SP coupling technique. To alleviate this problem of SP-coupling induced energy loss, a weak energy-dependent or broad-spectrum SP coupling process is recommended.

Effects of Surface Plasmon Coupling on the Color Conversion of an InGaN/GaN Quantum-Well Structure into Colloidal Quantum Dots Inserted into a Nearby Porous Structure

To further enhance the color conversion from a quantum-well (QW) structure into a color-converting colloidal quantum dot (QD) through Förster resonance energy transfer (FRET), we designed and implemented a device structure with QDs inserted into a GaN nano-porous structure near the QWs to gain the advantageous nanoscale-cavity effect. Additionally, surface Ag nanoparticles were deposited for inducing surface plasmon (SP) coupling with the QW structure. Based on the measurements of time-resolved and continuous-wave photoluminescence spectroscopies, the FRET efficiency from QW into QD is enhanced through the SP coupling. In particular, performance in the polarization perpendicular to the essentially extended direction of the fabricated pores in the nano-porous structure is more strongly enhanced when compared with the other linear polarization. A numerical simulation study was undertaken, and showed consistent results with the experimental observations.

Featured Properties of the Adsorption of Tebuconazole on Ag Surface Characterized through SERS Spectroscopy

Pesticides present utmost importance in modern agriculture and are extensively used in countries with strong agricultural activity, such as Brazil. However, these substances are considered a significant part of environmental contamination by organic compounds. In the present work, Raman spectroscopy was employed in the vibrational characterization of the fungicide tebuconazole and surface-enhanced Raman scattering spectroscopy to the study of the adsorption of this compound on the surface of Ag nanoparticles. The proposed chemical interaction between tebuconazole and the metallic surface was inferred by relating experimental results and vibrational assignment supported by density functional theory calculations. The vibrational assignments of surface-enhanced Raman scattering spectra, by considering surface selection rules, suggest that the adsorption of the tebuconazole with Ag surface occurs by interactions of phenyl and triazole groups simultaneously. For the case of the interaction with the phenyl group, a modification of the charge distribution in the ring after adsorption was hypothesized, which was supported through the analysis of the frontier molecular orbitals of the Ag-tebuconazole complex calculated by density functional theory.

Tribological Properties of Polydopamine-Modified Ag as Lubricant Oil Additives

Nanoparticles agglomerate easily because of their high surface energy, which seriously reduces their tribological properties as lubricant additives. In this work, the core-shell nanoparticles Ag@polydopamine (PDA) were successfully prepared by the self-oxidation of dopamine hydrochloride on the surface of Ag nanoparticles and the dispersion of Ag nanoparticles in PAO6 was improved to promote anti-wear behaviors. The tribological properties of Ag@PDA nanocomposites as additives in poly alpha olefin (PAO) oil were studied under different concentrations, pressure and speed conditions by UMT-5 tribometer. It was demonstrated that the strong electrostatic repulsion of the PDA structure made the Ag nanoparticles better dispersed in PAO oil, thus playing a better lubricating role. When the concentration of the modified nanoparticles was 0.25 wt%, the friction coefficient of the lubricating oil decreased by 18.67% and no obvious wear was observed on the friction pair surface. When the Ag@PDA content was higher than 0.25 wt%, the tribological performance of the lubricating oil was weakened, which may be due to excessive Ag@PDA acting as an abrasive on the friction surface, thereby increasing friction and wear. The friction coefficient of the lubricating oil containing Ag@PDA decreased with the increase in load, but hardly changed with the increase in frequency.

Localized surface plasmon resonance phenomenon in Ag/Au-WO3-x nanocomposite thin films

• Ag/Au-WO 3-x thin films prepared by radio-frequency magnetron sputtering. • The Ag/Au-WO 3-x films demonstrate localized surface plasmon resonance (LSPR) phenomenon. • Blueshift of the LSPR band in Ag-WO 3-x film. The localized surface plasmon resonance was investigated in composite thin films based on amorphous sub-stoichiometric tungsten oxide (WO 3-x ) matrix and noble metal nanoparticles, such as silver (Ag), gold (Au), and their alloy (Ag/Au). The films were prepared by radio-frequency magnetron sputtering of a combined target consisting of lemon-colored tungsten trioxide powder and Ag and/or Au pellets. It was found that the mean size of nanoparticles for all composite thin films according to the results of transmission electron microscopy is less than 5 nm. The obtained films demonstrate tunable plasmon absorption band. The position of the localized surface plasmon resonance peak was experimentally observed at 435, 494, and 582 nm for Ag-WO 3-x , Ag/Au-WO 3-x and Au-WO 3-x composite thin films, respectively. Blueshift of the localized surface plasmon resonance band in contrast with the results of Mie calculations for Ag-WO 3-x film was explained by possible formation of oxide shell on the surface of Ag nanoparticles.