Monolayer Of Silver Nanoparticles Research Articles

Quantitative and qualitative analyses of drug adsorption on silver nanoparticle monolayers: QCM, SERS, and TEIRA nanospectroscopy studies.

In this study for the first time, surface-enhanced Raman spectroscopy (SERS) and tip-enhanced infrared (TEIRA) nanospectrocopy together with a quartz crystal microbalance (QCM) are postulated as powerful tools for comprehensive qualitative and quantitative analyses of drug/metal nanocarrier conjugates. The development of efficient drug/carrier systems requires that the stability of the drug/carrier connection be estimated and the number of drug molecules immobilized on the carrier surface be determined. Thus, such a characterization study is highly desirable. Here, the SERS technique was applied to identify how erlotinib, a drug applied in non-small cell lung cancer (NSCLC) therapy, interacts with silver nanoparticles (AgNPs) that are considered as drug carriers. These investigations indicate that in the erlotinib/AgNP suspension, the drug strongly connects with the NPs mainly through the phenylacetylene moiety. The QCM was used to prepare an AgNP monolayer with a monitored degree of coverage and to perform controlled erlotinib adsorption as a next step. The results indicate that the drug forms a stable layer on the AgNP monolayer and also show the amount of the erlotinib molecules which underwent immobilization on the metal nanosurface. Simultaneously, it was identified how the erlotinib layer adsorbs on the AgNP monolayer using TEIRA nanospectroscopy with ultra-high spatial resolution. The obtained results show that the phenylacetylene, ethoxy, and methoxy moieties are mainly responsible for the drug/AgNP monolayer connection. Additionally, the performed studies also try to explain the surface-enhanced phenomena that occur during the TEIRA experiments and attempt to prove the statement that the "tip-enhanced" effect plays a crucial role in the detection of the thin erlotinib layer deposited on the AgNP monolayer.

Facial Fabrication of Large-Scale SERS-Active Substrate Based on Self-Assembled Monolayer of Silver Nanoparticles on CTAB-Modified Silicon for Analytical Applications.

Surface-enhanced Raman spectroscopy (SERS) has been proven to be a promising analytical technique with sensitivity at the single-molecule level. However, one of the key problems preventing its real-world application lies in the great challenges that are encountered in the preparation of large-scale, reproducible, and highly sensitive SERS-active substrates. In this work, a new strategy is developed to fabricate an Ag collide SERS substrate by using cetyltrimethylammonium bromide (CTAB) as a connection agent. The developed SERS substrate can be developed on a large scale and is highly efficient, and it has high-density “hot spots” that enhance the yield enormously. We employed 4-methylbenzenethiol(4-MBT) as the SERS probe due to the strong Ag–S linkage. The SERS enhancement factor (EF) was calculated to be ~2.6 × 106. The efficacy of the proposed substrate is demonstrated for the detection of malachite green (MG) as an example. The limit of detection (LOD) for the MG assay is brought down to 1.0 × 10−11 M, and the relative standard deviation (RSD) for the intensity of the main Raman vibration modes (1620, 1038 cm−1) is less than 20%.

Highly efficient SERS substrates with different Ag interparticle nanogaps based on hyperbolic metamaterials

Surface-enhanced Raman scattering (SERS) substrates based on Hyperbolic metamaterials (HMM) have received tremendous attention due to the presence of confined optical modes, i.e., the surface plasmon polaritons (SPP) and bulk plasmon polaritons (BPP). In the present study, a multilayer HMM SERS substrate was fabricated, comprising a monolayer of silver nanoparticles (Ag NPs) and Au-Al2O3 films. Our study demonstrates that the Ag NPs layer excited SPP and BPP, and the localized surface plasmon (LSP) resonance of the Ag NPs layer coupled with BPP, creating a strong electromagnetic field at the interparticle gaps of the Ag NPs. Interestingly, increasing the multilayer stacking of HMM will strengthen the SERS activity until a certain threshold. On the top of HMM, the interparticle gaps of the Ag NPs were adjusted to enhance the SERS characteristics and the maximum EF appeared at the gap of 10 nm. Performing theoretical simulations as well as experiments, the ultra-sensitivity, good reproducibility, reusability, and high enhancement factor of the proposed SERS substrate were assessed. Lastly, the ultralow limits of detection for melamine in milk were 10−7 M, satisfying the needs for successful implementation in the food safety field.

Polarized Stimulated Emission of 2D Ensembles of Plasmonic Nanolasers

Plasmonic nanolasers produce coherent light with wavelengths on a scale similar to their own or larger. In the past decade they have attracted intense interest, particularly from the emerging areas of integrated photonic circuits and biomedicine. Despite these capabilities, plasmonic nanolasers are still not completely understood, and this lack of understanding leads to confusing them with spasers and random lasers. Herein, the operation of pure spaser‐based plasmonic nanolaser arrays is presented. For this, a monolayer of silver nanoparticles (NPs) affixed to a dielectric surface and covered with a fluorescent polymethyl methacrylate (PMMA)–coumarin solid composite is investigated. The input–output characteristic measured for the composites on a bare substrate (without Ag NPs) reveals that the emission at pump pulse energies above 2.4 mJ (at 355 nm excitation wavelength) stops growing, and instead is inhibited by saturation. In contrast, in such structures with Ag NPs an additional emission band pops up over a fluorescence background. It has a spectral width order of units of nanometers and its intensity grows faster than at lower pump pulse energies, revealing a nonlinear dependence of the input–output characteristic. The spaser‐based lasing observed is completely linearly polarized and clearly directed as 45° from the substrate.

Nanoscale image of the drug/metal mono-layer interaction: Tapping AFM-IR investigations

The application of metal nanoparticles as an efficient drug delivery system is one of the directions of cancer therapy development. However, this strategy requires precise information about how the drug interacts with the applied nanocarrier. In this study, atomic force microscopy combined with infrared spectroscopy (AFM-IR) was used for the first time to investigate the erlotinib adsorption structure on two different types of 15 nm metal nanoparticle mono-layers, namely, silver nanoparticle (AgNP) and gold nanoparticle (AuNP) mono-layers. Because the metal nanoparticles are loosely bound samples, only the tapping AFM-IR mode is suitable for the collection of IR maps and spectra for such a system. The obtained results indicated the relevance of the AFM-IR technique for characterizing drug interactions with a metal mono-layer surface. The investigated drug interacts with the AgNPs mainly through phenyl rings and methoxy moieties, while quinazoline, amino, and ethoxy moieties appear to be farther from the surface. For the AuNPs, the interaction occurs through both the phenyl ring and the quinazoline moiety. Additionally, the aliphatic groups of erlotinib directly participate in this interaction. The novelty of the present work is also related to the use of the tapping AFM-IR mode to study metal NP mono-layers with a drug adsorbed on them. The collected IR maps for the most enhanced erlotinib bands show specific areas with very high signal intensity. The connection between these areas and the “hot spots” typical for the surface plasmon resonance phenomenon of metals is considered.

Enhanced biodegradation of an endocrine disrupting micro-pollutant: Di (2-ethylhexyl) phthalate using biogenic self-assembled monolayer of silver nanoparticles

Di (2-ethylhexyl) phthalate (DEHP) is one of the predominant plasticizer and an endocrine disrupting chemical occurring almost in all partitions of the environment. Though DEHP occur at lower concentration, reluctance arises due to their ability to disrupt endocrine system even lower concentration. In the present study, DEHP was assessed for degradation at minimal level (1–100 μg L−1) by a novel bacterial strain, Rhodococcus jostii PEVJ9. In the experimental design, significant variables were concentration of silver nitrate and DEHP, pH, temperature, time and agitation. Degradation without SAM-silver nanoparticles was 30–66% (predicted value = 30.8–66.8%, R2 = 99.7%) while, degradation in the presence of SAM-silver nanoparticles onto bacterial cells was 100% (predicted value = 98.4–102.1%, R2 = 99.6%) within 72 h. In short, this is the first report illustrating the experimental designs in biogenic synthesis of SAM-silver nanoparticles and enhanced degradation of DEHP at minimal level. The study overcomes poor bioavailability and assimilation of DEHP at lower concentration by the microbial population present in the environment. Thus, an efficient clean-up would prevent or minimize DEHP exposure at all trophic levels ranging from feminization of fishes to reproductive disorders in humans.

Characteristics of fiber-optic photoacoustic transducers with monolayer of metal nanoparticles for systems of technical diagnostics

The work is devoted to the experimental study of the microstructural and morphological properties of nanostructures as part of a prototype of fiber-optic photoacoustic transducer. The transducer has been created to confirm the theoretical investigations previously obtained by the authors during the study the conditions of the most effective photoacoustic gene ration. To solve the main problem that arises when creating photoacoustic transducers, namely reducing the thickness of the absorbing layer, we used a nanostructure based on a monolayer of silver nanoparticles with size gamma-distribution, the average diameter of 35 nm with RMS-size of 12 nm. The method of simultaneous measuring both efficiency of photoacoustic conversion and frequency response of a photoacoustic transducer is proposed for the first time. The method allows experimental investigation of transduces output parameters versus the modulation mode of the optical signal. The proposed method is based on the usage of the main measurement channel for irradiating the photoacoustic transducer and a reference channel based on fiber optical coupler and photodiode. The experiment shows the reliable generation of ultrasound at frequencies of 10 –18 MHz with a prototype of photoacoustic transducer. During one hour irradiation, degradation of two-dimensional surface nanostructures has not been observed. This allows such type of photoacoustic transducer to be used as part of a new generation of technical diagnostics systems.

Direct enhancement of luminescence of CdxZn1−xSeyS1−y/ZnS nanocrystals with gradient chemical composition by plasmonic nanoantennas

Flat photonic materials such as thin films or metasurfaces form the basis of new optics and laser technology. However, their characteristics, for example, absorption and luminescence, are drastically limited in contrast to bulk materials. This problem can be overcome using plasmonic nanostructures. While the quantum dots absorption is enhanced by the plasmonic nanostructure near fields in almost all circumstances, more sophisticated approaches are needed to obtain the fluorescent enhancement because of the concurrent quenching by the metallic surface. Here we report on the results of an illustrative experiment demonstrating the luminescence enhancement of a new type of semiconductor nanocrystals CdxZn1−xSeyS1−y/ZnS (alloyed quantum dots) at their direct contact with a monolayer of silver nanoparticles. This type of nanocrystals consists of a CdSe core, a ZnS shell, and a transition layer in between where the composition smoothly changes, thus representing an alloy with variable x and y. We found that at the resonant plasmon–exciton coupling of such nanostructures, the fluorescence enhancement is accompanied by the reduction of the luminescence decay time – the main signature of the Purcell effect. Unlike previously studied compositions, these new hybrid structures do not require additional components to avoid fluorescence quenching which is promising for practical applications in flat optical devices.

A versatile β-cyclodextrin functionalized silver nanoparticle monolayer for capture of methyl orange from complex wastewater

The toxic organic dye contaminants in wastewater are extremely harmful to the ecosystem. Surface enhanced Raman scattering (SERS) is a technique with high sensitivity and chemical specificity which fulfills the requirements for monitoring dye contaminants in wastewater. However, as one of the common dye contaminants, methyl orange (MO) has very weak affinity to metallic surfaces and is difficult to be detected by SERS at low concentrations. Therefore, a new type of SERS substrate with Ag nanoparticle monolayer functionalized by mono-6-deoxy-6-thio-β-cyclodextrin (β-CD-SH) was prepared to efficiently capture and detect MO in wastewater with a limit of detection of 5 × 10−7 mol/L. The hydrophobic cavity of β-CD is responsible for the efficient trap and enrichment of MO on the Ag NPs surface, achieving a strong SERS signal of MO at low concentrations and at different pH values. This study provides new insight into designing a well-performed adsorbent for the capture and detection of organic contaminants.

Comparison of the mechanical strength of a monolayer of silver nanoparticles both in the freestanding state and on a soft substrate

A 7-nm-thick monolayer comprising myristate-capped silver nanoparticles (AgNPs) was fabricated by first drop casting an AgNP solution on the surface of a 10–100 μl water drop placed on a solid substrate. With the natural evaporation of the water, a monolayer slowly descended onto the substrate, the latter containing an array of 2.5-μm-diameter and 200-nm-deep holes, and finally formed circular freestanding monolayers in the holes. Nanoindentation measurement based on atomic force microscopy was carried out on the circular freestanding monolayer at its center, and the extending and retracting force–indentation curves were recorded to analyze further the mechanical properties of the monolayer. The force–indentation curves were evidently nonlinear, and so a two-term continuum-mechanics theory was used to interpret the results. By fitting the force–indentation curves using a two-term equation, the prestress and Young’s modulus of the freestanding AgNP monolayer were obtained as approximately 0.05 N/m and several gigapascals, respectively, which are consistent with the results reported in the literature. For comparison, we also studied the mechanical responses of AgNP monolayers and bilayers on a soft polydimethylsiloxane (PDMS) substrate by using nanoindentation. Because the AgNP monolayer was stiffer than the PDMS substrate, it was possible to measure the mechanical response of the former despite it being only 7 nm thick. The mechanical strength of the freestanding AgNP monolayers was considered to be dominated by the attractive interactions between the interdigitated hydrocarbon chains of the myristate.

Monolayers of silver nanoparticles obtained by green synthesis on macrocation modified substrates

Abstract Formation of silver nanoparticle monolayers on polydiallyldimethylammonium chloride (PDADMAC), modified mica was studied in situ by the streaming potential measurements, ex situ atomic force microscopy (AFM), and scanning electron microscopy (SEM). The silver nanoparticles were obtained in a green synthesis involving AgNO3 precursor, using glucose and sucrose serving as both reducing and stabilizing agents. The average size of the nanoparticles was 48 nm. The dynamic light scattering measurements showed that the silver nanoparticle suspension was stable for the time period up to 60 days. The electrophoretic mobility measurements revealed that the nanoparticles were negatively charged, with zeta potential increasing with the ionic strength from −75 mV at 10−5 M to −42 mV at 2 × 10−2 M. The effect of ionic strength on the nanoparticle deposition kinetics on PDADMAC monolayer was also quantitatively determined. A significant increase of the nanoparticle coverage with macrocation coverage suggested that the deposition of the nanoparticles occurred only on local adsorption sites, consisting of a few macrocation molecules exhibiting large positive charge. The obtained results can find practical applications in constructing biocompatible materials serving for bioparticle immobilization and biofilm formation.

Spectral-Kinetic Properties of Nanosized Nickel Phthalocyanine Films on Silver Nanoparticle Monolayers

We have investigated spectral and spectral-kinetic properties of hybrid (organic semiconductor-plasmonic metal) nanocomposites on the base of silver nanoparticle monolayers and thin nickel phthalocyanine (NiPc) films. The spectroscopic results obtained by the femtosecond pump-probe technique demonstrate an enhancement of the fast optical response in the range of long-wavelength NiPc electronic absorption bands when the NiPc thin films contact with silver nanoparticles. This could be assigned to the plasmon-related modification and the enhancement of hybrid structures absorption at its steady-state absorption spectra.

Self‐Assembled Monolayers of Silver Nanoparticles: From Intrinsic to Switchable Inorganic Antibacterial Surfaces

The layer‐by‐layer technique allows to graft molecular monolayers on bulk surfaces that, in turn, allow to graft monolayers of metal nanoparticles. This microreview focuses on the preparation of such materials featuring a monolayer of silver nanoparticles (AgNP) and their use as antimicrobial surfaces against both planktonic bacteria and biofilms. The role of Ag+ release and of direct cell/AgNP contact in the antibacterial action will be stressed as a function of the adhesive molecular layer, of the AgNP dimension and shape, of their surface density, and of the molecular overcoating. While these surfaces display an intrinsic antibacterial action, a further evolution will also be reviewed, in which additional photothermal antibacterial action can be switched on demand, using near‐IR radiation and non‐spherical AgNP or a combination of AgNP with non‐spherical AuNP. The intrinsic and switchable photothermal action of these surfaces will be unraveled, and their synergistic effect stressed.

Silver Nanoparticle Effect on Spectral-Kinetic Properties of Thin Nickel Phthalocyanine Films

We have investigated spectral and spectral-kinetic properties of hybrid plasmonic nanocomposites on silver nanoparticle monolayers and thin nickel phthalocyanine films. The spectroscopic results obtained by the femtosecond pump-probe technique demonstrate that a fast optical response in the range of long-wavelength nickel phthalocyanine electronic absorption bands becomes observable and registered when the nickel phthalocyanine thin films contact with silver nanoparticles. This could be assigned to the plasmon-related modification and the enhancement of organic subsistent absorption at steady-state absorption spectra of hybrid nanostructures.

Formation, properties and stability of silver nanoparticle monolayers at PDADMAC modified polystyrene microparticles

A facile self-assembly procedure was developed for the preparation of silver nanoparticle shells at polystyrene microparticles (PSMPs) modified by poly(diallyldimethylammonium chloride) (PDADMAC). Initially, physicochemical properties of microparticles, silver particles and (PDADMAC) were determined for various ionic strength and pHs. Then, PDADAMAC adsorption on the PSMPs was studied in situ via electrokinetic measurements. The influence of polyelectrolyte bulk concentration on electrokinetic properties of PDADMAC-coated microparticles for different ionic strength was investigated. The coverage of PDADMAC monolayer was estimated applying an electrokinetic model. The stability of PDADMAC-modified microparticles under controlled conditions of pH and ionic strength was also evaluated. It was confirmed that under acidic conditions (pH 4–5.6) the microparticles were stable for at least two weeks. The modified microparticles were used as substrate for silver nanoparticle immobilization carried out under a diffusion controlled self-assembly process. The coverage of nanoparticles was precisely determined using electrophoretic mobility measurements, the concentration depletion method involving atomic force microscopy and via direct scanning electron microscopy imaging of particles. A large stability of the silver particle monolayers was confirmed. These monolayers of well-defined coverage and acid-base properties can be used for controlled delivery of silver nanoparticles.

Decoration of Inorganic Nanostructures by Metallic Nanoparticles to Induce Fluorescence, Enhance Solubility, and Tune Band Gap

We report here a unique and efficient methodology for the surface functionalization of closed-cage inorganic fullerene-like (IF) nanoparticles and inorganic nanotubes (INTs) composed of two-dimensional nanomaterials of transition-metal chalcogenides (MS2; M = W or Mo). The first step is the physical coverage of these robust inorganic materials with monodispersed and dense monolayers of gold, silver, and palladium nanoparticles. The structural continuity at the interface between the IF/INT and the metallic nanoparticles is investigated. Lattice matching between these nanocrystalline materials and strong chemical affinity lead to efficient binding of the metallic nanoparticles onto the outer sulfide layer of the MS2-based structures. It is shown that this functionalization results in narrowing of the IF/INT optical band gap, increased work function, and improved surface-enhanced Raman scattering. In the second step, functionalization of the surface-bound nanoparticles is carried out by a ligand-exchange rea...

A hybrid biocatalyst consisting of silver nanoparticle and naphthalenethiol self-assembled monolayer prepared for anchoring glucose oxidase and its use for an enzymatic biofuel cell

A novel hybrid biocatalyst is synthesized by the enzyme composite consisting of silver nanoparticle (AgNP), naphthalene-thiol based couplers (Naph-SH) and glucose oxidase (GOx), which is then bonded with the supporter consisting of polyethyleneimine (PEI) and carbon nanotube (CNT) (CNT/PEI/AgNPs/Naph-SH/GOx) to facilitate glucose oxidation reaction (GOR). Here, the AgNPs play a role in obstructing denaturation of the GOx molecules from the supporter because of Ag-thiol bond, while the PEIs have the AgNPs keep their states without getting ionized by hydrogen peroxide produced during anodic reaction. The Naph-SHs also prevent ionization of the AgNP by forming self-assembled monolayer on their surface. Such roles of each component enable the catalyst to form (i) hydrophobic interaction between the GOx molecules and supporter and (ii) π-conjugated electron pathway between the GOx molecules and AgNP, promoting electron transfer. Catalytic nature of the catalyst is characterized by measuring catalytic activity and performance of enzymatic biofuel cell (EBC) using the catalyst. Regarding the catalytic activity, the catalyst leads to high electron transfer rate constant (9.6±0.4s−1), low Michaelis-Menten constant (0.51±0.04mM), and low charge transfer resistance (7.3Ωcm2) and high amount of immobilized GOx (54.6%), while regarding the EBC performance, high maximum power density (1.46±0.07mWcm−2) with superior long-term stability result are observed.

One-step flame synthesis of silver nanoparticles for roll-to-roll production of antibacterial paper

Nanoparticles are used in several applications due to the unique properties they possess compared to bulk materials. Production techniques have continuously evolved over the years. Recently, there has been emphasis on environmentally friendly manufacturing processes. Substrate properties often limit the possible production techniques and, for example; until recently, it has been difficult to incorporate nanoparticles into paper. Chemical reduction of a precursor in the presence of paper changes the bulk properties of paper, which may limit intended end-use. In this study, we present a novel technique for incorporating silver nanoparticles into paper surface using a flame pyrolysis procedure known as Liquid Flame Spray. Papers precoated with mineral pigments and plastic are used as substrates. Silver nanoparticles were analyzed using SEM and XPS measurements. Results show a homogeneous monolayer of silver nanoparticles on the surface of paper, which demonstrated antibacterial properties against E. coli. Paper precoated with plastic showed more nanoparticles on the surface compared to pigment coated paper samples except for polyethylene-precoated paper. The results demonstrate a dry synthesis approach for depositing silver nanoparticles directly onto paper surface in a process which produces no effluents. The production technique used herein is up scalable for industrial production of antibacterial paper.

Quantitative determination of melamine in milk using Ag nanoparticle monolayer film as SERS substrate

A Raman method employing silver nanoparticle (Ag NP) monolayer film as Surface-enhanced Raman Scattering (SERS) substrate was presented to rapidly detect melamine in milk. The Ag NPs with 80nm diameter were modified by polyvinylpyrrolidone to improve their uniformity and chemical stability. The treatment procedure of liquid milk required only addition of acetic acid and centrifugation, and required time is less than 15min. The Ag NP monolayer film significantly enhanced Raman signal from melamine and allowed experimentally reproducible determination of the melamine concentration. A good linear relationship (R2=0.994) between the concentration and Raman peak intensity of melamine at 681cm−1 was obtained for melamine concentrations between 0.10mgL−1 and 5.00mgL−1. This implies that this method can detect melamine concentrations below 1.0mgL−1, the concentration currently considered unsafe.

Preparation of Mono-Layered Ag Nanoparticles for Charge-Trap Sites of Memory Thin-Film Transistors Using In-Ga-Zn-O Channel

We propose a methodology for the formation of silver (Ag) nanoparticle monolayer as charge trapping layer of nonvolatile memory thin-film transistor using an indium-gallium-zinc oxide semiconductor channel layer. Atomic-layer-deposited Al2O3-amine treatment Ag configuration were employed as tunneling/charge-trap layers, respectively. The memory devices showed wide memory window of 8.0 V, when the gate voltage was swept from −20 to 20 V. The high on/off current ratios of 5.81 × 105 and 1.29 × 103 could be obtained for the memory device, when the program pulse duration was reduced to 1 μs and 5 ns, respectively. The Ag nanoparticle monolayer could be prepared by using the amine-functionalized Al2O3 layer. The areal density of Ag nanoparticle was controlled by modulating the Ag ratio in polystyrene (PS) mixture and optimized at Ag:PS ratio of 5:5.