Self-assembled Ag Nanoparticles Research Articles

Dual-mode sensing of hydrogen peroxide on self-assembled Ag nanoparticles anchored on polydopamine wrapping 2D Cu-MOFs.

In this study, we have fabricated a dual-signal sensor for H2O2 determination based on 2D Cu-MOFs decorated with Ag NPs. A novel polydopamine (PDA) reduction method was utilized to reduce [Ag(NH3)2]+ to highly dispersed Ag NPs in situ without other reductive agents, and Cu-MOF@PDA-Ag was obtained. For the electrochemical sensor, the Cu-MOF@PDA-Ag modified electrode exhibits outstanding electrocatalytic properties toward H2O2 reduction with a high sensitivity of 103.7 μA mM-1 cm-2, a wide linear range from 1 μM to 35 mM and a low detection limit of 2.3 μM (S/N = 3). Moreover, the proposed sensor shows good feasibility in an orange juice sample. For the colorimetric sensor, colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be oxidized by the Cu-MOF@PDA-Ag composite in the presence of H2O2. A Cu-MOF@PDA-Ag catalysis-based colorimetric platform is further established for the quantitative analysis of H2O2 ranging from 0 to 1 mM with a lower detection limit of 0.5 nM. Importantly, such a dual-signal method for the detection of H2O2 could potentially have wide practical applications.

Identification of antibiotic residues in aquatic products with surface-enhanced Raman scattering powered by 1-D convolutional neural networks

Universal and fast antibiotic residues detection technology is imperative for the control of food safety in aquatic products. However, accurate surface-enhanced Raman scattering (SERS) quantitative detection of complicated samples is still a challenge. A recognition method powered by deep learning and took advantage of the unique fingerprint information merits of SERS was proposed. Herein, the spectra were collected by Ag nanofilm SERS substrate prepared by self-assembly of Ag nanoparticles on water/oil interface. A SERS-based database of commonly used antibiotics in aquatic products was set up, which is suitable for employed as input data for learning and training. The results show that the five types of antibiotics are successfully distinguished through principal component analysis (PCA) and each antibiotic in every type was successfully distinguished. Furthermore, one-dimensional convolutional neural networks (1-D CNN) was used to distinguish the antibiotics, and the results show that all the test samples were correctly predicted by 1-D CNN model. The results of this research suggest the great potential of the combination of SERS spectra with deep learning as a method for rapid and highly accurate identification of antibiotic residues in aquatic products.

Combined Small-Angle Neutron Scattering/Small-Angle X-ray Scattering Analysis for the Characterization of Silver Nanoparticles Prepared via Photoreduction in Water-in-Oil Microemulsions.

In this study, we used small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to investigate the formation process of silver (Ag) nanoparticles (NPs) in water-in-oil (w/o) reverse microemulsions comprising sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water, and organic solvents (such as benzene, octane, and decane) by the photoreduction of silver perchlorate (AgClO4). Combining SANS and SAXS, the structural changes in the w/o microemulsions before and after the formation of Ag NPs via photoreduction were quantitatively evaluated. From the SANS experiments performed using the contrast-variation method, the size of water cores containing Ag NPs and the thickness of the AOT shells were calculated using the core-shell hard-sphere model. The size of the Ag NPs and their aggregates was calculated via SAXS analysis based on the polydisperse sphere model with a Schulz-Zimm distribution. We found that aggregates of three or four primary Ag NPs are formed by, first, the aggregation of water droplets through the entanglement of the tails of the AOT shell, followed by the self-assembly of Ag NPs into their aggregates because of particle-particle attractive interactions.

Sandwich optoplasmonic hybrid structure for surface enhanced Raman spectroscopy

Combined with photonic microstructure and plasmonic nanostructure, the optoplasmonic hybrid structure with fantastic optical properties attracts lots of attentions in recent years. With the help of light enrichment by dielectric photonic microenvironment, the embedded plasmonic nanoantennas generate much greater electromagnetic field enhancement at surface for light harvesting compared to conventional plasmonic nanostructures. In this work, a sandwich optoplasmonic hybrid structure is developed for surface enhanced Raman spectroscopy (SERS) detection, which is consisted of polymethyl methacrylate (PMMA) microspheres array, self-assembled Ag nanoparticles (AgNPs) film and SiO2 microsphere (PMMA@AgNPs@SiO2). The SERS spectra collected on this optoplasmonic substrate point out it has high sensitivity with limit of detection (LOD) at 10 fM. The experimental data demonstrate both the PMMA microarray and SiO2 microsphere play important roles in enrichment of light illuminating at AgNPs for SERS detection, which is confirmed by the simulated electric field distributions. This sandwich optoplasmonic hybrid structure not only enlarges research field of surface plasmon, but also provides a novel SERS subtract for sensitive analysis in chem/bio-field.

Interface-Induced Ag Monolayer Film for Surface-Enhanced Raman Scattering Detection of Water-Insoluble Enrofloxacin

Water-insoluble molecules usually show poor surface-enhanced Raman scattering (SERS) signals, because they are hardly adsorbed on the surface of most commonly used SERS substrates, such as aqueous Ag or Au colloids. In this work, a highly sensitive and reproducible Ag monolayer film (Ag MLF) SERS substrate prepared by self-assembly of Ag nanoparticles (Ag NPs) on water/oil interface can realize the trace SERS detection of water-insoluble enrofloxacin. The positively charged phase transfer catalyst can transfer the negatively charged Ag nanoparticles in aqueous solution to the water/oil interface. At the same time, the water-insoluble enrofloxacin can also be attracted to the interface because of its lipophilic group. The type/volume of the oil phase and phase transfer catalyst and the vortex mixing time were all optimized to maximize the SERS effect of Ag MLF. Results showed that trace water-insoluble enrofloxacin can be identified by Ag MLF and its detection sensitivity was significantly improved. The proposed novel Ag MLF can be further applied to detect other water-insoluble molecules in SERS.

Insights on the enhanced Raman scattering of monolayer TMDCs (Mo, W)(S, Se)2 with Ag nanoparticles via rapid thermal annealing

Light interactions between metallic nanostructures and ultra-thin two-dimensional transition metal dichalcogenides (TMDCs) exhibit unique physical properties that are promising for fundamental interests and technological applications. Herein, we successfully demonstrate that self-assembled Ag nanoparticles fabricated by a rapid thermal annealing (RTA) process at certain temperature can be hybridized on systematical monolayer (ML) TMDC (Mo, W)(S, Se)2 surfaces. The morphologies, diameters, and heights of RTA-formed Ag nanoparticles on ML TMDCs are estimated from a statistical perspective. The optical properties of four pristine ML (MoS2, WS2, MoSe2, WSe2) triangular flakes and their corresponding hybrid Ag-ML TMDC nanostructures are comprehensively studied by high-resolution laser confocal micro-Raman spectroscopy. It is found that significant enhancement of typical E2g1 and A1g active modes of Raman scattering in the four ML TMDCs is achieved by integrating self-assembled Ag plasmonic nanoparticles, resulting from a localized surface plasmon resonance (LSPR) at the boundaries of the hybrid nanocomposites. The underlying regime of plasmonic resonance between self-assembled Ag nanoparticles and ML TMDCs can be categorized as weak plasmon-exciton coupling, which has been demonstrated by more detailed physical simulations based on the finite-difference time-domain (FDTD) method.

Fabrication of transparent composites for non-invasive Surface Enhanced Raman Scattering (SERS) analysis of modern art works

Surface Enhanced Raman Scattering (SERS) has become an invaluable tool for the identification of colorants in artworks, due to its enhanced sensitivity and ability to quench fluorescence interference compared to Raman spectroscopy. However, the application of SERS to artwork analysis is still limited by its inherent invasiveness and the need for extraction procedures. In this work non-invasive transparent SERS probes were fabricated by self-assembly of Ag nanoparticles into glass and PDMS surfaces and used for identification of dye content in artistic drawings. SERS measurements were performed directly on the selected analytical surfaces by laser back illumination through the SERS probe. The non-invasiveness of fabricated probes was tested by optical microscopy. It was found that Ag nanoparticle/glass probes left no Ag nanoparticle residue after four consecutive depositions on sacrificial surfaces, whereas Ag nanoparticle/PDMS composites could be deposited and subsequently peeled off the analytical surfaces leaving no contamination traces. The high conformability, flexibility and transparency of Ag nanoparticle/PDMS composites enabled good adhesion to the surface of analyzed artistic drawings and therefore the generation of in situ SERS spectra from artistic drawings. The use of this method allowed identification of main dye components in real artworks comprising a red BIC ballpoint drawing and a Japanese woodblock print.

Enhanced Surface-Enhanced Raman Scattering (SERS) Sensitivity by the Self-Assembly of Silver Nanoparticles (Ag NPs) Laminated on Polydimethylsiloxane (PDMS)

Herein, a transparent and reproducible substrate, fabricated using polydimethylsiloxane (PDMS) laminated with self-assembled Ag nanoparticles (Ag NPs), was employed as a universal surface-enhanced Raman scattering (SERS) substrate for the detection of targets with various matrices. The Ag NPs were assembled in a two-dimensional manner via a self-assembly technique. Due to the electrostatic interaction between the Ag NPs, the reproducibility of the assembly was ensured by the fixed density of the assembled Ag NPs at saturated assembly states. The assembled pattern and plasmon resonance of the Ag NPs were well preserved during the molding and curing of PDMS. As a result, the Ag NP laminated PDMS film exhibited a SERS effect to the adsorbed p-aminothiophenol comparable to that of the assembled Ag NPs on a glass slide. Extra SERS enhancement was achieved by construction of a Ag (PDMS)/molecule/Ag (glass) configuration due to the electromagnetic coupling between the Ag NPs. The Raman scattering of 4-mercaptobenzoic acid and benzotriazole modified on the surfaces of a smooth Au electrode and copper foil, respectively, was detected with the aid of the Ag NP-laminated PDMS film. Furthermore, malachite green dispersed in a KBr solid matrix was quantitatively determined with a detection limit of 0.5 μg/g. It is suggested that the SERS enhancement and consequential SERS detection sensitivity of the target molecules may be further maximized by adjusting the distance between the target molecules and the Ag NPs laminated on the PDMS film.

Optimization of indium tin oxide layer thickness for surface-plasmon-enhanced green light-emitting diodes

Surface-plasmon (SP)-enhanced light-emitting diodes (LEDs) covering self-assembled Ag nanoparticles (NPs) on top of a p-GaN layer are broadly studied to improve luminescence efficiency in green LEDs. However, the enhancement factor of SP-enhanced LEDs is reduced under electrical injection compared to that under external optical pumping. For current injection, indium tin oxide (ITO) is typically deposited on top of a p-GaN layer for current spreading and ohmic contact. In this paper, we investigate the effect of the ITO layer on the performance of SP-enhanced green LEDs. We prepared samples with varying ITO thicknesses, from 30 nm to 200 nm, and investigated their optical and electrical characteristics. From the ITO thickness-dependent measurements, we show ITO thickness has a significant impact on electroluminescence intensity and current–voltage characteristics. Finally, we propose the optimized ITO thickness for SP-enhanced LEDs.

Optical and Structural Properties of Ag and c-Si Nanostructures Formed During the Metal-Assisted Chemical Etching of Silicon

This study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

How to make microscale pores on a self-assembled Ag nanoparticle monolayer

In this short communication, we report a procedure for the fabrication of microscale pores on a rigid self-assembled Ag nanoparticle monolayer with nanothickness. Here, condensed water droplets on a hydrophobic substrate are used as a pore formation template for Langmuir-Schaefer film deposition. The optical properties of the Ag nanoparticle monolayer were influenced by the porous structure, e.g., the localized surface plasmon resonance (LSPR) peak was weakened and broadened for the porous monolayer compared with the homogeneous monolayer, even though the number of particles on the substrate should be the same between them. The pores obtained by this method were robust and could be used as a mask for metal deposition or local fluorescence imaging. This environmentally friendly technique can provide a micropatterned surface with a minimal cytotoxicity, which has high potential for LSPR mediated biosensing and bioimaging applications.

Оптические и структурные свойства наноструктур Ag и c-Si, формирующихся в процессе металл-стимулированного химического травления кремния

AbstractThis study consisting of two parts is concerned with the features of the three-stage process of the metal-assisted chemical etching (MACE) of silicon. This process is used to fabricate silicon nanostructures. In the first part of this work, a layer of self-assembled Ag nanoparticles chemically deposited from a solution on the surface of single-crystal silicon (c-Si) (MACE stage 1) was studied, and the second part includes of investigation of Si nanostructures formed in stages 2 and 3. By means of spectroscopic ellipsometry (in the range of wavelengths λ = 250–900 nm), the pseudodielectric functions of the nanostructures were determined and compared for all the three stages of the MACE process. In addition, for the Si nanostructures, the parameters of layers (the thickness and void fraction) were calculated in the context of the multilayer optical model, with the use of Bruggeman’s effective-medium approximation and fitting procedures.

Fabrication of capillary force induced DNA template Ag nanopatterns for sensitive and selective enzyme-free glucose sensors

The self-patterned silver (Ag) nanowires on Indium Tin Oxide (ITO) were developed and exploited as the enzyme-free sensor probes for glucose detection. Deoxyribonucleic acid (DNA) template increased the capillary force channels of Ag and facilitated the homogeneous and high mobility of Ag-DNA toward the scribe via the coffee ring effect. The subsequent removal of DNA template from Ag-DNA/ITO through the enzymatic hydrolysis process led to the formation of Ag nanowires on ITO. Under alkaline conditions, Ag nanopatterns developed on ITO realized the considerable enzyme-free glucose sensor performances. The fabricated sensor system is reproducible and stable and was pertained with an analysis of spiked human blood serum, where it provided excellent recoveries. Thus these findings have not only showered insights on the self assembly of Ag nanoparticles without the exploitation of any surfactants and harsh conditions but have also provided the fundamental perceptive on the influences of self-assembled nanowires in enzyme free glucose sensor applications.

Self-assembly of Ag nanoparticles on the woven cotton fabrics as mechanical flexible substrates for surface enhanced Raman scattering

Flexible surface-enhanced Raman scattering (SERS) substrates were fabricated based on the natural woven cotton fabrics by a simple self-assembly method in which silver nanoparticles (Ag NPs) were deposited on the fabric. The SERS signal can be controlled by changing the assemble cycle times, leading to different decorated Ag amount on the surface of woven cotton fabrics. SERS woven cotton fabrics displayed excellent reproducibility and SERS sensitivity with a detection limit of p-Aminothiophenol (PATP) at 10−7 M. Moreover, the SERS woven cotton fabrics exhibited remarkable flexibility and practicality, allowing for a close contact the samples surface by swabbing. The approach could be readily extended to other fabrics, such as wool fabrics and other natural fiber fabrics, paving on a new way for the low-cost, portable and flexible SERS substrates.

Random mesh-like Ag networks prepared via self-assembled Ag nanoparticles for ITO-free flexible organic solar cells

Highly-transparent and flexible random mesh-like Ag networks formed by self-assembled Ag nanoparticles for use in transparent and flexible electrodes for ITO-free flexible organic solar cells (FOSCs) was demonstrated. By transferring a self-assembled Ag nanoparticle network onto a PET substrate, embossed and intaglio-type mesh-like Ag network electrodes were fabricated. Electrical, optical, morphological, and mechanical properties of the embossed and intaglio-type mesh-like Ag network electrodes were compared in detail. Although both mesh-like Ag networks exhibited similar sheet resistance, optical transmittance, and flexibility, the intaglio-type Ag networks were advantageous to use as transparent electrodes for FOSCs due to the high aspect ratio of emboss-type Ag networks. Regardless of organic active materials, FOSCs with intaglio-type Ag networks exhibited better performance than FOSCs with emboss-type Ag networks due to ease in forming uniform organic layer coatings on the intaglio-type Ag networks embedded in the substrate. This indicated that intaglio-type mesh-like Ag network electrodes are a promising flexible and transparent anode for printable ITO-free FOSCs.

Experimental quantification of useful and parasitic absorption of light in plasmon-enhanced thin silicon films for solar cells application.

A combination of photocurrent and photothermal spectroscopic techniques is applied to experimentally quantify the useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (μc-Si:H) films incorporating optimized metal nanoparticle arrays, located at the rear surface, for improved light trapping via resonant plasmonic scattering. The photothermal technique accounts for the total absorptance and the photocurrent signal accounts only for the photons absorbed in the μc-Si:H layer (useful absorptance); therefore, the method allows for independent quantification of the useful and parasitic absorptance of the plasmonic (or any other) light trapping structure. We demonstrate that with a 0.9 μm thick absorber layer the optical losses related to the plasmonic light trapping in the whole structure are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. An average useful absorption of 43% and an average parasitic absorption of 19% over 400–1100 nm wavelength range is measured for μc-Si:H films deposited on optimized self-assembled Ag nanoparticles coupled with a flat mirror (plasmonic back reflector). For this sample, we demonstrate a significant broadband enhancement of the useful absorption resulting in the achievement of 91% of the maximum theoretical Lambertian limit of absorption.

Self-assembled Ag nanoparticle network passivated by a nano-sized ZnO layer for transparent and flexible film heaters

We investigated a self-assembled Ag nanoparticle network electrode passivated by a nano-sized ZnO layer for use in high-performance transparent and flexible film heaters (TFFHs). The low temperature atomic layer deposition of a nano-sized ZnO layer effectively filled the uncovered area of Ag network and improved the current spreading in the self-assembled Ag network without a change in the sheet resistance and optical transmittance as well as mechanical flexibility. The time-temperature profiles and heat distribution analysis demonstrate that the performance of the TFTH with the ZnO/Ag network is superior to that of a TFFH with Ag nanowire electrodes. In addition, the TFTHs with ZnO/Ag network exhibited better stability than the TFFH with a bare Ag network due to the effective current spreading through the nano-sized ZnO layer.

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm2, and a factor of 8.1 at 1 W/cm2. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.

Thermal kinetics of self-aggregation and self-assembly of Ag nanoparticles with different capping agents

In this study, the thermal kinetics of Ag nanoparticles (NPs) with different capping agents was studied during self-aggregation and self-assembly, which is important for the usage of Ag conductive ink. Ag NPs were synthesized with polyvinylpyrrolidone (PVP) and l-Cysteine (L-cys) as capping agents. After self-aggregation and self-assembly by heat treatment, the Ag nanoparticles fabricate a homogeneous surface morphology. By TG measurements, the equations of thermal kinetics were established. Flynne Walle Ozawa model was used to calculate the activation energies of self-aggregation and self-assembly of Ag/PVP and Ag/L-cys. The activation energy values have showed a continuous increase as a function of degree of conversion. The activation energy value for Ag/PVP is smaller than Ag/L-cys because PVP binds weaker to the silver nanoparticle surface than thiols.

Surface-enhanced Raman spectroscopy for DNA detection by the self-assembly of Ag nanoparticles onto Ag nanoparticle-graphene oxide nanocomposites.

A novel surface-enhanced Raman scattering (SERS) sensing system which operates by the self-assembly of Ag nanoparticles (AgNPs) onto the nanocomposite of AgNPs and graphene oxide (AgNP-GO) in the presence of two complementary DNAs has been developed. In this system, AgNP-GO serves as a SERS-active substrate. The AgNPs with the modification of non-fluorescent 4-mercaptobenzoic acid (4-MBA) act as highly efficient Raman probes for DNA hybridization. When probe DNAs on AgNP-GO are complementary to target DNAs on AgNPs functionalized with 4-MBA, the DNA hybridization occurring directs the self-assembly of AgNPs onto AgNP-GO, leading to the creation of SERS hot spots. Due to the fact that partial 4-MBA molecules are located in the region of the hot spots, their SERS signals are greatly enhanced, indicating successful DNA hybridization. It is noteworthy that the size of AgNPs contributes significantly to the enhancement of SERS activity. The detection limit of the target DNAs at the pM level can be achieved through the self-assembly of large sized AgNPs onto AgNP-GO. More importantly, the AgNP-AgNP-GO system shows reproducible SERS signals in proportion to the logarithm of the target DNA concentrations spanning from 10(-6) to 10(-12) M and the excellent capability for multiplex DNA detection.