Ag NFs Research Articles

Rapid production of silver nanofibers using a self-reducing solution

Silver nanofibers (Ag NFs) have gained considerable attention because of their high transmittance resulting from the size effect, excellent electrical conductivity, and mechanical properties. However, synthesizing high-quality Ag NFs remains a challenge. This paper reports a novel self-reducing solution that contains platinum nanoparticles for the rapid production of Ag NFs. The method involves generating the precursor NFs and heating them in air, which reduces silver nitrate to Ag NFs within a few minutes. The as-prepared solution is characterized by its simple preparation, cost-effectiveness, and broad applicability. Additionally, the use of high-pressure airflow to directly spin the solution and a complete self-reduction system that does not depend on external conditions broadens the application prospects of the as-developed solution. Furthermore, we provide insights into the self-reduction mechanism and guidance on the preparation of self-reducing solutions.

Ag nanoflowers as single-particle, multi-wavelength SERS active platforms

Surface-enhanced Raman spectroscopy (SERS) has been successfully employed in several fields of interest such as biosensing, in-situ catalysis studies, and archeology, in this regard, the production of nanostructures for the SERS effect is the core of scientific research. Up to now a lot of different types of metallic nanoparticles and nanosurfaces were produced in trying to match the theoretical enhancement of 1014. This work presents a novel SERS active substrate with a high enhancement and a wide range of exciting wavelengths. Specifically, we synthesize Ag Nanoflowers (AgNFs), spherical silver micro-particles with a diameter of 1.7 μm and a nano-rough surface. When AgNFs are deposited onto a substrate thanks to their dimension is possible, to find a single isolated micro-particle and study the signal enhancement of an analyte adsorbed onto its surface. The SERS properties at a single-particle level were studied using a standard molecule 4-mercaptobenzoic acid (4-MBA). Thanks to their extinction spectrum, expanding throughout the visible range, we were able to systematically study the enhancement for several single Ag NFs with 532, 633, and 785 nm laser wavelengths, finding a maximum enhancement factor in the order of 108- 109. This result is of great interest because demonstrates that such nanomaterial can be easily used to study every kind of analyte at low concentrations with any exciting wavelength thus avoiding other undesired optical phenomena, such as luminescence or degradation of the analyte.

A facile and controllable method to fabricate Ag nanofilaments from [formula omitted]-silver sulfide for highly sensitive SERS substrates

In this work, a facile and controllable method to fabricate high-density silver nanofilaments (Ag NFs) from β-silver sulfide (β-Ag2S) for surface-enhanced Raman scattering (SERS) substrates was reported. The β-Ag2S crystal structure affects the growth of Ag NF significantly. The optimal silver nanofilaments with a density of 5.93 × 109 NF/cm 2 and length of 0.46±0.04μm were formed when the β-Ag2S substrate was irradiated by a 20kV electron beam for 10 min. The Ag NF substrate possesses the SERS enhancement factor (EF) of 1.57 × 106 at 1 mM Methylene blue (MB), nevertheless, the detection limit for Methylene blue can reach up to 1.18 × 10−11 M. It was found that by controlling the accelerating voltage and irradiation time, the surface morphology of the Ag NFs as SERS substrates can be tailored to obtain the optimal SERS EF. The simple yet controllable method presented here opens a new path to fabricate Ag nanofilament SERS substrates for ultra-low chemical concentration analysis.

Green preparation of silver nanofilms as SERS-active substrates for Rhodamine 6G detection

A green and reliable seed-mediated electroless deposition method using the Sargentgloryvine stem extract as reducing and capping agent is explored to prepare silver nanofilms (Ag NFs) as surface-enhanced Raman scattering (SERS) active substrates. The average particle size of Ag NFs can be facilely controlled only by adjusting the amount of AgNO3 in the growth solution. Furthermore, the SERS properties of Ag NFs are established experimentally and their Raman enhancement mechanism is revealed by means of the scanning electron microscopy and the finite-difference time-domain simulation. It is found that high surface coverage and slight surface agglomeration of Ag NFs are beneficial for the amplification of Raman signal. Optimized Ag NFs display superior sensitivity towards Rhodamine 6G molecules and good reproducibility, indicating potential applications in SERS-based detection and analysis. Meanwhile, the proposed method to obtain Ag NFs provide a promising route for the preparation of other metal nanofilm.

In-situ deposition of silver nanoparticles on silver nanoflowers for ultrasensitive and simultaneous SERS detection of organic pollutants

Recently, a great deal of research has been stepped forward to implement real-time detection of multiple targets using surface-enhanced Raman spectroscopy (SERS). Herein, a novel incorporation of silver nanoparticles (AgNPs) on silver nanoflowers (AgNFs) via the in-situ process offers high SERS enhancement by its unique plasmonic resonance. The electromagnetic mechanism of AgNFs incorporated with AgNPs generates numerous hotspots from abundant nanogaps on nanoflowers and between nanoparticles for ultrasensitive detection of probe molecules. The increment in the SERS signal is demonstrated by depositing the probe molecules, rhodamine 6G (R6G) and Congo Red (CR), on the proposed nanostructure. The proposed AgNF@AgNP nanostructure provides stronger SERS activity than the individual AgNPs and Ag NFs, and possesses superior detection ability towards R6G (10−14 M) and CR (10−9 M) with excellent uniformity (<10.27%) and analytical enhancement factor (AEF) (1012 for R6G and 107 for CR). Moreover, the simultaneous SERS detection of R6G and CR has been demonstrated with trace-level detection of CR at 10−8 M and R6G at 10−13 M. The AgNF@AgNP nanostructure with dense hotspots offers remarkable SERS activity, and becomes as a potential tool to analyze organic molecules from environment for real-world applications.

Histidine-directed formation of nearly monodispersed silver nanoflowers and their ultra-high peroxidase-like activity under physiological pH

In this work, we demonstrated a new approach for the preparation of nearly monodispersed silver nanoflowers (Ag NFs) with ultra-high peroxidase-like activity under physiological pH (6.0) by using histidine as both ligand and shape-directing agent and hydroxylamine as reductant. It was identified that the histidine could tune the activity of the silver precursor effectively and direct the preferential growth of the (111) facet of Ag particles via the random attachment. Under the appropriate concentration of histidine, both increase in the concentration of the reductant and elevation in pH of the reaction solution (to improve the activity of reductant) favorited the formation of Ag NF. The resulting histidine-coated Ag NFs showed ultra-high peroxidase-like activity at pH 6.0 due to the critical role of histidine in the enhanced binding affinity of Ag NFs towards both H2O2 and 3,3,5,5-tetramethylbenzidine (TMB) substrates. Based on the reducing ability of ascorbic acid (AA) towards the oxidized TMB, a simple and efficient colorimetric method was developed for the detection of AA under physiological pH.

Synthesis of antibacterial flower‐like silver nanostructures by self‐assembly of diphenylalanine peptide on graphite

Preparation of silver nanoflowers (Ag NFs) was carried out through the self-assembly process of diphenylalanine (FF) peptide on the graphite surface. Pencil graphite rods were used as a substrate for the self-assembly process. A reduction reaction by hydrazine was employed in the synthesis procedure of the Ag NFs. scanning electron microscope, Fourier transform infrared spectroscopy (FT-IR) spectroscopy and X-ray diffraction (XRD) were employed to characterise the obtained Ag NFs. The morphological analysis of the Ag NFs revealed assemblies constructed by multiple sheet nanostructures designed as flower petals and positioned in the form of 3D semi-spherical arrangements. The successful synthesis of Ag NFs was confirmed by FT-IR characteristic bands of FF and Ag components. The cubic lattice structure of the Ag NFs was revealed by XRD. Standard Kirby–Bauer disk diffusion tests using Gram-positive and Gram-negative bacterial strains exhibited the promising antibacterial performance of the Ag NFs against all of the tested bacterial species.

A Biodegradable and Stretchable Protein-Based Sensor as Artificial Electronic Skin for Human Motion Detection.

Due to the natural biodegradability and biocompatibility, silk fibroin (SF) is one of the ideal platforms for on-skin and implantable electronic devices. However, the development of SF-based electronics is still at a preliminary stage due to the SF film intrinsic brittleness as well as the solubility in water, which prevent the fabrication of SF-based electronics through traditional techniques. In this article, a flexible and stretchable silver nanofibers (Ag NFs)/SF based electrode is synthesized through water-free procedures, which demonstrates outstanding performance, i.e., low sheet resistance (10.5 Ω sq-1 ), high transmittance (>90%), excellent stability even after bending cycles >2200 times, and good extensibility (>60% stretching). In addition, on the basis of such advanced (Ag NFs)/SF electrode, a flexible and tactile sensor is further fabricated, which can simultaneously detect pressure and strain signals with a large monitoring window (35 Pa-700 kPa). Besides, this sensor is air-permeable and inflammation-free, so that it can be directly laminated onto human skins for long-term health monitoring. Considering the biodegradable and skin-comfortable features, this sensor may become promising to find potential applications in on-skin or implantable health-monitoring devices.

SnS2 Quantum Dots as New Emitters with Strong Electrochemiluminescence for Ultrasensitive Antibody Detection.

Herein, we designed an electrochemiluminescence (ECL) biosensor with SnS2 quantum dots (SnS2 QDs) as novel emitters for the ultrasensitive assay of cytomegalovirus pp65 antibody (anti-CMV pp65) via smart circular peptide-DNA nanomachine amplification. First, the novel ECL biosensing platform was constructed by self-assembly of water-soluble, nontoxic, and earth-abundant SnS2 QDs on the 3D hierarchical silver nanoflowers (Ag NFs) surface, where the Ag NFs, as coreaction accelerator in the ECL ternary (SnS2 QDs/S2O82-/Ag NFs) system, could efficiently boost the ECL intensity of SnS2 QDs. Furthermore, we designed a specific nucleic acid sequence labeled antigenic peptide to act as multifunctionalized capture probe (CP), which could specifically recognize the target antibody assisting with two auxiliary DNA strands via the proximity hybridization of DNA motifs to form a smart circular peptide-DNA nanomachine. Then, with the aid of nuclease, the resultant circular peptide-DNA nanomachine could initiate the subsequent cascade recycling amplification to output massive DNA products as mimic target (MT). As a result, the proposed ECL biosensor for anti-CMV pp65 detection exhibited high sensitivity with a wide linear range from 1 fM to 100 nM and a low detection limit (0.33 fM). Importantly, this work not only first utilized SnS2 QDs as promising ECL emitters for biosensing platform construction but also opened an efficient way for highly sensitive and selective detection of antibody in disease diagnosis and clinical analysis.

Silver Nanoflower Decorated Graphene Oxide Sponges for Highly Sensitive Variable Stiffness Stress Sensors.

Soft conductive materials should enable large deformation while keeping high electrical conductivity and elasticity. The graphene oxide (GO)-based sponge is a potential candidate to endow large deformation. However, it typically exhibits low conductivity and elasticity. Here, the highly conductive and elastic sponge composed of GO, flower-shaped silver nanoparticles (AgNFs), and polyimide (GO-AgNF-PI sponge) are demonstrated. The average pore size and porosity are 114 µm and 94.7%, respectively. Ag NFs have thin petals (8-20 nm) protruding out of the surface of a spherical bud (300-350 nm) significantly enhancing the specific surface area (2.83 m2 g-1 ). The electrical conductivity (0.306 S m-1 at 0% strain) of the GO-AgNF-PI sponge is increased by more than an order of magnitude with the addition of Ag NFs. A nearly perfect elasticity is obtained over a wide compressive strain range (0-90%). The strain-dependent, nonlinear variation of Young's modulus of the sponge provides a unique opportunity as a variable stiffness stress sensor that operates over a wide stress range (0-10 kPa) with a high maximum sensitivity (0.572 kPa-1 ). It allows grasping of a soft rose and a hard bottle, with the minimal object deformation, when attached on the finger of a robot gripper.

Broadband plasmonic silver nanoflowers for high-performance random lasing covering visible region

Abstract Multicolor random lasing has broad potential applications in the fields of imaging, sensing, and optoelectronics. Here, silver nanoflowers (Ag NF) with abundant nanogaps are fabricated by a rapid one-step solution-phase synthesis method and are first proposed as effective broadband plasmonic scatterers to achieve different color random lasing. With abundant nanogaps and spiky tips near the surface and the interparticle coupling effect, Ag NFs greatly enhance the local electromagnetic field and induce broadband plasmonic scattering spectra over the whole visible range. The extremely low working threshold and the high-quality factor for Ag NF-based random lasers are thus demonstrated as 0.24 MW cm−2 and 11,851, respectively. Further, coherent colorful random lasing covering the visible range is realized using the dye molecules oxazine (red), Coumarin 440 (blue), and Coumarin 153 (green), showing high-quality factor of more than 10,000. All these features show that Ag NF are highly efficient scatterers for high-performance coherent random lasing and colorful random lasers.

Hierarchically-structured silver nanoflowers for highly conductive metallic inks with dramatically reduced filler concentration.

Silver has long been employed as an electrically conductive component, and morphology-dependent properties have been actively investigated. Here we present a novel scalable synthesis method of flower-shaped silver nanoparticles (silver nanoflowers, Ag NFs). The preferential affinity of citrate molecules on (111) surface of silver enabled spontaneous anisotropic growth of Ag NFs (bud size: 250~580 nm, single crystalline petal thickness: 9~22 nm) with high reproducibility and a high yield of >99.5%. The unique hierarchical structure resulted in coalescence of petals over 80~120 °C which was practically employed in conductive inks to construct percolation pathways among Ag NFs. The ink with only 3 wt% of Ag NFs provided two orders of magnitude greater conductivity (1.008 × 105 Scm−1), at a low curing temperature of 120 °C, compared with the silver nanoparticle ink with a much higher silver concentration (50 wt%). This extraordinary property may provide an excellent opportunity for Ag NFs for practical applications in printable and flexible electronics.

Thermal Conductivity Enhancement of Ethylene Glycol-Based Suspensions in the Presence of Silver Nanoparticles of Various Shapes

In this technical brief, the effect of adding silver (Ag) nanoparticles of various shapes on the thermal conductivity enhancement of ethylene glycol (EG)-based suspensions was investigated experimentally. These included Ag nanospheres (Ag NSs), Ag nanowires (Ag NWs), and Ag nanoflakes (Ag NFs). Measurements of the thermal conductivity of the suspensions were performed from 10 to 30 °C at an increment of 5 °C. It was shown that the thermal conductivity of the EG-based suspensions increases with raising the temperature. The Ag NWs of a high aspect ratio (∼500) caused greatest relative enhancement up to 15.6% at the highest loading of nearly 0.1 vol. %, whereas the other two shapes of nanoparticles, Ag NSs and Ag NFs with much smaller aspect ratios, only led to enhancements up to 5%. The formation of a network of Ag NWs that facilitates heat conduction was likely responsible for their better performance. The relative enhancement was also predicted by the Hamilton-Crosser model that takes the particle shape effect into consideration. It was shown that the predictions far underestimate the thermal conductivity enhancements but are qualitatively consistent with their shape dependence. As a penalty, however, the presence of Ag NWs was shown to give rise to significant increase in the viscosity of the EG-based suspensions.

Trisodium Citrate-Assisted Biosynthesis of Silver Nanoflowers by Canarium album Foliar Broths as a Platform for SERS Detection

The synthesis and applications of anisotropic nanostructures have attracted much attention in modern nanotechnology. Recently, biosynthesis has been demonstrated to be a viable green alternative to traditional chemical and physical methods for synthesizing metal nanostructures. Herein, we developed a new, green one-pot synthetic protocol in which silver nanoflowers (Ag NFs) with three-dimensional structures were synthesized by Canarium album foliar broths in the presence of trisodium citrate (TSC) at room temperature. The effects of silver nitrate, TSC, and foliar broths on these synthesis processes were investigated to determine the optimum synthesis conditions. Further exploration of the formation mechanism of Ag NFs showed that both the biomolecules and TSC played very important roles. The improved insight into the specific roles of the bioprotective components and the controlled synthesizing ability are expected to help explain the formation mechanism of this interesting nanostructure that exhibited an excellent performance in surface-enhanced Raman scattering.

Core/shell nanofibers of TiO2@carbon embedded by Ag nanoparticles with enhanced visible photocatalytic activity

Core/shell nanofibers of TiO2@carbon embedded by Ag nanoparticles (TiO2@C/Ag NFs) were fabricated by combining the electrospinning technique, the hydrothermal method and an in situreduction approach. The results showed that a uniform graphite carbon layer of approximately 8 nm in thickness was formed around the electrospun TiO2 nanofiber and small Ag nanoparticles (Ag NPs) were dispersed well inside the carbon layer. And, the TiO2@C/Ag NFs had remarkable light absorption in the visible region. The photocatalytic studies revealed that the TiO2@C/Ag NFs exhibited enhanced photocatalytic efficiency of photodegradation of Rhodamine B (RB) and Methyl Orange (MO) compared with the pure TiO2 nanofibers, TiO2@carbon core/shell nanofibers and TiO2/Ag nanofibers under visible light irradiation, which might be attributed to the good light absorption capability and high separation efficiency of photogenerated electron–hole pairs based on the photosynergistic effect among the three components of TiO2, carbon and Ag. And, the TiO2@C/Ag NFs could be easily recycled due to their one-dimensional nanostructural property.