Silver Nanoplates: Size Control in Two Dimensions and Formation Mechanisms

An Approach to a Silver Conductive Ink for Inkjet Printer Technology

Silver-based metal-organic decomposition inks composed of silver salts, complexing agents and volatile solvents are now the subject of much research due to the simplicity and variability of their preparation, their high stability and their relatively low sintering temperature. The use of this type of ink in inkjet printing allows for improved cost-effective and environmentally friendly technology for the production of electrical devices, including flexible electronics. An approach to producing a silver salt-based reactive ink for jet printing has been developed. The test images were printed with an inkjet printer onto polyimide substrates, and two-stage thermal sintering was carried out at temperatures of 60 °C and 100-180 °C. The structure and electrical properties of the obtained conductive lines were investigated. As a result, under optimal conditions an electrically conductive film with low surface resistance of approximately 3 Ω/square can be formed.

Effects of rice root exudates on aggregation, dissolution and bioaccumulation of differently-charged Ag nanoparticles

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability. The stability of MNPs not only depends on their own properties but also on the effects of biological and environmental factors. To better understand the interaction between biological factors and MNPs in aquatic environments, the effects of total rice root exudates (T-RRE) on the aggregation, dissolution and bioaccumulation of Ag nanoparticles (AgNPs) with different surface charges were investigated in detail. Results indicated that T-RRE can induce the aggregation and sedimentation, and hinder the dissolution of polyethyleneimine-coated AgNPs (AgNPs@PEI) with positive surface charges as well as reducing the bioaccumulation of Ag in rice roots. T-RRE had no obvious effect on the dispersion stability of AgNPs@Cit (negatively charged citrate-coated AgNPs) and AgNPs@PVP (near electrically neutral polyvinylpyrrolidone-coated AgNPs), although T-RRE could induce the dissolution of AgNPs@Cit and AgNPs@PVP. In the molecular fractions of T-RRE, high-molecular-weight root exudates (H-RRE) play a key role in inducing the aggregation of AgNPs@PEI and hindering the bioaccumulation of Ag in rice roots. Compared with H-RRE, low-molecular-weight root exudates (L-RRE) can promote the dissolution of AgNPs@Cit and AgNPs@PVP, but it can obviously promote silver accumulation in rice roots. The difference in charge intensity between L-RRE and T-RRE plays a key role in inducing the aggregation and dissolution of AgNPs with different charges. These findings provide a foundation for investigation of the interactions between rice root exudates and nanoparticles with different surface charges in complex environmental systems.

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability.

Green synthesis of silver nanoplates using the special category of plant leaves showing the lotus effect

This paper reports the first ever green synthesis of silver nanoplates using plant leaves having the special feature of showing the lotus effect. Eichhornia crassipes and Colocasia esculenta plant leaves were chosen for the purpose. The aqueous leaf extract of these plants was used as a reducing as well as stabilizing agent in the hydrothermal synthesis of silver nanoplates using silver nitrate as the precursor. Well dispersed silver nanoplates were formed. The appearance of two SPR (Surface Plasmon Resonance) bands corresponding to in-plane and out of plane vibration confirmed the formation of anisotropic nanostructures. The blue shift in peaks of the nanostructures in UV-visible spectra gave information about the stability of the nanoplates with time. Dynamic Light Scattering (DLS) and powder XRD were used to evaluate the ultimate average diameter and crystal structure of these nanostructures respectively. FESEM/EDX and HRTEM/SAED images also confirmed the formation of silver nanoplates. The FT-IR spectra helped to identify the reducing and stabilizing component of plant leaves extract in the formation of 2-D nanostructures. Preliminary antibacterial activity was examined using these nanoplates. A significant zone of inhibition was observed for S. aureus, a Gram positive bacterium.

Green Chemistry Synthesis of Silver Nanoparticles and Their Potential Anticancer Effects

Nanobiotechnology has grown rapidly and become an integral part of modern disease diagnosis and treatment. Biosynthesized silver nanoparticles (AgNPs) are a class of eco-friendly, cost-effective and biocompatible agents that have attracted attention for their possible biomedical and bioengineering applications. Like many other inorganic and organic nanoparticles, such as AuNPs, iron oxide and quantum dots, AgNPs have also been widely studied as components of advanced anticancer agents in order to better manage cancer in the clinic. AgNPs are typically produced by the action of reducing reagents on silver ions. In addition to numerous laboratory-based methods for reduction of silver ions, living organisms and natural products can be effective and superior source for synthesis of AgNPs precursors. Currently, plants, bacteria and fungi can afford biogenic AgNPs precursors with diverse geometries and surface properties. In this review, we summarized the recent progress and achievements in biogenic AgNPs synthesis and their potential uses as anticancer agents.

A preliminary study of the interactions between microplastics and citrate-coated silver nanoparticles in aquatic environments

Microplastics and silver nanoparticles (AgNPs) are considered two emerging environmental contaminants that have adverse effects on aquatic environments. Knowledge on the interactions between AgNPs and microplastics may improve our understanding of these pollutants, posing to surrounding environments and public health. However, current knowledge regarding this issue is limited. Here, we investigate, for the first time, the interactions between AgNPs and the microplastics polyethylene (PE), polypropylene (PP), and polystyrene (PS) in aquatic environments. Results showed no significant interactions between AgNPs and PE or PP microplastics. However, AgNPs were efficiently removed by PS microplastics. These differences are mainly attributed to the presence of π-π interactions. Meanwhile, AgNPs aggregations were generated due to higher concentrations of leaching additives derived from PS microplastics. Interestingly, AgNPs are significantly captured on PS microplastic surfaces in the form of Ag⁰ rather than Ag⁺. The capture process is a monolayer adsorption and influenced greatly by the mass ratio of AgNPs and PS microplastics. These observations may provide a novel environmental fate of AgNPs, and indicate a new potential method for their removal to some degree. These findings demonstrate the complexities of AgNPs absorption onto microplastics and enhance present understanding of interactions between nanoparticles and microplastics in aquatic environments.

Synthesis of Palladium Nanodendrites Using a Mixture of Cationic and Anionic Surfactants

Surfactants are used widely to control the synthesis of shaped noble-metal nanoparticles. In this work, a mixture of hexadecyltrimethylammonium bromide (CTAB), a cationic surfactant; sodium oleate (NaOL), an anionic surfactant; palladium chloride; and a reducing agent were used in the seed-mediated synthesis of palladium nanoparticles. By controlling the surfactant mixture ratio, we initially discovered that palladium nanodendrites with narrow size distribution were formed instead of the traditional nanocubes, synthesized with only CTAB. In order to investigate the optimal ratio to produce Pd nanodendrites with a high yield and narrow size distribution, samples synthesized with multiple molar ratios of the two surfactants were prepared and studied by transmission electron microscopy, dynamic light scattering, conductance, and ultraviolet-visible spectroscopy. We propose that the addition of NaOL alters the arrangement of surfactants on the Pd seed surface, leading to a new pattern of growth and aggregation. By studying the nanodendrite growth over time, we identified the reduction period of Pd²⁺ ions and the formation period of the nanodendrites. Our further experiments, including the replacement of CTAB with hexadecyltrimethylammonium chloride (CTAC) and the replacement of NaOL with sodium stearate, showed that CTA⁺ ions in CTAB and OL^- ions in NaOL play the main roles in the formation of nanodendrites. The formation of palladium nanodendrites was robust and achieved with a range of temperatures, pH and mixing speeds.

Ultrathin Pd-based nanosheets: syntheses, properties and applications

Two-dimensional (2D) noble metal-based nanosheets (NSs) have received considerable interest in recent years due to their unique properties and widespread applications. Pd-based NSs, as a typical member of 2D noble metal-based NSs, have been most extensively studied. In this review, we first summarize the research progress on the synthesis of Pd-based NSs, including pure Pd NSs, Pd-based alloy NSs, Pd-based core-shell NSs and Pd-based hybrid NSs. The synthetic strategy and growth mechanism are systematically discussed. Then their properties and applications in catalysis, biotherapy, gas sensing and so on are introduced in detail. Finally, the challenges and opportunities towards the rational design and controlled synthesis of Pd-based NSs are proposed.

Environmental fate and behavior of silver nanoparticles in natural estuarine systems

Silver nanoparticles (AgNPs) are widely used in many consumer products, whereas their environmental behaviors in natural aquatic systems remain unknown, especially in natural brackish media. Therefore, it is urgent to investigate the environmental fate of AgNPs in natural brackish waters. Here, we investigated the stability of citrate-coated AgNPs in natural brackish water collected from 6 different sites with distinct salinities in the Xinglinwan Reservoir, located in Xiamen City, southeast China. The obtained results showed that AgNP colloids remained stable in low-salinity waters, which was mainly determined by the effects of dissolved organic matter (DOM) promoting the stability of the nanoparticles. However, the environmental fate of AgNPs in high-salinity waters was dominated by the salinity or ionic strength, especially the free ion concentrations of Cl^-, SO₄^2-, or S^2-, resulting in rapid sedimentation and dissolution. In addition, both DOM and salinity contributed to the environmental behavior of AgNPs in moderate-salinity waters, ultimately resulting in either colloidal stability or sedimentation. Overall, these results may reveal that AgNPs remain relatively stable for a long period in low-salinity natural waters, and that the stability might gradually decrease as AgNPs are transferred from freshwaters through brackish waters and eventually end up in seawater along the bay. Our findings also further indicate that the toxicity and potential risks of AgNPs may present more serious threats to the environment and organisms in natural freshwaters than in natural estuarine systems or seawater.

2D nanostructures beyond graphene: preparation, biocompatibility and biodegradation behaviors

The research advances of the preparation, biocompatibility and biodegradation of 2D nanomaterials are introduced. The prospects and challenges of the biomedical applications of 2D nanomaterials are summarized.

Silver nanoparticles fabricated by reducing property of cellulose derivatives

The aim of this study was to synthesize silver nanoparticles (AgNPs) by using cellulose derivatives as a reducing agent. Methyl cellulose (MC), hydroxy ethylcellulose (HEC), and hydroxypropyl methylcellulose (HPMC) were compared for their reducing property. HPMC presented the highest reducing power, with equilibrium concentration (EC) of 84.6 ± 4.5 µmol Fe²⁺/g, followed by MC and HEC, with the EC of 62.3 ± 1.4, and 38.1 ± 3.2 µmol Fe²⁺/g, respectively. Using these cellulose derivatives as a reducing agent and silver nitrate as a precursor in fabrication of silver nanoparticles (AgNPs), three cellulose-AgNPs, HEC-AgNPs, MC-AgNPs, and HPMC-AgNPs, were obtained. The cellulose-AgNPs showed different maximum absorptions confirming AgNPs spectra at 415, 425, and 418 nm, respectively. Reaction parameters such as pH, temperature, and period of reaction affected intensity of the maximum absorptions and size of AgNPs. Using 0.3% cellulose solution at pH 9 and reaction at 70°C for 90 min, the particle size of MC-AgNPs, HEC-AgNPs, and HPMC-AgNPs was 97.7 ± 2.4, 165.6 ± 10.6, and 51.8 ± 1.6 nm, respectively. AgNPs obtained from different cellulose derivatives and various preparation parameters possess different inhibition potential against Escherichia coli and Staphylococcus aureus. The cellulose-AgNPs have higher effective against E. coli than S. aureus. HPMC-AgNPs showed significantly higher antibacterial activity than MC- AgNPs and HEC-AgNPs, respectively. These results suggest that the type of cellulose derivatives and the reaction parameters of the synthesis such as pH, temperature, and reaction period play an important role to the yield and physicochemical property of the obtained AgNPs.

Robust Synthesis of Size-Dispersal Triangular Silver Nanoprisms via Chemical Reduction Route and Their Cytotoxicity

Triangular silver nanocrystals, well-known as nanoprisms (Ag-NPrs), were successfully developed via a robust and straightforward direct chemical reduction synthetic approach, producing desirable tiny and well-controlled Ag-NPrs. This procedure was accomplished by fabricating a mixture of di-sodium succinate hexa-hydrate (DSSH) and tri-sodium citrate di-hydrate (TSCD) as capping agents at optimal synthetic conditions and under an open-air condition, which proved to be an enormous challenge. Additionally, the Ag-NPrs were fully characterized by UV-vis spectra, X-ray diffraction (XRD), scanning electron microscope (SEM), and dynamic light scattering (DLS). Likewise, the formation stages from spherical silver nanoparticles (Ag-NPs) to triangular Ag-NPrs were also captured simultaneously via transmission electron microscope (TEM) and high-resolution transmission electron microscope (HR-TEM) images. More interestingly, an active thin silica-shell was efficiently applied on the Ag-NPrs outer-layer to increase their functionality. Furthermore, to confirm their biocompatibility, we also carried out cell viability assays for the Ag-NPs, Ag-NPrs, and Ag-NPrs@SiO2 with different concentrations at 62.5, 125, and 250 µg/mL after 12, 24, and 48 h of exposure time, respectively, on a regular African green monkey kidney cell line. The cell viability test results exemplified that the three silver nanostructures were toxic-free and suitable for further potential biological applications in the near future.

Microstructure and Resistivity Analysis of Silver Nanoparticle-Based Crystalline Conductive Films Synthesized using PEG Surfactant

Silver nanoparticle-based crystalline conductive films were synthesized using a simple and environmentally friendly method centered on chemical reduction. A stoichiometric balance of three different molecular weights of polyethylene glycol (PEG) was used as a capping agent. Resistivity, and its correlation with temperature and the particle size of nanoparticle films, was probed. The silver nanoparticles were characterized using thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). Further silver films deposited on a glass substrate were characterized by FESEM, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and resistivity measurements. Particle size distribution and room temperature electrical conductivity were also investigated. The high conductivity of sintered films suggested applications for the ink-jet printing of electronic circuitry on thermally sensitive substrates.

Mechanism and modeling of poly[vinylpyrrolidone] (PVP) facilitated synthesis of silver nanoplates

Silver triangular nanoplates (AgTNP) present unique surface plasmonic and catalytic properties depending upon the thickness and edge length. AgTNP are synthesized in a kinetically controlled growth process, by and large, using the polymer poly-vinylpyrrolidone (PVP) as a reductant. In this work, we present a systematic study to uncover the effect of the molecular weight (MW) of PVP and the PVP to silver salt (AgNO3) molar ratio ([P : S]) on the physical dimensions of AgTNP. The edge length of AgTNP shows a non-monotonic variation with respect to [P : S] for all MWs. Based on several control experiments, a kinetic mechanism is proposed and a mathematical model is developed to explain the formation of AgTNP. The elementary processes of the model include the reduction of Ag+ by the -OH group in PVP, followed by instantaneous nucleation. This phase is then followed by a slow reduction of Ag+ and growth of the nuclei to AgTNP. The model shows a reasonable agreement with experiments on the non-monotonic variation of edge length of AgTNP with respect to [P : S], as well as on the temporal evolution of the edge length.

Seedless synthesis and efficient recyclable catalytic activity of Ag@Fe nanocomposites towards methyl orange

This work demonstrates a competitive reduction method of synthesis of nanomaterials. In this method along cetyltrimethylammonium bromide (CTAB), the reduction of Ag+ and Fe3+ ions is achieved by ascorbic acid-to-bimetallic Ag@Fe yellow-colored nanomaterials. The shape of UV–visible spectra and wavelengths absorbed of Ag@Fe can be tuned from ca. 290–600 nm by controlling [CTAB] and [Ag+]. The apparent first-order rate constants were calculated within the approximation of 6.1 × 10−3 s−1. The as-prepared Ag@Fe NPs have been found to be very important catalyst in terms of depredate methyl orange in vicinity of sodium borohydride (NaBH4), which exhibits excellent efficiency and re-usability in the prototypical reaction. The cmc of cationic surfactant CTAB has been determined by conductivity method under different experimental conditions. In the presence of CTAB, Ag+ and Fe3+ ions reduce to Ag@Fe core/shell nanoparticles, comprehend a change in wavelength and intensity of SRP band. The apparent first-order rate constant, activation energy, and turnover frequency for the methyl orange reduction catalyzed by Ag@Fe NPs were found to be 1.6 × 10−3 s−1, 58.2 kJ mol−1, and 1.1 × 10−3 s−1, respectively.

CTAB-assisted growth of self-supported Zn2GeO4 nanosheet network on a conductive foam as a binder-free electrode for long-life lithium-ion batteries

The Ge-based compounds show great potential as replacements for traditional graphite anode in lithium-ion batteries (LIBs). However, large volume changes and low conductivity of such materials result in a poor electrochemical cycling and rate performance. Herein, we fabricate a self-supported and three-dimensional (3D) sponge-like structure of interlinked Zn₂GeO₄ ultrathin nanosheets anchored vertically on a nickel foam (ZGO NSs@NF) via a simple hydrothermal process assisted by cetyltrimethyl ammonium bromide (CTAB). Such robust self-supported hybrid structures greatly improve the structural tolerance of the active materials and accommodate the volume variation that occurs during repeated electrochemical cycling. As expected, the self-supported ZGO NSs@NF composites demonstrate an excellent lithium storage with a high discharge capacity, a long cycling life, and a good rate capability when used as binder-free anodes for LIBs. A high reversible discharge capacity of 794 mA h g^-1 is maintained after 500 cycles at 200 mA g^-1, corresponding to 81% capacity retention of the second cycle. Further evaluation at a higher current density (2 A g^-1) also delivers a reversible discharge capacity (537 mA h g^-1) for this binder-free anode. This novel 3D structure of the self-supported ultrathin nanosheets on a conductive substrate, with its volume buffer effect and good interfacial contacts, can stimulate the progress of other energy-efficient technologies.

Synthesis of nanobelt-like 1-dimensional silver/nanocarbon hybrid materials for flexible and wearable electroncs

Most synthetic processes of metallic nanostructures were assisted by organic/inorganic or polymeric materials to control their shapes to one-dimension or two-dimension. However, these additives have to be removed after synthesis of metal nanostructures for applications. Here we report a straightforward method for the low-temperature and additive-free synthesis of nanobelt-like silver nanostructures templated by nanocarbon (NC) materials via bio-inspired shape control by introducing supramolecular 2-ureido-4[1H]pyrimidinone (UPy) groups into the NC surface. The growth of the Ag nanobelt structure was found to be induced by these UPy groups through observation of the selective formation of Ag nanobelts on UPy-modified carbon nanotubes and graphene surfaces. The synthesized NC/Ag nanobelt hybrid materials were subsequently used to fabricate the highly conductive fibres (>1000S/cm) that can function as a conformable electrode and highly tolerant strain sensor, as well as a highly conductive and robust paper (>10000S/cm after thermal treatment).

Synthesis of well-defined pentagonally prismatic silver nanoparticles: role of bromide in (100) stabilization and facet preservation

Use of bromide ions for (100) facet formation was demonstrated to produce silver pentagonal prism nanoparticles size and shape selectively.

Symmetry Breaking by Surface Blocking: Synthesis of Bimorphic Silver Nanoparticles, Nanoscale Fishes and Apples

A powerful approach to augment the diversity of well-defined metal nanoparticle (MNP) morphologies, essential for MNP advanced applications, is symmetry breaking combined with seeded growth. Utilizing this approach enabled the formation of bimorphic silver nanoparticles (bi-AgNPs) consisting of two shapes linked by one regrowth point. Bi-AgNPs were formed by using an adsorbing polymer, poly(acrylic acid), PAA, to block the surface of a decahedral AgNP seed and restricting growth of new silver to a single nucleation point. First, we have realized 2-D growth of platelets attached to decahedra producing nanoscale shapes reminiscent of apples, fishes, mushrooms and kites. 1-D bimorphic growth of rods (with chloride) and 3-D bimorphic growth of cubes and bipyramids (with bromide) were achieved by using halides to induce preferential (100) stabilization over (111) of platelets. Furthermore, the universality of the formation of bimorphic nanoparticles was demonstrated by using different seeds. Bi-AgNPs exhibit strong SERS enhancement due to regular cavities at the necks. Overall, the reported approach to symmetry breaking and bimorphic nanoparticle growth offers a powerful methodology for nanoscale shape design.

“Green” gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering

The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs.

Differential role of PVP on the synthesis of plasmonic gold nanostructures and their catalytic and SERS properties

Differential role of PVP modified with halide ions has been meticulously studied for in situ tuning of Au nanoparticle growth utilizing XRD measurements together with FTIR data, thus quantifying their catalysis and SERS applications.

Tailoring Plasmonic Enhanced Upconversion in Single NaYF4:Yb(3+)/Er(3+) Nanocrystals

By using silver nanoplatelets with a widely tunable localized surface plasmon resonance (LSPR), and their corresponding local field enhancement, here we show large manipulation of plasmonic enhanced upconversion in NaYF4:Yb(3+)/Er(3+) nanocrystals at the single particle level. In particular, we show that when the plasmonic resonance of silver nanolplatelets is tuned to 656 nm, matching the emission wavelength, an upconversion enhancement factor ~5 is obtained. However, when the plasmonic resonance is tuned to 980 nm, matching the nanocrystal absorption wavelength, we achieve an enhancement factor of ~22 folds. The precise geometric arrangement between fluorescent nanoparticles and silver nanoplatelets allows us to make, for the first time, a comparative analysis between experimental results and numerical simulations, yielding a quantitative agreement at the single particle level. Such a comparison lays the foundations for a rational design of hybrid metal-fluorescent nanocrystals to harness the upconversion enhancement for biosensing and light harvesting applications.

Thin metal nanostructures: synthesis, properties and applications

Two-dimensional nanomaterials, especially graphene and single- or few-layer transition metal dichalcogenide nanosheets, have attracted great research interest in recent years due to their distinctive physical, chemical and electronic properties as well as their great potentials for a broad range of applications. Recently, great efforts have also been devoted to the controlled synthesis of thin nanostructures of metals, one of the most studied traditional materials, for various applications. In this minireview, we review the recent progress in the synthesis and applications of thin metal nanostructures with a focus on metal nanoplates and nanosheets. First of all, various methods for the synthesis of metal nanoplates and nanosheets are summarized. After a brief introduction of their properties, some applications of metal nanoplates and nanosheets, such as catalysis, surface enhanced Raman scattering (SERS), sensing and near-infrared photothermal therapy are described.

Synthesis, stabilization, growth behavior, and catalytic activity of highly concentrated silver nanoparticles using a multifunctional polymer in an aqueous-phase

Highly concentrated Ag nanoparticles (above 20 g L⁻¹) synthesized by the reaction AgNO₃ with BPEI exhibited long-term stability over more than 40 days.

Thermal synthesis of silver nanoplates revisited: a modified photochemical process

The well-known photochemical and thermal methods for silver nanoplate synthesis have been generally regarded as two parallel processes without strong connections. Here we report a surprising finding that both visible light and ambient O2, which are critically important in the photochemical process, also play determining roles in the thermal synthesis. By designing a series of control experiments, we reveal that the typical thermal synthesis is essentially a modified photochemical synthesis coupled with the unique redox properties of H2O2. Light irradiation and dissolved O2 are found to be essential for initiating the formation of nanoplates, but the continued growth of nanoplates is supported by the oxidative etching and subsequent reduction of Ag due to H2O2. O2 resulting from the catalytic decomposition of H2O2 etches small nanoparticles to produce Ag(+) ions, which are then reduced back to Ag(0) by anions of H2O2 to support the growth of nanoplate seeds. The involvement of H2O2 in the reaction significantly speeds up the nanoplate formation process. These findings not only greatly improve our understanding of the unique functions of H2O2 in the thermal synthesis, but also bridge the two well established synthesis processes with a unified mechanism, and significantly enhance the reproducibility of the thermal synthesis of Ag nanoplates by identifying the critical importance of ambient light and O2.

Synthesis of cellulose nanofibril bound silver nanoprism for surface enhanced Raman scattering

Silver nanoprisms (AgNPs) were robustly synthesized using TEMPO-oxidized cellulose nanofibrils (CNFs) as a dual capping and shape-regulating agent for the first time. Reducing AgNO3 with NaBH4 in CNF suspensions produced smaller but more uniform Ag nanospheres (AgNSs) with increasing Ag(+)/CNF ratios. CNF bound AgNSs were facilely transformed to AgNPs by etching with H2O2, supporting the capping and shape-regulating capability of CNFs. AgNPs could also be synthesized directly in a one-shot reduction reaction with NaBH4 in the presence of both CNFs and H2O2. The AgNPs transformed from CNF bound AgNSs are similar to those synthesized directly, but more stable against H2O2. Successful synthesis of AgNPs with 80-320 nm truncated edges was confirmed by light blue solution color, sharp out-of-plane quadruple resonance peak at 334 nm and prominent in-plane dipole resonance peaks at 762-900 nm. The [111] lattice plane of AgNP was clearly evident by its predominant XRD peak at 38°, confirming the unique shape-regulating ability of the nearly fully surface carboxylated CNFs. The CNF surface bound AgNPs were easily fabricated into freestanding CNF/AgNPs films that showed excellent surface enhanced Raman scattering of Rhodamine 6G with analytical enhancement factor of 5 × 10(3) in contrast to none from the CNF/AgNSs film.

LSPR-dependent SERS performance of silver nanoplates with highly stable and broad tunable LSPRs prepared through an improved seed-mediated strategy

The application of the silver plates as a proper substrate for surface enhanced Raman spectroscopy (SERS) was performed to give deep insight on LSPR-dependent SERS performance. Firstly, an improved seed-mediated method is developed to synthesize silver nanoplates (NP) with broad-tuning localized surface plasmon resonance (LSPR) and high stability. The LSPR peaks could be tuned in the range from 485 to ∼1200 nm by controlling the experimental parameters. With the treatment of sodium dodecyl sulfate (SDS), silver NPs exhibit high stability for SERS tests. The LSPR-dependent SERS study was performed by taking four typical silver NPs with LSPR peaks at 485 nm, 614 nm, 906 nm and 1130 nm as substrates. Also, two probe molecules, 4-amino-thiophenol (4-ATP) and rhodamine-6G (R-6G), were used, and both the 458 nm and 633 nm lasers were selected as excitation for the LSPR-dependent SERS study. Our results indicated that the SERS performance is largely dependent on the LSPR of the silver NP substrate at a given excitation wavelength. Specifically, the Raman signals were greatly enhanced when the laser excitation line matched (close to the LSPR band) the peak position of LSPR band. When at the excitation of 633 nm, two orders of magnitude stronger SERS signals would be observed for the Ag-614 substrate than that of the Ag-485 and Ag-1130 substrates with their LSPR peak positions far away from 633 nm. The same result can also be observed when the laser excitation at 458 nm was selected for the Ag-485 substrate. Our study gives a deep insight into LSPR-dependent SERS performance. It also gives a method for giving large SERS enhancement just by selecting a proper excitation wavelength matched to the LSPR of the substrate.

Amino acid-dependent transformations of citrate-coated silver nanoparticles: impact on morphology, stability and toxicity

Humans face the risk of exposure to silver nanoparticles (AgNPs) due to their extensive application in consumer products. AgNPs can interact with many substances in the human body due to their chemically unstable nature and high activity properties, which might result in unknown hazards and even some serious diseases for humans. As the basic constituent element of human bodies, amino acids (AAs) differ in concentration and variety in different cells and tissues. Thus, understanding the transformation of citrate-coated AgNPs in the presence of AAs is crucial for determining their fate and toxicity in the human body. Our study focused on the transformation of the morphology, dissolution behavior and reaction product of AgNPs in different AA-containing systems and then evaluated the effect of these transformations on the cytotoxicity of AgNPs. The obtained results indicated that the addition of glycine with the lowest Ag(+) binding energy had little effect on the transformations and toxicity of AgNPs. While in the presence of histidine with higher Ag(+) binding energy, the Ag(+) release and particle size of AgNPs obviously increased. These transformations resulted in a decrease in the cytotoxicity of AgNPs due to the formation of Ag-His complex and the growth of AgNPs. Furthermore, l-cysteine with the highest Ag(+) binding energy could easily interact with AgNPs, transforming them completely to form [Ag(Cys)n](+) and Ag2S precipitates, which induced the largest decrease in AgNP toxicity. In summary, our results may provide useful information to understand the fate, transformation, and toxicity of citrate-coated AgNPs in the human body.

One-step growth of triangular silver nanoplates with predictable sizes on a large scale

A one-step growth of triangular silver nanoplates on a large scale is developed by a coordination-based kinetically controlled seeded growth method, with their edge length precisely tuned from 150 nm to 1.5 μm, and surface plasmon resonance extends to full near-infrared.

Raman spectroscopy in the analysis of food and pharmaceutical nanomaterials

Raman scattering is an inelastic phenomenon. Although its cross section is very small, recent advances in electronics, lasers, optics, and nanotechnology have made Raman spectroscopy suitable in many areas of application. The present article reviews the applications of Raman spectroscopy in food and drug analysis and inspection, including those associated with nanomaterials. Brief overviews of basic Raman scattering theory, instrumentation, and statistical data analysis are also given. With the advent of Raman enhancement mechanisms and the progress being made in metal nanomaterials and nanoscale metal surfaces fabrications, surface enhanced Raman scattering spectroscopy has become an extra sensitive method, which is applicable not only for analysis of foods and drugs, but also for intracellular and intercellular imaging. A Raman spectrometer coupled with a fiber optics probe has great potential in applications such as monitoring and quality control in industrial food processing, food safety in agricultural plant production, and convenient inspection of pharmaceutical products, even through different types of packing. A challenge for the routine application of surface enhanced Raman scattering for quantitative analysis is reproducibility. Success in this area can be approached with each or a combination of the following methods: (1) fabrication of nanostructurally regular and uniform substrates; (2) application of statistic data analysis; and (3) isotopic dilution.

Shape and size control of Cu nanoparticles by tailoring the surface morphologies of TiN-coated electrodes for biosensing applications

A method for controlling the shapes and sizes of Cu nanoparticles during electrodeposition has been developed by tailoring the surface morphologies of TiN-coated electrodes. Larger octahedral Cu NPs grew on a granular TiN film; smaller, irregular Cu NPs formed on a pyramidal TiN film. The surface morphology of the TiN film affected the accumulation of Cu(2+) and hexadecyltrimethylammonium (CTA(+)) ions, leading to the different shapes and sizes of the resulting Cu NPs. The significant steric effect of the CTA(+) ions was confirmed when using the film of pyramidal TiN as the electrode in the CTAB-containing electrolyte; it contributed to the growth of the smaller, irregular Cu NPs. The sensitivity of the smaller, irregular Cu NPs in the detection of glucose was better than that of the larger, octahedral Cu NPs because of the former's greater increase in the Cu(2+)-to-Cu(0) ratio.

Rapid synthesis of silver nanoparticles from Fusarium oxysporum by optimizing physicocultural conditions

Synthesis of silver nanoparticles (SNPs) by fungi is emerging as an important branch of nanotechnology due to its ecofriendly, safe, and cost-effective nature. In order to increase the yield of biosynthesized SNPs of desired shape and size, it is necessary to control the cultural and physical parameters during the synthesis. We report optimum synthesis of SNPs on malt extract glucose yeast extract peptone (MGYP) medium at pH 9–11, 40–60°C, and 190.7 Lux and in sun light. The salt concentrations, volume of filtrate and biomass quantity were found to be directly proportional to the yield. The optimized conditions for the stable and rapid synthesis will help in large scale synthesis of monodispersed SNPs. The main aim of the present study was to optimize different media, temperature, pH, light intensity, salt concentration, volume of filtrate, and biomass quantity for the synthesis of SNPs by Fusarium oxysporum.

A facile approach to a silver conductive ink with high performance for macroelectronics

An unusual kind of transparent and high-efficiency organic silver conductive ink (OSC ink) was synthesized with silver acetate as silver carrier, ethanolamine as additive, and different kinds of aldehyde-based materials as reduction agents and was characterized by using a thermogravimetric analyzer, X-ray diffraction, a scanning electron microscope, and a four-point probe. The results show that different reduction agents all have an important influence on the conductive properties of the ink through a series of complex chemical reactions, and especially when formic acid or dimethylformamide was used as the reduction agent and sintered at 120°C for 30 s, the resistivity can be lowered to 6 to 9 μΩ·cm. Furthermore, formula mechanism, conductive properties, temperature, and dynamic fatigue properties were investigated systematically, and the feasibility of the OSC ink was also verified through the preparation of an antenna pattern.