Silver Nanoplates Research Articles

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Simultaneous detection of enrofloxacin and chloramphenicol antibiotics using surface-enhanced Raman spectroscopy combined with triangular silver nanoplates

The emergence of antibiotic residues in the environment and food requires the development of sensitive and selective detection methods for monitoring these contaminants. In fact, many different types of antibiotics will be used simultaneously to prevent diseases in livestock and aquatic animals, causing antibiotic residues in food and the environment. Rapid and accurate simultaneous analysis of multiple antibiotics at low concentrations remains a major challenge in in the field of rapid detection. This study presents a sensitive and selective method for the simultaneous detection of two widely used antibiotics, enrofloxacin and chloramphenicol, by combining surface-enhanced Raman spectroscopy (SERS) with triangular silver nanoplates. Triangular silver nanoplates (TAgNPls) in the form of colloid were simply synthesized by chemical reduction method and then used as an effective SERS substrate, enhancing the Raman signals of the target antibiotics and enabling the detection of these antibiotics at trace levels. It was found that with a SERS substrate assembled from the above TAgNPls, the antibiotics enrofloxacin and chloramphenicol could be detected with detection limits of 2.6 µg/L and 4.3 µg/L, respectively. In addition, this SERS substrate also allows simultaneous detection of the above two antibiotics in one analytical sample with concentrations as low as 10 µg/L for both substances. The proposed method holds promise for addressing concerns related to antibiotic contamination in various environments and food sources, contributing to the advancement of analytical techniques for the trace detection of pharmaceutical residues.

Nanoflower Microreactor Based Versatile Enhancer for Recognition Cofactor-Dependent Enzyme Biocatalysis toward Saxitoxin Detection.

Investigating organic carriers' utilization efficiency and bioactivity within organic-inorganic hybrid nanoflowers is critical to constructing sensitive immunosensors. Nevertheless, the sensitivity of immunosensors is interactively regulated by different classes of biomolecules such as antibodies and enzymes. In this work, we introduced a new alkaline phosphatase-antibody-CaHPO4 hybrid nanoflowers (AAHNFs) microreactor based colorimetric immunoprobe. This system integrates a biometric unit (antibody) with a signal amplification element (enzyme) through the biomineralization process. Specifically, the critical factors affecting antibody recognition activity in the formation mechanism of AAHNFs are investigated. The designed AAHNFs retain antibody recognition ability with enhanced protection for encapsulated proteins against high temperature, organic solvents, and long-term storage, facilitating the selective construction of lock structures against antigens. Additionally, a colorimetric immunosensor based on AAHNFs was developed. After ascorbic acid 2-phosphate hydrolysis by alkaline phosphatase (ALP), the generated ascorbic acid decomposes I2 to I-, inducing the localized surface plasmon resonance in the silver nanoplate, which is effectively tuned through shape conversion to develop the sensor. Further, a 3D-printed portable device is fabricated, integrated with a smartphone sensing platform, and applied to the data of collection and analysis. Notably, the immunosensor exhibits improved analytical performance with a 0.1-6.25 ng·mL-1 detection range and a 0.06 ng·mL-1 detection limit for quantitative saxitoxin (STX) analysis. The average recoveries of STX in real samples ranged from 85.9% to 105.9%. This study presents a more in-depth investigation of the recognition element performance, providing insights for improved antibody performance in practical applications.

Solvothermal Preparation of Crystal Seeds and Anisotropy-Controlled Growth of Silver Nanoplates.

We synthesized silver nanoplates using the solvothermal method and, for the first time, placed them as crystal seeds in a water-based growth solution, thereby successfully achieving the large-scale production of silver nanoplates. The synthesis method enabled independent control of the lateral size and vertical size of the silver nanoplates. More specifically, the lateral size could be adjusted within the range of 565 nm-1.682 μm, while the vertical size was achieved by introducing Cl- as a capping agent and the vertical size was thickened from 18.28 to 40.41 nm.

Uniform monolayer of branched silver nanoplates-assembled nanoparticles for sensitive and reproducible SERS detection of harmful molecules

Surface-enhanced Raman scattering (SERS) technique can offer the fingerprint information of trace substances, and thus has wide potential applications in many fields. There is still a requirement to develop new and effective methods to construct high-performance SERS substrates. Here, a facile electrodeposition method is presented for fabricating large-scale uniform films assembled by branched silver (Ag) nanoplates. The morphology and structure of such film are highly uniform over a large area, which can ensure good spectral uniformity and reproducibility. There are dense sub-10 nm gaps between neighboring Ag nanoplates and between neighboring branches, forming plenty of hot spots. Therefore, the Ag nanoparticle monolayer exhibits high SERS activity along with excellent spectral repeatability. It is found that the limits of detection (LODs) towards rhodamine 6G and 4-aminothiophenol can reach 0.387 pM and 49.0 pM, respectively, showing high sensitivity of the designed SERS substrate. The enhancement factor of the prepared roughened Ag nanoparticle monolayer is computed to be as large as 2.37 × 108. Then, the highly roughened nanoparticle monolayer is used to detect cationic dye and fungicide (methylene blue, MB) and a synthetic cytokinin (6-benzylaminopurine, 6-BAP), and the corresponding LODs are determined down to 1.1 nM and 28.8 pM, respectively. Such LODs are much lower than the tolerance for MB and 6-BAP residues established by some authoritative regulations. Sensitive monitoring of 6-BAP residue on vegetables and fruits can also be achieved using such SERS substrate, indicating its promising application in environment monitoring and food safety supervision.

Encapsulation of silver nanoplates into poly(lactic-co-glycolic) acid nanoparticles and the antibacterial activity against intracellular bacteria

Abstract We encapsulated silver nanoplates (AgNPLs) into poly(lactic-co-glycolic) acid (PLGA) nanoparticles. The encapsulation stabilized the AgNPLs in a physiological environment and the antibacterial activity of the AgNPLs against planktonic bacteria was reduced. However, the PLGA nanoparticles encapsulating the AgNPLs were internalized into macrophages and showed antibacterial activity against intracellular bacteria. AgNPL-loaded PLGA nanoparticles are promising for treating intractable infectious diseases caused by bacteria-infecting macrophages.

Radially polarized light in single particle optical extinction microscopy identifies silver nanoplates

Quantifying the optical extinction cross section of a single plasmonic nanoparticle (NP) has recently emerged as a powerful method to characterize the NP morphometry, i.e., size and shape, with a precision comparable to electron microscopy while using a simple optical microscope. Here, we enhance the capabilities of extinction microscopy by introducing a high numerical aperture annular illumination coupled with a radial polarizer to generate a strong axial polarization component. This enables us to probe the NP response to axial polarized light, and, in turn, to distinguish flat-lying nanoplates from other geometries. Polarization-resolved optical extinction cross sections were acquired on 219 individual colloidal silver NPs of a nominally triangular nanoplate shape but, in practice, exhibiting heterogeneous morphometries, including decahedrons and non-plate spheroids. An unsupervised machine learning cluster analysis algorithm was developed, which allowed us to separate NPs into different groups, owing to the measured differences in cross sections. Comparison of the measurements with a computational model of the absorption and scattering cross section accounting for nanoplates of varying geometries beyond simple triangles provided insight into the NP shape of each group. The results provide a significant improvement of polarization-resolved optical extinction microscopy to reconstruct NP shapes, further boosting the utility of the method as an alternative to electron microscopy analysis.

Guar gum assisted synthesis of high‐quality silver nanoplates and their polyimide matrix nanocomposites for electromagnetic interference shielding applications

AbstractTwo‐dimensional (2D) silver nanoplates are chemically synthesized in the presence of guar gum – a naturally occurring biopolymer. The polymer directs anisotropic growth of silver nuclei into high aspect ratio nanoplates spanning 4500 ± 500 nm lateral length with thickness as small as 40 ± 10 nm. After a thorough investigation of the reaction parameters (temperature, precursor to reductant ratio, and polymer quantity) on the morphology of the product, a scalable synthetic protocol to achieve good yields (95%–98%) of highly pure (~100%) 2D silver nanoplates (AgNPls) in a facile, inexpensive, room temperature, aqueous phase chemical reaction of only about 5 min is devised. The optimized AgNPls induce appreciable conductivity of 5.5 ± 0.38 S/cm in polyimide at only 12 wt% loading. Consequently, the resulting polymer nanocomposite (containing 12 wt% AgNPls), at only 130 ± 15 μm thickness and 0.45 g/cm3 density, effectively blocks electromagnetic radiation in X‐band with a total shield effectiveness of about 10 dB resulting in substantially high specific shielding effectiveness and absolute shielding effectiveness of 22.48 and 1729.23 dB cm3 g−1, respectively. Additionally, the nanocomposites remain thermally stable up to 500°C in oxidative environment and possess an appreciably high storage modulus of 3.113 GPa at 50°C. These low‐density conductive polyimide films, therefore, present great prospects in shielding against electromagnetic interference under extreme conditions.

Rapid and tailorable silver nanoplate (SNP) synthesis for a promising SERS substrate in sulfathiazole detection

Silver nanoplates (SNPs) are particularly appealing for surface-enhanced Raman scattering (SERS) applications due to their localized surface plasmon resonance (LSPR) and the presence of “hot spots” near their tips and edges.

Bi-enzyme assay coupled with silver nanoplate transformation for insecticide detection.

A novel colorimetric method utilizing a bi-enzyme assay using silver nanoplates (AgNPls) as a direct signal source was developed to enable rapid insecticide detection. This innovative system leverages the in situ generated H2O2 from the consecutive enzyme-catalyzed reactions of acetylcholine hydrolysis and choline oxidation to introduce oxidative etching of AgNPls, transforming them into aggregated silver nanospheres (AgNSs). The morphological transformation of silver nanoparticles could be observed with the naked eye due to the solution's color shifts from pink-violet to blue-violet. The presence of insecticide, i.e., dichlorvos (DDVP), could inhibit acetylcholinesterase activity, thereby limiting H2O2 production and affecting the transformation of AgNPls into aggregated AgNSs. Furthermore, the extent of AgNPl-to-aggregated AgNS transformation and the subsequent solution's color change was inversely proportional to the amount of DDVP. Under optimal conditions, the developed bi-enzyme assay enables the quantification of DDVP within 5 minutes, achieving detection limits of 0.5 ppm and 0.1 ppm by naked-eye detection and UV-visible spectrophotometry, respectively. Furthermore, the practical application of this assay was validated for detecting insecticides in real vegetable samples, demonstrating both accuracy and reliability.

Lysozyme-sensitive plasmonic hydrogel nanocomposite for colorimetric dry-eye inflammation biosensing.

Detection of lysozyme levels in ocular fluids is considered crucial for diagnosing and monitoring various health and eye conditions, including dry-eye syndrome. Hydrogel-based nanocomposites have been demonstrated to be one of the most promising platforms for fast and accurate sensing of different biomolecules. In this work, hydrogel, electrospun nanofibers, and plasmonic nanoparticles are combined to fabricate a sensitive and easy-to-use biosensor for lysozyme. Poly(L-lactide-co-caprolactone) (PLCL) nanofibers were covered with silver nanoplates (AgNPls), providing a stable plasmonic platform, where a poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogel layer allows mobility and good integration of the biomolecules. By integrating these components, the platform can also exhibit a colorimetric response to the concentration of lysozyme, allowing for easy and non-invasive monitoring. Quantitative biosensing operates on the principle of localized surface plasmon resonance (LSPR) induced by plasmonic nanoparticles. Chemical, structural, thermal, and optical characterizations were performed on each platform layer, and the platform's ability to detect lysozyme at concentrations relevant to those found in tears of patients with dry-eye syndrome and other related diseases was investigated by colorimetry and UV-Vis spectroscopy. This biosensor's sensitivity and rapid response time, alongside the easy detection by the naked eye, make it a promising tool for early diagnosis and treatment monitoring of eye diseases.

The Effect of Pore Size on the Mechanical Properties of Biaxially Stretched Silver Nanoplates

In this study, we investigate the mechanical properties of silver nanoplates with pores under biaxial stretching using energy, natural strain, and stress as characterization parameters. Furthermore, we analyze the effect of different pore radius ratios on these mechanical properties. Our analysis, using molecular dynamics methods, reveals that shear stress on dislocations leads to the destruction of the silver nanoplates model. We also found that the fracture time of silver nanoplates is affected by the pore radius ratio; models with larger pore radius ratios have smaller shear stresses and are destroyed earlier. Moreover, we observed that dislocation forms at the corners of square silver nanoplates, and as deformation increases, the dislocation gradually approaches the center of the hole. The closer the hole position is to the model boundary, the greater the shear stress will be. Finally, we demonstrate that when the hole is oval, it creates a new asymmetric dislocation line at its tip, which causes differences in mechanical properties.

{111}‐ Faceted Silver Nanoplates: An Automated and Customized Design for Functionality

AbstractSilver nanoparticles (Ag‐NPs) exhibit the highest efficiency of localized surface plasmon resonance (LSPR) excitation that can be tuned to any wave length in the visible spectrum. Its performance depends to a large extent on its physicochemical characteristics such as size and shape; which, in turn, can be modulated by the selective growth of their crystalline facets. We used a simple direct chemical reduction method with a precise manipulation of seed‐mediated growth control through an automated single‐phase continuous flow‐batch system to induce customized geometries on Ag‐NPs. Optimization of the experimental design was carried out from a multivariate analysis, where the height/width ratio of LSPR band was used as response signal. Proposed methodology controls the critical steps in the synthesis of Ag‐NPs that modulate their morphology to attain customized surface plasmon resonance in an interval of 380 nm (spherical‐shaped nanoparticles) to 925 nm ({111}‐ faceted prism‐shaped nanoplates) absorptions, leading to a versatile platform to extend their potential applications. Although the present work focused on silver nanoparticles, we believe that this methodology can be extended to any free‐electron metals.

Role of Plasmonic Antenna in Hot Carrier-Driven Reactions on Bimetallic Nanostructures.

Noble metal nanostructures can efficiently harvest electromagnetic radiation, which, in turn, is used to generate localized surface plasmon resonances. Surface plasmons decay, producing hot carriers, that is, short-lived species that can trigger chemical reactions on metallic surfaces. However, noble metal nanostructures catalyze only a very small number of chemical reactions. This limitation can be overcome by coupling such nanostructures with catalytic-active metals. Although the role of such catalytically active metals in plasmon-driven catalysis is well-understood, the mechanistics of a noble metal antenna in such chemistry remains unclear. In this study, we utilize tip-enhanced Raman spectroscopy, an innovative nanoscale imaging technique, to investigate the rates and yields of plasmon-driven reactions on mono- and bimetallic gold- and silver-based nanostructures. We found that silver nanoplates (AgNPs) demonstrate a significantly higher yield of 4-nitrobenzenehtiol to p,p'-dimercaptoazobisbenzene (DMAB) reduction than gold nanoplates (AuNPs). We also observed substantially greater yields of DMAB on silver-platinum and silver-palladium nanoplates (Ag@PtNPs and Ag@PdNPs) compared to their gold analogues, Au@PtNPs and Au@PdNPs. Furthermore, Ag@PtNPs exhibited enhanced reactivity in 4-mercatophenylmethanol to 4-mercaptobenzoic acid oxidation compared to Au@PtNPs. These results showed that silver-based bimetallic nanostructures feature much greater reactivity compared to their gold-based analogues.

Limits of antibacterial activity of triangular silver nanoplates and photothermal enhancement thereof for Bacillus subtilis

Currently, nanoparticles are being actively explored for antimicrobial applications involving variety of pathogens. Bacillus subtilis is a major concern considering its sporulation and biofilm formation capability which involves high bacteria loadings. Also, there is natural ability of B subtilis to adapt and develop resistance to the silver nanoparticles alone. So, this study reports the limits of antibacterial activity of triangular silver nanoplates (∆AgNPs) and further photothermal enhancement for B. subtilis ATCC 6051 for considerably high bacterial load of 2.5 × 107 to 5 × 108 CFU/ml.Triangular silver nanoplates were synthesized using one pot synthesis method and showed significant photothermal response i.e., ∼36 °C temperature rise on near infrared irradiation as well as photothermal stability. Triangular silver nanoplates alone showed absolute destruction for 2.5 × 107 CFU/ml initial B. subtilis load in 5 min. Whereas, for further higher bacterial loads, the antibacterial efficacy of ∆AgNPs is observed to be insignificant. For higher initial bacterial loads of 5 × 107 CFU/ml and 5 × 108 CFU/ml, photothermally enhanced triangular silver nanoplates resulted in complete destruction of bacteria in about 5 and 10 min, respectively. Antibacterial efficacy and mechanism of the destruction assessed via scanning electron microscopy and LIVE/DEAD assay confirmed morphological deformities. Further the generation of higher levels of reactive oxygen species is also confirmed due to photothermal activation of ∆AgNPs. The study concludes that ∆AgNPs alone are effective only up to bacterial load of 2.5 × 107 CFU/ml. Whereas, for higher bacterial loads of B. subtilis, photothermally activated ∆AgNPs lead to irreversible damage due to multiple targeting mechanisms leading to absolute elimination in short span of 5–10 min for the chosen irradiation conditions.Ultimately, this study demonstrates photothermally enhanced silver nanoplates as a potential antimicrobial agent for considerably high bacterial loads of B. subtilis. Overall, the broader window of considered high bacterial loadings and its irradiation by this technique shows the full-proof nature of photothermal applications for scenarios involving high cell density such as biofilms and wound infections etc. Further, the concept may be useful for sterilization or decontamination of samples, devices, etc. because B. subtilis and its spores are the challenges during sterilization.

3D Printing Assisted‐Fabrication of Low‐Temperature Strain Sensors with Large Working Range and Outstanding Stability

Recently, low‐temperature wearable strain sensors, referring to those working at sub‐zero temperatures, are attracting increasing attentions. However, the fabrication of low‐temperature strain sensors with large working ranges, high sensitivity, and good stability remains a major challenge. In this study, a novel low‐temperature wearable strain sensor is fabricated by depositing the silver nanoplates (Ag NPs)/carbon nanotubes (CNTs) composite onto a cured silicone (DS) substrate that is constructed by using a 3D printing technology. The synergistic effect of the Ag NPs with positive temperature coefficient of resistance (TCR) and the CNTs with negative TCR enable the Ag NPs/CNTs/DS strain sensor's TCR value (−1.16 × 10−5 K−1) to approach zero. The Ag NPs/CNTs/DS strain sensor demonstrates a high gauge factor over a large working range (0–100%) and fast response and recovery rates. Simultaneously, the Ag NPs/CNTs/DS strain sensor displays outstanding reproducibility and long‐term stability at −40 °C as well as excellent temperature cycling resistance under cyclic temperature of −40 to 60 °C. The Ag NPs/CNTs/DS strain sensor is further validated by incorporating into a wireless sensing system for remotely monitoring various human activities at −40 °C. This work provides wearable strain sensors for monitoring human‐machine interaction under low‐temperature condition.

Comparative Study on Thermal and Laser Sintering of Silver Nanocubes and Silver Nanoplates

Compared with silver nanowires and silver nanospheres, silver nanocubes and silver nanoplates with larger curvature structures like sharp vertices and edges have great potential in optical applications. In general, the controllable joining of silver nanomaterials has become an effective way to change the electrical and optical properties of silver nanomaterials in recent years. However, urgent research on the controllable joining of silver nanocubes or silver nanocubes is still rarely reported. After being thermal treated at 250 °C for 8 min, a good joining among silver nanocubes can be obtained without significant damage to the cubic structure. For laser sintering, with the increase of laser energy input, silver nanocubes gradually transform to spherical particles. Joining among few particles can be observed when silver nanocubes are scanned by 5 W of laser at 1.0 mm s−1. Obvious joining among silver nanocubes can be obtained by thermal treating at 300 °C for 5 min and laser scanning at 7 W at 0.2 mm s−1. Thermal heating is more suitable for forming different degrees of connection between silver nanocubes or between silver nanocubes, while laser treatment is suitable for changing the shape of silver nanocubes or silver nanocubes without obvious connection.

Effects of Synthesized Silver Nanoplate Structures on the Electrochemical Reduction of CO2

Using a tunable electroless nanoplating reaction, different silver structures including two nanoplate-based structures were synthesized, characterized and tested as catalysts to improve the electrochemical reduction of CO2 towards CO. Relative to a planar polycrystalline silver surface, the faradaic efficiency to CO was significantly improved, from 7% to 67% at −0.6 V vs RHE and from 51% to 97% at −1.0 V vs RHE, decreasing the parasitic evolution of hydrogen and formate. By comparing the catalytic performance of three intensively characterized silver structure types, namely high aspect ratio nanoplates, particulate nanoplate clusters, and interconnected grain-like particles, in-depth insights into various effects that influence the observed reactions are presented. In particular, at low potentials and high current densities, the catalytic performance is more related to the electrochemical surface area and local transport effects. The obtained results demonstrate the relevance of structural control in electrocatalysts and the special effects of nanoplate structures. Thus, our findings provide a useful groundwork for the practical design of electrocatalysts for CO2 reduction.

Triangular silver nanoplates-BiVO4 composite for the photocatalytic CO2 reduction under irradiating LED light source

In this study, triangular silver nanoplates (TagNPts)/BiVO4 nanomaterials were prepared by hydrothermal method and are used as a photocatalyst in a photoreaction system to convert carbon dioxide into methane and carbon monoxide. The as prepared material was characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and ultraviolet–visible spectrometer (UV–vis). The absorbance increases in the visible light region due to the incorporation of nano-silver (triangular plate) metal and pulls electrons, reduces the recombination rate of electron-hole pairs, and improves the photoreduction activity. The transmittance ratio is measured and the specific wavelengths of blue LED 412–505 nm and green LED 427–622 nm are measured. It shows that the irradiation of targeted wavelength bands will increase the absorbance and effectively reduces the recombination of electron-hole pairs. The best performance in this study was achieved after irradiating blue light source with 0.9% TAgNPts/BiVO4. The cumulative production of photoreduced carbon monoxide is 30.11 μmol g−1 and the quantum yield is 0.07%. After a green light source, the cumulative carbon monoxide yield using 0.9 wt% TAgNPts/BiVO4 is 24.77 μmol g− and the quantum yield is 0.06%.

Shape Dependence of Silver-Nanoparticle-Mediated Synthesis of Gold Nanoclusters with Small Molecules as Capping Ligands.

In this study, differently shaped silver nanoparticles used for the synthesis of gold nanoclusters with small capping ligands were demonstrated. Silver nanoparticles provide a reaction platform that plays dual roles in the formation of Au NCs. One is to reduce gold ions and the other is to attract capping ligands to the surface of nanoparticles. The binding of capping ligands to the AgNP surface creates a restricted space on the surface while gold ions are being reduced by the particles. Four different shapes of AgNPs were prepared and used to examine whether or not this approach is dependent on the morphology of AgNPs. Quasi-spherical AgNPs and silver nanoplates showed excellent results when they were used to synthesize Au NCs. Spherical AgNPs and triangular nanoplates exhibited limited synthesis of Au NCs. TEM images demonstrated that Au NCs were transiently assembled on the surface of silver nanoparticles in the method. The formation of Au NCs was observed on the whole surface of the QS-AgNPs if the synthesis of Au NCs was mediated by QS-AgNPs. In contrast, formation of Au NCs was only observed on the edges and corners of AgNPts if the synthesis of Au NCs was mediated by AgNPts. All of the synthesized Au NCs emitted bright red fluorescence under UV-box irradiation. The synthesized Au NCs displayed similar fluorescent properties, including quantum yields and excitation and emission wavelengths.