Silver Nanoshells Research Articles

Simple and sensitive galactose monitoring based on capillary SERS sensor.

Galactosemia, a severe genetic metabolic disorder, results from the absence of galactose-degrading enzymes, leading to harmful galactose accumulation. In this study, we introduce a novel capillary-based surface-enhanced Raman spectroscopy (SERS) sensor for convenient and sensitive galactose detection. The developed sensor enhances SERS signals by introducing gold nanoparticles (Au NPs) onto the surface of silver nanoshells (Ag NSs) within a capillary, creating Ag NSs with Au NPs as satellites. Utilizing 4-mercaptophenylboronic acid (4-MPBA) as a Raman reporter molecule, the detection method relies on the conversion of 4-MPBA to 4-mercaptophenol (4-MPhOH) driven by hydrogen peroxide (H2O2) generated during galactose oxidation by galactose oxidase (GOx). A new SERS signal was observed, which was generated by H2O2 produced when galactose and GOx reacted. Our strategy yielded a quantitative change in the SERS signal, specifically in the band intensity ratio of 998 to 1076 cm-1 (I998/I1076) as the galactose concentration increased. Our capillary-based SERS biosensor provides a promising platform for early galactosemia diagnosis.

Seedless and electroless plating of silver on silica particles by using microreactor

Synthesis of silver nanoshells is still a challenge especially in the absence of surface modification of core particles and/or metal seed decoration on core surfaces. In this study, we applied a microrector to seedless and electroless plating of silver on bare silica particles, and investigated the effects of reaction temperatures and silver ion concentrations on the morphology and surface coverage of silver on the core particle surface. Our experiments demonstrated that the use of the microreactor enabled the one-step direct deposition of silver with a morphology close to complete shells and that silver ion concentrations from 0.2 to 0.5 mM at a moderate temperature of 50 °C produced high coverage and yield. Besides, the mixing sequence of NH3 and HCHO in the synthesis procedure was found to be a key factor to achieve the high silver coverage. In addition, we demonstrated that the addition of polyvinylpyrrolidone (PVP) after the silver shell growth reaction increases the stability without decreasing the reaction rate.

Fast Label-Free Metabolic Profile Recognition Identifies Phenylketonuria and Subtypes.

Phenylketonuria (PKU) is the most common inherited metabolic disease in humans. Clinical screening of newborn heel blood samples for PKU is costly and time-consuming because it requires multiple procedures, like isotope labeling and derivatization, and PKU subtype identification requires an additional urine sample. Delayed diagnosis of PKU, or subtype identification can result in mental disability. Here, plasmonic silver nanoshells are used for laser desorption/ionization mass spectrometry (MS) detection of PKU with label-free assay by recognizing metabolic profile in dried blood spot (DBS) samples. A total of 1100 subjects are recruited and each DBS sample can be processed in seconds. This platform achieves PKU screening with a sensitivity of 0.985 and specificity of 0.995, which is comparable to existing clinical liquid chromatography MS (LC-MS) methods. This method can process 360 samples per hour, compared with the LC-MS method which processes only 30 samples per hour. Moreover, this assay enables precise identification of PKU subtypes without the need for a urine sample. It is demonstrated that this platform enables high-performance and fast, low-cost PKU screening and subtype identification. This approach might be suitable for the detection of other clinically relevant biomarkers in blood or other clinical samples.

Strong-field effects in the photo-induced dissociation of the hydrogen molecule on a silver nanoshell.

Plasmonic catalysis is a rapidly growing field of research, both from experimental and computational perspectives. Experimental observations demonstrate an enhanced dissociation rate for molecules in the presence of plasmonic nanoparticles under low-intensity visible light. The hot-carrier transfer from the nanoparticle to the molecule is often claimed as the mechanism for dissociation. However, the charge transfer time scale is on the order of a few femtoseconds and cannot be resolved experimentally. In this situation, ab initio non-adiabatic calculations can provide a solution. Such simulations, however, have their own limitations related to the computational cost. To accelerate plasmonic catalysis simulations, many researchers resort to applying high-intensity external fields to nanoparticle-molecule systems. Here, we show why such an approach can be problematic and emphasize the importance of considering strong-field effects when interpreting the results of time-dependent density functional theory simulations of plasmonic catalysis. By studying the hydrogen molecule dissociation on the surface of a silver nanoshell and analyzing the electron transfer at different field frequencies and high intensities, we demonstrate that the molecule dissociates due to multiphoton absorption and subsequent ionization.

No-Stirring Synthesis of sub-50 nm Hollow Silver Nanoshells with Dimethylglyoxime-Induced Plasmons in Visible and Second NIR Windows for Biomedical Applications

No-Stirring Synthesis of sub-50 nm Hollow Silver Nanoshells with Dimethylglyoxime-Induced Plasmons in Visible and Second NIR Windows for Biomedical Applications

Dual-Function Meta-Grating Based on Tunable Fano Resonance for Reflective Filter and Sensor Applications.

Localized surface plasmon resonance (LSPR)-based sensors exhibit enormous potential in the areas of medical diagnosis, food safety regulation and environmental monitoring. However, the broadband spectral lineshape of LSPR hampers the observation of wavelength shifts in sensing processes, thus preventing its widespread applications in sensors. Here, we describe an improved plasmonic sensor based on Fano resonances between LSPR and the Rayleigh anomaly (RA) in a metal-insulator-metal (MIM) meta-grating, which is composed of silver nanoshell array, an isolation grating mask and a continuous gold film. The MIM configuration offers more freedom to control the optical properties of LSPR, RA and the Fano resonance between them. Strong couplings between LSPR and RA formed a series of narrowband reflection peaks (with a linewidth of ~20 nm in full width at half maximum (FWHM) and a reflectivity nearing 100%) within an LSPR-based broadband extinction window in the experiment, making the meta-grating promising for applications of high-efficiency reflective filters. A Fano resonance that is well optimized between LSPR and RA by carefully adjusting the angles of incident light can switch such a nano-device to an improved biological/chemical sensor with a figure of merit (FOM) larger than 57 and capability of detecting the local refractive index changes caused by the bonding of target molecules on the surface of the nano-device. The figure of merit of the hybrid sensor in the detection of target molecules is 6 and 15 times higher than that of the simple RA- and LSPR-based sensors, respectively.

Selecting plasmonic nanoshells for colorimetric sensors

In this work, the use of gold and silver nanoshells was evaluated as a starting point for the establishment of colorimetric sensor platforms. The sensitivity and linearity of the nanoplatforms (SiO2 core–metallic shell nanoparticles) were assessed under the influence of the nanoshell configuration, color space, and light source illuminant. A computational procedure for selecting high-performance plasmonic colorimetric sensor platforms is described. The evaluation methodology involves considering five different color spaces and 15 different color components. By exploring crucial figures of merit for sensing, the performance of the plasmonic nanoplatforms was evaluated, exploring Mie theory. We determined that gold nanoshells are highly efficient on colorimetric sensing, while silver nanoshells are a better choice for spectroscopic sensors. Plasmonic nanoplatforms based on nanoshells with 10 nm SiO2 core radii and 5 nm thick Au shells presented sensitivity values up to 4.70RIU−1, considering the hue angle of the HSV color space. Color variation of up to 40% was observed, due to the adsorption of a 10 nm thick molecular layer on the gold nanoshell surface. In the search for advances in colorimetric biosensors, the optimization approach used in this work can be extended to different nanostructures.

Silver Nanoshells with Optimized Infrared Optical Response: Synthesis for Thin-Shell Formation, and Optical/Thermal Properties after Embedding in Polymeric Films.

We describe a new approach to making ultrathin Ag nanoshells with a higher level of extinction in the infrared than in the visible. The combination of near-infrared active ultrathin nanoshells with their isotropic optical properties is of interest for energy-saving applications. For such applications, the morphology must be precisely controlled, since the optical response is sensitive to nanometer-scale variations. To achieve this precision, we use a multi-step, reproducible, colloidal chemical synthesis. It includes the reduction of Tollens' reactant onto Sn2+-sensitized silica particles, followed by silver-nitrate reduction by formaldehyde and ammonia. The smooth shells are about 10 nm thick, on average, and have different morphologies: continuous, percolated, and patchy, depending on the quantity of the silver nitrate used. The shell-formation mechanism, studied by optical spectroscopy and high-resolution microscopy, seems to consist of two steps: the formation of very thin and flat patches, followed by their guided regrowth around the silica particle, which is favored by a high reaction rate. The optical and thermal properties of the core-shell particles, embedded in a transparent poly(vinylpyrrolidone) film on a glass substrate, were also investigated. We found that the Ag-nanoshell films can convert 30% of the power of incident near-infrared light into heat, making them very suitable in window glazing for radiative screening from solar light.

Plasmon Resonances in a Convex–Concave Silver Nanoshell

Plasmon Resonances in a Convex–Concave Silver Nanoshell

A wide-range pH indicator based on colorimetric patterns of gold@silver nanorods

The potential of hydrogen (pH) is a basic and critical parameter representing the function of numerous chemicals/biomolecules. Due to the widespread applications of pH in diverse fields, the development of rapid and simple yet reliable probes for the determination of pH has attracted significant interest. In this paper, by using AuNRs, silver ions, and ascorbic acid as colorimetric pH sensor, a multicolorimetric nanosensor is described for pH measurement. The reduction of silver ions by ascorbic acid which is strongly influenced by pH, results in silver nanoshell deposition on the surface of AuNRs. Consequently, the formation of Au@Ag core-shell NRs causes a series of blue shifts in the longitudinal peaks of AuNRs and elegant color changes according to pH values ranging from 2.0 to 12.0. As a result of spectral shifting, distinct color variations were observed from brownish pink/light green color (acidic media) to dark green/blue color (neutral media) and eventually purple/brown color (basic media). Furthermore, a paper-based analytical device (PAD) was introduced for on-site pH screening. The pH-sensitive PAD was simply fabricated by immobilizing AuNRs on the surface of filter paper. Finally, the developed plasmonic probe was validated to be capable of accurate pH monitoring in urine, spoiled meat, drinking water, and seawater samples.

Etched-spiky Au@Ag plasmonic-superstructure monolayer films for triple amplification of surface-enhanced Raman scattering signals.

Generally, a high quality surface-enhanced Raman spectroscopy (SERS) substrate often requires a highly-tailorable electromagnetic (EM) field generated at nanoparticle (NP) surfaces by the regulation of the morphologies, components and roughness of NPs. However, most recent universal approaches are restricted to single components, and integrating these key factors into one system to achieve the theoretically maximum signal amplification is still challenging. Herein, we design a triple SERS signal amplification platform by the coordination of spiky Au NPs with rich-tip nanostructures, controllable silver nanoshell, as well as tailorable surface roughness into one nano-system. As a result, the theoretical electromagnetic field of the interfacial self-assembled 2D substrate can be improved by nearly 5 orders of magnitude, and the ideal tracing capability for the model SERS molecule can be achieved at levels of 5 × 10-11 M. Finally, diverse analytes in pesticide residues, environmental pollutants as well as medically diagnose down to 10-11 M and can be fingerprinted by the proposed SERS nano-platform. Our integrated triple amplification platform not only provides an effective SERS sensing strategy, but also makes it possible to simultaneously achieve high sensitivity, stability as well as universality into one plasmonic-based SERS sensing system.

Incorporating silver nanoshell-coated mesoporous silica nanoparticles improves physicochemical and antimicrobial properties of chitosan films

Tailoring nanomaterials with tunable properties is of great importance to develop multifunctional candidates in the biomedical field. In the present study, we aimed to develop a promising nano-hybrid system composed of chitosan (CS) and mesoporous silica nanoparticles with a silver nanoshell coat (CS-AgMSNs).The physicochemical properties of CS-AgMSNs films were characterized using various techniques. Further, the mechanical properties of CS-AgMSNs were evaluated and compared with those of undoped CS film. Moreover, the antimicrobial activities of CS-AgMSNs (with different concentrations) were assessed against E-coli, S. aureus, C. albicans, and A. niger.Our results demonstrated that increasing the concentrations of doped AgMSNs (10 to 40 mg) in CS films lowered their transparency and blocked light transmission effectively. The measured elastic modulus of CS-AgMSNs films (20 and 30 mg) showed a decrease in the stiffness of CS films. Also, the elongation at break for CS-AgMSNs (40 mg) indicated a better flexibility. CS-AgMSNs films (10–40 mg) showed an enhanced antimicrobial activity in a concentration-dependent manner compared to undoped CS films.Collectively, the results suggest that our nano-hybrid CS-AgMSNs matrix has unique and promising properties, and holds potential for use in the biomedical field, food packaging, and textile industry.

Enhancing Solar Water Splitting of Textured BiVO4 by Dual Effect of a Plasmonic Silver Nanoshell: Plasmon-Induced Light Absorption and Enhanced Hole Transport

Herein, we demonstrate high-efficiency photoelectrochemical (PEC) water oxidation by combining a textured BiVO4 (t-BVO) photoanode with double-deck structured SiO2@Ag nanoparticles (NPs) with a Ag ...

Facile Tuning and Refractive Index Sensitivity of Localized Surface Plasmon Resonance Inflection Points in Hollow Silver Nanoshells

Hollow metal nanostructures are fascinating because of their unique and surrounding environment-sensitive localized surface plasmon resonances (LSPRs). Herein, we have investigated the hollow silver nanoshell (HSN) sensitivity of different inner core radii and shell thicknesses with respect to change in surrounding medium refractive index. Also, we have shown that the extinction peak of HSNs can be fine-tuned in the visible region as well as biological windows by manipulating the size parameters. Moreover, an enhancement in refractive index sensitivity of 133 to 283 nm/RIU can be achieved in the biological windows by thick hollow silver nanoshells in comparison to thin ones. To achieve a comprehensive study, the sensitivity of homogeneous LSPR extinction inflection points with change in refractive index is also investigated. A consistent improvement in bulk refractive index sensitivity of 36% and 15% is predicted with thick and thin shell layers, respectively. Finally, thick HSNs showed higher refractive index sensitivity when compared with thin ones. Moreover, we envision the idea of more than one molecule detection by tracking the curvature changes. Therefore, we provide a deeper insight into the refractive index sensitivity of homogeneous LSPR inflection points for their use in LSPR-based sensors.

Hybridization of plasmon modes in multishell bimetallic nanoparticles: a numerical study

We study the near-infrared properties of spherical multishell nanoparticles comprising a loss-less dielectric core enclosed by a concentric layering of metallic–dielectric–metallic nanoshells. The coupling between the metallic shells induces plasmon resonance redshifts and peak splitting in the absorption spectra of the layered particle relative those of the metallic constituents. We use full-wave electromagnetic analysis to investigate changes in the absorption spectra as a function of key parameters including the material properties of the inner and outer metallic shells and the aspect ratio of their inner and outer radii. We systematically vary the aspect ratios and quantify the degree of plasmonic coupling between the metallic nanoshells. Our analysis reveals conditions under which the spectral resonance peaks blueshift and/or redshift. We consider bimetallic particles with gold and silver nanoshells and determine the dependency of plasmon resonance peak shifting and splitting as a function of the order of these material layers, i.e., as inner or outer shells.

Antimony- and Zinc-Doped Tin Oxide Shells Coated on Gold Nanoparticles and Gold–Silver Nanoshells Having Tunable Extinctions for Sensing and Photonic Applications

This paper reports the synthesis and study of doped metal oxides as the shell in core-shell nanoparticle architectures. Specifically, the manuscript describes the synthesis of gold nanoparticles (A...

Dual Enzyme-Induced Au-Ag Alloy Nanorods as Colorful Chromogenic Substrates for Sensitive Detection of Staphylococcus aureus.

Herein, we report a colorful colorimetric method for semiquantitative visual identification of Staphylococcus aureus (S. aureus) based on dual enzyme-induced gold-silver (Au-Ag) alloy nanorods (NRs). Alkaline phosphatase-oligonucleotide-functionalized magnetic beads (MBs-DNA-ALP) were designed as probes to monitor the concentration of S. aureus. When S. aureus was present, a naturally secreted nuclease, micrococcal nuclease, cut the AT-rich DNA sequences of MBs-DNA-ALP into fragments, resulting in the release of alkaline phosphatase (ALP). After magnetic separation, ALP induced the generation of a silver nanoshell coating on gold nanorods. The obtained Au-Ag alloy NRs caused a significant shift of the localized surface plasmon resonance peak, resulting in detection solutions of rainbow-like colors. Through naked eye observation, approximately 25 CFU/mL S. aureus could be easily detected. Additionally, quantification studies using samples spiked with S. aureus exhibited satisfactory recovery rates. The good performance of the colorful colorimetric method highlighted the effectiveness and applicability of the determination of S. aureus contamination in low-resource circumstances.

Complementary Dark and Bright Plasmonic Nanocavities with Controllable Energy Exchange for SERS Sensing

AbstractA 3D nanocavity array with each unit composed of complementarily arranged downward and upward silver nanoshells is reported. Due to the underneath planar gold film, the two differently oriented nanoshells form alternatively closed and semi‐closed nanocavities, respectively, which support dark and bright resonance modes of localized surface plasmons (LSPs). For the symmetric design of such nanocavities, mutually independent multipolar LSPs are directly excited at normal incidence, so that the near‐field coupling between them is inhibited. However, when the geometrical symmetry is broken by introducing a breach on a common sidewall of the two adjacent nanocavities, strong interaction and consequently energy exchange between them become allowed. As a result, Fano coupling between the dark and bright LSPs is clearly observed as a sharp spectroscopic resonance. The most important feature of such a coupled dark‐ and bright‐plasmon system is that the resonance modes of two different LSPs can be tuned separately, enhancing largely the flexibility of the photophysical performance and controllability. In particular, these features enable promising applications of such structures in single‐molecular detection through fluorescence enhancement, surface enhanced Raman scattering (SERS), and surface plasmon lasers. SERS measurements verify excellent performance of such nanocavity arrays in high‐sensitivity detection of low‐concentration molecules.

Preparation and characterization of silver mesoporous silica nanoshells with promising antibacterial activity

Silver nanoparticles are highly efficient antibacterial agents. The applications of silver nanoparticles in the biological environment are always obstructed by oxidation that causes aggregation of nanoparticles which lowers its antibacterial activity. In this research, silver nanoparticles were coated on the surface of mesoporous silica forming mesoporous silver nanoshells (Ag@MSNs). The prepared nanoparticles were characterized by their zeta potential, particle size, UV absorption spectroscopy, and transmission electron microscopy. Additionally, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were also performed. The antimicrobial activity of the prepared Ag@MSNs was evaluated against gram-positive and gram-negative pathogens. The results showed that Ag@MSNs are monodispersed with an average size distribution 272 ± 61 nm. Ag@MSNs are highly stable with zeta potential value of 43.3 ± 6.5 mV and an absorption peak at 235 nm. Small-angle X-ray diffraction demonstrated a narrow and strong peak at 2ϴ = 1.71ο indicating that the Ag@MSNs have an ordered porous structure. Surface coating of mesoporous silica nanoparticles with silver shells increased the contact surface area with the bacterial membrane. Thus, Ag@MSNs significantly inhibited the growth of Staphylococcus aureus and E-coli. In conclusion the present study gives new insights into the synthesis of antimicrobial nano-formulation that can offer a variety of uses in industry and biomedical applications.

Gain-Assisted Optomechanical Position Locking of Metal/Dielectric Nanoshells in Optical Potentials

We investigate gain-assisted optical forces on dye-enriched silver nanoshell in the quasi-static limit. We demonstrate the onset of nonlinear optical trapping of these resonant nanostructures in a ...