Ag Nanoprisms Research Articles

Colorimetric sensing of barium ion in water based on polyelectrolyte-induced chemical etching of silver nanoprisms

Because water contamination by barium ion (Ba2+) is still common, the ability to detect Ba2+ in aqueous media is important. However, the development of an easy-to-use and point-of-care sensing method for detecting Ba2+ in aqueous media has proven challenging. In the present study, a colorimetric sensing platform for detecting Ba2+ in an aqueous medium was developed. The platform stands on the basis of the localized surface plasmon resonance (LSPR) properties of Ag nanoprisms, where a strong polyelectrolyte, poly(styrene-4-sulfonate) (PSS), is used as a powerful chemical etchant for the nanoprisms. Upon the addition of PSS to a solution of the Ag nanoprisms, the sharp tips of the Ag nanoprisms were immediately etched and the nanoprisms spontaneously transformed into spheroidal nanostructures, giving rise to dramatic changes in their LSPR properties. The chemical etching reaction of Ag nanoprisms exposed to PSS was retarded in the presence of Ba2+, which enabled the design of a new chemical sensing platform for the sensitive and selective detection of Ba2+ in aqueous media. The proposed Ba2+ sensing platform using highly anisotropic Ag nanostructures and a polyelectrolyte etchant offers numerous advantages over existing platforms, including naked-eye recognition and safe use and handling; hence, the developed platform can be used at the point of care.

Synthesis of Ag Nanoprisms with Precisely-tuned Localized Surface Plasmon Wavelengths by Sequential Irradiation of Light of Two Different Wavelengths

Synthesis of anisotropic Ag nanoprisms (AgPRs) contributes to the development of high performance plasmonic devices. The localized surface plasmon resonance wavelength of AgPRs was successfully tun...

Plasmonic Effects on the Growth of Ag Nanocrystals in Solution.

The light-stimulated transformation of ensembles of spherical nanoparticles into anisotropic metal nanostructures mediated by localized surface plasmon resonance (LSPR) excitation is an elegant way of synthesizing triangular silver nanoprisms with extraordinary control over size and shape. Generally, the transformation occurs in oxidizing environments along a pathway that involves the oxidative etching of small preexisting Ag seeds, followed by plasmon-mediated reduction of the resulting Ag ions and Ag0 incorporation into the anisotropic nanocrystals. Here, we investigate pathways toward Ag nanoprisms from initially homogeneous AgNO3 solutions held under reducing conditions. Observations using in situ electron microscopy show that reducing environments and high Ag precursor concentrations in the presence of sodium citrate favor two alternative transformation routes of initial spherical nuclei into anisotropic nanoprisms: (i) the aggregation of spherical nanoparticles and plasmon-mediated conversion of small clusters into triangular prisms; (ii) shape fluctuations of individual small nanoparticles. Simulated field distributions confirm that the coupling of the LSPR excitation between closely spaced nanoparticles causes significant field enhancements near the local plasmonic hot spots, which facilitates accelerated Ag incorporation and thus supports the transformation into nanoprisms.

Dimers of triangular Ag nanoprisms: computer simulation of optical properties

In this paper the properties of a nanostructure comprised of a pair of distorted triangular Ag nanoparticles are studied using computer simulation. It is shown that upon excitation of localized surface plasmon resonance the electromagnetic field enhancement can reach the value | E | / | E0 | = 48.

Plasmon-enhanced exciton emissions and Raman scattering of CVD-grown monolayer WS2 on Ag nanoprism arrays

Monolayer transition metal dichalcogenides (TMDs) usually have weak optical emission due to the poor light absorption as being atomically thin. Enhancing their optical properties by surface plasmon resonance is attractive for applying atomically thin TMDs in optoelectronic and photonic devices. Here, Ag/WS2 hybrid structure was fabricated by transferring monolayer WS2 grown via chemical vapor deposition (CVD) onto optimized periodic Ag nanoprism array with well-matched resonance by controlling the mask geometry and etching time of polystyrene (PS) nanospheres. Significant enhanced photoluminescence (PL) emission and Raman scattering were successfully achieved. Especially, the higher enhancement is realized for neutral excitons of monolayer WS2. Theoretical calculations reveal that the plasmonic enhancement mainly results from the highly enhanced local electric field and the charge transfer. This work explores the feasibility of exciton emission and Raman scattering enhancement for TMDs with plasmonic nanostructures fabricated by low-cost and easily-manipulated nanosphere lithography (NSL), which paves a way towards the applications of plasmon-enhanced TMD sensors, emitters, and photodetectors.

Particle‐in‐a‐Frame Nanostructures with Interior Nanogaps

AbstractDesigning plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle‐in‐a‐frame nanostructures with well‐defined sub‐2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface‐enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.

Particle-in-a-Frame Nanostructures with Interior Nanogaps.

Designing plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle-in-a-frame nanostructures with well-defined sub-2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface-enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.

Metal ions regulated Ag NPRs etching colorimetric sensor array for discrimination of Chinese Baijiu

One quick and exact Baijiu identification is meaningful in production and market management. Herein, we report a metal ions regulated Baijiu colorimetric sensor array. This is the first time metal ions used to regulate etching microenvironment of Ag nanoprism (Ag NPRs) in Baijiu discrimination sensor array. Edges of Ag NPRs are easier to be etched than other regions, in which morphology transition from nanoprism to nanodisk. The addition of different metal ions lead to the change of the Ag NPRs etching microenvironment in Baijiu forming different etching morphologies with dazzling colors. Transmission electron microscope with energy spectrum analysis (TEM-ESA) were employed to exhibits general process. RGB (the red, green and blue color model) values of final Ag NPRs were captured as the optical single for the further data processes. Pattern recognition and neural network simulation shows the outstanding discrimination ability of provided array for 16 Baijiu samples. Furthermore, selectivity experiments, which are not available in other paper, shows that our arrays have considerable selectivity and have great potential in practical detection.

Synthesis of uniform hexagonal Ag nanoprisms with controlled thickness and tunable surface plasmon bands

In this work, we synthesized monodispersed hexagonal Ag nanoprisms in high yields in a system of poly(vinylpyrrolidone) (PVP) in N-methylpyrrolidone (NMP). A blue shift occurred and was strongly dependent on the thickness of the uniform Ag nanoprisms, which had almost the same radial area. When the Ag nanoprisms grew thicker, their in-plane dipole resonance peaks markedly shifted toward shorter wavelengths (i.e., blue shift). PVP played a critical role of favoring vertical growth of the Ag nanoplates, preventing aggregation, and inducing the formation of Ag hexagonal nanoprisms (HNPs) through the transformation from thin Ag triangular nanoprisms (TNPs). Compared with similar previous research, the present study provides quite uniform Ag hexagonal nanoplates, which makes the blue shift related more solely and distinctly to the thickness of the Ag nanoprisms. The findings of this work provide a new perspective toward understanding the unique optical characteristics of Ag HNPs with different aspect ratios.

Polarization-Controllable Plasmonic Enhancement on the Optical Response of Two-Dimensional GaSe Layers.

Resonant plasmonic coupling has been considered as a promising strategy to enhance the optical response and manipulate the polarization of two-dimensional (2D) layer materials toward the practical applications. Here, a hybrid structure with periodic Ag nanoprism arrays was designed and fabricated on 2D GaSe layers to enhance these optical properties. By using the optimized hybrid structure with well-matched resonance, significant enhanced Raman scattering and band edge emission were successfully realized, and it is also interestingly found that the higher enhancement would be achieved while decreasing the thickness of GaSe layers. Theoretical simulation indicated that the strongly enhanced local field and the modified charge densities are the main reasons. By further introducing the patterned gratings on the plasmonic hybrid structure, selective excitation with controllable polarization was readily realized, besides the strongly enhanced photoluminescence intensity. This work provides a strategy for the plasmonic engineering of polarization controllable 2D optoelectronic devices.

A novel Ag nanoprism@SiO2@QD composite nanostructure for nano-optics

The fabrication of nanocomposite structures for Nano-Optics is facing many challenges due to the special performance requirements. In this work, a novel Ag nanoprism@SiO2@QD composite nanostructure is designed and fabricated to meet the desire of optical experiments. This material has good morphology and high monodispersity, and quantum dots can stably attach to the silica layer through chemical bonds. Simulation results confirm that this nanostructure can generates a Rabi splitting with a maximum value of 112 meV. Our coupling system creates a new combination of Ag nanoprisms and quantum dots, providing a high performance nanostructure for future photonic systems.

Single-Photon-Single-Electron Transition for Interpretation of Optical Spectra of Nonspherical Metal Nanoparticles in Aqueous Colloidal Solutions

Noble metal nanoparticles—especially shape anisotropic particles—have pronounced resonances in the optical spectrum. These sensitive absorption modes attract great interest in various fields of application. For nonspherical particles, no analytic description of the absorption spectra according to the commonly used Mie theory is possible. In this work, we present a semi-empirical approach for the explanation of the optical spectra of shape anisotropic particles such as silver nanoprisms and gold nanorods. We found an interpretation of the optical absorption spectra which is based on a single-photon-single-electron transition. This model is in a better agreement with the basic assumptions of quantum mechanics than the electrodynamic model of a localized surface plasmon excitation. Based on microfluidically obtained Ag nanoprisms and Au nanorods with very high ensemble homogeneities, dependencies between the geometrical properties of the shape anisotropic noble metal nanoparticles and the spectral position of the longitudinal absorption mode could be derived, which show that the assumption of a composed relative permittivity and the inclusion of the Rydberg constant is sufficient to describe the optical properties of the shape anisotropic particles. Within the scope of the measuring accuracy, the calculations furthermore lead to the value of the refractive index of the particle-surrounding medium.

Plasmonic Effects of Silver Nanoparticles Embedded in the Counter Electrode on the Enhanced Performance of Dye-Sensitized Solar Cells.

The plasmonic effects of silver (Ag) nanoparticles (NPs) with various morphologies (sphere, rod, and prism) embedded into the platinum (Pt) counter electrodes (CEs) of dye-sensitized solar cells (DSCs) were systematically investigated. It was shown that the power conversion efficiencies (PCEs) of the incorporated devices are notably improved from 7.60%, for the reference device without Ag NPs, to 8.10, 8.68, and 8.55% with Ag nanospheres, nanorods, and nanoprism devices, respectively. Moreover, the photocurrent and fill factor enhancement is attributed to the better optical and electrical properties of the integrated devices. Among all of the NP morphologies studied, Ag nanorods offer the best improvement to the device efficiency, as they have longitudinal localized surface plasmon resonance (L-LSPR) and strong scattering effects correlate within the morphology.

Surface-enhanced Raman scattering of EDOT and PEDOT on silver and gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its monomer 3,4-ethylenedioxythiophene (EDOT) on Ag and Au nanoparticles presenting different morphologies and stabilizing agents have been obtained using the excitation radiation at 633 nm. The SERS spectra of the monomer and polymer are strongly dependent both on the metal and capping agent of the substrate. SERS spectra of EDOT on Au nanospheres indicates that adsorption occurs with the thiophene ring perpendicular to the metal surface. In contrast, polymerization takes place on the silver surface of Ag nanospheres. EDOT adsorption on Ag nanoprisms with polyvinylpyrrolidone (PVP) as capping agent occurs similarly to that observed on gold. Surface-enhanced resonance Raman scattering (SERRS) spectra of PEDOT on gold nanostars that present a thick layer of PVP show no chemical interaction of PEDOT with the metal surface; however, when PEDOT is adsorbed on citrate stabilized gold nanospheres, the SERRS spectra suggest that thiophene rings are perpendicular to the surface. Oxidation of PEDOT also is observed on Ag nanospheres. The investigation of the interface between PEDOT and metal surface is crucial for the development in polymer-based optoelectronic devices since this interface plays a crucial role in their stability and performance.

Surface-Enhanced Raman Scattering of MEH-PPV on Gold and Silver Nanoparticles

The interaction of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with Au or Ag nanospheres, Au nanostars, and Ag nanoprisms was investigated using surface-enhanced Raman scattering (SERS). The SERS investigation showed that adsorption of MEH-PPV strongly depends on the nature of the nanoparticle surface. On gold nanostars that present a thick layer of capping polymer, SERS spectrum is only observed in relatively concentrated MEH-PPV solution (1 mmol L−1). On the other hand, Au and Ag nanospheres present SERS spectra down to 10−6 mol L−1 and no chemical interaction of MEH-PPV and metal surface is observed. The spectra of MEH-PPV on Ag nanoprisms with PVP as stabilizing agent suggest that the capping polymer induces a planar conformation of MEH-PPV and consequently an increase of conjugation length. These results give support for the application of MEH-PPV on optoelectronics in which interfacial effects are critical in the device efficiency and stability.

Synthesis of Triangular Silver and Gold Nanoprisms Using Consensus Sequence Tetratricopeptide Repeat Proteins.

Anisotropic metallic nanoparticles, such as Au and Ag nanoprisms (NPSMs), have received tremendous attention for their application in catalysis, molecular sensing, signal amplification, bioimaging, and therapeutic applications due to their shape-dependent optical and physical properties. Herein, we present a protein-enabled synthetic strategy for the seeded growth of silver and gold NPSMs with low shape polydispersity, narrow size distribution, and tailored plasmonic absorbance. During the initial seed nucleation step, consensus sequence tetratricopeptide repeat (CTPR) proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. High yield production of well-defined Ag/Au NPSMs is achieved, respectively, by adding CTPR-stabilized Ag seeds into the growth solutions containing metal precursor, mild reducing agent, sodium halide, and additional CTPR.

Triangular AgAu@Pt core-shell nanoframes with a dendritic Pt shell and enhanced electrocatalytic performance toward the methanol oxidation reaction.

Triangular AgAu@Pt nanoframes with a dendritic Pt shell were synthesized by employing Ag nanoprisms as sacrificial templates. Due to the unique frame-like nanostructure and ternary components, the AgAu@Pt nanoframes exhibit impressive electrocatalytic performance toward the methanol oxidation reaction with much higher activity, and better anti-poisoning capability than commercial Pt/C catalysts.

UV plasmonic device for sensing ethanol and acetone

In the present study, we demonstrate efficient detection of volatile organic vapors with improved sensitivity, exploiting the localized surface plasmon resonance of indium nanograins in the UV range (UV-LSPR). The sensitivity of deep-UV-LSPR measurements toward ethanol was observed to be 0.004 nm/ppm, which is 10 times higher than that of a previously reported visible-LSPR device based on Ag nanoprisms [Sensors 11, 8643 (2011)]. Although practical issues such as improving detection limits are still remaining, the results of the present study suggest that the new approach based on UV-LSPR may open new avenues to the detection of organic molecules in solid, liquid, and gas phases using plasmonic sensors.

Ag nanoprism metamaterial based tunable plasmonic logic gate

A metamaterial comprised of asymmetrically arranged Ag nanoprisms has been proposed and investigated in this paper. The metamaterial shows a polarization dependent PIT effect. The metamaterial with its periodic length along a y-axis less than 400 nm shows two tunable transmission dips. When the periodicity is increased above 400 nm, the metamaterial shows three adjustable transmission dips against the polarization state. By choosing different wavelengths of incident light, the metamaterial can be used as plasmonic Boolean logic gates. The working wavelengths of these plasmonic devices can then be adjusted by controlling the fillet radius of Ag nanoprism in metamaterial. These results offer great potential in developing polarization dependent tunable plasmonic information processing devices.

Robust hybrid enzyme nanoreactor mediated plasmonic sensing strategy for ultrasensitive screening of anti-diabetic drug

Enzyme inhibition based drug screening strategy has been widely employed for new drug discovery. But this strategy faces some challenges in practical application especially for the trace active compound screening from natural products such as the stability of enzyme and the sensitivity of screening approach. Inspired by the above, we for the first time demonstrate the self-assembly of α-glucosidase (GAA) and glucose oxidase (GOx) into one multi-enzymes-inorganic nanoreactor with hierarchical structure (flower shape). The hybrid enzyme nanoreactor enjoys the merits including the character of assembly line, the enhanced enzymatic activity and robust stability. The flower shape of enzyme nanoreactor possessed a bigger specific surface area, facilitating the trace GAA inhibitor detection. Based on the above, we proposed an enzyme nanoreactor mediated plasmonic sensing strategy for anti-diabetic drug screening. First, maltose was chosen as the substrate for GAA and the generated glucose were immediately utilized by GOx to generate H2O2, and finally, H2O2 etched the Ag nanoprism to round nanodiscs, resulting in the blue shift of surface plasmon resonance (SPR) absorption band. With the aid of hybrid enzyme nanoreactor guided SPR, the ultrasensitive screening of GAA inhibitor (i.e. anti-diabetic drug) can be realized with the detection limit of 5nM for acarbose. The proposed approach was successfully utilized for GAA inhibitor screening from natural products. We anticipate that the proposed sensing method may provide new insights and inspirations in the enzyme inhibition based drug discovery and clinical diagnosis.