Silver Nanoprisms Research Articles

Picosecond time of spontaneous emission in plasmonic patch nanoantennas

A significant (to 12 ps) decrease in the lifetime of excited states of quantum emitters in the form of three-layer colloidal quantum dots (CdSe/CdS/ZnS) placed in an aluminum–triangular silver nanoprism cavity (patch nanoantenna) has been experimentally demonstrated. The decrease in the time of spontaneous emission of quantum dots has been explained by the Purcell effect. The Purcell coefficient for an emitter in the resonator has been found to be 625. Such a significant increase in the rate of spontaneous emission in the patch nanoantenna is due to an increase in the local density of photon states in the plasmonic cavity.

Colorimetric detection of catalase and catalase-positive bacteria (E. coli) using silver nanoprisms

The sensitivity of the formation of plasmonic silver nanoprisms to hydrogen peroxide is explored for the colorimetric detection of catalase activity in bacteria.

Tracking of photochemical Ostwald ripening of nanoparticles through voltammetric atom counting.

We report the tracking of atom count in individual nanoparticles during photochemical Ostwald ripening. The nano-impact technique, in conjunction with UV-Vis and TEM analysis, is used to follow the photochemical formation of silver nano-prisms from spherical seed particles. A mechanism of photochemical Ostwald ripening is deduced and key growth stages are identified.

Just What Is It That Makes Silver Nanoprisms so Different, so Appealing?

Thanks to their unique physicochemical properties (e.g., surface plasmon resonance), noble metal nanoparticles are at the cornerstone of nanotechnology. Silver triangular nanoprisms are presented here as an ideal playground to introduce students to nanochemistry concepts such as the formation of shape-controlled nanostructures. Not only a reliable and straightforward protocol for the synthesis of silver nanoprisms is described, but also their formation is explained in terms of basic oxidation–reduction mechanisms; their peculiar optical properties are compared with those displayed by silver nanospheres and discussed in relation to their shape.

Single nanoparticle plasmonic sensors.

The adoption of plasmonic nanomaterials in optical sensors, coupled with the advances in detection techniques, has opened the way for biosensing with single plasmonic particles. Single nanoparticle sensors offer the potential to analyse biochemical interactions at a single-molecule level, thereby allowing us to capture even more information than ensemble measurements. We introduce the concepts behind single nanoparticle sensing and how the localised surface plasmon resonances of these nanoparticles are dependent upon their materials, shape and size. Then we outline the different synthetic approaches, like citrate reduction, seed-mediated and seedless growth, that enable the synthesis of gold and silver nanospheres, nanorods, nanostars, nanoprisms and other nanostructures with tunable sizes. Further, we go into the aspects related to purification and functionalisation of nanoparticles, prior to the fabrication of sensing surfaces. Finally, the recent developments in single nanoparticle detection, spectroscopy and sensing applications are discussed.

Protein Detection: An Optical Nanoruler Based on a Conjugated Polymer−Silver Nanoprism Pair for Label‐Free Protein Detection (Adv. Mater. 39/2015)

An optical nanoruler system based on a conjugated polyelectrolyte (CP)-silver nanoprism (Ag NPR) pair is developed for label-free biological detection by taking advantage of the metal-enhanced fluorescence (MEF) effect of Ag nanostructures. The system described by L. Li, S. Wang, and co-workers on page 6040 effectively transduces and amplifies the change of the metal–fluorophore distance into the response of the CP fluorescence, which is used to monitor the presence of specific antigens and even mammalian cells with high sensitivity and good selectivity.

An optical nanoruler based on a conjugated polymer-silver nanoprism pair for label-free protein detection.

An optical nanoruler system based on a conjugated polyelectrolyte-silver nanoprism pair is developed for label-free protein detection by taking advantage of the metal-enhanced fluorescence effect of silver nanostructures. Antibody-antigen interactions induce a change in the metal-fluorophore distance, followed by the response of a fluorescent signal of the conjugated polyelectrolyte. The system is used to detect target antigens sensitively and selectively.

Uricase-stimulated etching of silver nanoprisms for highly selective and sensitive colorimetric detection of uric acid in human serum

The easy-to-use method for detecting uric acid in human serum is of great importance because of its crucial role in physiological and pathological processes. Herein, a simple and effective strategy was designed for colorimetric sensing of uric acid using the morphological transition of Ag nanoprisms. In the presence of uricase, uric acid was oxidized to produce H2O2. Subsequently, the morphology of Ag nanoprisms changed from triangle to round by etching of H2O2, leading to a more than 120nm blue shift of surface plasmon resonance spectral band. The color change from pale blue to purple related to concentration change of uric acid can be judged by naked eyes. A linear relationship between the blue shift of peak of Ag nanoprisms and uric acid concentration ranged from 1.0 to 40μM. The detection limit of uric acid was 0.7μM. Some potential interferents (e.g., ascorbic acid, glucose, dopamine, hypoxanthine and various amino acids) in human serum showed no interference. Serum samples could be directly added into Ag nanoprism–uricase sensing system, and the assay can be completed within one hour. The proposed sensor was successfully applied for detecting uric acid in human serum with the recoveries over 95%. The obtained results are in agreement with those measured by biochemistry analyzer with the average relative error of 5.1%. The Ag nanoprism–uricase sensor offers advantages of high selectivity and sensitivity, low-cost instruments, and rapid assay without sample pretreatment. Thus, the present uric acid sensor has great potential in applications for biochemical analysis and clinical diagnosis.

Selective deposition of HgS at the corner sites of triangular silver nanoprism and its tunable LSPR for colorimetric Hg2+ detection

This paper developed a novel colorimetric strategy for the detection of Hg2+ based on the apical activation and passivation of unmodified triangular silver nanoprism (AgNPR). Triangular AgNPR can be rapidly etched into round nanodiscs by thiosulfate anion (S2O32−), leading to a change in colloid color from blue to yellow. However, if Hg2+ is introduced into the system together with S2O32−, changes in the shape and color of the AgNPR can be effectively prevented by the specific precipitation reaction between Hg2+ and S2O32−. The shape evolution of AgNPR was clearly revealed by the TEM measurements, including apical corrosion at the three corner sites and selectively HgS deposited over the etched zones. The spectroscopic changes in localized surface plasmon resonance (LSPR) wavelength of the AgNPR were used as the analytical signal, and a novel colorimetric platform for Hg2+ detection was established in a label-free fashion. It provides reliable and sensitive quantification with a detection limit as low as 0.2nM and a dynamic range of 5.0nM to 10.0μM. Furthermore, this method has been successfully implemented for the determination of Hg2+ in wastewater samples.

Synthesis of silver nanoprisms on reduced graphene oxide for high-performance catalyst

We developed a facile hydrothermal method to synthesize Ag nanoprism on reduced graphene oxide (rGO) with the assistance of sodium alginate (SA). It was found that most of the Ag nanoparticles have {111} external facets which are parallel to the (0001) of the reduced graphene oxide matrix and thus the Ag nano-particles have shown a triangle morphology. When used as a catalyst in the oxidation of hydroquinone, the obtained SA–Ag–rGO showed an outstanding performance: the catalytic rate constant of the hybrid is more than 12 times higher than that of Ag spherical particles on graphene sheets.

Rapid Thermal Synthesis of Silver Nanoprisms with Chemically Tailorable Thickness

Rapid Thermal Synthesis of Silver Nanoprisms with Chemically Tailorable Thickness

Development of highly thermoresponsive fluorescent sensors consisting of plasmonic silver nanoprisms and poly(N-isopropylacrylamide)-fluorophore composites.

We developed a new hybrid consisting of Ag nanoprisms, poly(N-isopropylacrylamide) (PNIPAm), and fluorophores via layer-by-layer assembly. The fluorescence intensity below the lower critical solution temperature (LCST) of PNIPAm was 6.4 times stronger than that above the LCST, meaning that the hybrids can function as nanosized highly thermoresponsive fluorescent sensors.

Realizing Strong Light-Matter Interactions between Single-Nanoparticle Plasmons and Molecular Excitons at Ambient Conditions.

Realizing strong light-matter interactions between individual two-level systems and resonating cavities in atomic and solid state systems opens up possibilities to study optical nonlinearities on a single-photon level, which can be useful for future quantum information processing networks. However, these efforts have been hampered by unfavorable experimental conditions, such as cryogenic temperatures and ultrahigh vacuum, required to study such systems and phenomena. Although several attempts to realize strong light-matter interactions at room temperature using plasmon resonances have been made, successful realizations on the single-nanoparticle level are still lacking. Here, we demonstrate the strong coupling between plasmons confined within a single silver nanoprism and excitons in molecular J aggregates at ambient conditions. Our findings show that deep subwavelength mode volumes V together with quality factors Q that are reasonably high for plasmonic nanostructures result in a strong-coupling figure of merit-Q/sqrt[V] as high as ∼6×10^{3} μm^{-3/2}, a value comparable to state-of-the-art photonic crystal and microring resonator cavities. This suggests that plasmonic nanocavities, and specifically silver nanoprisms, can be used for room temperature quantum optics.

Silver nanoprisms self-assembly on differently functionalized silica surface

In this work colloidal silica/silver nanoprisms (NPRs) composite coatings were made. Firstly colloidal silica sols were synthesized by sol-gel method and produced coatings on glass by dip-coating technique. Next coatings were silanized by (3-Aminopropyl)triethoxysilane (APTES), N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEAPTMS), (3- Mercaptopropyl)trimethoxysilane (MPTMS). Silver NPRs where synthesized via seed-mediated method and high yield of 94±15 nm average edge length silver NPRs were obtained with surface plasmon resonance peak at 921 nm. Silica-Silver NPRs composite coatings obtained by selfassembly on silica coated-functionalized surface. In order to find the most appropriate silanization way for Silver NPRs self-assembly, the composite coatings were characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), water contact angle (CA) and surface free energy (SFE) methods. Results have showed that surface functionalization is necessary to achieve self-assembled Ag NPRs layer. MPTMS silanized coatings resulted sparse distribution of Ag NPRs. Most homogeneous, even distribution composite coatings obtained on APTES functionalized silica coatings, while AEAPTMS induced strong aggregation of Silver NPRs.

Interaction between Nanoprisms with Different Coupling Strength

The aggregated noble metal system, consisting of two or more nanoparticles, possesses unique optical properties. The most important is the ability to generate larger local electric field enhancement than a single particle. In this work, we have modeled the system composed of silver nanoprisms with different geometries. For this purpose, the optical properties of the single silver nanoprism and the aggregated nanoprism dimer with adjacent and coplanar bases configuration have been studied by the finite integration technique. The relationship between the geometrical parameters, in particular the radius of the edges of curvature of a single nanoprism, and the position of the extinction peak has been described in a form of a mathematical equation. By moving and rotating one of the nanoprisms relative to the other in the dimer system, the coupling strength between them has been investigated by analyzing the near-field and far-field properties. On the basis of these results, a hybridization model of the nanopri...

Crystallinity effects on scaling properties of photoinduced modes in silver nanoprisms.

The crystallinity effects on scaling properties of photoinduced modes in crystalline silver nanoprisms with C3v symmetry are studied using a realistic atomistic model and group theory. Among all vibrational modes, photoinduced modes can be identified as those vibrational modes which possess larger in-phase radial atomic displacement and can be projected out by the projected density of states method. We found that the properties of vibrations in silver nanoprisms strongly depend on the particle's aspect ratio (bisector length over thickness). By considering crystallinity of silver nanoprisms, the dominant modes with the in-plane oscillation become several closely spaced modes, and become obvious for nanoprisms with a smaller aspect ratio. The oscillation spectra show that the dominant planar modes are insensitive to thickness change. On the contrary, the atomic displacements show significantly different patterns for nanoprisms of different thicknesses. We also found that, for nanoprisms with same aspect ratio that is larger than 4, the vibrational properties of dominant modes exhibit scaling similarity. By using a simple linear transformation, the vibration frequencies for large-sized nanoprisms of aspect ratio 6 can be obtained by a corresponding scaling factor. The calculated results are in good agreement with experimental data.

Silver nanoprism etching-based plasmonic ELISA for the high sensitive detection of prostate-specific antigen.

Ultrasensitive and quantitative detection using simple and low-cost assays is critical in clinical diagnostics. In this report, we developed a triangular silver nanoprism (AgNPRs) etching-based plasmonic biosensor for the detection of cancer biomarkers. The triangular AgNPRs-based plasmonic biosensor is an enzyme-linked immunosorbent assay combined with the enzyme-mediated surface plasmon resonance (SPR) of triangular AgNPRs. Triangular AgNPRs uses the immune response of prostate-specific antigen (PSA) to trigger the glucose oxidase (GOx)-catalysed oxidation of glucose (Glu), producing hydrogen peroxide. Hydrogen peroxide acts as an oxidant to etch the triangular AgNPRs into smaller spherical silver nanoparticles, which is accompanied by a substantial blueshift of the SPR peak and a colourimetric blue-to-purple change that can be observed by the naked eye. The SPR peak shift enables the quantitative assessment of PSA due to the remarkable colour change. The triangular AgNPRs-based plasmonic ELISA approach exhibited a quasilinear response to logarithmic PSA concentrations in the range of 10fg/mL to 100pg/mL with a limit of detection (LOD) of 4.1fg/mL. In addition, the LOD of PSA in this approach exceeds that of the conventional HRP-based ELISA (1.25ng/mL) approach by more than 5 orders of magnitude. Patient serum samples from 16 donors were assayed with triangular AgNPRs-based plasmonic ELISA. The results from the triangular AgNPRs-based immunoassay and the time-resolved fluorescence immunoassay showed excellent correlation, and there were no significant differences in the quantified amounts of PSA. The triangular AgNPRs-based plasmonic ELISA approach has advantages (ultrasensitive, cost-effective, ease of operation) that are expected to be of great interest in diagnostics and to be suitable for a point-of-care test.

Preparation of a fluorescent silver nanoprism–dye complex for detection of hydrogen peroxide in milk

A simple and sensitive “turn-on” fluorescence detection method for H2O2in milk was developed based on H2O2induced morphology transitions of fluorescent dye–protein complex-capped silver nanoprisms (FDSNPs).

Formation, Optical Properties and Applications of Edge Gold-Coated Silver Nanoprisms

ABSTRACTA facile, high-yield synthesis of edge gold-coated silver nanoprisms (GSNPs) with a gold nanoframe as thin as 1.7 nm and their comprehensive characterizations by using various spectroscopic and microscopic techniques is introduced. The GSNPs exhibit remarkably higher stability than silver nanoprisms (SNPs) and are therefore explored as effective optical antennae for light-harvesting applications. When embedded into a bulk heterojunctions film of P3HT:PCBM, plasmonic GSNPs with a localized surface plasmon resonance (LSPR) around 500 nm can effectively act as optical antennae to enhance light harvesting in the active layer. As a result, we measured up to 7-fold enhancement in the polaron generation yield through photoinduced absorption spectroscopy. Owing to the high stability and strong field enhancement, the presented GSNPs feature great potential as plasmonic probes for photovoltaic applications and LSPR sensing.

A novel triangular silver nanoprisms-based surface plasmon resonance assay for free chlorine.

In this study, a novel assay for the detection of free chlorine is proposed for the first time. It is based on a redox reaction that occurs between triangular silver nanoprisms and free chlorine, which results in a morphological transformation and a change of the localized surface plasmon resonance (SPR) of the triangular silver nanoprisms. In the assay, the presence of free chlorine would etch triangular silver nanoprisms from triangle to round, leading to a significant blue-shift SPR absorption band of triangular silver nanoprisms. The wavelength shift was used for facile and reliable free chlorine quantification in the range of 0.1-20 μM. The obtained detection limit was as low as 0.07 μM, which was about one and half orders of magnitude lower than that of the most widely used N-N-diethyl-p-phenylenediamine (DPD) colorimetric methods. Moreover, this assay was employed to determine the free residual chlorine in local tap water samples. The obtained results were in accordance with those obtained by the DPD colorimetric method.