Silver Island Research Articles

Enhancement of the Chemiluminescence Response of Enzymatic Reactions by Plasmonic Surfaces for Biosensing Applications.

We report the enhancement of chemiluminescence response of horseradish peroxidase (HRP) in bioassays by plasmonic surfaces, which are comprised of (i) silver island films (SIFs) and (ii) metal thin films (silver, gold, copper, and nickel, 1 nm thick) deposited onto glass slides. A model bioassay, based on the interactions of avidin-modified HRP with a monolayer of biotinylated poly(ethylene-glycol)-amine, was employed to evaluate the ability of plasmonic surfaces to enhance chemiluminescence response of HRP. Chemiluminescence response of HRP in model bioassays were increased up to ~3.7-fold as compared to the control samples (i.e. glass slides without plasmonic nanoparticles), where the largest enhancement of the chemiluminescence response was observed on SIFs with high loading. These findings allowed us to demonstrate the use of SIFs (high loading) for the detection of a biologically relevant target protein (glial fibrillary acidic protein or GFAP), where the chemiluminescence response of the standard bioassay for GFAP was enhanced up to ~50% as compared to bioassay on glass slides.

Raman spectroscopic probing of plant material using SERS

We report surface‐enhanced Raman studies on intact plant material using onion layers as a biological target, and silver nanoaggregates and silver island films as enhancing plasmonic structures. Surface‐enhanced Raman scattering (SERS) enhancement allows the detection of strong Raman signatures of chemical constituents of the surface of the onion layer such as cellulose, proteins, and flavonols. Because of long‐time incubation, SERS sensors can access the extracellular space in the inner of the layer. The location of silver nanoparticles inside the onion layer has been monitored by the SERS images collected from chemicals present in the onion and/or reporter molecules attached to the nanoparticles. Our studies show a competitive adsorption of intrinsic bio molecules of the onion layer and reporter molecules. Different spectra from different places of the layer indicate the complex heterogeneous chemical structure of the plant material. The pH‐sensitive reporter molecule para mercapto benzoic acid attached to the nanoparticles allows us to infer pH values inside the extracellular matrix of the onion layer. Copyright © 2015 John Wiley & Sons, Ltd.

Silver island film substrates for ultrasensitive fluorescence detection of (bio)molecules.

A silver island film (SIF) substrate was used to demonstrate that Metal-Enhanced Fluorescence (MEF) is a powerful tool to enable detection of emission from (bio)molecules at very low concentrations. The experiments were carried out with the Fenna-Matthews-Olson (FMO) pigment-protein complex from the photosynthetic green sulfur bacterium Chlorobaculum tepidum. FMO was diluted to a level, at which no emission was detectable on a glass substrate. In contrast, the fluorescence of FMO was readily observed on the SIF substrate, even though the emission wavelength of FMO is displaced by over 300nm from the maximum of the plasmon resonance of the SIF layer. Estimated enhancements of the fluorescence intensity of FMO on SIF are about 40-fold. The enhancement factor correlates with the improvement of the signal-to-noise ratio for FMO emission on SIF substrates.

Well-ordered “tooth-shaped” silver-microstructures on poly(methyl methacrylate) patterned by laser writing

A method for the preparation of “tooth-shaped” periodical, silver structures on poly(methyl methacrylate) (PMMA) is described. The method consists in laser beam patterning of porphyrine doped PMMA coated with thin silver film. Laser light absorption caused local PMMA heating, followed by distortion of PMMA surface layer and cutting of top silver film. The laser patterning was accomplished in two perpendicular directions, leading to creation of “tooth-shaped” silver microstructures. Analyses by AFM, SEM and EDS techniques shown that the structures prepared in this way consist of periodically arranged elements with elevated edges, partially covered by silver islands. Such ordered structures may find application in optics and optoelectronics.

Effective medium analysis of thermally evaporated Ag nanoparticle films for plasmonic enhancement in organic solar cell

Films of silver nanoparticles have optical properties that are useful for applications such as plasmonic light trapping in solar cells. We report on the simple fabrication of Ag nanoparticle films via thermal evaporation, with and without subsequent annealing. These films result in a random array of particles of various shapes and sizes. The modeling of such a vast collection of particles is still beyond reach of the modern computers. We show that it is possible to represent the silver island films by the Bergman effective mediums with the same optical properties. The effective medium method provides us with deep insight about the shape, the size and the distribution of nanoparticles. The far field simulations of solar cells, in which the silver island film is replaced with an effective medium layer, show a reduction in the absorption of active layer. Besides, the near field simulations based on finite-difference time-domain technique demonstrate that the near field effects on active layer absorption are negligible and this method highlights the importance of nanoparticles shapes. The PCPDTBT:PCBM solar cells with embedded silver island films are fabricated, and it is found that their performances show the similar trend. This insight can be used for the optical analysis of thermally evaporated Ag nanoparticle films for the improvement of organic solar cells.

Tunable lasing on silver island films by coupling to the localized surface plasmon

Lasing of N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1':4',1”-terphenyl]-4,4”-diamine (BMT-TPD) films on silver island films (SIFs) was investigated. The size of silver nanoparticles (NPs) of SIFs ranged from 8 to 500 nm, which showed the different localized surface plasmon resonance (LSPR). It was found that the lasing wavelength of BMT-TPD was tuned by the LSPR peaks of silver NPs. This was attributed to the coupling between gain medium and plasmonic silver NPs, that is, the surface plasmon amplification by stimulated emission of radiation which resulted in the lasing at the corresponding wavelengths. This is expected to be a new and easy approach for the tuning of wavelength of lasing.

Grating-Vector-Assisted Plasmonic Coupling in a Hexagonally Arranged Silver Island Array

We experimentally and numerically investigated the attenuated total reflection (ATR) spectra of hexagonally periodic structures of discrete silver nano islands array (NIA) and that of continuous silver film with nanohole array (NHA). Some peculiar reflection fine dips in the ATR spectra of the NIA structures were observed. In comparison with the ATR results between NHA and NIA structures as well as carefully analyzing the multiwavelengths numerical ATR spectra of the NIA, we found out the mechanisms leading to the ATR fine dips. They are resulted from the effects of surface plasmon resonances (SPR) and Wood’s anomalies that occur at the silver/air or silver/prism interface with the assistance of two-dimensional reciprocal grating-vectors provided by the NIA. Particularly, our results demonstrated that there are continuous-film-like SPR modes existing in the NIA structures, which can be excited through the coupling between the incident light and the two-dimensional grating-vectors of the NIA.

Circular economy of a papermaking park in China: a case study

Papermaking is regarded as an industry that consumes a great amount of energy and produces serious pollution. The papermaking industry in China, which has a large population and rapid economic development, is indispensable and presents a trend of rapid development. China and the rest of the world pay considerable attention to resource conservation and environmental protection. Therefore, determining how the papermaking industry can realize cleaner production and sustainable development is an urgent issue that should be addressed. This paper introduces Guangdong Silver Island Lake (GSIL) Papermaking Park, which realizes cleaner production and sustainable development by developing circular economy (CE). This park constructs a CE industrial mode by recycling energy, water, and materials. After 10 years of implementation, the CE plan of GSIL Papermaking Park has integrated the resources of the papermaking and power industries horizontally, thus forming the unique development mode of its CE. The resource consumption, resource comprehensive utilization, and pollutant emission indexes of the park have reached the advanced level in the papermaking industry of China.

Plasmonics in atomically thin materials

The observation and electrical manipulation of infrared surface plasmons in graphene have triggered a search for similar photonic capabilities in other atomically thin materials that enable electrical modulation of light at visible and near-infrared frequencies, as well as strong interaction with optical quantum emitters. Here, we present a simple analytical description of the optical response of such kinds of structures, which we exploit to investigate their application to light modulation and quantum optics. Specifically, we show that plasmons in one-atom-thick noble-metal layers can be used both to produce complete tunable optical absorption and to reach the strong-coupling regime in the interaction with neighboring quantum emitters. Our methods are applicable to any plasmon-supporting thin materials, and in particular, we provide parameters that allow us to readily calculate the response of silver, gold, and graphene islands. Besides their interest for nanoscale electro-optics, the present study emphasizes the great potential of these structures for the design of quantum nanophotonics devices.

Formation and characterization of silver nanoparticles embedded in optical transparent materials for plasmonic sensor surfaces

• We analyzed particle forming behavior of thin Ag seed films before/after annealing. • We examined passivation layers produced via different deposition methods. • Ag particles embedded in Al 2 O 3 films were tested as LSPR-sensor-surface. • LSPR shifted 6.15 nm for a refractive index change of 0.07 using glucose solutions. Plasmonic nanostructures promise sensing capabilities with the potential for ultrasensitive and robust assays in life sciences and biomedicine. Silver island films represent an interesting and straightforward alternative for the implementation of substrate-attached plasmonic nanostructures. The temperature-induced particle-forming behavior of thin silver seed films deposited on glass substrates and on polycrystalline silicon films is represented. The measured extinction spectra reflect the different size distributions and shapes. The covering of the particles with different optical transparent film materials like ZnO, Al 2 O 3 , SiN x , and SiO x leads to a further shift in the resonance maximum due to their refractive index. The SiO x system shows an additional long term change in the extinction spectrum in contrast to ZnO, Al 2 O 3 , and SiN x . Thin silver films covered with Al 2 O 3 were used in order to proof the system as a sensor element for analyte detection (glucose solution).

Metal-Enhanced S1 and Alpha- S1 Fluorescence: Effects of Far-Field Excitation Irradiance on Enhanced Fluorescence

Metal-enhanced fluorescence (MEF) and delayed fluorescence (alpha α-S1) studies of acriflavin have been undertaken using steady-state and time-resolved fluorescence measurements on silver island films (SiFs) supporting a thin poly(vinyl alcohol) (PVA) polymer film. Nearly a 3.5-fold enhancement in the far-field fluorescence intensity of acriflavin is observed coupled with a decrease in decay times and an improved fluorophore photostability. Our findings are consistent with our proposed model of the coupling and transferring of the excited state energies of fluorophores to silver surface plasmons. Further, an excitation power dependence of MEF is observed in these films, consistent with our postulate of MEF EVE (MEF excitation volumetric effect) and, ultimately, resulting in a ∼7-fold enhancement in fluorescence intensity. Our findings suggest a significant opportunity for the development of shorter-lived, brighter, high photon flux luminescent materials for multifarious applications in the life-sciences.

Galvanic synthesis of three-dimensional and hollow metallic nanostructures.

We report a low-cost, facile, and template-free electrochemical method of synthesizing three-dimensional (3D) hollow metallic nanostructures. The 3D nanoporous gold (3D-NPG) nanostructures were synthesized by a galvanic replacement reaction (GRR) using the different reduction potentials of silver and gold; hemispherical silver nanoislands were electrochemically deposited on cathodic substrates by a reverse-pulse potentiodynamic method without templates and then nanoporous gold layer replicated the shape of silver islands during the GRR process in an ultra-dilute electrolyte of gold(III) chloride trihydrate. Finally, the wet etching process of remaining silver resulted in the formation of 3D-NPG. During the GRR process, the application of bias voltage to the cathode decreased the porosity of 3D-NPG in the voltage range of 0.2 to -0.62 V. And the GRR process of silver nanoislands was also applicable to fabrication of the 3D hollow nanostructures of platinum and palladium. The 3D-NPG nanostructures were found to effectively enhance the SERS sensitivity of rhodamine 6G (R6G) molecules with a concentration up to 10-8 M.Electronic supplementary materialThe online version of this article (doi:10.1186/1556-276X-9-679) contains supplementary material, which is available to authorized users.

Absence of high surface spin-flip rate in mesoscopic silver channels

Large spin signals up to 38 mΩ are demonstrated in mesoscopic nonlocal spin valves with silver channels. Scanning electron microscope images reveal Volmer–Weber growth of the silver channels, which consist of coalesced silver islands from 30 to 80 nm in size. The temperature dependence of the spin signals is monotonic, in contrast to previously observed non-monotonic features due to high surface spin-flip rate. We hypothesize that magnetic impurities in the silver are primarily segregated at the bulk grain boundaries instead of near the side surfaces of the channel, resulting in an absence of high surface spin-flip rate.

5-color multiplexed microwave-accelerated metal-enhanced fluorescence: detection and analysis of multiple DNA sequences from within one sample well within a few seconds.

We present a potentially highly sensitive and selective bio-assay for the potential detection of any five different DNA sequences from one sample in one well. The assay is based on a DNA "rapid catch and signal" (DNA-RCS) technology developed for the detection of different DNA sequences from a sample well area. Our signal amplification utilizes the metal-enhanced fluorescence (MEF) of dyes attached to the probe-DNAs, which hybridizes with the pre-formed mixture of anchor-DNA scaffolds on silver island films (SiFs). Low-power microwave irradiation accelerates both the formation of the anchor-DNA scaffold on the SiF-surface and anchor/probe DNA hybridization, i.e. "rapid catch" of target DNAs from a bulk solution, decreasing the assay run time from hours to only a few seconds. Localization of signaling dye-labels close to the SiFs make them extremely photostable, which allows for collecting/integrating the signal over a long time period. To demonstrate a 5 color DNA assay (5-plex) we have used a range of readily available Alexa™ dyes. Advantages and perspectives of the RCS-technologies ability to detect 5 different DNA sequences from within one plate-well are discussed.

Enhanced Fluorescence Using an Optical Interference Mirror Overlaid with Silver Island Film

Fluorophores overlaid on an optical interference mirror composed of a metal and thin dielectric layer demonstrate enhanced fluorescence. Fluorescence is also enhanced by silver nanostructures such as silver island films, which excite localized surface plasmon resonance. An optical interference mirror surface was overlaid with a silver island film to amplify the fluorescence enhancement. The optimal thickness of the silver island film (100 nm) was evaluated from transmittance and surface roughness measurements. At this thickness, the fluorescence was amplified sixteen-fold. The thickness of the interference layer was optimized at 40 nm providing a one hundred-sixty fold fluorescence enhancement of rhodamine B. However, only a four-fold improvement in sensitivity was achieved for the determination of a labeled streptavidin using biotin immobilized on the silver island film interference mirror.

Out-diffused silver island films for surface-enhanced Raman scattering protected with TiO2 films using atomic layer deposition.

We fabricated self-assembled silver nanoisland films using a recently developed technique based on out-diffusion of silver from an ion-exchanged glass substrate in reducing atmosphere. We demonstrate that the position of the surface plasmon resonance of the films depends on the conditions of the film growth. The resonance can be gradually shifted up to 100 nm towards longer wavelengths by using atomic layer deposition of titania, from 3 to 100 nm in thickness, upon the film. Examination of the nanoisland films in surface-enhanced Raman spectrometry showed that, in spite of a drop of the surface-enhanced Raman spectroscopy (SERS) signal after the titania spacer deposition, the Raman signal can be observed with spacers up to 7 nm in thickness. Denser nanoisland films show slower decay of the SERS signal with the increase in spacer thickness.PACS78.67.Sc (nanoaggregates; nanocomposites); 81.16.Dn (self-assembly); 74.25.nd (Raman and optical spectroscopy)

Large plasmonic fluorescence enhancement of cyanobacterial photosystem I coupled to silver island films

A large, two-orders-of-magnitude enhancement of fluorescence emission from cyanobacterial Photosystem I (PSI) coupled to plasmonic excitations in silver island films was observed. Such a high value has not been reported for metal-enhanced fluorescence of photosynthetic pigment-protein complexes before. The dramatic enhancement of the PSI emission occurs when PSI is excited resonantly into the Qx and Qy bands of chlorophyll a. In contrast, excitation in the carotenoid absorption band yields ten times lower enhancement factors. We attribute these large values of enhancement factor to plasmon-induced activation of excitation and emission channels absent for isolated PSI complexes.

A label-free aptasensor for highly sensitive detection of ATP and thrombin based on metal-enhanced PicoGreen fluorescence

A label-free fluorescence aptasensor for highly selective and sensitive detection of ATP and thrombin was developed by using PicoGreen (PG) as signal molecule and surface-bound metal-enhanced fluorescence (MEF) substrates (silver island films, SIFs) as signal enhancers. On binding with ATP or thrombin, aptamers undergo structure switching, leading to a reduction of fluorescence intensity of PG. Chang of fluorescence intensity can be magnified by SIFs. The limit of detection for ATP and thrombin is 1.3nM and 0.073nM, respectively. The fluorescence quenching efficiency is linear in the logarithmic scale with ATP concentration range from 10nM to 100μM (R2=0.995) and thrombin concentration range from 0.1nM to 100nM (R2=0.997). The coefficients of variation of the intra-assay reproducibility and inter-assay reproducibility for ATP (10μM) assay are 3.8% and 5.2%, respectively. In addition, the aptasensor is stable and can be reliably used for ATP measurement in biological samples. Overall, the aptasensor can be a useful and cost effective tool for the specific detection of ATP, thrombin and potentially other biomolecules in biological samples.

Enhancement of enzymatic colorimetric response by silver island films on high throughput screening microplates

In this study, we report the use of an enzyme-based hybrid platform, which is comprised of silver island films, enzymes (HRP and AP) and high-throughput screening (HTS) microplates, to enhance the colorimetric response of enzymatic reactions. The hybrid platform was designed in a two-step process: (i) deposition of SIFs onto HTS microplates with low, medium, and high loading (refers to the extent of the surface plasmon resonance peak of SIFs at 460nm) using Tollen's reaction scheme; and (ii) attachment of b-BSA or BEA as linkers for the immobilization of enzymes. The presence of SIFs within the wells of the HTS microplates was confirmed using an optical spectrophotometer and real-color photography. Control experiments, where SIFs were omitted from the surfaces were carried out to confirm the effect of SIFs on the enzymatic colorimetric response. Significant colorimetric signal enhancement was observed for HRP or AP on SIFs (high loading) deposited HTS microplates using b-BSA (up to ~3-fold for AP and ~6-fold HRP) or BEA (up to ~7-fold for both HRP and AP), as compared to our control samples. The observed increase in colorimetric response can be attributed to the nature of BEA, which exposes surface-bound enzymes to the substrate present in bulk more efficiently than b-BSA. This study proves that SIFs can serve as a valuable tool to improve the signal output of existing bioassays carried out in HTS microplates, which can be applicable to the field biosensors and plasmonics.

Manifestation of the Difference in Reactivity of Silver Clusters in Contrast to Its Ions and Nanoparticles: The Growth of Metal Tipped Te Nanowires

Reactivity of two different nanosystems of silver, namely nanoparticles and atomically precise clusters, toward 1D tellurium nanowires (NWs) was probed and compared with the reaction of silver ions. While the reaction of nanoparticles and ions led to silver telluride nanowires, a different reactivity was exhibited by clusters which resulted in silver islands at different positions on the Te NWs. These hybrid Ag nodule-decorated Te NWs are sensitive to temperature, and they transform to dumbbell-shaped silver-tipped Te NWs upon solution phase annealing. Differences in chemical reactivity of nanoparticles of two different size regimes with nanowires are demonstrated. Synthetic methods of this kind will be useful in creating complex nanostructures which are difficult to be made in the solution phase.