Silver Island Research Articles

Experimental and theoretical study of the distance dependence of metal-enhanced fluorescence, phosphorescence and delayed fluorescence in a single system

Distance dependent singlet and triplet metal-enhanced emission of eosin from silica coated silver island films (SiFs) has been studied by steady-state and time resolved fluorescence techniques, along with theoretical finite difference time domain (FDTD) numerical simulations, to understand how the thickness of the dielectric coating surrounding silver nanoparticles fundamentally affects luminescence enhancement. Our findings suggest that the distance dependence of metal-enhanced phenomena such as fluorescence, phosphorescence and delayed fluorescence is underpinned by the decay of the electric near-field, and depending on the actual silver silica sample embodiment, one can see either decreased or enhanced luminescence. These results not only expand our current MEF thinking but also suggest that one may well be able to approximate plasmon-enhanced luminescence values.

Metal-dielectric composite optical coatings: underlying physics, main models, characterization, design and application aspects

Abstract Metal island films are a matter of research in different branches of applied physics and technology. One possible future application field is their use as a substantial part of optical interference coatings, forming metal-dielectric composite multilayer coatings. This tutorial provides background on optical specifics of metal island films and ideas how these specifics could be exploited in coating technology. Consideration is given to effective optical constants of copper and silver island films, characterization methods and design strategies pursuing neutral density filters, asymmetric beamsplitters and decorative coating specifications.

Photolithographic processing of silver loaded dielectric coatings based on preformed colloidal TiO2 nanoparticles dispersed in a mesoporous silica binder

Titanium dioxide is a well known photocatalyst for reactions involving surface trapped photogenerated carriers. Noble metal photo-reduction may be used for the processing of silver/TiO2 nanocomposite coatings that may exhibit interesting optical and electrical properties. We present here results of our investigations performed on an original system consisting of preformed colloidal TiO2 nanoparticles homogeneously dispersed within a mesoporous silica host matrix. Light irradiation of samples immerged in an aqueous silver salt solution leads to the homogeneous deposition of silver islands in the vicinity of the TiO2 particles and throughout the film thickness. The silver volume fraction is directly controlled by the irradiation dose up to a value of about 16 vol.%. Films exhibit tunable plasmonic properties that correspond to silver nanoparticles in interaction, and a percolation threshold is observed at 8–10 vol.%, leading to films with a conductivity of about 40 S cm−1. The major interest of this method lies in the high silver reduction quantum efficiency (about 50%) and the possibility to modulate optical and electronic properties by light irradiation while the low temperature of processing permits the photolithographic deposition of metallic patterns on organic flexible substrates.

"Beneath the Surface (of Language)" and "Searching for Ludwig Wittgenstein" introduced by Monica Manolescu and Chantal Bax

A short introduction to Beneath the Surface (of Language). Silver Island Mountain Byway. Wendover, Utah, USA (Jan Estep, 2009)Monica Manolescu Beneath the Surface (of Language) is a hybrid form combining a map and an essay that deal with the relationship between language and surface, word and world, by the conceptual artist Jan Estep. The philosophical questions formulated by the artist in her essay are anchored in a personal context, set in a specific geographical space and illustrated by ph...

Properties of coatings on RFID p-Chips that support plasmonic fluorescence enhancement in bioassays.

Microtransponders (RFID p-Chips) derivatized with silver island film (SIF) have previously seen success as a platform for the quantification of low-abundance biomolecules in nucleic acid based assays and immunoassays. In this study, we further characterized the morphology of the SIF as well as the polymer matrix enveloping it by scanning electron microscopy (SEM). The polymer was a two-layer silane-based matrix engulfing the p-Chip and SIF. Through a series of SEM and confocal fluorescence microscopy experiments, we found the depth of the polymer matrix to be 1-2 μm. The radiative effects of the SIF/polymer layer were assessed by fluorescence lifetime imaging (FLIM) of p-Chips coated with the polymer to which a fluorophore (Alexa Fluor 555) was conjugated. FLIM images showed an 8.7-fold increase in fluorescence intensity and an increased rate of radiative decay, the latter of which is associated with improved photostability and both of which are linked to plasmonic enhancement by the SIF. Plasmonic enhancement was found to extend uniformly across the p-Chip and, interestingly, to a depth of about 1.2 μm. The substantial depth of enhancement suggests that the SIF/polymer layer constitutes a three-dimensional matrix that is accessible to solvent and small molecules such as fluorescent dyes. Finally, we confirmed that no surface-enhanced Raman scattering is seen from the SIF/polymer combination. The analysis provides a possible mechanism by which the SIF/polymer-coated p-Chips allow a highly sensitive immunoassay and, as a result, leads to an improved bioassay platform.

Interactions of Photosystem I with Plasmonic nanostructures

The plasmonic interaction e ects of various nanostructures on the uorescence properties of photosystem I as found by single-molecule spectroscopy are summarized. The used nanostructures are spherical Au nanoparticles, silver island lms as well as hexagonal arrays of nanometer-sized Auand Ag-triangles (the Fischer patterns). The uorescence emission of photosystem I is intensi ed due to coupling with these nanostructures. For single photosystem I complexes, enhancement factors of up to 37 were observed. The average enhancements vary between 2.2 for Au Fischer pattern and 9 for spherical Au nanoparticles. The enhancement of the uorescence of photosystem I demonstrates in all cases a strong wavelength dependence. This wavelength dependence can be explained by the spatially largely extended multichromophore composition of photosystem I complexes. From the viewpoint of the usability of these nanostructures for spectroscopic signal enhancement, the Fischer patterns are bene cial, due to their very low autoluminescence.

Bacterial adhesion on biomedical surfaces covered by micrometric silver Islands

A set of Cu-Mn-O and Ag-Cu-Mn-O films were sputter-deposited onto polished Ti-6Al-4V coupons and the microbiological adherence of Staphylococcus sp. was studied in these biomedical surfaces modified by using advanced ternary and quaternary oxides, these latter incorporated micrometric silver islands. Silver is known to have a natural biocidal character and its presence in the surface of Ti-6Al-4V forming large micrometric islands. In principle, predicted to enhance the antimicrobial properties of biomedical surfaces. Microbial adhesion tests were performed using collection strains and six clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The adherence study was performed using a previously published protocol by Kinnari et al. Collection strains and clinical strains showed decreased adherence to modified materials; however, only on the clinical strains were there statistically significant differences between Cu-Mn-O and Ag-Cu-Mn-O containing silver islands. Nanocrystalline silver dissolves and releases both Ag(+) and Ag(0) whereas other silver sources release only Ag+. We can conclude that nanocrystalline silver coating, confirmed by XRD, appears to alter the biological properties of the solution, particularly antimicrobial activity.

Ultra-fast pg/ml anthrax toxin (protective antigen) detection assay based on microwave-accelerated metal-enhanced fluorescence

Rapid presymptomatic diagnosis of Bacillus anthracis at early stages of infection plays a crucial role in prompt medical intervention to prevent rapid disease progression and accumulation of lethal levels of toxin. To detect low levels of the anthrax protective antigen (PA) exotoxin in biological fluids, we have developed a metal-enhanced fluorescence (MEF)–PA assay using a combination of the MEF effect and microwave-accelerated PA protein surface absorption. The assay is based on a modified version of our “rapid catch and signal” (RCS) technology previously designed for the ultra-fast and sensitive analysis of genomic DNA sequences. Technologically, the proposed MEF–PA assay uses standard 96-well plastic plates modified with silver island films (SiFs) grown within the wells. It is shown that the fluorescent probe, covalently attached to the secondary antibody, plays a crucial role of indicating complex formation (i.e., shows a strong MEF response to the recognition event). Microwave irradiation rapidly accelerates PA deposition onto the surface (“rapid catch”), significantly speeding up the MEF–PA assay and resulting in a total assay run time of less than 40min with an analytical sensitivity of less than 1pg/ml PA.

Plasmon-Enhanced Enzymatic Reactions 2:Optimization of Enzyme Activity by Surface Modification of Silver Island Films with Biotin-Poly (Ethylene-glycol)-Amine

Surface modification of silver island films (SIFs) was carried out with Biotin-Poly (Ethylene-glycol)-Amine (BEA), which acts as a cross-linker between the silver surface and horse radish peroxidase (HRP) enzyme for optimum plasmon-enhanced enzymatic activity. SIFs-deposited blank glass slides and SIFs-deposited 3-Aminopropyltriethoxysilane(APTES)-coated glass slides were used as our plasmonic surfaces.In this regard, three different extent of loading of SIFs were also prepared (low, medium and high) on APTES-coated glass slides. Streptavidin-linked HRP enzyme was attached to SIFs-deposited blank glass slides and SIFs-deposited APTES-coated glass slides through the well-known biotin-streptavidin interactions. The characterization of these surfaces was done using optical absorption spectroscopy. The loading of SIFs on glass slides was observed to have significant effect on the efficiency of plasmon-enhanced enzymatic activity, where an enhancement of 200% in the enzymatic activity was observed when compared to our previously used strategies for enzyme immobilization in our preceding work[1]. In addition, SIFs-deposited on APTES-coated glass slides were found to be re-usable for plasmon-enhanced enzymatic reactions unlike SIFs deposited on to blank glass slides.

Application of plasmonic silver island films in thin-film silicon solar cells

Silver nanoparticles can be used as light scattering elements for enhancing solar cell energyconversion efficiencies. The objective of our work is to gain more insight into the opticalproperties of silver nanoparticle films and their effect on the performance of solar cells. Weuse a common self-assembly technique to fabricate a range of silver island films ontransparent substrates and measure their reflectance and transmittance for visible and nearinfrared light. We demonstrate that it is possible to represent silver island films by aneffective medium with the same optical properties. The observed strong dependence onillumination side of the reflectance and absorptance, attributed to driving field effects, isreproduced very well. Thin-film silicon solar cells with embedded silver islandfilms were fabricated and it was found that their performance is reduced due toparasitic absorption of light in the silver island film. Simulations of these solar cells,where the silver island film is represented as an effective medium layer, show asimilar trend. This highlights the importance of minimizing parasitic absorption.

Mechanisms, timing, and rates of arid region mountain front recharge

Summary Arid region mountain front recharge (MFR) for two catchments (17.5 and 25.6 km 2 ) in the Silver Island Mountains, Utah, USA was evaluated by an analysis of catchment precipitation, mountain front and playa infiltration rates, aquifer parameters, and groundwater level responses in 59 shallow monitoring wells located at the distal end of the catchments. The 3–7 km long mountain front surfaces transition from alluvial fan deposits to a thin alluvial covering on lacustrine pediment surfaces. Precipitation and groundwater level data were collected from October 2005 to October 2010, which represents five recharge cycles. Average annual precipitation for all rain gauges during the 2005–2010 water years was 14.9 cm. Monitoring well water levels increased 91–97% of the time in response to storm events during times of general monitoring well water level increases and 29–38% of the time during times of general monitoring well water level declines. A surprising 81.7% of total catchment precipitation resulted in positive water level responses. Precipitation events as small as 2 mm resulted in positive water level responses and initial responses occurred within hours of some precipitation events. Water level responses that occur within hours of the larger precipitation events are attributed to focused groundwater recharge in near field braided stream channels. The time lag between the end of precipitation events and the maximum water level responses, which may be several days, is attributed to far field recharge. Direct MFR was calculated using a modified version of the water table fluctuation method. For the two catchments the average calculated direct MFR was 2.7–3.2% using PRISM precipitation data, and 3.7–4.5% using rain gauge data.

Rapid crystallization of l-arginine acetate on engineered surfaces using metal-assisted and microwave-accelerated evaporative crystallization

We report the application of our newly described crystallization technique, which employs silver island films (SIFs) and microwave heating, to rapid crystallization of L-arginine acetate (LAA). Using our technique, LAA crystals (~ 1.2 mm in length) were grown from a 20 μl solution in 1 min on surface functionalized SIFs. In control experiments (glass slides and at room temperature) the growth of LAA crystals (0.1-0.3 mm) took ~ 55 min.

Thermal stability of silver thin films on zirconia substrates

The thermal stability of silver thin films between 100nm and 820nm thick deposited onto single crystal yttria-stabilised zirconia (YSZ) substrates by evaporation was investigated by annealing the films between 250°C and 550°C for different durations. Films approximately 100nm thick were thermally unstable at temperatures as low as 250°C. A dewetting process occurred in which grain boundaries ruptured, to uncover the substrate and reduce the overall energy of the system, by a combination of grain boundary grooving at the outer surface and void growth at the Ag–YSZ interface. The surface self diffusion coefficient of Ag was determined from the kinetics of the process to be 2.6±0.3×10−5 cm2s−1 at 500°C. The resulting silver morphology ranged from ‘self-organised’ interconnected silver network structures to completely isolated silver islands. A structure predominance map of the rearrangement process is presented.

Rapid Crystallization of l-Alanine on Engineered Surfaces by Use of Metal-Assisted and Microwave-Accelerated Evaporative Crystallization

This study demonstrates the application of metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique to rapid crystallization of L-alanine on surface engineered silver nanostructures. In this regard, silver island films (SIFs) were modified with hexamethylenediamine (HMA), 1-undecanethiol (UDET), and 11-mercaptoundecanoic acid (MUDA), which introduced -NH(2), -CH(3) and -COOH functional groups to SIFs, respectively. L-Alanine was crystallized on these engineered surfaces and blank SIFs at room temperature and using MA-MAEC technique. Significant improvements in crystal size, shape, and quality were observed on HMA-, MUDA- and UDET-modified SIFs at room temperature (crystallization time = 144, 40 and 147 min, respectively) as compared to those crystals grown on blank SIFs. Using the MA-MAEC technique, the crystallization time of L-alanine on engineered surfaces were reduced to 17 sec for microwave power level 10 (i.e., duty cycle 100%) and 7 min for microwave power level 1 (duty cycle 10%). Raman spectroscopy and powder x-ray diffraction (XRD) measurements showed that L-Alanine crystals grown on engineered surfaces using MA-MAEC technique had identical characteristic peaks of L-alanine crystals grown using traditional evaporative crystallization.

Surface-Enhanced Fluorescence of Rhodamine 6G on the Assembled Silver Nanostructures

The fluorescence emission and enhancement of Rhodamine 6G on the silver island films (SiFs) with and without 4-Aminothiophenol molecules have been investigated. It was found that the SiFs without 4-Aminothiophenol molecules (PATP) have less contribution to the fluorescence enhancement. However, when PATP molecules as a spacer were deposited on the SiFs, obvious fluorescence enhanced effect was observed. The results show that the fluorescence enhancement depends on the morphology of the substrate surface and the distance between fluorophore molecules and the substrate surface. The experimental observations can be explained by local surface plasmon resonance and local field enhancement theory.

Metal-enhanced fluorescence exciplex emission

In this letter, we report the first observation of metal-enhanced exciplex fluorescence, observed from anthracene in the presence of diethylaniline. Anthracene in the presence of diethylaniline in close proximity to Silver Island Films (SIFs) shows enhanced monomer and exciplex emission as compared to a non-silvered control sample containing no silver nanoparticles. Our findings suggest two complementary methods for the enhancement: (i) surface plasmons can radiate coupled monomer and exciplex fluorescence efficiently, and (ii) enhanced absorption (enhanced electric near-field) further facilitates enhanced emission. Our exciplex studies help us to further understand the complex photophysics of the metal-enhanced fluorescence technology.

Metal Nanoparticles Sensitize the Formation of Singlet Oxygen

Singlet oxygen (O2) is known to play an indispensible role in the photodynamic therapy (PDT) treatment of cancer, and is an important oxidant for hydroperoxidation of olefins in organic synthesis. Singlet O2 is conventionally formed by sensitization by organic photosensitizers, such as Rose Bengal, silicon phthalocyanine, etc. These organic or organometallic dyes are, however, prone to photoinduced degradation and enzymatic degradation, which becomes problematic in PDT treatments, and reduces the efficiency of the generation of singlet O2. [5,8] It is, therefore, important to search for photosensitizers with highly efficient singlet O2 generation and large absorption coefficients that are photochemically more stable and less prone to enzymatic degradation. Previously, it was reported that the yield of singlet oxygen production by a photosensitizer, namely, Rose Bengal, was enhanced by a silver island film through the metal-enhanced absorption of photosensitizer. It was also reported that a gold nanodisk could enhance the phosphorescence decay rate of singlet oxygen, leading to a larger characteristic phosphorescence emission band of singlet oxygen at 1270 nm. In another two studies, it was observed that the quantum yield of singlet O2 formation generated by phthalocyanine photosensitizers can be enhanced by the presence of gold nanoparticles. Herein we report an unprecedented observation that singlet oxygen can be formed through direct sensitization by metal nanoparticles (M NPs, M=Ag, Pt, and Au) without the presence of any organic photosensitizers. Unambiguous experimental evidence includes direct observation of singlet oxygen emission at roughly 1268 nm, hydroperoxidation of cyclohexene, green fluorescence from a selective singlet oxygen fluorescent sensor, namely, Singlet Oxygen Sensor Green (SOSG, Molecular Probe), and quenching of singlet oxygen phosphorescence by sodium azide. As shown in Figure 1, photoexcitation of M NPs at the surface plasmon resonance absorption bands of Ag (d= 55, 42 nm), Pt (10 nm), and Au (22 nm) in D2O results in characteristic singlet oxygen emission at 1264 and 1268 nm, respectively. Control experiments show that in the absence of metal nanoparticles, photoexcitation of poly(vinyl pyrrolidone (PVP) in D2O using either 254 or 508 nm light did not result in any detectable singlet O2 emission signal (see the

Plasmon-Enhanced Enzymatic Reactions: A Study of Nanoparticle-Enzyme Distance and Nanoparticle Loading-Dependent Enzymatic Activity

A detailed investigation of the dependence of the efficiency of plasmon-enhanced enzymatic reactions on the distance between silver island films (SIFs) and horse radish peroxidase (HRP) enzyme and on the loading of SIFs on glass surfaces is presented. Three different extent of loading of SIFs on glass slides were used: 1) low, 2) medium and 3) high, which was characterized by using optical absorption spectroscopy and scanning electron microscopy. Streptavidin-linked HRP enzyme was deposited onto SIFs and glass slides by using three different strategies: strategy 1: biotin-avidin protein assay (distance between SIFs and HRP = 4-8 nm), strategy 2: self assembled monolayers (SAMs) (1-5 nm), strategy 3: polymer layer (1-5 nm). The efficiency of enzymatic conversion of O-phenylenediamine dihydrochloride (OPD) to a colored product by HRP on SIFs and glass surfaces was assessed by optical absorption spectroscopy. The distance between SIFs and HRP and the extent of loading of SIFs on the glass surfaces were shown to have significant effect on the efficiency of plasmon-enhanced enzymatic reactions. In this regard, up to an %250 increase in enzymatic conversion of OPD was observed from SIFs with high loading using strategy 1. In addition, we have studied the potential of repeated use of SIFs in plasmon-enhanced enzymatic reactions.

Singlet Oxygen Phosphorescence Enhancement by Silver Islands Films

Optical detection of singlet oxygen, a reactive oxygen species that plays a crucial role in a variety of biomedical processes, is hampered by its extremely low emission probability. Using plasmonic effects induced in silver islands films coated with C60, we have been able to enhance the near-IR phosphorescence of singlet oxygen by a factor of ca. 35. Both an enhanced production of singlet oxygen via plasmon-induced light absorption and the perturbation of its radiative rate constant are shown to account for this effect. The dependence of the enhancement factor on the properties of the silver island films and on the amount of C60 coated are discussed.

Absorption Enhancement in Peridinin–Chlorophyll–Protein Light-Harvesting Complexes Coupled to Semicontinuous Silver Film

We report on experimental and theoretical studies of plasmon-induced effects in a hybrid nanostructure composed of light-harvesting complexes and metallic nanoparticles in the form of semicontinuous silver film. The results of continuous-wave and time-resolved spectroscopy indicate that absorption of the light-harvesting complexes is strongly enhanced upon coupling with the metallic film spaced by 25 nm of a dielectric silica layer. This conclusion is corroborated by modeling, which confirms the morphology of the silver island film.