Showing papers in "Plasmonics in 2007"

Review of Some Interesting Surface Plasmon Resonance-enhanced Properties of Noble Metal Nanoparticles and Their Applications to Biosystems

Abstract: Noble metal, especially gold (Au) and silver (Ag) nanoparticles exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR). In this review, we discuss the SPR-enhanced optical properties of noble metal nanoparticles, with an emphasis on the recent advances in the utility of these plasmonic properties in molecular-specific imaging and sensing, photo-diagnostics, and selective photothermal therapy. The strongly enhanced SPR scattering from Au nanoparticles makes them useful as bright optical tags for molecular-specific biological imaging and detection using simple dark-field optical microscopy. On the other hand, the SPR absorption of the nanoparticles has allowed their use in the selective laser photothermal therapy of cancer. We also discuss the sensitivity of the nanoparticle SPR frequency to the local medium dielectric constant, which has been successfully exploited for the optical sensing of chemical and biological analytes. Plasmon coupling between metal nanoparticle pairs is also discussed, which forms the basis for nanoparticle assembly-based biodiagnostics and the plasmon ruler for dynamic measurement of nanoscale distances in biological systems.

Gold Nanoparticle Based FRET for DNA Detection

Abstract: The nanoscience revolution that sprouted throughout the 1990s is having great impact in current and future DNA detection technology around the world. In this review, we report our recent progress on gold nanoparticle based fluorescence resonance energy transfer assay to monitor DNA hybridization as well as the cleavage of DNA by nucleases. We tried to discuss a reasonable account of the science and the important fundamental work carried out in this area. We also report the development of a compact, highly specific, inexpensive and user-friendly optical fiber laser-induced fluorescence sensor based on fluorescence quenching by nanoparticles to detect single-strand DNA hybridization at femtomolar level.

Long Range Surface Plasmons for Observation of Biomolecular Binding Events at Metallic Surfaces

Abstract: A long range surface plasmon (LRSP) is an electromagnetic wave propagating along a thin metal film with an order of magnitude lower damping than conventional surface plasmon (SP) waves. Thus, the excitation of LRSP is associated with a narrower resonance and it provides larger enhancement of intensity of the electromagnetic field. In surface plasmon resonance (SPR) biosensors, these features allow a more precise observation of the binding of biomolecules in the proximity to the metal surface by using the (label-free) measurement of refractive index (RI) variations and by SP-enhanced fluorescence spectroscopy. In this contribution, we investigate LRSPs excited on a layer structure consisting of a fluoropolymer buffer layer, a thin gold film, and an aqueous sample. By implementing such structure in an SPR sensor, we achieved a 2.4- and 4.4-fold improvement of the resolution in the label-free and fluorescence-based detection, respectively, of the binding of biomolecules in the close proximity to the surface. Moreover, we demonstrate that the sensor resolution can be improved by a factor of 14 and 12 for the label-free and fluorescence-based detection, respectively, if the biomolecular binding events occur within the whole evanescent field of LRSP.

Optical Nanofocusing on Tapered Metallic Waveguides

Abstract: Tapered metal wires show a remarkable ability to ‘squeeze’ the lateral extent of a propagating surface-plasmon-polariton mode as it travels toward the tip of the taper. The transformation can be continued well below the diffraction limit to terminate at a nanoscale apex where intense near-fields are created. We perform the first full numerical simulations to investigate and quantify this phenomenon. We find optimal angles for maximal tip-field enhancement on conical wires by considering absorption, scattering to radiation and reflection. The optimal parameters we obtain contradict the conditions for adiabatic tapering, thereby advocating the use of numerical simulations. Despite the influence of losses, nanofocusing is still highly efficient for a broad range of practical metals, visible wavelengths and taper geometries. Diverse nano-optic applications can benefit directly and significantly from the results.

Optimization of Nanoparticle Size for Plasmonic Enhancement of Fluorescence

Abstract: This paper reports on the enhancement of fluorescence that can result from the proximity of fluorophores to metallic nanoparticles (NPs). This plasmonic enhancement, which is a result of the localized surface plasmon resonance at the metal surface, can be exploited to improve the signal obtained from optical biochips and thereby lower the limits of detection. There are two distinct enhancement effects: an increase in the excitation of the fluorophore and an increase in its quantum efficiency. This study focuses on the first of these effects where the maximum enhancement occurs when the NP plasmon resonance wavelength coincides with the fluorophore absorption band. In this case, the excitation enhancement is proportional to the square of the amplitude of the electric field. The scale of the enhancement depends on many parameters, such as NP size and shape, metal type, and NP–fluorophore separation. A model system consisting of spherical gold/silver alloy NPs, surrounded by a silica spacer shell, to which is attached a fluorescent ruthenium dye, was chosen and the dependence of the fluorescence enhancement on NP diameter was investigated. Theoretical calculations, based on Mie theory, were carried out to predict the maximum possible enhancement factor for spherical NPs with a fixed composition and a range of diameters. Spherical NPs of the same composition were fabricated by chemical preparation techniques. The NPs were coated with a thin silica shell to overcome quenching effects and the dye was attached to the shell.

Aligned Silver Nanoparticles on Rippled Silicon Templates Exhibiting Anisotropic Plasmon Absorption

Abstract: Aligned silver nanoparticles, grown by combining two simple bottom-up techniques, are reported. Physical vapor-deposited silver adatoms are shown to form nanoparticles preferentially in the valleys of rippled silicon templates prepared by low-energy ion bombardment. A 35-nm ripple periodicity produced highly aligned structures with a 0.21 eV polarization-dependent shift in the plasmon resonance peak. The speed and simplicity of the method is viable for cost-effective, large-scale production of mesoscale aligned nanostructures with adjustable periodicity.

Fluorescence From Metallic Silver and Iron Nanoparticles Prepared by Exploding Wire Technique

Abstract: The observation of intense visible fluorescence from silver and iron nanoparticles in different solution phases and surface capping is reported here. Metallic silver and iron nanoparticles were obtained by exploding pure silver and iron wires in double distilled water. The adsorption of bovine serum albumin protein on the silver nanoparticles showed enhanced fluorescence. The presence of polyvinyl pyrrolidone polymer in the exploding medium resulted in a stabilized growth of iron nanoparticles with enhanced fluorescence intensity. The fluorescence was found to be surface/interface-dependant and is attributed to electronic transitions among characteristic interface energy bands. The magnetic nature of iron nanoparticles was confirmed from the hysteresis measurements.

Application of Surface-Enhanced Raman Spectroscopy for Detection of Beta Amyloid Using Nanoshells

Abstract: Currently, no methods exist for the definitive diagnosis of AD premortem. β-amyloid, the primary component of the senile plaques found in patients with this disease, is believed to play a role in its neurotoxicity. We are developing a nanoshell substrate, functionalized with sialic acid residues to mimic neuron cell surfaces, for the surface-enhanced Raman detection of β-amyloid. It is our hope that this sensing mechanism will be able to detect the toxic form of β-amyloid, with structural and concentration information, to aid in the diagnosis of AD and provide insight into the relationship between β-amyloid and disease progression. We have been successfully able to functionalize the nanoshells with the sialic acid residues to allow for the specific binding of β-amyloid to the substrate. We have also shown that a surface-enhanced Raman spectroscopy response using nanoshells is stable and concentration-dependent with detection into the picomolar range.

Importance of Metal–Adsorbate Interactions for the Surface-enhanced Raman Scattering of Molecules Adsorbed on Plasmonic Nanoparticles

Abstract: The interaction between adsorbates of different nature and plasmonic nanoparticles is reviewed here on the basis of the work done in our laboratory in the past few years. The paper is structured for analyzing the interaction of adsorbates with metal nanoparticles as function of the interacting atom (O, N, or S) and the adsorbate conforma- tion. In the study of the adsorption of molecular species on metals, it is necessary to take into account that different interaction mechanisms are possible, leading to the exis- tence of different molecular forms (isomers or conformers). These forms can be evidenced by changing the excitation wavelength, due to a resonant selection of these wave- lengths. Charge-transfer complexes and electrostatic inter- actions are the usual driving forces involved in the interaction of adsorbates on metal surfaces when these metallic systems are used in wet conditions. The under- standing of the metal-adsorbate interaction is crucial in the surface functionalization of metal surfaces, which has a growing importance in the development of sensing systems or optoelectronic devices. In relation to this, special attention is paid in this work to the study of the adsorption of calixarene host molecules on plasmonic nanoparticles.

Preparation and optical characterization of core-shell bi-metallic nanoparticles

Abstract: Chemical approaches allow for the synthesis of highly defined metal heterostructures, such as core-shell nanoparticles. As the material of metal nanoparticles determines the plasmon resonance-induced absorption band, the control of particle composition results in control of the absorption maximum position. Metal deposition on gold or silver nanoparticles was used to prepare core-shell particles with modified optical properties with respect to monometal nanoparticles. UV-vis spectroscopy on solution-grown and immobilized particles was conducted as ensemble measurements, complemented by single particle spectroscopy of selected structures. Increasing layers of a second metal, connected to a dominant contribution of the shell material to the extinction spectrum, lead to a shift in the absorption band. The extent of shell growth could be controlled by reaction time or the concentration of either the metal salt or the reducing agent. Additional to the optical characterization, the utilization of AFM, SEM and TEM yielded important information about the ultrastructure of the nanoparticle complexes.

Surface Plasmon-Enhanced Spectroscopy and Photochemistry

Abstract: A review of selected recent contributions to the area plasmon-enhanced spectroscopy and photochemistry is presented.

SPR-based DNA Detection with Metal Nanoparticles

Abstract: In this short review paper, we summarize some of our ideas to utilize gold nanoparticles for the enhancement of surface plasmon resonance signals on DNA microarray. The hybridization of target-DNA capped gold nanoparticles with probe DNA on surface provides ca. ten times stronger optical contrast compared with that of target-DNA molecules. Our simulation result based on the Maxwell-Garnet theory explains well our experimental data and proves a potential of metallic nanoparticles for the substantial sensitivity enhancements for biosensor application in DNA diagnostics and bio-affinity studies, which leads to the fabrication of high resolution DNA microarrays.

Single-Molecule Studies of Enhanced Fluorescence on Silver Island Films

Abstract: We investigated enhanced fluorescence of Cyanine 5 dyesnear silver island films (SIFs) by the use of single moleculespectroscopic method. We found that, on average, the Cy5molecules are 18-fold brighter on SIFs than on a glasssurface and that single-molecule lifetimes are 10-foldshorter on SIFs as compared to glass. We observed Cy5molecules until photobleaching occurred and found that themolecules on the SIF emitted 20-fold more photons ascompared to those on glass prior to photobleaching. Theseresults demonstrate that the use of fluorophore–metalinteractions can increase the brightness and photostabilityof fluorophores for single-molecule detection.During the past decade, there has been considerableprogress in the development of fluorescence probes. Manyprobes, such as the cyanine dyes, have high extinctioncoeffiecients and high quantum yields. Hence, it is unlikelythat the future probe development will result in dramaticincreases in detectability for small organic fluorphores. Forthis reason, there is an interest in quantum dots andpolymeric probes. In the past years we have taken adifferent approach to create improved probes, this being theuse of metallic nanoparticles [1–3]. Ensemble experimentshaverevealedthatproximitytosilverparticlescouldincreasethe intensity and photostability of fluorphores [4–9]. Thiseffect is due to the through-space near-field interactionbetween the fluorphore and surface plasmons on the metals.Thus, the use of metallic nanostructure to enhancefluorescence has great potential for applications in thefields of medical diagnostics and biotechnology.The fluorescence spectral properties of fluorphores areespecially important for sensitive detection. The photo-stability of the fluorphore resolves the time it can beobserved prior to photobleaching. Hence, it is of interest todetermine if the improved spectral properties observed atthe ensemble level extends to the single-molecule level.The interactions of fluorophores with metallic particleshave been studied theoretically and empirically at thesingle-molecule level in recent years [10–13]. In thesereports, the major concern was the dependence of theemission rate on the distance between the dye layer and themetallic surface. The emission can be quenched due toradiation energy transfer to the metal as molecules adsorbeddirectly on the surface [12, 13]. Another consideration is theenhanced fluorescence due to increased electromagneticfield of surface plasmon and/or enhanced quantum yield[10, 11]. Therefore, we examined the widely used fluores-cent probe Cy5 near SIFs. These films consist of sub-wavelength-size silver particles on a glass surface [4, 5].Our single-molecule experiments of this system reveal boththe spectral changes due to the metal particles and theheterogeniety due to a range of fluorophore–metaldistances.For these studies, the Cy5 molecules were spin-coatedonto the SIFs from an aqueous solution containing 0.5%polyvinyl alcohol (PVA). Initially, we examined theensemble emission spectra in which the Cy5 concentrationis 20-fold higher than for the single-molecule experiments(Figure 1). Both Cy5 spectra exhibit emission maxima near680 nm. A significant enhancement in fluorescenceemission is clearly evident on silvered surfaces. Thepresence of silver nanostructure did not distort the Cy5spectrum. Additionally, the SIF sample without Cy5 did notcontribute significant background. This initial ensembleresult indicates that the Cy5 dyes deposited on SIF display

Comparison of Performance Parameters of Conventional and Nano-plasmonic Fiber Optic Sensors

Abstract: A detailed comparative analysis is carried out between two fiber optic surface plasmon resonance (SPR) sensor probes with different bimetallic configurations One consists of a step arrangement of thin layers of silver and gold Another one consists of alloy layer formed of spherical silver and gold nanoparticles Their sensitivity and detection accuracy are compared Better configuration is predicted with proper logics and rationales

Sensitive and Label-Free Detection of DNA by Surface Plasmon Resonance

Abstract: While an array of technologies based on radioactive labels or luminescent tags are dominant in modern biomedical research on DNA, surface plasmon resonance (SPR) and SPR imaging measurements are sensitive, rapid, and label-free. This review summarizes recent advances in the development of SPR and coupled techniques and their applications in DNA research, including the gene analysis at trace levels and studies of DNA–protein and DNA–drug interactions.

Tunable Assembly of Peptide-coated Gold Nanoparticles

Abstract: The interaction between peptides and gold surfaces has increasingly been of interest for bionanotechnology applications To more fully understand how to control such interactions, we have studied the optical properties of peptide-modified gold nanoparticles as a function of peptide composition, pH of the surrounding medium, and peptide concentration We show using localized surface plasmon resonance, transmission electron microscopy, and surface-enhanced Raman scattering (SERS) that selected “gold-binding peptides” (GBPs), similar to those isolated for binding to gold films using yeast display, can bind to gold nanoparticles at a variety of pHs Peptide modifications of nanoparticles can lead to irreversible particle aggregation when the pH of the solution is kept below the isoelectric point (pI) of the peptide However, at pHs above the peptide’s pI, particles remain stable in solution, and peptides remain bound to the particles possibly through amine coordination of gold Additionally, we demonstrate the potential in using SERS for the direct detection of GBPs on gold-silica nanoshells, eliminating the need for indirect labeling methods

Modeling Fluorescence Enhancement from Metallic Nanocavities

Abstract: We study the excitation and emission enhancement mechanisms for fluorescence from molecules confined within subwavelength metal apertures, or nanocavities. The variation in these enhancements with wavelength is calculated for individual round nanocavities in gold of varying diameters and dielectric environments. Enhancement peaks are associated with localized surface plasmon resonances of the nanocavity. In addition, these enhancements strongly vary with location within the nanocavity. These results should aid future work in maximizing overall fluorescence enhancement from these structures.

Modulation of Optical Properties of Gold Nanorods on Addition of KOH

Abstract: Gold nanorods are known to exhibit two distinct surface plasmon oscillations namely, transverse and longitudinal bands corresponding to oscillations of conduction electrons along width and length of gold nanorods Considerable changes in these surface plasmon resonance peak positions occurred when KOH was added to the nanorod solution Nanorods with initial longitudinal plasmon band at 739, 796, and 895 nm are studied with variation in KOH concentration While the longitudinal plasmon resonance peak showed blue shift, transverse plasmon resonance peak exhibited only intensity variations Changes could be attributed to the shape transition of gold nanorods on variation of pH in the solution Shape transition of gold nanorods is confirmed by transmission electron microscopy images

Plasmonic DNA: Towards Genetic Diagnosis Chips

Abstract: The present paper summarizes some of our activities in the field of plasmonic DNA and genetic diagnosis, presenting our system and its capabilities before showing data related to the design and use of functionalized biochips of increasing complexity along with various experimental hybridization conditions, including solutions containing one type of purified synthetic short oligonucleotides or PCR-amplified DNA samples from patients. The diagnosis capability of our system was evaluated by detecting several point mutations that alter the function of the CFTR gene and cause cystic fibrosis, a frequent monogenic disorder selected as a clinical model system.

Assays Based on Differential Adsorption of Single-stranded and Double-stranded DNA on Unfunctionalized Gold Nanoparticles in a Colloidal Suspension

Abstract: Under certain conditions, single-stranded DNA adsorbs to negatively charged gold nanoparticles in a colloid whereas double-stranded DNA does not. We present evidence that this phenomenon can be explained by the difference in their electrostatic properties that in turn reflects conformational differences. The ability to discriminate the hybridization state of DNA on the basis of adsorption behavior can be utilized to design simple colorimetric and fluorimetric assays that take advantage of plasmon resonance in the gold nanoparticles. We present examples where we detect specific target sequences in oligonucleotides and in genomic DNA. Because conformational changes in special DNA sequences can also be induced by analytes such as potassium, we report a potassium ion detection scheme based on the same principle.

Surface Plasmon Dynamics of High-Aspect-Ratio Gold Nanorods

Abstract: Ultrafast transient absorption studies are reported for high-aspect-ratio gold nanorods that were fabricated by electrochemical deposition in polycarbonate templates The nanorods are 60 nm in diameter with distribution of lengths of up to 6 μm The average aspect ratio was ∼50, resulting in a longitudinal surface plasmon resonance (SPRL) band in the mid-IR, as well as a transverse (SPRT) band in the visible The rods were excited at 400 nm and probed at a range of wavelengths from the visible to the mid-IR to interrogate both SPR bands The dynamics observed, including the electron–phonon coupling time and coherent acoustic breathing mode oscillations, closely resemble those previously reported for gold spherical nanoparticles and smaller-aspect-ratio nanorods The electron–phonon coupling time was similarly determined to be 33 ± 02 ps for both of the SPR bands Also, oscillations with a 32-ps period were observed for probing near the SPRT band in the visible region due to impulsive coherent excitation of the acoustic breathing mode, which are consistent with the 60-nm diameter of the nanorods determined by scanning electron microscopy The results demonstrate that the dynamics for long gold nanorods are similar to those for smaller nanoparticles

Surface Plasmon Enhancement at a Liquid-Metal-Liquid Interface

Abstract: Herein, we report the first experimental demonstration of surface plasmon enhancement at a liquid–metal–liquid interface using a pseudo-Kretschmann geometry. Pumping gold nanoparticle clusters at the interface of a p-xylene–water mixture, we were able to measure a fluorescence enhancement of three orders of magnitude in Rose Bengal at an excitation wavelength of 532 nm. The observed increase is due to the local electric field enhancement and the reduction of the fluorescence lifetime of dye molecules in the close vicinity of the metal surface. Theoretical modeling using the T-matrix method of the electric field intensity enhancement of emulated surfaces supports the experimental results. This new approach will open a new road for the study of dynamic systems using plasmonics.

Phase Transition and Optical Properties of DNA–Gold Nanoparticle Assemblies

Abstract: We review recent work on DNA-linked gold nanoparticle assemblies. The synthesis, properties, and phase behavior of such DNA–gold nanoparticle assemblies are described. These nanoparticle assemblies have strong optical extinction in the ultraviolet and visible light regions; hence, the technique is used to study the kinetics and phase transitions of DNA–gold nanoparticle assemblies. The melting transition of DNA–gold nanoparticle assemblies shows unusual trends compared to those of free DNA. The phase transitions are influenced by many parameters, such as nanoparticle size, DNA sequence, DNA grafting density, DNA linker length, interparticle distance, base pairing defects, and disorders. The physics of the DNA–gold nanoparticle assemblies can be understood in terms of the phase behavior of complex fluids, with the colloidal gold interaction potential dominated by DNA hybridization energies.

Surface-plasmon enhancement of Brillouin light scattering from gold-nanodisk arrays on glass

Abstract: Enhancement of Brillouin light scattering (BLS) at the wavelength of 532 nm was observed from Rayleigh-like and Sezawa-like acoustic modes of alkaline-earth boro-aluminosilicate glass covered with periodic arrays of gold nanodisks. This enhancement is attributed to mediation of surface plasmons of the nanodisks. For nanodisks with diameters of 71 nm to 90 nm, heights of 30 nm, and periodicity of 100 nm, the maximum measured surface-plasmon enhancement of BLS intensity was, respectively, ~ 2.4 and ~ 5.6 for Rayleigh-like and Sezawa-like modes, relative to the intensity from a gold film with the same fractional coverage area but without surface-plasmon coupling. The maximum for the Rayleigh-like modes occurs with the smallest-diameter nanodisks, and that for the Sezawa-like modes occurs with the largest-diameter nanodisks. The angular dependence is relatively broad. Calculations employing the discrete dipole approximation were used to predict the electric-field intensities in the gold disks and nearby glass as a function of nanodisk diameter. The average calculated intensity at the top surface of the gold increases with decreasing diameter, consistent with the experimental results for Rayleigh-like modes and the expectation that surface ripple is the dominant scattering mechanism for such modes. The results of this study suggest that nanodisk arrays can provide a platform for practical implementation of surface-enhanced BLS analogous to other surface-enhanced spectroscopies, and suggest the additional possibility of substantially extending the range of wave numbers in BLS through plasmonic-crystal band folding.

The Use of Polarization-dependent SERS from Scratched Gold Films to Selectively Eliminate Solution-phase Interference

Abstract: Polarization-dependent surface-enhanced Raman scattering (SERS) was studied for oxazine 720 molecules adsorbed on a scratched gold surface placed in situ and under electrochemical control. A quantitative method for evaluating the observed polarization dependence will be introduced. This method takes into account the polarization artifacts caused by optical elements in the light microscope used for Raman microscopy. Intensity of the SERS obtained from oxazine 720 adsorbed on scratches in gold showed a polarization dependence after correction was made for these artifacts. In contrast, intensity of the ordinary Raman signal obtained from perchlorate ions in the solution above a scratched gold surface was found to be polarization-independent. Therefore, polarization effects can be used to selectively remove solution-phase interference signals from the SERS spectrum of an adsorbed analyte. These polarization effects were found to be independent of the applied potential, meaning the methodology is applicable to electrochemical SERS studies.

Tailoring the parameters of nanohole arrays in gold films for sensing applications

Abstract: Subwavelength hole arrays in metal films have the potential to exhibit narrow and high refractive index (RI) sensitive transmission features. We have previously demonstrated that such features can arise from the coupling between Wood anomalies (WAs) and surface Plasmon polaritons (SPPs) on opposite sides of the metal film, the "WA-SPP" effect. Rigorous coupled-wave analysis (RCWA) calculations on a 2D model, which are shown to give WA-SPP features very similar to that of 3D Finite-Difference Time- Domain (FDTD) calculations, are performed to determine how system parameters influence the strength of the WA-SPP effect. Herein we show that the optimum values for the film thickness and hole diameter are 45 and 175 nm, respectively.

Profile simulation and fabrication of gold nanostructures by separated nanospheres with oblique deposition and perpendicular etching

Abstract: This paper investigates in detail the profiles of the nanostructures fabricated by nanosphere lithography through oblique deposition and perpendicular etching. 2D or 3D nanostructures can be achieved by this cost-effective method. Because the optical response of a particular nanoparticle depends on its size and shape, this angle deposition method can produce various shapes of nanostructures, which are suitable for localized surface plasmon resonance biosensor applications. The nanostructure profiles under various deposition and etching conditions are simulated in our work. The calculated 3D profiles are verified by the 3D nanostructures fabricated in our experiments, and the calculated 2D profiles are in good agreement with the fabricated nanocrescents reported by another research group. This paper gives a full theoretical solution of the obtainable nanostructure shapes by nanosphere lithography utilizing oblique deposition and perpendicular etching.

Plasmon Enhancement of Organic Photovoltaic Efficiency in Tandem Cells of Pentacene/C 60

Abstract: The effects of thin silver films embedded in a tandem pentacene/C 60 photovoltaic cell are investigated. A 2 nm Ag film improves the device's power efficiency under white light illumination from 0.32% to 1.11% by almost doubling its open circuit voltage and enhancing its short circuit current density. The doubled open circuit voltage is due to the formation of two separated photovoltaic pentacene/C 60 cells in series where discontinuous silver clusters provide carrier recombination centers. The increased photocurrent density is partly ascribed to improved charge separation and transport associated with the silver layer. In addition, wavelength dependent measurements suggest that plasmon-enhanced light absorption by pentacene due to surface plasmon resonance of silver nanoparticles contributes as much as a factor of 4 to the power efficiency near the plasmon resonance around 450 nm.

Fluorescence Resonance Energy Transfer Near Thin Films on Surfaces

Abstract: A theory is developed for resonant energy transfer between donor and acceptor molecules outside of a solid coated with a thin film. The energy transfer rate is expressed in terms of a second-rank tensor, allowing one to consider all possible orientations of the transition dipole moments of the molecules. The theory of images is employed to construct expressions valid in the near-field approximation. This theory is extended to the full electrodynamic theory valid over all distances. Connections are made between the expressions for the image charges and the Fresnel coefficients from optics. It is found that the energy transfer rates are strongly influenced by surface resonances, including the interfacial surface plasmons and the two-dimensional plasmon of a metallic film. The possibility of the film supporting Fabry–Perot resonator modes is discussed.

Nanoscale fabrication of a plasmonic dimple lens for nano-focusing of light

Abstract: The extent to which light can be focused with conventional optics is limited to λ/2 by the phenomenon of diffraction. Optical energy needs to be focused to less than 100nm to enable improvement and innovation in nanoscale applications. A novel lens structure to focus surface plasmons to a few tens of nanometer with high throughput is described here. This paper outlines the theoretical design and fabrication considerations of this novel plasmonic lens structure.