(TFBG) covered by silver nanowires aligned perpendicularly to the fiber axis. TBFGs are a convenient way to measure surrounding refractive index, as they provide intrinsic temperature-insensitivity and preserve the optical fiber structural integrity. With bare TFBGs, sensitivity is about 60 nm/RIU (refractive index unit) while when coated with a gold thin film, surface plasmon resonance can be excited leading to a sensitivity about 600 nm/RIU. In our case, we show that localized plasmon resonances can be excited on silver nanowires. These nanowires (100 nm diameter and about 2.5 µm length) were synthetized by polyol process (ethylene glycol reducing silver nitrate in the presence of poly (vinyl pyrrolidone and sodium chloride). The nanowires were aligned and deposited perpendicularly to the fiber axis on the gratings using the Langmuir-Blodgett technique in order to maximise the coupling between azimuthally polarized light modes and the localized plasmons. Excitation of surface plasmons at wavelengths around 1.5 µm occurred, leading to a dip in the polarization dependent losses of the grating. This dip is highly dependent of the surrounding refractive index, leading to a sensitivity of 650 nm/RIU, which is a 10-fold increase compared to bare gratings. We obtain results equal or slightly higher than those obtained using a gold layer on TFBGs. In spite of the comparable bulk refractometric sensitivity, the use of these oriented nanowire layers provide significantly higher contact surface area for biochemical analysis using bioreceptors, and benefit from stronger polarization selectivity between azimuthal and radially polarized modes.
The present work investigates the plasmonic properties and behaviour of silver nanocube monolayers deposited on thin gold films. Monolayers were deposited via the Langmuir-Blodgett method using a phospholipid as a passive spacer. Interparticle coupling was minimized by depositing at low surface pressures. The interaction of the nanocube monolayers with the gold films was mediated by utilizing polyelectrolyte layering to generate a passive spacer to control the distance between the cubes and substrate. Silver nanocubes were characterized by UV-Visible spectroscopy and transmission electron microscopy, and the monolayers were characterized by UV-Vis, and atomic force microscopy.
The behaviour of the plasmonic modes of supported strongly coupled silver nanocubes is studied. Silver nanocube monolayers with controlled particle density were fabricated via the Langmuir-Blodgett technique and deposited on substrates with varying refractive indices. Substrates include glass, thin films of silicon, and titanium oxide on glass. The dipolar and bonded dipolar modes are red shifted with increasing refractive index of the substrate. Surface-enhanced Raman spectroscopy (SERS) is used as a tool to probe the electric field enhancements of the silver nanocube monolayers. SERS enhancement of silver nanocube monolayers is found to be highly substrate dependant, typically decreasing with increasing refractive index of the underlying substrate. This work aims to find the source of this enhancement decrease, and distinguishes between effects related electromagnetic enhancement and effects caused by the optics of the Raman spectroscopy system itself.
We present a design of implementing plasmonic nanoparticles made from silver onto the surface of amorphous silicon based solar cells. When adding these silver nanoparticles we expect to see enhancements to the solar cells due to the plasmonic effects induced by the metal nanoparticles. The nanoparticles are used as subwavelength scattering elements to couple and trap light within the cell. In addition, the excited surface plasmon-polaritons promote a strong localized field enhancement which increases the cells ability to absorb light. Our choice of geometry of the nanoparticle is cubic rather than the traditional spherical geometry. We expect to see the cell perform better with the cubic shape due to the larger surface area it spans. We investigate the effects of these particles on to the performance of the solar cells, as well as introduce an intrinsic layer between the active p and n region creating a p-i-n solar cell configuration. We report the use of an FDTD simulator to characterize the optical performance of the solar cell. Both cubical and spherical nanoparticles made from silver were studied. Our simulations predict an overall increase of 67% (from 7.5% to 12.5) based on the p-i-n configuration with inclusion of the plasmonic particles onto the surface of the cells. Experimentally we verified the results by first fabricating a crystalline silicon-based solar cell with a p-n configuration and then placing the silver nanocubes onto the surface of the cell. An overall increase of about 28% was experimentally demonstrated (from 3.97% to 5.081%). We anticipate further increases with the p-i-n configuration.
In the present work plasmonic properties of metal nanocrystals, monocrystalline gold or silver nanocubes, nanorods, or nanocages deposited on planar substrates or on tilted fiber Bragg grating (TFBG) sensors have been fine tuned to enhance the performance of such novel sensing platforms. Superior refractive index sensitivities of nanocrystal/substrate or nanocrystal/TFBG have been observed and correlated with their plasmonic properties. Surface enhancement of Raman signal using nanocrystal coated TFBG was detected. The study proposes a novel fiber based sensing platform utilizing localized surface plasmon resonances.
Plasmonic properties of monolayers of strongly interacting silver nanocubes (AgNC) with controlled interparticle spacing are investigated. Uniform monolayers with controlled particle densities are made using the Langmuir-Blodgett
technique with passive phospholipid spacers, such as dioleoyl phosphatidylcholine (DOPC). Both extinction intensity
and wavelength of dipole-dipole coupling modes are tuned via particle spacing. The refractive indices of the substrates are used to tune dipolar and interparticle coupling modes via deposition onto thin films of silicon (0 - 25nm). By varying silicon film thickness it is possible to shift and control peak widths and position for both the dipole and interparticle dipole-dipole coupling modes. Control of plasmon shifts and interparticle spacing is applied towards the optimization of SERS substrates. SERS substrates using a Rhodamine B label are tuned at different excitation wavelengths which are in resonance with either the plasmon dipole, fluorescent dye, or interparticle coupling mode. Substrates display reproducible enhancement across multiple sites. This work presents methodology to design and optimize uniform silver nanocube SERS substrates through tuning of plasmon shifts and particle spacing.
In the present work we investigated the properties and behavior of plasmonic modes of silver nanocube monolayers with
respect to reflection and transmission of visible radiation. Uniform monolayers of low particle densities were created
using the Langmuir-Blodgett technique using the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) as a
passive spacer. Dipole-dipole coupling modes were avoided by depositing at low pressures to ensure sufficient spacing
between the nanocubes. The refractive index sensitivities of plasmonic modes for monolayers on glass, silicon thin
films, and bulk silicon wafers were measured using varying solutions of water and ethylene glycol. By varying the
refractive index of the substrates it is possible to investigate the relative contribution of plasmonic modes with respect to
absorption of the incident signal.
We report a novel plasmonic solar cell design implemented on an amorphous silicon platform. The enhancement of
the scattering and trapping of the light is achieved by embedding nano-metallic cubic particles within the cell’s
junction. Amorphous silicon cell with a thickness of 1200nm is used. The spectral absorption of the silicon cell is
limited to wavelengths larger than 1.1 u. Our proposed solar cell has a p-i-n configuration, with the amorphous
silicon as the photo-active layer. Silver cubic nanoparticles are embedded at different locations within the photoactive
layers of the solar cell. With the use of an FDTD simulator, we are able to characterize the optical
performance of the solar cell. Our results show that the plasmonic properties of the cubic nanoparticles are more
attractive for sensing applications compared to the traditional spherical configuration. The geometry of the cubic
nanoparticles enables control over plasmon resonances both in the resonant wavelength and the degree of field
enhancement. This is done by improving the refractive-index sensitivity on a thin silicon film, as well as increasing
the scattering and trapping of light. Our simulations predict that the silver metallic nanoparticles will enhance the
solar cell efficiency, by optimizing the plasmonic properties of the silver nanocube monolayer. We have achieved a
67% increase (from 7.5% to 12.5%) in the cell’s efficiency by adding plasmonics to traditional amorphous p-i-n
solar cell.
This paper presents a Surface Plasmon Resonance (SPR) fiber sensor capable of monitoring the deposition of thin
nm-scale polymer films. The sensor was used for in situ monitoring of the adsorption of 30 mono-layers of oppositely
charged polyelectrolytes with an overall thickness of each individual monolayer less than 0.55 nm. The in situ
monitoring of the formation of multi-layer structures was implemented through the excitation of SPR on the surface of a
gold-coated fiber with a Tilted Fiber Bragg Grating (TFBG) written in the core of the optical fiber.
A new Surface Plasmon Resonance (SPR) sensor design is proposed and fabricated based on an optical fiber with a photo-written Tilted Fiber Bragg Grating (TFBG) and a thin gold deposited layer. The TFBG allows the transfer of light from the core mode into a multitude of cladding modes, each wavelength corresponding to a different incidence angle. The most pronounced SPR effect was obtained for a gold thickness of 20 nm, however every tested thickness showed SPR at a certain level. To characterize the uniformity of gold films, the coated fiber were imaged using Atomic Force Microscopy (AFM) and showed a high level of graininess, as expected from such thin layers. Scanning Electron Microscope (SEM) images were used to characterize the quality of the gold coating before and after experiments. Despite the high non-uniformity and graininess of gold coating, the angular spread of SPR is as narrow as expected from theory. The sensitivity obtained reaches 454 nm per refractive index unit.
Surface-Enhanced Raman Scattering (SERS) spectroscopy and Flow Linear Dichroism (FLD) technique have been employed to study the anticancer agent fagaronine and its derivative ethoxidine - double inhibitors of DNA topoisomerases I and II. Cooperative use of two methods permitted (i) to determine the molecular determinants of the drug-DNA interactions; (ii) to monitor in real time the process of topo I inhibition by these anticancer agents. FLD technique allowed us to identify the mode of drug interactions with the DNA as a 'major groove intercalation' and to determine orientation of the drugs chromophores within the complexes. Using SERS spectroscopy we have determined the drugs molecular determinants interacting with the DNA. FLD was also used for real time monitoring of the process of sc DNA relaxation by topo I and of inhibition of relaxation with the pharmaceuticals. Ethoxidine was found to exhibit the same activity of inhibition of sc DNA relaxation as fagaronine at the 10-fold less concentration. The proposed SERS-FLD combined approach demonstrates the new perspectives for screening new pharmaceuticals due to its relative simplicity and low expense, high sensitivity and selectivity, and, finally, possibility of real-time monitoring of the structure-function correlation within the series of drug derivatives.
Camptothecin (CPT) derivatives are the well known inhibitors of the human DNA topoisomerase (topo) I. Two of them, irinotecan and topotecan, are just in the clinics; 9-amino- CPT is on the stage II of clinical trials, and the active search for new derivatives is now in progress. Stability of the CPT derivatives on their way to the target and resistance of cancer cells to these drugs present the crucial problem of the chemotherapy. Human serum albumin (HSA) is the mediator of transport and metabolism of numerous pharmaceuticals in the blood and P-glycoprotein (P- gp) plays a crucial role of the mediator of the multidrug resistance (MDR) of the cancer cells. This paper present the result of analysis of molecular interactions of some drugs of CPT family with the HSA and P-gp. Induced circular dichroism (CD) and Raman techniques have been applied for monitoring molecular interaction of drugs with HSA as well as to identify the conformational transition of the protein induced by the drug binding. Drug molecular determinants responsible for interaction have been identified and their binding sites within the HSA have been localized. New cancer cells lines exhibiting an extremely high level of MDR resistance have been established and were shown to contain the P-gp overproduced in the quantities of 35 percent from the all membrane proteins. The membrane fractions of these cells with the controls presented by the membranes of the parental membrane proteins. The membrane fractions of these cells with the controls presented by the membranes of the parental sensitive cells may be used as a model system for spectroscopic analysis of the specific pharmaceuticals/P-gp interactions.
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