| 11. |
- Andreasson, Jakob, 1975, et al.
(författare)
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Franck-Condon higher order lattice excitations in the LaFe(1-x)Cr(x)O3 (x=0, 0.1, 0.5, 0.9, 1.0) perovskites due to Fe-Cr charge transfer effects
- 2007
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Ingår i: Physical Review B. ; 75, s. 104302-
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Tidskriftsartikel (refereegranskat)abstract
- First and higher order lattice excitiations in the B-site disordered perovskites LaFe(1-x)Cr(x)O3 (x = 0, 0.1, 0.5, 0.9, 1) and La(0.835)Sr(0.165)Fe(0.5)Cr(0.5)O(3-d) are investigated using temperature dependent and polarised inelastic light scattering [lambda = 515 nm (2.41 eV) and 676 nm (1.83 eV)] on oriented crystallites.A peak at approximately 2.4 eV in the imaginary part of the dielectric function of LaFe(0.5)Cr(0.5)O3 is assigned to a charge transfer from Fe 3+ (d5) to Cr 3+ (d3) ions and coupled the appearance of an intense Ag-like mode at approximately 700 cm-1 in the Raman data. This excitation is identified as a symmetric oxygen breathing mode activated by the Fe-Cr charge transfer through an orbital coupling mechanism. Higher order scattering (up to 7th order) of the intrinsic Raman active symmetric breathing mode is also explained by an orbital mediated, electron-phonon coupling, similar to the Franck-Condon effect observed in the Jahn-Teller active perovskite structured manganite LaMnO3. These results show that the Franck-Condon mechanism is a more common mechanism for resonant higher order scattering in solids than previously believed and propose the LaFe(1-x)Cr(x)O(3) system as a model system for electron-phonon coupling and higher order Raman scattering in solids.
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| 12. |
- Brian, Björn, 1980, et al.
(författare)
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Sensitivity enhancement of nanoplasmonic sensors on low refractive index substrates
- 2009
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 17:3, s. 2015-2023
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Tidskriftsartikel (refereegranskat)abstract
- Metal films perforated by nanoholes constitute a powerful platform for surface plasmon resonance biosensing. We find that the refractive index sensitivity of nanohole arrays increases if their resonance is red-shifted by increasing the separation distance between holes. However, an additional sensitivity enhancement occurs if the nanohole sensors are manufactured on low index substrates, despite the fact such substrates significantly blue-shift the resonance. We find a ∼40% higher bulk refractive index sensitivity for a system of -100 nm holes in 20 nm gold films fabricated on Teflon substrates (n=1.32) compared to the case when conventional glass substrates (n=1.52) are used. A similar improvement is observed for the case when a thin layer of dielectric material is deposited on the samples. These results can be understood by considering the electric field distribution induced by the so-called antisymmetric surface plasmon polariton in the thin gold films.
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| 13. |
- Chen, Si, 1985, et al.
(författare)
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Ultrahigh sensitivity made simple : nanoplasmonic label-free biosensing with an extremely low limit-of-detection for bacterial and cancer diagnostics.
- 2009
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Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 20:43
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Tidskriftsartikel (refereegranskat)abstract
- We present a simple and robust scheme for biosensing with an ultralow limit-of-detection down to several pg cm(-2) (or several tens of attomoles cm(-2)) based on optical label-free biodetection with localized surface plasmon resonances. The scheme utilizes cost-effective optical components and comprises a white light source, a properly functionalized sensor surface enclosed in a simple fluidics chip, and a spectral analyzer. The sensor surface is produced by a bottom-up nanofabrication technique with hole mask colloidal lithography. Despite its simplicity, the method is able to reliably detect protein-protein binding events at low picomolar and femtomolar concentrations, which is exemplified by the label-free detection of the extracellular adherence protein (EAP) found on the outer surface of the bacterium Staphylococcus aureus and of prostate-specific antigen (PSA), which is believed to be a prostate cancer marker. These experiments pave the way towards an ultra-sensitive yet compact biodetection platform for point-of-care diagnostics applications.
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| 14. |
- Dahlin, Andreas, 1980, et al.
(författare)
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High-Resolution Microspectroscopy of Plasmonic Nanostructures for Miniaturized Biosensing
- 2009
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Ingår i: Analytical Chemistry. - : American Chemical Society. - 0003-2700 .- 1520-6882. ; 81:16, s. 6572-6580
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we demonstrate how to perform microscale spectroscopy of plasmonic nanostructures in order to minimize the noise when determining the resonance peak wavelength. This is accomplished using an experimental setup containing standard optical components mounted on an ordinary light microscope. We present a detailed comparison between extinction spectroscopy in transmission mode and scattering spectroscopy under dark field illumination, which shows that extinction measurements provide higher signal-to-noise in almost all situations. Furthermore, it is shown that rational selection of nanostructure, hardware components, and data analysis algorithms enables tracking of the particle plasmon resonance wavelength from a 10 mu m x 50 mu m area with a resolution of 10(-3) nm in transmission mode. We investigate how the temporal resolution, which can be improved down to 17 Ins, affects, the noise characteristics. In addition, we show how data can be acquired from an area as small as 2 mu m x 10 mu m (similar to 240 particles) at the expense of higher noise on longer time scales. In comparison with previous work on macroscopic sensor designs, this represents a sensor miniaturization of 5 orders of magnitude, without any loss in signal-to-noise performance. As a model system, we illustrate biomolecular detection using gold nanodisks prepared by colloidal lithography. The microextinction measurements of nanodisks described here provide detection of protein surface coverages as low as 40 pg/cm(2) (less than0.1% of saturated binding). In fact, the miniaturized system provides a detection limit in terms of surface coverage comparable to state of the art macroscopic sensors, while simultaneously being as close to single protein molecule detection as sensors based on a single nanoparticle.
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| 15. |
- Dahlin, Andreas, 1980, et al.
(författare)
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Localized surface plasmon sensing of lipid-membrane-mediated biorecognition events
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 127:14, s. 5043-5048
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Tidskriftsartikel (refereegranskat)abstract
- Supported phospholipid bilayers (SPBs) have emerged as important model systems for studies of the natural cell membrane and its components, which are essential for the integrity and function of cells in all living organisms, and also constitute common targets for therapeutic drugs and in disease diagnosis. However, the preferential occurrence of spontaneous SPB formation on silicon-based substrates, but not on bare noble-metal surfaces, has so far excluded the use of the localized surface plasmon resonance (LSPR) sensing principle for studies of lipid-membrane-mediated biorecognition reactions. This is because the LSPR phenomenon is associated with, and strongly confined to, the interfacial region of nanometric noble-metal particles. This problem has been overcome in this study by a self-assembly process utilizing localized rupture of phospholipid vesicles on silicon dioxide in the bottom of nanometric holes in a thin gold film. The hole-induced localization of the LSPR field to the voids of the holes is demonstrated to provide an extension of the LSPR sensing concept to studies of reactions confined exclusively to SPB-patches supported on SiO2. In particular, we emphasize the possibility of performing label-free studies of lipid-membrane-mediated reaction kinetics, including the compatibility of the assay with array-based reading (similar to 7 x 7 mu m(2)) and detection of signals originating from bound protein in the zeptomole regime.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Fredriksson, Hans, 1974, et al.
(författare)
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Resonant optical absorption in graphite nanostructures
- 2009
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Ingår i: Journal of Optics A: Pure and Applied Optics. - 1361-6617 .- 1464-4258. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the correlation between optical absorption and the size of graphitenanostructures is presented. Five different samples with structure diameters ranging from ∼160to 330 nm and heights from ∼60 to 190 nm were prepared. The disk-like nanostructures wereetched out of the basal plane surface of highly oriented pyrolytic graphite, using hole-maskcolloidal lithography and oxygen reactive ion etching. Optical absorption spectra forwavelengths between 200 and 2500 nm were then measured. Furthermore, electrodynamicscalculations were conducted to model the optical properties of graphite nanostructures ofsimilar sizes. Both the experimental and the theoretical work revealed resonant absorptioncorrelated to the nanostructure diameters and heights. These absorption peaks are red-shifted,from the visible for the smallest structures to near infrared for the largest. Simultaneously, theintensity of the absorption peaks increases for increasing structure heights, while increasingdiameters results in decreased absorption.
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| 20. |
- Gonzalez-Diaz, J. B., et al.
(författare)
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Plasmonic Au/Co/Au nanosandwiches with enhanced magneto-optical activity
- 2008
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 4:2, s. 202-205
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Tidskriftsartikel (refereegranskat)abstract
- A study was conducted to analyzed magneto-optical (MO) activity of thin films prepared by Au/Co/Au trilayers as surface plasmon polaritons. Trilyers exhibit a magnetic-field-induced nonreciprocal effect in the surface plasmon polariton propagation. The Au/Co/Au nanosandwiches, prepared by a self-assembly process, show localized surface plasmon resonances (LSPRs) that affect the optical properties of metallic nanostructures. The fabrication of the nanostructures was performed using colloidal lithography (CL). An atomic force microscopy was used to analyze the structure of thin films. The polar Kerr ellipticity and rotation spectra for an array of nanoparticles with identical dimensions were examined. Metal trilyer films were sputtered onto glass substrates. Results show that nanoparticles can be used for the development of high-sensitive magnetoplasmonic nanosensors with multiplexing capabilities.
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