131 research outputs found
Towards unimolecular luminescent solar concentrators: bodipy-based dendritic energy-transfer cascade with panchromatic absorption and monochromatized emission
Cataloged from PDF version of article.Ein in ein Polymer eingebetteter, panchromatischer Bodipy-Absorber mit eingebautem Energiegradienten konzentriert einfallende Sonnenstrahlung an einem endständigen Chromophor und erzeugt so eine monochromatische Emission an den Seiten des Polymer-Wellenleiters (siehe Bild). Dieses besondere Design minimiert Selbstabsorptionsverluste der peripheren Antennen-Einheiten mit einem beeindruckenden S-Faktor von 10 000
Counting molecules with a mobile phone camera using plasmonic enhancement
Cataloged from PDF version of article.Plasmonic field enhancement enables the acquisition of Raman spectra at a single molecule level. Here we investigate the detection of surface enhanced Raman signal using the unmodified image sensor of a smart phone, integrated onto a confocal Raman system. The sensitivity of a contemporary smart phone camera is compared to a photomultiplier and a cooled charge-coupled device. The camera displays a remarkably high sensitivity, enabling the observation of the weak unenhanced Raman scattering signal from a silicon surface, as well as from liquids, such as ethanol. Using high performance wide area plasmonic substrates that enhance the Raman signal 10(6) to 10(7) times, blink events typically associated with single molecule motion, are observed on the smart phone camera. Raman spectra can also be collected on the smart phone by converting the camera into a low resolution spectrometer with the inclusion of a collimator and a dispersive optical element in front of the camera. In this way, spectral content of the blink events can be observed on the plasmonic substrate, in real time, at 30 frames per second
Reversible Electrical Reduction and Oxidation of Graphene Oxide
Cataloged from PDF version of article.We demonstrate that graphene oxide can be reversibly reduced and oxidized using
electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer
graphene oxide films are shown to result in switching between partially reduced graphene oxide and
graphene, a process which modifies the electronic and optical properties. High-resolution tunneling
current and electrostatic force imaging reveal that graphene oxide islands are formed on multilayer
graphene, turning graphene into a self-assembled heterostructure random nanomesh. Charge
storage and resistive switching behavior is observed in two-terminal devices made of multilayer
graphene oxide films, correlated with electrochromic effects. Tip-induced reduction and oxidation
are also demonstrated. Results are discussed in terms of thermodynamics of oxidation and reduction
reactions
Grating coupler integrated photodiodes for plasmon resonance based sensing
Cataloged from PDF version of article.In this work, we demonstrate an integrated sensor combining a grating-coupled plasmon resonance surface with a planar photodiode. Plasmon enhanced transmission is employed as a sensitive refractive index (RI) sensing mechanism. Enhanced transmission of light is monitored via the integrated photodiode by tuning the angle of incidence of a collimated beam near the sharp plasmon resonance condition. Slight changes of the effective refractive index (RI) shift the resonance angle, resulting in a change in the photocurrent. Owing to the planar sensing mechanism, the design permits a high areal density of sensing spots. In the design, absence of holes that facilitate resonant transmission of light, allows an easy-to-implement fabrication procedure and relative insensitivity to fabrication errors. Theoretical and experimental results agree well. An equivalent long-term RI noise of 6.3 x 10(-6) RIU/root Hz is obtained by using an 8 mW He-Ne laser, compared to a shot-noise limited theoretical sensitivity of 5.61 x 10(-9) RIU/root Hz. The device features full benefits of grating-coupled plasmon resonance, such as enhancement of sensitivity for non-zero azimuthal angle of incidence. Further sensitivity enhancement using balanced detection and optimal plasmon coupling conditions are discussed
Raman Enhancement on a Broadband Meta-Surface
Cataloged from PDF version of article.Plasmonic metamaterials allow confinement of light to deep subwavelength dimensions, while allowing for the tailoring of dispersion and electromagnetic mode density to enhance specific photonic properties. Optical resonances of plasmonic molecules have been extensively investigated; however, benefits of strong coupling of dimers have been overlooked. Here, we construct a plasmonic meta-surface through coupling of diatomic plasmonic molecules which contain a heavy and light meta-atom. Presence and coupling of two distinct types of localized modes in the plasmonic molecule allow formation and engineering of a rich band structure in a seemingly simple and common geometry, resulting in a broadband and quasi-omni-directional meta-surface. Surface-enhanced Raman scattering benefits from the simultaneous presence of plasmonic resonances at the excitation and scattering frequencies, and by proper design of the band structure to satisfy this condition, highly repeatable and spatially uniform Raman enhancement is demonstrated. On the basis of calculations of the field enhancement distribution within a unit cell, spatial uniformity of the enhancement at the nanoscale is discussed. Raman scattering constitutes an example of nonlinear optical processes, where the wavelength conversion during scattering may be viewed as a photonic transition between the bands of the meta-material
Presentation of functional groups on self-assembled supramolecular peptide nanofibers mimicking glycosaminoglycans for directed mesenchymal stem cell differentiation
Organizational complexity and functional diversity of the extracellular matrix regulate cellular behaviors. The extracellular matrix is composed of various proteins in the form of proteoglycans, glycoproteins, and nanofibers whose types and combinations change depending on the tissue type. Proteoglycans, which are proteins that are covalently attached to glycosaminoglycans, contribute to the complexity of the microenvironment of the cells. The sulfation degree of the glycosaminoglycans is an important and distinct feature at specific developmental stages and tissue types. Peptide amphiphile nanofibers can mimic natural glycosaminoglycans and/or proteoglycans, and they form a synthetic nanofibrous microenvironment where cells can proliferate and differentiate towards different lineages. In this study, peptide nanofibers were used to provide varying degrees of sulfonation mimicking the natural glycosaminoglycans by forming a microenvironment for the survival and differentiation of stem cells. The effects of glucose, carboxylate, and sulfonate groups on the peptide nanofibers were investigated by considering the changes in the differentiation profiles of rat mesenchymal stem cells in the absence of any specific differentiation inducers in the culture medium. The results showed that a higher sulfonate-to-glucose ratio is associated with adipogenic differentiation and a higher carboxylate-to-glucose ratio is associated with osteochondrogenic differentiation of the rat mesenchymal stem cells. Overall, these results demonstrate that supramolecular peptide nanosystems can be used to understand the fine-tunings of the extracellular matrix such as sulfation profile on specific cell types. © 2017 The Royal Society of Chemistry
Facile synthesis of cross-linked patchy fluorescent conjugated polymer nanoparticles by click reactions
Here, we report a novel method to synthesize multifunctional nanoparticles that can be used in biological studies, such as in cell imaging and as a carrier for biomolecules/drugs. The nanoparticles were prepared either via Cu-catalyzed or cucurbit[6]uril (CB6)-catalyzed click reactions between azide groups containing hydrophobic blue, green and yellow emitting fluorene-based conjugated polymers and a hydrophilic diaminodialkyne containing cross-linker. Through the click reaction, not only does the cross-linking confer stability, but it also introduces functional groups, such as triazoles and amines, to the nanoparticles. Moreover, CB6 not only acted as a catalyst to facilitate the copper-free click reaction, but it also allowed us to obtain nanoparticles containing rotaxanes in which the triazole units were encapsulated by CB6 units. TEM images of the nanoparticles also showed that they display very interesting morphologies. Incorporation of hydrophilic functional groups to the hydrophobic conjugated polymers resulted in a distinct phase separation, producing Janus-like or patchy particles. © 2011 The Royal Society of Chemistry
CalibFPA: A Focal Plane Array Imaging System based on Online Deep-Learning Calibration
Compressive focal plane arrays (FPA) enable cost-effective high-resolution
(HR) imaging by acquisition of several multiplexed measurements on a
low-resolution (LR) sensor. Multiplexed encoding of the visual scene is
typically performed via electronically controllable spatial light modulators
(SLM). An HR image is then reconstructed from the encoded measurements by
solving an inverse problem that involves the forward model of the imaging
system. To capture system non-idealities such as optical aberrations, a
mainstream approach is to conduct an offline calibration scan to measure the
system response for a point source at each spatial location on the imaging
grid. However, it is challenging to run calibration scans when using structured
SLMs as they cannot encode individual grid locations. In this study, we propose
a novel compressive FPA system based on online deep-learning calibration of
multiplexed LR measurements (CalibFPA). We introduce a piezo-stage that
locomotes a pre-printed fixed coded aperture. A deep neural network is then
leveraged to correct for the influences of system non-idealities in multiplexed
measurements without the need for offline calibration scans. Finally, a deep
plug-and-play algorithm is used to reconstruct images from corrected
measurements. On simulated and experimental datasets, we demonstrate that
CalibFPA outperforms state-of-the-art compressive FPA methods. We also report
analyses to validate the design elements in CalibFPA and assess computational
complexity
Plasmonic absorbers for multispectral and broadband absorption
We present polarization dependent multispectral and broadband plasmonic absorbers in the visible spectrum. The spectral characteristics of these structures are tunable over a broad spectrum. Experimental results are verified with the FDTD and RCWA analysis methods. These structures are used as surface enhanced raman spectroscopy(SERS) substrates. Designed structures have resonances that span the Raman Stokes and excitation wavelength. Such structures can be used for energy, LED and other spectroscopy applications. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)
Electrochemically tunable ultrafast optical response of graphene oxide
Cataloged from PDF version of article.We demonstrate reversible and irreversible changes in the ultrafast optical response of multilayer graphene oxide thin films upon electrical and optical stimulus. The reversible effects are due to electrochemical modification of graphene oxide, which allows tuning of the optical response by externally applied bias. Increasing the degree of reduction in graphene oxide causes excited state absorption to gradually switch to saturable absorption for shorter probe wavelengths. Spectral and temporal properties as well as the sign of the ultrafast response can be tuned either by changing the applied bias or exposing to high intensity femtosecond pulses. © 2011 American Institute of Physics
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