ABSTRACT
In this work we demonstrate a DNA biosensor based on fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er nanoparticles and graphene oxide (GO). Monodisperse NaYF4:Yb,Er nanoparticles with a mean diameter of 29.1 ± 2.2 nm were synthesized and coated with a SiO2 shell of 11 nm, which allowed the attachment of single strands of DNA. When these DNA-functionalized NaYF4:Yb,Er@SiO2 nanoparticles were in the proximity of the GO surface, the π-π stacking interaction between the nucleobases of the DNA and the sp(2) carbons of the GO induced a FRET fluorescence quenching due to the overlap of the fluorescence emission of the NaYF4:Yb,Er@SiO2 and the absorption spectrum of GO. By contrast, in the presence of the complementary DNA strands, the hybridization leads to double-stranded DNA that does not interact with the GO surface, and thus the NaYF4:Yb,Er@SiO2 nanoparticles remain unquenched and fluorescent. The high sensitivity and specificity of this sensor introduces a new method for the detection of DNA with a detection limit of 5 pM.
Subject(s)
Biosensing Techniques/methods , DNA, Single-Stranded/analysis , Fluorescence Resonance Energy Transfer/methods , Graphite/chemistry , Nanoparticles/chemistry , Oxides/chemistry , Erbium , Fluorides , Ytterbium , YttriumABSTRACT
Spatial modulation microscopy (SMM) is a technique originally developed for quantitative spectroscopy of individual nano-objects. Here, a parallel implementation of the SMM technique is demonstrated based on a line detector capable of demodulation at kHz frequencies. The capabilities of the imaging system are shown using an array of plasmonic nanoantennas and dendritic cells incubated with gold nanoparticles.
Subject(s)
Dendritic Cells/cytology , Microscopy/methods , Molecular Imaging/methods , Nanoparticles , Time FactorsABSTRACT
We present a broadband technique for the measurement of diffuse light transport through opaque scattering media. Using the spectral correlations introduced by a scattering medium onto a white-light supercontinuum spectrum, the diffusion constant of light is determined over a wide spectral range in the visible and the near IR. Independent broadband measurements of both the transport mean free path and the diffusion constant are used to calculate the spectral dependence of the energy velocity in a porous GaP slab. Broadband correlation spectroscopy is found to be an excellent tool for the characterization of random scattering media.
Subject(s)
Optics and Photonics , Equipment Design , Interferometry/methods , Light , Models, Statistical , Reproducibility of Results , Scattering, Radiation , Spectrophotometry/methods , Spectroscopy, Fourier Transform InfraredABSTRACT
We report on a new experimental method for enhanced backscattering spectroscopy (EBS) of strongly scattering media over a bandwidth from 530-1000 nm. The instrument consists of a supercontinuum light source and an angle-dependent detection system using a fiber-coupled grating spectrometer. Using a combination of two setups, the backscattered intensity is obtained over a large angular range and using circularly polarized light. We present broadband EBS of a TiO(2) powder and of a strongly scattering porous GaP layer. In combination with theoretical model fits, the EBS system yields the optical transport mean free path over the available spectral window.
Subject(s)
Nanostructures/chemistry , Nanotechnology/instrumentation , Spectrum Analysis/instrumentation , Spectrum Analysis/methods , Equipment Design , Equipment Failure Analysis , Light , Microwaves , Nanotechnology/methods , Scattering, RadiationABSTRACT
We demonstrate a novel functionality of semiconductor nanowires as local sources for surface plasmon polaritons (SPPs). Photoexcited semiconductor nanowires decay non-radiatively exciting SPPs when they are on top of a metallic surface. We have investigated the anisotropic excitation of SPPs by nanowires by placing individual InP nanowires inside gold bullseye gratings. The gratings serve to couple SPPs to free space radiation that is detected with a scanning confocal microscope. The circular geometry of the grating allows to conclude that SPPs are preferentially generated in the direction along the nanowire axis.
Subject(s)
Lighting/instrumentation , Luminescent Measurements/instrumentation , Nanotubes/chemistry , Nanotubes/ultrastructure , Refractometry/instrumentation , Semiconductors , Surface Plasmon Resonance/instrumentationABSTRACT
We demonstrate a strong, 5-fold enhancement of the radiative decay rate from highly efficient fluorescent dye molecules around resonant optical nanoantennas. The plasmonic modes of individual gold dimer antennas are tuned by the particle length and the antenna gap, providing control over both the spectral resonance position and the near-field mode profile of the nanoantenna. Resonant enhancement of the radiative and nonradiative decay rates of a fluorescent dye is observed, resulting in an increase of the internal quantum efficiency from 40% up to 53% for single antennas, and up to 59% for antenna clusters. This improvement of the already high quantum efficiency of the dye molecules is in agreement with electrodynamic model calculations that predict a maximum attainable efficiency around 80% due to nonradiative losses in the metal.
Subject(s)
Fluorescent Dyes/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Spectrometry, Fluorescence/methods , Surface Plasmon Resonance/methods , Half-Life , Kinetics , Materials Testing , Particle SizeABSTRACT
We demonstrate efficient modification of the polarized light emission from single semiconductor nanowires by coupling this emission to surface plasmon polaritons on a metal grating. The polarization anisotropy of the emitted photoluminescence from single nanowires is compared for wires deposited on silica, a flat gold film, and a shallow gold grating. By varying the orientation of the nanowire with respect to the grating grooves, the large intrinsic polarization anisotropy can be either suppressed or enhanced. This modification is interpreted by the appearance of an additional emission channel induced by surface plasmon polaritons and their conversion to p-polarized radiation at the grating.
ABSTRACT
The optical resonances of individual plasmonic dimer antennas are investigated using confocal darkfield spectroscopy. Experiments on an array of antennas with varying arm lengths and interparticle gap sizes show large spectral shifts of the plasmon modes due to a combination of geometrical resonances and plasmon hybridization. The resonances of the coupled-dimer antennas are considerably broadened compared to those of single nanorods, which is attributed to a superradiant damping of the coupled antenna modes. The scattering spectra are compared with electrodynamic model calculations that demonstrate both the near-field and far-field characteristics of a half-wave antenna.
