Surface-enhanced Fluorescence Spectroscopy Research Articles

DNA-assembled advanced plasmonic nanostructures

The global vibration of the free electrons on the surface of the metal nanoparticles forms surface plasmon on the surface of the particles. When multiple nanoparticles are close to each other, the electromagnetic fields between different particles will be coupled, and the electromagnetic field strength and spatial distribution after coupling will change significantly. It is necessary to construct a plasmonic resonance structure with a precise spatial conformation and tunable optical properties, provided that the spatial arrangement of the metal nanoparticles can be precisely controlled. DNA molecules are biological macromolecules that carry genetic information. Different bases in the DNA molecule (adenine A, thymine T, guanine G, cytosine C) can hybridize to each other to form stable double helixes through strict base-pairing principle. Using this property of DNA molecules, through rational design, people can obtain DNA self-assembled nanostructures with various shapes and sizes. This field was afterward named structural DNA nanotechnology. DNA nanotechnology offers a variety of new methods for constructing novel plasmonic resonance nanostructures. Using DNA-functionalized metal nanoparticles in combination with DNA templates, a variety of static or dynamic plasmonic resonance nanostructures have been successfully constructed. The plasmon resonance nanostructures constructed by DNA self-assembly have a variety of interesting nanophotonic effects, such as chiral signals in the visible range, surface-enhanced Raman spectroscopy, and surface-enhanced fluorescence spectroscopy. Dynamic DNA self-assembly plasmon resonance nanostructures not only have good optical properties but also have good structural reconfigurability. In recent years, dynamic plasmon resonance nanostructures based on DNA self-assemblies have attracted much attention. This dynamic plasmon resonance nanostructure has a wide application space in single molecule detection and chemical reaction process monitoring. The advantages of DNA self-assembled plasmonic resonance nanostructures in nanophotonics and nanoelectronics are obvious. The controllable positioning of metal nanoparticles is achieved while self-assembly of a large number of DNA molecules, making it possible to mass-produce plasmonic nanostructures. In the next step, how to accurately locate the DNA self-assembled plasmonic resonance nanostructures has become a major problem that restricts its application on nanodevices. Moreover, the mass production of DNA assembled plasmonic resonance nanostructure is still a challenge. Another strategy for scaling up the DNA assembled plasmonic resonance nanostructure is fabrication of DNA superstructure using multiple DNA nanostructures. The development of DNA self-assembly and plasmonic resonance nanostructures makes it possible to construct nanocircuits and nano-factories for chemical reactions. It is believed that in the near future, DNA self-assembled plasmonic resonance nanostructures will glow in more fields, bringing more surprises to people.

Surface enhanced fluorescence effect of SiO2 coated silver nanoparticles and clusters

Composite Ag@SiO2 nanoparticles are prepared for investigating a metal-enhanced fluorescence effect. Due to the competition between enhanced electromagnetic field intensity and fluorescence emission decay, the distance between the molecules and metal surface is an important surface-enhanced fluorescence factor for enhancing or quenching. This distance can be controlled by the size of the separation-layer, and thus the surface-enhanced fluorescence enhancement can be controlled. To avoid fluorescence quenching and obtain a considerable fluorescence enhancement, SiO2 shell is used to separate the molecules from the metal surface. The surface modification of metallic nanoparticles by SiO2 can not only improve the dispersibility and stability of metal particles, but also expanding its application effectively in the biological field. For fluorophores located around metal nanostructures, many factors would affect a fluorescence enhancement effect. Investigation of the enhancement mechanism usually becomes difficult and complicated due to too many variables and factors involved in the enhancement process. In order to systematically study the influence of these factors on fluorescence intensity, single polymer nanoparticles are chosen to be an enhanced substrate. The particle distribution is labeled through electron beam lithography and the surface-enhanced fluorescence spectroscopy of single nanoparticle or cluster is achieved by in - situ measurement method. The influence of metal particle size, cluster property and excitation polarization on the surface enhanced fluorescence is studied by using Rh6G as the probe molecule. Obvious fluorescence enhancement effect of Rh6G molecules at the surface of Ag@SiO2 is observed with nanocomposite, and the enhancement effect is controlled by the metal core particle size, aggregation property, and the polarization direction of the excitation light.

Probing the Plasmonic Properties of Heterometallic Nanoprisms with Near-Field Fluorescence Microscopy

In an effort to optimize both the optical properties and chemical stability of plasmonic platforms for surface-enhanced fluorescence spectroscopy, a series of multilayered heterometallic structures were prepared. Gold–silver multilayered array of prisms were designed, where the gold layers acts as protective layers for the silver and extends the spectral range of the resulting localized surface plasmon resonances. Herein, we report an experimental study of the enhanced near-field fluorescence from quantum dots deposited at the surface of these platforms. This was performed using near-field scanning optical microscopy yielding simultaneous measurements of topographical features and near-field fluorescence of the prismatic arrays. Hence, the individual localized fluorescent hot-spots could be imaged and spatially correlated with the geometry of the nanostructures for distinct polarization configuration of the excitation light with respect to the orientation of the structures. Furthermore, the fluorescence enhancement was evaluated spatially and temporally for the series of the nanoprism platforms. In particular, the quenching of the near-field fluorescence due to the metal structures was carefully evaluated for the metal–fluorophore hybrid systems.

Highly sensitive superhydrophobic Ag nanorods array substrates for surface enhanced fluorescence studies

We report a facile method to fabricate highly sensitive superhydrophobic Ag nanorods (AgNR) arrays based surface enhanced fluorescence spectroscopy (SEFS) substrates using glancing angle deposition technique at a substrate temperature of 133 K and then subsequent coating of heptadecafluoro-1-decanethiol (HDFT) molecules. The SEFS enhancement behaviour of these substrates was determined by using aqueous solution of Rhodamine 6G. The HDFT coated superhydrophobic AgNR arrays SEFS substrates exhibit more then 3-fold fluorescence signal enhancement than conventional AgNR films. These HDFT coated superhydrophobic AgNR SEFS substrates based sensors may find application for the purpose of trace analysis and biosensing.