Tunable Surface Plasmon Resonance Properties Research Articles

Superparamagnetic iron oxide-enclosed hollow gold nanostructure with tunable surface plasmon resonances to promote near-infrared photothermal conversion

In this study, to enhance deep tissue penetration by near-infrared (NIR) light, a novel superparamagnetic iron oxide-enclosed hollow gold nanoshell (SPIO-HGNS) structure with tunable size and surface plasmon resonance (SPR) in the NIR range was designed and synthesized through a two-step template-enabled galvanic replacement reaction. Here, Ag-coated SPIO (SPIO-Ag) was prepared as a template with tunable outer diameters by way of adjusting the Ag content. SPIO-HGNS with variable hollow gold inner diameters can then be synthesized based on the determined outer diameter of the SPIO-Ag template through a galvanic replacement reaction between HAuCl3 and Ag coating on the SPIO surface. With incrementing amounts of Ag, three SPIO-HGNS structures were synthesized with comparable shell thicknesses around 6.7 nm and an average inner diameter of 38.7, 39.4, and 40.7 nm, respectively, evidenced by TEM and ICP results. The structure of SPIO-HGNS was confirmed by identifying Au111 lattice and the elemental mapping of Fe and Au using energy-dispersive X-ray spectroscopy. The ultraviolet–visible-NIR absorption spectra showed red-shifted SPR peaks (820, 855, and 945 nm) with the increasing inner diameters of SPIO-HGNS, which was also supported by an absorption cross-section simulation. The photothermal results showed that the three SPIO-HGNS structures, when exposed to ~ 30 s of 400 mW laser irradiation, exhibited photothermal temperature rises of 5.9, 4.6, and 2.9 ℃, respectively. This study explored the tuning of SPR properties in NIR-responsive magneto-plasmonic nanoparticles through a facile preparation procedure, paving the way for potential applications in photothermal therapies.Graphical abstractThe NIR-responsive magneto-plasmonic SPIO-HGNS nanostructures were developed with tunable SPR properties and strong photothermal conversion capacities.

Au@HgxCd1-xTe core@shell nanorods by sequential aqueous cation exchange for near-infrared photodetectors

We have explored the synthesis of Au@HgxCd1-xTe core@shell nanorods by sequential aqueous cation exchange (ACE) for near-infrared photodetector application. A number of related Au@telluride core/shell nanorod structures were put forwarded, taking advantage of multi-step transformations through a binary and then a ternary phase for the telluride shells. The latter have a high degree of crystallinity thanks to the step-wise ACE method. The use of only trace amounts of Cd2+ coordinated with tri-n-butylphosphine, assisted the phase transformation from an amorphous Ag2Te shell to a highly crystalline Ag3AuTe2 shell in the first stage; this was followed by a further cation exchange (CE) step with far higher Cd2+ levels to fabricate a highly crystalline CdTe shell, and with an additional CE with Hg2+ to convert it to a HgxCd1-xTe shell. The composition of the shell components and the well-controlled thickness of the shells enabled tunable surface plasmon resonance properties of the Au@telluride nanorods in the NIR region. Utilizing the enhanced NIR absorption, a hybrid photodetector structure of Au@HgxCd1-xTe nanorods on graphene was fabricated, showing visible to NIR (vis-NIR) broadband detection with high photoresponsivity (~106 A/W).

Thermo-responsiveness and tunable optical properties of asymmetric polystyrene/PNIPAM-gold composite particles

Environmentally responsive polystyrene/poly (N-isopropylacrylamide)-gold composite particles are successfully synthesized via a Pickering emulsion polymerization method. It is found that the core–shell and asymmetric structured particles are simultaneously formed during the polymerization. Compared with the core–shell structured composite particles, the asymmetric particles have a higher thermo-responsiveness as a result of differences in morphology and formation mechanism. For asymmetric composite particles, an increase in N-isopropylacrylamide (NIPAAM) content leads to more significant size variation upon temperature changes. From rheology measurements, the viscosity of asymmetric particles suspension greatly decreases as temperature is increased above the lower critical solution temperature (LCST). The large size decrease in asymmetric composite particles gives rise to a significant scattering intensity increase, as a result of increased refractive index contrast between the PNIPAM content and surrounding water. The resulting size decrease also leads to tunable surface plasmon resonance properties.

Laser-Induced Growth of Monodisperse Silver Nanoparticles with Tunable Surface Plasmon Resonance Properties and a Wavelength Self-Limiting Effect

We present a method for the tunable production of monodisperse silver nanoparticles. Using monochromatic light of different laser wavelengths to irradiate an initial solution of seed crystals, the size and shape of the products can be controlled. By monitoring the absorption spectrum during growth, it is found that initially the absorption maximum shifts to longer wavelengths and broadens, indicating an increase in particle size and size dispersion. Remarkably, this effect comes to a halt and reverses, displaying a shift to shorter wavelengths and simultaneously narrower bandwidths until, on completion, a final size and relatively narrow distribution are reached. The final size and shape is found to depend on laser wavelength and power. Both discs and triangular prisms as well as pyramidal and pentagonal prisms may be produced. A mechanism based on a wavelength-dependent self-limiting process governed by the surface plasmon resonance controlling the photochemical reduction of particles is suggested.

Solvothermal Synthesis of Multiple Shapes of Silver Nanoparticles and Their SERS Properties

The controllable synthesis of nanocrystals with different shapes is very important and challenging. In the present work, silver nanoparticles with different structural architectures, from nanorods, triangular plates, hexagonal plates, and nanocubes to polyhedrons have been synthesized successfully in high yield by a solvothermal process. Especially, the unique silver enneahedral nanoplates are also observed. These nanoparticles exhibit tunable surface plasmon resonance properties from the visible to near-infrared regions. Those nanoparticles were also self-assembled on glass substrates and evaluated as potential surface-enhanced Raman scattering (SERS) substrates using trans-1,2-bis(4-pyridyl)ethylene molecules. Thanks to the enhanced local field effect around their sharp corners and edges, those Ag triangular plates exhibit enhanced SERS properties and can serve as high-sensitivity substrates for SERS-based measurements.