Plasmonic processes exposed


Rebecca Pool

Tuesday, December 4, 2018 - 14:45
Image: Snapshot hyperspectral imaging reveals differences in plasmonic nanoparticles by taking snapshots of particles and the light they scatter or emit when excited. [Rice University]
US-based researchers have developed 'snapshot hyperspectral imaging' to gather exquisite detail on groups of plasmonic nanoparticles.
The new method aligns a microscope, two CMOS cameras, a laser and diffraction grating to capture images of particles as well as information about the light emitted every millisecond.
As Professor Stephan Link from Rice University writes in The Journal of Physical Chemistry C:  "The novel two-detector approach to parallel, single-particle spectroscopic imaging allows the in situ and high-quality mapping of ∼100 individual plasmonic NPs."
"The new metrology facilitates in situ readout of a tube lens image and first-order diffraction image of the dark-field scattering from the plasmonic nanoparticles to extract their respective spectra simultaneously," he adds.
The data gathered from this new technique could help industries fine-tune nanoparticles that capture and use light.
Fast spectroscopic imaging
Plasmonic nanoparticles, characterised by their strong interaction with light and a high surface-to-volume ratio, play a crucial role as light-harvesting nanoantennas in photocatalysis, photovoltaics, surface-enhanced Raman spectroscopy, spectroelectrochemistry and more.
However, the photophysical response of a plasmonic nanoantenna strongly depends on its shape, surface morphology, composition, environment as well as charge carrier density variations.
To better understand the influence of this complex set of variables, Link and colleagues developed a novel hyperspectral imaging system that provides fast, parallel, in situ spectroscopic mapping of many individual nanostructures.
As Link highlights, the principle of snapshot hyperspectral imaging system is based on the synchronised acquisition of the spatial positions and the spectral dispersions of many single nanoparticles.
The system includes a diffracting optical element and two CMOS cameras that enable separate and parallel readout of the spatial and spectral dark-field scattering images of multiple single nanoparticles.
Precise camera correlation also enables extraction of nanoparticle wavelength spectra.
The researchers also devised a novel dark-field excitation approach that used a supercontinuum laser with a reflecting objective for polarization-controlled snapshot hyperspectral imaging.
Using their system, the researchers observed, for the first time, an electrochemical surface reduction-oxidation reaction for gold nanoparticles at the microsecond timescale.
In the future, the researchers hope to enhance the snapshot hyperspectral imaging system to capture images of nanoparticles as they grow.
"The two-detector approach [is set to] enable spectroscopic imaging of non-stationary nanoparticles and particle growth from small and initially non-detectable seeds," says Link.
Research is published in The Journal of Physical Chemistry C.
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