5 research outputs found
Three-Dimensional and Time-Ordered Surface-Enhanced Raman Scattering Hotspot Matrix
The “fixed” or “flexible”
design of
plasmonic hotspots is a frontier area of research in the field of
surface-enhanced Raman scattering (SERS). Most reported SERS hotspots
have been shown to exist in zero-dimensional point-like, one-dimensional
linear, or two-dimensional planar geometries. Here, we demonstrate
a novel three-dimensional (3D) hotspot matrix that can hold hotspots
between every two adjacent particles in 3D space, simply achieved
by evaporating a droplet of citrate-Ag sols on a fluorosilylated silicon
wafer. In situ synchrotron-radiation small-angle X-ray scattering
(SR-SAXS), combined with dark-field microscopy and in situ micro-UV,
was employed to explore the evolution of the 3D geometry and plasmonic
properties of Ag nanoparticles in a single droplet. In such a droplet,
there is a distinct 3D geometry with minimal polydispersity of particle
size and maximal uniformity of interparticle distance, significantly
different from the dry state. According to theoretical simulations,
the liquid adhesive force promotes a closely packed assembly of particles,
and the interparticle distance is not fixed but can be balanced in
a small range by the interplay of the van der Waals attraction and
electrostatic repulsion experienced by a particle. The “trapping
well” for immobilizing particles in 3D space can result in
a large number of hotspots in a 3D geometry. Both theoretical and
experimental results demonstrate that the 3D hotspots are predictable
and time-ordered in the absence of any sample manipulation. Use of
the matrix not only produces giant Raman enhancement at least 2 orders
of magnitude larger than that of dried substrates, but also provides
the structural basis for trapping molecules. Even a single molecule
of resonant dye can generate a large SERS signal. With a portable
Raman spectrometer, the detection capability is also greatly improved
for various analytes with different natures, including pesticides
and drugs. This 3D hotspot matrix overcomes the long-standing limitations
of SERS for the ultrasensitive characterization of various substrates
and analytes and promises to transform SERS into a practical analytical
technique
Three-Dimensional and Time-Ordered Surface-Enhanced Raman Scattering Hotspot Matrix
The “fixed” or “flexible”
design of
plasmonic hotspots is a frontier area of research in the field of
surface-enhanced Raman scattering (SERS). Most reported SERS hotspots
have been shown to exist in zero-dimensional point-like, one-dimensional
linear, or two-dimensional planar geometries. Here, we demonstrate
a novel three-dimensional (3D) hotspot matrix that can hold hotspots
between every two adjacent particles in 3D space, simply achieved
by evaporating a droplet of citrate-Ag sols on a fluorosilylated silicon
wafer. In situ synchrotron-radiation small-angle X-ray scattering
(SR-SAXS), combined with dark-field microscopy and in situ micro-UV,
was employed to explore the evolution of the 3D geometry and plasmonic
properties of Ag nanoparticles in a single droplet. In such a droplet,
there is a distinct 3D geometry with minimal polydispersity of particle
size and maximal uniformity of interparticle distance, significantly
different from the dry state. According to theoretical simulations,
the liquid adhesive force promotes a closely packed assembly of particles,
and the interparticle distance is not fixed but can be balanced in
a small range by the interplay of the van der Waals attraction and
electrostatic repulsion experienced by a particle. The “trapping
well” for immobilizing particles in 3D space can result in
a large number of hotspots in a 3D geometry. Both theoretical and
experimental results demonstrate that the 3D hotspots are predictable
and time-ordered in the absence of any sample manipulation. Use of
the matrix not only produces giant Raman enhancement at least 2 orders
of magnitude larger than that of dried substrates, but also provides
the structural basis for trapping molecules. Even a single molecule
of resonant dye can generate a large SERS signal. With a portable
Raman spectrometer, the detection capability is also greatly improved
for various analytes with different natures, including pesticides
and drugs. This 3D hotspot matrix overcomes the long-standing limitations
of SERS for the ultrasensitive characterization of various substrates
and analytes and promises to transform SERS into a practical analytical
technique
Probing the Location of Hot Spots by Surface-Enhanced Raman Spectroscopy: Toward Uniform Substrates
Wide applications of surface plasmon resonance rely on the in-depth understanding of the near-field distribution over a metallic nanostructure. However, precisely locating the strongest electric field in a metallic nanostructure still remains a great challenge in experiments because the field strength decays exponentially from the surface. Here, we demonstrate that the hot spot position for gold nanoparticles over a metal film can be precisely located using surface-enhanced Raman spectroscopy (SERS) by rationally choosing the probe molecules and excitation wavelengths. The finite difference time domain simulation verifies the experimental results and further reveals that the enhancement for the above system is sensitive to the distance between nanoparticles and the metal film but insensitive to the distance of nanoparticles. On the basis of this finding, we propose and demonstrate an approach of using a nanoparticles-on-metal film substrate as a uniform SERS substrate. This work provides a convenient way to probe the location of strong near-field enhancement with SERS and will have important implications in both surface analysis and surface plasmonics
Three-Dimensional and Time-Ordered Surface-Enhanced Raman Scattering Hotspot Matrix
The “fixed” or “flexible”
design of
plasmonic hotspots is a frontier area of research in the field of
surface-enhanced Raman scattering (SERS). Most reported SERS hotspots
have been shown to exist in zero-dimensional point-like, one-dimensional
linear, or two-dimensional planar geometries. Here, we demonstrate
a novel three-dimensional (3D) hotspot matrix that can hold hotspots
between every two adjacent particles in 3D space, simply achieved
by evaporating a droplet of citrate-Ag sols on a fluorosilylated silicon
wafer. In situ synchrotron-radiation small-angle X-ray scattering
(SR-SAXS), combined with dark-field microscopy and in situ micro-UV,
was employed to explore the evolution of the 3D geometry and plasmonic
properties of Ag nanoparticles in a single droplet. In such a droplet,
there is a distinct 3D geometry with minimal polydispersity of particle
size and maximal uniformity of interparticle distance, significantly
different from the dry state. According to theoretical simulations,
the liquid adhesive force promotes a closely packed assembly of particles,
and the interparticle distance is not fixed but can be balanced in
a small range by the interplay of the van der Waals attraction and
electrostatic repulsion experienced by a particle. The “trapping
well” for immobilizing particles in 3D space can result in
a large number of hotspots in a 3D geometry. Both theoretical and
experimental results demonstrate that the 3D hotspots are predictable
and time-ordered in the absence of any sample manipulation. Use of
the matrix not only produces giant Raman enhancement at least 2 orders
of magnitude larger than that of dried substrates, but also provides
the structural basis for trapping molecules. Even a single molecule
of resonant dye can generate a large SERS signal. With a portable
Raman spectrometer, the detection capability is also greatly improved
for various analytes with different natures, including pesticides
and drugs. This 3D hotspot matrix overcomes the long-standing limitations
of SERS for the ultrasensitive characterization of various substrates
and analytes and promises to transform SERS into a practical analytical
technique
Plasmon-Enhanced Second-Harmonic Generation Nanorulers with Ultrahigh Sensitivities
Attainment
of spatial resolutions far below diffraction limits by means of optical
methods constitutes a challenging task. Here, we design nonlinear
nanorulers that are capable of accomplishing approximately 1 nm resolutions
by utilizing the mechanism of plasmon-enhanced second-harmonic generation
(PESHG). Through introducing Au@SiO<sub>2</sub> (core@shell) shell-isolated
nanoparticles, we strive to maneuver electric-field-related gap modes
such that a reliable relationship between PESHG responses and gap
sizes, represented by “PESHG nanoruler equation”, can
be obtained. Additionally validated by both experiments and simulations,
we have transferred “hot spots” to the film-nanoparticle-gap
region, ensuring that retrieved PESHG emissions nearly exclusively
originate from this region and are significantly amplified. The PESHG
nanoruler can be potentially developed as an ultrasensitive optical
method for measuring nanoscale distances with higher spectral accuracies
and signal-to-noise ratios