2 research outputs found
Tip-Functionalized Au@Ag Nanorods as Ultrabright Surface-Enhanced Raman Scattering Probes for Bioimaging in Off-Resonance Mode
Surface-enhanced
Raman scattering (SERS) performance of Au nanorods
(AuNRs) can be enhanced by the tip adsorption of Raman molecules (RMs)
through anisotropic polymer stabilization or through the embedding
of RMs between AuNR cores and Ag shells of AuNR@RM@Ag composite particles.
We propose a new strategy to design ultrabright SERS probes composed
of high-aspect-ratio AuNRs with anisotropic Ag coatings, with preferred
adsorption of RMs to open AuNR tips. Specifically, for 4-nitrobenzenethiol
(NBT) concentrations above a threshold value <i>c</i> > <i>c</i><sub>tr</sub>, the fabricated Au@NBT@Ag particles had NBT-functionalized
open Au tips, as well as anisotropic Ag shells grown on the AuNR sides.
The SERS response of these probes with an optimal Ag shell was highest
in the off-resonance mode, when the excitation wavelength was far
from the plasmon resonance of the Au@NBT@Ag composites. Growing the
Ag shell further to completely cover the AuNRs decreased the SERS
enhancement. For biocompatibility and stability, the probes were additionally
covered with a thin silica layer. Under optimal conditions, the probes
demonstrated superstrong and superstable SERS spectra, as compared
to those from common SERS tags (AuNRs, nanostars, and Au@Ag NRs) with
surface-adsorbed NBT. The excellent SERS performance of the developed
ultrabright probes is illustrated by single-particle detection of
SERS spectra, Raman imaging of living cells, and deep tissue imaging
Gold Nanoisland Films as Reproducible SERS Substrates for Highly Sensitive Detection of Fungicides
A wet-chemical approach is used to
fabricate centimeter-scale gold
nanoisland films (NIFs) with tunable morphology of islands and with
strong electromagnetic coupling between them. The approach consists
in a uniform seeding of small gold nanoparticles on a glass or silicon
substrate, followed by controllable growth of the seeds into small
nanoislands. A special technique for TEM sampling was developed to
follow the gradual formation of larger-sized isolated nanoparticles,
nanoislands of sintered overgrown seeds, and a complete gold layer
with nanoscale cracks. The electromagnetic field distribution inside
the fabricated NIFs was calculated by FDTD simulations applied to
actual TEM images of the fabricated samples rather than to artificial
models commonly used. SERS measurements with 1,4-aminothiophenol (ATP)
molecules demonstrated the analytical enhancement factor about of
10<sup>7</sup> and the fundamental enhancement factor about of 10<sup>8</sup> for optimized substrates. These values were at least 1 order
of magnitude higher than that for self-assembled arrays of gold nanostars
and silver nanocubes. SERS spectra of independent samples demonstrated
good sample-to-sample reproducibility in terms of the relative standard
deviation (RSD) of the main peaks less than 20%. Additionally, Raman
maps with 1 μm increment in <i>X</i>–<i>Y</i> directions of NIFs (800 spectral spots) demonstrated good
point-to-point repeatability in the intensity of the main Raman vibration
modes (RSD varied from 5% to 15% for 50 randomly selected points).
A real-life application of the fabricated SERS substrates is exemplified
by the detection of the thiram fungicide in apple peels within the
5–250 ppb linear detection range. Specifically, the NIF-based
SERS technology detected thiram on apple peel down to level of 5 ng/cm<sup>2</sup>