Eosin Y (EY) is a fluorescein derivative dye that can
be reduced
by accepting either one or two electrons. The one- or two-electron
reduction potentials have comparable values. The two-electron reduction
pathway dominates when sodium borohydride is used, whereas the reduction
pathway changes to a one-electron reduction pathway when gold solid
(AuNS) or hollow (AuHS) nanosphere catalysts are used. The reduction
reaction of EY by borohydride proceeds via one kinetic stage, whereas
in the presence of gold nanocatalysts, three different stages are
identified. The first stage has the same reaction rate as in the absence
of the nanocatalyst, and no one-electron product is observed (absorption
peak at 405 nm). The second stage starts when the rate of the disappearance
of EY is suddenly increased; a new peak at 405 nm beings to appear.
This stage ends when the rate of the disappearance of EY decreases.
The third stage has a rate close to that of the first stage, and the
EY is reduced again by accepting two electrons. The lifetime of the
first stage is greatly affected by the concentration of the nanocatalyst
and decreases as the concentration of the nanocatalyst is increased.
The conversion ratio of EY to its one-electron reduced form is found
to increase proportionally with the concentration of the gold nanocatalyst.
In the case of using hollow nanospheres as a catalyst, the conversion
ratio is found to be 3 times higher than that when using the solid
nanospheres due to the cage effect.
The
identification and detection of cancer biomarkers in early
stages is an important issue for the therapy of cancer. However, most
methods are time-consuming and have limited sensing sensitivity and
specificity. In this work, we prepared a novel plasmonic multilayered
core–shell–satellite nanostructure (Au@Ag@SiO2–AuNP) consisting of a gold nanosphere with a silver coating
core (Au@Ag), an ultrathin continuous silica (SiO2) shell,
and a high coverage of gold nanosphere (AuNP) satellites. The Au@Ag
core is a prominent surface enhanced Raman scattering (SERS) platform,
and the thin SiO2 layer exhibits a long-range plasmon coupling
between the Au@Ag core to the AuNP satellites, further leading to
enhanced Raman scattering. Meanwhile, the outer AuNP satellites have
a high biocompatibility and long-term stability. Combining the above
advantages, the well-designed metallic nanoassemblies would be a promising
candidate for SERS-based applications in biochemistry. For specific
detection of alpha-fetoprotein (AFP), we utilized the SERS-active
core–shell–satellite nanostructures modified with AFP
antibody as immune probes and nitrocellulose membrane (NC) stabilized
captured anti-AFP antibodies as solid substrate. To improve the detection
performance, we further systematically optimized the parameters, including
the silver coating thickness of the Au@Ag core and the density and
size of the satellite AuNPs. Under the optimized conditions, AFP could
be detected by the SERS-based sandwich immunoassay with an ultralow
detection limit of 0.3 fg/mL, and the method exhibited a wide linear
response from 1 fg/mL to 1 ng/mL. The limit of detection (LOD) was
considerably lower than conventional methods in the literature. This
work relies on the unique Au@Ag@SiO2–AuNP nanostructures
as the immune probe develops a new outlook for the application of
multilayered nanoassemblies and demonstrates the great potential in
early tumor marker detection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.