Conventional research on surface-enhanced Raman scattering (SERS)-based pH sensors often depends on nanoparticle aggregation, whereas the variability in nanoparticle aggregation gives rise to poor repeatability in the SERS signal. Herein, we fabricated a gold nanorod array platform via an efficient evaporative self-assembly method. The platform exhibits great SERS sensitivity with an enhancement factor of 5.6 × 10 and maintains excellent recyclability and reproducibility with relative standard deviation (RSD) values of less than 8%. On the basis of the platform, we developed a highly sensitive bovine serum albumin (BSA)-coated 4-mercaptopyridine (4-MPy)-linked (BMP) SERS-based pH sensor to report pH ranging from pH 3.0 to pH 8.0. The intensity ratio variation of 1004 and 1096 cm in 4-MPy showed excellent pH sensitivity, which decreased as the surrounding pH increased. Furthermore, this BMP SERS-based pH sensor was employed to measure the pH value in C57BL/6 mouse blood. We have demonstrated that the pH sensor has great advantages such as good stability, reliability, and accuracy, which could be extended for the design of point-of-care devices.
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.
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