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h. Chon and J. Choo
overcomes the slow immunoreaction problems caused by diffusion-limited kinetics
on a solid substrate because the reaction occurs in solution. In addition, the loading density of the capture antibody on a magnetic bead is dramatically increased
because three-dimensional microspheres were used instead of two-dimensional microarrays. As a result, the assay time is greatly reduced, and the detection sensitivity
is greatly increased. Furthermore, it is possible to obtain more reproducible results
because the SERS signals are measured for the average nanoparticle ensemble in
solution.
R. Yu and co-workers [46] demonstrated a SERS immunoassay method combining a glass-encapsulated silver nanotag as a detection probe and glass-encapsulated
magnetic nanoparticles as an immobilization matrix and separation tool for an
immunoassay of alpha-fetoprotein (AFP). When silver nanoparticles are used for
quantitative measurements, optimal aggregation conditions are required for signal
enhancement. however, in many cases, the over-aggregation of silver nanoparticles
leads to particle precipitation over time, and this reduces the reproducibility of the
SERS signals.
to resolve this problem, J. Choo and co-workers [47] fabricated hollow gold
nanospheres (hgNs) and used them as single nanoparticle SERS agents. these particles show strong enhancement effects from individual particles because of their
ability to localize the surface electromagnetic fields through pinholes in the hollow particle structures. As a result, they can be used as highly reproducible sensing probes for the quantitative immune-analysis of specific markers. the feasibility
of the SERS-based detection method was investigated using hgNs and magnetic
beads for a well-known lung cancer marker, carcinoembryonic antigen (CEA).
here, the Lod (limit of detection) was determined to be 1–10 pg/mL, and this
value shows that SERS is approximately 100–1000 times more sensitive than an
ELISA [48]. this SERS-based immunoassay technique has several advantages over
previously reported SERS detection methods using the immobilization of an immunocomplex on a solid substrate with respect to good reproducibility and a fast
assay time. Figure 14.4 displays schematic illustrations of hgNs, immunoassay
processes, and corresponding Raman spectra.
Q. Zhang and co-workers [49] used Fe 3 o 4 /Au core-shell nanoparticles as SERS
substrates instead of magnetic beads. the particles were prepared by combining
microwave-assisted synthesis of Fe 3 o 4 cores with Amal’s method of coating Au
shells with the aid of poly(ethyleneimine). this SERS-based immunoassay technique provides additional hot spots between gold and core-shell nanoparticles. the
assay technique was applied for the detection of free prostate cancer antigens.
Z. Zhang and co-workers [50] fabricated new SERS nanoprobes with hybrid
multilayered nanoshells prepared by the layer-by-layer (LBL) assembly of small
silver nanoparticles on the surface of silica particles using poly(ethyleneimine). the
huge electromagnetic enhancement was achieved by strong plasmon coupling between shell multilayers, and uncertain effects on SERS signals resulting from the
variability of configurations are minimized by the assembly of small silver nanoparticles. Figure 14.5 shows the SERS-based sandwich immunoassay process using silica-encapsulated magnetic nanoparticles and multilayered silver shell nanoprobes.
h. Chon and J. Choo
overcomes the slow immunoreaction problems caused by diffusion-limited kinetics
on a solid substrate because the reaction occurs in solution. In addition, the loading density of the capture antibody on a magnetic bead is dramatically increased
because three-dimensional microspheres were used instead of two-dimensional microarrays. As a result, the assay time is greatly reduced, and the detection sensitivity
is greatly increased. Furthermore, it is possible to obtain more reproducible results
because the SERS signals are measured for the average nanoparticle ensemble in
solution.
R. Yu and co-workers [46] demonstrated a SERS immunoassay method combining a glass-encapsulated silver nanotag as a detection probe and glass-encapsulated
magnetic nanoparticles as an immobilization matrix and separation tool for an
immunoassay of alpha-fetoprotein (AFP). When silver nanoparticles are used for
quantitative measurements, optimal aggregation conditions are required for signal
enhancement. however, in many cases, the over-aggregation of silver nanoparticles
leads to particle precipitation over time, and this reduces the reproducibility of the
SERS signals.
to resolve this problem, J. Choo and co-workers [47] fabricated hollow gold
nanospheres (hgNs) and used them as single nanoparticle SERS agents. these particles show strong enhancement effects from individual particles because of their
ability to localize the surface electromagnetic fields through pinholes in the hollow particle structures. As a result, they can be used as highly reproducible sensing probes for the quantitative immune-analysis of specific markers. the feasibility
of the SERS-based detection method was investigated using hgNs and magnetic
beads for a well-known lung cancer marker, carcinoembryonic antigen (CEA).
here, the Lod (limit of detection) was determined to be 1–10 pg/mL, and this
value shows that SERS is approximately 100–1000 times more sensitive than an
ELISA [48]. this SERS-based immunoassay technique has several advantages over
previously reported SERS detection methods using the immobilization of an immunocomplex on a solid substrate with respect to good reproducibility and a fast
assay time. Figure 14.4 displays schematic illustrations of hgNs, immunoassay
processes, and corresponding Raman spectra.
Q. Zhang and co-workers [49] used Fe 3 o 4 /Au core-shell nanoparticles as SERS
substrates instead of magnetic beads. the particles were prepared by combining
microwave-assisted synthesis of Fe 3 o 4 cores with Amal’s method of coating Au
shells with the aid of poly(ethyleneimine). this SERS-based immunoassay technique provides additional hot spots between gold and core-shell nanoparticles. the
assay technique was applied for the detection of free prostate cancer antigens.
Z. Zhang and co-workers [50] fabricated new SERS nanoprobes with hybrid
multilayered nanoshells prepared by the layer-by-layer (LBL) assembly of small
silver nanoparticles on the surface of silica particles using poly(ethyleneimine). the
huge electromagnetic enhancement was achieved by strong plasmon coupling between shell multilayers, and uncertain effects on SERS signals resulting from the
variability of configurations are minimized by the assembly of small silver nanoparticles. Figure 14.5 shows the SERS-based sandwich immunoassay process using silica-encapsulated magnetic nanoparticles and multilayered silver shell nanoprobes.