404
h. Chon and J. Choo
through thiols or disulfides is the most popular choice for gold nanoparticles. various types of biomolecules, such as antibodies, peptides, oligonucleotides, and other
ligands, have been conjugated to the surfaces of metal nanoparticles using this covalent bonding.
halas and co-workers [39] used o-pyridyldisulfide-n-hydroxysuccinimide
polyethylene glycol (oPSS-PEg-NhS) to tether antibodies to the surface of gold
nanoshells. the S-S terminal group of o-pyridyldisulfide was cleaved and chemically bonded to the metal surface. the other terminal group, succinimidyl propionate, was bound to an amine group on the antibody. When PEg was used, the space
between the probe and antibody was enlarged, and the more favorable antibody
movement greatly improved the efficiency of the antibody-antigen interaction.
Choo and co-workers [40] used dihydrolipoic acid (dhLA) for the antibody conjugation. two –Sh terminal groups of dhLA were cleaved and chemically bound
to the nanoparticles surface. then, –Cooh terminal groups were activated using
N-hydroxysuccinimide (NhS)/1-ethyl-3-(3-dimethylaminopropyl) carbodiimide
hydrochloride (EdC) coupling. Finally, antibody immobilization to the nanoparticles occurred by displacing the NhS group with lysine residues of the antibody.
J. Irudayaraj and co-workers [41] used 11-mercaptoundecanoic acid (mudA)
as the alkanethiol to react with gold nanorods to produce an activated surface for
biofunctionalization. here, antibodies were replaced using an NhS/EdC coupling
reaction. m. A. El-Sayed and co-workers demonstrated gold nanorods directly conjugated to a specific peptide through a thioalkyl-triazole linker molecule. C. A. mirkin and co-workers [42] demonstrated the detection of specific dNA sequences by
tethering probe oligonucleotides to the surface of gold nanoparticles. gold nanoparticles modified with alkylthiol-capped oligonucleotide strands were used as probes
to monitor the presence of target dNA strands. various bioconjugated gold and
silver nanoparticles and their applications are well summarized and reviewed by
v. Biju et al. [43].
14.3 SERS-Based Immunoassay Using Gold-Patterned
Substrates
typically, the SERS technique utilizes the sandwich immunocomplex assay. Capture antibodies are immobilized to a solid substrate, and then antigen solutions
and specific Raman reporter-labelled immuno-Au nanoparticles are sequentially
added. Antigen biomarkers can be quantitatively assayed by monitoring the intensity change of a characteristic SERS peak of the reporter molecule. When reporter
molecules are adsorbed to roughened metal surfaces, their SERS signals are greatly
increased due to electromagnetic and chemical enhancement at SERS active sites
known as “hot junctions” when they are exposed to the excitation laser source. this
enhancement effect shows a promise in overcoming the low sensitivity problem
inherent to conventional Raman spectroscopy. Figure 14.1 displays the SERS-based
immunoassay platform using gold substrates.
h. Chon and J. Choo
through thiols or disulfides is the most popular choice for gold nanoparticles. various types of biomolecules, such as antibodies, peptides, oligonucleotides, and other
ligands, have been conjugated to the surfaces of metal nanoparticles using this covalent bonding.
halas and co-workers [39] used o-pyridyldisulfide-n-hydroxysuccinimide
polyethylene glycol (oPSS-PEg-NhS) to tether antibodies to the surface of gold
nanoshells. the S-S terminal group of o-pyridyldisulfide was cleaved and chemically bonded to the metal surface. the other terminal group, succinimidyl propionate, was bound to an amine group on the antibody. When PEg was used, the space
between the probe and antibody was enlarged, and the more favorable antibody
movement greatly improved the efficiency of the antibody-antigen interaction.
Choo and co-workers [40] used dihydrolipoic acid (dhLA) for the antibody conjugation. two –Sh terminal groups of dhLA were cleaved and chemically bound
to the nanoparticles surface. then, –Cooh terminal groups were activated using
N-hydroxysuccinimide (NhS)/1-ethyl-3-(3-dimethylaminopropyl) carbodiimide
hydrochloride (EdC) coupling. Finally, antibody immobilization to the nanoparticles occurred by displacing the NhS group with lysine residues of the antibody.
J. Irudayaraj and co-workers [41] used 11-mercaptoundecanoic acid (mudA)
as the alkanethiol to react with gold nanorods to produce an activated surface for
biofunctionalization. here, antibodies were replaced using an NhS/EdC coupling
reaction. m. A. El-Sayed and co-workers demonstrated gold nanorods directly conjugated to a specific peptide through a thioalkyl-triazole linker molecule. C. A. mirkin and co-workers [42] demonstrated the detection of specific dNA sequences by
tethering probe oligonucleotides to the surface of gold nanoparticles. gold nanoparticles modified with alkylthiol-capped oligonucleotide strands were used as probes
to monitor the presence of target dNA strands. various bioconjugated gold and
silver nanoparticles and their applications are well summarized and reviewed by
v. Biju et al. [43].
14.3 SERS-Based Immunoassay Using Gold-Patterned
Substrates
typically, the SERS technique utilizes the sandwich immunocomplex assay. Capture antibodies are immobilized to a solid substrate, and then antigen solutions
and specific Raman reporter-labelled immuno-Au nanoparticles are sequentially
added. Antigen biomarkers can be quantitatively assayed by monitoring the intensity change of a characteristic SERS peak of the reporter molecule. When reporter
molecules are adsorbed to roughened metal surfaces, their SERS signals are greatly
increased due to electromagnetic and chemical enhancement at SERS active sites
known as “hot junctions” when they are exposed to the excitation laser source. this
enhancement effect shows a promise in overcoming the low sensitivity problem
inherent to conventional Raman spectroscopy. Figure 14.1 displays the SERS-based
immunoassay platform using gold substrates.