Synthesis of Ag_coreAu_shell Bimetallic Nanoparticles for Immunoassay Based on Surface-Enhanced Raman Spectroscopy

Abstract

Layered core-shell bimetallic silver-gold nanoparticles were prepared by coating Au layers over Ag seeds by a seed-growth method. The composition of Ag100-xAux particles can vary from x=0 to 30. TEM and SEM images clearly show that the bimetallic nanoparticles are of core-shell structure with some pinholes on the surface. Strong surface-enhanced Raman (SER) signals of thiophenol and p-aminothiophenol have been obtained with these colloids. It was found that the SERS activity of aggregated colloids critically depends on the molar ratio of Ag to Au. With the increase of the Au molar fraction, the SERS activity enhances first and then weakens, with the maximal intensity being 10 times stronger than that of Ag colloids. The AgcoreAushell nanoparticles were then labeled with monoclonal antibodies and SERS probes and used for immunoassay analysis. In the proposed system, antibodies immobilized on a solid substrate can interact with the corresponding antigens to form a composite substrate, which can capture reporter-labeled AgcoreAushell nanoparticles modified with the same antibodies. The immunoreaction between the antibodies and antigens was demonstrated by the detection of characteristic Raman bands of the probe molecules. AgcoreAushell bimetallic nanoparticles, as a new SERS active and biocompatible substrate, will be expected to improve the detection sensitivity of immunoassay.

Aqueous synthesis and characterization of Ag and Ag–Au nanoparticles: addressing challenges in size, monodispersity and structure

“…Silver metal has many desirable chemical and physical traits, such as conductivity, catalytic activity and abundance, but it is the optical properties of silver NPs that make it an exceptional candidate for use in bio-diagnostics and sensing, which has been illustrated by such researchers as Cao et al (2001), Cui et al (2006) and Lu et al (2006). The exceptionally high extinction coefficient of Ag NPs associated with the very high enhancement ability in Raman spectroscopy has led to their use as sensing agents in several biological applications, such as the detection of proteins, amino acids, or DNA, by several researchers, including Cao et al (2001) and Cui et al (2006).…”

“…Silver metal has many desirable chemical and physical traits, such as conductivity, catalytic activity and abundance, but it is the optical properties of silver NPs that make it an exceptional candidate for use in bio-diagnostics and sensing, which has been illustrated by such researchers as Cao et al (2001), Cui et al (2006) and Lu et al (2006). The exceptionally high extinction coefficient of Ag NPs associated with the very high enhancement ability in Raman spectroscopy has led to their use as sensing agents in several biological applications, such as the detection of proteins, amino acids, or DNA, by several researchers, including Cao et al (2001) and Cui et al (2006). Despite the promising properties displayed by Ag NPs though, there have been several difficult challenges to address, namely the ability to synthesize Ag NPs in aqueous phase with a desired size, shape or monodispersity (Sharma et al 2009), and the ability to associate the resulting Ag particles with the desired biomolecules so that detection can be performed (Cao et al 2001).…”

Rational design and synthesis of SERS labels

“…40 Ag core/Au shell and Au core/Ag shell NPs are also used as SERS substrates. 42,43 Advantages include the tunability of their LSPR peaks, which can be achieved by changing the composition but without signicantly changing the overall particle diameter; the surface chemistry is dened by the shell material.…”

Magnetic and noble metal nanocomposites for separation and optical detection of biological species

“…Core@shell structures. In an early example of a nanoalloy applied in a SERS sandwich assay, Tian and co-workers 101 described fabrication of Ag@Au (core@shell) NPs labelled with monoclonal goat anti mouse antibodies for IgG for immunorecognition and with thiophenol as the Raman reporter. Synthesis of Ag@Au NPs was carried out by the seed-growth method.…”