Preparation and Characterization of Multicore SERS Labels by Controlled Aggregation of Gold Nanoparticles
in: Vibrational Spectroscopy (2012)
Optimized labels for surface enhanced Raman spectroscopy (SERS) give comparable sensitivities than fluorescence labels. Most important advantages of the SERS approach are the narrow width of Raman bands and the fingerprint-like specificity of the vibrational signature allowing for the simultaneous detection of different SERS labels. We developed photo-stable and multiplexing-compatible multicore SERS labels (MSL) for excitation at 785 nm. MSL consist of single gold nanoparticles, whose aggregation is controlled by a specific diamine. The synthesis was optimized to obtain clusters of gold-silver nanoparticles with an average diameter of 120 nm. At the interface of two or more individual nanoparticles within the clusters the electromagnetic enhancement is most intense. Furthermore, nanoparticles above 100 nm were shown to be less toxic in living biological materials. As SERS markers we use molecules with aromatic ring structures with high polarizability and characteristic Raman signature to allow multiplexing. All markers have sulfur groups to conjugate them covalently to the gold surface. A stable silica shell protects the MSL against impurities by other markers in multiplexing applications. This shell is coated with silanes to provide the binding site for conjugation of biomolecules. The MSL will be functionalized with antibodies to bind specific antigens of biological samples. These properties make differently labeled MSL with a biocompatible size a promising candidate for diagnostic applications.