Preparation and characterization of multicore SERS labels by controlled aggregation of gold nanoparticles

The preparation and characterization of multicore labels for surface enhanced Raman scattering (SERS) at 785 nm excitation are described. These labels consist of gold nanoparticles whose aggregation was controlled by a diamine. SERS reporters were attached that contain sulfur groups for covalent conjugation to the gold surface and aromatic ring structures for distinct Raman signatures. A thin silver layer was deposited onto aggregated gold nanoparticles to further enhance the SERS signals. Two polymers were deposited to prepare the surface for encapsulation by silica and stabilize nanoparticles. The thickness of the silica layer depended on ammonia concentration and was determined by transmission electron microscopy. Treatment with APTMS provided amino groups for subsequent conjugation with antibodies. N–H bending vibrations of amino silane were detected by infrared spectroscopy. Functionalization of the silica coated multicore labels by a FITC labeled antibody was confirmed by fluorescence microscopy. A Zetasizer determined an average radius of 60 nm. SERS spectra of labels with three different reporters and a SERS spectrum of mixed labels with exposure time between 10 ms and 1 s demonstrated the high sensitivity and multiplexing capacity. This design of multicore labels offers 785 nm near-infrared excitation for reduced laser-induced cell degradation, size above 100 nm for low toxicity under in vivo investigations as reported elsewhere, high stability due to silica encapsulation, and capability of antibody binding. These biocompatible properties make multicore labels with different reporters a promising candidate for diagnostic applications.