Gold-aggregated, dye-embedded, polymer-protected nanoparticles (GDPNs): A new type of tags for detection with SERS

Gold-aggregated, dye-embedded, polymer-protected nanoparticles (GDPNs) are unusual aggregates that involve charge-driven aggregation of gold nanoparticles/poly(l-lysine) functionalized with Raman dye and a poly(l-lysine) (PLL) outer layer. Discrete, submicrometer-sized spherical aggregates are formed through three-step layer-by-layer assembly of polymer/nanoparticle. Unlike most of traditional Raman tags, aggregative gold nanoparticles (Au NPs) are used in GDPNs as the active substrate for increasing the signal of surface enhanced Raman scattering (SERS). Furthermore, the outer PLL layer could lock in Au NPs modified with rhodamine B isothiocyanate (RBITC) and lock out external dye molecules. Specifically, PLL as the outer layer exposes an amino-group rich surface to the surrounding environment that should facilitate the conjugation of GDPNs with biomolecules (antibody/antigen, nucleic acid). These advantages suggest the potential of using GDPNs as Raman tags for multiplex and ultrasensitive detection of biomolecules. The Raman tags were characterized using transmission electron microscopy (TEM), UV–vis absorption spectrometry, and Raman spectrometry.