Moreover, the hybridization of plasmons localized at the core and the tips of the stars results in the increased Wortmannin molecular weight effective dipole moment of the tip plasmons and the enlarged cross section for plasmon excitation [19]. In this study, we use these advantages of gold nanostars to develop their hybrid structures with J-aggregates of different organic dyes operating in the strong coupling regime. Methods Gold nanostars were synthesized in an aqueous solution using cetyltrimethylammonium bromide (CTAB) as the capping and growth-regulating
agent [17]. A transmission electron microscopy (TEM) image of nanostars (obtained using Philips CM20 TEM, Amsterdam, The Netherlands) is shown in Figure 2. TEM image of a single HDAC inhibitor multispiked nanostar is shown as inset in Figure 2. Figure 2 TEM image of star-shaped gold see more nanoparticles. J-aggregates were formed from the following two dyes: JC1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-imidacarbocyanine iodide) and S2165 2-[3-[1,1-dimethyl-3-(4-sulfobutyl)-1,3-dihydro-benzo[e]indol-2-ylidene]-propenyl]-1,1-dimethyl-3-(4-sulfobutyl)-1H-benzo[e]indolium hydroxide. J-aggregates of the JC1 dye form spontaneously upon dissolution of this dye in deionized water at pH7, while the formation of J-aggregates
of S2165 required the addition of polyethyleneimine (PEI). The reason why we choose these particular dyes was that upon aggregation they develop very narrow absorption bands (J-bands) both located very close to the maximum of nanostar absorption which favors the regime of strong plasmon-exciton coupling in hybrid systems. Hybrid structures of gold nanostars and the J-aggregates GNAT2 of the JC1 dye were produced by the addition of the concentrated ethanol solution of the dye to an aqueous solution of gold nanostars in the presence of ammonia at pH8. Interactions between nanostars and JC1 molecules of J-aggregates resulted in the formation of chain-like tightly bound agglomerates of gold nanostars interconnected by an organic matter, with a typical appearance exemplified in the scanning electron microscopy image (obtained using an environmental scanning electron
microscope Quanta 250 FEG, FEI, Hillsboro, OR, USA) in Figure 3. These agglomerates were separated from the excess of dye molecules or J-aggregates not bound to gold nanostars by centrifugation at 3,800 rpm for 2 min and redispersed in aqueous solution. CTAB, which was used in the synthesis of nanostars, is not only the shape-directing agent for anisotropic growth but also the stabilizer [17] which provides a net positive surface charge to the nanoparticles, making them suitable for the formation of agglomerates with oppositely charged species like J-aggregates due to electrostatic interactions [22–24]. In our case, these interactions favored the formation of chain-like organic/inorganic structures (Figure 3). Figure 3 Surface-enhanced Raman spectra, scanning electron microscopy image, and Raman micromapping.