@conference{
author = "Ralević, Uroš and Isić, Goran and Laban, Bojana and Vodnik, Vesna and Vasić, Vesna and Gajić, Radoš",
year = "2015",
abstract = "Dye-coated colloidal metal nanoparticles (NPs) exhibit interesting optical properties originating from the interaction between metal core and dye shell. Depending on the interaction mechanism between the two, optical properties of dyes or NPs can be changed separately or jointly within the dye-NP assembly [1]. Many of the recent studies are focused on dyes which are able to self-assemble in highly oriented structures called Jaggregates on the surface of metallic NPs [2,3]. Owing to the variety of mechanisms by which dyes and their J-aggregates can interact with metallic NPs, dye-NP assemblies can lead to applications ranging from nanoscale sensing [4] to advanced composite materials for novel active and nonlinear optical devices [5]. Here we study the influence of TC concentration on its J-aggregation on the surface of AgNPs assemblies using Raman mapping and atomic force microscopy (AFM). Aqueous solutions (colloids) of citrate stabilized AgNPs with an average diameter of ~10 nm are mixed with TC dye solution and then deposited onto freshly cleaved highly oriented pyrolytic graphite and mica surfaces. The spectral signature of citrate ions is identified by (i) the O-H band around 220 cm-1, (ii) the C-H band around 2950 cm-1 and (iii) pronounced blinking in the 1000-1800 cm-1 range. In contrast, dye molecules adsorbed on nanoparticles are recognized by several stable Raman bands between 200 and 1600 cm-1. In situ AFM measurements show that SERS 'hot spots' are formed either on large single nanoparticles (diameter > 100 nm) or within assemblies of small nanoparticles (with diameters in the 10 - 50 nm range). However, only the latter are found to yield a citrate or TC dye SERS signal. We find that the TC dye adsorbed on the surface of AgNP nanoassemblies always forms J-aggregates when the dye concentration in the TC-AgNP solution is varied between 0.5μM and 17μM. Even though, a clear SERS spectra of dye Jaggregates can be acquired for high dye concentration (17μM) the citrate ions always exist on the AgNP surface and so does their SERS signature in form of O-H (220 cm-1) and C-H (2960 cm-1) bands. Assemblies with low TC concentration (0.5μM) do not have a clear dye SERS spectra, but rather spectra similar to the one of citrate ions meaning that either not all AgNPs are dye coated, or rather that the amount of TC molecules adsorbed on the surface of the nanoparticle is small and hence not detectable. We are grateful to the Serbian Ministry of Education, Science and Technological Development for financial support through projects Nos. OI 171005, OI 172023. This work was performed in the context of the European COST Action MP1302 Nanospectroscopy.",
publisher = "Belgrade : Vinča Institute of Nuclear Sciences",
journal = "PHOTONICA2015 : 5th International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 : book of abstracts; August 24-28, 2015; Belgrade",
title = "Surface enhanced Raman spectroscopy of thiacyanine dye J-aggregates on single silver nanoaggregates",
pages = "97-98",
url = "https://hdl.handle.net/21.15107/rcub_vinar_12006"
}
