Nanocomposites With Strong Optical Resonances: Silver Nanoparticles-Organic Molecules Systems

The ability of selected molecular species to link Ag nanoparticles into dimers and/or small aggregates has been tested. Dimercaptocarborane and ethidium bromide have been shown to link Ag nanoparticles via their bonding to Ag nanoparticle surface probably by the two strongly argentophilic groups in para-positions. Alternatively, dimers and small aggregates were assembled through an electrostatic interaction between negatively charged citrate-modified and positively charged polylysine-modified Ag nanoparticles, and a subsequent incorporation of 5, 10, 15, 20-tetrakis(4-sulphonato-phenyl)porphine (TSPP) into such preprepared nanoobjects has been probed by SERRS (surface-enhanced resonance Raman scattering). Formation of dimers and small aggregates has been established by TEM (transmission electron microscopy) and SEM (scanning electron microscopy). SE(R)RS spectral measurements from specific locations of samples containing molecularly-linked dimers and aggregates have shown temporal fluctuations (blinking) of the SE(R)RS signal, which indicates, that the signal likely originates from molecules located in the strong, nanoscale localized optical fields dubbed hot spots. In addition to that, characteristic bands of graphitic carbon were observed in the spectra and their intensities (together with the spectral background intensities) strongly varied with time and from one spectrum to another. One of the possible explanations of these observations is a photochemical and/or thermal decomposition of the molecules located in hot spots combined with diffusion of unperturbed molecules into hot spots.