Published: September 16, 2011 r2011 American Chemical Society 20419 dx.doi.org/10.1021/jp205997u | J. Phys. Chem. C 2011, 115, 20419–20424 ARTICLE pubs.acs.org/JPCC Plasmon-Enhanced Fluorescence and Spectral Modification in SHINEF Ricardo F. Aroca,* ,† Geok Yi Teo, † Haider Mohan, † Ariel R. Guerrero, † Pablo Albella, ‡ and Fernando Moreno § † Department of Chemistry and Biochemistry. Faculty of Science, University of Windsor, Windsor, Ontario N9B 3P4, Canada ‡ Centro de Física de Materiales CSIC-UPV/EHU and Donostia International Physics Center, DIPC, Paseo Manuel Lardiz  abal 5, Donostia-San Sebasti  an 20018, Spain § Departamento Física Aplicada, Grupo de  Optica, Facultad de Ciencias, Universidad de Cantabria, Cantabria, Spain b S Supporting Information ’ INTRODUCTION The introduction of shell-isolated gold nanoparticles to obtain enhanced fluorescence, 1 or SHINEF, invites the question of fine- tuning the properties of the coated nanoparticles for maximum enhancement, such as the core size and shape as well as shell thickness. In addition, the versatility provided by the easy use of the SHINs, offers a unique opportunity to investigate the question of spectral profile modification and extract further understanding of the nature of plasmon enhanced fluorescence. Here, we present experimental results with SHINs of different sizes and shell thick- ness, and the interpretation of results is helped by computational modeling using finite-difference time-domain and DDA methods. In addition, the question of spectral profile modification 2,3 is exam- ined using well-defined two-dimensional structures or LangmuirÀ Blodgett monolayers of two emitters (monomer and excimer) of the same fluorophore. The emission of the fluorophore is strongly affected by its interactions with the electromagnetic environment. The fluor- ophore can completely lose its ability to emit by transferring its excitation energy to a metal surface 4 (fluorescence quenching). However, some metal nanostructures sustaining localized surface plasmon resonances 5,6 (LSPR) can enhance the emission under the right conditions of excitation, geometry, and metalÀmolecule spacing, producing surface-enhanced fluorescence (SEF). Once the LSPR is excited, the key parameter is the metalÀmolecule separation. In SHINEF, a plasmon-enhancing nanostructure with a built-in spacer is used for practical applications. In surface- enhanced Raman scattering (SERS), 6À8 the highest enhance- ment comes from molecules either directly attached to the metal nanostructure or very close to it, 9 and consequently, the spectral properties (wavenumber and relative intensities) of the species adsorbed onto the metal nanoparticles may change on account of the chemical or physical interactions with the nanostructure. Correspondingly, the far field scattering of electromagnetically enhanced SERS spectrum will contain the information that sheds light on these moleculeÀnanostructure interactions. The spec- tral modification in SERS due to the properties of the far field scattering itself is difficult to separate in the observed SERS spectra, although it has been identified by several groups. 10,11 For physisorbed molecules and submonolayer surface coverage the plasmon effects can be clearly captured in the far field scattering. 12 In SHINEF (or SEF, in general) the molecule is about 10 nm away from the metal surface, and the spectral modi fication is almost entirely due to the plasmonic modi fication of the observed enhanced spectrum. ’ EXPERIMENTAL SECTION All glassware used was cleaned with aqua regia (1:3 ratio of HNO 3 /HCl) and rinsed thoroughly with ultrapure (Milli-Q, 18.2 MΩ 3 cm) water. The solvent used in all solution preparations is ultrapure Milli-Q water, unless stated otherwise. Tetrachloroauric acid (HAuCl 4 3 3H 2 O), cetyltrimethylammonium bromide (CTAB), sodium borohydride (NaBH 4 ), ascorbic acid, tetraethylorthosi- licate (TEOS), and arachidic acid (AA) were purchased from Sigma-Aldrich and used without further purification. SHIN Particle Synthesis. SHINs were prepared according to the method described by Grabar et al. 13 and Li et al. 9 with slight Received: June 25, 2011 Revised: August 15, 2011 ABSTRACT: Shell-isolated gold nanoparticles provide a reliable, portable, and efficient substrate for luminescence enhancement giving surface-enhanced fluorescence, termed SHINEF. The objectives of the present work are 2-fold: first, tuning the size of the gold core and the shell thickness for maximum SHINEF enhancement, and second, to use the shell isolated nanoparticles (SHINs) to demonstrate the spectral profile modification of the fluorescence spectrum. It is shown, using LangmuirÀBlodgett monolayers of a dye with two distinct emissions (monomer and excimer), that the far field radiation of the nanostructure modulate the observed emission from the target fluorophore located in the near field zone of the nanostructure sustaining localized surface plasmon resonances (LSPR).