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Very monodisperse water-soluble silica core-surfactant shell nanoparticles (SCSS NPs) doped with a rhodamine B derivative were prepared using micelles of F127 as nanoreactors for the hydrolysis and condensation of the silica precursor tetraethoxysilane (TEOS). The functionalization of the rhodamines with a triethoxysilane group allowed the covalent binding of the fluorophores to the silica core: no leaking of the dye was observed when the NPs were purified either by ultrafiltration (UF) or dialysis. The diameter of the core (d(c) = 10 ± 1 nm) was determined by TEM and subtracted from the hydrodynamic diameter, measured by DLS, (d(H) = 24 nm, PdI = 0.1) to calculate the shell thickness (∼7 nm). The presence of a single population of NPs with a radius compatible with the one measured by DLS after UF was confirmed by AF4-MALS-RI measurements. The concentration of the NPs was measured by MALS-RI. This allowed us to determine the average number of rhodamine molecules per NP (10). The ability of the NPs to host hydrophobic species as cyanines in the SS was confirmed by fluorescence anisotropy measurements. Steady-state and time-resolved fluorescence measurements allowed us to observe the occurrence of a very efficient Förster resonance energy transfer process from the covalently linked rhodamines to the hosted cyanines. In particular, the analysis of the TCSPC data and steady-state measurements revealed that the adsorption of a single cyanine molecule causes an almost complete quenching of the fluorescence of the NP. Thanks to these observations, it was possible to easily determine the concentration of the NPs by fluorescence titration experiments. Results are in good agreement with the concentration values obtained by MALS-RI. Finally, the hosted cyanine molecule could be extracted with (±)-2-octanol, demonstrating the reversibility of the adsorption process.

Biocompatible highly bright silica nanoparticles were designed, prepared and tested in small living organisms for both in vivo and ex vivo imaging. The results that we report here demonstrate that they are suitable for optical imaging applications as a possible alternative to commercially available fluorescent materials including quantum dots. Moreover, the tunability of their photophysical properties, which was enhanced by the use of different dyes as doping agents, constitutes a very important added value in the field of medical diagnostics.

Seven new bio-inspired chemosensors (2-4 and 7-10) based on fluorescent peptides were synthesized and characterized by elemental analysis, 1H-NMR, 13C-NMR, melting point, matrix assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), infrared, UV-vis absorption and emission spectroscopy. The interaction with transition and post-transition metal ions (Cu2+, Ni2+, Ag+, Zn2+, Cd2+, Hg2+, Pb2+ and Fe3+) has been explored by absorption and fluorescence emission spectroscopy and MALDI-TOF mass spectrometry. The reported fluorescent peptide systems, introducing biological molecules in the skeleton of the probes, enhance their sensitivity and confer them strong potentials for applications in biological fields. Gold and silica nanoparticles functionalized with these peptides were also obtained. All nanoparticles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), UV-vis absorption and fluorescence spectroscopy. Stable gold nanoparticles (diameter 2-10 nm) bearing ligands 1 and 4 were obtained by common reductive synthesis. Commercial silica nanoparticles were decorated at their surface using compounds 8 to 10, linked through a silane spacer. The same chemosensors were also taken into aqueous solutions through their dispersion in the outer layer of silica core/PEG shell nanoparticles. In both cases, these complex nanoarchitectures behaved as new sensitive materials for Ag+ and Hg2+ in water. The possibility to use these species in this solvent is particularly valuable since the impact on human health of heavy and transition metal ions pollution is very severe, and all analytical and diagnostics investigations involve a water environment., Fundação para a Ciência e a Tecnologia (FCT), Universidade do Minho (UM)

Silica nanoparticles are versatile platforms with many intrinsic features, such as low toxicity. Proper design and derivatization yields particularly stable colloids, even in physiological conditions, and provides them with multiple functions. A suitable choice of dyes and synthetic strategy may, in particular, yield a very bright nanosystem. Silica nanoparticles thus offer unique potential in the nanotechnology arena, and further improvement and optimization could substantially increase their application in fields of high social and economic impact, such as medical diagnostics and therapy, environmental and food analysis, and security. This paper describes silica-based, multicomponent nanosystems with intrinsic directional energy- and electron- transfer processes, on which highly valued functions like light harvesting and signal amplification are based.

The design of fluorescent chemosensors for biologicallyrelevant chemical species has important impacts in many ap-plications, and for this reason it has been the subject ofactive research in many laboratories worldwide. The ach-ievements in this wide research topic have promoted enor-mous steps forwards, for example, in the field of cell biology,thanks to the comprehension of the role of different chemi-cal species in many biological processes. Recently, research-ers have been moving from molecular chemosensors basedon two communicating units, a receptor and a dye, towardmore complex and sophisticated structures, and have triedto push further the limits of sensitivity and selectivity. Manydifferent solutions have been proposed but, among them,sensing systems based on nanoparticles are certainly one ofthe most interesting and promising.

Electronic energy transfer is a crucial photophysical process, since it is at the basis of essential natural phenomena such as photosynthesis, as well as of widely spread artificial molecular devices; moreover, it is a very valuable tool for measuring distances at the nanometer level. For artificial systems, the possibility to take profit of energy transfer processes has enormously increased with the advent of supramolecular chemistry,1 and a new additional boost is expected to be observed with the very rapid growth of nanotechnology, in many different fields, ranging from medical diagnostics to solar energy conversion. In the context of nanotechnology, a great and increasing interest is devoted to nanoparticles.2 Nanoparticles can be made of many different materials, including polymers, metals, semiconductors, or a combination of them. Their versatility and different properties have already gained them many industrial applications in a wide range of fields, such as electronics, medicine and material sciences. One of the cut-edge fields in nanoparticle research is the enhancement of biological imaging for medical diagnostics and drug delivery. In this article, we will focus our attention on the potentialities offered by the use of energy transfer processes in dye-doped or dye-coated silica nanoparticles (DDSN or DCSN respectively),3-10 which conjugate a simple and low-cost preparation with the possibility to obtain sophisticated, but robust, multifunctional systems, especially when they are designed as ‘onion-like’, multilayer structures. The design of these systems is not trivial and it has to be carefully studied to be able to foresee the photophysical characteristics of the resulting materials. On the other hand, despite the complexity of these systems, their synthesis is relatively simple and very versatile. These features make them a very powerful tool to obtain very complex and precious functions from low cost and easy to prepare nanoobjects. In the next paragraphs we will present the most common synthetic strategies to obtain dye doped and dye covered silica nanoparticles and discuss many examples, but we would like to start introducing the energy transfer process and its great scientific and applicative importance.