Riccardo Juris

Luminescent Silica Nanoparticles: Extending the Frontiers of Brightness

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.

Iridium Doped Silica−PEG Nanoparticles: Enabling Electrochemiluminescence of Neutral Complexes in Aqueous Media

We report for the first time the stable electrochemiluminescence of a completely insoluble neutral Ir(III) complex in aqueous media. The strategy adopted is the encapsulation of emitting dye into silica-PEG nanoparticles. This nanoassembly by limiting water and oxygen quenching and allowing solubilization makes the electrogeneration of the excited state feasible under typical bioassay conditions.

Energy transfer from silica core-surfactant shell nanoparticles to hosted molecular fluorophores.

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.

Prevention of Self‐Quenching in Fluorescent Silica Nanoparticles by Efficient Energy Transfer

Stars that shine bright: A high local dye concentration in doped silica-based core–shell nanoparticles causes self-quenching and spectral broadening (top images). This phenomenon jeopardizes the potential advantages of heavily doped systems. Förster resonance energy transfer (FRET) to an acceptor co-included in the silica led to ultrabright nanoparticles (bottom images) with a preselected narrow-band emission and a pseudo-Stokes shift of 129 nm.

Luminescent Chemosensors Based on Silica Nanoparticles

The field of nanoparticles is amazingly many-sided and consequently their applications range between many different areas from industry to bio-analysis and catalysis. In particular, luminescent nanoparticles attract close attention in the areas of biology, medical diagnosis and therapy, where they already find many applications. In this so fascinating and wide framework we have focussed our attention on luminescent silica nanoparticles able to act as sensing materials. We highlight here the importance, especially with the aim of sensing, of gaining precise knowledge and control of their structures; the performance of a chemosensor is, in fact, totally dependent on its design. We then briefly present the state of the art and the progress both in the synthetic protocols and in the application of luminescent silica nanoparticles as chemosensors. We present many recent examples, organized into two main sections, the first dealing with systems presenting the signalling units on the surface (dye coated silica nanoparticles, DCSNs) and the second with systems entrapping the dyes inside the silica matrix (dye doped silica nanoparticles, DDSNs).

Bioinspired Systems for Metal-Ion Sensing: New Emissive Peptide Probes Based on Benzo(d)oxazole Derivatives and Their Gold and Silica Nanoparticles )

Seven new bioinspired chemosensors (2-4 and 7-10) based on fluorescent peptides were synthesized and characterized by elemental analysis, (1)H and (13)C NMR, melting point, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and IR and UV-vis absorption and emission spectroscopy. The interaction with transition- and post-transition-metal ions (Cu(2+), Ni(2+), Ag(+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Fe(3+)) has been explored by absorption and fluorescence emission spectroscopy and MALDI-TOF-MS. The reported fluorescent peptide systems, introducing biological molecules in the skeleton of the probes, enhance their sensitivity and confer them strong potential for applications in biological fields. Gold and silica nanoparticles functionalized with these peptides were also obtained. All nanoparticles were characterized by dynamic light scattering, transmission electron microscopy, and 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 8-10, linked through a silane spacer. The same chemosensors were also taken into aqueous solutions through their dispersion in the outer layer of silica core/poly(ethylene glycol) shell nanoparticles. In both cases, these complex nanoarchitectures behaved as new sensitive materials for Ag(+) and Hg(2+) in water. The possibility of using these species in this solvent is particularly valuable because the impact on human health of heavy- and transition-metal-ion pollution is very severe, and all analytical and diagnostics investigations involve a water environment.

A Versatile Strategy for Signal Amplification Based on Core/Shell Silica Nanoparticles

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.

Targeted dual-color silica nanoparticles provide univocal identification of micrometastases in preclinical models of colorectal cancer

Background and methods Despite the recent introduction of targeted bio-drugs, the scarcity of successful therapeutic options for advanced colorectal cancer remains a limiting factor in patient management. The efficacy of curative surgical interventions can only be extended through earlier detection of metastatic foci, which is dependent on both the sensitivity and specificity of the diagnostic tools. Results We propose a high-performance imaging platform based on silica-poly(ethylene glycol) nanoparticles doped with rhodamine B and cyanine 5. Simultaneous detection of these dyes is the basis for background subtraction and signal amplification, thus providing high-sensitivity imaging. The functionalization of poly(ethylene glycol) tails on the external face of the nanoparticles with metastasis-specific peptides guarantees their homing to and accumulation at target tissues, resulting in specific visualization, even of submillimetric metastases. Conclusions The results reported here demonstrate that our rationally designed modular nanosystems have the ability to produce a breakthrough in the detection of micrometastases for subsequent translation to clinics in the immediate future.

Energy Transfer in Silica Nanoparticles: An Essential Tool for the Amplification of the Fluorescence Signal

The careful design of dye doped silica nanoparticles in order to induce controllable energy transfer processes can yield very sophisticated species able to perform precious and complex functions. They can be therefore exploited in many fields of great economical and social importance, such as medical diagnostics, molecular biology, and solar energy conversion. In this chapter, we present the characterization of some functionalized silica nanoparticles with a particular emphasis on the discussion of the the energy transfer processes at the basis of their properties. Since a careful design is fundamental in the realization of more and more sophisticated materials, we also discuss the synthesis of these systems, in order to suggest new routes for the preparation of such valuable and versatile objects.

Dual-Mode, Anisotropy-Encoded, Ratiometric Fluorescent Nanosensors: Towards Multiplexed Detection

A nanosensor with dual-mode fluorescence response to pH and an encoded identification signal, was developed by exploiting excitation energy transfer and tailored control of molecular organization in core-shell nanoparticles. Multiple signals were acquired in a simple single-excitation dual-emission channels set-up.