Search

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(II), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal–chelating agent. The fluorophore–analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

Homo- and heterobimetallic homoleptic complexes of general formula ErxYb3–xQ9 (Q = 8-quinolinolato; x = 0, 1; x = 1, 2; x = 2, 3) and the corresponding heteroleptic complexes ErxYb3–xQ8NO3 (x = 0, 1b; x = 1, 2b; x = 2, 3b), where one Q ligand is replaced by a nitrate anion, have been synthesized and fully characterized by means of compositional (energy-dispersive X-ray spectrometry, inductively-coupled plasma-mass spectrometry, and electrospray ionization mass spectrometry) and structural (X-ray diffraction) investigations to study the effects of ligand substitution and variation of metal composition on their chemical and photophysical properties. Advanced spectroscopic and photophysical studies in the visible and near-infrared spectral regions have allowed the achievement of a detailed picture of the photocycle leading to narrow-band lanthanide luminescent emission, providing evidence of highly efficient ligand-to-metal and metal-to-metal (Yb-to-Er) resonance energy transfers thanks to the short intermet...

Nanoporous thin films with silver nanoparticles were synthesized with a bottom–up approach, and its potential as effective surface-enhanced Raman scattering (SERS) substrates was demonstrated. The use of mesoporous titania films as substrates allowed to control the growth of nanoparticles on the film surface. Atomic force microscopy measurements, Ultraviolet-visible and X-ray diffraction analysis confirmed the photoreduction of Ag+ to Ag0 with the formation of nanoparticles with crystallite dimensions of 32 to 36 nm. The new substrates allowed the detection of two analytes (rhodamine B isothiocyanate and cytochrome c), present in solutions at very low concentrations, highlighting their potential in SERS sensing. Reproducibility, homogeneity, enhancement factor of the substrate, consistency of results and detection limits were also assessed. Copyright © 2012 John Wiley & Sons, Ltd.

Time resolved infrared spectroscopy has been applied to study in situ the evaporation process of a 3-glycidoxypropyltrimethoxysilane hybrid sol by casting a droplet on a ZnSe substrate; the analysis has been performed in the middle-infrared range and in the near-infrared range. The experiment has allowed following the structural changes induced by water evaporation and the formation of ordered structures within the cast film; the CH 2 scissoring bands have been used as a fingerprint for the disorder to order transition of the hybrid. The experiment has been done using both a fresh sol and an aged sol which produce respectively an amorphous material and a crystalline hybrid material. The analysis has shown that the epoxy groups do not react during the evaporation while the silica structure shows only a slight condensation and an increase in open cage-like species. At the end of evaporation the hybrid has a “soft-like” state which allows structural rearrangements to self-order.

Hybrid organic–inorganic films containing layered organosilicate nanocrystals have been obtained through self-organization from aqueous precursor sols containing 3-glycidoxypropyltrimethoxysilane. Diethoxydiphenylsilane has been added, in different amounts, to the precursor sol containing 3-glycidoxypropyltrimethoxysilane to prepare hybrid films with the ordered nanostructures. The effect of aging time of the precursor sol has been studied preparing different samples from sols aged up to 8 days; the formation of crystalline layered films has been observed in the samples obtained from sols of higher aging time. The hybrid films have been characterized by gracing incidence X-ray diffraction, Raman and Fourier transform infrared spectroscopy, transmission electron microscopy and UV–Vis spectroscopy. The change of the surface contact angle as a function of sol aging time and composition has been also measured. The capability of the films to be used in devices through lithographic techniques has been tested by writing the films with direct exposition to deep X-ray lithography and soft lithography with micromolds; patterns of different geometries with a thickness up to 100 μm have been obtained.

Hybrid organic–inorganic materials can organize into layered crystalline structures through self-organization when bridged silsesquioxanes are used in the sol–gel synthesis. Crystallization is, however, also observed in hybrid materials when 3-glycidoxypropyltrimethoxysilane is left to react in highly basic conditions; this synthesis route shows a peculiar property which is the possibility of preparing also crystalline hybrid films by controlling the sol–gel process. The crystalline films exhibit optical anisotropy and are optically transparent. In this article we briefly review the main achievements of our research group in the field.

Organic–inorganic films containing hybrid nanocrystals have been prepared by sol–gel processing in controlled conditions. We have systematically changed the temperature and the aging time of a precursor sol containing an organically modified alkoxide bearing an epoxy group, 3-glycidoxypropyltrimethoxysilane, to obtain a controlled crystallization of hybrid layered structures in hybrid films. The precursor sol has been aged at different temperatures, from 5 to 60 °C, and for 1, 2 or 3 days; the films have been deposited from the aged sol and immediately after characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. We have observed that the formation of the hybrid crystals can be obtained only when at least 50% of the epoxies are opened and a larger silica condensation is achieved. These conditions are reached after aging at 60 °C for 1 day, or at longer aging times when the sol is aged at lower temperatures. Transmission electron microscopy and optical polarized images have confirmed the formation of the hybrid crystals.

Ultrathin films of silica realized by sol-gel synthesis and dip-coating techniques were successfully applied to predefined metal/polymer plasmonic nanostructures to spectrally tune their resonance modes and to increase their sensitivity to local refractive index changes. Plasmon resonance spectral shifts up to 100 nm with slope efficiencies of ∼8 nm/nm for increasing layer thickness were attained. In the ultrathin layer regime (

Organic-inorganic perovskites are a class of solution-processed semiconductors holding promise for the realization of low-cost efficient solar cells and on-chip lasers. Despite the recent attention they have attracted, fundamental aspects of the photophysics underlying device operation still remain elusive. Here we use photoluminescence and transmission spectroscopy to show that photoexcitations give rise to a conducting plasma of unbound but Coulomb-correlated electron-hole pairs at all excitations of interest for light-energy conversion and stimulated optical amplification. The conductive nature of the photoexcited plasma has crucial consequences for perovskite-based devices: in solar cells, it ensures efficient charge separation and ambipolar transport while, concerning lasing, it provides a low threshold for light amplification and justifies a favourable outlook for the demonstration of an electrically driven laser. We find a significant trap density, whose cross-section for carrier capture is however low, yielding a minor impact on device performance.

Biosensing technologies based on plasmonic nanostructures have recently attracted significant attention due to their small dimensions, low-cost and high sensitivity but are often limited in terms of affinity, selectivity and stability. Consequently, several methods have been employed to functionalize plasmonic surfaces used for detection in order to increase their stability. Herein, a plasmonic surface was modified through a controlled, silica platform, which enables the improvement of the plasmonic-based sensor functionality. The key processing parameters that allow for the fine-tuning of the silica layer thickness on the plasmonic structure were studied. Control of the silica coating thickness was achieved through a combined approach involving sol–gel and dip-coating techniques. The silica films were characterized using spectroscopic ellipsometry, contact angle measurements, atomic force microscopy and dispersive spectroscopy. The effect of the use of silica layers on the optical properties of the plasmonic structures was evaluated. The obtained results show that the silica coating enables surface protection of the plasmonic structures, preserving their stability for an extended time and inducing a suitable reduction of the regeneration time of the chip.

Plasmonics has recently received considerable interest due to its potentiality in many fields as well as in nanobio-technology applications. In this regard, various strategies are required for modifying the surfaces of plasmonic nanostructures and to control their optical properties in view of interesting application such as bio-sensing, We report a simple method for depositing silica layers of controlled thickness on planar plasmonic structures. Tetraethoxysilane (TEOS) was used as silica precursor. The control of the silica layer thickness was obtained by optimizing the sol-gel method and dip-coating technique, in particular by properly tuning different parameters such as pH, solvent concentration, and withdrawal speed. The resulting films were characterized via atomic force microscopy (AFM), Fourier-transform (FT) spectroscopy, and spectroscopic ellipsometry (SE). Furthermore, by performing the analysis of surface plasmon resonances before and after the coating of the nanostructures, it was observed that the position of the resonance structures could be properly shifted by finely controlling the silica layer thickness. The effect of silica coating was assessed also in view of sensing applications, due to important advantages, such as surface protection of the plasmonic structure.

We report on the development of a plasmonic-photonic coupled platform based on a plasmonic periodic nanostructure and a host matrix for active media in the visible-near infrared range, constituted by a thin film of sol-gel glass. Here, we report on preliminary results about two main tasks of the research work. On one side, we have studied and optimized the surface that supports plasmonic resonances with tunable wavelengths. On the other side, we focused on improving the sol-gel techniques to form and deposit thin films appropriate for covering the previous surface as well as to protect it (i.e. for sensing applications), embed suitable fluorophores (for active device applications) while avoiding metal-induced radiative emission quenching. Besides structural and optical characterization of the considered structures and films, finite-difference time-domain numerical simulations have been performed, in order to give a feedback on the structure features and thereby interpret its optical response.

Sol-gel silica thin films embedding an ytterbium quinolinolato complex (YbClQ4) have been obtained using different alkoxides. Homogeneous, crack- and defect-free thin films of optical quality have been successfully deposited on glass substrate by dip-coating. The silica thin films have been characterized by time-resolved photoluminescence. The luminescence properties of the YbClQ4 are preserved in silica films prepared through an optimized sol-gel approach. The excited state lifetime of the lanthanide is comparable to those observed in bulk and longer than the corresponding ones in solution.

The controlled release of nanoparticles from a hybrid organic-inorganic surface allows for developing several applications based on a slow delivery of oxygen scavengers into specific environments. We have successfully grafted ceria nanoparticles on a hybrid film surface and tested their release in a buffer solution; the tests have shown that the particles are continuously delivered within a time scale of hours. The hybrid film has been synthesized using 3-glycidoxypropyltrimethoxysilane as precursor alkoxide; the synthesis has been performed in highly basic conditions to control the polycondensation reactions of both organic and inorganic networks via controlled aging of the solution. Only films prepared from aged solutions are able to graft ceria nanoparticles on their surface. The ceria nanoparticles have been characterized by X-ray diffraction, transmission electron microscopy and UV-vis spectroscopy, the hybrid films have been analyzed by Fourier transform infrared spectroscopy, atomic force microscopy and Raman spectroscopy. Raman imaging has been used for the release test. The hybrid film-ceria nanoparticles system fulfils the requirements of optical transparency and stability in buffer solutions which are necessary for biomedical applications.

The reactions of 3-glycidoxypropyltrimethoxysilane in a highly basic aqueous solution have been studied by multinuclear magnetic resonance and light scattering techniques. The study has shown that in this peculiar chemical environment the alkoxy groups of 3-glycidoxypropyltrimethoxysilane undergo a fast hydrolysis and condensation which favor the formation of open hybrid silica cages. The silica condensation reaches 90% at a short aging time but does not go to completion even after 9 days. The highly basic conditions also slow down the opening of the epoxies which fully react only after several days of aging. The epoxy opening generates different chemical species and several reaction pathways have been observed; in particular, the formation of polyethylene oxide chains, diols, termination of the organic chain by methyl ether groups and formation of dioxane species. These reactions are slow and proceed gradually with aging; light scattering analysis has shown that clusters of dimensions lower than 20 nm are formed after two days of reactions, but their further growth is hindered by the highly basic conditions which limit full silica condensation and formation of organic chains.

We report on the study of a plasmonic nanostructure that could be adopted as platform for emitting and sensing applications. Several devices have been prepared and characterized by atomic force microscopy (AFM) and Fourier transform micro-reflectance (FT- pR) techniques. In addition, a modelling via finite-difference time-domain (FDTD) simulations have been developed in order to interpret the morphological shape and the optical response of the considered structures. Until now, remarkable performances as surface plasmon resonance (SPR) based optical sensor have been founded. Moreover, we are performing preliminary trials in order to establish a coupling between photoluminescence (PL) features of suitable emitters with respect to the plasmonic resonances.

Strain driven micro and nanoroll fabrication is generally restricted to multilayer and multiprocessing systems, limiting the ability to exploit self-organization at different length scales. We have designed a hybrid organic–inorganic single-layered film with a surface that responds selectively to external stimuli, resulting in mechanical strain and self-rolling in one-step fabrication. The scrolling is initiated by water and any aqueous solution of molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls; the constrained environment at the interface of the roll walls pushes the particles to organize into ordered structures. We used this rolling process to create self-assembled hybrid films with well-ordered layers of gold nanoparticles and opals of polystyrene nanospheres. These films also respond selectively to solvents, allowing the easy release of molecules/particles entrapped at the interface. Researchers from Japan and Italy have devised a one-step strategy to roll single-layer films into microtubes. Films of materials ranging from metals to semiconductors to polymers have previously been rolled up. They typically consist of two or more mismatched layers, so that the scrolling process relies on the strain between layers. The researchers have now prepared a self-rolling single-layer film by ‘sol–gel’ synthesis of a glycidoxy-organosilane derivative in basic conditions, spin-coating of the product obtained on a silica substrate and subsequent drying. The bottom part of the film formed, less condensed than its upper counterpart, takes up water preferentially. Simply dipping it in water creates a strain that is sufficient to provoke scrolling. Species such as molecules or particles can be trapped within the resulting microtubes, whose diameters are controlled by adjusting the processing conditions. This simple and convenient method may facilitate preparation of rolls for functional materials. Strain-driven micro- and nanorolls fabrication is generally restricted to multilayer and multiprocessing systems, which limit the possibility of exploiting the self-organization at different length scales. We have designed a hybrid organic–inorganic film whose surface shows a selective response to external stimuli, which induces mechanical strain and self-rolling in one-step–one-layer fabrication. The scrolling is initiated by water and any aqueous solution that also contains molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls, giving rise to functional microrolls.