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Semiconductor nanomaterials are often proposed as photocatalysts for wastewater treatment; silica nanomaterials are still largely unexploited because their photocatalytic performances need improvements, especially under visible light. The present study is a proof-of-concept that amorphous silica colloids once submitted to the proper surface modifications change into an efficient photocatalyst even under low-energy illumination source. For this reason, silica-based colloidal nanomaterials, such as bare (SiO2 NPs), aminated (NH2-SiO2 NPs), and Ag NPs-decorated (Ag-SiO2 NPs) silica, are tested as photocatalysts for the degradation of 9-anthracenecarboxylic acid (9ACA), taken as a model aromatic compound. Interestingly, upon irradiation at 313 nm, NH2-SiO2 NPs induce 9ACA degradation, and the effect is even improved when Ag-SiO2 NPs are used. On the other hand, irradiation at 405 nm activates the plasmon of Ag-SiO2 NPs photocatalyst, providing a faster and more efficient photodegradation. The photodegradation experiments are also performed under white light illumination, employing a low-intensity fluorescent lamp, confirming satisfying efficiencies. The catalytic effect of SiO2-based nanoparticles is thought to originate from photo-excitable surface defects and Ag NP plasmons since the catalytic degradation takes place only when the 9ACA is adsorbed on the surface. In addition, the involvement of reactive oxygen species was demonstrated through a scavenger use, obtaining a yield of 17%. In conclusion, this work shows the applicability of silica-based nanoparticles as photocatalysts through the involvement of silica surface defects, confirming that the silica colloids can act as photocatalysts under irradiation with monochromatic and white light. Graphic abstract Silica and Ag-decorated silica colloids photosensitize the formation of Reactive Oxygen Species with 17% efficiencies. ROS are able to oxidase aromatic pollutants chemi-adsorbed on the surface of the colloids. Silica-silver nanocomposites present a photocatalytic activity useful to degrade aromatic compounds.

The use of plasmonic nanomaterials is a challenging strategy to control radiation and radiation-induced processes at a nanometric scale. The localized surface plasmons of metal nanoparticles have been shown to affect the efficiency of a variety of radiative and non-radiative processes occurring in organic molecules. In this contribution, we present an overview of the results obtained through an original approach based on the hierarchical assembly of plasmonic gold colloids on silica templates, covalently doped with organic dyes. The detailed morphological characterization demonstrates the disposition of gold colloids on silica achieved through the tight control of the synthetic conditions. The studies carried out while gradually increasing the concentration of gold nanoparticles allow the detailed investigation of the effects of the progressive addition of plasmonic particles on the photophysical behaviour of organic molecules. In particular, the fluorescence behaviour of three dyes with different spectral properties, namely fluorescein, rhodamine B and 9-aminoacridine, are investigated in the presence of increasing concentrations of gold nanoparticles. In order to fix the distance between the dye and the gold nanoparticles, the dyes are anchored to silica nanoparticles, and the metal colloids are chemically adsorbed on the silica surface. The steady state and time-resolved data are analysed to evaluate the impact of plasmonic nanoparticles on the radiative and non-radiative processes of the dyes; the data provide evidence that the modulation of the fluorescence intensity (enhancement or quenching) can be achieved by changing the concentration of gold colloids. The plasmonic nanostructures can be employed to favour one deactivation process over the others. For example, we demonstrate that the photoinduced formation of reactive oxygen species (ROS) can be enhanced upon the plasmonic engineering of a photosensitizing agent (Protoporphyrin IX, PpIX). The Vis-excitation of silica-PpIX samples in the presence of gold nanoparticles results in a faster and more efficient photoinduced formation of ROS species either in solution or in a hydrogel. The ROS efficiency data and the fluorescence behaviour of PpIX in the presence of gold colloids suggest that the enhancement of the excitation field occurs through a plasmonic effect. For the application of the assembled hybrid materials, further advantages come from the development of photosensitizer-containing hydrogel films that are able to efficiently produce ROS upon visible excitation. Our preliminary results are herein reported and discussed.

The understanding of charge carrier dynamics in hybrid materials based on colloidal semiconductor nanocrystals (or quantum dots) and organic moieties is fundamental for the design of efficient photonic and photovoltaic devices. In the present work, we investigate the interactions occurring between CdTe quantum dots, capped with a strong capping agent such as 3-mercaptopropionic acid, and a well known electron acceptor such as methylviologen molecule. The nature of the interactions and of exciton dynamics is investigated by stationary and time-resolved spectroscopies. Luminescence data recorded in presence of increasing methylviologen concentrations, indicate that the organic molecule is able to statically interact with the surface sites of CdTe quantum dots; a biphasic interaction behavior is evidenced by determining the apparent association constants. These latter are obtained through the analysis of luminescence data, and values in the range 10(3)-10(4) are determined. The nature of the interactions is characterized by nanosecond and femtosecond transient absorption spectroscopies, to clarify the dynamics and the conditions able to foster charge mobility. Nanosecond flash photolysis measurements, carried out upon quantum dots excitation, shows the absorption of methylviologen radical cation specie at 605 nm, suggesting the occurrence of electron transfer from CdTe nanocrystals to the organic acceptor; the relatively long decay time of the transient signal (10.3 mu s) indicates that back electron transfer processes are negligible. Ultrafast transient absorption measurements confirm the occurrence of an ultrafast electron transfer process; spectral and kinetic analysis of the transient data show that methylviologen radical cation is formed almost instantaneously on the ps-time scale but mainly when the samples are pumped in the energy continuum at 400 nm. This finding suggests that electron mobility from the nanocrystals to the organic units is achieved mainly when the excitonic states possess an excess of energy. The comparison of the kinetic behaviour of the signals at increasing methylviologen concentrations indicates that the electron transfer process competes with the radiative exciton recombination. In addition, the kinetic data suggests that surface trapping and Auger recombination processes might slow down the charge mobility. (C) 2017 Elsevier B.V. All rights reserved.

The interactions of dye molecules with gold nanoparticles are of great interest owing to the potential applications in the areas of bioimaging, sensing and photodynamic therapy applications. In many cases the distances between fluorophores and the metal particles can change during the experiment and the spectral features of the units are not taken into account. In this work, the fluorescence behaviour of two dyes with different spectral properties (Rhodamine B and 9-aminoacridine) are investigated in the presence of gold nanoparticles having diameters of 2 or 26 nm and hence different plasmonic properties. In order to fix the distance between the dye and the gold nanoparticles, the dyes are entrapped in 20 nm silica nanoparticles, and the metal colloids are adsorbed on the silica surface. The distance between the fluorescent units and the metal particles is tuned by growing additional silica layers on the pristine nanoparticles. Steady-state and time-resolved fluorescence measurements show that in the presence of gold nanoparticles, having 2 nm diameter, a drastic quenching of the dye emission is observed, for all the prepared samples, despite the average dye-metal distances. When gold nanoparticles with 26 nm diameters are used, their interactions with the dyes are strongly dependent on the averaged distances between the metal colloids and the dyes and on the overlap of their spectral properties. Indeed, an enhanced emission is observed for 9-aminoacridine while the fluorescence of longer wavelength emitting Rhodamine B is quenched. The steady state and time-resolved data are analysed to evaluate the plasmonic impact of the radiative and non-radiative rate constants of the dyes.

The capability of three quaternized styryl-azinium iodides to bind cellular RNA has been tested by means of Fluorescence Confocal Microscopy imaging of stained MCF-7 cells treated with RNase. Their association constants have been estimated through spectrophotometric and fluorimetric titrations with tRNA and compared to their affinity toward DNA. Transient absorption spectroscopy with femtosecond resolution confirmed the binding of the investigated compounds with tRNA and shed new light on the excited state dynamics of their complexes, by revealing a significant lengthening of the lifetime of S1 upon complexation, which parallels the fluorescence quantum yield enhancement.

Photobleaching of fluorophores is one of the key problems in fluorescence microscopy. Overcoming the limitation of the maximum number of photons, which can be detected from a single emitter, would allow one to enhance the signal-to-noise ratio and thus the temporal and spatial resolution in fluorescence imaging. It would be a breakthrough for many applications of fluorescence spectroscopy, which are unachievable up to now. So far, the only approach for diminishing the effect of photobleaching has been to enhance the photostability of an emitter. Here, we present a fundamentally new solution for increasing the number of photons emitted by a fluorophore. We show that, by exposing a single SiO2 nanoparticle to UV illumination, one can create new luminescent centers within this particle. By analogy with nanodiamonds, SiO2 nanoparticles can possess luminescent defects in their regular SiO2 structure. However, due to the much weaker chemical bonds, it is possible to generate new defects in SiO2 nanostructures using UV light. This allows for the reactivation of the nanoparticle's fluorescence after its photobleaching.

The luminescent behavior of semiconductor nanocrystals is a sensitive reporter of their electronic properties and of the impact of surface passivation on the excitonic state. In this work, CdSe nanocrystals (CdSe-Nc) are prepared in microemulsions and the effects of tripeptide Glutathione (GSH) as a stabilizing ligand, are examined. The CdSe samples are investigated by steady-state and time-resolved luminescence methods. The luminescent properties of CdSe without GSH spectrally evolve over time, and a dramatic reduction of luminescence intensity and decay times are observed. This behavior suggests that although the colloids are in microemulsion media, they undergo progressive aging that ruins their luminescent properties. The presence of GSH in the microemulsions at the beginning of the synthesis stops the nanocrystal aging, thus acting as an efficient stabilizing agent, freezing the luminescence properties of CdSe nanocrystals. The effects of GSH on the colloids are also documented by a detailed analysis of luminescence decay times, carried out through the Maximum Entropy Method. Interestingly, the addition of GSH on aged CdSe colloids is able to not only stabilize the structures but also recover the luminescent efficiency leading to an attractive “brightening” effect.

The immobilization of proteins on inorganic supports is attracting increasing interest since the realization of active surfaces finds application in enzyme-assisted catalysis, environmental sciences, and medical fields. In the present study, cytochrome c (cyt c) is adsorbed on silica nanoparticles (SNPs) and amino-functionalized silica nanoparticles (SNPs-APTES), which are prepared for this purpose and having a diameter of about 50 nm. The peroxidase activity of the protein is investigated under different experimental conditions, to evaluate the impact of differently charged surfaces on the catalytic activity of the biomolecule. The peroxidase activity of cyt c increases upon adsorption on SNPs, and it shows a linear behavior with nanoparticles concentration; on the other hand, the contact with increasing amounts of SNPs-APTES does not affect the catalytic activity of the protein. The kinetic profile of the oxidation reaction is altered for cyt c-SNPs sample, suggesting that upon adsorption, changes in the catalytic process take place. Moreover, we observe that the enhancement of peroxidase activity of cyt c-SNPs is almost completely inhibited in high-ionic-strength buffer: this indicates that the protein establishes electrostatic interactions with SNP. The spectroscopic properties of the adsorbed protein on the two different matrices are investigated by using fluorescence and Raman spectroscopies to account for the enzymatic activity of the hybrid materials. The fluorescence spectra of cyt c-silica bio-composites reveal that the adsorption on silica modifies the microenvironments of the emitting amino acid residues of the protein. Indeed, their fluorescence gains intensity and appears blue-shifted compared to that of the native protein; these modifications are more evident when cyt c is adsorbed on SNPs. Raman spectra suggest that both oxidation and spin state of heme iron change when cyt c is adsorbed on SNPs but not on SNPs-APTES. The spectroscopic data of biocomposite materials are discussed in terms of structural changes to account for the increment of peroxidase activity upon adsorption on the negatively charged surface of SNPs.

Silica nanomaterials have been proposed as promising candidates for the delivery of drugs, including purified proteins, thus a systematic investigation on the role of silica surface porosity, for optimal protein loading and release, represents an urgent need. Herein, we report the studies of the loading and releasing processes of different volume-proteins, namely Myoglobin, Bovine Serum Albumin and Factor VIII (FVIII), performed using three porous silica samples. To this aim, silica nanoparticles are prepared through modified sol-gel methods, in which suitable templating and swelling agents are used to enlarge the surface pores from few nm to 25 nm, but retaining the average dimensions of the nanoparticles (80 –90 nm). TEM imaging and Zeta-Potential measurements are used to characterize the silica samples. In this study, the loading process is carried out at pH values close to the isoelectric point of each protein, and the amount of adsorbed protein is quantified and values in the range of μgprotein per mgsilica are obtained. Then, the release profiles are monitored at physiological conditions; for all systems, the release of the proteins is detected, although different behavior are observed. The release profiles are analyzed through the power law equation and through a modular exponential function to achieve information on the mechanism and on kinetics of the release profile. The data show the release from silica particles with small pores follows a diffusion-controlled mechanism, while the kinetic analysis enables to distinguish two-components associated to superficially adsorbed protein and to the portion of protein allocated inside the pores. On the other hand, the particles characterized by the largest pore size (ca. 25 nm) display non-Fickian release profile and a mono-exponential dependency, indicating a mono-modal distribution of the proteins on the silica matrix. Moreover, the conformation or the biological activity of the released proteins has been evaluated through in-vitro methods and the data demonstrate the excellent quality of the recovered proteins. The loading and release data were rationalized in terms of mesoporous structures of the silica nanoparticles in relation to the protein dimensions.

The thermal aggregation of lysozyme has been analyzed in water/ethanol solutions at low pH to induce the specific protein aggregation pathway which leads to fibrillar structures in a few hours. In this solvating medium, the protein undergoes a conformational rearrangement promoting the formation of fibrils that are structurally similar to amyloid ones. As the process evolves with different steps, a multitechnique approach has been used by means of analytical probes that can be selectively sensitive in the detection of the different stages of protein association. Fourier transform infrared spectroscopy, intrinsic fluorescence, stationary fluorescence anisotropy, transmission electron microscopy (TEM), and atomic force microscopy (AFM) measurements have been carried out at different times to access and characterize the whole aggregation pathway. The data recorded with different experimental setups revealed different sensitivity to different stages of protein assembling. The whole set of data together with the direct visualization of different aggregate structures by use of TEM and AFM imaging enable to discuss a possible mechanism of fibrillation.

Silica nanostructured materials are often used as catalyst support but their catalytic role has not been deeply investigated yet. In the present study, the photocatalytic degradation of acridine orange zinc chloride double salt (AO) has been studied using silica nanoparticles (NPs) as catalysts. NPs of different size (55 and 146 nm) were prepared by a sol–gel procedure and their surface was modified with amino groups to investigate the role of the chemical groups linked to the silica surface on the dye degradation. The silica nanomaterials were fully characterized by use of transmission electron microscopy (TEM), zeta potential measurements and UV–vis spectrophotometric methods. The photodegradation experiments were carried out irradiating at 313 or 490 nm for 50 min the aqueous samples containing the dye and the silica NPs of 55 or 146 nm in diameter. The photocatalytic degradation of the dye was determined from the decrease of its fluorescence intensity. AO fluorescence intensity did not change when bare SiO2 beads were used as catalysts, whereas an efficient decoloration (up to 58%) was achieved with amino functionalized NPs, with a photodegradation rate constant value of 0.136 m−1. The data collected from the degradation experiments demonstrated that the functional groups on the silica surface have a fundamental role in the efficiency of the degradation processes.

Transmembrane proteins play important roles in intercellular signaling to regulate interactions among the adjacent cells and influence cell fate. The study of interactions between membrane proteins and nanomaterials is paramount for the design of nanomaterial-based therapies. In the present work, the fluorescence properties of the transmembrane receptor Notch2 have been investigated. In particular, the steady-state and time-resolved fluorescence methods have been used to characterize the emission of tryptophan residues of Notch2 and then this emission is used to monitor the effect of silver colloids on protein behavior. To this aim, silver colloids are prepared with two different methods to make sure that they bear hydrophilic (citrate ions, C-AgNPs) or hydrophobic (dodecanethiol molecules, D-AgNPs) capping agents. The preparation procedures are tightly controlled to obtain metal cores with similar size distributions (7.4 ± 2.5 and 5.0 ± 0.8 nm, respectively), thus, making the comparison of the results easier. The occurrence of strong interactions between Notch2 and D-AgNPs is suggested by the efficient and statistically relevant quenching of the stationary protein emission already at low nanoparticle (NP) concentrations (ca. 12% quenching with [D-AgNPs] = 0.6 nM). The quenching becomes even more pronounced (ca. 60%) when [D-AgNPs] is raised to 8.72 nM. On the other hand, the addition of increasing concentrations of C-AgNPs to Notch2 does not affect the protein fluorescence (intensity variations below 5%) indicating that negligible interactions are taking place. The fluorescence data, recorded in the presence of increasing concentrations of silver nanoparticles, are then analyzed through the Stern-Volmer equation and the sphere of action model to discuss the nature of interactions. The effect of D-AgNPs on the fluorescence decay times of Notch2 is also investigated and a decrease in the average decay time is observed (from 4.64 to 3.42 ns). The observed variations of the stationary and time-resolved fluorescence behavior of the protein are discussed in terms of static and collisional interactions. These results document that the capping shell is able to drive the protein-particle interactions, which likely have a hydrophobic nature.

Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as DNA and nonionic micelles were investigated using steady-state and ultrafast time-resolved spectroscopy. Spectrophotometric and fluorimetric titrations of the investigated compounds with salmon testes DNA supplied evidence of a good interaction between the salts and DNA with binding constants of 10(4)-10(6) M(-1), making them interesting for pharmaceutical applications. The interaction with DNA also changes the photobehavior of the compounds, increasing the radiative deactivation pathway to the detriment of internal conversion and slowing down the excited state dynamics. The interaction of the azinium salts with the nonionic surfactant Triton X-100 from premicellar to postmicellar concentration was studied by spectrophotometric and fluorimetric titrations evidencing the ability of the micelles to associate the studied salts in their hydrophobic portion and to release them in the presence of DNA, acting as promising drug carriers. Also transient absorption spectroscopy with femtosecond resolution demonstrated the insertion of the investigated compounds into micellar aggregates. Preliminary measurements by confocal fluorescence microscopy on MCF-7 cells in the presence of the studied azinium salts showed that they are able to cross the cellular membrane and that their cytotoxicity can be expressed through interaction with DNA (RNA). In fact, they showed a significant fluorescence signal in all cell compartments, particularly (for 2 and 3) into punctuate structures within the nuclei compatible with a localization into the nucleoli.

We present the results of a comprehensive photoluminescence study of defect centres in single SiO2 nanoparticles. We show that the photo-physical properties of the luminescent centres strongly resemble those of single dye molecules. However, these properties exhibit a large variability from particle to particle due to the different local chemical environment around each centre of each particle. This variability provides new insight into the complex photo-physics of single quantum emitters embedded into a random chemical environment. Moreover, a better understanding of the fundamental mechanism of the photoluminescence of defect centres in SiO2 structure is paramount for their application as white-light sources, non-toxic labels for bio-imaging, or for combining them with metallic and semiconductor nanostructures. unReviewed

Polymer-stabilized perylene nanoparticles were prepared through a solvent exchange method. The formation of the nanostructures in aqueous solution was confirmed by the appearance of a red-shifted emission attributable to the formation of excimer-like aggregates. The behavior of organic nanostructures in the presence of lipid vesicles was investigated through steady-state and time-resolved fluorescence measurements. When no further surface treatment is applied to the nanoparticles, changes in the decay times and emission spectra demonstrate that inside the lipid bilayers the nanoparticles redissolve into the monomeric form with a rate and efficiency determined by the working temperature (above and below the transition temperature Tm of the phospholipid). On the other hand, when the stabilized shell is UV-cured to induce photo-cross-linking of the polymeric chains, the nanoparticle stability increases and their redissolution in the membrane is prevented. Confocal fluorescence images support the data obtained in bulk. The results indicate that the prepared nanostructures could be successfully used either as nanometric carriers for the delivery of poor water-soluble lipophilic compounds or as imaging tools depending on the rigidity/cross-linking degree of their polymeric stabilizer shell.

The synthesis and characterization of new biodegradable polymeric NPs loaded with bovine serum albumin marked with fluorescein isothiocyanate (FITC-BSA) is reported. The protein is encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) NPs by the double emulsion method with subsequent solvent evaporation. The NPs display a spherical shape with a narrow size distribution and no aggregation is observed after drying. Steady-state and time-resolved fluorescence measurements appear to be a sensitive method to investigate the protein environment on the nanometer-scale. Finally, FITC-BSA-loaded NPs are rapidly internalized in stem cells. Interestingly, 25% cells were slightly positive after 28 days.

Photodynamic treatments represent a non-invasive tool to intervene in the cell cycle, only when needed, but high excitation power is an important limitation. In this work, protoporphyrin IX (PpIX) is covalently anchored to the surface of silica particles. The hybrid colloids are prepared with different photosensitizer loadings and characterized by TEM, SEM-EDX and spectroscopic methods. The visible excitation of the colloidal samples generates reactive oxygen species, which are quantified by use of a specific chemical scavenger agent (1,3-diphenylisobenzofuran). The determined efficiencies depend on the PpIX loading, being higher in the sample where the aggregation is reduced. To enhance further the photosensitizing performance of silica-PpIX samples, increasing amounts of gold nanoparticles are conjugated to the silica surface in order to exploit the antenna effect of plasmonic nanostructures. The visible excitation of silica-PpIX systems in the presence of gold nanoparticles results in a faster and more efficient photoinduced formation of ROS species reaching a 230 % enhancement of ROS photosensitization when 1013 Au nanoparticles mL−1 (corresponding to circa 75 ppm of gold) are present. The efficiency data are discussed in terms of plasmonic enhancement of the excitation field.

In the development of a nanodevice for biomedical applications, the study of the interactions with the biomolecules is essential. Proteins, in particular, are known to be easily adsorbed on the surface of the nanoparticles and the resulting complex is the one that will be effectively internalized by the target cells. Owing to the versatility of the preparation methods available and the unique optical properties, gold nanomaterials represent an excellent choice to study this interaction. This chapter will initially describe the synthesis of gold nanorods and nanoshells that are able to absorb light in the near-infrared (NIR) region. Then, the methods available for the function‐ alization of their surface will be discussed. The surface plasmon absorption will be used as an optical tool to monitor the process of preparation and surface modifica‐ tion. In the last section of the chapter, fluorescence and microscopy techniques will be used to follow the formation and characterize the protein-nanoparticle complex. The modifications of the emission spectra of two model proteins, bovine serum albumin (BSA) and myoglobin (Mb), will be analyzed in detail. The data will demonstrate that structural rearrangements following the adsorption on the surface of the nanoparticles are responsible for the changes in the fluorescence of the tryptophan residues of the protein. The data will be discussed in terms of static and dynamic quenching, proving the formation of a protein-nanoparticle complex. Atomic force microscopy (AFM) measurements will allow the direct visualization of this complex.

Nanosized hydrotalcite-like compounds (HTlc) with different chemical composition were prepared and used to study protein adsorption. Two soft proteins, myoglobin (Mb) and bovine serum albumin (BSA), were chosen to investigate the nature of the forces controlling the adsorption and how these depend on the chemical composition of the support. Both proteins strongly interact with HTlc exhibiting in most cases a Langmuir-type adsorption. Mb showed a higher affinity for Nickel Chromium (NiCr-HTlc) than for Nickel Aluminum (NiAl-HTlc), while for BSA no significant differences between supports were found. Adsorption experiments in the presence of additives showed that proteins exhibited different types of interactions onto the same HTlc surface and that the adsorption was strongly suppressed by the addition of disodium hydrogen phosphate (Na 2 HPO 4 ). Atomic force microscopy images showed that the adsorption of both proteins onto nanoparticles was followed by the aggregation of biocomposites, with a more disordered structure for BSA. Fluorescence measurements for adsorbed Mb showed that the inorganic nanoparticles induced conformational changes in the biomolecules; in particular, the interactions with HTlc surface quenched the tryptophan fluorescence and this process was particularly efficient for NiCr-HTlc. The adsorption of BSA onto the HTlc nanoparticles induced a selective quenching of the exposed fluorescent residues, as indicated by the blue-shift of the emission spectra of tryptophan residues and by the shortening of the fluorescence decay times.

Polycyclic aromatic hydrocarbons (PAHs) adsorbed on the surface of particulates collected in a working environment have been analyzed using fluorescence techniques. In particular, fluorescence measurements were carried out directly on the sampling filters, in solid phase, and for comparison, on the extract samples in solution. Fluorescence synchronous acquisitions allowed the detection of signals from different PAH compounds and, on the basis of the 0–0 transition energy, the assignment of the emission signals to chemical structures. In particular, the contribution of benzo-α-pyrene was easily detected and used to evaluate the sensitivity of the measurements, which is a few nanograms per milliliter, comparable with other analytical tools. The results of the fluorimetric investigation were validated through the comparison with the data obtained by gas chromatography (GC) analysis on the extracted samples, which allowed identification of the PAHs and the quantification of their distribution on the filters with different cut sizes. The agreement between the two series of data led to the conclusion that fluorimetric analysis directly on the sampling filter could be a new and cost-effective approach for the analysis of PAHs.

Hydrotalcite nanocrystals doped with Eu(III) ions were prepared by the microemulsion method. XRPD measurements revealed that europium ions are very likely incorporated in a low-symmetry hydrotalcite-type layer. TEM and AFM imaging indicated that nanocrystals have a 150 nm width and a plate shape. Luminescence measurements showed that the doped powder is luminescent and the Eu(III) ions are located in a low symmetry site.

The preparation of tailored nanomaterials able to support cell growth and viability is mandatory for tissue engineering applications. In the present work, silica nanoparticles were prepared by a sol-gel procedure and were then functionalized by condensation of amino groups and by adsorption of silver nanoparticles. Transmission electron microscopy (TEM) imaging was used to establish the morphology and the average dimensions of about 130 nm, which were not affected by the functionalization. The three silica samples were deposited (1 mg/mL) on cover glasses, which were used as a substrate to culture adult human bone marrow-mesenchymal stem cells (hBM-MSCs) and human adipose-derived stem cells (hASCs). The good cell viability over the different silica surfaces was evaluated by monitoring the mitochondrial dehydrogenase activity. The analysis of the morphological parameters (aspect ratio, cell length, and nuclear shape Index) yielded information about the interactions of stem cells with the surface of three different nanoparticles. The data are discussed in terms of chemical properties of the surface of silica nanoparticles.

Nickel nanoparticles are prepared through thermolysis or polyol procedures and they are fully characterized through TEM and XRD. The catalytic efficiencies are tested toward the hydrogenation reaction of 4-nitrophenol, which was spectrophotometrically detected. A significant improvement of the reaction rate and turnover number (TON) and frequency (TOF) is observed using alkyl amine-stabilized nanoparticles, likely due to their reduced surface steric hindrance. However, the polymer stabilized-nanocatalysts show a better selectivity for product formation, since only hydrogenation products are observed, while azo-benzene derivatives are detected when alkyl amine-stabilized nanoparticles are used. The findings indicate an important impact of surface properties of colloids on the catalysed reaction.

The hydrolytic degradation of poly( d , l -lactide- co -glycolide) (PLGA) nanoparticles loaded with bovine serum albumin (BSA) covalently labelled with a fluorescent dye (FITC) was investigated spectrally resolving the fluorescence signals. Studies have been conducted in-vitro in phosphate buffer saline and in human adult bone marrow-mesenchymal stem cell cultures. We demonstrated that PLGA nanoparticles degraded in heterogeneous manner and a particle agglomeration process occurs after 21 days of incubation owing to particle fragmentation and leading to cargo release. Additionally, we showed that degradation of up-taken FITC-BSA-PLGA nanoparticles by stem cells may be monitored by the emission spectrum of the released FITC-BSA that shifted towards shorter wavelengths and becomes narrower, after 230 h. Moreover, the changes of fluorescence spectra revealed that the loaded protein is released in the cells during polymer degradation.

The exciton generation and recombination dynamics in semiconductor nanocrystals are very sensitive to small variations in dimensions, shape and surface capping. In the present work CdTe quantum dots are synthesized in water using 3-mercaptopropionic acid and 1-thioglycerol as stabilizers. Nanocrystals with an average dimension of 4.0 ± 1.0 and 3.7 ± 0.9 nm were obtained, when 3-mercaptopropionic acid or 1-thioglycerol, respectively, was used as a capping agent. The steady-state characterization shows that the two types of colloids have different luminescence behavior. In order to investigate the electronic structure and the dynamics of the exciton state, a combined study in the time domain has been carried out by using fluorescence time-correlated single photon counting and femtosecond transient absorption techniques. The electron–hole radiative recombination follows the non-exponential decay law for both colloids, which results in different average decay time values (of the order of tens of nanoseconds) for the two samples. The data demonstrate that the process is slower for 1-thioglycerol-stabilized colloids. The ultrafast transient absorption measurements are performed at two different excitation wavelengths (at the band gap and at higher energies). The spectra are dominated in both types of samples by the negative band-gap bleaching signals although transient positive absorption bands due to the electrons in the conduction band are observable. The analysis of the signals is affected by the different interactions with the defect states, due to ligand capping capacities. In particular, the data indicate that in 1-thioglycerol-stabilized colloids the non-radiative recombination processes are kinetically more competitive than the radiative recombination. Therefore the comparison of the data obtained from the two samples is interpreted in terms of the effects of the capping agents on the electronic relaxation of the colloids.

Fluorescein has been covalently entrapped into 120 nm silica beads in order to measure the effect of plasmonic gold nanoparticles, having 25 nm diameter, on the radiative processes of the dye. Two distinct regimes of enhancement and quenching of fluorescein emission have been observed, depending on the concentration of the metal adsorbed on the silica surface and the overlap between the SPR and the fluorescein spectra. At particle concentrations below 5.0 × 10(13) nanoparticles mL(-1), the fluorescence of the dye is enhanced, and this effect is more pronounced when the excitation wavelength matches the maximum of the extinction spectrum of the gold nanoparticles. When the concentration of gold is further increased, quenching occurs and it has been attributed to the SPR shift following the aggregation of the gold colloids on the silica surface. The invariance of the fluorescence lifetimes during the whole process indicates that the mechanism of fluorophore-nanoparticle interaction is mainly based on changes in the absorption efficiency of the organic dye.

The synthesis and characterization of new biodegradable polymeric NPs loaded with bovine serum albumin marked with fluorescein isothiocyanate (FITC-BSA) is reported. The protein is encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) NPs by the double emulsion method with subsequent solvent evaporation. The NPs display a spherical shape with a narrow size distribution and no aggregation is observed after drying. Steady-state and time-resolved fluorescence measurements appear to be a sensitive method to investigate the protein environment on the nanometer-scale. Finally, FITC-BSA-loaded NPs are rapidly internalized in stem cells. Interestingly, 25% cells were slightly positive after 28 days.

Nanosized Layered Double Hydroxides (LDH) were prepared in confined environment through the microemulsion method in the presence of different lanthanide cations (Ln(III) = Eu(III), Yb(III), Tb(III), and Nd(III)). To investigate the effects of lanthanide insertion in the sheets of LDH materials, several samples were prepared upon progressively increasing the content of Ln ions and properly reducing the Al(III) amount; the samples were characterized in terms of metal content, structure, morphology, thermal behavior, and spectroscopic properties. The data revealed that Ln(III) content in the LDH samples depends on the ionic radius of the lanthanide cations and on its concentration in the starting microemulsion. X-ray powder diffraction (XRPD) indicated that Eu(III) can be inserted into the LDH structure in average atomic percentages lower than 2.7%, leading to the formation of a low symmetry phase, as confirmed by steady state luminescence spectra; while Yb(III) can be incorporated into the layer structure up to about 10% forming a pure layered phase containing the lanthanide in the sheet. The incorporation of Yb(III) and Eu(III) into the LDH sheets is also supported by FT-IR measurements. Coupled thermogravimetrical (TG) and differential scanning calorimetric (DSC) studies indicated that water molecules are essential in the coordination sphere of incorporated Ln cations; this observation accounts for the lower thermal stability of Ln-doped LDH compared to the undoped ones. Furthermore, Eu-luminescence measurements indicates that the lanthanide inclusion does not compromise its luminescence although the spectral position and brightness can be tuned by the loading.

In recent years much attention has been paid to the development of metrology methods to investigate particulate matter and its interaction with bio-molecules. This interest is triggered by the potential applications of nanoparticle-biomolecule hybrid systems in different areas such as bio-sensing, catalysis, target delivery, selective recognition, etc. (Amelia et al., 2010; Bellezza et al., 2009; Latterini & Amelia, 2009; Joralemon et al., 2005; Nehilla et al., 2005; Rosi & Mirkin, 2005). Furthermore, a better understanding of the interactions between particles and biomolecules could help to optimize the ability to reduce the exposure to particulate matter in working environments.

A colloidal dispersion of zinc aluminum hydrotalcite nanoparticles (ZnAl-HTlc) has been used for in vitro experimental procedures in order to provide reliable data on their potential application in cellular delivery. Two different cell lines (HeLa tumor cells and MDCK normal cells) with a similar epithelial derivation have been used. Sedimentation studies performed in the presence of different constituents of the cell culture medium revealed the importance of serum components to stabilize the colloidal dispersions of nanosized ZnAl-HTlc. Cell viability assay showed for nanosized ZnAl-HTlc a higher cell growth inhibition on tumor cells compared to normal cells whereas LDH test showed the absence of toxicity for both cell lines. Cellular uptake experiments indicated a preferential internalization of ZnAl-HTlc nanoparticles in HeLa tumor cells. Adsorption study and steady state fluorescence measurements on the phenol red/HTlc hybrid were carried out in order to verify the possibility of using phenol red as fluorescent dye for ZnAl-HTlc nanoparticles. The observed spectral behavior indicated a strong interaction between the dye and the inorganic matrix and the preferential adsorption of the dye on the nanoparticle surface has been confirmed by the XRPD data. Fluorescence confocal imaging showed a different localization pattern of nanosized HTlc in the two cell lines and a higher fluorescence signals in tumor cells supporting the occurrence of more efficient internalization processes in the pathogen cell line as observed in the cellular uptake experiments.

Hybrid nanoparticles are designed and produced by a two-step procedure with the aim to obtain optically controlled multifunctional nanomaterials. In particular, using a sol–gel method in alcoholic/water media, silica particles doped with 9-aminoacridine molecules are prepared with a mean diameter of 31 nm, which preserves the fluorescent properties of the dye. In a second step, these nanoparticles are capped with a thin (7 nm-size) gold shell whose growth does not quench the emission of the dye as proven by steady-state and time-resolved fluorescence measurements. The careful choice of the organic dye and the control of the metal layer growth make possible to completely uncouple the fluorescence and the plasmon bands of gold. The selective photoexcitation of fluorescence or plasmon absorption, leading to heat release, has been tested on phospholipidic membranes loaded with the prepared hybrid particles. Under 400-nm irradiation fluorescence is activated, which is used to image the membranes; upon 650-nm i...

We have used short laser pulses to generate transient vapor nanobubbles around plasmonic nanoparticles. The photothermal, mechanical, and optical properties of such bubbles were found to be different from those of plasmonic nanoparticle and vapor bubbles, as well. This phenomenon was considered as a new complex nanosystem—plasmonic nanobubble (PNB). Mechanical and optical scattering properties of PNB depended upon the nanoparticle surface and heat capacity, clusterization state, and the optical pulse length. The generation of the PNB required much higher laser pulse fluence thresholds than the explosive boiling level and was characterized by the relatively high lower threshold of the minimal size (lifetime) of PNB. Optical scattering by PNB and its diameter (measured as the lifetime) has been varied with the fluence of laser pulse, and this has demonstrated the tunable nature of PNB.