The Formation of Carbon Dots from D-Glucose Studied by Infrared Spectroscopy.

Carbon dots (C-dots) obtained from D-glucose have attracted great interest because of their properties and as a model for understanding the synthesis process and the origin of photoluminescence in carbon-based nanostructures. Synthesising C-dots under hydrothermal conditions has become one of the most common methods for their preparation. Understanding the details of this process is quite difficult. To tackle this challenge, we have adopted a multi-technique approach in our present work. We have correlated different spectroscopic analyses, such as infrared, Raman, fluorescence, NMR, and UV-Vis, to connect the emissions with specific chemical groups. In particular, in situ infrared analysis as a function of temperature has allowed following the formation of C=C, C=O, and COOH species and the rise of specific emissions. Only weak emissions due to n-π* transitions are detected upon post-synthesis thermal annealing.

Polymerization-Driven Photoluminescence in Alkanolamine-Based C-Dots.

Carbonized polymer dots (CPDs), a peculiar type of carbon dots, show extremely high quantum yields, making them very attractive nanostructures for application in optics and biophotonics. The origin of the strong photoluminescence of CPDs resides in a complicated interplay of several radiative mechanisms. To understand the correlation between CPD processing and properties, the early stage formation of carbonized polymer dots has been studied. In the synthesis, citric acid monohydrate and 2-amino-2-(hydroxymethyl)propane-1,3-diol have been thermally degraded at 180 °C. The use of an oil bath instead of a more traditional hydrothermal reactor has allowed the CPD properties to be monitored at different reactions times. Transmission electron microscopy, time-resolved photoluminescence, nuclear magnetic resonance, infrared, and Raman spectroscopy have revealed the formation of polymeric species with amide and ester bonds. Quantum chemistry calculations have been employed to investigate the origin of CPD electronic transitions. At short reaction times, amorphous C-dots with 80 % quantum yield, have been obtained.

Boron Nitride-Titania Mesoporous Film Heterostructures.

The fabrication of optically active heterostructures in the shape of mesostructured thin films is a highly challenging task. It requires an integrated process to allow in one-step incorporating the two-dimensional materials within the mesoporous ordered host without disrupting the pore organization. Hexagonal boron nitride (BN) nanosheets have been successfully introduced into titania mesoporous films using a template-assisted sol-gel synthesis and evaporation-induced self-assembly. Two types of BN sheets have been used, with and without defects, to investigate the role of defects in heterostructure properties. It has been found that the defects increase the ultraviolet radiation A (UVA) absorbance and enhance the photocatalytic response of the film. The BN sheets are optically transparent and do not exhibit any photocatalytic property but contribute to anatase crystallization via heterogeneous nucleation.

Modulating the Optical Properties of Citrazinic Acid through the Monomer-to-Dimer Transformation.

Understanding the luminescence of carbon dots is a highly challenging task because of the complex reactions involved in the synthesis process. Several by-products form at different reaction stages and become possible sources of emission. Citrazinic acid and its derivatives, in particular, have been identified as intermediates that give rise to blue fluorescence. Full comprehension of the optical properties of citrazinic acid itself is, however, still lacking. In particular, citrazinic acid has the property of forming different tautomers and aggregates such as dimers. However, the nature of these chemical species and the correlation with their relative optical properties have been only partially explored. In the present work, we have used a combination of spectroscopic techniques, UV-visible and fluorescence spectroscopy, time-resolved photoluminescence and computational simulation, to study the different species which citrazinic acid forms in water as a function of CZA molarity. A monomer-to-dimer transformation and a hypsochromic shift are observed with concentration. The monomer is in the keto structure and does not form other tautomers while the dimers are fluorescent J-type aggregates. The formation of aggregates strongly modulates the optical properties of citrazinic acid.

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition.

Thermal decomposition of citric acid is one of the most common synthesis methods for fluorescent carbon dots; the reaction pathway is, however, quite complex and the details are still far from being understood. For instance, several intermediates form during the process and they also give rise to fluorescent species. In the present work, the formation of fluorescent C-dots from citric acid has been studied as a function of reaction time by coupling infrared analysis, X-ray photoelectron spectroscopy, liquid chromatography/mass spectroscopy (LC/MS) with the change of the optical properties, absorption and emission. The reaction intermediates, which have been identified at different stages, produce two main emissive species, in the green and blue, as also indicated by the decay time analysis. C-dots formed from the intermediates have also been synthesised by thermal decomposition, which gave an emission maximum around 450 nm. The citric acid C-dots in water show short temporal stability, but their functionalisation with 3-aminopropyltriethoxysilane reduces the quenching. The understanding of the citric acid thermal decomposition reaction is expected to improve the control and reproducibility of C-dots synthesis.

Effect of exposure to CeO2 nanoparticles on ram spermatozoa during storage at 4 °C for 96 hours.

BACKGROUND: Cerium oxide nanoparticles (CeO2 NPs) are able to store and release oxygen, conferring them scavenger activity against oxidative stress. However, their effects in reproductive systems are not yet well understood. The aim of the study was to investigate the effects of exposure of refrigerated ram semen to CeO2 NPs for 96 h on the main structural and kinematic parameters of spermatozoa. METHODS: The ejaculates of 5 Sarda rams were collected, pooled and diluted in a soybean lecithin extender. Samples were exposed to increasing doses of CeO2 NPs (0, 44 and 220 µg/mL) and stored at 4 °C for 96 h. Analyses of kinematic parameters (computer assisted sperm analysis, CASA), integrity of membranes (PI/PSA staining), ROS production (H2DCFDA staining) and DNA damage (sperm chromatin structure assay with acridine orange, SCSA) were performed every 24 h (0, 24, 48, 72 and 96 h of incubation). The experiment was carried out in 6 replicates. Data were analysed by repeated measures ANOVA with Bonferroni's as post hoc test. When the assumption of normality was not met (ROS), non-parametric Kruskal-Wallis rank test was carried out. RESULTS: Exposure of ram spermatozoa to increasing doses of CeO2 NPs had a beneficial effect on the main motility parameters from 48 h of incubation onward. Velocity of sperm cells was enhanced in the groups exposed to CeO2 NPs compared to the control. Incubation with NPs had beneficial effects on the integrity of plasma membranes of spermatozoa, with higher percentage of damaged cells in the control group compared to the exposed ones. Production of ROS was not affected by exposure to NPs and its levels rose at 96 h of incubation. The integrity of DNA remained stable throughout the 96 h of storage regardless of co-incubation with NPs. CONCLUSIONS: We reported beneficial effects of CeO2 NPs on kinematic and morphologic parameters of ram semen, such as motility and membrane integrity following 96 h of exposure. Furthermore, we also proved no genotoxic effects of CeO2 NPs. These effects could not be related to an antioxidant activity of CeO2 NPs, since ROS levels in exposed cells were similar to those of unexposed ones.

Sol-Gel Chemistry for Carbon Dots.

Carbon dots are an emerging class of carbon-based nanostructures produced by low-cost raw materials which exhibit a widely-tunable photoluminescence and a high quantum yield. The potential of these nanomaterials as a substitute of semiconductor quantum dots in optoelectronics and biomedicine is very high, however they need a customized chemistry to be integrated in host-guest systems or functionalized in core-shell structures. This review is focused on recent advances of the sol-gel chemistry applied to the C-dots technology. The surface modification, the fine tailoring of the chemical composition and the embedding into a complex nanostructured material are the main targets of combining sol-gel processing with C-dots chemistry. In addition, the synergistic effect of the sol-gel precursor combined with the C-dots contribute to modify the intrinsic chemo-physical properties of the dots, empowering the emission efficiency or enabling the tuning of the photoluminescence over a wide range of the visible spectrum.

Hard X-rays for processing hybrid organic-inorganic thick films.

Hard X-rays, deriving from a synchrotron light source, have been used as an effective tool for processing hybrid organic-inorganic films and thick coatings up to several micrometres. These coatings could be directly modified, in terms of composition and properties, by controlled exposure to X-rays. The physico-chemical properties of the coatings, such as hardness, refractive index and fluorescence, can be properly tuned using the interaction of hard X-rays with the sol-gel hybrid films. The changes in the microstructure have been correlated especially with the modification of the optical and the mechanical properties. A relationship between the degradation rate of the organic groups and the rise of fluorescence from the hybrid material has been observed; nanoindentation analysis of the coatings as a function of the X-ray doses has shown a not linear dependence between thickness and film hardness.

Tuning the phase transition of ZnO thin films through lithography: an integrated bottom-up and top-down processing.

An innovative approach towards the physico-chemical tailoring of zinc oxide thin films is reported. The films have been deposited by liquid phase using the sol-gel method and then exposed to hard X-rays, provided by a synchrotron storage ring, for lithography. The use of surfactant and chelating agents in the sol allows easy-to-pattern films made by an organic-inorganic matrix to be deposited. The exposure to hard X-rays strongly affects the nucleation and growth of crystalline ZnO, triggering the formation of two intermediate phases before obtaining a wurtzite-like structure. At the same time, X-ray lithography allows for a fast patterning of the coatings enabling microfabrication for sensing and arrays technology.

Sol-to-Gel Transition in Fast Evaporating Systems Observed by in Situ Time-Resolved Infrared Spectroscopy.

The in situ observation of a sol-to-gel transition in fast evaporating systems is a challenging task and the lack of a suitable experimental design, which includes the chemistry and the analytical method, has limited the observations. We synthesise an acidic sol, employing only tetraethylorthosilicate, SiCl4 as catalyst and deuterated water; the absence of water added to the sol allows us to follow the absorption from the external environment and the evaporation of deuterated water. The time-resolved data, obtained by attenuated total reflection infrared spectroscopy on an evaporating droplet, enables us to identify four different stages during evaporation. They are linked to specific hydrolysis and condensation rates that affect the uptake of water from external environment. The second stage is characterized by a decrease in hydroxyl content, a fast rise of condensation rate and an almost stationary absorption of water. This stage has been associated with the sol-to-gel transition.

Getting order in mesostructured thin films, from pore organization to crystalline walls, the case of 3-glycidoxypropyltrimethoxysilane.

A new type of mesostructured hybrid organic-inorganic film has been synthesised by evaporation-induced self-assembly using 3-glycidoxypropyltrimethoxysilane as the precursor and a tri-block copolymer, Pluronic F127, as the template. The chemistry has been tuned to form bridged polysilsesquioxanes that self-organise into ordered lamellar structures. Controlled aging under highly basic conditions, which has been monitored by Raman and infrared spectroscopy, has been used to obtain the layered ordered hybrid structures in the precursor sol. The pH of the sol has been adjusted to form the micelles that act as templates during solvent evaporation. The self-assembly of the system has been studied in situ by small and wide angle X-ray scattering using a synchrotron light source, which has confirmed both the formation of hybrid layered structures and the long-range organization of the mesophase in the hybrid films. The present approach allows ordering the hybrid film on two different length scales; at the end of film processing, hybrid crystals are incorporated into the pore walls and the micelles are arranged within the films with long range order.

Graphene-mediated surface enhanced Raman scattering in silica mesoporous nanocomposite films.

Silica mesoporous nanocomposite films containing graphene nanosheets and gold nanoparticles have been prepared via a one-pot synthesis using silicon tetrachloride, gold(III) chloride tetrahydrate, a 1-N-vinyl-2-pyrrolidone dispersion of exfoliated graphene and Pluronic F127 as a structuring agent. The composite films have shown graphene-mediated surface-enhanced Raman scattering (G-SERS). Graphene has been introduced as dispersed bilayer sheets while gold has been thermally reduced in situ to form nanoparticles of around 6 nm which preferentially nucleate on the surface of the graphene nanosheets. The presence of graphene and gold nanoparticles does not interfere with the self-assembly process and the formation of silica mesoporous films ordered as 2D hexagonal structures. The material has shown a remarkable analytical enhancement factor ranging from 80 up to 136 using rhodamine 6G as a Raman probe. The films have been characterised by grazing incidence X-ray diffraction, FTIR and UV-vis spectroscopy studies; transmission electron microscopy and spectroscopic ellipsometry have been used to study the morphology, thickness and porosities of the samples. Raman spectroscopy has been employed to characterise the graphene nanosheets embedded into the mesoporous films and the enhanced Raman scattering.

Mesoporous thin films: properties and applications.

In this review we present a short overview of the main fields of application of mesoporous ordered films obtained via templating self-assembly. These materials, because of their very special properties such as high surface area, ordered porosity, versatile functionalization of the pore surface, have been widely used for developing advanced functional applications. Mesoporous ordered films have also shown a high capability of integration in current material processing technologies also taking advantage of the high flexibility of the synthesis. A surprisingly large variety of devices and applications have been developed so far which ranges from sensors to supercapacitors and biodevices. All these applications have in common the exploitation of ordered porosity on the mesoscale and in general a strong dependence on pore topology, the nature of the pore surface and pore accessibility has been demonstrated for most of the cases. Even if a high number of examples of applications have been reported still many more are expected to come in the near future.

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography.

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.

Bidimensional SnSe2-Mesoporous Ordered Titania Heterostructures for Photocatalytically Activated Anti-Fingerprint Optically Transparent Layers.

The design of functional coatings for touchscreens and haptic interfaces is of paramount importance for smartphones, tablets, and computers. Among the functional properties, the ability to suppress or eliminate fingerprints from specific surfaces is one of the most critical. We produced photoactivated anti-fingerprint coatings by embedding 2D-SnSe2 nanoflakes in ordered mesoporous titania thin films. The SnSe2 nanostructures were produced by solvent-assisted sonication employing 1-Methyl-2-pyrrolidinone. The combination of SnSe2 and nanocrystalline anatase titania enables the formation of photoactivated heterostructures with an enhanced ability to remove fingerprints from their surface. These results were achieved through careful design of the heterostructure and controlled processing of the films by liquid phase deposition. The self-assembly process is unaffected by the addition of SnSe2, and the titania mesoporous films keep their three-dimensional pore organization. The coating layers show high optical transparency and a homogeneous distribution of SnSe2 within the matrix. An evaluation of photocatalytic activity was performed by observing the degradation of stearic acid and Rhodamine B layers deposited on the photoactive films as a function of radiation exposure time. FTIR and UV-Vis spectroscopies were used for the photodegradation tests. Additionally, infrared imaging was employed to assess the anti-fingerprinting property. The photodegradation process, following pseudo-first-order kinetics, shows a tremendous improvement over bare mesoporous titania films. Furthermore, exposure of the films to sunlight and UV light completely removes the fingerprints, opening the route to several self-cleaning applications.

In Vitro Antiviral Activity of Hyperbranched Poly-L-Lysine Modified by L-Arginine against Different SARS-CoV-2 Variants.

The emergence of SARS-CoV-2 variants requires close monitoring to prevent the reoccurrence of a new pandemic in the near future. The Omicron variant, in particular, is one of the fastest-spreading viruses, showing a high ability to infect people and evade neutralization by antibodies elicited upon infection or vaccination. Therefore, the search for broad-spectrum antivirals that can inhibit the infectious capacity of SARS-CoV-2 is still the focus of intense research. In the present work, hyperbranched poly-L-lysine nanopolymers, which have shown an excellent ability to block the original strain of SARS-CoV-2 infection, were modified with L-arginine. A thermal reaction at 240 °C catalyzed by boric acid yielded Lys-Arg hyperbranched nanopolymers. The ability of these nanopolymers to inhibit viral replication were assessed for the original, Delta, and Omicron strains of SARS-CoV-2 together with their cytotoxicity. A reliable indication of the safety profile and effectiveness of the various polymeric compositions in inhibiting or suppressing viral infection was obtained by the evaluation of the therapeutic index in an in vitro prevention model. The hyperbranched L-arginine-modified nanopolymers exhibited a twelve-fold greater therapeutic index when tested with the original strain. The nanopolymers could also effectively limit the replication of the Omicron strain in a cell culture.

Hybrid materials with an increased resistance to hard X-rays using fullerenes as radical sponges.

The protection of organic and hybrid organic-inorganic materials from X-ray damage is a fundamental technological issue for broadening the range of applications of these materials. In the present article it is shown that doping hybrid films with fullerenes C(60) gives a significant reduction of damage upon exposure to hard X-rays generated by a synchrotron source. At low X-ray dose the fullerene molecules act as `radical scavengers', considerably reducing the degradation of organic species triggered by radical formation. At higher doses the gradual hydroxylation of the fullerenes converts C(60) into fullerol and a bleaching of the radical sinking properties is observed.

IR and X-ray time-resolved simultaneous experiments: an opportunity to investigate the dynamics of complex systems and non-equilibrium phenomena using third-generation synchrotron radiation sources.

Third-generation storage rings are modern facilities working with high currents and designed to host powerful radiation sources, like undulators and wigglers, and to deliver high-brilliance beams to users. Many experiments at high spatial resolution, such as spectromicroscopy at the nanometre scale and with high temporal resolution to investigate kinetics down to the picosecond regime, are now possible. The next frontier is certainly the combination of different methods in a unique set-up with the ultimate available spatial and temporal resolutions. In the last decade much synchrotron-based research has exploited the advantage of complementary information provided by time-resolved X-ray techniques and optical methods in the UV/Vis and IR domains. New time-resolved and concurrent approaches are necessary to characterize complex systems where physical-chemical phenomena occur under the same experimental conditions, for example to detect kinetic intermediates via complementary but independent observations. In this contribution we present scientific cases from original works and literature reviews to support the proposed IR/X-ray simultaneous approach, with both probes exploiting synchrotron radiation sources. In addition, simple experimental layouts that may take advantage of the high brilliance and the wide spectral distribution of the synchrotron radiation emission will be given for specific researches or applications to investigate dynamic processes and non-equilibrium phenomena occurring in many condensed matter and biological systems, of great interest for both fundamental research and technological applications.

Raman microspectroscopy as a non-invasive tool to assess the vitrification-induced changes of ovine oocyte zona pellucida.

Cryopreservation-induced modifications of zona pellucida (ZP) have been explored to a lesser extent compared to other oocyte compartments. Different methods have been applied to identify ZP changes, but most of them are invasive and measure only few properties of ZP. Raman microspectroscopy (RMS) is a powerful technique for studying the molecular composition of cells but to date few studies have been performed on the oocytes using this method. The aim of the present study is to investigate the structural modifications of ZP of vitrified/warmed in vitro matured ovine oocytes by means of RMS. Cumulus-oocyte complexes were recovered from the ovaries of slaughtered adult sheep, matured in vitro and vitrified following the Minimum Essential Volume method using cryotops. ZPs of vitrified/warmed oocytes (VITRI), were exposed to vitrification solutions but not cryopreserved (CPA-exp) and untreated oocytes (CTR) were analyzed by RMS. We focused our analysis on the ZP protein and carbohydrate components by analyzing the 1230-1300 cm(-1) amide III region and the 1020-1140 cm(-1) spectral range in RMS spectra, respectively. The spectral profiles in the ranges of proteins and carbohydrates were comparable between CTR and CPA-exp ZPs, whereas VITRI ZPs showed a significantly altered protein secondary structure characterized by an increase in ß-sheet content and a decrease in the α-helix content. A significant modification of the carbohydrate components was also observed. This study demonstrates that vitrification of ovine oocytes induces biochemical changes of ZP related to the secondary structure of proteins and carbohydrate residues. Cryoprotectants do not strongly alter the molecular composition of ZP which is affected mainly by cooling. Raman technology offers a powerful and non-invasive tool to assess molecular modifications induced by cryopreservation in oocytes.

Hybrid materials for optics and photonics.

The interest in organic-inorganic hybrids as materials for optics and photonics started more than 25 years ago and since then has known a continuous and strong growth. The high versatility of sol-gel processing offers a wide range of possibilities to design tailor-made materials in terms of structure, texture, functionality, properties and shape modelling. From the first hybrid material with optical functional properties that has been obtained by incorporation of an organic dye in a silica matrix, the research in the field has quickly evolved towards more sophisticated systems, such as multifunctional and/or multicomponent materials, nanoscale and self-assembled hybrids and devices for integrated optics. In the present critical review, we have focused our attention on three main research areas: passive and active optical hybrid sol-gel materials, and integrated optics. This is far from exhaustive but enough to give an overview of the huge potential of these materials in photonics and optics (254 references).