Luminescent Oil-Soluble Carbon Dots toward White Light Emission: A Spectroscopic Study

Carbon dots (C-dots) are emerging as new emitting nanomaterials for optoelectronics, bioimaging, and biosensing thanks to their high quantum yield (QY), biocompatibility, low toxicity, and cost-effective sources. Although the origin of their photoluminescence (PL) mechanism (i.e., their strong blue-green emission and excitation dependent fluorescence) is still controversial, it has been demonstrated to depend on the synthetic protocols and experimental conditions, able to modify the surface properties. Here oil-dispersible C-dots, synthesized by carbonization of citric acid in the presence of hexadecylamine in high boiling organic solvent, are thoroughly investigated by systematically controlling the synthetic reaction parameters. Similarly to what was found for water-soluble C-dots, citric acid in the presence of amine-containing passivating agents improves the PL emission of C-dots via the formation of molecular fluorescent derivatives alongside the carbonization process. We demonstrate that at growth temperature of 200 °C such C-dots exhibit an interesting and intense white emission, when excited in the blue region, thus resulting in a biocompatible colloidal white emitting single nano-objects. The incorporation of the nanoparticles in a poly(methyl methacrylate) (PMMA) host matrix, to obtain free-standing nanocomposite films, is demonstrated not to affect the color point, which still falls in the white color region of the 1931 CIE diagram. Remarkably, the emission properties are retained even after several months of films exposure to air and sunlight, thus confirming the color stability of the nanoparticles against aging

Enhanced performances of RGO-AuNPs hybrids towards electroanalytical applications

In recent years, lot of attention has been devoted to understanding the properties of hybrid nanocomposites, \u201cbrave new materials\u201d made of two or more organic and inorganic components. These systems show enhanced or novel physico-chemical properties with respect to the single components, resulting not only from the sum of the precursors\u2019 ones, but also from interactions occurring at their interface, the so-called \u201cheterojunction\u201d. However, a remaining challenge is to understand in depth the phenomena here originating. In the present work, to start fulfilling this gap, a deep electrochemical study of hybrids made of Reduced Graphene Oxide (RGO) and Au nanoparticles (NPs) is performed, analysing carefully the role played by each single component of the material on the electrochemical properties. In more details, RGO platforms are surface functionalized with 1-aminopyrene or 1-pyrene carboxylic acid that act as heteronucleation and growing sites of the amine- or thiol-coated Au NPs of different dimensions (from 3 to 20 nm). At first, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) measurements are carried out in order to characterize the different hybrids. Then, the materials are applied as electroanalytical sensors for both organic and inorganic molecules (dopamine and As, respectively) with very promising results, comparable or even better than analogous systems reported in literature. Moreover, preliminary tests on H2O2 detection open the venue to the application of these materials in biosensor applications. The properties of the hybrid nanocomposite, enhanced with respect to those of the single components, are ascribed to charge transfer occurring at the heterojunction from the Au NPs to the RGO, assisted and channelled by the pyrene linker

Low temperature synthesis of photocatalytic mesoporous tio2 nanomaterials

We report the synthesis of mesoporous TiO2 nanostructures based on the decomposition of TiOSO4 in aqueous alkaline solution at room temperature, followed by mild thermal treatment (110◦C) in an oven and suitable to yield up to 40 g of product per batch. The duration of the thermal treatment was found to be crucial to control crystalline phase composition, specific surface area, surface chemistry and, accordingly, the photocatalytic properties of the obtained TiO2 nanocrystals. The thorough investigation of the prepared samples allowed us to explain the relationship between the structure of the obtained nanoparticles and their photocatalytic behavior, that was tested in a model reaction. In addition, the advantage of the mild treatment against a harsher calcination at 450◦C was illustrated. The proposed approach represents a facile and sustainable route to promptly access an effective photocatalyst, thus holding a significant promise for the development of solutions suitable to real technological application in environmental depollution

Uniform TiO2/In2O3 surface films effective in bacterial inactivation under visible light

This study shows that the surface modification of TiO2 is an effective route to increase the TiO2 absorption in the visible region up to similar to 600 nm for photocatalytic applications. The In2O3 decorated TiO2 films on polyester obtained by reactive sputtering were shown to accelerate the Escherichia coli inactivation under actinic and simulated solar light. TiO2 sputtered films for 10 min inactivated bacteria within 300 min under actinic light. The inactivation time was reduced when using a TiO2 10 min-In2O3 10 s sample to 150 min when using actinic light and 90 min by simulated sunlight with 50 mW/cm(2) (one half of AM1). Thinner TiO2-In2O3 coatings led to faster bacterial inactivation compared to thicker TiO2-In2O3 layers due to the reverse diffusion of the generated charges. The increase in the optical absorption of the green coloured TiO2-In2O3 film was a function of the In2O3 loading as detected by diffuse reflectance spectroscopy (DRS). Evidence of the lack of TiO2 lattice doping by the sputtered In2O3 was found by X-ray diffraction spectroscopy (XRD). The deconvolution of TiO2 bands detected by X-ray photoelectron spectroscopy (XPS) revealed the existence of Ti4+/Ti3+ signals suggesting redox catalysis at the surface of the TiO2-In2O3. The photo-induced interfacial charge transfer (IFCT) between TiO2 and In2O3 can be accounted for by the band position potentials of both semiconductors. The faster kinetics of TiO2-In2O3 inducing E. coli inactivation with a higher quantum efficiency compared to TiO2 takes place in spite of the low intensity of the IFCT optical absorption bands >400 nm

Nanostructured Photoelectrochemical Biosensing Platform for Cancer Biomarker Detection

The innovative photoelectrochemical properties of multifunctional nanomaterials are here investigated for the development of biosensing platforms for rapid and sensitive detection of a class of cancer biomarker candidates, known as microRNAs. Many different transducers have been proposed, so far, for microRNA detection. Recently, with the emergence of novel photoelectrochemically active species and new detection schemes, photoelectrochemistry has received increasing attention. Gold nanostructures have been, here, used to modify TiO2 electrodes. The surface of the nanostructured platform has been modified by nucleic acid capture probes (CPs). Biotinylated target miRNAs have been recognized by the specific CPs. The biosensing platform has been incubated with streptavidin alkaline phosphatase and exposed to a proper substrate. The product of the enzymatic reaction has been photoelectrochemically monitored. A compact and hand-held analytical device has been developed in order to have a final prototype in line with the concept of point of care testing. (C) 2017 The Authors. Published by Elsevier Ltd

A cast-mold approach to iron oxide and Pt/iron oxide nanocontainers and nanoparticles with a reactive concave surface.

We report the synthesis of various iron oxide nanocontainers and Pt−iron oxide nanoparticles based on a cast-mold approach, starting from nanoparticles having a metal core (either Au or AuPt) and an iron oxide shell. Upon annealing, the particles evolve to asymmetric core−shells and then to heterodimers. If iodine is used to leach Au out of these structures, asymmetric core−shells evolve into "nanocontainers", that is, iron oxide nanoparticles enclosing a cavity accessible through nanometer-sized pores, while heterodimers evolve into particles with a concave region. When starting from a metal domain made of AuPt, selective leaching of the Au atoms yields the same iron oxide nanoparticle morphologies but now encasing Pt domains (in their concave region or in their cavity). We found that the concave nanoparticles are capable of destabilizing Au nanocrystals of sizes matching that of the concave region. In addition, for the nanocontainers, we propose two different applications: (i) we demonstrate loading of ..

Lipid-based systems loaded with PbS nanocrystals: near infrared emitting trackable nanovectors

Hydrophobic PbS nanocrystals (NCs) emitting in the near infrared spectral region were encapsulated in the core of micelles and in the bilayer of liposomes, respectively, to form polyethylene glycol (PEG)-grafted phospholipids. The phospholipid-based functionalization process of PbS NCs required the replacement of the pristine capping ligand at the NC surface with thiol molecules. The procedures carried out for two systems, micelles and liposomes, using PEG-modified phospholipids were carefully monitored by optical, morphological and structural investigations. The hydrodynamic diameter and the colloidal stability of both micelles and liposomes loaded with PbS NCs were evaluated using Dynamic Light Scattering (DLS) and z-potential experiments, and both were satisfactorily stable in physiological media. The cytotoxicity of the resulting PbS NC-loaded nanovectors was assessed by the in vitro investigation on Saos-2 cells, indicating that the toxicity of the PbS NC loaded liposomes was lower than that of the micelles with the same NC cargo, which is reasonable due to the different overall composition of the two prepared nanocarriers. Finally, the cellular uptake in the Saos-2 cells of both the NC containing systems was evaluated by means of confocal microscopy studies by exploiting a visible fluorescent phospholipid and demonstrating the ability of both luminescent nanovectors to be internalized. The obtained results show the great potential of the prepared emitting nanoprobes for imaging applications in the second biological window

Ascorbic acid-sensitized Au nanorods-functionalized nanostructured TiO2 transparent electrodes for photoelectrochemical genosensing

Au nanorods (NRs) modified nanostructured TiO2/ITO electrodes have been fabricated and characterized in order to develop a biosensing platform for the photoelectrochemical determination of microRNAs. The proposed method is based on the use of thiolated DNA capture-probes (CPs) immobilized onto Au NR surface. The Au NRs are chemically bound at the surface of TiO2/ITO electrodes by means of the mercaptosuccinic acid linker. Subsequently, the DNA CPs are bound to the Au NR surface through the thiolate group, and reacted with the target RNA sequence. Finally, the obtained biosensing platform is incubated with alkaline phosphatase and l-ascorbic acid 2-phosphate (AAP) enzymatic substrate, for the in situ generation of ascorbic acid (AA). Such AA molecule, coordinating to surface Ti atoms, generates a charge transfer complex, that results in a shift of the UV absorption threshold toward the visible spectral region of the nanostructured TiO2 forming the electrode and, hence, in the occurrence of an absorption band centered at 450\u202fnm. The photoelectrochemical monitoring of the formation of the AA-TiO2 complex, under the visible light of a commercial LED light source, allows the selective and quantitative detection of the target microRNA strands

Towards individual electrical contact of nanoparticles in nanocomposites

A new technological approach that will allow contacting individual nano-objects is presented. An ultra-thin nanocomposite layer is formed by embedding semiconductor and metal nanoparticles in a highly insulating epoxy based negative photoresist. The role of the photoresist is to support and electrically insulate the nanoparticles. In order to perform electrical contacts, an array of gold micro/nano-electrodes has been defined by electron beam lithography on top of the nanocomposite layer. Promising initial results of the electrical characterization are presented, evidencing significant differences between bare resist and nanocomposite films. © 2011 Elsevier B.V. All rights reserved

Hybrid junctions of Zn(II) and Mg(II) phthalocyanine with wide band gap semiconductor nano-oxides: spectroscopical and photoelectrochemical characterization

The optical properties of zinc phthalocyanine (ZnIIPc) and magnesium phthalocyanine (MgIIPc) in DMSO and DMF solutions have been extensively investigated, and the photoelectrochemical behaviors of layer-bylayer hybrid junctions formed of the two metallo(II) phthalocyanines (MIIPcs) and wide-band-gap colloidal semiconductors, namely, ZnO and TiO2 nanocrystals (NCs), have been probed. Different experimental conditions, such as the Pc center metal ion, dye concentration, and solvent identity, were investigated in order to elucidate their effects on the photoelectrochemical performances of the prepared heterojunctions. Finally, thermal treatment of either dye and NC films and control of the NC shape and surface chemistry were also studied and, interestingly, were found to be critical in affecting the performance of photochemical sensitization processes, occurring at the dye/oxide and oxide/solution interfaces