SERS-Based Methodology for the Quantification of Ultratrace Graphene Oxide in Water Samples.

The extensive use of graphene materials in real-world applications has increased their potential release into the environment. To evaluate their possible health and ecological risks, there is a need for analytical methods that can quantify these materials at very low concentrations in environmental media such as water. In this work, a simple, reproducible, and sensitive method to detect graphene oxide (GO) in water samples using the surface-enhanced Raman spectroscopy (SERS) technique is presented. The Raman signal of graphene is enhanced when deposited on a substrate of gold nanoparticles (AuNPs), thus enabling its determination at low concentrations with no need for any preconcentration step. The practical limit of quantification achieved with the proposed method was 0.1 ng mL-1, which is lower than the predicted concentrations for graphene in effluent water reported to date. The optimized procedure has been successively applied to the determination of ultratraces of GO in water samples.

Graphene Quantum Dot-Aerogel: From Nanoscopic to Macroscopic Fluorescent Materials. Sensing Polyaromatic Compounds in Water.

Fluorescence based on quantum confinement is a property restricted to the nanoscopic range. The incorporation of nanoparticles in a three-dimensional polymeric network could afford macroscopic scaffolds that show nanoscopic properties. Moreover, if these scaffolds are based on strong bonds, the stability of the resulting materials can be preserved, thus enhancing their final applications. We report for the first time the preparation of a graphene quantum dot (GQD) composite based on a cationic covalent network. This new material has unusual features: (i) the final composite remains stable after several swelling-deswelling cycles, thus demonstrating strong interactions between GQDs and the polymeric material, and therefore it could be used as a portable system. (ii) Fluorescence emission in the composite and in solution is quasi-independent to the excitation wavelength. (iii) However, and in contrast to the behavior observed in GQD solutions, the fluorescence of the composite remains unaltered over a wide pH range and in the presence of different ions commonly found in tap water. (iv) Fluorescence quenching is only observed as a consequence of molecules that bear aromatic systems, and this could be applied to the preparation of in situ water sensors.

Advantageous Microwave-Assisted Suzuki Polycondensation for the Synthesis of Aniline-Fluorene Alternate Copolymers as Molecular Model with Solvent Sensing Properties.

Polymerization via Suzuki coupling under microwave (µW) irradiation has been studied for the synthesis of poly{1,4-(2/3-aminobenzene)-alt-2,7-(9,9-dihexylfluorene)} (PAF), chosen as molecular model. Briefly, µW-assisted procedures accelerated by two orders of magnitude the time required when using classical polymerization processes, and the production yield was increased (>95%). In contrast, although the sizes of the polymers that were obtained by non-conventional heating reactions were reproducible and adequate for most applications, with this methodology the molecular weight of final polymers were not increased with respect to conventional heating. Asymmetric orientation of the amine group within the monomer and the assignments of each dyad or regioregularity, whose values ranged from 38% to 95% with this molecule, were analysed using common NMR spectroscopic data. Additionally, the synthesis of a new cationic polyelectrolyte, poly{1,4-(2/3-aminobenzene)-co-alt-2,7-[9,9´-bis(6''-N,N,N-trimethylammonium-hexyl)fluorene]} dibromide (PAFAm), from poly{1,4-(2/3-aminobenzene)-co-alt-2,7-[9,9´-bis(6''-bromohexyl)fluorene]} (PAFBr) by using previously optimized conditions for µW-assisted heating procedures was reported. Finally, the characterization of the final products from these batches showed unkown interesting solvatochromic properties of the PAF molecule. The study of the solvatochromism phenomena, which was investigated as a function of the polarity of the solvents, showed a well-defined Lippert correlation, indicating that the emission shift observed in PAF might be due to its interaction with surrounding environment. Proven high sensitivity to changes of its environment makes PAF a promising candidate of sensing applications.

Carbon Nanohorns Modified with Conjugated Terthienyl/Terthiophene Structures: Additives to Enhance the Performance of Dye-Sensitized Solar Cells.

A series of carbon nanohorns (CNHs) constituted by the aggregation of about 2000 individual conical graphene tubes (diameters from 2 nm to 5 nm and a length of 40-50 nm) that have been modified with dyes of two, three, or four terthienyl groups has been prepared by adsorbing the corresponding dye on the CNH. Persistent inks in o-dichlorobenzene (o-DCB) of these dye-CNH conjugates were obtained by laser irradiation of o-DCB suspensions of the dye-CNH solids. These inks were used in combination or not with N719 dye for the preparation of dye-sensitized solar cells (DSSC) of TiO2. It was measured that the terthienyl dye with the largest conjugation deposited on the CNH additively increased the performance of an analogous TiO2 cell from an efficiency of 4.07% to 6.24%. This result shows the potential of dye-modified CNHs as additives in the construction of more efficient DSSCs.

Targeted killing of prostate cancer cells using antibody-drug conjugated carbon nanohorns.

The ability of carbon nanohorns (CNHs) to cross biological barriers makes them potential carriers for delivery purposes. In this work, we report the design of a new selective antibody-drug nanosystem based on CNHs for the treatment of prostate cancer (PCa). In particular, cisplatin in a prodrug form and the monoclonal antibody (Ab) D2B, selective for PSMA+ cancer cells, have been attached to CNHs due to the current application of this antigen in PCa therapy. The hybrids Ab-CNHs, cisplatin-CNHs and functionalised-CNHs have also been synthesized to be used as control systems. The efficacy and specificity of the D2B-cisplatin-CNH conjugate to selectively target and kill PSMA+ prostate cancer cells have been demonstrated in comparison with other derivatives. The developed strategy to functionalise CNHs is fascinating because it can allow the fine tuning of both drug and Ab molecules attached to the nanostructure in order to modulate the activity of the nanosystem. Finally, the herein described methodology can be used for the incorporation of almost any drugs or Abs in the platforms in order to create new targeted drugs for the treatment of different diseases.

Triazine-Carbon Nanotubes: New Platforms for the Design of Flavin Receptors.

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single-walled and multi-walled, have been functionalised with 1,3,5-triazines and p-tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the π-π stacking interactions between riboflavin and the nanotube walls. Comparison of p-tolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern-Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin.

Carbon nanohorns as integrative materials for efficient dye-sensitized solar cells.

Different nanocarbons, that is, single-wall carbon nanotubes, graphene, single-wall carbon nanohorns (SWCNHs), and their respective oxidized analogs have been used to fabricate novel doped TiO2 electrodes for DSSCs. Our results indicate that all of the nanocarbons significantly enhance the device characteristics when compared to standard TiO2 electrodes. Overall, our most outstanding finding is that SWCNH derivatives are also a plausible material for developing highly-efficient DSSCs.

In vivo degradation of functionalized carbon nanotubes after stereotactic administration in the brain cortex.

AIM: Carbon nanotubes (CNTs) are increasingly being utilized in neurological applications as components of implants, electrodes or as delivery vehicles. Any application that involves implantation or injection of CNTs into the CNS needs to address the distribution and fate of the material following interaction and residence within the neuronal tissue. Here we report a preliminary study investigating the fate and structural integrity of amino-functionalized CNTs following stereotactic administration in the brain cortex. MATERIALS & METHODS: The CNTs investigated had previously shown the capacity to internalize in various cell types of the CNS. An aqueous suspension of multiwalled CNT-NH(3) (+) was stereotactically injected into the mouse brain cortex. Their interaction with neural cells and consequent effects on the CNT structural integrity was investigated by optical, transmission electron microscopy and Raman spectroscopy of brain tissue sections for a period between 2 and 14 days post cortical administration. RESULTS & DISCUSSION: The occurrence of severe nanotube structure deformation leading to partial degradation of the chemically functionalized-multiwalled CNT-NH(3) (+) in vivo following internalization within microglia was revealed even at early time points. Such initial observations of CNT degradation within the brain tissue render further systematic investigations using high-resolution tools imperative.

Hybrid materials based on Pd nanoparticles on carbon nanostructures for environmentally benign C-C coupling chemistry.

The combination of different nanomaterials such as metallic nanoparticles and carbon nanostructures in a new hybrid material should give rise to interesting properties that combine the advantages of each of the nanocomponents. This review highlights the latest advances in the synthetic design of these hybrid materials where carbon nanostructures act as supports as well as stabilizing agents for very reactive metallic nanoparticles. The striking applications of Pd nanoparticles anchored on the surface of carbon nanostructures in C-C coupling chemistry are analyzed. Special emphasis is placed on the stability of these materials, which is linked to their recyclability. Numerous examples are given that involve the use of these catalysts in Heck, Suzuki and Sonogashira coupling reactions.

Enhanced cellular internalization and gene silencing with a series of cationic dendron-multiwalled carbon nanotube:siRNA complexes.

One of the major obstacles to the clinical development of gene silencing by small interfering RNA (siRNA) is its effective cytoplasmic delivery. Carbon nanotubes have been proposed as novel nanomaterials that can offer significant advantages for the intracellular delivery of nucleic acids, such as siRNA. We recently demonstrated in a proof-of-principle study that amino-functionalized multiwalled carbon nanotubes (f-MWNT) can effectively deliver in vivo an siRNA sequence, triggering cell apoptosis that results in human lung xenograft eradication and prolonged survival. In the present study, we demonstrate how a newly synthesized series of polycationic dendron-MWNT constructs with a precisely tailored number of amino functions (dendron generations) can complex and effectively deliver double-stranded siRNA to achieve gene silencing in vitro. A systematic comparison between the f-MWNT series in terms of cellular uptake, cytotoxicity, and siRNA complexation is offered. Significant improvement in siRNA delivery with the dendron-MWNT conjugates is shown, and gene silencing was obtained in 2 human cell lines using 2 different siRNA sequences. The study reveals that through f-MWNT structure-biological function analysis novel nanotube-based siRNA transfer vectors can be designed with minimal cytotoxicity and effective delivery and gene-silencing capabilities.