Effects of the interaction of single-walled carbon nanotubes with 4-nonylphenol on their in vitro toxicity.

The aim of this study was to assess the toxicological risks arising from the coexistence of polyethylene glycol coated single-walled carbon nanotubes (SWCNTs-PEG) and a known environmental contaminant: 4-nonylphenol (NP). To this end, in vitro toxicity assays involving the exposure of 3T3-L1 cells (mouse embryonic fibroblasts) to SWCNTs-PEG alone or in combination with NP for 24 or 48 h were performed. Experimental treatments were conducted in both presence (10%) and absence of serum in order to evaluate its influence on the toxicity of SWCNTs-PEG. Although the results provided no unambiguous evidences of synergistic toxicity between SWCNTs-PEG and NP, some specific treatments with mixtures (SWCNTs-PEG+NP) resulted in an unexpected combined toxicity in relation to the individual treatments. Only in those cases the interaction between SWCNTs-PEG and NP could have a synergistic effect on the resulting toxicity. The addition of 10% serum increased the stability of SWCNTs-PEG in the culture medium-possibly by steric repulsions-and reduced the toxicity of nanoparticles as a result. Overall, the serum had a "protective effect" on cells against all treatments: SWCNTs-PEG, NP or their mixtures (SWCNTs-PEG+NP). Raman spectroscopy allowed the intracellular distribution of SWCNTs-PEG to be elucidated.

Characterization of stainless steel assisted bare gold nanoparticles and their analytical potential.

A simple, environmentally friendly, one-pot method to synthesize highly stable bare gold nanoparticles (AuNPs) has been developed. AuNPs have been synthesized from tetrachloroauric acid solution using steel or stainless steel as solid reducing agent, which can be reused. The proposed method yields bare gold nanoparticles at atmospheric pressure and room temperature for potentially producing large quantities. The obtained AuNPs have been characterized by SEM, TEM and AFM finding an average diameter of around 20 nm, polygonal yet nearly spherical shape and a narrow size distribution. The mechanism of reaction has been investigated by UV-vis spectroscopy, ICP-OES and EDX analysis. The obtained dispersed gold nanoparticles proved to be stable if stored a 4 °C for over four months without the addition of a stabilizing agent. Their analytical potential as SERS substrate has been demonstrated and their performance compared with that showed by citrate-coated gold nanoparticles. Thanks to their unique properties, their use as analytical tools provides analytical processes with enhanced selectivity and precision.

Raman spectroscopic characterization of single walled carbon nanotubes: influence of the sample aggregation state.

Raman spectroscopy has been employed in analytical sciences for purity determination of carbon nanotube samples based on the consideration of G-/D-band intensity ratios. This work demonstrates the role of aggregation in these feature bands, which, in the case of single walled carbon nanotubes (SWNTs), has proved to be crucial for G-/D-band intensity ratio measurements. We have found variation in the relative intensities of G- and D-bands across a sample of SWNTs without any other treatment, discarding the possible influence of the laser beam or sample focusing. In the case of multiwalled carbon nanotubes (MWNTs), this effect is less notorious. Thus, to achieve a good representativeness of Raman measurements, it is important to consider the sample preparation procedure in order to avoid aggregation, which has an effect over the signals, making difficult the subsequent interpretation of results.

Bare gold nanoparticles mediated surface-enhanced Raman spectroscopic determination and quantification of carboxylated single-walled carbon nanotubes.

The paper proposes a simple and portable approach for the surface enhanced Raman scattering (SERS) spectroscopy in situ determination of carboxylated single walled carbon nanotubes (SWNTs) in river water samples. The method is based on the subsequent microfiltration of a bare gold nanoparticles solution and the water sample containing soluble carbon nanotubes by using a home-made filtration device with a small filtration diameter. An acetate cellulose membrane with a pore size of 0.2 µm first traps gold nanoparticles to form the SERS-active substrate and then concentrates the carbon nanotubes. The measured SERS intensity data were closely fit with a Langmuir isotherm. A portable Raman spectrometer was employed to measure SERS spectra, which enables in situ determination of SWNTs in river waters. The limit of detection was 10 µg L(-1). The precision, for a 10 mg L(-1) concentration of carbon nanotubes, is 1.19% intra-membrane and 10.5% inter-membrane.

Simple and fast fluorimetric determination of the critical gel concentration of soft nanomaterials.

Soft materials or gels are new interesting materials resulting from the combination of carbon nanotubes with ionic liquids. However, it should be noted that not all ionic liquid/carbon nanotubes combinations lead to the formation of gels. In fact, this requires using an optimum concentration of CNTs known as "critical gel concentration" (CGC) in the mixture. Up to now, this critical concentration has been determined by means of rheological measurements or by observing a change of a physical property in the new material such as density. On the basis of the high stability of gels in solvents, owing to the presence of carbon nanotubes, this paper reports for the first time a simple and fast method to determine the critical gel concentration for the formation of soft materials by means of fluorescence measurements. We have determined the critical gel concentration of four gels obtained by the combination of three different types of multi walled carbon nanotubes and one single walled carbon nanotubes with the ionic liquid 1-hexyl 3-methylimidazolium hexafluorophosphate. The main characteristics of carbon nanotubes and gels resulting of them were established by Raman spectroscopy. The proposed methodology is presented as an alternative to traditional complex rheological measurements.

Solid phase extraction-capillary electrophoresis determination of sulphonamide residues in milk samples by use of C18-carbon nanotubes as hybrid sorbent materials.

The exceptional sorption capabilities of carbon nanotubes were used to preconcentrate trace sulphonamides from milk samples. To this end, single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) dispersed in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate were retained on a C18 stationary phase to obtain a hybrid material in a simple manner. In this approach ionic liquids are an excellent alternative to improve the dispersion of CNTs, without chemical modification or the use of solid substances or organic solvents. MWNTs provided better results than SWNTs. Carbon nanotubes retained in the C18 sorbent matrix were found to confer aromatic character, increasing its preconcentration capacity as a result. The conventional C18 stationary phase played a two-fold role: as a support to retain carbon nanotubes in the cartridge and as a medium to prevent their aggregation. The modified MWNT/C18 and SWNT/C18 materials were used to preconcentrate residual sulphonamides (SAs) in milk samples for their determination at concentrations as low as 0.03-0.069 mg L(-1) by capillary electrophoresis. Analyte recoveries from spiked samples ranged from 103.2 to 98.8% and precision, as RSD, from 8.2 to 5.4%.

Determination of carboxylic SWCNTs in river water by microextraction in ionic liquid and determination by Raman spectroscopy.

The paper proposes a simple approach for the preconcentration of carboxylated single-walled carbon nanotubes and their determination in river water samples. The method is based on a microliquid-liquid extraction into an ionic liquid (bmim PF6) in the presence of a cationic surfactant (CTAC). 10 µL of the ionic liquid phase are microfiltrated by using a home-made filtration device having a small diameter. The membrane was of cellulose with a pore size of 5 µm. Finally, the carbon nanotubes retained in the membrane are directly analyzed by Raman spectroscopy, which allows their direct characterization and quantification. The limit of detection was 0.050 mg L(-1). The precision, for a 1.4 mg L(-1) concentration of carbon nanotubes, is 3.2%.

Effect of carbon nanotubes on properties of soft materials based on carbon nanotubes-ionic liquid combinations.

Soft materials resulting from the combination of carbon nanotubes with ionic liquids have aroused analytical interest; thank to their peculiar characteristics. This paper compares the sorption capacity of eight different soft materials obtained from the combination of 1-hexyl 3-methylimidazolium hexafluorophosphate (ionic liquid) with different types of carbon nanotubes. The main characteristics of carbon nanotubes were established by Raman spectroscopy. The results obtained pointed out the critical role of the carbon nanotube types on the stability as well as the sorption capacity of the soft material. By using the adequate carbon nanotube it is possible to improve the LOD 4 times when they are used as sorbent materials for SPE. Working in the recommended conditions the LOD for the analysis of 5 mL of water sample was 5 µg/L of fluoranthene and the precision 5.9%.

Qualitative detection and quantitative determination of single-walled carbon nanotubes in mixtures of carbon nanotubes with a portable Raman spectrometer.

The main aim of this work is to develop a one-step method for the characterization of mixtures of single- and multi-walled carbon nanotubes using a simple and inexpensive tool, a portable Raman spectrometer. In order to overcome the problem of heat dissipation in solid samples, the suitability of three surfactants-SDS, Triton X-100 and CTAB-to disperse nanotubes has been evaluated. A systematic study of the wavelength and relative intensity of the D and G bands has been carried out with six samples of multiwalled carbon nanotubes (MWNTs) and one of single-walled carbon nanotubes (SWNTs) dispersed in these surfactants, and this has been compared with solid samples. Finally, the possibility has been demonstrated to identify and (semi)quantify the presence of SWNTs in a mixture containing MWNTs.

Coiled carbon nanotubes combined with ionic liquid: a new soft material for SPE.

For the first time a soft material formed from coiled carbon nanotubes and 1-hexyl-3-methylimidazolium hexafluorophosphate has been used as sorbent material. The soft material has high stability as well as a high capacity to adsorb analytes. In this work we propose using a natural cotton fiber impregnated with the soft material to miniaturize the system. The system was tested for the analysis of polycyclic aromatic hydrocarbons in spiked river water samples. The absolute recovery ranged between 97.5 and 105.5%, demonstrating the usefulness of the soft material. The limit of detection ranged from 2.5 to 6.1 µg/L and the precision expressed as the relative standard deviation for the analysis of five consecutive analyses ranged between 2.5 and 5.8%.

Rapid analysis of gold nanoparticles in liver and river water samples.

This paper describes a simple approach to determine gold nanoparticles in liver and river water samples. The method of purification of nanoparticles from the matrix is based on the stabilization of gold nanoparticles with a cationic surfactant followed by a microliquid-liquid extraction in ionic liquid. Finally, the extracted nanoparticles can be analysed by UV/Vis detection or Raman spectroscopy. The precision of the proposed method for the analysis of liver tissue and river water samples was 9.7% and 18% respectively for UV/Vis analysis. The sensitivity was 1.17 × 10(-12) M for the analysis of 3 mL of liver homogenate or river water sample.

Combination of carbon nanotubes modified filters with microextraction by packed sorbent for the NACE analysis of trace levels of ionic liquids in river water samples.

This paper reports for the first time the use of microextraction by packed sorbents in combination with Capillary electrophoresis (CE) for carry out the preconcentration and determination of three characteristics cations of ionic liquids in river water. Before analysis a carbon nanotubes modified filter was used to remove potential organic interferences from the samples. The system was automated by connecting the syringe-microextraction by packed sorbents (MEPS) assembly to a syringe pump and interfacing it to a computer. After preconcentration, analytes were determined by NACE. The limits of quantification of analytes were of 0.02 mg L(-1) from only 5 mL of sample with an RSD of less than 7%. The values of recovery range between 85 and 97%.

Analytical potential of hybrid nanoparticles.

The growing use of nanoparticles in the analytical process in recent years has set a new trend towards the simplification of analytical methods and improvement of their performance. Miniaturization and nanotechnology have allowed new analytical challenges to be met. Hybrid nanoparticles in particular possess exceptional properties enabling further improvement of analytical methods. Despite the continuous developments in their synthesis and characterization, hybrid nanomaterials have scarcely been used in analytical chemistry, however. This paper discusses the analytical potential of hybrid nanoparticles in terms of their special characteristics and properties, and describes their analytical applications.

Potential of nanoparticles in sample preparation.

The paper presents a general overview of the use of nanoparticles to perform sample preparation. In this way the main uses of nanoparticles to carry out solid phase extraction, solid phase microextraction, liquid-liquid extraction and filtration techniques are described for a wide range of nanoparticles including carbon nanoparticles, metallic, silica and molecular imprinted polymer nanoparticles.

Characterisation of alkylamine ethoxylates (ANEOs) in commercial herbicide formulations using liquid chromatography/electrospray ionisation mass spectrometry.

A quantitative method is described for the characterization of alkylamine ethoxylate (ANEO) surfactants in commercial herbicide formulations using reversed-phase high-performance liquid chromatography with electrospray ionization mass spectrometric detection. The proposed protocol allows the simultaneous determination of a full range of oligomers which were monitored as [M-H](+) ions in positive ion mode. The instrumental detection limits (LODs) were 0.5 µg. The method developed was successfully applied to the determination of ANEOs in a number of glyphosate formulations. Both the total concentration of these surfactants and the oligomer distribution varied between the different commercial herbicides analysed. The precision of the determination of the oligomers in samples ranged from 0.5 to 15%.

The potential of carbon nanotube membranes for analytical separations.

Advances in nanotechnology have enabled the development of nanoporous membranes based on carbon nanotubes, which, by virtue of their exceptional properties, constitute excellent supports for analytical processes, including the selective separation of some molecules.

Determination of 2-ethylhexyl 4-(dimethylamino) benzoate using membrane-assisted liquid-liquid extraction and gas chromatography-mass spectrometric detection.

A flow-cell for micro-porous membrane liquid-liquid extraction with a sheet membrane was used to extract 2-ethylhexyl 4-(dimethylamino) benzoate (EDB) from urine of solar-cream users and spiked wine samples. The cell enabled the target analyte to be extracted from 7.9 mL of donor solution into 200 microL of acceptor solution (decane). After extraction, the acceptor solution was transferred to a micro-vial for GC-MS analysis without derivation. In this work, variables affecting the enrichment factor were also studied, such as organic solvent, extraction time, recirculation flow of the donor solution through the donor chamber, presence of potassium chloride and ethanol in the donor solution and pH. The method has been evaluated in terms of linearity, sensitivity, precision, limits of detection and quantification and extraction efficiency. Limits of quantification were 1 and 3 microg L(-1) EDB for urine and wine, respectively. Quantitative analysis has been carried out by applying the method of standard additions. Within- and between-day relative standard deviations were lower than 12% and 20%, respectively. EDB was found in the urine of users of cream containing EDB in the concentration interval 1.2-7.2 microg L(-1). Therefore, this provides evidence of EDB dermal absorption and subsequent excretion through the urinary tract. EDB was not found in the analysed wine samples.

Monitoring nanoparticles in the environment.

The presence of nanoparticles in the environment can have important implications for both environmental and human health. Nanoscience and nanotechnology are expected to change industrial production and the economy as we know them today. However, nanotechnologies can also be a source of risks. The increasing use of nanoparticles in industrial applications will inevitably lead to the release of such materials into the environment. Accurately assessing the environmental risks posed by nanoparticles requires using effective quantitative analytical methods to determine their mobility, reactivity, ecotoxicity and persistency, many of which have still to be developed. This overview describes some methodological aspects relating to the fields of nanoparticle analysis, nanometrology and analytical chemistry.

Analytical nanoscience and nanotechnology today and tomorrow.

This article discusses the mutual impact of nanotechnology and analytical science and illustrates how this technical trend can be expected to strengthen the role of analytical chemists. To this end, it defines the limits of actual nanotechnological approaches and uses selected examples to illustrate the three major relationships between nanotechnology and analytical science, namely: the design and use of nanodevices; the use of nanoparticles (and nanostructures) in analytical processes; and the extraction of accurate chemical information from the nanoworld. Finally, the future of analytical nanotechnology in the short and medium term is briefly addressed.