Graphene quantum dots sensor for the determination of graphene oxide in environmental water samples.

The paper proposes a simple and sensitive approach for the preconcentration and determination of graphene oxide (GO) in environmental samples by using fluorescent graphene quantum dots (GQDs). The method is based on the preconcentration of GO on a cellulose membrane and their subsequent elution prior to fluorescence analysis of the quenching effect produced on the GQD solution due to the hydrophobic interactions between GO and GQDs. The limit of detection was 35 µg·L(-1). The precision, for a 200 µg·L(-1) concentration of GO, is 5.16%. The optimized procedure has been successively applied to the determination of traces of GO in river water samples.

Infrared attenuated total reflection spectroscopy for the characterization of gold nanoparticles in solution.

In situ synthesis of bare gold nanoparticles mediated by stainless steel as reducing agent was monitored via infrared attenuated total reflection (IR-ATR) spectroscopy. Gold nanoparticles were directly synthesized within the liquid cell of the ATR unit taking immediate advantage of the stainless steel walls of the ATR cell. As nanoparticles were formed, a layer of particles was deposited at the SiO2 ATR waveguide surface. Incidentally, the absorption bands of water increased resulting from surface-enhanced infrared absorption (SEIRA) effects arising from the presence of the gold nanoparticles within the evanescent field. Next to the influence of the Au(III) precursor concentration and the temperature, the suitability of IR-ATR spectroscopy as an innovative tool for investigating changes of nanoparticles in solution, including their aggregation promoted by an increase of the ionic strength or via a pH decrease, and for detailing the sedimentation process of gold nanoparticles was confirmed.

Sequential preconcentration and on-membrane Raman determination of carboxylic single-walled carbon nanotubes in river water samples.

This article proposes a simple and sensitive approach for the preconcentration and determination of carboxylated single-walled carbon nanotubes (c-SWNTs) in environmental samples using membranes modified with multiwalled carbon nanotubes (MWNTs). The method is based on the preconcentration of c-SWNTs and their direct on-filter Raman spectroscopic analysis. The preconcentration of c-SWNTs is performed by microfiltrating the sample through a cellulose membrane modified with MWNTs fabricated from a surfactant dispersion of the same. The analytes are retained in the membrane through π-π interactions with MWNTs forming the membrane. The G-/D-band ratio of the carbon nanotubes has been used as an analytical parameter to quantify the presence of c-SWNTs, which mainly contribute to the intensity of the G band. The limit of detection was found to be 1 µg·L(-1), and the precision, for a 10 µg·L(-1) concentration of c-SWNTs, was 4.74% intramembrane and 6.3% intermembrane. The optimized procedure was successfully applied to the determination of traces of c-SWNTs in river water samples.

Polymeric ionic liquid immobilized onto paper as sorptive phase in microextraction.

A new planar sorptive phase based on the simple immobilization of polymeric ionic liquids on paper is proposed. The sorptive phase can develop hydrophobic or mixed-mode (combining hydrophobic and ion exchange) interactions with the target analytes. The polymer is prepared by the Radziszewski reaction, which takes place in aqueous media, and it has been thoroughly characterized by different techniques including infrared spectroscopy, matrix-assisted laser desorption/ionization coupled to high-resolution mass spectrometry and proton nuclear magnetic resonance. Three different strategies aimed to immobilize the polymeric ionic liquid on paper have been evaluated. Among them, simple thermal curing at 120 °C was selected. The as-prepared paper has been evaluated for the extraction of several non-steroidal anti-inflammatory drugs from urine, the analytes being finally determined by liquid chromatography with tandem mass spectrometry. The method detection limits were 3.8, 7.2, 6.8, 9.4, 15.7, and 5.1 µg/L for indomethacin, diclofenac, tolmetin, ketoprofen, naproxen, and ibuprofen, respectively. Calibration models were linear (R2 > 0.9949) up to 1000 µg/L. The intra-day precision, expressed as relative standard deviation and calculated at three different concentrations levels (limit of quantification, 250 µg/L, and 1000 µg/L), varied between 1.1 and 13%. The accuracy, calculated as relative recovery, was in the range from 72 to 95%, thus being considered appropriate. The easiness of polymeric ionic liquid paper synthesis and the multi-sample extraction protocol designed allows the processing of a high number of samples at the same time.

Effect of synthesis, purification and growth determination methods on the antibacterial and antifungal activity of gold nanoparticles.

In recent years, both nanotechnology and the use of nanomaterials have been growing in fields as diverse as biomedicine, food or electronics. Particularly metal nanoparticles, such as gold nanoparticles (AuNPs), are being widely studied with different applications, for example as an antimicrobial agent, in hyperthermic therapy or drug transport. Gold nanoparticles can be synthesized by different methods, such as stand out reduction with citrate or greener methods that use greener reducing agents (e.g. stainless steel). In the present work, both the effect of the synthesis method yielding AuNPs with similar size and purification of AuNPs affect the antibacterial and antifungal activities of the AuNPs obtained by citrate reduction and with stainless steel. The growth curves of the gram-negative (E. coli) and gram-positive bacteria (S. aureus) and the yeast C. albicans were constructed and the cell viability was evaluated by (2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide (XTT). According to our results, the purification of the AuNPs after their synthesis and the growth determination method affect the antibacterial and antifungal activities while the synthesis method shows no significant differences.