Graphene quantum dots-silver nanoparticles as a novel sensitive and selective luminescence probe for the detection of glyphosate in food samples.

Glyphosate (Gly) is the most widely used herbicide at the moment. It presents a broad spectrum of action, hence its use for many different crops. Regulatory agencies have constantly mentioned the low hazard potential of Gly to mammals. However, the International Agency for Research on Cancer concluded in 2015 that glyphosate is "probably carcinogenic to humans". For this reason, it is important to develop reliable analytical methods to quantify Gly in food samples. Here, we propose an analytical method that makes use of graphene quantum dots (GQDs) and cysteine-capped silver nanoparticles (AgNPs) for the screening of glyphosate, using QuEChERS as sample treatment. Gly quenched the luminescence of GQDs-AgNPs system, achieving an excellent sensitivity (detection limit of 9 ng mL-1) and selectivity. The method developed was applied to different types of pulses (peas and lupins), obtaining recoveries close to 100% and relative standard deviations lower than 4% in all cases. Its simplicity and rapidity make this method an interesting alternative to other existing methodologies for the analysis of this pesticide in food samples.

Phytochemical profile, mineral content, and antioxidant activity of Olea europaea L. cv. Cornezuelo table olives. Influence of in vitro simulated gastrointestinal digestion.

The main goals of this study were to determine the phenolic composition and antioxidant activity of table olives from Olea europaea L. cv. Cornezuelo, as well as the effect caused by a simulated in vitro digestion to evaluate compounds bioavailability. High-performance liquid chromatography with diode-array and mass spectrometry detection (HPLC-DAD-MSn) was used to evaluate the phytochemical profile, whereas conventional spectrophotometric methods (ABTS·+ and DPPH) were used to determine the antioxidant activity. The mineral content was also quantified by inductively coupled plasma - mass spectrometry. Thirty compounds were identified, mainly polyphenols, quantifying the major compounds by HPLC-DAD. After the simulated digestion, the phenolic content suffered an important decrease - more than 50% - reaching losses of up to 75% for oleuropein and comselogoside isomers. This decrease also resulted in a loss of antioxidant activity, observing significant differences for all parameters. However, the analyzed extracts still retained considerable antioxidant potential.

Exploiting the fluorescence resonance energy transfer (FRET) between CdTe quantum dots and Au nanoparticles for the determination of bioactive thiols.

This work focused the implementation of FRET processes between CdTe quantum dots (QDs), acting as donors, and gold nanoparticles (AuNPs), behaving as acceptors, for the determination of several bioactive thiols such as captopril, glutathione, l-cysteine, thiomalic acid and coenzyme M. The surface chemistry of the QDs and AuNPs was adjusted with adequate capping ligands, i.e. mercaptopropionic acid and cysteamine, respectively, to guarantee the establishment of strong electrostatic interaction between them and promoting the formation of stable FRET assemblies. Under these circumstances the fluorescence emission of the QDs was completely suppressed by the AuNPs. The assayed target analytes were capable of disrupting the donor-acceptor assemblies yielding a concentration-related reversion of the FRET process and restoring QDs fluorescence emission. Distinct mechanisms, involving enhancing of the QDs quantum yield (QY), AuNPs agglomeration, nanoparticles detachment, etc., could be proposed to explain the referred FRET reversion. The developed approach assured good analytical working ranges and demonstrate adequate sensitivity for the assayed compounds, anticipating great prospective for implementing rapid, simple and reliable sensing methodologies for the monitoring of pharmaceutical, food and environmental species. However, selectivity could be a hindrance in the detection of these bioactive thiols in more complex matrices such as environmental and food samples. This problem could be circumvented through the employment of multivariate chemometric methods for the analysis and processing of whole fluorometric response. Moreover, the proposed methodology shows a great analytical versatility since it is possible to easily adapt the surface chemistry, of both QDs and AuNPs, to the chemical nature of the target analyte.

Phytochemical profile and antioxidant activity of caper berries (Capparis spinosa L.): Evaluation of the influence of the fermentation process.

In this work, we report the phytochemical profile and antioxidant activity of caper berries (Capparis spinosa L.) before and after a fermentation process. The phytochemical profiles were evaluated by high-performance liquid chromatography with UV and electrospray ionization mass spectrometry detection (HPLC-DAD-ESI-MSn). Twenty-one compounds were characterized, and seven of them quantified. The main component of non-fermented berries was glucocapparin, which was degraded upon the fermentation process. Most of the compounds were quercetin and kaempferol glycosides, epicatechin, and proanthocyanidins. The main differences observed upon the fermentation process were a decrease in epicatechin concentration, the hydrolysis of quercetin glycosides, and the degradation of glucosinolates. Total phenolic and flavonoid contents, as well as the antioxidant activities by the in vitro antioxidant assays DPPH and ABTS+, were determined, observing that the values were slightly higher after the fermentation process.

Multi-commutated fluorometric optosensor for the determination of citrinin in rice and red yeast rice supplements.

Citrinin is a toxic secondary metabolite first isolated from Penicillium citrinum, although is also produced by other species of Penicillium and Aspergillus. It has highly toxic, mutagenic, teratogenic and carcinogenic properties and is often found in crops, vegetables and fruit. To our knowledge there is no specific legislation on maximum levels permitted for citrinin, so no official analytical method is currently available for its determination. Our laboratory developed a fluorometric flow-through optosensor using Sephadex SPC-25 as solid support. Multi-commutated flow injection analysis was used for the construction of the manifold and for handling solutions. In this way, we minimised waste generation and human intervention, which are critical aspects when dealing with highly toxic compounds such as citrinin. The optimum excitation/emission wavelengths were set at 330/494 nm; the calibration curve was linear in the concentration range 35-900 ng ml⁻¹. A detection limit of 10.5 ng ml⁻¹ and relative standard deviations (RSDs) lower than 3% were obtained. The developed optosensor was applied to the determination of citrinin in rice and dietary supplements containing red yeast rice.

Fluorescence enhancement of CdTe MPA-capped quantum dots by glutathione for hydrogen peroxide determination.

The manipulation of the surface chemistry of semiconductor nanocrystals has been exploited to implement distinct sensing strategies in many analytical applications. In this work, reduced glutathione (GSH) was added at reaction time, as an electron-donor ligand, to markedly increase the quantum yield and the emission efficiency of MPA-capped CdTe quantum dots. The developed approach was employed in the implementation of an automated flow methodology for hydrogen peroxide determination, as this can oxidize GSH preventing its surface passivating effect and producing a manifest fluorescence quenching. After optimization, linear working calibration curve for hydrogen peroxide concentrations between 0.0025% and 0.040% were obtained (n=6), with a correlation coefficient of 0.9975. The detection limit was approximately 0.0012%. The developed approach was employed in the determination of H2O2 in contact lens preservation solutions and the obtained results complied with those furnished by the reference method, with relative deviations comprised between -1.18 and 4.81%.

Separation of a binary mixture of pesticides in fruits using a flow-through optosensor.

A flow-through optosensor is here proposed for the determination of mixtures of two widely used pesticides, carbendazim and o-phenylphenol, in fruits. The pesticides are separated on-line using an additional amount of solid support, C18 silica gel, in the flow-through cell. The resolution is performed due to the different retention/desorption kinetics of the analytes when interacting with the C18 microbeads. Therefore, both separation and determination are integrated in the same cell, considerably simplifying the system. In addition, the use of Sequential Injection Analysis provides a high degree of automation and minimum wastes generation. After the analytes are separated, their native fluorescence is measured, obtaining linearity in the 2.0-30 and 1.1-20 mg kg(-1) ranges for carbendazim and o-phenylphenol. The detection limits are 0.60 and 0.33 mg kg(-1) for carbendazim and o-phenylphenol respectively. The proposed method fulfills the maximum residue limits (MRLs) established in Europe and USA for these pesticides in cherries, pineapple, and mango: 5-10 mg kg(-1). In order to demonstrate the suitability of the method, several samples have been analyzed and the obtained results compared with a chromatographic method.

Determination of pesticides in olives by gas chromatography using different detection systems.

A multiresidue method has been developed and optimized for the quantitative analysis of 32 pesticides in olives. The extraction was based on homogenization with light petroleum using a high speed homogenizer. A gel permeation chromatography (GPC) clean-up process with ethyl acetate/cyclohexane (1:1) as mobile phase was applied to the extracts to separate the low-molecular mass pesticides from the high-molecular mass fat constituents of the oil. The target compounds were quantified in the final extract by gas chromatography (GC) using thermoionic specific detection (TSD) and electron-capture detection (ECD). In the case of positive samples, the amounts found were confirmed by GC-MS/MS. The obtained recovery (with mean values between 70 and 121, 71 and 114, and 82 and 134% for ECD, TSD and MS/MS systems, respectively) and RSD values (repeatability, n=10) below 16% in all cases confirm the usefulness of the proposed method for the analysis of this complex sample. Diuron, terbuthylazine and endosulfan sulfate were the most frequently detected residues in olive samples collected during the harvest 2004-2005. Finally, in order to know the proportion of pesticides that are transferred to the oil during olive oil production in olive mills, obtained results in some of the sampled olives applying the proposed method were compared to levels found in the corresponding olive oil, which was obtained by means of the Abencor method.