Innovative and versatile nanoplasmonic approach for the full sensing of proteinogenic aminoacids in nutritional supplements.

A current nourishment issue is the development of smart and reliable analytical strategies to control in a simple way main bioactive compounds of nutritional supplements whose increasing use is deemed a trend nowadays. With this aim a quick and highly sensitive plasmonic sensor using simple citrate coated gold nanoparticles (AuNPs) as optical probe, was developed for both qualitative and quantitative global assessment of all the proteinogenic amino acids in nutritional supplements. AuNPs of five different sizes (from 19 to 74 nm) were synthesized, characterized and evaluated as optimal transductor element for the sensing approach. Critical physic-chemical conditions controlling aggregation (pH, incubation time, AuNPs amount and ionic strength) were investigated on the main five types of aas, structurally different attending to their R-side chain and with expected distinctive behaviour on aggregation mechanisms, which are also discussed. All proteinogenic amino acids induced AuNPs aggregation at low pH (2.5) causing a change in the colour solution from red to blue, as well as a redshift in the plasmon band from 518 nm (disperse NPs) to 650 nm (aggregated NPs). Based on this sensing approach two different strategies are allowed, a preliminary qualitative/semi-quantitative screening just by the naked eye (simple spot test) and a second quantitative confirmation procedure using the analytical signal (A650/A518). Reliability of quantitative approach was assessed by an exhaustive validation procedure, where matrix effects and potential interferences usually present in commercial samples and affecting the analytical signal were mainly focussed. The results for the analysis of complex nutritional samples were validated by means of a statistical comparison with those ones of the official reference Kjeldahl method (paired Student test-t) at a 95% confidence level. This is the first sensing approach able to provide the global estimation of proteinogenic aas amount based on their simply AuNPs aggregation induction, irrespectively of their R-side chain structure.

A screen-printed electrode modified with silver nanoparticles and carbon nanofibers in a nafion matrix for ionic liquid-based dispersive liquid-liquid microextraction and voltammetric assay of heterocyclic amine 8-MeIQx in food.

An electrochemical method is described for the determination of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx) which is a heterocyclic aromatic amine formed in cooked food samples. The method uses a screen-printed carbon nanofiber electrode that is modified with silver nanoparticles (AgNPs) in a Nafion matrix. The surface of the modified electrode was characterized by UV-vis spectrometry, dynamic light scattering, scanning electron microscopy and Raman spectroscopy. The average size of the AgNPs is 14 nm. The modified electrode exhibits good properties in terms of reversibility, fast kinetics of electron transfer, and large electroactive area toward the reduction of 8-MeIQx. Differential pulse voltammetry is the most suitable electrochemical technique for quantification of 8-MeIQx, best at a voltage of -0.21 V (versus Ag reference electrode). The first derivative serves as the analytical signal that increases linearly in the 0.015-40 mg L-1 8-MeIQx concentration range, with a 5 µg L-1 detection limit. A dispersive liquid-liquid microextraction procedure assisted via ionic liquid was developed to isolate the analyte from real samples. The whole extraction-preconcentration and voltammetric method allows to determine 30 and 70 µg L-1 in (spiked) bouillon cube, meat broth, beer and wine, with recoveries in the 93.6-110.4% range. Graphical abstractSchematic presentation for the analysis of aromatic amine 8-MeIQx, resultant compound from cooking meat. Extracted sample solution was placed onto modified electrode surface thus obtaining voltammetric analytical signal. So, quantification atrelevant levels can be performed.

Magnetic/non-magnetic argan press cake nanocellulose for the selective extraction of sudan dyes in food samples prior to the determination by capillary liquid chromatograpy.

Two methods for the determination of Sudan dyes (Sudan I, Sudan II, Sudan III and Sudan IV) in food samples, by solid phase extraction - capillary liquid chromatography, are proposed. Both methods use nanocellulose (NC) extracted from bleached argan press cake (APC), as a nano-adsorbent recycled from an agricultural waste material. One of the methods involves the dispersion of NC in food sample extracts, along with the waste and eluents being separated by centrifugation. In the other method, NC was modified by magnetic iron nanoparticles before using it in the extraction of Sudan dyes. The use of a magnetic component in the extraction process allows magnetic separation to replace the centrifugation step in a convenient and economical way. The two proposed methods allows the determination of Sudan dye amounts at the 0.25-2.00µgL-1 concentration range. The limit of detections, limit of quantifications and standard deviations achieved were lower than 0.1µgL-1, 0.20µgL-1 and 3.46% respectively, when using NC as a nano-adsorbent, and lower than 0.07µgL-1, 0.23µgL-1 and 2.62%, respectively, with the magnetic nanocellulose (MNC) was used. Both methods were applied to the determination of Sudan dyes in barbeque and ketchup sauce samples, obtaining recoveries between 93.4% and 109.6%.

Development of a novel biotoxicity screening assay for analytical use.

A new biotoxicity assay has been developed and employed as an analytical screening tool. The proposed biotoxicity assay is simple and represents the first example of the use of Lactobacillus plantarum as a test micro-organism. The applicability of this method was demonstrated by evaluating the pollution of water due to the presence of several toxicants. Traditional parameters such as effective concentration (EC(50)) and lowest observed effect concentration (LOEC) provided by all the biotoxicity tests were employed in a screening method based on a binary toxic/non-toxic response. The threshold of the response was characterized by defining a mortality index (I(m)), which in this case was obtained by monitoring the consumption of glucose in the culture medium (Somogyi-Nelson method) or by turbidimetric measurements. Cut-off values established by the current legislation (or other preset values) were used as criteria to classify samples as positive or negative. Bacterial growth was inhibited by the presence of heavy metals such as mercury, cadmium, lead, copper and zinc. This methodology was applied to study the toxicity of heavy metals in different water samples.