112 research outputs found
Electrochemical evaluation of total antioxidant capacity of beverages using a purine-biosensor
In this paper, it was evaluated the total antioxidant capacity (TAC) of beverages using an electrochemical
biosensor. The biosensor consisted on the purine base (guanine or adenine) electro-immobilization on a
glassy carbon electrode surface (GCE). Purine base damage was induced by the hydroxyl radical generated
by Fenton-type reaction. Five antioxidants were applied to counteract the deleterious effects of
the hydroxyl radical. The antioxidants used were ascorbic acid, gallic acid, caffeic acid, coumaric acid
and resveratrol. These antioxidants have the ability to scavenger the hydroxyl radical and protect the
guanine and adenine immobilized on the GCE surface. The interaction carried out between the purinebase
immobilized and the free radical in the absence and presence of antioxidants was evaluated by
means of changes in the guanine and adenine anodic peak obtained by square wave voltammetry
(SWV). The results demonstrated that the purine-biosensors are suitable for rapid assessment of TAC
in beverages
Electrochemical DNA-sensor for evaluation of total antioxidant capacity of flavours and flavoured waters using superoxide radical damage
In this paper, a biosensor based on a glassy carbon electrode (GCE) was used for the evaluation of the total
antioxidant capacity (TAC) of flavours and flavoured waters. This biosensor was constructed by immobilising
purine bases, guanine and adenine, on a GCE. Square wave voltammetry (SWV) was selected for
the development of this methodology. Damage caused by the reactive oxygen species (ROS), superoxide
radical (O2·−), generated by the xanthine/xanthine oxidase (XOD) system on the DNA-biosensor was
evaluated. DNA-biosensor encountered with oxidative lesion when it was in contact with the O2·−. There
was less oxidative damage when reactive antioxidants were added. The antioxidants used in this work
were ascorbic acid, gallic acid, caffeic acid, coumaric acid and resveratrol. These antioxidants are capable
of scavenging the superoxide radical and therefore protect the purine bases immobilized on the GCE
surface. The results demonstrated that the DNA-based biosensor is suitable for the rapid assess of TAC in
beverages
Contribution of different vegetable types to exogenous nitrate and nitrite exposure
This study reports the levels of nitrate and nitrite of 34 vegetable samples, including different varieties of
cabbage, lettuce, spinaches, parsley and turnips, collected in several locations of an intensive agricultural
area (Modivas, Vila do Conde, northern Portugal). Nitrate levels ranged between 54 and
2440 mg NO-3 kg-1, while nitrite levels ranged between 1.1 and 57 mg NO-2 kg-1. The maximum residue
levels established for nitrate in spinach and lettuce samples were not exceeded. Nitrate and nitrite levels
reported in the literature for the same type of samples are reviewed, as well as the contribution of
vegetables to nitrate and nitrite dietary exposure of populations
Electrochemical study of butylate: application to the analysis of water
The electroactivity of butylate (BTL) is studied by cyclic voltammetry (CV) and
square wave voltammetry (SWV) at a glassy carbon electrode (GCE) and
a hanging mercury drop electrode (HMDE). Britton–Robinson buffer solutions
of pH 1.9–11.5 are used as supporting electrolyte. CV voltammograms using GCE
show a single anodic peak regarding the oxidation of BTL at +1.7V versus AgCl/
Ag, an irreversible process controlled by diffusion. Using a HMDE, a single
cathodic peak is observed, at 1.0V versus AgCl/Ag. The reduction of BTL is
irreversible and controlled by adsorption. Mechanism proposals are presented for
these redox transformations. Optimisation is carried out univaryingly. Linearity
ranges were 0.10–0.50 mmol L-1 and 2.0–9.0 µmolL-1 for anodic and cathodic
peaks, respectively. The proposed method is applied to the determination of BTL
in waters. Analytical results compare well with those obtained by an HPLC
method
Gold electrode modified by self-assembled monolayers of thiols to determine DNA sequences hybridization
The process of immobilization of biological molecules is one of the most important steps in
the construction of a biosensor. In the case of DNA, the way it exposes its bases can result in electrochemical
signals to acceptable levels. The use of self-assembled monolayer that allows a connection to
the gold thiol group and DNA binding to an aldehydic ligand resulted in the possibility of determining
DNA hybridization. Immobilized single strand of DNA (ssDNA) from calf thymus pre-formed from
alkanethiol film was formed by incubating a solution of 2-aminoethanothiol (Cys) followed by glutaraldehyde
(Glu). Cyclic voltammetry (CV) was used to characterize the self-assembled monolayer on the
gold electrode and, also, to study the immobilization of ssDNA probe and hybridization with the complementary
sequence (target ssDNA). The ssDNA probe presents a well-defined oxidation peak at
+0.158 V. When the hybridization occurs, this peak disappears which confirms the efficacy of the annealing
and the DNA double helix performing without the presence of electroactive indicators. The use of
SAM resulted in a stable immobilization of the ssDNA probe, enabling the hybridization detection without
labels. This study represents a promising approach for molecular biosensor with sensible and reproducible
results
Subcritical water extraction of antioxidants from mountain germander (Teucrium montanum L.)
In the present work, antioxidant compounds from Teucrium montanum were extracted by subcritical water. The influence of extraction temperature and pressure on antioxidant activity of extracts has been investigated in terms of extraction yield (EY), total phenolic content (TPC), and DPPH-radical scavenging activity (DPPH-RSA) and ferric reducing antioxidant power (FRAP). Additionally, the compounds responsible for the antioxidant activity were identified and quantified by high performance liquid chromatography (HPLC). The highest EY (42.63%), TPC (174.61 ± 4.09 mg GAE/g DE) and antioxidant activity by DPPH-RSA (176.23 ± 8.76 mg TE/g DE) and FRAP (141.71 ± 5.21 mg AAE/g DE) were seen in extracts obtained at temperature of 160 °C and pressure of 10 bar. HPLC analysis revealed that naringin and gallic acid were the principle antioxidant compounds in subcritical extracts. According to the results, SWE has a great potential in exploitation of natural sources of bioactive compounds and production of pharmacologically-active fractions.The project 6818 – Transnational Cooperation, Agreement between Portugal (FCT) and Serbia (MSTD) is acknowledged. This work was also funded by project TR 31014 financially supported by the Serbian Ministry of Education, Science and Technological Development. Authors are also grateful for financial support from project NORTE-01-0145-FEDER-000011-311 Qualidade e Segurança Alimentar-uma abordagem (nano) tecnológica. The financial support from FCT/MEC through national funds and co-financed by FEDER, under the Partnership Agreement PT2020 through the project UID/QUI/50006/2013-POCI/01/0145/FEDER/007265, is also acknowledged. M.F. Barroso (SFRH/BPD/78845/2011) and Manuela M. Moreira (SFRH/BPD/97049/2013) are grateful to Fundação para a Ciência e Tecnologia for their postdoctoral fellowships.info:eu-repo/semantics/publishedVersio
Chronoamperometric magnetogenosensing for simultaneous detection of two Roundup Ready™ soybean lines: GTS 40-3-2 and MON89788
This work received financial support from the European Union (FEDER funds through COMPETE), National Funds (FCT, Fundação para a Ciência e a Tecnologia) through project UID/QUI/50006/2013. A.P. and M.F.B. are grateful to FCT grants SFRH/BD/97995/2013 and SFRH/BPD/78845/2011, financed by POPH–QREN–Tipologia 4.1–Formação Avançada, subsidized by Fundo Social Europeu and Ministério da Ciência, Tecnologia e Ensino Superior. C.P. thanks FCT for the FCT Investigator contract IF/01080/2015.Development of expeditious analytical methods for the detection of genetically modified organisms (GMOs) is increasingly necessary, not only to verify compliance with labelling, but also to help industry to efficiently control the reception of raw materials. On the basis of this, a disposable electrochemical magnetogenoassay is proposed for simultaneous detection of two Roundup Ready (RR) soybean lines GTS 40-3-2 and MON89788, using gold-coated magnetic nanoparticles (Fe3O4@Au) as nanosupport. To perform this magnetogenoassay, a sandwich-type hybridization assay was used with different enzymatic labelling systems (fluorescein isothiocyanate and digoxigenin) and dual screen-printed carbon electrodes (SPdCEs), which allowed the simultaneous readout of each target. A linear relationship ranging from 0.1 to 2.5 nM and from 0.1 to 1.0 nM was achieved for GTS 40-3-2 and MON89788 events, respectively, and both assays showed a similar detection limit of about 0.1 nM. Furthermore, a good performance in terms of precision and selectivity was achieved. The proposed approach is a step forward for event-specific multiplex detection.info:eu-repo/semantics/publishedVersio
In situ formation of gold nanoparticles in polymer inclusion membrane: Application as platform in a label-free potentiometric immunosensor for Salmonella typhimurium detection
Polymeric ion selective electrodes are highly sensitive to changes in zero current ion flow and this offers a route to signal amplification in label-free potentiometric immunosensors. In this work, a label-free potentiometric immunosensor toward Salmonella typhimurium (ST) assembled in a home-made pipette-tip electrode is described. The signal-output amplification was implemented on a gold nanoparticle polymer inclusion membrane (AuNPs-PIM) which was used as sensing platform and for antibody immobilization. Additionally, a marker ion was used to detect the antibody-antigen binding event at the electrode surface. The immunosensor construction was performed in several steps: i) gold salt ions extraction in PVC membrane; ii) AuNPs formation using Na2EDTA as reduction agent; iii) antibody anti-Salmonella conjugation on AuNPs-PIM in pipette-tip electrodes. The potential shift observed in potentiometric measurements was derived simply from the blocking effect in the ionic flux caused by antigen-antibody conjugation, without no extra steps, mimetizing the ion-channel sensors. A detection limit of 6 cells mL-1 was attained. As proof-of-concept, recovery studies were performed in spiked commercial apple juice samples with success. Due to the simplicity of use, the appealing cost of equipment and sensor production and being able to provide a quick analytical response (less than 1 h for a complete assay, including sample preparation for analysis), this scheme represents a good prototype device for the detection of foodborne pathogens like ST or other immune-responsive bacteria.This work received financial support from the European Union (FEDER funds through COMPETE) and National Funds from Portugal; FCT-Fundação para a Ciência e a Tecnologia through projects UID/QUI/50006/2013 and Norte-01-0145-FEDER-000011-RL1-QUALIFOOD. N.F.D Silva and M.F. Barroso are gratefully to FCT grant SFRH/BD/112414/2015 and SFRH/BPD/78845/2011, financed by POPH–QREN–Tipologia 4.1–Formação Avançada, subsidized by FSE and MCTES.info:eu-repo/semantics/publishedVersio
Development of electrochemical genosensors for the detection of toxic dinoflagellate alexandrium spp.
Microalgae represent a photosynthetic microorganisms’ group that inhabit both salt and fresh waters. These microorganisms, namely several species of dinoflagellates (e.g. Alexandrium spp.)1 , are mostly harmless; however, some species produce toxins classified as unsafe to human health. The uncontrolled proliferation of such species results in a hazardous occurring event designated harmful algal blooms (HAB). The effects of these episodes can lead to severe ecological and socio-economic impacts (e.g. decrease of the local tourism, fishing and port activities, the contamination or death of the nearby wildlife, discoloration of the beach coasts). Therefore, the need for a rapid, selective and in real time detection device that can monitor the presence of these microalgae in aquaculture waters is critical to prevent human, ecological and economical losses. In this work, an analytical approach based on electrochemical genosensor techniques was developed to create a low cost platform able to detect the dinoflagellates: Alexandrium minutum and Alexandrium ostenfledii. The design of this genosensor consisted of several steps including: i) Sensing phase: Creation of a mixed self assembled monolayer (SAM) composed by a linear DNA capture probe (DNA-CP) and mercaptohexanol (MCH) onto screen-printed gold electrodes (SPGE) surface; ii) Heterogenous hybridization of complementary DNA sequence (DNA target) by using a sandwich format assay with enzymatic labels and iii) Electrochemical detection by chronoamperometry using an enzymatic scheme to amplify the electrochemical signal (Figure 1). The best analytical conditions were used to study the relationship between electrochemical signal and DNA target concentration.info:eu-repo/semantics/publishedVersio
Investigating the Antioxidant Capacity of Fruits and Fruit Byproducts through an Introductory Food Chemistry Experiment for High School
This paper reports a laboratorial internship included in the Portuguese Science and Technology promotion program “Internships for Young People in Laboratories (Ciência Viva no Laboratório)”, which provided high school students an opportunity to approach the reality of scientific and technological research in a higher education institution. During this internship, students acquired knowledge related to the assessment of the total antioxidant capacity (TAC) of fruits and their byproducts while learning techniques, such as molecular spectrophotometry, as an analytical methodology to measure TAC using the ferric reducing antioxidant power (FRAP) and the total phenolic content (TPC) assays. First, the students were introduced to solid–liquid extraction as a conventional technique to extract antioxidants from the selected matrices. In order to optimize the extraction yield, different solvents, temperatures, and extraction times were used. Then, the students developed skills on TPC and FRAP assays by performing calibration curves using standard antioxidants, namely, gallic acid and ascorbic acid, prior to the measurement of the TAC of fruits (apple and orange) and respective byproducts. Final analysis included TAC values for comparison between fruits and their byproducts and also the influence of the extraction conditions on the TAC levels. At the end, the students presented their findings in a scientific poster and in a postlaboratory quiz. This laboratorial internship has been carried out since 2012 and was designed to be performed during a week, 7 h per day, in groups of two young students
antioxidant power (FRAP) and the total phenolic content (TPC) assays. First, the students were introduced to solid−liquid extraction as a conventional technique to extract antioxidants from the selected matrices. In order to optimize the extraction yield, different solvents, temperatures, and extraction times were used. Then, the students developed skills on TPC and FRAP assays by performing calibration curves using standard antioxidants, namely, gallic acid and ascorbic acid, prior to the measurement of the TAC of fruits (apple and orange) and respective byproducts. Final analysis included TAC values for comparison between fruits and their byproducts and also the influence of the extraction conditions on the TAC levels. At the end, the students presented their findings in a scientific poster and in a postlaboratory quiz. This laboratorial internship has been carried out since 2012 and was designed to be performed during a week, 7 h per day, in groups of two young students.info:eu-repo/semantics/publishedVersio
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