Irina Mirela Apetrei

Combination of an e-nose, an e-tongue and an e-eye for the characterisation of olive oils with different degree of bitterness.

An electronic panel has been used to characterise the organoleptic characteristics of twenty-five extra virgin olive oils from varieties Hojiblanca, Picual and Arbequina, with different degree of bitterness. The method consists in the combination of three systems: electronic nose, electronic tongue and electronic eye. The Principal Component Analysis (PCA), where PC1, PC2 and PC3 explained 59% of the total variance between the samples, has demonstrated that the capability of discrimination of the combined system is superior to that obtained with the three instruments separately. This improvement is due to the increased information extracted from each sample. Partial Least Squares-Discriminant Analysis (PLS-DA) has allowed separation of the groups in function of olive variety with a root mean square error of prediction (RMSEP) lower than 0.099. Using PLS1 and PLS2 regression models, good correlations have been found between the signals obtained from the electronic tongue and the polyphenolic content (measured by chromatographic methods) or the bitterness index (scored by a panel of experts) with correlation coefficients higher than 0.9 in calibration and validation. These preliminary results indicate that the combination of an e-nose, an e-tongue and an e-eye can be a useful tool for the analysis of olive oil bitterness.

Carbon Paste Electrodes Made from Different Carbonaceous Materials: Application in the Study of Antioxidants

This work describes the sensing properties of carbon paste electrodes (CPEs) prepared from three different types of carbonaceous materials: graphite, carbon microspheres and carbon nanotubes. The electrochemical responses towards antioxidants including vanillic acid, catechol, gallic acid, l-ascorbic acid and l-glutathione have been analyzed and compared. It has been demonstrated that the electrodes based on carbon microspheres show the best performances in terms of kinetics and stability, whereas G-CPEs presented the smallest detection limit for all the antioxidants analyzed. An array of electrodes has been constructed using the three types of electrodes. As demonstrated by means of Principal Component Analysis, the system is able to discriminate among antioxidants as a function of their chemical structure and reactivity.

Fish Freshness Monitoring Using an E-Tongue Based on Polypyrrole Modified Screen-Printed Electrodes

In this paper, a novel e-tongue for evaluating biogenic amine compounds is reported. The method uses an array of voltammetric electrodes chemically modified based on screen-printed electrodes. The electrochemical signals toward amines consist in complex voltammetric curves. Cyclic voltammograms show redox processes related to the electrochemical activity of the amine under study, and redox peaks associated with the electrochemical activity of the electroactive material. Additionally, the electroactivity and basic character of amines influences considerably the electrochemical behavior of the electrodic material. The viability of the method is tested for the fish freshness monitoring. The samples are Pontic shad (Alosa Pontica), a fish living in the northwestern part of the Black Sea. Pontic shad migrates in the Danube River for spawning. The pattern of responses provided by the array can be used to discriminate and evaluate the fish freshness state. Principal component analysis confirmed the capability of the sensors array to fish freshness monitoring. Partial least squares–discriminant analysis showed that this method could be used for the analysis and determination of fish freshness as well as determination the postmortem time elapsed.

Study of Different Carbonaceous Materials as Modifiers of Screen-Printed Electrodes for Detection of Catecholamines

This paper describes the sensing properties of carbon-based screen-printed electrodes modified with three types of carbonaceous materials: 1) carbon nanotubes; 2) carbon microfibers; and 3) graphene. The electrochemical signals of screen-printed electrodes toward catechol derivatives were registered. It was demonstrated that the screen-printed electrodes modified with carbon nanofibers show the best performances in terms of kinetics, stability, and the smallest detection limit for all the catechol derivatives analyzed. Experimental conditions on the sensing performance of the screen-printed electrodes were investigated and optimized. The sensors displayed linear responses to catecholamines over concentration ranges from 1 μM to 60 μM with detection limits in the range of 0.84-3.52 μM. An array of electrodes was constructed using the signals of three types of electrodes. Principal component analysis of voltammetric data shows that the array was able to discriminate among catechol derivatives. The sensors were successfully applied to determine trace amounts of catecholamines in plasma.

Amperometric Biosensor Based on Diamine Oxidase/Platinum Nanoparticles/Graphene/Chitosan Modified Screen-Printed Carbon Electrode for Histamine Detection

This work describes the development and optimization studies of a novel biosensor employed in the detection and quantification of histamine in freshwater fish samples. The proposed biosensor is based on a modified carbon screen-printed electrode with diamineoxidase, graphene and platinum nanoparticles, which detects the hydrogen peroxide formed by the chemical process biocatalysed by the enzyme diamine oxidase and immobilized onto the nanostructurated surface of the receptor element. The amperometric measurements with the biosensor have been implemented in buffer solution of pH 7.4, applying an optimal low potential of +0.4 V. The novel biosensor shows high sensitivity (0.0631 μA·μM), low detection limit (2.54 × 10−8 M) and a broad linear domain from 0.1 to 300 μM. The applicability in natural complex samples and the analytical parameters of this enzyme sensor have been performed in the quantification of histamine in freshwater fish. An excellent correlation among results achieved with the developed biosensor and results found with the standard method for all freshwater fish samples has been achieved.

Biosensor based on tyrosinase immobilized on a single-walled carbon nanotube-modified glassy carbon electrode for detection of epinephrine.

A biosensor comprising tyrosinase immobilized on a single-walled carbon nanotube-modified glassy carbon electrode has been developed. The sensitive element, ie, tyrosinase, was immobilized using a drop-and-dry method followed by cross-linking. Tyrosinase maintained high bioactivity on this nanomaterial, catalyzing the oxidation of epinephrine to epinephrine-quinone, which was electrochemically reduced (−0.07 V versus Ag/AgCl) on the biosensor surface. Under optimum conditions, the biosensor showed a linear response in the range of 10–110 μM. The limit of detection was calculated to be 2.54 μM with a correlation coefficient of 0.977. The repeatability, expressed as the relative standard deviation for five consecutive determinations of 10−5 M epinephrine solution was 3.4%. A good correlation was obtained between results obtained by the biosensor and those obtained by ultraviolet spectrophotometric methods.

Voltammetric determination of melatonin using a graphene-based sensor in pharmaceutical products

Melatonin can be sensitively detected in pharmaceuticals by cyclic voltammetry and fixed-potential amperometry using a graphene-based sensor. The sensor characterization of cyclic voltammetry constantly provides high values of electrode active area and heterogeneous rate constant. In optimal conditions, the sensor was applied for the determination of melatonin in different pharmaceutical samples. The sensitivity to melatonin was 0.0371 A M−1, and the limit of detection was 0.87×10−6 M. The data obtained by using the graphene-based sensor for the detection of melatonin in pharmaceutical products were in good agreement with the data provided by the producer. Since no interferences from the excipients were found, using a separation technique was not necessary. Additionally, the low price, ease of handling, small amount of sample, short time per analysis, and possibility of automation are the important advantages that recommend this methodology for quality control of pharmaceuticals.

Chapter 27 – Olive Oil and Combined Electronic Nose and Tongue

Virgin olive oils contain natural compounds of high added value and specific organoleptic properties. Using reliable, precise, and accurate equipment is essential in the detection of inadequate characteristics of virgin olive oil. However, the use of traditional analytical techniques is limited by the need for expensive instrumentation and complex sample preparation. One of the most promising ways of developing rapid, sensitive, and inexpensive methods for quality control in virgin olive oils is the use of multisensor systems. However, using the electronic nose or the electronic tongue individually can provide incomplete information about virgin olive oils. Therefore, the use of fusion technology to study olive oil properties can provide a complete characterization of olive oils. The most important contributions dealing with the electronic sensory characterization of virgin olive oils using the fusion technology between electronic noses and electronic tongues are described in this chapter.

Biosensing Application of Hybrid Thin-Film Layers-Based Biosensors

Biosensor based on immobilized tyrosinase on Langmuir-Blodgett thin film of arachidic acid and dysprosium bis-phthalocyanine has been developed. The biocomposite thin film has been characterized by UV-Vis spectroscopy, Fourier transformed infrared absorption spectroscopy, atomic force microscopy, and electrochemistry. Enzyme immobilization has been proved, and it maintain well the biocatalytic properties onto solid biocomposite film. The electrochemical detection of biosensor has been performed by measuring the cathodic current due to the reduction of the corresponding quinone at 0.024 V. Under optimum conditions, the performance characteristics of biosensors have been obtained. A linear response range from 5 up to 75 μM of dopamine has been obtained. The detection limit is 7.11 × 10-7 M for developed biosensors. The biosensor construction is highly reproducible due to use of Langmuir-Blodgett nanotechnology. Finally, the developed biosensor has been applied to the determination of dopamine content in pharmaceutical samples.

P1.1.16 Development of Amperometric Biosensor Based on Tyrosinase Immobilized in Phosphate-Doped Polypyrrole Film for Detection of Biogenic Amines

An electrochemical tyrosinase electrode for detection of tyramine and dopamine was developed via cross-linking immobilization method in phosphate-doped polypyrrole film. The enzyme tyrosinase preserves its biocatalytic activity well within the polypyrrole thin film. Tyramine and dopamine were determined by the direct reduction of biocatalytically formed dopaquinone species at -0.250V. The analytical characteristics of this biosensor, including linear range, detection limit, and storage stability are described. For both biogenic amines analyzed, the kinetics of the enzymatic reaction fitted into a Michaelis–Menten type kinetics. The sensitivity followed the decreasing order dopamine>tyramine. The greater value of maximum velocity rate and the lowest Michaelis-Menten constant was found for dopamine.