Manuel Gutiérrez-Capitán

Thin-film electrochemical sensor for diphenylamine detection using molecularly imprinted polymers

This work reports on the development of a new voltammetric sensor for diphenylamine based on the use of a miniaturized gold electrode modified with a molecularly imprinted polymer recognition element. Molecularly imprinted particles were synthesized ex situ and further entrapped into a poly(3,4-ethylenedioxythiophene) polymer membrane, which was electropolymerized on the surface of the gold electrode. The thickness of the polymer layer was optimized in order to get an adequate diffusion of the target analyte and in turn to achieve an adequate charge transfer at the electrode surface. The resulting modified electrodes showed a selective response to diphenylamine and a high sensitivity compared with the bare gold electrode and the electrode modified with poly(3,4-ethylenedioxythiophene) and non-imprinted polymer particles. The sensor showed a linear range from 4.95 to 115 μM diphenylamine, a limit of detection of 3.9 μM and a good selectivity in the presence of other structurally related molecules. This sensor was successfully applied to the quantification of diphenylamine in spiked apple juice samples.

Classification and characterization of different white grape juices by using a hybrid electronic tongue

A multisensor system combined with multivariate analysis is applied for the characterization and classification of white grape juices. The proposed system, known as hybrid electronic tongue, consists of an array of electrochemical microsensors and a colorimetric optofluidic system. A total of 25 white grape juices representing the large variability of vines grown in the Northwest Iberian Peninsula were studied. The data obtained were treated with Principal Component Analysis (PCA) and Soft Independent Modeling Class Analogy (SIMCA). The first tool was used to train the system with the reference genotypes -Albariño, Muscat à Petit Grains Blanc and Palomino- and the second to study the feasibility of the hybrid electronic tongue to distinguish between different grape juice varieties. The results show that the three reference genotypes are well differentiated in the PCA model and this can be used to interpolate the rest of varieties and predict their basic characteristics. Besides, using the SIMCA, the system demonstrates high potential for classifying and discriminating grape varieties.

Electrochemical Nanocomposite-Derived Sensor for the Analysis of Chemical Oxygen Demand in Urban Wastewaters

This work reports on the fabrication and comparative analytical assessment of electrochemical sensors applied to the rapid analysis of chemical oxygen demand (COD) in urban waste waters. These devices incorporate a carbon nanotube-polystyrene composite, containing different inorganic electrocatalysts, namely, Ni, NiCu alloy, CoO, and CuO/AgO nanoparticles. The sensor responses were initially evaluated using glucose as standard analyte and then by analyzing a set of real samples from urban wastewater treatment plants. The estimated COD values in the samples were compared with those provided by an accredited laboratory using the standard dichromate method. The sensor prepared with the CuO/AgO-based nanocomposite showed the best analytical performance. The recorded COD values of both the sensor and the standard method were overlapped, considering the 95% confidence intervals. In order to show the feasible application of this approach for the detection of COD online and in continuous mode, the CuO/AgO-based nanocomposite sensor was integrated in a compact flow system and applied to the detection of wastewater samples, showing again a good agreement with the values provided by the dichromate method.

Monitoring of malolactic fermentation in wine using an electrochemical bienzymatic biosensor for L-lactate with long term stability.

L-lactic acid is monitored during malolactic fermentation process of wine and its evolution is strongly related with the quality of the final product. The analysis of L-lactic acid is carried out off-line in a laboratory. Therefore, there is a clear demand for analytical tools that enabled real-time monitoring of this process in field and biosensors have positioned as a feasible alternative in this regard. The development of an amperometric biosensor for L-lactate determination showing long-term stability is reported in this work. The biosensor architecture includes a thin-film gold electrochemical transducer selectively modified with an enzymatic membrane, based on a three-dimensional matrix of polypyrrole (PPy) entrapping lactate oxidase (LOX) and horseradish peroxidase (HRP) enzymes. The experimental conditions of the biosensor fabrication regarding the pyrrole polymerization and the enzymes entrapment are optimized. The biosensor response to L-lactate is linear in a concentration range of 1 × 10(-6)-1 × 10(-4) M, with a detection limit of 5.2 × 10(-7) M and a sensitivity of - (13500 ± 600) μA M(-1) cm(-2). The biosensor shows an excellent working stability, retaining more than 90% of its original sensitivity after 40 days. This is the determining factor that allowed for the application of this biosensor to monitor the malolactic fermentation of three red wines, showing a good agreement with the standard colorimetric method.

Hybrid Electronic Tongues Applied to the Quality Control of Wines

The legislation of food industry is becoming increasingly strict with regard to the quality of food products. Therefore, the market is demanding for automatic systems of analysis that allow fast and accurate monitoring of the evolution of quality parameters in agrofood products or permit obtaining information to optimize production processes. In this context, sensors and more specifically microsensors play an important role since they allow fast and reproducible measurement of a large number of quality parameters with good reliability and can be implemented in portable systems. This paper presents a review of the results obtained with an electronic tongue based on different kinds of microsensors applied to wine analysis by the team of IMB-CNM. This multisensor system allows on one hand classifying the wine according to its features like grape variety, geographic origin, year, and organoleptic characteristics and on the other hand quantifying some parameters of interest in quality control, such as alcoholic degree, pH, ions, total acidity, glycerol, and color.

Analysis of free and total sulfur dioxide in wine by using a gas-diffusion analytical system with pH detection

The use of sulfur dioxide as preservative in winemaking industry has a direct impact on wine quality. The standard methods to analyze this parameter require several processes and are time consuming. In this paper a simple and rapid analytical method for free and total sulfur dioxide detection is proposed. This method is based on the separation of the analyte from the sample with a permeable gas diffusion membrane and its indirect detection with a pH sensor. The system has been validated and optimized for free sulfur dioxide detection in the range of 1-60mgL-1 and for total sulfur dioxide in the range of 30-300mgL-1 with a limit of detection of 0.5mgL-1. Validation of the system has been carried out using a total of 70 samples of white and red wines and two standard methods, the Ripper and the Paul method. The obtained values have demonstrated a good agreement for both methods.

Portable Electronic Tongue Based on Microsensors for the Analysis of Cava Wines

Cava is a quality sparkling wine produced in Spain. As a product with a designation of origin, Cava wine has to meet certain quality requirements throughout its production process; therefore, the analysis of several parameters is of great interest. In this work, a portable electronic tongue for the analysis of Cava wine is described. The system is comprised of compact and low-power-consumption electronic equipment and an array of microsensors formed by six ion-selective field effect transistors sensitive to pH, Na+, K+, Ca2+, Cl−, and CO32−, one conductivity sensor, one redox potential sensor, and two amperometric gold microelectrodes. This system, combined with chemometric tools, has been applied to the analysis of 78 Cava wine samples. Results demonstrate that the electronic tongue is able to classify the samples according to the aging time, with a percentage of correct prediction between 80% and 96%, by using linear discriminant analysis, as well as to quantify the total acidity, pH, volumetric alcoholic degree, potassium, conductivity, glycerol, and methanol parameters, with mean relative errors between 2.3% and 6.0%, by using partial least squares regressions.

Hybrid electronic tongues based on microsensors applied to wine quality control

In this work an hybrid electronic tongue for the analysis of wine is presented. Its main novelty is the joint use of different kind of sensors- potentiometric ISFETs, thin film metal microelectrodes as amperometric and conductivity sensors and an optofluidic system- thus allowing an unprecedented measurement of information of a specific sample. Moreover, this electronic tongue is completed with the use of data processing tools like Principal Component Analysis (PCA) Partial Least Square (PLS) and Soft Independent Modeling Class Analogy (SIMCA). The so-called hybrid electronic tongue, here developed, has been applied to classify the wine according to its distinct features like grape variety, geographic origin, year and organoleptic characteristics. This approach has also allowed performing quantitative measurements of parameters of interest in quality control, such as alcoholic degree, pH, ions, total acidity, glycerol and color.

Electronic Tongues Applied to Grape and Fruit Juice Analysis

Legislation is increasingly demanding more quality and sustainability in food production. This implies the need for automated measuring systems that allow rapid and accurate monitoring of quality parameters in food. Among these, fruit juices are consumed worldwide and their health benefits are well known because of the content in polyphenolic compounds and vitamin C. At present, the quality control of fruit juices during processing and the final product are performed with conventional methods which are time consuming and require expensive laboratory equipment. Electronic tongues can play an important role here as they allow quick measurements of a large number of quality parameters with good reliability and can be implemented in portable systems. This chapter reviews the most significant work done on the implementation of electronic tongues and multisensor systems for the analysis of various types of fruit juices, grape juice, and tomato juice.

Stripping voltammetric detection of trace heavy metals using gold ultramicroelectrode arrays

The sensitive and simultaneous detection of zinc (Zn), cadmium (Cd) and lead (Pb) at gold ultramicroelectrode arrays (UMEAs) is reported. The device performance was based on the square-wave anodic stripping voltammetric technique. This consisted of the co-deposition of a layer of bismuth (Bi) together with the heavy metal target analytes onto the UMEA surface by applying a constant negative potential of -1.3 V for 360 s, followed by the stripping of the heavy metal alloy deposited by an anodic potential scan in a suitable potential window. Peaks at potentials ca. -1.0, -0.75 and -0.5 V were recorded and could be ascribed to the Zn, Cd and Pb stripping processes, respectively. Measurements were carried out in standard 0.1 M acetate buffer solutions pH 4.5, containing increasing concentrations of the three analytes. By using the peak areas, the corresponding calibration curves were constructed. The results showed a good sensitivity with a linear range from 10 to 70 ppb and a limit of detection of 7.5 ppb Pb, 5.3 ppb Cd and 9.2 ppb Zn, respectively.