Carbon paste electrodes made from different carbonaceous materials: application in the study of antioxidants

Electrochemical Determination of Cyclobenzaprine Hydrochloride Muscle Relaxant Using Novel S-GCN/TiO2-Based Carbon Electrode

We have successfully prepared the titanium dioxide (TiO2) nanoparticles (NPs) and sulfur-incorporated graphitic carbon nitride (S-GCN)-modified carbon paste electrode (CPE). The CPEs modified with TiO2 NPs and S-GCN were employed for detecting and quantifying the skeletal muscle relaxant cyclobenzaprine hydrochloride (CBP) using cyclic voltammetry and square wave voltammetry (SWV) techniques. Optimal electrochemical conditions were indicated by the pH study results, with the highest peak current observed at a physiological pH of 7.4. The electrochemical process was determined to involve an equivalent number of protons (H+) and electrons (e-). The concentration variation of CBP (ranging from 0.06 to 10 × 10-7 mol L-1) was explored using SWV. The limits of detection and quantification were determined as 6.4 × 10-9 and 2.1 × 10-8 M, respectively. The proposed electrode configuration was applied to analyze real samples, including water, biomedical, and pharmaceutical specimens.

Preparation, Characterization, and Activation of Natural Glassy Carbon Paste Electrodes as New Sensors for Determining the Total Antioxidant Capacity of Plant Extracts

The continuous search for new sensing materials with high recognition capabilities is necessary to improve existing analytical procedures and to develop new ones. Natural glassy carbon and polydimethylsiloxane were shown to be used for the preparation of carbon paste electrodes to employ them in new, voltammetric, green-chemistry-friendly electroanalytical procedures aimed at evaluating the antioxidant capacity of plant extracts, dietary supplements, and hydrolats. The developed electrodes provided well-shaped and reproducible voltammetric signals (RSD = 1%) of the oxidation of epigallocatechin gallate, the main component of many plants and plant-based formulations with antioxidative activity, in the 1-12.5 µM range (DPV mode, LOD = 0.08 µM). If needed, the performance of new carbon paste electrodes can be further enhanced by the introduction of trivalent rare earth oxides to carbon paste to increase its active surface, facilitate electron transfer, and improve the resolution of recorded signals.

Using a disposable platform based on reduced graphene oxide, iron nanoparticles and molecularly imprinted polymer for voltammetric determination of vanillic acid in fruit peels

This work reports the development and application of a disposable electrochemical platform for vanillic acid (VA) detection using screen-printed electrode modified with reduced graphene oxide, iron nanoparticles and molecularly imprinted poly(pyrrole) film. The electrochemical platform was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Using optimized conditions, the proposed disposable platform presented linear concentration ranges of 1.0 × 10^-9 to 1.5 × 10^-7 mol/L. The limits of detection and quantification obtained for the device were 3.1 × 10^-10 and 1.0 × 10^-9 mol/L, respectively. The electrochemical platform was found to be selective for VA recognition and presented voltammetric responses with good repeatability and stability. The analytical methodology developed was applied for VA determination in banana and orange peels. The results obtained showed that the proposed electrochemical platform has a good accuracy when applied for the determination of VA.

Transducer Technologies for Biosensors and Their Wearable Applications

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.

Antioxidant Determination with the Use of Carbon-Based Electrodes

Antioxidants are compounds that prevent or delay the oxidation process, acting at a much smaller concentration, in comparison to that of the preserved substrate. Primary antioxidants act as scavenging or chain breaking antioxidants, delaying initiation or interrupting propagation step. Secondary antioxidants quench singlet oxygen, decompose peroxides in non-radical species, chelate prooxidative metal ions, inhibit oxidative enzymes. Based on antioxidants’ reactivity, four lines of defense have been described: Preventative antioxidants, radical scavengers, repair antioxidants, and antioxidants relying on adaptation mechanisms. Carbon-based electrodes are largely employed in electroanalysis given their special features, that encompass large surface area, high electroconductivity, chemical stability, nanostructuring possibilities, facility of manufacturing at low cost, and easiness of surface modification. Largely employed methods encompass voltammetry, amperometry, biamperometry and potentiometry. Determination of key endogenous and exogenous individual antioxidants, as well as of antioxidant activity and its main contributors relied on unmodified or modified carbon electrodes, whose analytical parameters are detailed. Recent advances based on modifications with carbon-nanotubes or the use of hybrid nanocomposite materials are described. Large effective surface area, increased mass transport, electrocatalytical effects, improved sensitivity, and low detection limits in the nanomolar range were reported, with applications validated in complex media such as foodstuffs and biological samples.

The Importance of Developing Electrochemical Sensors Based on Molecularly Imprinted Polymers for a Rapid Detection of Antioxidants

This review aims to pin out the importance of developing a technique for rapid detection of antioxidants, based on molecular imprinting techniques. It covers three major areas that have made great progress over the years in the field of research, namely: antioxidants characterization, molecular imprinting and electrochemistry, alone or combined. It also reveals the importance of bringing these three areas together for a good evaluation of antioxidants in a simple or complex medium, based on selectivity and specificity. Although numerous studies have associated antioxidants with molecular imprinting, or antioxidants with electrochemistry, but even electrochemistry with molecular imprinting to valorize different compounds, the growing prominence of antioxidants in the food, medical, and paramedical sectors deserves to combine the three areas, which may lead to innovative industrial applications with satisfactory results for both manufacturers and consumers.

Smart materials-integrated sensor technologies for COVID-19 diagnosis

After the first case has appeared in China, the COVID-19 pandemic continues to pose an omnipresent threat to global health, affecting more than 70 million patients and leading to around 1.6 million deaths. To implement rapid and effective clinical management, early diagnosis is the mainstay. Today, real-time reverse transcriptase (RT)-PCR test is the major diagnostic practice as a gold standard method for accurate diagnosis of this disease. On the other side, serological assays are easy to be implemented for the disease screening. Considering the limitations of today's tests including lengthy assay time, cost, the need for skilled personnel, and specialized infrastructure, both strategies, however, have impediments to be applied to the resource-scarce settings. Therefore, there is an urgent need to democratize all these practices to be applicable across the globe, specifically to the locations comprising of very limited infrastructure. In this regard, sensor systems have been utilized in clinical diagnostics largely, holding great potential to have pivotal roles as an alternative or complementary options to these current tests, providing crucial fashions such as being suitable for point-of-care settings, cost-effective, and having short turnover time. In particular, the integration of smart materials into sensor technologies leverages their analytical performances, including sensitivity, linear dynamic range, and specificity. Herein, we comprehensively review major smart materials such as nanomaterials, photosensitive materials, electrically sensitive materials, their integration with sensor platforms, and applications as wearable tools within the scope of the COVID-19 diagnosis.

Electrochemical Sensors Coupled with Multivariate Statistical Analysis as Screening Tools for Wine Authentication Issues: A Review

Consumers are increasingly interested in the characteristics of the products they consume, including aroma, taste, and appearance, and hence, scientific research was conducted in order to develop electronic senses devices that mimic the human senses. Thanks to the utilization of electroanalytical techniques that used various sensors modified with different electroactive materials coupled with pattern recognition methods, artificial senses such as electronic tongues (ETs) are widely applied in food analysis for quality and authenticity approaches. This paper summarizes the applications of electrochemical sensors (voltammetric, amperometric, and potentiometric) coupled with unsupervised and supervised pattern recognition methods (principal components analysis (PCA), linear discriminant analysis (LDA), partial least square (PLS) regression, artificial neural network (ANN)) for wine authenticity assessments including the discrimination of varietal and geographical origins, monitoring the ageing processes, vintage year discrimination, and detection of frauds and adulterations. Different wine electrochemical authentication methodologies covering the electrochemical techniques, electrodes types, functionalization sensitive materials and multivariate statistical analysis are emphasized and the main advantages and disadvantages of using the proposed methodologies for real applications were concluded.

Natural phenolic antioxidants electrochemistry: Towards a new food science methodology

Natural phenolic compounds are abundant in the vegetable kingdom, occurring mainly as secondary metabolites in a wide variety of chemical structures. Around 10,000 different plant phenolic derivatives have been isolated and identified. This review provides an exhaustive overview concerning the electron transfer reactions in natural polyphenols, from the point of view of their in vitro antioxidant and/or pro-oxidant mode of action, as well as their identification in highly complex matrixes, for example, fruits, vegetables, wine, food supplements, relevant for food quality control, nutrition, and health research. The accurate assessment of polyphenols' redox behavior is essential, and the application of the electrochemical methods in routine quality control of natural products and foods, where the polyphenols antioxidant activity needs to be quantified in vitro, is of the utmost importance. The phenol moiety oxidation pathways and the effect of substituents and experimental conditions on their electrochemical behavior will be reviewed. The fundamental principles concerning the redox behavior of natural polyphenols, specifically flavonoids and other benzopyran derivatives, phenolic acids and ester derivatives, quinones, lignins, tannins, lignans, essential oils, stilbenes, curcuminoids, and chalcones, will be described. The final sections will focus on the electroanalysis of phenolic antioxidants in natural products and the electroanalytical evaluation of in vitro total antioxidant capacity.

Voltammetric Sensors Based on Nanomaterials for Detection of Caffeic Acid in Food Supplements

Caffeic acid may be accurately detected in food supplements by using cyclic voltammetry and carbon screen-printed sensors modified with various nanomaterials. Sensor characterization by cyclic voltammetry in reference solutions has shown that carbon nanotubes or carbon nanofibers significantly improve the sensor response in terms of sensitivity and reversibility. Screen-printed sensors were then used in order to study the electrochemical behavior of caffeic acid in aqueous solution at pH 3.6. A redox process was observed in all cases, which corresponds to a reversible redox process involving the transfer of two electrons and two protons. The role of nanomaterials in the increment of sensor performance characteristics was evidenced. Calibration curves were developed for each sensor, and the detection (LOD) and quantification (LOQ) limits were calculated. Low LOD and LOQ values were obtained, in the 10−7 to 10−9 M range, which demonstrates that the method is feasible for quantification of caffeic acid in real samples. Caffeic acid was quantitatively determined in three food supplements using the most sensitive sensor, namely the carbon nanofiber sensor. The Folin–Ciocalteu spectrophotometric assay was used to validate the results obtained with the sensor. The results obtained by using the voltammetric method were consistent with those obtained by using the spectrophotometric method, with no statistically significant differences between the results obtained at 95% confidence level.

Chitosan coated magnetite nanoparticle as a working electrode for determination of Cr(VI) using square wave adsorptive cathodic stripping voltammetry

The application of chitosan coated magnetite nanoparticle modified carbon paste electrode as a working electrode (chitosan@Fe₃O₄/CPE) for Cr(VI) analysis is presented. The electrochemical detection mode of square wave adsorptive cathodic stripping voltammetry (SWAdCSV) was selected for determination of Cr(VI) due to the high sensitivity and selectivity. The optimal conditions for electrode preparation and the electrode behavior including parameters affecting the SWAdCSV signal were investigated. Two linear ranges of Cr(VI) determination were observed 0.01-0.3 μg L^-1 and 0.5-30 μg L^-1 with limits of detection of 0.0061 and 0.078 μg L^-1, respectively. The precision of the electrode output in terms of %RSD was 11.4% (n = 30). The method was successfully applied to determine Cr(VI) in drinking water and sea water samples with recovery percentages in range 87-110%. Moreover, the results obtained agree with a paired t-test at the 95% confidence level which were comparable to the standard UV-visible spectrophotometric method.

Interaction between Amorphous Zirconia Nanoparticles and Graphite: Electrochemical Applications for Gallic Acid Sensing Using Carbon Paste Electrodes in Wine

Amorphous zirconium oxide nanoparticles (ZrO₂) have been used for the first time, to modify carbon paste electrode (CPE) and used as a sensor for the electrochemical determination of gallic acid (GA). The voltammetric results of the ZrO₂ nanoparticles-modified CPE showed efficient electrochemical oxidation of gallic acid, with a significantly enhanced peak current from 261 µA ± 3 to about 451 µA ± 1. The modified surface of the electrode and the synthesised zirconia nanoparticles were characterised by scanning electrode microscopy (SEM), Energy-dispersive x-ray spectroscopy (EDXA), X-ray powdered diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Meanwhile, the electrochemical behaviour of GA on the surface of the modified electrode was studied using differential pulse voltammetry (DPV), showing a sensitivity of the electrode for GA determination, within a concentration range of 1 × 10⁻⁶ mol L⁻¹ to 1 × 10⁻³ mol L⁻¹ with a correlation coefficient of R² of 0.9945 and a limit of detection of 1.24 × 10⁻⁷ mol L⁻¹ (S/N = 3). The proposed ZrO₂ nanoparticles modified CPE was successfully used for the determination of GA in red and white wine, with concentrations of 0.103 mmol L⁻¹ and 0.049 mmol L⁻¹ respectively.

Electrochemical strategies for gallic acid detection: Potential for application in clinical, food or environmental analyses

Polyphenols are important to human health thus making it interesting and necessary to identify and assess methods for their detection. Gallic acid (GA) is a well-known antioxidant compound, found in tea leaves, various fruits, fruit seeds and in fruit-derived foods and beverages. In this study, to electrochemically detect this compound and assess the potential for GA detection, different analytical conditions at pH values of 5.8, 7 and 8 were tried. Two types of device were used for GA detection: (1) Lazar ORP-146C reduction-oxidation microsensors, coupled with a Jenco device, for estimation of antioxidant capacities of different electroactive media, and (2) screen-printed carbon sensors coupled with a mobile PalmSens device using differential pulse voltammetry (qualitative and quantitative GA determination). These proposed methods were validated by analysing some real samples: wine, green tea, apple juice and serum fortified with GA. Detection was evaluated in terms of specific calibration curves, with low limit of detection (LOD) and limit of quantification (LOQ), low response time, and high sensitivities. The analytical characteristics obtained recommend these methods to be tested on more other types of real samples. Our proposed methods, used in the established conditions of pH, may have further application in other clinical, food or environmental samples analyses in which the results of total antioxidants contents are usually expressed in GA equivalents.

Voltammetric determination of nitro compound 4-nitroaniline in aqueous medium at chitosan gelified modified carbon paste electrode (CS@CPE)

A sensitive, selective and reproducible electrochemical method has been established for the electroanalysis of 4-nitroaniline (4-NA) using a carbon paste electrode modified with a chitosan solution gelled in acetic acid (CS@CPE). The modified electrode was then characterized spectroscopically using Fourier Transform Infrared (FTIR) spectroscopy. In addition, the electrochemical and interfacial characteristics of the as-prepared modified electrode were assessed by potentiodynamic cyclic voltammetry (CV) and AC electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was additionally used to deduce the trace amounts of (4-NA) in phosphate buffered saline (PBS) of pH7.0 as an ideal electrolyte. Under optimized conditions, the peak current of 4-NA increased linearly with the increasing 4-NA concentration over the range of 0.1μM to 0.1Mm. The calibration curve presents two linear ranges of current versus 4-NA concentration with a detection limit of 93.4nM (3sb/B). The repeatability of the current peak registered at CS@CPE was performed at a level of 0.5μM 4-NA employing one sensor on the same day for eight measurements. The relative standard deviation was 3.5%.

Untargeted voltammetric approaches for characterization of oxidation patterns in white wines

Chemical and electrochemical changes associated with controlled oxidation were measured in thirteen commercial white wines, in order to evaluate the potential of linear sweep voltammetry to provide relevant information on the oxidative behavior of individual wines. For a given amount of oxygen consumed, substantial diversity of oxidative behaviors was observed. A good correlation (R² = 0.69) was observed between the rate of O₂ consumption of individual wines and the total charged passed during linear sweep voltammetry, but not with their Folin-Ciocalteu values. Onset potential of anodic oxidation was also related to oxygen consumption capacity of wine, indicating an important contribution of easily oxidizable substrates. Subtraction of voltammograms of oxidized wines from their corresponding non-oxidized controls generated new voltammograms representative of the global changes induced by oxidation. These new voltammograms contained several features related to oxygen consumption rates of each wine, and could be considered as a 'wine oxidation signature'.

Monitoring the Phenolic Ripening of Red Grapes Using a Multisensor System Based on Metal-Oxide Nanoparticles

The maturity of grapes is usually monitored by means of the sugar concentration. However, the assessment of other parameters such as the phenolic content is also important because the phenolic maturity has an important impact on the organoleptic characteristics of wines. In this work, voltammetric sensors able to detect phenols in red grapes have been developed. They are based on metal oxide nanoparticles (CeO2, NiO, and TiO2,) whose excellent electrocatalytic properties toward phenols allows obtaining sensors with detection limits in the range of 10-8 M and coefficients of variation lower than 7%. An electronic tongue constructed using a combination of the nanoparticle-based sensors is capable to monitor the phenolic maturity of red grapes from véraison to maturity. Principal Component Analysis (PCA) can be successfully used to discriminate samples according to the ripeness. Regression models performed using Partial Least Squares (PLS-1) have established good correlations between voltammetric data obtained with the electrochemical sensors and the Total Polyphenolic Index, the Brix degree and the Total Acidity, with correlation coefficients close to 1 and low number of latent variables. An advantage of this system is that the electronic tongue can be used for the simultaneous assessment of these three parameters which are the main factors used to monitor the maturity of grapes. Thus the electronic tongue based on metal oxide nanoparticles can be a valuable tool to monitor ripeness. These results demonstrate the exciting possible applications of metal oxide nanoparticles in the field of electronic tongues.

A different approach for the analysis of grapes: Using the skin as sensing element

In this work, an alternative method to monitor the phenolic maturity of grapes was developed. In this approach, the skins of grapes were used to cover the surface of carbon paste electrodes and the voltammetric signals obtained with the skin-modified sensors were used to obtain information about the phenolic content of the skins. These sensors could easily detect differences in the phenolic composition of different Spanish varieties of grapes (Mencía, Prieto Picudo and Juan García). Moreover, sensors were able to monitor changes in the phenolic content throughout the ripening process from véraison until harvest. Using PLS-1 (Partial Least Squares), correlations were established between the voltammetric signals registered with the skin-modified sensors and the phenolic content measured by classical methods (Glories or Total Polyphenol Index). PLS-1 models provided additional information about Brix degree, density or sugar content, which usually used to establish the harvesting date. The quality of the correlations was influenced by the maturation process and the structural and mechanical skin properties. Thus the skin sensors fabricated with Juan García and Prieto Picudo grapes (that showed faster polyphenolic maturation and a higher amount of extractable polyphenols than Mencía), showed good correlations and therefore could be used to monitor the ripening.

Electrochemical Biosensors: A Solution to Pollution Detection with Reference to Environmental Contaminants

The increasing environmental pollution with particular reference to emerging contaminants, toxic heavy elements, and other hazardous agents is a serious concern worldwide. Considering this global issue, there is an urgent need to design and develop strategic measuring techniques with higher efficacy and precision to detect a broader spectrum of numerous contaminants. The development of precise instruments can further help in real-time and in-process monitoring of the generation and release of environmental pollutants from different industrial sectors. Moreover, real-time monitoring can also reduce the excessive consumption of several harsh chemicals and reagents with an added advantage of on-site determination of contaminant composition prior to discharge into the environment. With key scientific advances, electrochemical biosensors have gained considerable attention to solve this problem. Electrochemical biosensors can be an excellent fit as an analytical tool for monitoring programs to implement legislation. Herein, we reviewed the current trends in the use of electrochemical biosensors as novel tools to detect various contaminant types including toxic heavy elements. A particular emphasis was given to screen-printed electrodes, nanowire sensors, and paper-based biosensors and their role in the pollution detection processes. Towards the end, the work is wrapped up with concluding remarks and future perspectives. In summary, electrochemical biosensors and related areas such as bioelectronics, and (bio)-nanotechnology seem to be growing areas that will have a marked influence on the development of new bio-sensing strategies in future studies.

Highly sensitive voltamperometric determination of pyritinol using carbon nanofiber/gold nanoparticle composite screen-printed carbon electrode

A novel and highly sensitive electrochemical method for the detection of pyritinol in pharmaceutical products and serum samples has been accomplished based on voltamperometric response of pyritinol in carbon nanofiber-gold nanoparticle (CNF-GNP)-modified screen-printed carbon electrode (SPCE). The electrochemical response of pyritinol to CNF-GNP-modified SPCE was studied by cyclic voltammetry and square-wave voltammetry (SWV). Under optimized working conditions, the novel sensor shows excellent voltamperometric response toward pyritinol. The SWV study shows significantly enhanced electrochemical response for pyritinol in CNF-GNP-modified SPCE providing high sensitivity to the novel sensor for pyritinol detection. The peak current for pyritinol is found to be linear with the concentration in the range 1.0×10^-8-5.0×10^-5 M with a detection limit of 6.23×10^-9 M using SWV as the detection method. The viability of the new developed sensor for the analytical purposes was studied by performing experiments on various commercial pharmaceutical products and blood serum samples, which yielded adequate recoveries of pyritinol. The novel electrochemical sensor provides high sensitivity, enhanced selectivity, good reproducibility and practical applicability.

Discrimination of Apple Liqueurs (Nalewka) Using a Voltammetric Electronic Tongue, UV-Vis and Raman Spectroscopy

The capability of a phthalocyanine-based voltammetric electronic tongue to analyze strong alcoholic beverages has been evaluated and compared with the performance of spectroscopic techniques coupled to chemometrics. Nalewka Polish liqueurs prepared from five apple varieties have been used as a model of strong liqueurs. Principal Component Analysis has demonstrated that the best discrimination between liqueurs prepared from different apple varieties is achieved using the e-tongue and UV-Vis spectroscopy. Raman spectra coupled to chemometrics have not been efficient in discriminating liqueurs. The calculated Euclidean distances and the k-Nearest Neighbors algorithm (kNN) confirmed these results. The main advantage of the e-tongue is that, using PLS-1, good correlations have been found simultaneously with the phenolic content measured by the Folin-Ciocalteu method (R² of 0.97 in calibration and R² of 0.93 in validation) and also with the density, a marker of the alcoholic content method (R² of 0.93 in calibration and R² of 0.88 in validation). UV-Vis coupled with chemometrics has shown good correlations only with the phenolic content (R² of 0.99 in calibration and R² of 0.99 in validation) but correlations with the alcoholic content were low. Raman coupled with chemometrics has shown good correlations only with density (R² of 0.96 in calibration and R² of 0.85 in validation). In summary, from the three holistic methods evaluated to analyze strong alcoholic liqueurs, the voltammetric electronic tongue using phthalocyanines as sensing elements is superior to Raman or UV-Vis techniques because it shows an excellent discrimination capability and remarkable correlations with both antioxidant capacity and alcoholic content-the most important parameters to be measured in this type of liqueurs.

Improvement of electrocatalytic effect in voltammetric sensors based on phthalocyanines

Voltammetric sensors based on phthalocyanines have been used to detect a variety of compounds. In this paper, the state of the art of sensors prepared using classical techniques will be revised. Then, new strategies to improve the performance of the sensors will be described using as example sensors chemically modified with lutetium bisphthalocyanine (LuPc[Formula: see text] dedicated to the detection of phenols of interest in the food industry. Classical LuPc2 carbon paste electrodes can detect phenols such as catechol, caffeic acid or pyrogallol with limits of detection in the range of 10[Formula: see text]–10[Formula: see text] M. The performance can be improved by using nanostructured Langmuir–Blodgett (LB) or Layer by Layer (LbL) films. The enhanced surface to volume ratio produce an increase in the sensitivity of the sensors. Limits of detection of 10[Formula: see text]–10[Formula: see text] M are attained, which are one order of magnitude lower than those obtained using conventional carbon paste electrodes. Moreover, these techniques can be used to co-immobilize two electrocatalytic materials in the same device. The limits of detection obtained in LB sensors combining LuPc2/AuNPs or LuPc2/CNT are further improved. Finally, the LB technique has been used to prepare biosensors where a phenol oxydase (such as tyrosinase or lacasse) is immobilized in a biomimetic environment that preserves the enzymatic activity. Moreover, LuPc2 can be co-immobilized with the enzyme in a lipidic film formed by arachidic acid (AA). LuPc2 can act as an electron mediator facilitating the electron transfer. These biomimetic sensors formed by LuPc2/AA/enzyme show Limits of detection of 10[Formula: see text] M and an enhanced selectivity.

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.

Electrochemical Methods for Total Antioxidant Capacity and its Main Contributors Determination: A review

Backround: The present review focuses on electrochemical methods for antioxidant capacity and its main contributors assessment. The main reactive oxygen species, responsible for low density lipoprotein oxidation, and their reactivity are reminded. The role of antioxidants in counteracting the factors leading to oxidative stress-related degenerative diseases occurence, is then discussed. Antioxidants can scavenge free radicals, can chelate pro-oxidative metal ions, or quench singlet oxygen. When endogenous factors (uric acid, bilirubin, albumin, metallothioneins, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase) cannot accomplish their protective role against reactive oxygen species, the intervention of exogenous antioxidants (vitamin C, tocopherols, flavonoids, carotenoids etc) is required, as intake from food, as nutritional supplements or as pharmaceutical products.

Literature study: The main advantages of electrochemical methods with respect to traditional, more laborious instrumental techniques are described: sensitivity, rapidity, simplicity of the applied analytical procedure which does not require complicated sample pre-treatment etc.

The paper reviews minutiously the voltammetric, amperometric, biamperometric, potentiometric and coulometric methods for total antioxidant capacity estimation. For each method presented, the electroactivity and the mechanism of electro-oxidation of antioxidant molecules at various electrodes, as well as the influences on the electroactive properties are discussed. The characteristics of the developed methods are viewed from the perspective of the antioxidant molecule structure influence, as well as from the importance of electrode material and/or surface groups standpoint.

The antioxidant molecule-electrode surface interaction, the detection system chosen, the use of modifiers, as well as the nature of the analysed matrix are the factors discussed, which influence the performances of the studied electrochemical techniques.

Conclusions: The electrochemical methods reviewed in this paper allow the successful determination of the total antioxidant capacity and of its main contributors in various media: foodstuffs and beverages, biological fluids, pharmaceuticals. The advantages and disadvantages of the electrochemical methods applied to antioxidant content and antioxidant activity assay are treated and interpreted, in the case of various analysed matrixes. Combining advanced materials with classical electrode construction, provides viable results and can constitute an alternative for the future.

Analysis of organic acids and phenols of interest in the wine industry using Langmuir-Blodgett films based on functionalized nanoparticles

A chemically modified electrode consisting of Langmuir-Blodgett (LB) films of n-dodecanethiol functionalized gold nanoparticles (SDODAuNP-LB), was investigated as a voltammetric sensor of organic and phenolic acids of interest in the wine industry. The nanostructured films demonstrated interfacial properties being able to detect the main organic acids present in grapes and wines (tartaric, malic, lactic and citric). Compared to a bare ITO electrode, the modified electrodes exhibited a shift of the reduction potential in the less positive direction and a marked enhancement in the current response. Moreover, the increased electrocatalytic properties made it possible to distinguish between the different dissociable protons of polyprotic acids. The SDODAuNP-LB sensor was also able to provide enhanced responses toward aqueous solutions of phenolic acids commonly found in wines (caffeic and gallic acids). The presence of nanoparticles increased drastically the sensitivity toward organic acids and phenolic compounds. Limits of detection as low as 10(-6) mol L(-1) were achieved. Efficient catalytic activity was also observed in mixtures of phenolic acid/tartaric in the range of pHs typically found in wines. In such mixtures, the electrode was able to provide simultaneous information about the acid and the phenol concentrations with a complete absence of interferences. The excellent sensing properties shown by these sensors could be attributed to the electrocatalytic properties of the nanoparticles combined with the high surface to volume ratio and homogeneity provided by the LB technique used for the immobilization. Moreover, the LB technique also provided an accurate method to immobilize the gold nanoparticles giving rise to stable and reproducible sensors showing repeatability lower than 2% and reproducibility lower than 4% for all the compounds analyzed.

Rapid and specific sensing of gallic acid with a photoelectrochemical platform based on polyaniline-reduced graphene oxide-TiO2

A novel photoelectrochemical sensor has been designed with polyaniline-reduced graphene oxide-titanium dioxide, which was further applied to sense gallic acid and exhibited extraordinary rapid response, high sensitivity and excellent anti-inference. Meanwhile, the mechanism has been elaborately explored.

Electrochemical characterization of dilithium phthalocyanine carbonaceous electrodes

Carbonaceous electrodes of dilithium phthalocyanine were prepared using graphite, carbon microspheres and multiwall carbon nanotubes. The electrochemical behavior of the dilithium bisphthalocyanine electrodes was found to be dependent on the nature of the carbonaceous material and on the nature of the electrolytic solution. The electrocatalytic properties of the dilithium phthalocyanine electrodes for oxidation of ascorbic acid were evidenced by the enhancement of the oxidation peak current, (~10 fold compared to the bare carbon electrodes) and the decrease of the oxidation potential at which oxidation of ascorbic acid takes place. The combined use of multiwall carbon nanotubes and dilithium phthalocyanine produces a synergistic effect that improves the electrocatalytic effect towards ascorbic acid.