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

Gold nanoparticles decorated kaolinite mineral modified screen-printed electrode: Use for simple, sensitive determination of gallic acid in food samples

The current study offers the nanomolar quantification of gallic acid (GAL) based on gold nanoparticles (AuNps) and kaolinite minerals (KNT) modified on a screen-printed electrode (SPE). The electrochemical behavior of GAL was performed using differential pulse voltammetry (DPV) in Britton Robinson (BR) buffer solution at pH 2.0 as a supporting electrolyte. Under the optimized DPV mode parameters, the oxidation peak current of GAL (at 0.72 V vs Ag/AgCl) increased linearly in the range between 0.002 μmolL-1 and 40.0 μmolL-1 with a detection limit of 0.50 nmolL-1. The effect of common interfering agents was also investigated. Finally, the applicability of the proposed method was verified by quantification analysis of GAL in black tea and pomegranate juice samples.

A multichannel closed bipolar platform to visual electrochemiluminescence sensing of caffeic acid as a model: Potential for multiplex detection

In this study, a fully-featured electrochemiluminescence (ECL) sensing platform based on a multichannel closed bipolar system (closed-BP, C-BP) for the determination of caffeic acid (CA) was successfully developed. The system comprises three individual reservoirs connected to each other by two pairs of gold rods as bipolar electrodes. Moreover, a single pair of gold rods functions as the driving electrodes. Due to configuration consisting of three channels and double-bipolar electrodes, the detection of CA was accomplished in two oxidation and reduction pathways within a single device. Firstly, through close observation of the reactions occurring within the device and utilizing a universal pH indicator and bipolar electrodes, a precise mechanism for the current bipolar systems was initially proposed. Then, the concentration of CA was monitored in the reporting chamber through the following ECL intensities resulting from luminol oxidation and H2O2. The monitoring process was performed using both a photomultiplier tube (PMT) and a digital camera. In the process of analyte oxidation, the PMT and visual (camera)-based detection exhibited a linear response from 5 μmol L-1 to 700 μmol L-1 (limit of detection (LOD) 1.2 μmol L-1) and 50 μmol L-1 to 600 μmol L-1 (LOD 14.8 μmol L-1), respectively. In the analyte reduction pathway, the respective values were 30 μmol L-1 to 450 μmol L-1 (LOD 8.6 μmol L-1) and 55 μmol L-1 to 400 μmol L-1 (LOD 21.2 μmol L-1), for the PMT and visual-based detection, respectively. Our experiments have demonstrated the practical application of the sensor array for efficient and high-performance analysis. This innovative design holds significant potential for diverse fields and paves the way for the development of a user-friendly device.

Nanomaterial-based electrochemical sensors for detection of amino acids

Amino acids are the building blocks of proteins and muscle tissue. They also play a significant role in physiological processes related to energy, recovery, mood, muscle and brain function, fat burning and stimulating growth hormone or insulin secretion. Accurate determination of amino acids in biological fluids is necessary because any changes in their normal ranges in the body warn diseases like kidney disease, liver disease, type 2 diabetes and cancer. To date, many methods such as liquid chromatography, fluorescence mass spectrometry, etc. have been used for the determination of amino acids. Compared with the above techniques, electrochemical systems using modified electrodes offer a rapid, accurate, cheap, real-time analytical path through simple operations with high selectivity and sensitivity. Nanomaterials have found many interests to create smart electrochemical sensors in different application fields e.g. biomedical, environmental, and food analysis because of their exceptional properties. This review summarizes recent advances in the development of nanomaterial-based electrochemical sensors in 2017-2022 for the detection of amino acids in various matrices such as serum, urine, blood and pharmaceuticals.

Studies on the Detection of Oleuropein from Extra Virgin Olive Oils Using Enzymatic Biosensors

Oleuropein (OLEU) is an important indicator of the quality and authenticity of extra virgin olive oils (EVOO). Electrochemical sensors and biosensors for the detection of oleuropein can be used to test the adulteration of extra virgin olive oils. The present study aimed at the qualitative and quantitative determination of oleuropein in commercial EVOO samples by applying electrochemical techniques, cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensing devices used were two newly constructed enzyme biosensors, supported on single-layer carbon-nanotube-modified carbon screen-printed electrode (SPE/SWCNT) on whose surface tyrosinase (SPE/SWCNT/Tyr) and laccase (SPE/SWCNT/Lac) were immobilized, respectively. The active surfaces of the two biosensors were analyzed and characterized by different methods, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) and the results confirmed the efficient immobilization of the enzymes. SPE/SWCNT/Tyr was characterized by a low detection limit (LOD = 9.53 × 10⁻⁸ M) and a very good sensitivity (0.0718 μA·μM⁻¹·cm⁻²) over a wide linearity range from 0.49 to 11.22 μM. The process occurring at the biosensor surface corresponds to kinetics (h = 0.90), and tyrosinase showed a high affinity towards OLEU. The tyrosinase-based biosensor was shown to have superior sensitive properties to the laccase-based one. Quantitative determination of OLEU in EVOOs was performed using SPE/SWCNT/Tyr and the results confirmed the presence of the compound in close amounts in the EVOOs analysed, proving that they have very good sensory properties.

Sensitive Detection of Hydroxytyrosol in Extra Virgin Olive Oils with a Novel Biosensor Based on Single-Walled Carbon Nanotubes and Tyrosinase

Hydroxytyrosol (HT) is an important marker for the authenticity and quality assessment of extra virgin olive oils (EVOO). The aim of the study was the qualitative and quantitative determination of hydroxytyrosol in commercial extra virgin olive oils of different origins and varieties using a newly developed biosensor based on a screen-printed electrode modified with single-layer carbon nanotubes and tyrosinase (SPE-SWCNT-Ty). The enzyme was immobilized on a carbon-based screen-printed electrode previously modified with single-layer carbon nanotubes (SPE-SWCNT-Ty) by the drop-and-dry method, followed by cross-linking with glutaraldehyde. The modified electrode surface was characterized by different methods, including electrochemical (cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS)) and spectrometric (Fourier transform infrared (FTIR) spectroscopy) methods. Cyclic voltammetry was used for the quantitative determination of HT, obtaining a detection limit of 3.49 × 10⁻⁸ M and a quantification limit of 1.0 × 10⁻⁷ M, with a wide linearity range (0.49–15.602 µM). The electrochemical performance of the SPE-SWCNT-Ty biosensor was compared with that of the modified SPE-SWCNT sensor, and the results showed increased selectivity and sensitivity of the biosensor due to the electrocatalytic activity of tyrosinase. The results obtained from the quantitative determination of HT showed that commercial EVOOs contain significant amounts of HT, proving the high quality of the finished products. The determination of the antiradical activity of HT was carried out spectrophotometrically using the free reagent galvinoxyl. The results showed that there is a very good correlation between the antiradical capacity of EVOOs, the voltammetric response and implicitly the increased concentration of HT. SPE-SWCNT-Ty has multiple advantages such as sensitivity, selectivity, feasibility and low cost and could be used in routine analysis for quality control of food products such as vegetable oils.

Simultaneous Determination of Caffeic Acid and Ferulic Acid Using a Carbon Nanofiber-Based Screen-Printed Sensor

This work aims to achieve the simultaneous qualitative and quantitative determination of two hydroxycinnamic acids (ferulic acid and caffeic acid) from standard solutions and from a phyto-homeopathic product using a carbon nanofiber-based screen-printed sensor (CNF/SPE). The two compounds are mentioned in the manufacturer's specifications but without indicating their concentrations. The stability and reproducibility of the CNF/SPE were found to be effective and the sensitivity was high for both caffeic acid-CA (limit of detection 2.39 × 10^-7 M) and ferrulic acid-FA (limit of detection 2.33 × 10^-7 M). The antioxidant capacity of the compounds in the analyzed product was also determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. The electrochemical method was efficient and less expensive than other analytical methods; therefore, its use can be extended for the detection of these phenolic compounds in various dietary supplements or pharmaceutical products.

Evaluation of Olive Oil Quality with Electrochemical Sensors and Biosensors: A Review

Electrochemical sensors, sensor arrays and biosensors, alongside chemometric instruments, have progressed remarkably of late, being used on a wide scale in the qualitative and quantitative evaluation of olive oil. Olive oil is a natural product of significant importance, since it is a rich source of bioactive compounds with nutritional and therapeutic properties, and its quality is important both for consumers and for distributors. This review aims at analysing the progress reported in the literature regarding the use of devices based on electrochemical (bio)sensors to evaluate the bioactive compounds in olive oil. The main advantages and limitations of these approaches on construction technique, analysed compounds, calculus models, as well as results obtained, are discussed in view of estimation of future progress related to achieving a portable, practical and rapid miniature device for analysing the quality of virgin olive oil (VOO) at different stages in the manufacturing process.

Voltammetric Determination of Levodopa Using Mesoporous Carbon-Modified Screen-Printed Carbon Sensors

Levodopa is a precursor of dopamine, having important beneficial effects in the treatment of Parkinson’s disease. In this study, levodopa was accurately detected by means of cyclic voltammetry using carbon-based (C-SPCE), mesoporous carbon (MC-SPCE) and ordered mesoporous carbon (OMC-SPCE)-modified screen-printed sensors. Screen-printed carbon sensors were initially used for the electrochemical detection of levodopa in a 10⁻³ M solution at pH 7.0. The mesoporous carbon with an organized structure led to better electroanalysis results and to lower detection and quantification limits of the OMC-SPCE sensor as compared to the other two studied sensors. The range of linearity obtained and the low values of the detection (0.290 µM) and quantification (0.966 µM) limit demonstrate the high sensitivity and accuracy of the method for the determination of levodopa in real samples. Therefore, levodopa was detected by means of OMC-SPCE in three dietary supplements produced by different manufacturers and having various concentrations of the active compound, levodopa. The results obtained by cyclic voltammetry were compared with those obtained by using the FTIR method and no significant differences were observed. OMC-SPCE proved to be stable, and the electrochemical responses did not vary by more than 3% in repeated immersions in a solution with the same concentration of levodopa. In addition, the interfering compounds did not significantly influence the peaks related to the presence of levodopa in the solution to be analyzed.

Recent Advances in Electrochemical Chitosan-Based Chemosensors and Biosensors: Applications in Food Safety

Chitosan is a biopolymer derived from chitin. It is a non-toxic, biocompatible, bioactive, and biodegradable polymer. Due to its properties, chitosan has found applications in several and different fields such as agriculture, food industry, medicine, paper fabrication, textile industry, and water treatment. In addition to these properties, chitosan has a good film-forming ability which allows it to be widely used for the development of sensors and biosensors. This review is focused on the use of chitosan for the formulation of electrochemical chemosensors. It also aims to provide an overview of the advantages of using chitosan as an immobilization platform for biomolecules by highlighting its applications in electrochemical biosensors. Finally, applications of chitosan-based electrochemical chemosensors and biosensors in food safety are illustrated.

Development of a Novel Electrochemical Biosensor Based on Carbon Nanofibers-Cobalt Phthalocyanine-Laccase for the Detection of p-Coumaric Acid in Phytoproducts

The present paper developed a new enzymatic biosensor whose support is a screen-printed electrode based on carbon nanofibers modified with cobalt phthalocyanine and laccase (CNF-CoPc-Lac/SPE) to determine the p-coumaric acid (PCA) content by cyclic voltammetry and square wave voltammetry. Sensor modification was achieved by the casting and cross-linking technique, using glutaraldehyde as a reticulation agent. The biosensor’s response showed the PCA redox processes in a very stable and sensitive manner. The calibration curve was developed for the concentration range of p-coumaric acid of 0.1–202.5 μM, using cyclic voltammetry and chronoamperometry. The biosensor yielded optimal results for the linearity range 0.4–6.4 μM and stood out by low LOD and LOQ values, i.e., 4.83 × 10⁻⁷ M and 1.61 × 10⁻⁶ M, respectively. PCA was successfully determined in three phytoproducts of complex composition. The results obtained by the voltammetric method were compared to the ones obtained by the FTIR method. The amount of p-coumaric acid determined by means of CNF-CoPc-Lac/SPE was close to the one obtained by the standard spectrometric method.

Determination of Atorvastatin with Voltammetric Sensors Based on Nanomaterials

This paper presents an accurate and fast electrochemical method for atorvastatin determination in pharmaceutical products. Two screen-printed sensors, one—carbon based (SPCE) and one based on carbon nanotubes and gold nanoparticles (AuNP-CNT/SPCE) were used during the electrochemical analyses. At all experimental stages, cyclic voltammetry was employed, both for the characterization of the sensors and their electrochemical behavior, and for quantitative determinations. AuNP-CNT/SPCE has showed an extended active area, higher intensity peaks, better reversibility and lower background current than the unmodified sensor. For atorvastatin quantification, a calibration curve has been developed within the 1.2–606.25 µM concentration range. A linearity relation between the current of the anodic peak and concentration has been obtained in the range 1.2–53.33 µMfor both sensors. With the AuNP-CNT/SPCE sensor, low values of limit of detection, LOD (1.92 × 10−7 M) and limit of quantification, LOQ (6.39 × 10−7 M) have been obtained, which demonstrates the feasibility of the method of determining atorvastatin from real samples. Atorvastatin amount has been successfully determined from pharmaceutical products using AuNP-CNT/SPCE. The results were similar to the manufacturer’s specifications regarding the dosage per tablet and to the concentrations obtained by applying the FTIR spectrometric method.

Laccase and Tyrosinase Biosensors Used in the Determination of Hydroxycinnamic Acids

In recent years, researchers have focused on developing simple and efficient methods based on electrochemical biosensors to determine hydroxycinnamic acids from various real samples (wine, beer, propolis, tea, and coffee). Enzymatic biosensors represent a promising, low-cost technology for the direct monitoring of these biologically important compounds, which implies a fast response and simple sample processing procedures. The present review aims at highlighting the structural features of this class of compounds and the importance of hydroxycinnamic acids for the human body, as well as presenting a series of enzymatic biosensors commonly used to quantify these phenolic compounds. Enzyme immobilization techniques on support electrodes are very important for their stability and for obtaining adequate results. The following sections of this review will briefly describe some of the laccase (Lac) and tyrosinase (Tyr) biosensors used for determining the main hydroxycinnamic acids of interest in the food or cosmetics industry. Considering relevant studies in the field, the fact has been noticed that there is a greater number of studies on laccase-based biosensors as compared to those based on tyrosinase for the detection of hydroxycinnamic acids. Significant progress has been made in relation to using the synergy of nanomaterials and nanocomposites for more stable and efficient enzyme immobilization. These nanomaterials are mainly carbon- and/or polymer-based nanostructures and metallic nanoparticles which provide a suitable environment for maintaining the biocatalytic activity of the enzyme and for increasing the rate of electron transport.

Glassy Carbon Electrode Modified with C/Au Nanostructured Materials for Simultaneous Determination of Hydroquinone and Catechol in Water Matrices

The simultaneous determination of hydroquinone and catechol was conducted in aqueous and real samples by means of differential pulse voltammetry (DPV) using a glassy carbon electrode modified with Gold Nanoparticles (AuNP) and functionalized multiwalled carbon nanotubes by drop coating. A good response was obtained in the simultaneous determination of both isomers through standard addition to samples prepared with analytical grade water and multivariate calibration by partial least squares (PLS) in winery wastewater fortified with HQ and CT from 4.0 to 150.00 µM. A sensitivity of 0.154 µA µM−1 and 0.107 µA µM−1, and detection limits of 4.3 and 3.9 µM were found for hydroquinone and catechol, respectively. We verified the reliability of the developed method by simultaneously screening analytes in spiked tap water and industrial wastewater, achieving recoveries over 80%. In addition, this paper demonstrates the applicability of chemometric tools for the simultaneous quantification of both isomers in real matrices, obtaining prediction errors of lower than 10% in fortified wastewater.

Nanomaterials Based Electrochemical Sensors for Serotonin Detection: A Review

The present review deals with the recent progress made in the field of the electrochemical detection of serotonin by means of electrochemical sensors based on various nanomaterials incorporated in the sensitive element. Due to the unique chemical and physical properties of these nanomaterials, it was possible to develop sensitive electrochemical sensors with excellent analytical performances, useful in the practice. The main electrochemical sensors used in serotonin detection are based on carbon electrodes modified with carbon nanotubes and various materials, such as benzofuran, polyalizarin red-S, poly(L-arginine), Nafion/Ni(OH)2, or graphene oxide, incorporating silver-silver selenite nanoparticles, as well as screen-printed electrodes modified with zinc oxide or aluminium oxide. Also, the review describes the nanocomposite sensors based on conductive polymers, tin oxide-tin sulphide, silver/polypyrole/copper oxide or a hybrid structure of cerium oxide-gold oxide nanofibers together with ruthenium oxide nanowires. The presentation focused on describing the sensitive materials, characterizing the sensors, the detection techniques, electroanalytical properties, validation and use of sensors in lab practice.

Nanomaterials in Electrochemical Sensing Area: Applications and Challenges in Food Analysis

Recently, nanomaterials have received increasing attention due to their unique physical and chemical properties, which make them of considerable interest for applications in many fields, such as biotechnology, optics, electronics, and catalysis. The development of nanomaterials has proven fundamental for the development of smart electrochemical sensors to be used in different application fields such, as biomedical, environmental, and food analysis. In fact, they showed high performances in terms of sensitivity and selectivity. In this report, we present a survey of the application of different nanomaterials and nanocomposites with tailored morphological properties as sensing platforms for food analysis. Particular attention has been devoted to the sensors developed with nanomaterials such as carbon-based nanomaterials, metallic nanomaterials, and related nanocomposites. Finally, several examples of sensors for the detection of some analytes present in food and beverages, such as some hydroxycinnamic acids (caffeic acid, chlorogenic acid, and rosmarinic acid), caffeine (CAF), ascorbic acid (AA), and nitrite are reported and evidenced.

Voltamperometric Sensors and Biosensors Based on Carbon Nanomaterials Used for Detecting Caffeic Acid-A Review

Caffeic acid is one of the most important hydroxycinnamic acids found in various foods and plant products. It has multiple beneficial effects in the human body such as antioxidant, antibacterial, anti-inflammatory, and antineoplastic. Since overdoses of caffeic acid may have negative effects, the quality and quantity of this acid in foods, pharmaceuticals, food supplements, etc., needs to be accurately determined. The present paper analyzes the most representative scientific papers published mostly in the last 10 years which describe the development and characterization of voltamperometric sensors or biosensors based on carbon nanomaterials and/or enzyme commonly used for detecting caffeic acid and a series of methods which may improve the performance characteristics of such sensors.

Development of a Novel Electrochemical Biosensor Based on Carbon Nanofibers-Gold Nanoparticles-Tyrosinase for the Detection of Ferulic Acid in Cosmetics

The present paper deals with the electrochemical behavior of three types of sensors based on modified screen-printed electrodes (SPEs): a sensor based on carbon nanofibers (CNF/SPE), a sensor based on nanofibers of carbon modified with gold nanoparticles (CNF-GNP/SPE) and a biosensor based on nanofibers of carbon modified with gold nanoparticles and tyrosinase (CNF-GNP-Ty/SPE). To prepare the biosensor, the tyrosinase (Ty) was immobilized on the surface of the electrode already modified with carbon nanofibers and gold nanoparticles, by the drop-and-dry technique. The electrochemical properties of the three electrodes were studied by cyclic voltammetry in electroactive solutions, and the position and shape of the active redox peaks are according to the nature of the materials modifying the electrodes. In the case of ferulic acid, a series of characteristic peaks were observed, the processes being more intense for the biosensor, with the higher sensitivity and selectivity being due to the immobilization of tyrosinase, a specific enzyme for phenolic compounds. The calibration curve was subsequently created using CNF-GNP-Ty/SPE in ferulic acid solutions of various concentrations in the range 0.1-129.6 μM. This new biosensor allowed low values of the detection threshold and quantification limit, 2.89 × 10-9 mol·L-1 and 9.64 × 10-9 mol·L-1, respectively, which shows that the electroanalytical method is feasible for quantifying ferulic acid in real samples. The ferulic acid was quantitatively determined in three cosmetic products by means of the CNF-GNP-Ty/SPE biosensor. The results obtained were validated by means of the spectrometric method in the infrared range, the differences between the values of the ferulic acid concentrations obtained by the two methods being under 5%.

Voltammetric Determination of Phenylalanine Using Chemically Modified Screen-Printed Based Sensors

This paper describes the sensitive properties of screen-printed carbon electrodes (SPCE) modified by using three different electroactive chemical compounds: Meldola’s Blue, Cobalt Phthalocyanine and Prussian Blue, respectively. It was demonstrated that the Prussian Blue (PB) modified SPCE presented electrochemical signals with the highest performances in terms of electrochemical process kinetics and sensitivity in all the solutions analyzed. PB-SPCE was demonstrated to detect Phe through the influence it exerts on the redox processes of PB. The PB-SPCE calibration have shown a linearity range of 0.33–14.5 µM, a detection limit (LOD) of 1.23 × 10−8 M and the standard deviation relative to 3%. The PB-SPCE sensor was used to determine Phe by means of calibration and standard addition techniques on pure samples, on simple pharmaceutical samples or on multicomponent pharmaceutical samples. Direct determination of the concentration of 4 × 10−6–5 × 10−5 M Phe in KCl solution showed that the analytical recovery falls in the range of 99.75–100.28%, and relative standard deviations in the range of 2.28–3.02%. The sensors were successfully applied to determine the Phe in pharmaceuticals. The validation of the method was performed by using the FTIR, and by comparing the results obtained by PB-SPCE in the analysis of three pharmaceutical products of different concentrations with those indicated by the producer.

Estimation of Active Compounds Quantity from Pharmaceuticals Based on Ginkgo biloba

Ginkgo biloba is one of the most important sources of active compounds, mainly flavonoids and phenolic compounds. Due to its importance related to pharmaceutical practice, the making of a qualitative and quantitative method for the detection and quantification of active compounds from Ginkgo biloba pharmaceutical products is desirable. In this study, the content of biological active compounds from Ginkgo biloba products was estimated using cyclic voltammetry. The electrochemical determination of active compounds was carried out by using a screen-printed carbon electrode modified with carbon nanotubes. The studies regarding parameter optimization were made using solutions containing potassium ferrocyanide and catechol, respectively. In both cases, the redox processes of studied compounds was observed, which were controlled by the diffusion phenomenon. We analyzed two pharmaceutical products containing Ginkgo biloba, a RX product (recipe medicine requires a medical prescription to be dispensed) and an OTC (Over-The-Counter, which can be obtained without a prescription) product. The cyclic voltammograms of the two products showed two redox processes due to the antioxidant properties of the products. It was found that the RX product had a greater content of active compounds compared to the OTC product. Therefore, the voltammetric method has great utility for the determination of compounds with redox properties from pharmaceutical products containing Ginkgo biloba.

Electrochemical Methods and (Bio) Sensors for Rosmarinic Acid Investigation

Rosmarinic acid (RA) is an important bioactive phenolic acid with significant biochemical activities, including the antioxidant one. It is widely found in plants of the families Lamiaceae and Boraginaceae and has many uses in the food, pharmaceutical and cosmetics industries. RA is an electroactive species owing to the presence of the two catechol groups in its structure. Due to their inherent characteristics, such as sensitivity, selectivity, ease of operation and not too high costs, electrochemical methods of analysis are interesting tools for the assessment of redox-active compounds. Moreover, there is a good correlation between the redox potential of the analyte and its capability to donate electrons and, consequently, its antioxidant activity. Therefore, this paper presents a detailed overview of the electrochemical (bio)sensors and methods, in both stationary and dynamic systems, applied for RA investigation under different aspects. These comprise its antioxidant activity, its interaction with biological important molecules and the quantification of RA or total polyphenolic content in different samples.