Electrochemical Sensor Based on a Carbon Veil Modified by Phytosynthesized Gold Nanoparticles for Determination of Ascorbic Acid

Single laser synthesis of gold nanoparticles-polypyrrole-chitosan on laser-induced graphene for ascorbic acid detection

The simultaneous synthesis of gold nanoparticles (AuNPs) and graphene by laser ablation was demonstrated. The in-situ synthesis was performed by laser ablation of a polymer substrate covered with a gold precursor dispersion. The gold precursor was prepared in a copolymer solution of pyrrole (Py) and chitosan (Chi) to improve the nucleation of gold embedded on the laser-induced graphene electrode (LIGE). The morphology of AuNPs-pPy-Chi/LIGE was studied by scanning electron microscopy and characterized electrochemically by cyclic voltammetry. A comprehensive investigation of the electrochemical and physical features of the AuNPs-pPy-Chi/LIGE was carried out. The parameters of differential pulse voltammetry were adjusted to enhance the response to ascorbic acid (AA). The AuNPs-pPy-Chi/LIGE produced two linear ranges: from 0.25 to 5.00 and 5.00-25.00 mmol L-1. The limit of detection was 0.22 mmol L-1. Hundreds of electrodes were tested to demonstrate the excellent reproducibility of the AuNPs-pPy-Chi/LIGE fabrication. Overall, the proposed electrode allows the successful detection of AA in orange juice products with acceptable accuracy (recoveries = 97 ± 2 to 109.1 ± 0.7). The preparation strategy of the proposed AuNPs-pPy-Chi/LIGE could be adapted to detect other compounds or biomarkers.

Evaluation of a gold-nanoparticle-modified carbon-fiber microelectrode to quantify mercury in canned tuna sold in Ecuador

Seafood consumption is the primary exposure route for trace metals like mercury. Accordingly, canned tuna meat has been focused on by researchers because of the potential bioaccumulation of high amounts of mercury. This study aimed to test a novel and reliable electroanalytical method employing a working electrode consisting of gold-nanoparticle-modified carbon microfibers to quantify total mercury in canned tuna samples. Determination was achieved via differential pulse anodic stripping voltammetry. The proposed method had a limit of detection of 3.9781 ± 0.0001 μg L-1 and a limit of quantification of 33.6634 ± 0.0001 μg L-1, with a sensitivity of 0.3275 nA μg L-1. The modified electrode was evaluated in samples taken from three canned tuna brands sold in the Sangolquí parish in Rumiñahui, Ecuador. These brands, coded A, B, and C, represent 47.92%, 27.08%, and 11.98% of all canned tuna sold in the Ecuadorian market, respectively. The resulting respective total mercury concentrations were 0.5999 ± 0.0001 mg kg-1; 0.9387 ± 0.0001 mg kg-1; and 0.3442 ± 0.0001 mg kg-1 for A, B, and C. Method accuracy was determined through the recovery percentages of ≥98%, which indicated acceptable accuracy for the final optimized method. Mean mercury concentrations for all samples did not represent a carcinogenic risk for consumers. However, the values obtained for potential no-carcinogenic risk and daily consumption rate suggest that consumers of tuna canned in water, particularly brand C, may be at risk.

Highly sensitive voltammetric determination of Allura Red (E129) food colourant on a planar carbon fiber sensor modified with shungite

This article presents an original planar carbon fiber electrode (PCFE), in which shungite (SHU) is used as a modifier for the first time. Shungite is a unique natural nanostructured composite consisting of carbon in the form of aggregated graphene stacks, oxides of silicon, titanium, aluminum, iron, magnesium, potassium, etc. Macro- and micro-elements, biologically active components that are present in shungite provide it with attractive antioxidant properties, make it a biocompatible and environmentally friendly material that meets the principles of green chemistry. A unique supramolecular structure of shungite carbon presents a multilayer globular-cluster formation with mesopores in the internal volume. It determines specific physical, chemical, catalytic, and adsorption properties of shungite. Carbon fiber with an irregular 3D structure was used as an effective electrode platform for strong immobilization of shungite. The PCFE was fabricated using a simple and scalable hot lamination technology that produces very low cost flexible planar electrodes. The sensor (SHU/PCFE) was characterized by scanning electron microscopy; electrochemical impedance analysis; cyclic, differential-pulse and stripping voltammetry. The SHU/PCFE showed a 2.5-fold increase in the electroactive surface area, a 1.8-fold decrease in the electron transfer resistance compared with the bare PCFE. Under optimal experimental conditions and preconcentration at +0.2 V (vs. Ag/AgCl) 180 s, the developed sensor allowed the quantification of Allura Red in the ranges of 0.001-0.1 and 0.1-2 μmol L^-1 with an extremely low detection limit of 0.36 nmol L^-1. Moreover, this convenient and cost-effective sensor also has good repeatability, stability and anti-interference ability. The interfering effect of sweeteners and preservatives in the determination of Allura Red does not exceed 3.6%. The practical application of the SHU/PCFE was demonstrated using drink samples, lollipops and pharmaceuticals.

Carbon Paper Modified with Functionalized Poly(diallyldimethylammonium chloride) Graphene and Gold Phytonanoparticles as a Promising Sensing Material: Characterization and Electroanalysis of Ponceau 4R in Food Samples

This paper presents a novel eco-friendly sensing material based on carbon paper (CP) volumetrically modified with a composite nanomodifier that includes functionalized poly(diallyldimethylammonium chloride) graphene (PDDA-G) and phytosynthesized gold nanoparticles (phyto-AuNPs). The functionalization of graphene was justified by Fourier-transform infrared spectroscopy. The phyto-AuNPs (d = 6 nm) were prepared by "green" synthesis with the use of strawberry leaf extract. The sensing material was characterized using scanning electron microscopy, electrochemical impedance spectroscopy, and voltammetry. The research results indicated a more than double increase in the electroactive surface area; a decrease in the resistance of electron transfer on nanocomposite-modified CP, compared to bare CP. The phyto-AuNPs/PDDA-G/CP was used for the electrosensing of the synthetic dye Ponceau 4R. The oxidation signal of colorant enhanced 4-fold on phyto-AuNPs/PDDA-G/CP in comparison to CP. The effect of the quantity of nanomodifier, solution pH, potential scan rate, accumulation parameters, and differential pulse parameters on the peak current of Ponceau 4R was studied. Under optimal conditions, excellent sensory characteristics were established: LOD 0.6 nM and LR 0.001-2 μM for Ponceau 4R. High selectivity and sensitivity enable the use of the sensor for analyzing the content of Ponceau 4R in food products (soft drinks, candies, and popsicles) without additional sample preparation.

Electrochemical Digitization of Biological Fluids Samples

Digital medicine based on the integration of all medical data from a particular patient has become a reality today, thanks to information technology. Traditional medical examinations can be supplemented by assessment results of the oxidative-anti-oxidative (OAO) status of the body. Electrochemical sensors are able to not only determine the integral indicators of the OAO system of the body but also to depict details of the processes occurring in the system. The main obstacle to the widespread use of electrochemical sensors in medical diagnostics is the extremely small amount of received information in comparison to the tens of thousands of known human diseases. The problem can be eliminated only by rethinking the purpose of electrochemical measurement within the framework of thermodynamics of information processes and information theory. In the information paradigm of electrochemical analysis of biological fluids, a sample is considered an electrochemical message created by a sensor. The purpose of electrochemical measurement is to obtain information in a volume sufficient to identify the sample composition within the range of possible concentrations of its components. The fundamentals of the thermodynamics of information processes are considered and conclusions that are of practical importance for the development of electrochemical sensors and analyzers are derived. It is shown that the potentiostatic control of the sensor is physically impacted by the electromechanical instability of the electrical double layer, which is the main source of sensor signal noise. Estimates of a minimum amount of analytical signal information required for the identification of a sample of known composition, such as a biological fluid, are provided. Examples of highly informative analytical signals for flowing and stationary samples are presented. Problems related to the visualization of such signals are noted.

Precise and quick detection of ascorbic acid and eugenol in fruits, pharmaceuticals and medicinal herbs using hydroxyapatite-titanium dioxide nanocomposite-based electrode

Ascorbic acid (AA) and eugenol (EUG) are well-known antioxidants found in several fruits, spices and herbs. In particular, the EUG, one of the major phytocompounds present in clove, acts as pro-oxidant or anti-oxidant depending on its concentration. Considering the medical importance of AA and EUG and its extensive usage in the form of food and medicine, we have developed a voltammetric sensor based on hydroxyapatite-TiO₂ composite modified GCE for their selective and simultaneous determination over very wide linear range of 2.78-2490 µM for AA and 1.4-78 µM for EUG with the LODs of 63.3 nM and 94 nM respectively. Practical applicability of the prepared electrode has been demonstrated by detecting AA and EUG in lemon juice, vitamin tablet, clove oil and Kabasura Kudineer, an herbal decoction used as an immunity booster against number of diseases including Covid-19. The proposed HAP-TiO₂/GCE shall be useful for food and pharmaceutical industries.

An Electrochemical Sensor Based on Carbon Paper Modified with Graphite Powder for Sensitive Determination of Sunset Yellow and Tartrazine in Drinks

The paper describes the development of an electrochemical sensor to be used for the determination of synthetic food colorants such as Sunset Yellow FCF (SY) and Tartrazine (TZ). The sensor is a carbon paper (CP) electrode, manufactured by using hot lamination technology and volume modified with fine-grained graphite powder (GrP). The sensor (GrP/CP) was characterized by scanning electron microscopy, energy dispersive spectrometry, electrochemical impedance analysis, cyclic, linear sweep and differential pulse voltammetry. The mechanism of SY and TZ electrochemical oxidation on GrP/CP was studied. The developed sensor has good electron transfer characteristics and low electron resistance, high sensitivity and selectivity. Applying the differential pulse mode, linear dynamic ranges of 0.005–1.0 μM and 0.02–7.5 μM with limits of detection of 0.78 nM and 8.2 nM for SY and TZ, respectively, were obtained. The sensor was used to detect SY and TZ in non-alcoholic and alcoholic drinks. The results obtained from drink analysis prove good reproducibility (RSD ≤ 0.072) and accuracy (recovery 96–104%).

Electrochemical Properties of Phytosynthesized Gold Nanoparticles for Electrosensing

Gold nanoparticles are widely used in electrosensing. The current trend is to phytosynthesize gold nanoparticles (phyto-AuNPs) on the basis of the “green” chemistry approach. Phyto-AuNPs are biologically and catalytically active, stable and biocompatible, which opens up broad perspectives in a variety of applications, including tactile, wearable (bio)sensors. However, the electrochemistry of phytosynthesized nanoparticles is not sufficiently studied. This work offers a comprehensive study of the electrochemical activity of phyto-AuNPs depending on the synthesis conditions. It was found that with an increase in the aliquot of the plant extract, its antioxidant activity (AOA) and pH, the electrochemical activity of phyto-AuNPs grows, which is reflected in the peak potential decrease and an increase in the peak current of phyto-AuNPs electrooxidation. It has been shown that AOA is an important parameter for obtaining phyto-AuNPs with desired properties. Electrodes modified with phyto-AuNPs have demonstrated better analytical characteristics than electrodes with citrate AuNPs in detecting uric and ascorbic acids under model conditions. The data about the phyto-AuNPs’ electrochemistry may be useful for creating highly effective epidermal sensors with good biocompatibility.

An Analytical Method Based on Electrochemical Sensor for the Assessment of Insect Infestation in Flour

Uric acid is an important indicator of the insect infestation assessment in flour. In this work, we propose a method for uric acid detection based on voltammetry. This technique is particularly considered for the physicochemical properties of flour and contains a simple pretreatment process to rapidly achieve extraction and adsorption of uric acid in flour. To achieve specific recognition of uric acid, graphene and poly(3,4-ethylenedioxythiophene) (PEDOT) were used for the adsorption and concentration of uric acid in flour. The adsorbed mixture was immobilized on the surface of a screen-printed electrode for highly sensitive detection of the uric acid. The results showed that electrocatalytic oxidation of uric acid could be achieved after adsorption by graphene and PEDOT. This electrocatalytic reaction allows its oxidation peak to be distinguished from those of other substances that commonly possess electrochemical activity. This voltammetry-based detection method is a portable and disposable analytical method. Because it is simple to operate, requires no professional training, and is inexpensive, it is a field analysis method that can be promoted.

Selective Voltammetric Detection of Ascorbic Acid from Rosa Canina on a Modified Graphene Oxide Paste Electrode by a Manganese(II) Complex

Voltammetric techniques have been considered as an important analytical tool applied to the determination of trace concentrations of many biological molecules including ascorbic acid. In this paper, ascorbic acid was detected by square wave voltammetry, using graphene oxide paste as a working electrode, modified by a film of a manganese(II) complex compound. Various factors, such as the effect of pH, affecting the response characteristics of the modified electrode were investigated. The relationship between the peak height and ascorbic acid concentration within the modified working electrode was investigated, using the calibration graph. The equation of the calibration graph was found to be: I = 0.0550γac + 0.155 with R2 = 0.9998, where I is the SWV current and γac is the mass concentration of ascorbic acid. The LOD and LOQ of the proposed method were determined to be 1.288 μg/L and 3.903 μg/L, respectively. Several compounds, such as riboflavin, biotin, and ions, such as Fe and Cu, were tested and it seemed that they did not interfere with the analytic signal. The proposed procedure was successfully applied in the determination of ascorbic acid in Rosa canina hips.

Developing Activated Carbon Veil Electrode for Sensing Salivary Uric Acid

The paper describes the development of a carbon veil-based electrode (CVE) for determining uric acid (UA) in saliva. The electrode was manufactured by lamination technology, electrochemically activated and used as a highly sensitive voltammetric sensor (CVEact). Potentiostatic polarization of the electrode at 2.0 V in H2SO4 solution resulted in a higher number of oxygen and nitrogen-containing groups on the electrode surface; lower charge transfer resistance; a 1.5 times increase in the effective surface area and a decrease in the UA oxidation potential by over 0.4 V, compared with the non-activated CVE, which was confirmed by energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, chronoamperometry and linear sweep voltammetry. The developed sensor is characterized by a low detection limit of 0.05 µM and a wide linear range (0.09-700 µM). The results suggest that the sensor has perspective applications for quick determination of UA in artificial and human saliva. RSD does not exceed 3.9%, and recovery is 96-105%. UA makes a significant contribution to the antioxidant activity (AOA) of saliva (≈60%). In addition to its high analytical characteristics, the important advantages of the proposed CVEact are the simple, scalable, and cost-effective manufacturing technology and the absence of additional complex and time-consuming modification operations.

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.

Electrochemical Behaviour of Real-Time Sensor for Determination Mercury in Cosmetic Products Based on PANI/MWCNTs/AuNPs/ITO

Mercury is a common ingredient found in skin lightening soaps, creams, and makeup-cleansing products. It may cause skin rashes, skin discolouration, and scarring, as well as a reduction in the skin’s resistance to bacterial and fungal infections. By looking at this scenario, developing a sensor that involved a simple procedure and fasts for real-time detection without affecting mercury sensitivity is urgently needed. For that reason, a fast and sensitive electrochemical method was developed to determine mercury in cosmetic products with the composition of polyaniline/multi-walled carbon nanotubes/gold nanoparticles/indium tin oxide sheet using methylene blue as a redox indicator. The significantly enhanced electrochemical performance was observed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In order to detect mercury qualitatively and quantitatively, deposition potential and deposition time were respectively optimised to be 0.10 V and 70 s. The modified sensor was revealed a wide detection range of mercury from 0.01 to 10.00 ppm with a limit of detection of 0.08 ppm. The modified sensor towards mercury with a correlation coefficient (r2) was of 0.9948. Multiple cycling, reproducibility, and consistency of different modified sensors were investigated to verify the modified sensor’s performance. The developed sensing platform was highly selective toward mercury among the pool of possible interferents, and the stability of the developed sensor was ensured for at least 21 days after 10 repeated uses. The proposed method is a fast and simple procedure technique for analysing the mercury levels in cosmetic products.

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.

Optimization and Analytical Behavior of Electrochemical Sensors Based on the Modification of Indium Tin Oxide (ITO) Using PANI/MWCNTs/AuNPs for Mercury Detection

In the present study, indium tin oxide (ITO) was used as a transparent working electrode for the development of an electrochemical sensor for the detection of mercury (II) ions (Hg2+). The electrode was modified by direct electrodeposition of polyaniline (PANI), multiwalled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) followed by optimization of the analyte and operating conditions, aiming to improve the selectivity, sensitivity and reliability of the electrode for mercury detection. Successful immobilization of the PANI and nanomaterials (MWCNTs and AuNPs) on the ITO electrode was confirmed by Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX) and Fourier Transform Infrared Spectroscopy (FTIR) analyses. The optimum conditions for mercury detection using the modified ITO electrode were pH 7.0 of Tris-HCl buffer (50 mM) in the presence of 1 mM methylene blue (MB) as a redox indicator, a scan rate of 0.10 V·s-1 and a 70 s interaction time. The electrochemical behavior of the modified electrode under the optimized conditions indicated a high reproducibility and high sensitivity of mercury detection. It is therefore suggested that the PANI/MWCNT/AuNP-modified ITO electrode could be a promising material for the development of on-site mercury detection tools for applications in fields such as diagnostics, the environment, safety and security controls or other industries.

Electrochemical Hybrid Methods and Sensors for Antioxidant/Oxidant Activity Monitoring and Their Use as a Diagnostic Tool of Oxidative Stress: Future Perspectives and Challenges

The terminology used in electrochemical methods which are used to generate the measured signal in antioxidant/oxidant activity (AOA/OA) sensors is briefly considered. The review presents a hybrid version of electrochemical methods for the determination of AOA/OA. Invasive electrochemical methods/sensors for AOA/OA of blood/serum/plasma, and non-invasive ones for semen, sweat, saliva and skin determination are described. AOA/OA sensors application in health estimation, cosmetology, food and nutrients is presented. Attention is paid to widely described approaches and technologies used in chemical/biochemical sensors. It will be considered as base/prototypes for developing sensors of the kind for AOA/OA determination. Prospects for the development of wearable, written sensors and biosensors are considered. Miniature and wireless sensors will allow for the monitoring of the patient’s state, both at the bedside and far beyond the hospital. The development of wearable self-powered written and printed sensors is an important step towards personalized medicine.

Film Carbon Veil-Based Electrode Modified with Triton X-100 for Nitrite Determination

A film carbon veil-based electrode (FCVE) modified with non-ionic surfactant Triton X-100 (TrX100) has been developed for nitrite determination. A new simple and producible technique of hot lamination (heat sealing) has been used for the FCVE manufacturing. The paper presents the findings of investigating the FCVE and the TrX100/FCVE by using voltammetry, chronoamperometry, and scanning electron microscopy. Modification of the electrode with TrX100 improves the hydrophilic property of its surface, which results in a larger electrode active area and higher sensitivity. Optimal conditions for nitrite determination with the use of the TrX100/FCVE have been identified. The linear range (LR) and the limit of detection (LOD) are 0.1–100 μM and 0.01 μM, respectively. The relative standard deviation (RSD) does not exceed 2.3%. High selectivity of the sensor ensures its successful application for the analysis of real samples (sausage products and natural water). The obtained results accord well with the results of the standard spectrophotometric method.