Applications of stripping voltammetric techniques in food analysis

Multifolding Vertical-Flow Electrochemical Paper-Based Devices with Tunable Dual Preconcentration for Enhanced Multiplexed Assays of Heavy Metals

This work describes fully integrated multifolding electrochemical paper-based devices (ePADs) for enhanced multiplexed voltammetric determination of heavy metals (Zn(II), Cd(II), and Pb(II)) using tunable passive preconcentration. The paper devices integrate five circular sample preconcentration layers and a 3-electrode electrochemical cell. The hydrophobic barriers of the devices are drawn by pen-plotting with hydrophobic ink, while the electrodes are deposited by screen-printing. The devices exploit the wicking ability of cellulose paper to perform passive preconcentration of the target analytes, resulting in a ∼6-fold signal enhancement. For this purpose, drops of the sample are placed at the five sample pads of the preconcentration layers, the device is folded, and the target metals are eluted in a vertical-flow mode to the electrochemical cell, where they are measured directly by anodic stripping voltammetry (ASV). The working electrode of the ePADs is bulk-modified with bismuth citrate; during the ASV measurements, the bismuth precursor is converted to nanodomains of metallic bismuth at the surface of the working electrode. By combining the triplex signal amplification through passive preconcentration, electrochemical preconcentration, and judicious working electrode modification with in situ generated bismuth nanoparticles, ultrasensitive and multiplexed heavy metal assays can be achieved. Due to their high degree of integration, low cost, easy and fast fabrication, and sensitivity, the multifolding ePADs are particularly suitable for on-site heavy metals' monitoring applications.

Food Additives and Evolved Methods of Detection: A Review

Food additives are essential constituents of food products in the modern world. The necessity of food processing went up rapidly as to meet requirements including, imparting desirable properties like preservation, enhancement and regulation of color and taste. The methods of identification and analysis of such substances are crucial. With the advancement of technology, a variety of techniques are emerging for this purpose which have many advantages over the existing conventional ways. This review is on different kinds of additives used in the food industry and few prominent methods for their determination ranging from conventional chromatographic techniques to the recently evolved nano-sensor techniques.

Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 μg L-1 and 0.6 μg L-1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals.

One-step electrochemical elaboration of SnO2 modified electrode for lead ion trace detection in drinking water using SWASV

A facile method was proposed for the elaboration of an electrochemical sensor for heavy metal's trace detection by using square wave anodic stripping voltammetry (SWASV); this method is based on a simple anodic conversion of tin electrode into Sn/SnO₂ modified electrode. Both electrochemical and physico-chemical techniques were used to confirm the modification process and better understand the electrode's behavior. Then, depending on the operating conditions, the response signal was studied and adjusted in order to obtain optimal sensor performance. When optimized, the proposed method reached a lowest detection limit (LOD) of 2.15 μg L^-1 (0.0104 μM), and quantification limit (LOQ) of 5.36 μg L^-1 (0.0259 μM), in linearity range between from 6.2 and 20.7 μg L^-1. Additionally, after having used the elaborated electrode for ten successive measurements, the repeatability remains very high with an RSD of approximately 5.3%; furthermore, ten other species appear to have very slight effect on Pb(II) detection. Finally, for the method validation, the proposed electrode was able to sense different lead concentration integrated in a local bottled spring water by showing recovery levels ranging from 103.8 to 108.4%.

Plot-on-demand integrated paper-based sensors for drop-volume voltammetric monitoring of Pb(II) and Cd(II) using a bismuth nanoparticle-modified electrode

The fabrication of fully ink-drawn fluidic electrochemical paper-based analytical devices (ePADs) is reported for the determination of trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The fluidic pattern was formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Then, electrodes were deposited on the devices using a second x-y plotting step with a commercial technical pen filled with a graphite-based conductive ink prepared in house. The fabrication parameters of the ePADs were studied by cyclic voltammetry using the ferro/ferri couple as a probe and by scanning electron microscopy. The ePADs, featuring a bismuth nanoparticle-modified working electrode, were applied to the determination of Pb(II) and Cd(II) by DPASV. The chemical and instrumental conditions were studied. The limits of detection were 3.1 μg L^-1 for Cd(II) and 4.5 μg L^-1 for Pb(II) whereas the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 14%. Each ePAD requires 120 s to fabricate and costs less than 0.15 € in terms of consumables. The ePADs are suitable for the on-site determination of Pb(II) and Cd(II) in environmental and food samples.

Recent Advancement in Disposable Electrode Modified with Nanomaterials for Electrochemical Heavy Metal Sensors

Heavy metal pollution has gained global attention due to its high toxicity and non-biodegradability, even at a low level of exposure. Therefore, the development of a disposable electrode that is sensitive, simple, portable, rapid, and cost-effective as the sensor platform in electrochemical heavy metal detection is vital. Disposable electrodes have been modified with nanomaterials so that excellent electrochemical properties can be obtained. This review highlights the recent progress in the development of numerous types of disposable electrodes modified with nanomaterials for electrochemical heavy metal detection. The disposable electrodes made from carbon-based, glass-based, and paper-based electrodes are reviewed. In particular, the analytical performance, fabrication technique, and integration design of disposable electrodes modified with metal (such as gold, tin and bismuth), carbon (such as carbon nanotube and graphene), and metal oxide (such as iron oxide and zinc oxide) nanomaterials are summarized. In addition, the role of the nanomaterials in improving the electrochemical performance of the modified disposable electrodes is discussed. Finally, the current challenges and future prospect of the disposable electrode modified with nanomaterials are summarized.

Wearable and Mobile Sensors for Personalized Nutrition

While wearable and mobile chemical sensors have experienced tremendous growth over the past decade, their potential for tracking and guiding nutrition has emerged only over the past three years. Currently, guidelines from doctors and dietitians represent the most common approach for maintaining optimal nutrition status. However, such recommendations rely on population averages and do not take into account individual variability in responding to nutrients. Precision nutrition has recently emerged to address the large heterogeneity in individuals' responses to diet, by tailoring nutrition based on the specific requirements of each person. It aims at preventing and managing diseases by formulating personalized dietary interventions to individuals on the basis of their metabolic profile, background, and environmental exposure. Recent advances in digital nutrition technology, including calories-counting mobile apps and wearable motion tracking devices, lack the ability of monitoring nutrition at the molecular level. The realization of effective precision nutrition requires synergy from different sensor modalities in order to make timely reliable predictions and efficient feedback. This work reviews key opportunities and challenges toward the successful realization of effective wearable and mobile nutrition monitoring platforms. Non-invasive wearable and mobile electrochemical sensors, capable of monitoring temporal chemical variations upon the intake of food and supplements, are excellent candidates to bridge the gap between digital and biochemical analyses for a successful personalized nutrition approach. By providing timely (previously unavailable) dietary information, such wearable and mobile sensors offer the guidance necessary for supporting dietary behavior change toward a managed nutritional balance. Coupling of the rapidly emerging wearable chemical sensing devices-generating enormous dynamic analytical data-with efficient data-fusion and data-mining methods that identify patterns and make predictions is expected to revolutionize dietary decision-making toward effective precision nutrition.

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp² content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

Synthetic Food Dyes – Some Aspects Of Use And Methods Of Determination

Color is one of the key ingredients for increasing the appetizing of food, so food dyes have become firmly established in food production technologies. However, with the acquisition of toxicity data of synthetic food dyes (SFD), there were restrictions and standards for their content in food have emerged. Numerous papers published in recent years demonstrate the importance of the problem of the use and definition of SFD. The review contains over 180 literary references in the field of usage and methods of determination of synthetic food dyes, among them regulatory documents (regulations), official internet resources of international and Ukrainian organizations, review articles and original works. Varieties of chromatography, enzyme-linked immunoassay, optical and electrochemical methods are used to identify and determine SFD. Special attention was paid to voltammetry (VA) as a method that is cheaper than chromatography and completely satisfies selectivity, sensitivity, reliability requirements and is compatible with the concept of green analytical chemistry, as it doesn't need organic solvents. Moreover, single sweep voltammetry can be considered as a screening method with low limits of determination and rapid respons

Multielements determination and metal transfer investigation in herb medicine Bupleuri Radix by inductively coupled plasma-mass spectrometry

Bupleuri Radix is a famous traditional Chinese medicine (TCM) and an important raw material in TCM patent prescriptions. It is widely used in several countries, including China, Japan, South Korea, and America. However, the impact of heavy metal transfer rules on TCMs remains unknown. In this study, a total of 45 paired original medicines (OMs), decoction pieces (DPs), and vinegar-processed (VPs) samples were simultaneously determined via inductively coupled plasma-mass spectrometry after a microwave digestion. The concentrations of the elements were shown at three levels: (a) Al and Fe at the mg/g level; (b) Pb, Cu, Ba, Mn, Cr, and Ni at the mg/kg level; (c) Co, As, Cd, and Hg at μg/kg level. It is worth noting that the Cu levels were found to exceed the maximum concentration set by Chinese legislation (20.0 mg/kg). In addition, Mn, Ni, and Cu levels were higher in samples from the Gansu province than those from other provinces. The accumulation of the heavy metals decreased in the order of OMs > DPs > VPs; this was especially true for the Al and Fe levels. Furthermore, the results indicate that decocting the samples may reduce the intake of heavy metals. The element transfer ratios for decoctions were under 50% compared to herbal medicines and decreased in the order of Co > As > Mn > Hg > other metals. Our study strongly suggests that long-term and regular monitoring for heavy metals in the plant is necessary.

Electrode Modified by Reduced Graphene Oxide for Monitoring of Total Thallium in Grain Products

Grain products and the associated industry have a notable economic and social impact all over the world. The toxicological safety of grain products is a nutritional prerogative. This study focused on the determination of thallium content in grain product samples collected from a commercial brand commonly available in Poland. The samples were analyzed with the use of differential pulse anodic stripping voltammetry (DPASV) with graphene oxide based on glassy carbon. The stripping anodic peak current of thallium was linear over its concentration range from 9.78 × 10⁻⁹ to 97.8 × 10⁻⁹ M. The limit of detection (LOD) was calculated according to the formula LOD = (κ × SDa)/b, where κ is 3.3, SDa is the standard deviation of the intercept, and b is the slope. The determined value of LOD was 1.229 µg L⁻¹ (6.01 × 10⁻⁹ M). The proposed method was successfully applied for the determination of thallium ions in samples of actual grain products. The obtained results confirmed that thallium was present in the studied cereal samples (average content at 0.0268 ± 0.0798 mg/kg). Thallium has a half-life of 60 days; therefore, the consumption of foods with thallium content of approximately 0.08 mg/kg has the potential for harmful bioaccumulation in the body. Thallium contamination in cereal products should be a critical parameter for health environmental regulations.

Ultra-wide-range electrochemical sensing using continuous electrospun carbon nanofibers with high densities of states

Carbon-based sensors for wide-range electrochemical detection of redox-active chemical and biological molecules were fabricated by the electrospinning of polyacrylonitrile fibers directly onto a polyacrylonitrile-coated substrate followed by carbonization at 1200 °C. The resulting electrospun carbon nanofibers (ECNFs) were firmly attached to the substrate with good mesh integrity and had high densities of electronic states (DOS), which was achieved without need for further modifications or the use of any additives. The mass of ECNFs deposited, and thus the electroactive surface area (ESA) of the sensor, was adjusted by varying the electrospinning deposition time, thereby enabling the systematic manipulation of the dynamic range of the sensor. A standard redox probe (Fe(CN)6(3-/4-)) was used to demonstrate that the ECNF sensor exhibits strong electrocatalytic activity without current saturation at high analyte concentrations. Dopamine was used as a model analyte to evaluate the sensor performance; we find that the ECNF device exhibits a dynamic range ∼10(5) greater than that of many existing carbon-based sensors. The ECNF sensors exhibited excellent sensitivity, selectivity, stability, and reproducibility for dopamine detection.

Competitive biosorption of Yellow 2G and Reactive Brilliant Red K-2G onto inactive aerobic granules: simultaneous determination of two dyes by first-order derivative spectrophotometry and isotherm studies

This study focused on the competitive biosorption of Yellow 2G (Y2G) and Reactive Brilliant Red K-2G (RBR) by inactive aerobic granules in binary solutions. A first-order derivative spectrophotometric method for the simultaneous determination of Y2G and RBR in binary solutions was developed. Dubinin-Raduskevich (D-R) isotherm successfully predicted the biosorption of Y2G and RBR in both single and binary solutions. However, none of the tested binary adsorption isotherms could realistically represent the biosorption equilibrium data. Maximum biosorption capacity calculated from D-R isotherm for Y2G and RBR in single solution was 58.50 and 66.18 mg g(-1), respectively; in binary solutions, for Y2G it decreased to 40.38 mg g(-1), but for RBR it increased to 171.21 mg g(-1), showing their synergism and antagonistic interactions. The FTIR results indicated the main functional groups on aerobic granules for biosorption of Y2G and RBR would be amine, hydroxyl, carboxyl and either.