Electrochemical Methods for the Analysis of Milk

Electrochemical microfluidic sensing platforms for biosecurity analysis

Biosecurity encompasses the health and safety of humans, animals, plants, and the environment. In this article, "biosecurity" is defined as encompassing the comprehensive aspects of human, animal, plant, and environmental safety. Reliable biosecurity testing technology is the key point for effectively assessing biosecurity risks and ensuring biosecurity. Therefore, it is crucial to develop excellent detection technologies to detect risk factors that can affect biosecurity. An electrochemical microfluidic biosensing platform integrates fluid control, target recognition, signal transduction, and output and incorporates the advantages of electrochemical analysis technology and microfluidic technology. Thus, an electrochemical microfluidic biosensing platform, characterized by exceptional analytical sensitivity, portability, rapid analysis speed, low reagent consumption, and low risk of contamination, shows considerable promise for biosecurity detection compared to traditional, more complex, and time-consuming detection technologies. This review provides a concise introduction to electrochemical microfluidic biosensors and biosecurity. It highlights recent research advances in utilizing electrochemical microfluidic biosensing platforms to assess biosecurity risk factors. It includes the use of electrochemical microfluidic biosensors for the detection of risk factors directly endangering biosecurity (direct application: namely, risk factors directly endangering the health of human, animals, and plants) and for the detection of risk factors indirectly endangering biosecurity (indirect application: namely, risk factors endangering the safety of food and the environment). Finally, we outline the current challenges and future perspectives of electrochemical microfluidic biosensing platforms.

Disposable electrochemical sensors based on reduced graphene oxide/polyaniline/poly(alizarin red S)-modified integrated carbon electrodes for the detection of ciprofloxacin in milk

An electrochemical sensor based on an electroactive nanocomposite was designed for the first time consisting of electrochemically reduced graphene oxide (ERGO), polyaniline (PANI), and poly(alizarin red S) (PARS) for ciprofloxacin (CIPF) detection. The ERGO/PANI/PARS-modified screen-printed carbon electrode (SPCE) was constructed through a three-step electrochemical protocol and characterized using FTIR, UV-visible spectroscopy, FESEM, CV, LSV, and EIS. The new electrochemical CIPF sensor demonstrated a low detection limit of 0.0021 μM, a broad linear range of 0.01 to 69.8 μM, a high sensitivity of 5.09 μA/μM/cm2, and reasonable selectivity and reproducibility. Moreover, the ERGO/PANI/PARS/SPCE was successfully utilized to determine CIPF in milk with good recoveries and relative standard deviation (< 5%), which were close to those with HPLC analysis.

Sulfhydryl-functionalized 3D MXene-AuNPs enabled electrochemical sensors for the selective determination of Pb2+, Cu2+ and Hg2+ in grain

Herein, we made 3D MXene-AuNPs by in situ growth of gold nanoparticles (AuNPs) on the surface of MXene by chemical reduction method, and then introduced three sulfhydryl (-SH) compounds as functionalized modifiers attached to the AuNPs to form a highly selective composite material for the detection of Pb2+, Cu2+, and Hg2+, respectively. The doping of AuNPs changes the microstructure of 2D MXene and generates more active sites. On a sensing platform based on ITO array electrodes, the detection system was optimised with sensitivities up to 1.157, 0.846 and 0.799 μA·μg-1Lcm-2 (Pb2+, Cu2+, and Hg2+). The selectivity of MXene@AuNPs was effectively improved by sulfhydryl group modification. In the range of 1-1300 μg L-1, the detection limits of three ions were 0.07, 0.13 and 0.21 μg L-1. In addition, this method can efficiently and accurately detect heavy metal ions in four cereal samples with consistent results with inductively coupled plasma mass spectrometry.

Non-enzymatic electrochemical detection of melamine in dairy products by using CuO decorated carbon nanotubes nanocomposites

Melamine, a typical nitrogen enriched organic compound exhibiting great potential in the industrial sector, is exploited as an adulterant to inflate protein levels in dairy products, can pose serious threats to humans and therefore necessitates its swift detection and precise quantification at its first exposure. In this investigation, sensitive and reliable sensor probes were fabricated using CuO nanoparticles and its nanocomposites (NCs) with carbon nanotubes (CNTs), carbon black (CB), and graphene oxide (GO) to promptly quantify melamine in dairy products. The optical, morphological, and structural characteristics of the CuO-CNT NCs were achieved using diverse instrumental techniques including UV-visible spectroscopy, transmission electron microscopy, X- ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy and etc. The fabrication of glassy carbon electrodes (GCE) was accomplished by coating CuO-CNT NCs through a binder (5 % nafion). These sensor probes demonstrated outstanding electrochemical sensor performance with CuO-CNT NCs/Nafion/GCE sensor probe in terms of very low limit of detection (0.27 nM), good linearity range (0.05-0.5 nM), and relatively high sensitivity (93.924 µA µM-1 m-2) for melamine under optimized experimental conditions. Furthermore, the performance of CuO-CNT NCs/Nafion/GCE coated sensor probes was practically validated for the selective melamine detection in the real sample analysis of commercially available milk brands, which revealed significant figures of merit in a very short response time of 10 s. From the results, it was concluded that the current study might be helpful in the development of an efficient commercial sensor based on ultra-sensitive transition metal oxides in the field of health care monitoring, food stuffs in a broader scale as well as food applications.

Self-Responsive Fluorescence Aptasensor for Lactoferrin Determination in Dairy Products

In this study, a self-responsive fluorescence aptasensor was established for the determination of lactoferrin (Lf) in dairy products. Herein, the aptamer itself functions as both a recognition element that specifically binds to Lf and a fluorescent signal reporter in conjunction with fluorescent moiety. In the presence of Lf, the aptamer preferentially binds to Lf due to its specific and high-affinity recognition by folding into a self-assembled and three-dimensional spatial structure. Meanwhile, its reduced spatial distance in the aptamer-Lf complex induces a FRET phenomenon based on the quenching of 6-FAM by amino acids in the Lf protein, resulting in a turn-off of the fluorescence of the system. As a result, the Lf concentration can be determined straightforwardly corresponding to the change in the self-responsive fluorescence signal. Under the optimized conditions, good linearities (R2 > 0.99) were achieved in an Lf concentration range of 2~10 μg/mL for both standard solutions and the spiked matrix, as well as with the desirable detection limits of 0.68 μg/mL and 0.46 μg/mL, respectively. Moreover, the fluorescence aptasensor exhibited reliable recoveries (89.5-104.3%) in terms of detecting Lf in three commercial samples, which is comparable to the accuracy of the HPCE method. The fluorescence aptasensor offers a user-friendly, cost-efficient, and promising sensor platform for point-of-need detection.

Research progress of microfluidics-based food safety detection

High demands for food safety detection and analysis have been advocated with people's increasing living standards. Even though numerous analytical testing techniques have been proposed, their widespread adoption is still constrained by the high limit of detection, narrow detection ranges, and high implementation costs. Due to their advantages, such as reduced sample and reagent consumption, high sensitivity, automation, low cost, and portability, using microfluidic devices for food safety monitoring has generated significant interest. This review provides a comprehensive overview of the latest microfluidic detection platforms (published in recent 4 years) and their applications in food safety, aiming to provide references for developing efficient research strategies for food contaminant detection and facilitating the transition of these platforms from laboratory research to practical field use.

A voltammetric peptide biosensor for Cu2+ metal ion quantification in coffee seeds

A prion-derived copper(II)-binding peptide was assembled onto a gold electrode for the building of a voltammetric biosensor for measuring the Cu2+ metal ion in biological samples. The chosen sequence was H-CVNITKQHTVTTTT-NH2, with an appended cysteine residue for binding to the gold surface as a self-assembled monolayer and a histidine residue as the anchorage point for copper(II) complexation. The biosensor showed a linear range of 10-7 to 10-6 M with an 8.0 × 10-8 M detection limit and a 1.0 × 10-7 M quantification limit, with good precision, trueness, and absence of matrix effect. The quantification of Cu2+ was performed in the presence of other transition metal ions, such as Zn2+, Cd2+, Fe2+, or Ni2+, which indicates the excellent selectivity of the biosensor. When the modified electrode was applied for measuring copper(II) in calcined coffee seeds, a difference in copper amount was observed between two Coffea arabica cultivars that were submitted to a treatment with a copper-based antifungal, showing the applicability of the biosensor in the agricultural field.

Bimetallic Cu-Zn Zeolitic Imidazolate Frameworks as Peroxidase Mimics for the Detection of Hydrogen Peroxide: Electrochemical and Spectrophotometric Evaluation

A copper incorporated zeolitic imidazolate framework-8 (ZIF-8) has been synthesized and demonstrated to be a potential material for a peroxidase mimic. The resultant bimetallic Cu-Zn incorporated MOF is used for the dual mode sensing of hydrogen peroxide by following electrochemical as well as spectrophotometric methods. Using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate, spectrophotometric studies are carried out, and the steady state kinetic parameters are determined for two different concentrations of Cu incorporated ZIF-8 (viz Cu@ZIF-8-1 and Cu@ZIF-8-2). It is found that both Cu@ZIF-8-1 and Cu@ZIF-8-2 exhibit more affinity toward the TMB substrate than the horseradish peroxidase (HRP) enzyme as indicated by the low Km values obtained for the substrate. Also, as the concentration of incorporated Cu increases, Vmax values are also found to be enhanced. Electrochemically, the Cu@ZIF-8 modified glassy carbon electrode (GCE) showed a good response for peroxide detection in the concentration range from 0.5 mM to 5 mM at a working potential of -0.25 V in PBS (pH 7.0) with a limit of detection (LOD) value of 0.46 mM and a sensitivity of 20.25 μA/mM. Further, the chromogenic substrate TMB is successfully immobilized on the electrode surface and subsequently used for the peroxide detection along with Cu@ZIF-8. Here, TMB acts as a mediator and shifted the working potential to 0.1 V in acetate buffer (pH 5.0) in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.499 mM and a sensitivity of 0.097 μA/mM. Interestingly, the same electrode in PBS of pH 7.0 showed a response to peroxide at a working potential of -0.1 V in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.143 mM and a sensitivity of 0.33 μA/mM. Moreover, the applicability of this material for peroxide sensing is evaluated using milk samples, and the proposed material is able to recover the peroxide present in milk. Thus, the bimetallic Cu-Zn MOF can be utilized for the dual mode sensing of peroxide and can be extended for various real time applications.

On-Demand Portable Paper-Based Electrospray Ionization Mass Spectrometry for High-Sensitivity Analysis of Complex Samples

Paper spray ionization has been demonstrated to be the most promising substrate-based source, but this technique suffers from the low desorption efficiency of target compounds and poor portability. In the current study, we describe a portable paper-based electrospray ionization (PPESI) in which a piece of triangle paper and adsorbent are packed sequentially into a modified disposable micropipette tip. This source not only captures the feature of paper spray and adsorbent for highly efficient suppression of sample matrixes for target compound analysis but also takes advantage of a micropipette tip to prevent spray solvent from rapid evaporation. The performance of developed PPESI depends on the type and amount of packed adsorbent, paper substrate, and spray solvent and applied voltage. Moreover, by contrast to other related sources, the analytical sensitivity and the spray duration of PPESI in tandem with MS have been improved by factors of 2.8-32.3 and 2.0-13.3, respectively. Based on its high accuracy (>96%) and precision (less than 3% relative standard deviation), the PPESI coupled to a mass spectrometer has been used to determine diverse therapeutic drugs and pesticides in complex biological (e.g., whole blood, serum, and urine) and food (e.g., milk and orange juice) matrixes, and the limits of detection and quantification were 2-4 pg mL^-1 and 7-13 pg mL^-1, respectively. Taking the portability, high sensitivity, and repeatability, the technique may be a promising alternative for complex sample analysis.

Three-dimensional porous high boron-nitrogen-doped carbon for the ultrasensitive electrochemical detection of trace heavy metals in food samples

Exposure to even trace amounts of Cd(II) and Pb(II) in food can have serious effects on the human body. Therefore, the development of novel electrochemical sensors that can accurately detect the different toxicity levels of heavy metal ions in food is of great significance. Based on the principle of green chemistry, we propose a new type of boron and nitrogen co-doped carbon (BCN) material derived from a metal-organic framework material and study its synthesis, characterization, and heavy-metal ion detection ability. Under the optimum conditions, the BCN-modified glassy carbon electrode was studied using square-wave anodic stripping voltammetry, which showed good electrochemical responses to Cd(II) and Pb(II), with sensitivities as low as 0.459 and 0.509 μA/μM cm², respectively. The sensor was successfully used to detect Cd(II) and Pb(II) in Beta vulgaris var. cicla L samples, which is consistent with the results obtained using inductively coupled plasma-mass spectrometry. It also has a strong selectivity for complex samples. This study provides a novel approach for the detection of heavy metal ions in food and greatly expands the application of heteroatom-doped metal-free carbon materials in detection platforms.

A portable electrochemiluminescence aptasensor for β-lactoglobulin detection

Cow’s milk allergy is one of the most common food allergies in children with a prevalence of around 2.5%. Milk contains several allergens; the main ones are caseins and β-lactoglobulin (β-LG). At regulatory level, β-LG is not explicitly named, but milk is included in the list of substances or products causing allergies or intolerances. Hence, the presence of β-LG can be a useful marker for determining the presence of milk in food. In this work, we present an aptasensor based on electrochemiluminescence (ECL) for the quantification of β-LG in real food matrices displaying integrated advantages consisting of high specificity, good sensitivity, portability, and cost effectiveness. The performance and applicability of this sensor were tested by analyzing a sample of skimmed milk and an oat-based drink proposed as a vegetable substitute for milk of animal origin. We obtained a linear correlation between the intensity of the signal and the concentration of β-LG standard solutions (y = x * 0.00653 + 1.038, R² = 0.99). The limit of detection (LOD) and the limit of quantification (LOQ) were found to be 1.36 and 4.55 μg L⁻¹, respectively.

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met.

Nanographene-based electrochemical sensors for ultrasensitive determination of sorbic acid from food

Ultrasensitive determination of sorbic acid in food is essential for the assessment of the food quality. Therefore, two sensors based on nanographene decorated with gold nanoparticle paste modified with metal porphyrins (Zn protoporphyrin IX, and 2,3,7,8,12,13,17,18 octaethyl, 21H, 23H-porphirine Mn(III) chloride) were proposed for the determination of sorbic acid in food (bakery products and mayonnaise). Square-wave voltammetry was used for the characterization and validation of the proposed sensors. Response characteristics showed that the limits of detection for both sensors were 0.33 µmol L^-1 while the limits of quantification were 1.00 µmol L^-1. Both sensors can be used for the determination of sorbic acid in the concentration range 1-1000 µmol L^-1, the linear concentration range making them appropriate for the assay of sorbic acid in food. The highest sensitivity (0.35 nA/µmol L^-1) was recorded when the sensor based on 2,3,7,8,12,13,17,18 octaethyl, 21H, 23H-porphirine Mn(III) chloride was used, proving the higher electrocatalytic effect of this electrocatalyst versus the one of the Zn protoporphyrin IX. High recoveries (values higher than 95.00%) and low RSD (%) values (lower than 5.00%) were recorded for both sensors when used for the determination of sorbic acid in bread and mayonnaise, proving the high reliability of the proposed sensors and method.

Recent Advances in Electrochemical Sensing Strategies for Food Allergen Detection

Food allergy has been indicated as the most frequent adverse reaction to food ingredients over the past few years. Since the only way to avoid the occurrence of allergic phenomena is to eliminate allergenic foods, it is essential to have complete and accurate information on the components of foodstuff. In this framework, it is mandatory and crucial to provide fast, cost-effective, affordable, and reliable analysis methods for the screening of specific allergen content in food products. This review reports the research advancements concerning food allergen detection, involving electrochemical biosensors. It focuses on the sensing strategies evidencing different types of recognition elements such as antibodies, nucleic acids, and cells, among others, the nanomaterial role, the several electrochemical techniques involved and last, but not least, the ad hoc electrodic surface modification approaches. Moreover, a selection of the most recent electrochemical sensors for allergen detection are reported and critically analyzed in terms of the sensors’ analytical performances. Finally, advantages, limitations, and potentialities for practical applications of electrochemical biosensors for allergens are discussed.

Electrochemical Sensing of Vanillin Based on Fluorine-Doped Reduced Graphene Oxide Decorated with Gold Nanoparticles

4-hydroxy-3-methoxybenzaldehyde (vanillin) is a biophenol compound that is relatively abundant in the world’s most popular flavoring ingredient, natural vanilla. As a powerful antioxidant chemical with beneficial antimicrobial properties, vanillin is not only used as a flavoring agent in food, beverages, perfumery, and pharmaceutical products, it may also be employed as a food-preserving agent, and to fight against yeast and molds. The widespread use of vanilla in major industries warrants the need to develop simple and cost-effective strategies for the quantitative determination of its major component, vanillin. Herein, we explore the applications of a selective and sensitive electrochemical sensor (Au electrodeposited on a fluorine-doped reduced-graphene-oxide-modified glassy-carbon electrode (Au/F-rGO/GCE)) for the detection of vanillin. The electrochemical performance and analytical capabilities of this novel electrochemical sensor were investigated using electrochemical techniques including cyclic voltammetry and differential pulse voltammetry. The excellent sensitivity, selectivity, and reproducibility of the proposed electrochemical sensor may be attributed to the high conductivity and surface area of the formed nanocomposite. The high performance of the sensor developed in the present study was further demonstrated with real-sample analysis.

An updated review on properties, nanodelivery systems, and analytical methods for the determination of 5-fluorouracil in pharmaceutical and biological samples

Abstract:

5-Fluorouracil (5-FU) is an antimetabolite drug used for over 70 years as first-line chemotherapy to treat various types of cancer, such as head, neck, breast and colorectal cancer. 5-FU acts mainly by inhibiting thymidylate synthase, thereby interfering with deoxyribonucleic acid (DNA) replication or by 5-FU incorporating into DNA, causing damage to the sequence of nucleotides. Being analogous to uracil, 5-FU enters cells using the same transport mechanism, where a is converted into active metabolites such as fluorouridine triphosphate (FUTP), fluorodeoxyuridine monophosphate (FdUMP), and fluorodeoxyuridine triphosphate (FdUTP). Currently, there are several nanodelivery systems being developed and evaluated at the preclinical level to overcome existing limitations to 5-FU chemotherapy, including liposomes, polymeric nanoparticles, polymeric micelles, nanoemulsions, mesoporous silica nanoparticles, and solid lipid nanoparticles. Therefore, it is essential to choose and develop suitable analytical methods for the quantification of 5-FU and its metabolites (5-fluorouridine and 5-fluoro-2-deoxyuridine) in pharmaceutical and biological samples. Among the analytical techniques, chromatographic methods are commonly the most used for the quantification of 5-FU from different matrices. However, other analytical methods have also been developed for the determination of 5-FU, such as electrochemical methods, a sensitive, selective, and precise technique, in addition to having a reduced cost. Here, we first review the physicochemical properties, mechanism of action, and advances in 5-FU nanodelivery systems. Next, we summarize the current progress of other chromatographic methods described to determine 5-FU. Lastly, we discuss the advantages of electrochemical methods for the identification and quantification of 5-FU and its metabolites in pharmaceutical and biological samples.