Electrochemical oxidation of ochratoxin A at a glassy carbon electrode and in situ evaluation of the interaction with deoxyribonucleic acid using an electrochemical deoxyribonucleic acid-biosensor

Rational design of molecularly imprinted electrochemical sensor based on Nb2C-MWCNTs heterostructures for highly sensitive and selective detection of Ochratoxin a

Developing an efficient method for screening Ochratoxin A (OTA) in agriculture products is vital to ensure food safety and human health. However, the complex food matrix seriously affects the sensitivity and accuracy. To address this issue, we designed a novel molecularly imprinted polymer (MIP) electrochemical sensor based on multiwalled carbon nanotube-modified niobium carbide (Nb2C-MWCNTs) with the aid of the density functional theory (DFT). In this design, a glassy carbon electrode (GCE) was first modified by Nb2C-MWCNTs heterostructure. Afterward, the MIP layer was prepared, with ortho-toluidine as a functional monomer selected via DFT and OTA acting as a template on the surface of Nb2C-MWCNTs/GCE using in-situ electropolymerization. Electrochemical tests and physical characterization revealed that Nb2C-MWCNTs improved the sensor's active surface area and electron transmission capacity. Nb2C-MWCNTs had a good synergistic effect on MIP, endowing the sensor with high sensitivity and specific recognition of OTA in complex food matrix systems. The MIP sensor showed a wide linear range from 0.04 to 10.0 μM with a limit of detection (LOD) of 3.6 nM. Moreover, it presented good repeatability and stability for its highly antifouling effect on OTA. In real sample analysis, the recoveries, ranging from 89.77% to 103.70%, agreed well with the results obtained by HPLC methods, suggesting the sensor has good accuracy and high potential in practical applications.

Rapid and inexpensive voltammetric detection of ochratoxin A in wheat matrices

Produced as toxic metabolites by fungi, mycotoxins, such as ochratoxin A (OTA), contaminate grain and animal feed and cause great economic losses. Herein, we report the fabrication of an electrochemical sensor consisting of an inexpensive and label-free carbon black-graphite paste electrode (CB-G-CPE), which was fully optimized to detect OTA in durum wheat matrices using differential pulse voltammetry (DPV). The effect of carbon paste composition, electrolyte pH and DPV parameters were studied to determine the optimum conditions for the electroanalytical determination of OTA. Full factorial and central composite experimental designs (FFD and CCD) were used to optimize DPV parameters, namely pulse width, pulse height, step height and step time. The developed electrochemical sensor successfully detected OTA with detection and quantification limits equal to 57.2 nM (0.023 µg mL^-1) and 190.6 nM (0.077 µg mL^-1), respectively. The accuracy and precision of the presented CB-G-CPE was used to successfully quantify OTA in real wheat matrices. This study presents an inexpensive and user-friendly method with potential applications in grain quality control.

Simultaneous voltammetric determination of 7-methyl-guanine and 5-methyl-cytosine using a cathodically pre-treated boron-doped diamond electrode

Given the importance of identifying the presence of biomarkers of human diseases in DNA samples, the main objective of this work was to investigate, for the first time, the electro-catalytic oxidation of 7-methyl-guanine (7-mGua) and 5-methyl-cytosine (5-mCyt) on a boron doped diamond electrode pre-treated cathodically (red-BDDE), using differential pulse voltammetry (DPV) and cyclic voltammetry (CV). The anodic peak potentials of 7-mGua and 5-mCyt by DPV were at E = 1.04 V and E = 1.37 V at pH = 4.5, indicating excellent peak separation of approximately 330 mV between species. Using DPV, experimental conditions such as supporting electrolyte, pH and influence of interferents were also investigated to develop a sensitive and selective method for individual and simultaneous quantification of these biomarkers. The analytical curves for the simultaneous quantification of 7-mGua and 5-mCyt in the acid medium (pH = 4.5) were: concentration range of 0.50-5.00 μmol L^-1 (r = 0.999), detection limit of 0.27 μmol L^-1 for 7-mGua; from 3.00 to 25.00 μmol L^-1 (r = 0.998), with a detection limit of 1.69 μmol L^-1 for 5-mCyt. A new DP voltammetric method for the simultaneous detection and quantification of biomarkers 7-mGua and 5-mCyt using a red-BDDE is proposed.

Multiwalled carbon nanotubes modified two dimensional MXene with high antifouling property for sensitive detection of ochratoxin A

Electrochemical sensor has great potential in the detection of small molecules by virtues of low cost, fast response, and easy to miniaturization. However, electrochemical sensing of ochratoxin A (OTA) was seriously hindered by the heavy electrode-fouling effect and poor electrochemical activity inherent from OTA molecular. Herein, two-dimensional titanium carbide (2D Ti₃C₂) MXene incorporated with carboxylic multiwalled carbon nanotubes (cMWCNTs) was developed as a glassy carbon electrode modifier for rapid and sensitive detection of OTA. Physical characterizations combined with electrochemical techniques revealed that cMWCNTs can not only prevent the restacking of 2D Ti₃C₂nanosheets but also facile its electron transfer, leading to a nanohybrid with a high specific surface and good electrocatalytic activity to OTA. Under optimal conditions, the electrochemical sensor showed a good linear response to OTA in a concentration range from 0.09 to 10μmol·l^-1and a low detection limit (LOD) of 0.028μmol·l^-1. The proposed sensor was impelled successive times to detect OTA, a good repeatability was obtained, indicating the constructed sensor possessed good anti-fouling property. Moreover, satisfactory recoveries between 91.8% and 103.2% were obtained in the real sample analysis of grape and beer, showing that the developed sensing technique is reliable for the screening of trace OTA in food resources.

The Degradation of Deoxynivalenol by Using Electrochemical Oxidation with Graphite Electrodes and the Toxicity Assessment of Degradation Products

Deoxynivalenol (DON) is a common mycotoxin, which is known to be extremely harmful to human and livestock health. In this study, DON was degraded by electrochemical oxidation (ECO) using a graphite electrode and NaCl as the supporting electrolyte. The graphite electrode is advantageous due to its electrocatalytic activity, reusability, and security. The degradation process can be expressed by first-order kinetics. Approximately 86.4% of DON can be degraded within 30 min at a potential of 0.5 V. The degradation rate reached 93.2% within 30 min, when 0.5 V potential was used for electrocatalyzing a 10 mg/L DON solution. The degradation rate of DON in contaminated wet distiller's grain with solubles (WDGS) was 86.37% in 60 min. Moreover, results from the cell counting kit-8 (CCK-8) and 4,6-diamidino-2-phenylindole dihydrochloride (DAPI) staining assay indicated that ECO reduced the DON-induced cytotoxicity and apoptotic bodies in a gastric epithelial cell line (GES-1) compared to the DON-treated group. These findings provide new insights into the application of ECO techniques for degrading mycotoxins, preventing food contamination, and assessing DON-related hazards.

Impedimetric aptasensor for ochratoxin A determination based on Au nanoparticles stabilized with hyper-branched polymer

An impedimetric aptasensor for ochratoxin A (OTA) detection has been developed on the base of a gold electrode covered with a new modifier consisting of electropolymerized Neutral Red and a mixture of Au nanoparticles suspended in the dendrimeric polymer Botlorn H30®. Thiolated aptamer specific to OTA was covalently attached to Au nanoparticles via Au-S bonding. The interaction of the aptamer with OTA induced the conformational switch of the aptamer from linear to guanine quadruplex form followed by consolidation of the surface layer and an increase of the charge transfer resistance. The aptasensor makes it possible to detect from 0.1 to 100 nM of OTA (limit of detection: 0.02 nM) in the presence of at least 50 fold excess of ochratoxin B. The applicability of the aptasensor for real sample assay was confirmed by testing spiked beer samples. The recovery of 2 nM OTA was found to be 70% for light beer and 78% for dark beer.

Electrochemical affinity biosensors for detection of mycotoxins: A review

This review discusses the current state of electrochemical biosensors in the determination of mycotoxins in foods. Mycotoxins are highly toxic secondary metabolites produced by molds. The acute toxicity of these results in serious human and animal health problems, although it has been only since early 1960s when the first studied aflatoxins were found to be carcinogenic. Mycotoxins affect a broad range of agricultural products, most important cereals and cereal-based foods. A majority of countries, mentioning especially the European Union, have established preventive programs to control contamination and strict laws of the permitted levels in foods. Official methods of analysis of mycotoxins normally requires sophisticated instrumentation, e.g. liquid chromatography with fluorescence or mass detectors, combined with extraction procedures for sample preparation. For about sixteen years, the use of simpler and faster analytical procedures based on affinity biosensors has emerged in scientific literature as a very promising alternative, particularly electrochemical (i.e., amperometric, impedance, potentiometric or conductimetric) affinity biosensors due to their simplicity and sensitivity. Typically, electrochemical biosensors for mycotoxins use specific antibodies or aptamers as affinity ligands, although recombinant antibodies, artificial receptors and molecular imprinted polymers show potential utility. This article deals with recent advances in electrochemical affinity biosensors for mycotoxins and covers complete literature from the first reports about sixteen years ago.

Femtogram ultrasensitive aptasensor for the detection of Ochratoxin A

A simple and ultrasensitive method was developed for the detection of Ochratoxin A, utilizing an aptamer as a molecular recognition probe and real-time quantitative PCR (RT-qPCR) amplification of its complementary DNA as signal generators. Under the optimized conditions, the cycle threshold (Ct) increased linearly with 10-fold serial dilutions of Ochratoxin A (OTA) from 5×10⁻⁶ to 5 ng mL⁻¹, with a limit of detection (LOD) of 1 fg mL⁻¹. The specificity of this aptasensor was considered to be excellent, as when tested against four other toxins it produced no obvious Ct value change. Furthermore, a satisfactory analyte concentration recovery was obtained from a series of concentrations of OTA spiked into red wine. Therefore, this highly sensitive approach shows a significant potential in a wide range of target analytes.

Triazole-acridine conjugates: redox mechanisms and in situ electrochemical evaluation of interaction with double-stranded DNA

Redox mechanisms and in situ electrochemical interaction with double-stranded DNA were investigated using a DNA-electrochemical biosensor for two disubstituted triazole-linked acridine compounds (GL15 and GL7), previously reporting as quadruplex DNA-binding molecules. The redox properties of GL15 and GL7 involve a complex, pH-dependent, adsorption-controlled irreversible process and were investigated using cyclic, differential pulse, and square wave voltammetry at a glassy carbon electrode. The interaction between duplex DNA and GL15 or GL7 was investigated in incubated solutions using dsDNA-, poly[G]-, and poly[A]-electrochemical biosensors. It was demonstrated that the interaction is time-dependent, both GL15 and GL7 interacting with dsDNA, causing condensation of dsDNA morphological structure but not oxidative damage.

Synthetic toxicology: where engineering meets biology and toxicology

This article examines the implications of synthetic biology (SB) for toxicological sciences. Starting with a working definition of SB, we describe its current subfields, namely, DNA synthesis, the engineering of DNA-based biological circuits, minimal genome research, attempts to construct protocells and synthetic cells, and efforts to diversify the biochemistry of life through xenobiology. Based on the most important techniques, tools, and expected applications in SB, we describe the ramifications of SB for toxicology under the label of synthetic toxicology. We differentiate between cases where SB offers opportunities for toxicology and where SB poses challenges for toxicology. Among the opportunities, we identified the assistance of SB to construct novel toxicity testing platforms, define new toxicity-pathway assays, explore the potential of SB to improve in vivo biotransformation of toxins, present novel biosensors developed by SB for environmental toxicology, discuss cell-free protein synthesis of toxins, reflect on the contribution to toxic use reduction, and the democratization of toxicology through do-it-yourself biology. Among the identified challenges for toxicology, we identify synthetic toxins and novel xenobiotics, biosecurity and dual-use considerations, the potential bridging of toxic substances and infectious agents, and do-it-yourself toxin production.

Rapid visual tests: fast and reliable detection of ochratoxin A

This paper reviews the early detection strategies that have been employed for the rapid monitoring of ochratoxin A (OTA) contamination of food. OTA, a mycotoxin mainly produced by some Aspergillus and Penicillium species, is found in cereals, coffee, wine, pork and grapes. To minimize the entry of this mycotoxin into the food chain, rapid diagnostic tools are required. To this end, the potential use of lateral flow devices has also been developed. In this study, we analyze the robustness of test strips using published methods for colorimetric detection. Different test formats are discussed, and challenges in the development of lateral flow devices for on-site determination of OTA, with requirements such as robustness, speed, and cost-effectiveness, are discussed.

Sensitive enzyme-biosensor based on screen-printed electrodes for Ochratoxin A

Horseradish peroxidase has been successfully immobilized in a polypyrrole matrix onto disposable screen-printed carbon electrodes for the selective detection of Ochratoxin A. The chronoamperometric determination of this mycotoxin has been optimized by experimental design methodology, which implied the join evaluation of pH of the buffer solution, applied potential and concentration of H(2)O(2). The slopes of the calibration curves built under the optimum conditions of the experimental variables have been used to estimate the reproducibility and the repeatability of the developed biosensor for Ochratoxin A. Relative standard deviation values of 1.9% (n=5 and alpha=0.05) and 7.1% (n=4 and alpha=0.05) were obtained for reproducibility and repeatability, respectively. The capability of detection for this method was 0.1 ng mL(-1) (alpha=0.05 and beta<0.05). The viability of the developed biosensor in the determination of Ochratoxin A in spiked beer and in roasted coffee has been shown, yielding average recoveries of 103% and 99%, in that order, with relative standard deviation values less than 5% (n=3 and alpha=0.05) in both cases.

Label-free impedimetric immunosensor for sensitive detection of ochratoxin A

A novel label-free electrochemical impedimetric immunosensor for sensitive detection of ochratoxin A (OTA) was reported. A two-step reaction protocol was elaborated to modify the gold electrode. The electrode was first derivatized by electrochemical reduction of in situ generated 4-carboxyphenyl diazonium salt (4-CPDS) in acidic aqueous solution yielded stable 4-carboxyphenyl (4-CP) monolayer. The ochratoxin A antibody was then immobilized making use of the carbodiimide chemistry. The steps of the immunosensor elaboration and the immunochemical reaction between ochratoxin A and the surface-bound antibody were interrogated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The impedance change, due to the specific immuno-interaction at the immunosensor surface was utilized to detect ochratoxin A. The increase in electron-transfer resistance (DeltaR(et)) values was linearly proportional to the concentration of OTA in the range of 1-20ngmL(-1), with a detection limit of 0.5ngmL(-1).

Sensors and Biosensors for the Determination of Small Molecule Biological Toxins

The following review of sensors and biosensors focuses on the determination of commonly studied small molecule biological toxins, including mycotoxins and small molecule neurotoxins. Because of the high toxicity of small molecule toxins, an effective analysis technique for determining their toxicity is indispensable. Sensors and biosensors have emerged as sensitive and rapid techniques for toxicity analysis in the past decade. Several different sensors for the determination of mycotoxins and other small molecule neurotoxins have been reported in the literature, and many of these sensors such as tissue biosensors, enzyme sensors, optical immunosensors, electrochemical sensors, quartz crystal sensors, and surface plasmon resonance biosensors are reviewed in this paper. Sensors are a practical and convenient monitoring tool in the area of routine analysis, and their specificity, sensitivity, reproducibility and analysis stability should all be improved in future work. In addition, accuracy field portable sensing devices and multiplexing analysis devices will be important requirement for the future.