Magnetic beads-assisted fluorescence aptasensing approach based on dual DNA tweezers for detection of ochratoxin A and fumonisin B1 in wine and corn

Silver nanocluster-based aptasensor for the label-free and enzyme-free detection of ochratoxin A

Mycotoxin contamination in cereal is a global concern, threatening food safety and human health, necessitating the development of rapid on-site methods. Here, a label- and enzyme-free biosensor was developed based on aptamer-regulated DNA-silver nanoclusters (AgNCs) for rapid detection of ochratoxin A (OTA). A novel DNA-templated AgNCs emitting strong red fluorescence was designed and synthesized in this study. The partial sequence of the DNA template was selected from the complementary OTA aptamer (Apt-OTA) sequence, which can quench fluorescence from the AgNCs via hybridization in the absence of OTA. In the presence of OTA, the high OTA-Aptamer affinity prevented the Apt-OTA from quenching the AgNCs, resulting in "turn on" of the fluorescence. This biosensor eliminated the use of costly reagents, complex pretreatments, and sophisticated equipment, which could realize the point-of-care testing (POCT) of OTA with a limit of detection (LOD) of 1.3 nM and a detection time of 45 min.

Graphene oxide-Mn3O4nanocomposites for advanced electrochemical biosensor for fumonisin B1 detection

Occurrence of mycotoxins in food samples threat to its safety issue due to the presence of high toxicity and carcinogenic behavior, thus requiring highly sensitive and selective detection. Herein, the trimanganese tetraoxide (Mn3O4) nanoparticles in combination with graphene oxide (GO) nanocomposite were used to enhance the electrochemical performance for fabrication of electrochemical biosensor for fumonisin B1 (FB1) detection. The various characterization tools were used to validate the fabrication of GOMn3O4nanocomposites. To fabricate the electrochemical biosensor on an indium tin oxide (ITO) coated glass substrate, a thin film of GOMn3O4nanocomposite was prepared using electrophoretic deposition technique, and antibodies (ab-FB1) were immobilized onto the electrode for selective FB1 detection. The differential pulse voltammetry technique was used to observe the sensing performance. The non-binding sites of the ab-FB1 on the immunoelectrode were blocked with bovine serum albumin (BSA). The biosensor electrode was fabricated as BSA/ab-FB1/GOMn3O4/ITO for the detection of FB1. The sensitivity of the biosensor was obtained as 10.08μA ml ng-1cm-2in the detection range of 1 pg ml-1to 800 ng ml-1with a limit of detection of 0.195 pg ml-1. In addition, the recovery of BSA/ab-FB1/GOMn3O4/ITO immunoelectrodes was also performed on sweet corn samples and is calculated to be 98.91%.

Competitive ELISA based on pH-responsive persistent luminescence nanoparticles for autofluorescence-free biosensor determination of ochratoxin A in cereals

An accurate and sensitive competitive enzyme-linked immunosorbent assay (ELISA) based on persistent luminescence nanoparticles Zn₂GeO₄:Mn²⁺, Eu³⁺ (ZGME) was developed for detecting ochratoxin A (OTA), a powerfully toxic mycotoxin usually found in grains. As a signal output element of autofluorescence-free biosensors, ZGME can be integrated into ELISA with glucose oxidase (GOx)-binding OTA molecules due to its excellent pH-responsive persistent luminescence. In the absence of OTA, the OTA-GOx conjugate was captured by the anti-OTA monoclonal antibody (anti-OTA mAb) pre-coated on the 96-well plate. The results indicate a decrease in the pH value of the solution, which triggered the quenching of ZGME luminescence due to GOx-dependent gluconic acid production. The presence of OTA inhibited the binding of OTA-GOx on the plate, thus decreasing the production of gluconic acid and increasing the persistent luminous intensity of ZGME. Under the optimized concentrations of anti-OTA mAb and OTA-GOx, quantitative determination of OTA was achieved by plotting the increase or decrease in persistent luminescence intensity of ZGME at 535 nm. In this study, the linear range was from 0.1 μg L^-1 to 63 μg L^-1, and the limit of detection (LOD) was as low as 0.045 μg L^-1. In five food samples (corn grit, brown rice, soybean, rice, and wheat), the results exhibited good stability and repeatability, with a recovery range from 81.3% to 94.4% and a relative standard deviation (RSD) of less than 4.2%. Hence, the established method provides a sensitive, accurate, and autofluorescence-free approach for the determination of OTA in different grain samples.

Recent advances in simultaneous detection strategies for multi-mycotoxins in foods

Mycotoxin contamination has become a challenge in the field of food safety testing, given the increasing emphasis on food safety in recent years. Mycotoxins are widely distributed, in heavily polluted areas. Food contamination with these toxins is difficult to prevent and control. Mycotoxins, as are small-molecule toxic metabolites produced by several species belonging to the genera Aspergillus, Fusarium, and Penicillium growing in food. They are considered teratogenic, carcinogenic, and mutagenic to humans and animals. Food systems are often simultaneously contaminated with multiple mycotoxins. Due to the additive or synergistic toxicological effects caused by the co-existence of multiple mycotoxins, their individual detection requires reliable, accurate, and high-throughput techniques. Currently available, methods for the detection of multiple mycotoxins are mainly based on chromatography, spectroscopy (colorimetry, fluorescence, and surface-enhanced Raman scattering), and electrochemistry. This review provides a comprehensive overview of advances in the multiple detection methods of mycotoxins during the recent 5 years. The principles and features of these techniques are described. The practical applications and challenges associated with assays for multiple detection methods of mycotoxins are summarized. The potential for future development and application is discussed in an effort, to provide standards of references for further research.

Modulation of Aptamer-Ligand-Binding by Complementary Oligonucleotides: A G-Quadruplex Anti-Ochratoxin A Aptamer Case Study

Short oligonucleotides are widely used for the construction of aptamer-based sensors and logical bioelements to modulate aptamer-ligand binding. However, relationships between the parameters (length, location of the complementary region) of oligonucleotides and their influence on aptamer-ligand interactions remain unclear. Here, we addressed this task by comparing the effects of short complementary oligonucleotides (ssDNAs) on the structure and ligand-binding ability of an aptamer and identifying ssDNAs' features that determine these effects. Within this, the interactions between the OTA-specific G-quadruplex aptamer 1.12.2 (5'-GATCGGGTGTGGGTGGCGTAAAGGGA GCATCGGACA-3') and 21 single-stranded DNA (ssDNA) oligonucleotides complementary to different regions of the aptamer were studied. Two sets of aptamer-ssDNA dissociation constants were obtained in the absence and in the presence of OTA by isothermal calorimetry and fluorescence anisotropy, respectively. In both sets, the binding constants depend on the number of hydrogen bonds formed in the aptamer-ssDNA complex. The ssDNAs' having more than 23 hydrogen bonds with the aptamer have a lower aptamer dissociation constant than for aptamer-OTA interactions. The ssDNAs' having less than 18 hydrogen bonds did not affect the aptamer-OTA affinity. The location of ssDNA's complementary site in the aptamer affeced the kinetics of the interaction and retention of OTA-binding in aptamer-ssDNA complexes. The location of the ssDNA site in the aptamer G-quadruplex led to its unfolding. In the presence of OTA, the unfolding process was longer and takes from 20 to 70 min. The refolding in the presence of OTA was possible and depends on the length and location of the ssDNA's complementary site. The location of the ssDNA site in the tail region led to its rapid displacement and wasn't affecting the G-qaudruplex's integrity. It makes the tail region more perspective for the development of ssDNA-based tools using this aptamer.