A novel reduced graphene oxide/molybdenum disulfide/polyaniline nanocomposite-based electrochemical aptasensor for detection of aflatoxin B1

A signal-on electrochemical aptasensor for rapid detection of aflatoxin B1 based on competition with complementary DNA

Aflatoxin B1 (AFB1) is the most toxic mycotoxin, causing harmful effects on human and animal health, and the rapid and sensitive detection of AFB1 is highly demanded. We developed a simple electrochemical aptasensor achieving rapid detection of aflatoxin B1 (AFB1). A short anti-AFB1 aptamer having a methylene blue (MB) redox tag at the 3'-end was immobilized on the surface of a gold electrode. In the absence of AFB1, a complementary DNA (cDNA) strand hybridized with the MB-labeled aptamer, causing MB apart from the electrode surface and low current of MB. In the presence of AFB1, AFB1 competed with the cDNA in the binding to the MB-labeled aptamer, and the aptamer-AFB1 binding caused formation of a hairpin structure, making the MB close to the electrode surface and current of MB increase. Under optimized conditions, we achieved detection of AFB1 over dynamic concentration range of 2 nM-4 μM by using this signal-on electrochemical aptasensor. This method only required a simple 5-min incubation of sample solution prior to rapid electrochemical sensing, more rapid than other electrochemical aptasensors. The sensor could be well regenerated and reused. This sensor allowed to detect AFB1 spiked in 20-fold diluted beer and 50-fold diluted white wine, respectively. It shows potential for detection of AFB1 in wide applications.

A simple fluorescent aptamer based assay coupled with fluorescence scanning capillary array for aflatoxin B1

We developed a simple aptamer fluorescence assay for aflatoxin B1 (AFB1) detection by using an array of capillaries. The 34-nt aptamer having a single fluorescein (FAM) label on the 24th T nucleotide generated a remarkable fluorescence increase upon AFB1 binding. The use of fluorescence scanning capillary array allowed for the analysis of multiple samples with low sample consumption, showing advantages of simplicity, rapidity and high throughput analysis. The detection limit of AFB1 reached 0.5 nM. This assay has great potential for analysis in food safety and environmental monitoring.

Electrochemical Immuno- and Aptasensors for Mycotoxin Determination

Modern analysis of food and feed is mostly focused on development of fast and reliable portable devices intended for field applications. In this review, electrochemical biosensors based on immunological reactions and aptamers are considered in the determination of mycotoxins as one of most common contaminants able to negatively affect human health. The characteristics of biosensors are considered from the point of view of general principles of bioreceptor implementation and signal transduction providing sub-nanomolar detection limits of mycotoxins. Moreover, the modern trends of bioreceptor selection and modification are discussed as well as future trends of biosensor development for mycotoxin determination are considered.

GO-amplified fluorescence polarization assay for high-sensitivity detection of aflatoxin B1 with low dosage aptamer probe

Aflatoxin B₁ (AFB₁) is the most toxic mycotoxin of the aflatoxins (AFs) and shows carcinogenic, teratogenic and mutagenic effects in humans and animals. AFB₁ is widely seen in cereal products such as rice and wheat. This research proposed a low-cost, high-sensitivity fluorescence polarization (FP) assay for detection of AFB₁ using aptamer biosensors based on graphene oxide (GO). The aptamers labelled with fluorescein amidite (FAM) were adsorbed on the surface of GO through π-π stacking and electrostatic interaction, thus forming aptamer/GO macromolecular complexes. Under these conditions, the local rotation of fluorophores was limited and the system had a high FP value. When there was AFB₁ in the system, aptamers were dissociated from the GO surface and combined with AFB₁ owing to their specificity to form aptamer/AFB₁ complexes. As a result, large changes were observed in the molecular weights of aptamers before, and after, the combination, therefore leading to the apparent changes in FP value. The results showed that when only 10 nM of aptamer was used, the changes in FP and the AFB₁ concentration had a favourable linear relationship within 0.05 to 5 nM of AFB₁, and the lowest detection limit (LOD) was 0.05 nM. In addition, the recoveries of rice sample extract ranged from 89.2% to 112%. The method is simple, highly sensitive, cost-efficient and shows potential application prospects.

Electrochemical sensor based on a three dimensional nanostructured MoS2 nanosphere-PANI/reduced graphene oxide composite for simultaneous detection of ascorbic acid, dopamine, and uric acid

A three dimensional (3D) nanostructured composite based on the self-assembly of MoS₂ nanospheres and polyaniline (PANI) loaded on reduced graphene oxide (denoted by 3D MoS₂-PANI/rGO) was prepared via a feasible one-pot hydrothermal process. The 3D MoS₂-PANI/rGO nanocomposite not only exhibits good functionality and bioaffinity but also displays high electrochemical catalytic activity. As such, the developed 3D MoS₂-PANI/rGO nanocomposite can be employed as the sensing platform for simultaneously detecting small biomolecules, i.e., ascorbic acid (AA), dopamine (DA), and uric acid (UA). The peak currents obtained from the differential pulse voltammetry (DPV) measurements depended linearly on the concentrations in the wide range from 50 μM to 8.0 mM, 5.0 to 500 μM, and 1.0 to 500 μM, giving low detection limits of 22.20, 0.70, and 0.36 μM for AA, DA, and UA, respectively. Furthermore, the 3D MoS₂-PANI/rGO-based electrochemical sensor also exhibited high selectivity, good reproducibility and stability toward small molecule detection. The present sensing strategy based on 3D MoS₂-PANI/rGO suggests a good reliability in the trace determination of electroactive biomolecules.

A three dimensional (3D) nanostructured composite based on the self-assembly of MoS₂ nanospheres and polyaniline (PANI) loaded on reduced graphene oxide (denoted by 3D MoS₂-PANI/rGO) was prepared via a feasible one-pot hydrothermal process.

Label-Free Impedance Sensing of Aflatoxin B₁ with Polyaniline Nanofibers/Au Nanoparticle Electrode Array

Aflatoxin B1 (AFB₁) is produced by the Aspergillus flavus and Aspergillus parasiticus group of fungi which is most hepatotoxic and hepatocarcinogenic and occurs as a contaminant in a variety of foods. AFB₁ is mutagenic, teratogenic, and causes immunosuppression in animals and is mostly found in peanuts, corn, and food grains. Therefore, novel methodologies of sensitive and expedient strategy are often required to detect mycotoxins at the lowest level. Herein, we report an electrochemical impedance sensor that selectively detects AFB₁ at the lowest level by utilizing polyaniline nanofibers (PANI) coated with gold (Au) nanoparticles composite based indium tin oxide (ITO) disk electrodes. The Au-PANI nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and electrochemical impedance spectroscopy (EIS). The composite electrode exhibited a 14-fold decrement in |Z|1Hz in comparison with the bare electrode. The Au-PANI acted as an effective sensing platform having high surface area, electrochemical conductivity, and biocompatibility which enabled greater loading deposits of capture antibodies. As a result, the presence of AFB₁ was screened with high sensitivity and stability by monitoring the changes in impedance magnitude (|Z|) in the presence of a standard iron probe which was target specific and proportional to logarithmic AFB₁ concentrations (CAFB₁). The sensor exhibits a linear range 0.1 to 100 ng/mL with a detection limit (3) of 0.05 ng/mL and possesses good reproducibility and high selectivity against another fungal mycotoxin, Ochratoxin A (OTA). With regard to the practicability, the proposed sensor was successfully applied to spiked corn samples and proved excellent potential for AFB₁ detection and development of point-of-care (POC) disease sensing applications.