Simultaneous Hg2+ and Pb2+ detection in water samples using an electrochemical aptasensor with dual signal amplification by exonuclease III and metal-organic frameworks.

Heavy metal pollution in the environment has become a significant global concern due to its detrimental effects on human health and the environment. In this study, we report an electrochemical aptasensor for the simultaneous detection of Hg2+ and Pb2+. Gold nanoflower/polyethyleneimine-reduced graphene oxide (AuNFs/PEI-rGO) was introduced on the surface of a gold electrode to improve sensing performance. The aptasensor is based on the formation of a T-Hg2+-T mismatch structure and specific cleavage of the Pb2+-dependent DNAzyme, resulting in a dual signal generated by the Exo III specific digestion of methylene blue (MB) labeled at the 3' end of probe DNA-1 and the reduction of the substrate ascorbic acid (AA) catalyzed by the signal label. The decrease of MB signal and the increase of AA oxidation peak was used to indicate the content of Hg2+ and Pb2+, respectively, with detection limits of 0.11 pM (Hg2+) and 0.093 pM (Pb2+). The aptasensor was also used for detecting Hg2+ and Pb2+ in water samples with good recoveries. Overall, this electrochemical aptasensor shows promising potential for sensitive and selective detection of heavy metals in environmental samples.

Simultaneous Determination of Aflatoxin B1 and Ochratoxin A in Cereals by a Novel Electrochemical Aptasensor Using Metal-Organic Framework as Signal Carrier.

A novel electrochemical aptasensor was prepared for the simultaneous determination of aflatoxin B1 (AFB1) and ochratoxin A (OTA). Composites of Au nanoparticles and polyethyleneimine-reduced graphene oxide (AuNPs/PEI-RGO) with good electrical conductivity and high specific surface area were employed as the supporting substrate, demonstrating the ability to provide more binding sites for aptamers and accelerate the electron transfer. Aptamers were immobilized on a AuNPs/PEI-RGO surface to specifically recognize AFB1 and OTA. A metal-organic framework of UiO-66-NH2 served as the signal carrier to load metal ions of Cu2+ and Pb2+, which facilitated the generation of independent current peaks and effectively improved the electrochemical signals. The prepared aptasensor exhibited sensitive current responses for AFB1 and OTA with a linear range of 0.01 to 1000 ng/mL, with detection limits of 6.2 ng/L for AFB1 and 3.7 ng/L for OTA, respectively. The aptasensor was applied to detect AFB1 and OTA in cereal samples, achieving results comparable with HPLC-MS, with recovery results from 92.5% to 104.1%. With these merits of high sensitivity and good selectivity and stability, the prepared aptasensor proved to be a powerful tool for evaluating contaminated cereals.

Ultrasensitive label-free electrochemical aptasensor for Pb2+ detection exploiting Exo III amplification and AgPt/GO nanocomposite-enhanced transduction.

Lead ion pollution has become a serious public health concern worldwide. Therefore, sensitive detection of Pb2+ is critical to control lead pollution, assess risks, and safeguard the health of vulnerable populations. This study reports a highly sensitive labelling-free electrochemical aptasensor for Pb2+ detection. The aptasensor employs silver-platinum nanoparticles/graphene oxide (AgPt/GO) and Exonuclease III (Exo III) for signal amplification. GO provides high surface area and conductivity for immobilizing AgPt NPs, facilitating the immobilization of aptamer (Apt) probes on the electrode surface. Exo III enzymatically cleaves DNA strands on the electrode surface, releasing DNA segments to amplify the signal further. The synergistic amplification by AgPt/GO and ExoIII enables an extremely wide linear detection range of 0.05 pM-5 nM for Pb2+, with a low detection limit of 0.019 pM. Additionally, the G-quadruplex structure ensures excellent selectivity for Pb2+ detection, resulting in high reproducibility and stability of the aptasensor. The aptasensor was successfully applied to detect spiked Pb2+ in tap water samples, achieving recovery rates ranging from 96 to 108.4 %. By integrating nanomaterials, aptamers and enzymatic amplification, the aptasensor facilitates highly sensitive and selective detection of Pb2+, demonstrating potential for practical applications in environmental monitoring.

A novel electrochemical aptasensor based on AgPdNPs/PEI-GO and hollow nanobox-like Pt@Ni-CoHNBs for procymidone detection.

Herein, an aptasensor based on a signal amplification strategy was developed for the sensitive detection of procymidone (PCM). AgPd nanoparticles/Polenimine Graphite oxide (AgPdNPs/PEI-GO) was weaned as electrode modification material to facilitate electron transport and increase the active sites on the electrode surface. Besides, Pt@Ni-Co nanoboxes (Pt@Ni-CoHNBs) were utilized to be carriers for signaling tags, after hollowing ZIF-67 and growing Pt, the resulting Pt@Ni-CoHNBs has a tremendous amounts of folds occurred on the surface, enables it to carry a larger quantity of thionine, thus amplify the detectable electrochemical signal. In the presence of PCM, the binding of PCM to the signal probe would trigger a change in electrical signal. The aptasensor was demonstrated with excellent sensitivity and a low detection limit of 0.98 pg·mL-1, along with a wide linear range of 1 µg·mL-1 to 1 pg·mL-1. Meanwhile, the specificity, stability and reproducibility of the constructed aptasensor were proved to be satisfactory.

A fluorescence-electrochemical dual-mode aptasensor based on novel DNA-dependent PBNFs@PtPd for highly selective and sensitive detection of procymidone through hybridization chain reaction.

Herein, a study for the first application of a hybridization chain reaction, a 1,8-naphthalimides-DNA (NDs) intercalator, and DNA-dependent Prussian blue nanoflowers@PtPd materials (PBNFs@PtPd) in the development of a fluorescence-electrochemical (FL-EC) aptasensor. This construction establishes an efficient sensing platform for the detection of procymidone (PCM). In the context of the described experiment, dual-mode detection is achieved through the generation of FL signals by an aptamer labeled with a Cy5 moiety and the formation of DPV signals by the modification of a thionine-appended 1,8-naphthalimide (Thi-NDs). In the presence of PCM, specific recognition occurs, followed by the utilization of magnetic separation technology to release DNA1 (S1) and aptamer-Cy5 (Apt-Cy5), subsequently introducing them onto both fluorescence and EC platforms. The presence of S1 effectively activates hybridization chain reaction (HCR) for the electrode surface, thereby significantly increasing the binding sites for Thi-NDs and consequently greatly amplifying the response signal of differential pulse voltammetry (DPV). The developed FL-EC dual-mode sensing platform demonstrates high sensitivity in the detection of PCM, with the detection limits of 0.173 µg·ml-1 (within the detection range of 500 pg·ml-1 to 500 ng·ml-1) and 0.074 ng·ml-1 (within the detection range of 100 pg·ml-1 to 100 ng·ml-1), respectively. The designed dual-mode sensor exhibits notable characteristics, including high selectivity, reproducibility, synergy, and reliable monitoring/capability for PCM in real samples.

"Two-in-One" PtPdCu Trimetallic Multifunctional Nanoparticles-Mediated Dual-Signal-Integrated Aptasensor for Ultradetection of Enrofloxacin.

Balancing the accuracy and simplicity of aptasensors is a challenge in their construction. This study addresses this issue by leveraging the remarkable loading capacity and peroxidase-like catalytic activity of PtPdCu trimetallic nanoparticles, which reduces the reliance on precious metals. A dual-signal readout aptasensor for enrofloxacin (ENR) detection is designed, incorporating DNA dynamic network cascade reactions to further amplify the output signal. Exploiting the strong loading capacity of PtPdCu nanoparticles, they are self-assembled with thionine (Thi) to form a signal label capable of generating signals in two independent modes. The label exhibits excellent enzyme-like catalytic activity and enhances electron transfer capabilities. Differential pulse voltammetry (DPV) and square-wave voltammetry (SWV) are employed to independently read signals from the oxidation-reduction reaction of Thi and the catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) by H2O2. The introduced DNA dynamic network cascade reaction modularizes sample processing and electrode surface signal generation, avoiding electrode contamination and efficiently increasing the output of the catalyzed hairpin assembly (CHA) cycle. Under optimized conditions, the developed aptasensor demonstrates detection limits of 0.112 (DPV mode) and 0.0203 pg/mL (SWV mode). Additionally, the sensor successfully detected enrofloxacin in real samples, expanding avenues for designing dual-mode signal amplification strategies.

A dual-signal ratiometric electrochemical aptasensor based on Thi/Au/ZIF-8 and catalytic hairpin assembly for ultra-sensitive detection of aflatoxin B1.

A dual-signal ratiometric electrochemical aptasensor has been developed  for AFB1 detection using thionine/Au/zeolitic imidazolate framework-8 (Thi/Au/ZIF-8) nanomaterials and catalytic hairpin assembly (CHA) reaction. Thi/Au/ZIF-8 combined with DNA hairpin 2 (H2) was used as a signal probe. [Fe(CN)6]3-/4- was served as another signal probe, and the IThi/Au/ZIF-8/I[Fe(CN)6]3-/4- ratio was for the first time utilized to quantify AFB1. AFB1-induced CHA was used to expand the ratio of electrical signals. In the presence of AFB1, H2/Thi/Au/ZIF-8 bound to the electrode via CHA, enhanced  the current signal of Thi/Au/ZIF-8. H2 contained the DNA phosphate backbone hindered [Fe(CN)6]3-/4- redox reaction and resulted in a lower [Fe(CN)6]3-/4- current signal. This aptasensor exhibited high specificity for AFB1, a linear range of 0.1 pg mL-1 to 100 ng mL-1, and a detection limit of 0.089 pg mL-1. It demonstrated favorable sensitivity, selectivity, stability, and repeatability. The aptasensor was suitable for detecting AFB1 in peanuts and black tea and holds potential for real sample applications.

Pt@AuNF nanozyme and horseradish peroxidase-based lateral flow immunoassay dual enzymes signal amplification strategy for sensitive detection of zearalenone.

Lateral flow immunoassay (LFIA) has been employed extensively for the rapid, accurate, and portable detection of foodborne toxins. Here, the platinum gold nanoflower core-shell (Pt@AuNF) nanozyme with excellent optical properties, good catalytic ability and controllable reaction conditions were prepared to effectively improve the performance of lateral flow immunoassay (LFIA) strips. The Pt@AuNF nanozyme and horseradish peroxidase (HRP) combined with monoclonal antibody were used as signal probes based on the dual enzymes catalytic signal amplification strategy to detect Zearalenone sensitively. Dual enzymes catalyze the decomposition of hydrogen peroxide into hydroxyl radicals, and under the influence of hydroxyl radicals, colorless 3,3',5,5' -tetramethylbenzidine (TMB) is oxidized to blue ox-TMB, which is superimposed on the strips for signal amplification to broaden the detection range. The limit of detection (LOD) of the Pt@AuNF-HRP labeled LFIA strips after signal amplification was 0.052 ng/mL, and the detection range was 0.052-7.21 ng/mL. Compared with the Pt@AuNF labeled strips, while reducing the probes amount by half to achieve antibody conservation, the detection range was expanded by 5-fold based on achieving improved sensitivity. The study provided a meaningful reference for expanding the detection range based on immunoassay.

Mn2+-Triggered Swing-Arm Robot Strategy Using Anemone-Like Thi@AuPd@Cu-MOFs as Signaling Probes for the Detection of T-2 Toxin.

Herein, we synthesized anemone-like copper-based metal-organic frameworks (MOFs) loaded with gold-palladium nanoparticles (AuPd@Cu-MOFs) and polyethylenimine-reduced graphene oxide/gold-silver nanosheet composites (PEI-rGO/AuAg NSs) for the first time to construct the sensor and to detect T-2 toxin (T-2) using triple helix molecular switch (THMS) and signal amplification by swing-arm robot. The aptasensor used PEI-rGO/hexagonal AuAg NSs as the electrode modification materials and anemone-like AuPd@Cu-MOFs as the signal materials. The prepared PEI-rGO/hexagonal AuAg NSs had a large specific surface area, excellent electrical conductivity, and good stability, which successfully improved the electrochemical performance of the sensors. The AuPd@Cu-MOFs with high porosity provided a great deal of attachment sites for the signaling molecule thionine (Thi), thereby increasing the signal response. The aptasensor developed in this study demonstrated a remarkable detection limit of 0.054 fg mL-1 under optimized conditions. Furthermore, the successful detection of T-2 in real samples was achieved using the fabricated sensor. The simplicity of the THMS-based method, which entails modifying the aptamer sequence, allows for easy adaptation to different target analytes. Thus, the sensor holds immense potential for applications in quality supervision and food safety.

A novel magneto-mediated electrochemical biosensor integrated DNAzyme motor and hollow nanobox-like Pt@Ni-Co electrocatalyst as dual signal amplifiers for vanilla detection.

Herein, a novel magneto-mediated electrochemical aptasensor using the signal amplification technologies of DNAzyme motor and electrocatalyst for vanilla (VAN) detection was fabricated. The D/B duplex, formed by the DNAzyme motor that was each silenced by a blocker, and hairpin DNA1 (H1) containing adenosine ribonucleotide (rA) site were tethered on the sites of the gold nanoparticles@hollow porphyrinic-Metal-organic framework/polyethyleneimine-reduced graphene oxide (AuHPCN-222/PEI-rGO)-modified gold electrode (AuE). Then, after homogeneous and specific recognition in the presence of the VAN, trigger DNA was released and enriched by magnetic separation technique and introduced to the sensing platform to activate the DNAzyme motor, which efficiently improved target recognition capability and avoided the obstacle of multiple DNA strands tangling. More interestingly, the activated DNAzyme motor could repeatedly bind to and cleave H1 in the presence of Mg2+, leading to the exposure of a plethora of capture probes. The thionine (Thi) functionalized hairpin DNA2 (H2)-Pt@Ni-Co as signal probes could hybridize with capture probes. Additionally, the Pt@Ni-Co electrocatalysts presented catalytic activity towards Thi to obtain stronger electrochemical signals. VAN with concentrations ranging from 1 × 10-6 to 10 µM was determined and a detection limit was down to 0.15 pM. The designed electrochemical sensor was highly selective with specificity, stability, reproducibility, and reliable capability for monitoring the VAN in real samples.

Construction of an electrochemical-fluorescent dual-mode sensor with a dual-mode signal AgNC probe synthesized from cytosine-rich DNA for OTA detection.

Herein, we have used DNA-silver nanocluster (DNA-AgNC) signal probes with both electrochemical and fluorescent signals for the first time to construct an electrochemical-fluorescent dual-mode sensor. The sensor has an easy-to-prepare dual-signal property combined with the magnetic separation technique for dual-mode detection of ochratoxin A (OTA). In the absence of OTA, the DNA strand used to synthesize AgNCs was not available in the system after magnetic separation. DNA-AgNCs probes could not be synthesized in the system, resulting in low fluorescence and electrochemical signals. In the presence of OTA, it led to the shedding of sulfhydryl-modified and cytosine-rich DNA (C-DNA). DNA-AgNCs probes with high fluorescence and electrochemical signals were formed by adding AgNO3 and NaBH4 to the supernatant after magnetic separation. Dual-mode detection of OTA was achieved by the signal response of fluorescence and electrochemistry. The detection ranges were 2.5 × 10-4-50 ng mL-1 and 2.5 × 10-4-25 ng mL-1 in the fluorescence mode and electrochemical mode with detection limits of 0.11 pg mL-1 and 0.025 pg mL-1, respectively. Meanwhile, the dual-mode sensor displayed better specificity, repeatability and reproducibility than conventional electrochemical and fluorescent single-mode sensors. The results of the spiked peanut and wheat flour detection showed that the fluorescence and electrochemical modes of the sensor exhibited satisfactory average recoveries.

A novel fluorescent aptasensor based on 3D porous nitrogen-sulfur co-doped carbon mesh and hybridization chain reaction for sensitive detection of ochratoxin A.

A novel three-dimensional (3D) porous nitrogen-sulfur co-doped carbon (N-S-C) mesh was synthesized and used for the first time as the quenching material to construct a fluorescent aptasensor for ochratoxin A (OTA) detection. The fluorescent aptasensor with enzyme-free signal amplification strategy was developed by using cDNA as a promoter to trigger hybridization chain reaction (HCR), which effectively improved the sensitivity of this aptasensor. In the absence of OTA, 3D porous N-S-C mesh can adsorb carboxyfluorescein FAM-labeled hairpin DNA1 (H1-FAM) and hairpin DNA2 (H2) and quench the fluorescence of FAM. In the presence of the OTA, the OTA specifically binds to the aptamer strand and the DNA duplex undergoes dissociation. The released cDNA in turn serves as a promoter for HCR, and the strand assembly of H1-FAM and H2 is triggered by the promoter to generate long-strand DNA polymers via HCR, resulting in an increasing fluorescent signal. Under optimal conditions, there was a good linear relationship between lgCOTA and fluorescence intensity difference in the range 0.01-500 ng/mL (R2 = 0.993), and the detection limit was 2.7 pg/mL. The designed sensor platform was applied to determine spiked OTA in peanut, wheat flour, corn flour, black tea, and wine with recoveries in the range of 94.4-119.6%.

A convenient fluorescent/electrochemical dual-mode biosensor for accurate detection of Pb2+ based on DNAzyme cycle.

The presence of heavy metals in the ecological environment is a serious threat to human health. Therefore, it is very important to establish a simple and sensitive method for the detection of heavy metals. Currently, most of the methods are single-channel sensing, and these methods are prone to false-positive signals, which reduces the accuracy. In this work, Pb2+-DNAzyme was immobilized on magnetic beads (MBs) using a linkage of biotin and streptavidin and successfully applied to the construction of a fluorescent/electrochemical dual-mode (DM) biosensor. The supernatant after magnetic separation formed a double strand on the electrode, which was combined with methylene blue (MB) for electrochemical detection (EC). At the same time, FAM-d was added to the precipitate, and after magnetic separation, the supernatant was subjected to fluorescent detection (FL). Under optimal conditions, the signal response of the constructed dual-mode biosensor showed a good linear relationship with the concentration of Pb2+. The DNAzyme-based dual-mode biosensor achieved sensitive and selective detection of Pb2+ with good accuracy and reliability, opening a new way for the development of biosensing strategies for the detection of Pb2+. More importantly, the sensor has high sensitivity and accuracy for the detection of Pb2+ in actual sample analysis.

Electrochemical aptasensor based on exonuclease III-mediated signal amplification for sensitive detection of vomitoxin in cornmeal.

Vomitoxin (DON) residues in grains are of great concern to public health. Herein, a label-free aptasensor was constructed to detect DON distributed in grains. Cerium-based metal-organic framework composite gold nanoparticles (CeMOF@Au) were used as substrate materials to facilitate electron transfer and provided more binding sites for DNA. The separation of DON-aptamer (Apt) complex and cDNA was achieved by magnetic separation technique based on magnetic beads (MBs), ensuring the specificity of the aptasensor. Exonuclease III (Exo III)-assisted cDNA cycling process strategy would be triggered when cDNA was separated and introduced to the sensing interface for further signal amplification. Under optimal conditions, the constructed aptasensor presented a wide detection range from 1 × 10-8 mg·mL-1 to 5 × 10-4 mg·mL-1 for DON, and the detection limit was 1.79 × 10-9 mg·mL-1, including a satisfactory recovery in cornmeal sample spiked with DON. The results showed that the proposed aptasensor had high reliability and promising application potential in detecting DON.

AgPdNFs and AuNOs@GO nanocomposites for T-2 toxin detection by catalytic hairpin assembly.

T-2 toxin is the most potent and toxic mycotoxin, produced by various Fusarium species that can potentially affect human health, and widely exists in field crops and stored grain. In this work, an electrochemical aptasensor with nonenzymatic signal amplification strategy for the detection of T-2 toxin is presented, using noble metal nanocomposites and catalytic hairpin assembly as signal amplification strategy. Silver palladium nanoflowers and gold octahedron nanoparticles@graphene oxide nanocomposites are used for synergistic amplification of electrical signals. Simultaneously, the catalytic hairpin assembly strategy based on artificial molecular technology was introduced to further amplify the signal. Under optimal conditions, T-2 toxin was measured within a linear concentration range 1 × 10-2 ~ 1 × 104 pg·mL-1 with an extremely low detection limit of 6.71 fg·mL-1. The aptasensor exhibited high sensitivity, good selectivity, satisfactory stability, and excellent reproducibility. Moreover, this method had high accuracy in detecting T-2 toxin in beer sample. The encouraging results show the potential application in foodstuff analysis. A dual signal amplification electrochemical biosensor for the detection of T-2 toxins was constructed, through the signal amplification of noble metal nanomaterials and CHA strategy.

An efficient electrochemical biosensor for the detection of heavy metal lead in food based on magnetic separation strategy and Y-DNA structure.

Herein, an electrochemical biosensor was developed based on a magnetic separation strategy for the sensitive detection of the heavy metal Pb2+. The specific binding of Pb2+ and the aptamer (Apt) is used to trigger the release of the complementary chain (cDNA) on the magnetic bead system. The cDNA completes base complementary pairing with hairpins HP1 and HP2 at the electrode to form a Y-DNA structure. Then, the Y-DNA runs continuously with the assistance of the signal tag methylene blue (MB) and the current signal increases. However, in the absence of Pb2+, cDNA cannot be released and the Y-DNA structure cannot be formed on the electrode, resulting in a relatively low current signal. Under the optimal experimental conditions, the reduced peak current difference (ΔI) showed a good linear relationship with lg CPb2+ between 0.1 and 1000 nM, with a detection limit of 5.9 pM. In addition, the stability, reproducibility and detection capability of the sensors were investigated with satisfactory results.

Latest strategies for rapid and point of care detection of mycotoxins in food: A review.

Mycotoxins contaminated in agricultural products are often highly carcinogenic and genotoxic to humans. With the streamlining of the food industry chain and the improvement of food safety requirements, the traditional laboratory testing mode is constantly challenged due to the expensive equipment, complex operation steps, and lag in testing results. Therefore, rapid detection methods are urgently needed in the food safety system. This review focuses on the latest strategies that can achieve rapid and on-site testing, with particular attention to the nanomaterials integrated biosensors. To provide researchers with the latest trends and inspiration in the field of rapid detection, we summarize several strategies suitable for point of care testing (POCT) of mycotoxins, including enzyme-linked immunoassay (ELISA), lateral flow assay (LFA), fluorescence, electrochemistry, and colorimetry assay. POCT-based strategies are all developing towards intelligence and portability, especially when combined with smartphones, making it easier to read signals for intuitive access and analysis of test data. Detection performance of the devices has also improved considerably with the integration of biosensors and nanomaterials.

A convenient paper-based fluorescent aptasensor for high-throughput detection of Pb2+ in multiple real samples (water-soil-food).

Lead ion (Pb2+) is one of the most toxic and widely polluted heavy metal ions. Given the potential health risks and economic losses associated with Pb2+, the rapid detection of Pb2+ using fluorescent aptasensors is of significant importance in evaluating food safety. A rapid, facile and economic fluorescent aptasensor using convenient paper as the sensing substrate was designed to high-throughput detect Pb2+ in complex samples within about 45 min. The Pb2+ changed the conformation of FAM-modified Apt from a random coil to a stable G-quadruplex structure. And then Dabcyl-labeled cDNA was added to form double-stranded DNA with the Apt that did not form a G-quadruplex structure, resulting in a weak fluorescence due to the fluorescence resonance energy transfer (FRET). The fluorescent aptasensor showed a positive correlation with Pb2+ concentration, and a linear relationship was obtained in the range of 0.01-10 µM with LOD of 6.1 nM. In addition, this method has been successfully used for the determination of Pb2+ in water, soil and various foods containing complex substrates. Meanwhile, the high-throughput detection of Pb2+ has also reached an acceptable level. Therefore, this convenient strategy has potential application value for on-site rapid detection of Pb2+.

A label-free impedance-based electrochemical sensor based on self-assembled dendritic DNA nanostructures for Pb2+ detection.

Here, a label-free impedance-based electrochemical sensor was developed for the quantitative detection of Pb2+. Using conductive gold nanomaterials as electrode substrate materials can provide sensors with larger specific surface area, action sites and excellent conductivity. DNA nanostructures are used for the determination of biomolecules due to their good properties. The Y-DNA structure is formed by the annealing of three DNA sequences, which acts as a stable structure and forms a dendritic structure in combination with the hybrid chain reaction. In the presence of the target Pb2+, it induces the conversion of specific aptamers into G-quadruplexes, resulting in HCR and Y-DNA loading on the electrodes and a significant change in the impedance value signal. Therefore, the proposed biosensor realizes the quantitative detection of Pb2+. Under the optimal experimental conditions, the concentration of Pb2+ exhibited a linear correlation range from 0.5 to1000 nmol/L with a limit of detection (LOD) of 0.38 nmol/L. The designed sensors have good recoveries in real samples (tap water and tea). This flexible experimental protocol has broad application prospects.

An electrochemical apta-assay based on hybridization chain reaction and aflatoxin B1-driven Ag-DNAzyme as amplification strategy.

Herein, a novel electrochemical apta-assay based on hybridization chain reaction (HCR) and aflatoxin B1-driven Ag-DNAzyme was prepared. The combination of HCR and Ag-DNAzyme was designed for the first time as a dual signal amplification strategy for the detection of mycotoxins. The substrate DNA (sDNA) was fixed to the electrode surface, which contained the RNA A (rA) site and HCR initiation sequence. The sDNA opened the hairpin DNA structures and triggered a cascade of hybridization events. The DNA double strands formed by the HCR bound large amounts of methylene blue (MB). Aptamer and complementary DNA bound to Ag+ by C-Ag+-C complexes. AFB1 can drive Ag+ shedding, and Ag+ induced Ag-DNAzyme to shear the rA site of sDNA. The amount of binding MB decreased and the current signal decreased. Replaced biological enzymes with metal ion-mediated DNAzyme enhanced the stability of the prepared sensors while reducing the preparation cost. An adequate determination of AFB1 in corn flour, walnut powder, and other actual samples are validated, which indicated the good accuracy and potential application in real samples. The strategy is characterized by simple operation, good stability, and low preparation cost, and has good application prospects in food safety and quality control.