An ultrasensitive electrochemical aptasensor based on Pd@PCN-222 as a signal probe coupled with exonuclease III-assisted cycling amplification for the detection of ochratoxin A

Nucleic acid aptamer based thermally oxidized porous silicon/zinc oxide microarray chip for detection of ochratoxin A in cereals

A nucleic acid aptamer based thermally oxidized porous silicon/zinc oxide microarray chip was constructed for the detection of ochratoxin A. The hybrid chains formed by aptamer and complementary chains labeled with fluorescent groups and fluorescent burst groups were used as recognition molecules, and the detection of toxins was accomplished on the chip by the principle of fluorescence signal burst and recovery. The modified QuEChERS method was used for sample pretreatment and the performance of the method was evaluated. The results showed that the linear range was 0.02 ∼ 200 ng/kg with the detection limit of 0.0196 ng/kg under the optimal detection conditions. The method was applied to different cereals with the recoveries of 90.30 ∼ 111.69 %. The developed microarray chip has the advantages of being cost-effective, easy to prepare, sensitive and specific, and can provide a new method for the detection of other toxins.

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.

CRISPR-powered microfluidic biosensor for preamplification-free detection of ochratoxin A

The CRISPR technology, which does not require complex instruments, expensive reagents or professional operators, has attracted a lot of attention. When utilizing the CRISPR-Cas system for detection, the pre-amplification step is often necessary to enhance sensitivity. However, this approach tends to introduce complexity and prolong the time required. To address this issue, we employed Pd@PCN-222 nanozyme to label single-stranded DNA, referred to as Pd@PCN-222 CRISPR nanozyme, which serves as the reporter of the CRISPR system. Pd@PCN-222 nanozyme possess exceptional catalytic activity for the reduction of H2O2. Compared with traditional electrochemical probe ferrocene and methylene blue without catalytic activity, there is a significant amplification of the electrochemical signal. So the need for pre-amplification was eliminated. In this study, we constructed a CRISPR-Cas system for ochratoxin A, utilizing the Pd@PCN-222 CRISPR nanozyme to amplified signal avoiding pre-amplification with outstanding detection of 1.21 pg/mL. Furthermore, we developed a microfluidic electrochemical chip for the on-site detection of ochratoxin A. This achievement holds significant promise in establishing a practical on-site detection platform for identifying food safety hazards.

The Application of Hybridization Chain Reaction in the Detection of Foodborne Pathogens

Today, with the globalization of the food trade progressing, food safety continues to warrant widespread attention. Foodborne diseases caused by contaminated food, including foodborne pathogens, seriously threaten public health and the economy. This has led to the development of more sensitive and accurate methods for detecting pathogenic bacteria. Many signal amplification techniques have been used to improve the sensitivity of foodborne pathogen detection. Among them, hybridization chain reaction (HCR), an isothermal nucleic acid hybridization signal amplification technique, has received increasing attention due to its enzyme-free and isothermal characteristics, and pathogenic bacteria detection methods using HCR for signal amplification have experienced rapid development in the last five years. In this review, we first describe the development of detection technologies for food contaminants represented by pathogens and introduce the fundamental principles, classifications, and characteristics of HCR. Furthermore, we highlight the application of various biosensors based on HCR nucleic acid amplification technology in detecting foodborne pathogens. Lastly, we summarize and offer insights into the prospects of HCR technology and its application in pathogen detection.

Strategy of functional nucleic acids-mediated isothermal amplification for detection of foodborne microbial contaminants: A review

Foodborne microbial contamination (FMC) is the leading cause of food poisoning and foodborne illness. The foodborne microbial detection methods based on isothermal amplification have high sensitivity and short detection time, and functional nucleic acids (FNAs) could extend the detectable object of isothermal amplification to mycotoxins. Therefore, the strategy of FNAs-mediated isothermal amplification has been emergingly applied in biosensors for foodborne microbial contaminants detection, making biosensors more sensitive with lower cost and less dependent on nanomaterials for signal output. Here, the mechanism of six isothermal amplification technologies and their application in detecting FMC is firstly introduced. Then the strategy of FNAs-mediated isothermal amplification is systematically discussed from perspectives of FNAs' versatility including recognition elements (Aptamer, DNAzyme), programming tools (DNA tweezer, DNA walker and CRISPR-Cas) and signal units (G-quadruplex, FNAs-based nanomaterials). Finally, challenges and prospects are presented in terms of addressing the issue of nonspecific amplification reaction, developing better FNAs-based sensing elements and eliminating food matrix effects.

"Gold-plated" PCN-222(Fe) and superconductive carbon black-based sandwich-type immunosensor for detecting CYFRA21-1

Cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) is a protein fragment dissolved in the blood after apoptosis of lung epithelial cells, which is a predictive biomarker for the diagnosis of non-small cell lung cancer (NSCLC). Detection of serum CYFRA21-1 has a significant clinical value in diagnosis, monitoring and prognosis of NSCLC. Herein, a novel electrochemical immunosensor was constructed for the sensitive detection of CYFRA21-1. First, superconductive carbon black (KB) functionalized polyethyleneimine (PEI)-gold nanoparticles (AuNPs) were covered on the surface of methylene blue (MB) and used as substrate materials to immobilize the CYFRA21-1 antibody. Then, target CYFRA21-1 was successfully detected using an electrochemical immunosensor through specific recognition of antigen and antibody. The zirconium-based metal organic framework of PCN-222(Fe) with a large pore size and three-dimensional (3D) structure can absorb abundant AuNPs through strong electrostatic interaction, which enhances the conductive properties of PCN-222(Fe) and prevents the self-aggregation of AuNPs. However, PCN-222(Fe) with peroxidase-like activity can catalyze the generation of hydroxyl free radicals (˙OH) from H2O2, which oxidized MB, leading to a decrease in the current signal. The signal response to the degradation of MB was recorded using differential pulse voltammetry (DPV). This indirect method of immunosensor offered a new strategy to address the limitations imposed by the poor conductivity of PCN-222(Fe), further enabling the amplification of the signal through the oxidative degradation of MB. Compared with traditional electrochemical immunosensors, this method has the advantages of a stable current signal and good reproducibility, providing a promising reference for the broad application of PCN-222(Fe) in electrochemical biosensors.

Recent Advances in Electrochemical Biosensors for Food Control

The rapid and sensitive detection of food contaminants is becoming increasingly important for timely prevention and treatment of foodborne disease. In this review, we discuss recent developments of electrochemical biosensors as facile, rapid, sensitive, and user-friendly analytical devices and their applications in food safety analysis, owing to the analytical characteristics of electrochemical detection and to advances in the design and production of bioreceptors (antibodies, DNA, aptamers, peptides, molecular imprinted polymers, enzymes, bacteriophages, etc.). They can offer a low limit of detection required for food contaminants such as allergens, pesticides, antibiotic traces, toxins, bacteria, etc. We provide an overview of a broad range of electrochemical biosensing designs and consider future opportunities for this technology in food control.

An accurate and ultrasensitive ratiometric electrochemical aptasensor for determination of Ochratoxin A based on catalytic hairpin assembly

Ochratoxin A (OTA) pollution in agricultural products has raised the pressing to develop sensitive, accurate and convenient detection methods. Herein, an accurate and ultrasensitive ratiometric electrochemical aptasensor was proposed based on catalytic hairpin assembly (CHA) for OTA detection. In this strategy, the target recognition and CHA reaction were both accomplished in the same system, which avoided tedious multi-steps operation and extra reagents, providing the advantage of convenience with only a one-step reaction and without enzyme. The labeled Fc and MB were used as the signal-switching molecules, avoiding various interferences and greatly improving the reproducibility (RSD: 3.197%). This aptasensor achieved trace-level detection for OTA with LOD of 81 fg/mL in the linear range of lower concentration (100 fg/mL-50 ng/mL). Moreover, this strategy was successfully applied to OTA detection in cereals with comparable results of HPLC-MS. This aptasensor provided a viable platform for accurate, ultrasensitive, and one-step detection of OTA in food.

A portable paper-based aptasensor for simultaneous visual detection of two mycotoxins in corn flour using dual-color upconversion nanoparticles and Cu-TCPP nanosheets

A portable paper-based microfluidic aptasensor is established to simultaneously and visually detect zearalenone (ZEN) and ochratoxin A (OTA). The targets at the sample zone can migrate to two detection zones through dual-channels and result in green and blue fluorescence recovery. This is due to the specific recognition by a respective aptamer that destroys fluorescence resonance energy transfer (FRET) from dual-color upconversion nanoparticles (UCNPs) to Cu-TCPP nanosheets. By capturing fluorescent images and analyzing the corresponding RGB value via a smartphone, ZEN and OTA can be analyzed with limits of detection down to 0.44 ng/mL and 0.098 ng/mL in the linear ranges of 0.5-100 ng/mL and 0.1-50 ng/mL, respectively. Satisfactory recoveries are also obtained for ZEN (94.5-103.7 %) and OTA (92.2-106.8 %) in corn flour. With the advantages of simple operation, low sample consumption, and broad adaptability, this promising platform allows for the on-site detection of multiple hazards in food.

A sensing platform based on Cu-MOF encapsulated Dawson-type polyoxometalate crystal material for electrochemical detection of xanthine

A promising sensing platform based on polyoxometalate-based metal-organic framework (POMOF) was established for sensitive electrochemical detection of xanthine (XA). In the unique structure of POMOF, the Dawson polyoxoanions P₂W₁₈ were encapsulated into 3D open copper-mixed ligand nanotube framework Cu-MOF, in which the cavity of the metal-organic framework provides a specific shelter to prevent the aggregation and loss of polyoxometalate in electrocatalytic reactions; meanwhile, unsaturated Cu(II) active sites of Cu-MOF can also serve as electrocatalytic active center. The POMOF-based sensor (CuMOFP₂W₁₈/XC-72R) was fabricated by using acetylene black (XC-72R) as a support material to enhance the conductivity of POMOF. The performances of the POMOF-based sensor were studied by using different electrochemical testing methods. The composite displayed remarkable electrocatalytic activity for the oxidation of XA due to the synergistic effect of polyoxometalate (POM) and metal-organic framework (MOF). The electrochemical sensor demonstrated a wide linear range (0.5 μM-240 μM), low detection limit (0.26 μM), and excellent selectivity for detecting XA. Furthermore, the composite further demonstrated excellent reproducibility and great stability. More importantly, the proposed sensor was utilized to detect XA in real samples, which may provide a new way for early disease diagnosis.

Iron Porphyrin as a Cytochrome P450 Model for the Degradation of Dye

Organic dyes are widely used in the textile, biological, medical and other fields. However, a serious environmental problem has appeared because of the presence of organic dyes in industrial aqueous effluents. Thus, the efficient treatment of organic dyes in industrial wastewaters is currently in real demand. The current study investigated the oxidative degradation of the organic dye gentian violet by meso-tetra(carboxyphenyl) porphyriniron(III), [Fe^III(TCPP)] as a cytochrome P450 model and iodosylbenzene (PhIO) as an oxidant at room temperature. The degradation reaction was monitored by UV-vis absorption spectroscopy via the observation of UV-vis spectral changes of the gentian violet. The results showed that the efficiency of catalyzed degradation reached more than 90% in 1 h, indicating the remarkable oxidative degradation capacity of the [Fe^III(TCPP)]/PhIO system, which provided an efficient approach for the treatment of dyeing wastewater.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Dual-mode sensor based on the synergy of magnetic separation and functionalized probes for the ultrasensitive detection of Clostridium perfringens

Clostridium perfringens is an important foodborne pathogen, which has caused serious public health problems worldwide. So, there is an urgent need for rapid and ultrasensitive detection of C. perfringens. In this paper, a dual-mode sensing platform using the synergy between fluorescent and electrochemical signals for Clostridium perfringens detection was proposed. An electrochemical aptasensor was constructed by a dual-amplification technology based on a DNA walker and hybridization chain reaction (HCR). When the C. perfringens genomic DNA was present, it specifically bonded with FAM-labeled aptamer which triggered the DNA walker on hairpin DNA (hDNA) tracks to start the synthesis of double-stranded DNA. HCR occurred subsequently and produced long-chain DNA to absorb more methylene blue (MB). In this cycle, the fluorescent signals of released FAM-labeled aptamer could also be detected. The synergistic effects of MB and FAM significantly improved the sensitivity and accuracy of the dual-mode sensor. As a result, the biosensor displayed an excellent analytical performance for C. perfringens at a concentration of 1 to 10⁸ CFU g⁻¹. A minimum concentration of 1 CFU g⁻¹ and good accuracy were detected in real samples. The proposed ultrasensitive detection method for detecting C. perfringens in food showed great potential in controlling foodborne diseases.

Clostridium perfringens is an important foodborne pathogen, which has caused serious public health problems worldwide.