A signal on-off fluorescence sensor based on the self-assembly DNA tetrahedron for simultaneous detection of ochratoxin A and aflatoxin B1

Self-designed portable dual-mode fluorescence device with custom python-based analysis software for rapid detection via dual-color FRET aptasensor with IoT capabilities

An innovative aptasensor incorporating MoS2-modified bicolor quantum dots and a portable spectrometer, designed for the simultaneous detection of ochratoxin A (OTA) and aflatoxin B1 (AFB1) in corn was developed. Carbon dots and CdZnTe quantum dots were as nano-donors to label OTA and AFB1 aptamers, respectively. These labeled aptamers were subsequently attached to MoS2 receptors, enabling fluorescence resonance energy transfer (FRET). With targets, the labeled aptamers detached from the nano-donors, thereby disrupting the FRET process and resulting in fluorescence recovery. Furthermore, a portable dual-mode fluorescence detection system, complemented with customized python-based analysis software, was developed to facilitate rapid and convenient detection using this dual-color FRET aptasensor. The developed host program is connected to the spectrometer and transmits data to the cloud, enabling the device to have Internet of Things (IoT) characteristics. Connected to the cloud, this IoT-enabled device offers convenient and reliable fungal toxin detection for food safety.

A label-free ratiometric homogeneous electrochemical aptasensor based on dual catalytic hairpin self-assembly for rapid and sensitive detection of ochratoxin A in food

The food contamination with Ochratoxin A (OTA) has highlighted the need to create precise, sensitive, and convenient techniques. Herein, we proposed a label-free and immobilization-free ratiometric homogeneous electrochemical aptasensor based on dual catalytic hairpin self-assembly (CHA) for OTA detection. Methylene blue (MB) and ferrocene (Fc) in solution were utilized as label-free signaling molecules, generating a response signal (IMB) and a reference signal (IFc), respectively. The ratio of IMB/IFc was utilized as a measure to quantify OTA. Dual CHA was exploited to increase the ratiometric signal and enhance the amplification efficiency. This aptasensor achieved trace-level detection for OTA over a linear range of lower concentrations (1.0 × 10-3 ng/mL-1.0 × 103 ng/mL) with LOD of 92 fg/mL. The aptasensor was successfully applied to detect OTA in cereal and wine, with comparable results of HPLC-MS/MS. This strategy provided a viable platform for rapid, sensitive, and accurate detection of OTA in food.

Development of a reusable polymeric fluorescence sensor based on acryloyl β-cyclodextrin for the determination of aflatoxin B1 in grain products

AFB1 is a harmful substance that can be found in agricultural products and can seriously affect human health, even in trace amounts. Therefore, monitoring AFB1 levels to ensure food safety and protect public health is crucial. New, highly reliable, selective, and rapid detection methods are needed to achieve this goal. Our work involves the development of a polymeric membrane sensor using radical polymerization that can accurately detect AFB1. Various spectroscopic techniques (Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM)) were used to obtain information about the structural and morphological properties of the prepared sensor. The sensor displayed fluorescence selectively responsive to AFB1 at the excitation wavelength of 376 nm and emission wavelength of 423 nm. The polymeric fluorescence sensor showed good sensitivity and a wide linear range from 9.61 × 10-10 and 9.61 × 10-9 mol/L for AFB1quantification. The limit of detection (LOD) is as low as 3.84 × 10-10 mol/L for AFB1. Other mycotoxins, such as aflatoxin B2 and aflatoxin G1, did not interfere with the sensor's high selectivity towards AFB1. To test the sensor's effectiveness in detecting AFB1 in real samples, three different grain samples - peanuts, hazelnut butter, and peanuts with a sauce known to contain AFB1 - were utilized. The results were satisfactory and demonstrated that the sensor can be successfully employed in real samples, with an error range of 0.43 % to 12.10 %.

Novel Sensor Approaches of Aflatoxins Determination in Food and Beverage Samples

The rapid quantification of toxins in food and beverage products has become a significant issue in overcoming and preventing many life-threatening diseases. Aflatoxin-contaminated food is one of the reasons for primary liver cancer and induces some tumors and cancer types. Advancements in biosensors technology have brought out different analysis methods. Therefore, the sensing performance has been improved for agricultural and beverage industries or food control processes. Nanomaterials are widely used for the enhancement of sensing performance. The enzymes, molecularly imprinted polymers (MIP), antibodies, and aptamers can be used as biorecognition elements. The transducer part of the biosensor can be selected, such as optical, electrochemical, and mass-based. This review explains the classification of major types of aflatoxins, the importance of nanomaterials, electrochemical, optical biosensors, and QCM and their applications for the determination of aflatoxins.

Screening biotoxin aptamer and their application of optical aptasensor in food stuff: a review

Biotoxins are ranges of toxic substances produced by animals, plants, and microorganisms, which could contaminate foods during their production, processing, transportation, or storage, thus leading to foodborne illness, even food terrorism. Therefore, proposing simple, rapid, and effective detection methods for ensuring food free from biotoxin contamination shows a highly realistic demand. Aptamers are single-stranded oligonucleotides obtained from the systematic evolution of ligands by performing exponential enrichment (SELEX). They can specifically bind to wide ranges of targets with high affinity; thus, they have become important recognizing units in safety monitoring in food control and anti-terrorism. In this paper, we reviewed the technical points and difficulties of typical aptamer screening processes for biotoxins. For promoting the understanding of food control in the food supply chain, the latest progresses in rapid optical detection of biotoxins based on aptamers were summarized. In the end, we outlined some challenges and prospects in this field. We hope this paper could stimulate widespread interest in developing advanced sensing systems for ensuring food safety.

A controllable Y-shaped DNA structure assisted aptasensor for the simultaneous detection of AFB1 and OTA based on ARGET ATRP

The development of a simple, rapid, and sensitive technology for the simultaneous detection of mycotoxins is of great significance in ensuring the safety of foods and drugs. Herein, a fluorescence aptasensor with high sensitivity and reproducibility for the simultaneous detection of aflatoxin B1 (AFB1) and ochratoxin A (OTA) was developed. In this sensing system, AFB1 and OTA aptamers were co-immobilized on the surface of magnetic beads (MBs) to form a Y-shaped structure through the principle of complementary base pairing, and were used as recognition probes to specifically capture the target. Activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was used as a signal amplification strategy to improve the sensitivity. The initiator modified at the end of an antibody initiates the ARGET ATRP reaction. Different fluorescence signals were designed to achieve the simultaneous detection of OTA and AFB1 with limits of 426.18 and 79.55 fg mL-1 for AFB1 and OTA, respectively. In addition, experiments were conducted on three types of samples, and the recoveries of the two mycotoxins ranged from 87.30% to 109.50%, with relative standard deviations ranging from 0.50% to 4.92% under reproducible conditions. The results suggest that the developed aptasensor is sufficient to meet the different regulatory requirements of the two mycotoxins in food and drug safety and shows great potential.

Unlabelled LRET biosensor based on double-stranded DNA for the detection of anthraquinone anticancer drugs

Based on upconversion nanoparticles (UCNPs) as energy donor and herring sperm DNA (hsDNA) as molecular recognition element, an unlabelled upconversion luminescence (UCL) affinity biosensor was constructed for the detection of anthraquinone (AQ) anticancer drugs in biological fluids. AQ anticancer drugs can insert into the double helix structure of hsDNA on the surface of UCNPs, thereby shortening the distance from UCNPs. Therefore, the luminescence resonance energy transfer (LRET) phenomenon is effectively triggered between UCNPs and AQ anticancer drugs. Hence, AQ anticancer drugs can be quantitatively detected according to the UCL quenching rate. The biosensor showed good sensitivity and stability for the detection of daunorubicin (DNR) and doxorubicin (ADM). For the detection of DNR, the linear range is 1-100 μg·mL-1 with a limit of detection (LOD) of 0.60 μg·mL-1, and for ADM, the linear range is 0.5-100 μg·mL-1 with a LOD of 0.38 μg·mL-1. The proposed biosensor provides a convenient method for monitoring AQ anticancer drugs in clinical biological fluids in the future.

Intelligent Electrochemical Point-of-Care Test Method with Interface Control Based on DNA Pyramids: Aflatoxin B1 Detection in Food and the Environment

Sensitive, intelligent point-of-care test (iPOCT) methods for small molecules like aflatoxin B1 (AFB1) are urgently needed for food and the environment. The challenge remains of surface control in iPOCT. Herein, we developed an electrochemical sensor based on the DNA pyramid (DNP), combining a smartphone, app, and mobile electrochemical workstations to detect AFB1. The DNP's structure can reduce local overcrowding and entanglement between neighboring probes, control the density and orientation of recognition probes (antibodies), produce uniform and orientational surface assemblies, and improve antigen-antibody-specific recognition and binding efficiency. Simultaneously, the hollow structure of the DNP enhances the electron transfer capacity and increases the sensitivity of electrochemical detection. In this work, the biosensor based on DNP was first combined with electrochemical (Ec) iPOCT to simultaneously achieve ordered interface modulation of recognition probes and intelligent detection of AFB1. Under optimal conditions, we found a detection limit of 3 pg/mL and a linear range of 0.006-30 ng/mL (R2 = 0.995). Further, using peanut, soybean, corn, and lake water as complex matrices, it recorded recoveries of 82.15-100.53%, excellent selectivity, acceptable stability, and good reproducibility. Finally, this Ec iPOCT provides consistent results compared to the high-performance liquid chromatography-tandem mass spectrometry method.

Recognition-Activated Primer-Mediated Exponential Rolling Circle Amplification for Signal Probe Production and Ultrasensitive Visual Detection of Ochratoxin A with Nucleic Acid Lateral Flow Strips

We proposed a visual strategy for rapid and ultrasensitive detection of ochratoxin A (OTA) by integration of primer-mediated exponential rolling circle amplification (P-ERCA) with a designed nucleic acid lateral flow strip (LFS). The recognition component was preimmobilized in the tube by hybridization between the immobilized functionalized aptamer and complementary ssDNA. Recognition of OTA induces the release of complementary ssDNA from the tube, which will also act as the primer of the designed P-ERCA. Three nicking sites on the template P-ERCA could contribute to the production of enormous signal probes based on the simultaneous amplification-nicking model, which can be visually measured directly with the constructed nucleic acid LFS. Importantly, the nicked signal probe can also act as the trigger of the new-round RCA, achieving exponential growth of signal probes for measurement and signal enhancement. Taking advantage of the extraordinary amplification efficiency of P-ERCA and the simplicity of LFS, this P-ERCA-LFS method demonstrates ultrasensitive detection of OTA with a visual limit of detection as low as 100 fg/mL for qualitative screening and a limit of detection of 35 fg/mL for semiquantitative analysis. This designed strategy could also be utilized as a universal method for detection of other chemical analytes with the replacement of the aptamer for recognition, and the nucleic acid LFS unit could also be a useful protocol for direct ssDNA analysis.

MnO2 nanoflowers based colorimetric and fluorescent dual-mode aptasensor for sensitive detection of aflatoxin B1 in milk

Aflatoxin B1 (AFB1) with tremendous toxic effects has caused a serious threat to food security. Accurate quantification of AFB1 in food can effectively prevent the risk of human intake of AFB1. Herein, a colorimetric and fluorescent dual-mode aptasensor for accurate and sensitive detection of AFB1 has been developed based on MnO2 nanoflowers (MnO2NFs) for the first time. MnO2NFs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidation product (TMBox) by H2O2, which would be used for visible detection of AFB1. Simultaneously, MnO2NFs can be served as a signal amplifier and reduced by ascorbic acid to generate lots of Mn2+ which would quench the fluorescence of calcein for fluorescent detection of AFB1. Both colorimetric and fluorescent methods have been successfully applied for determination of AFB1 in milk samples with satisfactory results. The proposed dual-mode detection method with high detection sensitivity and accuracy showed great promise for monitoring AFB1 in food.

Development and analysis of a universal label-free micro/nano component for three-channel detection of silver ions, mercury ions, and tetracycline

In this paper, an enzyme-free and label-free fluorescent nanomodule is proposed for rapid, simple and sensitive detection of Ag+, Hg2+ and tetracycline (TC). The strategy is cleverly designed to enable multiple-purpose detection with as little as 31 nt of ssDNA. Both the embedded dye SYBR Green I and the nanomaterial graphene oxide (GO) are able to distinguish single-stranded DNA from double-stranded DNA; thus, the combination of the two instead of using traditional molecular beacon (MB)-labeled fluorophores and quencher groups can effectively reduce the cost of experiments while efficiently reducing the background noise. Performance testing experiments confirmed the stability and selectivity of the platform; the limits of detection (LODs) of Ag+ and Hg2+ were 1.41 nM and 1.79 nM, respectively, and the detection range were within the WHO standards. In addition, only some base sequences in the flexible functional domain of the nanoloop needed to be programmed to build a universal platform, which was feasible using TC as a target. Therefore, the designed nanomodule has the potential to detect various types of targets, such as antibiotics, proteins, and target genes, and has broad application prospects in environmental monitoring, food testing, and disease diagnosis.

Real-time monitoring ATP variation in human cancer organoids for a long term by DNA-based nanosensor

Cancer organoids have become promising tools for predicting drug responses on many different types of cancer. Detecting the adenosine triphosphate (ATP) has currently been considered as a decisive test to profile the growth status and drug responses of organoids. ATP profiling using commercial ATP detection kits, which involve cell lysis, can be performed at a single time spot, causing a clinical dilemma of selecting the optimal time spot to adopt diverse cancer types and patients. This study provides a feasible solution to this dilemma by developing a DNA-based ATP nanosensor to realize real-time ATP monitoring in organoids for a long term. The employment of DNA materials ensures high biocompatibility and low cytotoxicity, which are crucial for fragile organoids; The usage of tetrahedral DNA framework ensures cell permeability and intracellular ATP detection; The introduction of ATP-mediated molecular replacement ensures the high sensitivity and selectivity of ATP recognition. These features result in the first successful attempt on real-time monitoring ATP in organoids for up to 26 days and gaining growth status curves for the whole duration of a drug sensitivity test on human lung cancer organoids.

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.

Programmable Nanostructures Based on Framework-DNA for Applications in Biosensing

DNA has been actively utilized as bricks to construct exquisite nanostructures due to their unparalleled programmability. Particularly, nanostructures based on framework DNA (F-DNA) with controllable size, tailorable functionality, and precise addressability hold excellent promise for molecular biology studies and versatile tools for biosensor applications. In this review, we provide an overview of the current development of F-DNA-enabled biosensors. Firstly, we summarize the design and working principle of F-DNA-based nanodevices. Then, recent advances in their use in different kinds of target sensing with effectiveness have been exhibited. Finally, we envision potential perspectives on the future opportunities and challenges of biosensing platforms.

A Novel Fluorescent Aptasensor Based on Dual-labeled DNA Nanostructure for Simultaneous Detection of Ochratoxin A and Aflatoxin B1

Based on DNA strand replacement reaction and aptamer-specific recognition, a simple dual-labeled DNA nanostructure is designed for the simultaneous detection of Ochratoxin A (OTA) and aflatoxin B1 (AFB₁). C1 is labeled with Cy3 and Cy5, while C2 and C3 are labeled with BHQ2. The fluorescence intensity of DNA nanostructure composed of C1, C2 and C3 is weak because of fluorescence resonance energy transfer. When OTA Aptamer (OTA-Apt) and AFB1 Aptamer (AFB₁-Apt) are added to the homogeneous system at the same time, C1 can be replaced with the help of toehold strand displacement, resulting in fluorescence enhancement. In the presence of both OTA and AFB₁, the toehold strand displacement reaction is inhibited due to preferential binding between the target and their corresponding aptamers. The limit of detection of OTA was 0.007 ng/mL and that of AFB₁ was 0.03 ng/mL. The recoveries of OTA and AFB₁ were 96%-101% and 97%-101% in the corn sample, and 99%-101% and 92%-106% in the wine sample. Compared with other sensors, the preparation of this aptasensor needs simpler experimental steps and a shorter total-preparing time, confirming the convenient, rapid, and time-saving operation process.

A SERS-Fluorescence dual-signal aptasensor for sensitive and robust determination of AFB1 in nut samples based on Apt-Cy5 and MNP@Ag-PEI

Food aflatoxin B1 (AFB1) contamination greatly threatens human health and its sensitive determination is imperative. In this study, a surface-enhanced Raman scattering (SERS) and fluorescence dual-signal aptasensor was constructed for sensitive AFB1 detection in peanuts, walnuts, and almonds samples. Fluorescent dye cy5 was used as fluorophore and Raman reporter, while polyethyleneimine modified Ag coating magnetic nanoparticles (MNP@Ag-PEI) were utilized to absorb the cy5 modified aptamer (apt-cy5). Results indicated that linear ranges of 0.001-1000 ng/mL and 0.2-20,000 ng/mL with detection limits of 0.45 pg/mL and 0.135 ng/mL for the SERS and fluorescence methods were obtained, respectively, and AFB1 detection in the nut samples using the aptasensor achieved satisfactory recoveries of 95.2%-108.6% for SERS and 94.7%-109.7% for fluorescence. Compared with other mono signal detection, the established aptasensor facilely fused the merits of the two signals and improved the detection accuracy and flexibility.

An electrochemical aptasensor based on target triggered multiple-channel DNAzymes cycling amplification strategy with PtFe@Co-MOF as signal amplifier

A novel electrochemical aptasensor for the detection of Aflatoxin B1 (AFB1) was developed for the first time by using the target-triggered multiple-channel deoxyribozymes (DNAzymes) cycling amplified assay with Pt Fe doped NH₂-Co-MOF (PtFe@Co-MOF) as a signal amplifier. In the presence of AFB1, a self-assembling cross-over nucleic structure could be triggered by AFB1 via two aptamers' structure switching for strand displacement, resulting in four channels of Mg²⁺-dependent DNAzyme recycling simultaneously to multiply the detection signals. These DNAzymes cyclically split the substrate sequence to release the PtFe@Co-MOF labeled detection probe (DP), which is subsequently hybridized with the capture probes on the Au-deposited glassy carbon electrode. The fabrication procedure was characterized by differential pulse voltammetry, and the results of the morphological and element composition characteristics methods were analyzed to determine the successful preparation of PtFe@Co-MOF. The limit of detection (LOD) for AFB1 detection was 2 pg mL^-1 with a linear range from 5 pg mL^-1 to 80 ng mL^-1. By comparison, the enhanced detection sensitivity has been found to originate from the efficient shearing of DNAzymes, enhanced peroxidase-like capability, and multiple active sites of PtFe@Co-MOF. Besides, this aptasensor showed high specificity for AFB1 compared with similar mycotoxins and exhibited high accuracy with low experimental cost and easy operation. Furthermore, the unique design of electrochemical aptasensors could provide a promising platform for the onsite determination of AFB1, as well as other targets by replacing the aptamer and other core recognition sequences.