A signal-enhancement fluorescent aptasensor based on the stable dual cross DNA nanostructure for simultaneous detection of OTA and AFB1

Molecularly imprinted Fe3O4 nanoparticles-based magnetic 3D photonic crystal microspheres for specific adsorption of aflatoxin B1 in grains

Aflatoxin B1 (AFB1) is the major toxic mycotoxin that contaminates grains at trace levels, necessitating the development of an efficient and simple extraction method to enrich it in samples. Here, magnetic molecularly imprinted Fe3O4 nanoparticles (MMIPs) were first synthesized by employing 5,7-dimethoxy coumarin as the template and methacrylic acid combined with styrene as the functional monomers. These MMIPs exhibited excellent selective recognition capabilities for AFB1, based on which, a novel molecularly imprinted magnetic inverse opal photonic crystal microsphere (MIP@MIPCM) was fabricated via a droplet-based microfluidic self-assembly technique. The MIP@MIPCMs enabled specific recognition of AFB1 and were used as an extraction material, achieving a binding capacity of 842.7 ng/mg within 20 min. Coupled with high-performance liquid chromatography (HPLC), a sensitive and accurate analytical method was established for AFB1 detection with a detection limit of 0.35 μg/kg and recovery rates of 90-109 % in real samples.

Simultaneous Detection of Ochratoxin A and Aflatoxin B1 Based on Stable Tuning Fork-shaped DNA Fluorescent Aptasensor

Tuning fork, consisting of two fork arms and a fork handle, has a stable and rigid structure. Inspired by this structure, a tuning fork-shaped DNA (TF-DNA) fluorescence aptasensor was constructed to detect ochratoxin A (OTA) and aflatoxin B1 (AFB1). A TF-DNA double-stranded structure capable of attaching both OTA aptamer labeled with the FAM fluorescent group (FAM-Apt) and AFB1 aptamer labeled with the ROX fluorescent group (ROX-Apt) was designed and linked to magnetic beads. This TF-DNA double-stranded structure can provide a stable platform for dual-target detection. In the presence of OTA and AFB1, FAM-Apt and ROX-Apt preferentially bound to them and detached from the TF-DNA double-stranded structure. Dual-signal fluorescent probes were collected from the supernatant by magnetic separation, and achieved fluorescence enhancement at 520 nm and 607 nm, respectively. The linear ranges are 0.05 ng/mL to 100 ng/mL for OTA and 0.1 ng/mL to 100 ng/mL for AFB1, and the detection limits are 0.015 ng/mL and 0.045 ng/mL, respectively. The developed sensor has the advantages of simple and fast preparation, good specificity and reproducibility, which is promising for the simultaneous determination of multiple hazardous substances in food.

Fluorescence sensing techniques for quality evaluation of traditional Chinese medicines: a review

Traditional Chinese medicines (TCMs) are highly valued and widely used worldwide. However, their complex compositions and various preparation processes have brought considerable challenges to the quality evaluation of Chinese medicines. The traditional methods for TCM quality evaluation suffer from the problems of cumbersome sample preparation, a long detection time, low sensitivity, etc. A more efficient and accurate evaluation method is urgently needed to ensure the stability and reliability of the quality of TCMs. As an emerging analytical technology, a fluorescent probe has the advantages of high sensitivity, high selectivity, easy operation, etc. It is capable of generating a specific fluorescent signal response to specific components in traditional Chinese medicines, realizing rapid and accurate detection of target components, which effectively solves the many difficulties of traditional methods. The purpose of this paper is to discuss the application of fluorescent probes in the quality evaluation of traditional Chinese medicines and the challenges they face. By introducing the principles, advantages and specific application cases of fluorescent probe technology in the quality evaluation of traditional Chinese medicines, we hope to provide new and efficient analytical ideas for the quality evaluation of traditional Chinese medicines.

Development of a colorimetric/fluorescence dual-mode immunoassay for aflatoxin B1 based on streptavidin-induced gold nanoparticle aggregation

A dual-mode immunoassay method was developed for colorimetric and fluorescence detection of aflatoxin B1 (AFB1) based on streptavidin-induced gold nanoparticle aggregation (AuNP@SA). AuNP-modified streptavidin-biotin labeling AFB1 complete antigen aggregations (AuNP@SA@Bio-BSA-AFB1) were synthesized as the competitive binding and dual-mode probe. AuNP@SA@Bio-BSA-AFB1 aggregations possessed high colorimetric and fluorescence quenching intensities. AFB1 antibodies modified immunomagnetic microspheres were used as the capture probe. The competitive binding between AFB1 and AuNP@SA@Bio-BSA-AFB1 leads to changes in color and fluorescence intensity. The detection limit of the colorimetric method is 6.95 ng·mL-1, while that of the fluorescence method is 0.07 ng·mL-1. The practicality of the proposed strategy was demonstrated by determining AFB1 in spiked peanut samples.

Perspectives in Aptasensor-Based Portable Detection for Biotoxins

Biotoxins are pervasive in food and the environment, posing significant risk to human health. The most effective strategy to mitigate the risk arising from biotoxin exposure is through their specific and sensitive detection. Aptasensors have emerged as pivotal tools, leveraging aptamers as biorecognition elements to transduce the specificity of aptamer-target interactions into quantifiable signals for analytical applications, thereby facilitating the meticulous detection of biotoxins. When integrated with readily portable devices such as lateral flow assays (LFAs), personal glucose meters (PGMs), smartphones, and various meters measuring parameters like pH and pressure, aptasensors have significantly advanced the field of biotoxin monitoring. These commercially available devices enable precise, in situ, and real-time analysis, offering great potential for portable biotoxin detection in food and environmental matrices. This review highlights the recent progress in biotoxin monitoring using portable aptasensors, discussing both their potential applications and the challenges encountered. By addressing these impediments, we anticipate that a portable aptasensor-based detection system will open new avenues in biotoxin monitoring in the future.

Fluorescence/visual aptasensor based on Au/MOF nanocomposite for accurate and convenient aflatoxin B1 detection

A dual-mode fluorescence/visual aptasensor was developed for straightforward and accurate determination of aflatoxin B1 (AFB1) based on an Au/metal-organic framework (Au/MOF) composite. Aptamer-modified Au/Fe3O4 (Apt/Au/Fe3O4) served as the recognition element, and Au/MOF modified with complementary chains and 3,3',5,5'-tetramethylbenzidine (cDNA/TMB/Au/MOF) acted as the fluorescence and visual probes. These components are integrated to form conjugates (Apt/Au/Fe3O4-cDNA/TMB/Au/MOF). Upon the introduction of AFB1, some cDNA/TMB/Au/MOF dissociated from Apt/Au/Fe3O4, enabling the use of detached probes for visual detection. The undecomposed conjugates were isolated magnetically for use in fluorescence detection. As the AFB1 concentration increases, the visual signal intensifies and fluorescence intensity diminishes. Thus, the proposed aptasensor achieves the simultaneous fluorescence and visual determination of AFB1, obviating the need for material and reagent substitutions. The detection limits were established at 0.07 ng mL-1 for the fluorescence mode and 0.08 ng mL-1 for the visual mode. The effectiveness of the aptasensor was further validated by quantifying AFB1 in real samples.

Simultaneous detection of AFB1 and aflD gene by "Y" shaped aptamer fluorescent biosensor based on double quantum dots

The developed method for simultaneous detection of aflatoxin B1 (AFB1) and aflD genes can effectively monitor from the source and reduce the safety problems and economic losses caused by the production of aflatoxin, which can be of great significance for food safety regulations. In this paper, we constructed a sensitive and convenient fluorescent biosensor to detect AFB1 and aflD genes simultaneously based on fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and a black hole quenching agent. A stable "Y" shaped aptasensor was employed as the detection platform and a double quantum dot labeled DNA fragment was utilized to be the sensing element in this work. When the targets of AFB1 and aflD genes were presented in the solution, the aptamer in the "Y" shaped probe is specifically recognized by the target. At this time, both Si-carbon quantum dots (Si-CDs) and CdTe QDs are far away from the BHQ1 and BHQ3 to recover the fluorescence. The linear range of the prepared fluorescence simultaneous detection method was as wide as 0.5-500 ng·mL-1 with detection lines of 0.64 ng·mL-1 for AFB1 and 0.5-500 nM with detection lines of 0.75 nM for aflD genes (3σ/k). This fabricated fluorescent biosensor was further validated in real rice flour and corn flour samples, which also achieved good results. The recoveries were calculated by comparing the known and found amounts of AFB1 which ranged from 88.4 to approximately 115.32% in the rice flour samples and 90.7 ~ 102.58% in the corn flour samples. The recoveries of aflD genes ranged from 84.32 to approximately 109.3% in the rice flour samples and 89.48 ~ 100.99% in the corn flour samples. Therefore, the proposed biosensor can significantly improve food safety and quality control through a simple, fast, and sensitive agricultural product monitoring and detection system.

Recent Advances in Biological Applications of Aptamer-Based Fluorescent Biosensors

Aptamers have been spotlighted as promising bio-recognition elements because they can be tailored to specific target molecules, bind to targets with a high affinity and specificity, and are easy to chemically synthesize and introduce functional groups to. In particular, fluorescent aptasensors are widely used in biological applications to diagnose diseases as well as prevent diseases by detecting cancer cells, viruses, and various biomarkers including nucleic acids and proteins as well as biotoxins and bacteria from food because they have the advantages of a high sensitivity, selectivity, rapidity, a simple detection process, and a low price. We introduce screening methods for isolating aptamers with q high specificity and summarize the sequences and affinities of the aptamers in a table. This review focuses on aptamer-based fluorescence detection sensors for biological applications, from fluorescent probes to mechanisms of action and signal amplification strategies.

Ionic liquids functionalized Fe3O4-based colorimetric biosensor for rapid determination of ochratoxin A

A stainless steel mesh (SSM) with the feature of flexibility was employed as the colorimetric biosensor substrate, and aptamer was bond onto the surface of the SSM. Through the cross-linking of ionic liquids (ILs), AuPt nanoparticles were deposited  onto the surface of Fe3O4 material to obtain a magnetic nanozyme with high peroxidase catalytic activity and rapid color change. Through the competing interaction of OTA and cDNA with aptamer, AuPt@IL@Fe3O4 signal probe was separated to catalyze the 3,3',5,5'-tetramethylbenzidine/hydrogen peroxide (TMB/H2O2) system to observe the color by bare eye and record the absorbance at 652 nm using a UV-spectrophotometer. Through the study of the catalytic properties on the basis of the Michaelis equation, AuPt@IL@Fe3O4 nanozyme presented a Vmax of 3.85 × 10-8 M s-1 and Km of 0.01 mM. Under the optimized conditions, the linear range of the colorimetric biosensor towards OTA was 5-100 ng mL-1, and the detection limit was 0.078 ng mL-1. This biosensor was applied to beer and corn samples with recoveries of 70.4-102.6% and 93.3-104.7%, respectively. Results showed that this sensor is a portable, rapid, economical, sensitive visual sensing platform towards mycotoxin in real samples.

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.

Fluorescence-based aptasensors for small molecular food contaminants: From energy transfer to optical polarization

Small molecular food contaminants, such as mycotoxins, pesticide residues and antibiotics, are highly probable to be passively introduced in food at all stages of its processing, including planting, harvest, production, transportation and storage. Owing to the high risks caused by the unknowing intake and accumulation in human, there is an urgent need to develop rapid, sensitive and efficient methods to monitor them. Fluorescence-based aptasensors provide a promising platform for this area owing to its simple operation, high sensitivity, wide application range and economical practicability. In this paper, the common sorts of small molecular contaminants in foods, namely mycotoxins, pesticides, antibiotics, etc, are briefly introduced. Then, we make a comprehensive review, from fluorescence resonance energy transfer (in turn-on, turn-off, and ratiometric mode, as well as energy upconversion) to fluorescence polarization, of the fluorescence-based aptasensors for the determination of these food contaminants reported in the last five years. The principle of signal generation, the advances of each sort of fluorescent aptasensors, as well as their applications are introduced in detail. Additionally, we also discussed the challenges and perspectives of the fluorescent aptasensors for small molecular food contaminants. This work will offer systematic overview and inspiration for amateurs, researchers and developers of fluorescence-based aptasensors for the detection of small molecules.

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.

A novel COOH-GO-COOH-MWNT/pDA/AuNPs based electrochemical aptasensor for detection of AFB1

Aflatoxin B1 (AFB1), one of the most common mycotoxins in food matrixes, has been identified as the most toxic contaminant with mutagenic, teratogenic, immunosuppressive, and carcinogenic effects. In this study, an electrochemical aptamer sensor was developed for the on-site detection of AFB1. Carboxylated graphene oxide (COOH-GO) and carboxylated multi-walled carbon nanotubes (COOH-MWNT) nanocomposites, dopamine polymers (pDA) and gold nanoparticles (AuNPs) were used to enhance the electrochemical activity and the biocompatibility of the screen-printed electrodes (SPE). Once AFB1 was captured by the aptamer immobilized on the electrode surface, the redox current of [Fe(CN)6]3-/4- decreased. Therefore, the binding of aptamer (Apt) and AFB1 can be reflected by the change of the peak current. The as-prepared sensor showed a wide detection range of 0.1 fg ml-1-100 pg ml-1 and a low detection limit of 15.16 ag ml-1. It is also simple and low-cost, which shows great potential in practical application.

High-Sensitive FAM Labeled Aptasensor Based on Fe3O4/Au/g-C3N4 for the Detection of Sulfamethazine in Food Matrix

In this study, we developed a fluorescent aptasensor based on Fe₃O₄/Au/g-C₃N₄ and a FAM-labeled aptamer (FAM-SMZ1S) against sulfamethazine (SMZ) for the specific and sensitive detection of SMZ in food matrix. The FAM-SMZ1S was adsorbed by the Fe₃O₄/Au/g-C₃N₄ via π–π stacking and electrostatic adsorption, serving as a basis for the ultrasensitive detection of SMZ. Molecular dynamics was used to explain the reasons why SMZ1S and SMZ were combined. This aptasensor presented sensitive recognition performance, with a limit of detection of 0.16 ng/mL and a linear range of 1–100 ng/mL. The recovery rate ranged from 91.6% to 106.8%, and the coefficient of variation (CV) ranged from 2.8% to 13.4%. In addition, we tested the aptasensor for the monitoring of SMZ in various matrix samples, and the results were well-correlated (R² ≥ 0.9153) with those obtained for HPLC detection. According to these results, the aptasensor was sensitive and accurate, representing a potentially useful tool for the detection of SMZ in food matrix.