Nanozyme and aptamer- based immunosorbent assay for aflatoxin B1

Visual and colorimetric detection of microRNA in clinical samples based on strand displacement amplification and nanozyme-mediated CRISPR-Cas12a system

The sensitive and accurate detection of target microRNA is especially important for the diagnosis, staging, and treatment of hepatocellular carcinoma (HCC). Herein, we report a simple strand displacement and CRISPR-Cas12a amplification strategy with nanozymes as a signal reporter for the binary visual and colorimetric detection of the HCC related microRNA. Pt@Au nanozymes with excellent peroxidase enzyme activity were prepared and linked to magnetic beads via a single-stranded DNA (ssDNA) linker. The target microRNA was designed to trigger strand displacement amplification and release a DNA promoter to activate the CRISPR-Cas12a system. The activated CRISPR-Cas12a system efficiently cleaved the linker ssDNA and released Pt@Au nanozymes from magnetic beads to induce the colorimetric reaction of 3,3',5,5'-tetramethylbenzidine. The strand displacement amplification converted the single microRNA input into abundant DNA promoter output, which improved the detection sensitivity by over two orders of magnitude. Through integration of strand displacement amplification and the nanozyme-mediated CRISPR-Cas12a system, limits of detection of 0.5 pM and 10 pM for miRNA-21 were achieved with colorimetric and visual readouts, respectively. The proposed strategy can achieve accurate quantitative detection of miRNA-21 in the range from 1 pM to 500 pM. The detection results for miRNA-21 using both colorimetric and visual readouts were validated in 40 clinical serum samples. Significantly, the proposed strategy achieved visual HCC diagnosis with the naked eye and could distinguish distinct Barcelona clinical HCC stages by colorimetric detection, showing good application prospects for sensitive and facile point-of-care testing for HCC.

Click Reaction-Mediated Fluorescent Immunosensor Based on Cu-MOF Nanoparticles for Ultrasensitive and High-Throughput Detection of Aflatoxin B1 in Food Samples

Due to the high toxicity of aflatoxin B1 and its risks to human health, we developed a click reaction-mediated automated fluorescent immunosensor (CAFI) for sensitive detection of aflatoxin B1 based on the Cu(I)-catalyzed click reaction. With its large specific surface area, a copper-based metal-organic framework (Cu-MOF) was synthesized to adsorb and enrich the copper ion (Cu(II)) and then load the complete antigen (BSA-AFB1). After the immunoreaction, Cu(II) inside the Cu-MOF-Antigen conjugate would be reduced to Cu(I) in the presence of sodium ascorbate, which triggered the click reaction between the fluorescent donor-modified DNA and the receptor-modified complementary DNA to lead to a fluorescence signal readout. The whole reaction steps were finished by the self-developed automated immunoreaction device. This CAFI method showed a limit of detection (LOD) of 0.48 pg/mL as well as a 670-fold enhancement in sensitivity compared to conventional ELISA, revealing its great potential in practical applications and automated detection.

The Nanozyme Revolution: Enhancing the Performance of Medical Biosensing Platforms

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with "gold-standard" techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

Guest adaptative supramolecular sensing strategy for warning the risky aflatoxins in contaminated cereals

In the face of diversified analytes, it is a great challenge and infeasible task to design and synthesize corresponding macrocyclic hosts to realize the ideal supramolecular sensing. Herein, we proposed a novel supramolecular sensing strategy, guest adaptative assay (GAA), in which analyte was quantitatively transformed under mild conditions to perfectly adapt to macrocyclic host. As a health-threatening "landmine" in cereals, aflatoxins were converted by the aid of alkali hydrolysis to satisfactorily obtain aflatoxins transformants in ionic state, resulting in sensitive response by the guanidinocalix[5]arene•fluorescein reporter pair. Surprisingly, the established strategy not only exhibited effective practicality in screening out high-risk cereals contaminated with aflatoxins, but also relieved the laborious task of macrocycle design and screening in supramolecular sensing.

Magnetic nanoparticle-based immunosensors and aptasensors for mycotoxin detection in foodstuffs: An update

Mycotoxin contamination of food crops is a global challenge due to their unpredictable occurrence and severe adverse health effects on humans. Therefore, it is of great importance to develop effective tools to prevent the accumulation of mycotoxins through the food chain. The use of magnetic nanoparticle (MNP)-assisted biosensors for detecting mycotoxin in complex foodstuffs has garnered great interest due to the significantly enhanced sensitivity and accuracy. Within such a context, this review includes the fundamentals and recent advances (2020-2023) in the area of mycotoxin monitoring in food matrices using MNP-based aptasensors and immunosensors. In this review, we start by providing a comprehensive introduction to the design of immunosensors (natural antibody or nanobody, random or site-oriented immobilization) and aptasensors (techniques for aptamer selection, characterization, and truncation). Meanwhile, special attention is paid to the multifunctionalities of MNPs (recoverable adsorbent, versatile carrier, and signal indicator) in preparing mycotoxin-specific biosensors. Further, the contribution of MNPs to the multiplexing determination of various mycotoxins is summarized. Finally, challenges and future perspectives for the practical applications of MNP-assisted biosensors are also discussed. The progress and updates of MNP-based biosensors shown in this review are expected to offer readers valuable insights about the design of MNP-based tools for the effective detection of mycotoxins in practical applications.

A Label-Free Aptasensor for Turn-On Fluorescent Detection of Aflatoxin B1 Based on an Aggregation-Induced-Emission-Active Probe and Single-Walled Carbon Nanohorns

The determination of the aflatoxin B1 (AFB1) content has received widespread attention in the context of food safety, which is a global public health issue. Accordingly, a label-free and turn-on fluorescent AFB1 determination method is developed herein with an ss-DNA aptamer as the recognition element, 4, 4-(1E,1E)-2, 2-(anthracene-9, 10-diyl) bis(ethene-2, 1-diyl) bis(N, N, N-trimethylbenzenaminium iodide) (DSAI) as the aggregation-induced emission (AIE) fluorescent probe, and single-walled carbon nanohorns (SWCNHs) as the selective part with a fluorescence quenching effect. In the presence of AFB1, the AFB1-specific aptamer undergoes a structural transformation and switches from being a random helix to a folded structure. DSAI's fluorescence is protected as a result of the resistance of the transformed aptamer adsorbed on the SWCNHs' surface. Because DSAI's fluorescence is not quenchable, the fluorescence intensity is calculated as a function of the AFB1 concentration. By simply mixing DSAI, aptamer, AFB1 samples, and SWCNHs, the method can be carried out in 2 h, with a limit of detection (LOD) of 1.83 ng/mL. It has a high selectivity in the presence of other mycotoxins, and its performance is confirmed in soybean sauce with a known concentration of AFB1. The LOD was 1.92 ng/mL in the soy sauce samples and the recovery ranged from 95 to 106%, implying that the presented aptasensor has great potential for food analysis.

Smart and Multifunctional Nanomaterials and Applications for Food Safety

Due to growing concerns about food safety and public health, the contaminants or residues of various harmful substances in food have received much attention in recent years [...].

Computer vision-assisted smartphone microscope imaging digital immunosensor based on click chemistry-mediated microsphere counting technology for the detection of aflatoxin B1 in peanuts

Aflatoxin B1 is a carcinogenic contaminant in food or feed, and it poses a serious health risk to humans. Herein, a computer vision-assisted smartphone microscope imaging digital (SMID) immunosensor based on the click chemistry-mediated microsphere counting technology was designed for the detection of aflatoxin B1 in peanuts. In this SMID immunosensor, the modified polystyrene (PS) microspheres were used as the signal probes and were recorded by a smartphone microscopic imaging system after immunoreaction and click chemistry reaction. The number of PS probes is adjusted by aflatoxin B1. The customized computer vision procedure was used to efficiently identify and count the obtained PS probes. This SMID immunosensor enables sensitive detection of aflatoxin B1 with a linear range from 0.001 ng/mL to 500 ng/mL, providing a simple, sensitive, and portable tool for food safety supervision.

Rapid and sensitive point-of-need aflatoxin B1 testing in feedstuffs using a smartphone-powered mobile microfluidic lab-on-fiber device

Rapid, high-frequency, and accurate identification of aflatoxin B1 (AFB1) is crucial for ensuring food safety and reducing population mortality. Herein, we constructed Smartphone powered Mobile mIcrofluidic Lab-on-fiber dEvice (SMILE) comprising a compact optical system, fiber nano-bioprobe-embedded microfluidic-chip system, mini-photodetector, and software application to facilitate the rapid and sensitive point-of-need quantitative testing for AFB1. The elegant optical design of SMILE significantly improves light transmission efficiency, detection sensitivity, and portability by integrating a compacted all-fiber optical structure with a fiber nano-bioprobe-embedded microfluidic chip. Furthermore, the nanopore layer of the fiber nano-bioprobe improves detection sensitivity by increasing the biorecognition molecule number and enhancing the interaction between the evanescent field and dye. Through an indirect competitive immunoassay mechanism, SMILE achieves sensitive quantitative detection of AFB1 with a detection limit of 0.08 µg/L. Herein, SMILE was validated using several feedstuff samples tested with a simple aqueous extraction protocol, demonstrating good correlation with high-performance liquid chromatography for AFB1-contaminated feedstuffs. The immunoassay process is completed within 12 min, boasting high sensitivity, specificity, reusability, and reproducibility. Owing to its sensitivity, portability, flexibility, plug-and-play, and smartphone integration, SMILE is highly scalable for rapid and high-frequency point-of-need testing for AFB1 and other trace contaminants.

Highly catalytic and stable Au@AuPt nanoparticles for visual and quantitative detection of E. coli O157:H7

A visual and quantitative ELISA-like method for Escherichia coli O157:H7 is developed based on highly catalytic and stable Au@AuPt nanoparticles. The proposed enhanced ELISA method can visually detect 100 CFU mL-1 O157:H7 with high specificity and without the need for strict low-temperature reagent storage, thereby increasing the utility. Moreover, it is applicable to spiked tap water and milk tea samples without additional treatments.

Recent Advances in Nanoplatform Construction Strategy for Alleviating Tumor Hypoxia

Hypoxia is a typical feature of most solid tumors and has important effects on tumor cells' proliferation, invasion, and metastasis. This is the key factor that leads to poor efficacy of different kinds of therapy including chemotherapy, radiotherapy, photodynamic therapy, etc. In recent years, the construction of hypoxia-relieving functional nanoplatforms through nanotechnology has become a new strategy to reverse the current situation of tumor microenvironment hypoxia and improve the effectiveness of tumor treatment. Here, the main strategies and recent progress in constructing nanoplatforms are focused on to directly carry oxygen, generate oxygen in situ, inhibit mitochondrial respiration, and enhance blood perfusion to alleviate tumor hypoxia. The advantages and disadvantages of these nanoplatforms are compared. Meanwhile, nanoplatforms based on organic and inorganic substances are also summarized and classified. Through the comprehensive overview, it is hoped that the summary of these nanoplatforms for alleviating hypoxia could provide new enlightenment and prospects for the construction of nanomaterials in this field.

Magnetic three-phase single-drop microextraction for highly sensitive detection of aflatoxin B1 in agricultural product samples based on peroxidase-like spatial network structure

In this work, a highly sensitive method for aflatoxin B₁ (AFB₁) detection was developed based on a peroxidase-like spatial network structure. The specific antibody and antigen of AFB₁ were coated on a histidine-modified Fe₃O₄ nanozyme to form the capture/detection probes. Based on the competition/affinity effect, the spatial network structure was constructed by the probes, which could be rapidly (8 s) separated by a magnetic three-phase single-drop microextraction process. In this single-drop microreactor, the network structure was applied to catalyze a colorimetric 3,3',5,5'-tetramethylbenzidine oxidation reaction for AFB₁ detection. The signal was amplified significantly due to the strong peroxidase-like ability of the spatial network structure and the enrichment effect of the microextraction. Thus, a low detection limit (0.034 pg/mL) was achieved. The matrix effect of real sample can be eliminated by the extraction approach, and the practicability of this method was proved by agricultural product samples analysis.

Scope of Onsite, Portable Prevention Diagnostic Strategies for Alternaria Infections in Medicinal Plants

Medicinal plants are constantly challenged by different biotic inconveniences, which not only cause yield and economic losses but also affect the quality of products derived from them. Among them, Alternaria pathogens are one of the harmful fungal pathogens in medicinal plants across the globe. Therefore, a fast and accurate detection method in the early stage is needed to avoid significant economic losses. Although traditional methods are available to detect Alternaria, they are more time-consuming and costly and need good expertise. Nevertheless, numerous biochemical- and molecular-based techniques are available for the detection of plant diseases, but their efficacy is constrained by differences in their accuracy, specificity, sensitivity, dependability, and speed in addition to being unsuitable for direct on-field studies. Considering the effect of Alternaria on medicinal plants, the development of novel and early detection measures is required to detect causal Alternaria species accurately, sensitively, and rapidly that can be further applied in fields to speed up the advancement process in detection strategies. In this regard, nanotechnology can be employed to develop portable biosensors suitable for early and correct pathogenic disease detection on the field. It also provides an efficient future scope to convert innovative nanoparticle-derived fabricated biomolecules and biosensor approaches in the diagnostics of disease-causing pathogens in important medicinal plants. In this review, we summarize the traditional methods, including immunological and molecular methods, utilized in plant-disease diagnostics. We also brief advanced automobile and efficient sensing technologies for diagnostics. Here we are proposing an idea with a focus on the development of electrochemical and/or colorimetric properties-based nano-biosensors that could be useful in the early detection of Alternaria and other plant pathogens in important medicinal plants. In addition, we discuss challenges faced during the fabrication of biosensors and new capabilities of the technology that provide information regarding disease management strategies.

Determination Methods of the Risk Factors in Food Based on Nanozymes: A Review

Food safety issues caused by foodborne pathogens, chemical pollutants, and heavy metals have aroused widespread concern because they are closely related to human health. Nanozyme-based biosensors have excellent characteristics such as high sensitivity, selectivity, and cost-effectiveness and have been used to detect the risk factors in foods. In this work, the common detection methods for pathogenic microorganisms, toxins, heavy metals, pesticide residues, veterinary drugs, and illegal additives are firstly reviewed. Then, the principles and applications of immunosensors based on various nanozymes are reviewed and explained. Applying nanozymes to the detection of pathogenic bacteria holds great potential for real-time evaluation and detection protocols for food risk factors.

An electrochemical biosensor for the detection of aflatoxin B1 based on the specific aptamer and HCR biological magnification

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin, which causes severe acute or cumulative poisoning. Therefore, it is important to develop sensitive and selective detection methods for AFB1 for the safety of food and medicinal herbs. Herein, we have developed a "signal-on" electrochemical aptasensor based on the high specificity of the aptamer and hybridization chain reaction (HCR) biological amplification for AFB1 detection. In this work, thiol-modified complementary DNA (cDNA) immobilized on the surface of a gold electrode (GE) served as an initiator DNA. When AFB1 was present, it competed with the cDNA for binding to the aptamers, which resulted in the detaching of aptamers from the cDNA-aptamer duplexes. Then, the single-stranded cDNA acted as an initiator to trigger the HCR signal amplification. Therefore, long double-stranded DNA (dsDNA) products were produced, which could load large amounts of methylene blue (MB) molecules to generate a distinct electrochemical signal. Under the optimized conditions, the proposed electrochemical aptasensor achieved the ultrasensitive detection of AFB1 with a linear detection range of 0.01-100 pg mL^-1, and a limit of detection (LOD) down to 2.84 fg mL^-1. Furthermore, the electrochemical aptasensor was successfully applied for detecting AFB1 in corn and two kinds of traditional Chinese medicine samples, indicating the potential value for AFB1 detection in practical samples.

Construction of an aflatoxin aptamer sensor based on a DNA nanoprism structure

Aflatoxin B1 (AFB1) is a group of heterocyclic aromatic hydrocarbon secondary metabolites, which are the most toxic among the known fungal toxins. Therefore, it becomes particularly important to develop sensitive, accurate, rapid and simple methods for the detection of AFB1. In this work, a method of constructing aflatoxin aptasensor with black phosphorus nano sheet loaded with gold nanoparticles as electrode modification material, Ce-metal organic framework (MOF) material as signal label and prism DNA nano structure modified electrode as recognition interface is proposed. The hybridization between prism DNA and primer probe was used to trigger rolling circle amplification (RCA) on the electrode surface, and then the complementary chain modified with Au NPs@Ce-MOF is bound to the amplification chain to provide electrochemical signals. In the range of 0.024-100 ng mL^-1, the response current showed a good linear relationship with the logarithm of aflatoxin concentration, the linear equation was I = 6.4181 lg c + 11.975 with the linear correlation coefficient of 0.9973, and the detection limit was 1.48 pg mL^-1 (S/N = 3).

A Dual-Mode Method Based on Aptamer Recognition and Time-Resolved Fluorescence Resonance Energy Transfer for Histamine Detection in Fish

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2-1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness.

MnO2 Nanozyme-Mediated CRISPR-Cas12a System for the Detection of SARS-CoV-2

The CRISPR-Cas system was developed into a molecular diagnostic tool with high sensitivity, low cost, and high specificity in recent years. Colorimetric assays based on nanozymes offer an attractive point-of-care testing method for their low cost of use and user-friendly operation. Here, a MnO2 nanozyme-mediated CRISPR-Cas12a system was instituted to detect SARS-CoV-2. MnO2 nanorods linked to magnetic beads via a single-stranded DNA (ssDNA) linker used as an oxidase-like nanozyme inducing the color change of 3,3',5,5'-tetramethylbenzidine, which can be distinguished by the naked eye. The detection buffer color will change when the Cas12a is activated by SARS-CoV-2 and indiscriminately cleave the linker ssDNA. The detection limit was 10 copies per microliter and showed no cross-reaction with other coronaviruses. The nanozyme-mediated CRISPR-Cas12a system shows high selectivity and facile operation, with great potential for molecular diagnosis in point-of-care testing applications.

Use of MALDI-TOF MS to Discriminate between Aflatoxin B1-Producing and Non-Producing Strains of Aspergillus flavus

Aflatoxin B₁ (AFB₁) is one of the most toxic mycotoxins. One of the producers of AFB₁ is Aspergillus flavus. Therefore, its rapid identification plays a key role in various sectors of the food and feed industry. MALDI-TOF mass spectrometry is one of the fastest and most accurate methods today. Therefore, the aim of this research was to develop the rapid identification of producing and non-producing strains of A. flavus based on the entire mass spectrum. To accomplish the main goal a different confirmatory MALDI-TOF MS and TLC procedures such as direct AFB₁ identification by scraping from TLC plates, A. flavus mycelium, nutrient media around A. flavus growth, and finally direct AFB₁ identification from infected wheat and barley grains had to be conducted. In this experiment, MALDI-TOF mass spectrometry with various modifications was the main supporting technology. All confirmatory methods confirmed the presence of AFB₁ in the samples of aflatoxin-producing strains of A. flavus and vice versa; AFB₁ was not detected in the case of non-producing strains. Entire mass spectra (from 2 to 20 kDa) of aflatoxin-producing and non-producing A. flavus strains were collected, statistically analyzed and clustered. An in-depth analysis of the obtained entire mass spectra showed differences between AFB₁-producing and non-producing strains of A. flavus. Statistical and cluster analysis divided AFB₁-producing and non-producing strains of A. flavus into two monasteries. The results indicate that it is possible to distinguish between AFB₁ producers and non-producers by comparing the entire mass spectra using MALDI-TOF MS. Finally, we demonstrated that if there are established local AFB₁-producing and non-producing strains of A. flavus, the entire mass spectrum database identification of aflatoxigenic A. flavus strains can be even faster and cheaper, without the need to identify the toxin itself.

Polydopamine-based nanozyme with dual-recognition strategy-driven fluorescence-colorimetric dual-mode platform for Listeria monocytogenes detection

Development of a simple and efficient dual-mode analytical technique with the built-in cross reference correction feature is benefit to achieve the highly accurate detection of the target pollutants and avoid the false-positive outputs in environmental media. Here, we synthesized a Fe-doped polydopamine (Fe@PDA)-based nanozyme with prominent peroxide-mimetic enzyme activity and high fluorescence emission ability. On this basis, we designed a dual-recognition strategy-driven fluorescence-colorimetric dual-mode detection platform, consisting of Listeria monocytogenes (L. monocytogenes) recognition aptamer-modified Fe@PDA (apt/Fe@PDA) and vancomycin-functionalized Fe₃O₄ (van/Fe₃O₄), for L. monocytogenes. Owing to van/Fe₃O₄-powered magnetic separation, there was a L. monocytogenes concentration-dependent fluorescence enhancement of apt/Fe@PDA for performing fluorescence assay in the precipitate. In this case, the prominent peroxide-mimetic enzyme activity of the residual apt/Fe@PDA in the precipitation could catalyze H₂O₂ to further oxidate colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB, which displayed a L. monocytogenes concentration-dependent absorbance enhancement for carrying out colorimetric assay as well. As a result, a fluorescence-colorimetric dual-mode analytical platform was proposed to successfully detect the residual L. monocytogenes in real environmental media with acceptable results. This work showed the great prospects by integrating dual-recognition strategy into fluorescence nanozyme to develop efficient and reliable dual-mode analytical platforms for safeguarding environmental health.

Recent Advances in Construction and Application of Metal-Nanozymes in Pharmaceutical Analysis

Nanozymes, made of emerging nanomaterials, have similar activity to natural enzyme and exhibit promising applications in in the fields of environment, biology and medicine, and food safety science. In recent years, with the deep finding and research to nanozymes by researchers, its application in field of pharmaceutical analysis has emerged gradually, possessing great significance in drug safety evaluation and quality control. This review summarizes the construction of metal nanozymes, strategies to improve their performance and their application in pharmaceutical detection and analysis, especially in detection of target analytes consisting of small molecule medicine macromolecule, toxic and others, which proposes theoretical foundation for development of nanozymes in this field. At the same time, it also provides opportunities and challenges for the construction and application of new nanozymes.

Towards Development of Molecularly Imprinted Electrochemical Sensors for Food and Drug Safety: Progress and Trends

Due to their advantages of good flexibility, low cost, simple operations, and small equipment size, electrochemical sensors have been commonly employed in food safety. However, when they are applied to detect various food or drug samples, their stability and specificity can be greatly influenced by the complex matrix. By combining electrochemical sensors with molecular imprinting techniques (MIT), they will be endowed with new functions of specific recognition and separation, which make them powerful tools in analytical fields. MIT-based electrochemical sensors (MIECs) require preparing or modifying molecularly imprinted polymers (MIPs) on the electrode surface. In this review, we explored different MIECs regarding the design, working principle and functions. Additionally, the applications of MIECs in food and drug safety were discussed, as well as the challenges and prospects for developing new electrochemical methods. The strengths and weaknesses of MIECs including low stability and electrode fouling are discussed to indicate the research direction for future electrochemical sensors.

Application of Nanomaterials for Coping with Mycotoxin Contamination in Food Safety: From Detection to Control

Mycotoxins, which are toxic secondary metabolites produced by fungi, are harmful to humans. Mycotoxin-induced contamination has drawn attention worldwide. Consequently, the development of reliable and sensitive detection methods and high-efficiency control strategies for mycotoxins is important to safeguard food industry safety and public health. With the rapid development of nanotechnology, many novel nanomaterials that provide tremendous opportunities for greatly improving the detection and control performance of mycotoxins because of their unique properties have emerged. This review comprehensively summarizes recent trends in the application of nanomaterials for detecting mycotoxins (fluorescence, colorimetric, surface-enhanced Raman scattering, electrochemical, and point-of-care testing) and controlling mycotoxins (inhibition of fungal growth, mycotoxin absorption, and degradation). These detection methods possess the advantages of high sensitivity and selectivity, operational simplicity, and rapidity. With research attention on the control of mycotoxins and the gradual excavation of the properties of nanomaterials, nanomaterials are also employed for the inhibition of fungal growth, mycotoxin absorption, and mycotoxin degradation, and impressive controlling effects are obtained. This review is expected to provide the readers insight into this state-of-the-art area and a reference to design nanomaterials-based schemes for the detection and control of mycotoxins.

Ratiometric Luminescence Aptasensor Based on Dual-Emissive Persistent Luminescent Nanoparticles for Autofluorescence- and Exogenous Interference-Free Determination of Trace Aflatoxin B1 in Food Samples

Sensitive and accurate determination of aflatoxin B1 (AFB1) is of great significance to food safety and human health as it is recognized as the most toxic mycotoxin and carcinogenic. Herein, we report a ratiometric luminescence aptasensor based on dual-emissive persistent luminescent nanoparticles (PLNP) for the accurate determination of trace AFB1 in complex food samples without autofluorescence and exogenous interference. Dual-emissive PLNP ZnGa₂O₄:Cr_0.0001 was prepared first and acted as the donor for energy transfer as well as the signal unit with phosphorescence at 714 and 508 nm (the detection and the reference signal, respectively). AFB1 aptamer was then bonded on the surface of PLNP to offer specific recognition ability. Aptamer complementary DNA modified with Cy5.5 was employed as the acceptor for energy transfer and the quenching group to eventually develop a turn-on ratiometric luminescence aptasensor. The developed ratiometric luminescence aptasensor combined the merits of long-lasting luminescence, in situ excitation and autofluorescence-free of PLNP, exogenous interference-free and self-calibration reading of ratiometric sensor, as well as the high selectivity of aptamer, holding great promise for accurate determination of trace AFB1 in complex matrix. The developed ratiometric aptasensor exhibited excellent linearity (0.05-70 ng mL^-1), low limit of detection (0.016 ng mL^-1), and good precision (2.3% relative standard deviation for 11 replicate determination of 1 ng mL^-1 AFB1). The proposed ratiometric aptasensor was successfully applied for the determination of AFB1 in corn, wheat, peanut, millet, oats, and wheat kernels with recoveries of 95.1-106.5%.

Versatile Photoelectrochemical Biosensing for Hg2+ and Aflatoxin B1 Based on Enhanced Photocurrent of AgInS2 Quantum Dot-DNA Nanowires Sensitizing NPC-ZnO Nanopolyhedra

Eliminating false positives or negatives in analysis has been a challenge. Herein, a phenomenon of polarity-switching photocurrent of AgInS₂ quantum dot (QD)-DNA nanowires reversing nitrogen-doped porous carbon-ZnO (NPC-ZnO) nanopolyhedra was found for the first time, and a versatile photoelectrochemical (PEC) biosensor with a reversed signal was innovatively proposed for dual-target detection. NPC-ZnO is a photoactive material with excellent PEC properties, while AgInS₂ QDs as a photosensitive material match NPC-ZnO in the energy level, which not only promotes the transfer of photogenerated carriers but also switches the direction of PEC current. Furthermore, in order to prevent spontaneous agglomeration of AgInS₂ (AIS) QDs and improve its utilization rate, a new multiple-branched DNA nanowire was specially designed to assemble AgInS₂ QDs for constructing amplified signal probes, which not only greatly increased the load of AgInS₂ QDs but also further enhanced the photoelectric signal. When the target Hg²⁺-induced cyclic amplification process generated abundant RDNA, the DNA nanowire signal probe with plenty of QDs was linked to the NPC-ZnO/electrode by RDNA, generating greatly amplified polarity-reversed photocurrent for signal "ON" detection of Hg²⁺. After specific binding of the target (aflatoxin B1, AFB1) to its aptamer, the signal probes of AIS QD-DNA nanowires were released, realizing signal "OFF" assay of AFB1. Thus, the proposed new PEC biosensor provides a versatile method for detection of dual targets and also effectively avoids both false positive and negative phenomena in the assay process, which has great practical application potential in both environmental and food analysis.

Regulation Mechanism of ssDNA Aptamer in Nanozymes and Application of Nanozyme-Based Aptasensors in Food Safety

Food safety issues are a worldwide concern. Pathogens, toxins, pesticides, veterinary drugs, heavy metals, and illegal additives are frequently reported to contaminate food and pose a serious threat to human health. Conventional detection methods have difficulties fulfilling the requirements for food development in a modern society. Therefore, novel rapid detection methods are urgently needed for on-site and rapid screening of massive food samples. Due to the extraordinary properties of nanozymes and aptamers, biosensors composed of both of them provide considerable advantages in analytical performances, including sensitivity, specificity, repeatability, and accuracy. They are considered a promising complementary detection method on top of conventional ones for the rapid and accurate detection of food contaminants. In recent years, we have witnessed a flourishing of analytical strategies based on aptamers and nanozymes for the detection of food contaminants, especially novel detection models based on the regulation by single-stranded DNA (ssDNA) of nanozyme activity. However, the applications of nanozyme-based aptasensors in food safety are seldom reviewed. Thus, this paper aims to provide a comprehensive review on nanozyme-based aptasensors in food safety, which are arranged according to the different interaction modes of ssDNA and nanozymes: aptasensors based on nanozyme activity either inhibited or enhanced by ssDNA, nanozymes as signal tags, and other methods. Before introducing the nanozyme-based aptasensors, the regulation by ssDNA of nanozyme activity via diverse factors is discussed systematically for precisely tailoring nanozyme activity in biosensors. Furthermore, current challenges are emphasized, and future perspectives are discussed.

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Signal enhancing strategies in aptasensors for the detection of small molecular contaminants by nanomaterials and nucleic acid amplification

Small molecular contaminants (such as mycotoxins, antibiotics, pesticide residues, etc.) in food and environment have given rise to many biological and ecological toxicities, which has attracted worldwide attention in recent years. Meanwhile, due to the advantages of aptamers such as high specificity and stability, easy synthesis and modification, as well as low cost and immunogenicity, various aptasensors for the detection of small molecular contaminants have been flourishing. An aptasensor as a whole is composed of an aptamer-based target recognizer and a signal transducer, which are fields of concentrated research. In the practical detection applications, in order to achieve the quantitative detection of small molecular contaminants at low abundance in real samples, a large number of signal enhancing strategies have been utilized in the development of aptasensors. Recent years is a vintage period for efficient signal enhancing strategies of aptasensors by the aid of nanomaterials and nucleic acid amplification that are applied in the elements for target recognition and signal conversion. Therefore, this paper meticulously reviews the signal enhancing strategies based on nanomaterials (including the (quasi-)zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanomaterials) and nucleic acid amplification (including enzyme-assisted nucleic acid amplification and enzyme-free nucleic acid amplification). Furthermore, the challenges and future trends of the abovementioned signal enhancing strategies for application are also discussed in order to inspire the practitioners in the research and development of aptasensors for small molecular contaminants.

The recent development of nanozymes for food quality and safety detection

As potential mimics of natural enzymes, nanozymes overcome many disadvantages of natural enzymes such as complex preparation and purification process, high price, poor stability and low recycling efficiency. Combined with...

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.

A novel COOH–GO–COOH–MWNT/pDA/AuNPs based electrochemical aptasensor was developed for detection of AFB₁.

Nanozyme-based sensors for detection of food biomarkers: a review

Nanozymes have piqued the curiosity of scientists in recent years because of their ability to demonstrate enzyme-like activity combined with advantages such as high stability, inexpensive availability, robust activity, and tunable properties. These attributes have allowed the successful application of nanozymes in sensing to detect various chemical and biological target analytes, overcoming the shortcomings of conventional detection techniques. In this review, we discuss recent developments of nanozyme-based sensors to detect biomarkers associated with food quality and safety. First, we present a brief introduction to this topic, followed by discussing the different types of sensors used in food biomarker detection. We then highlight recent studies on nanozyme-based sensors to detect food markers such as toxins, pathogens, antibiotics, growth hormones, metal ions, additives, small molecules, and drug residues. In the subsequent section, we discuss the challenges and possible solutions towards the development of nanozyme-based sensors for application in the food industry. Finally, we conclude the review by discussing future perspectives of this field towards successful detection and monitoring of food analytes.

We present a discussion on different types of sensors used in food biomarker detection and highlight recent studies on nanozyme-based sensors to detect markers like toxins, pathogens, antibiotics, growth hormones, metal ions, additives, small molecules, drug residues.

A direct competitive nanozyme-linked immunosorbent assay based on MnO2 nanosheets as a catalytic label for the determination of fumonisin B1

A direct competitive nanozyme-linked immunosorbent assay (dcNLISA) based on MnO₂ nanosheets (MnO₂ NSs) as a nanozyme label was developed for the highly sensitive determination of fumonisin B₁ (FB₁). MnO₂ NS-labeled fumonisin B₁-bovine serum albumin was easily synthesized as a competing antigen for the dcNLISA. And color changes derived from the MnO₂-3,3',5,5'-tetramethylbenzidine (TMB) system were exploited as the output signals of the dcNLISA. Several experimental parameters including the concentrations of the coating antibody, pH values, ionic strength and methanol concentration were optimized. Under the optimal conditions, the proposed method demonstrated a linear range (1.17-20.74 ng mL^-1) with a reliable correlation coefficient (R² = 0.9989), a satisfactory limit of detection (0.63 ng mL^-1) and high selectivity for the detection of FB₁. The recoveries of FB₁ in spiked corn and wheat samples were in the range of 85.31-108.16% with coefficients of variation (CVs) ranging from 6.14% to 9.23%. Meanwhile, the testing results showed good consistency (R² = 0.9892) between the developed dcNLISA and the reference method, liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) method. The proposed method was proven to be simple, sensitive, cost-effective and reliable for the screening of FB₁ in cereals.

Highly sensitive magnetic relaxation sensing method for aflatoxin B1 detection based on Au NP-assisted triple self-assembly cascade signal amplification

Highly sensitive detection of aflatoxin B₁ (AFB₁) is of great significance because of its high toxicity and carcinogenesis. We propose a magnetic relaxation sensing method based on gold nanoparticles (Au NPs)-assisted triple self-assembly cascade signal amplification for highly sensitive detection of AFB₁. Both AFB₁ antibody and initiator DNA (iDNA) are labeled on Au NPs to form Ab-Au-iDNA probe. iDNA is enriched by Au NPs to achieve first signal amplification. Different amounts of Ab-Au-iDNA were bound with AFB₁ antigen by indirect competitive immunoassay, and then hybridization chain reaction event was initiated by iDNA to produce long hybridization chain reaction products to enrich more horseradish peroxidase-streptavidin for the second signal amplification. Dopamine could be rapidly converted to polydopamine by HRP catalysis, which is used as the third signal amplification. The Fe³⁺ solution, providing paramagnetic ions with a strong magnetic signal, could be adsorbed by the polydopamine due to the formation of coordination bonds of phenolic hydroxyl groups with Fe³⁺. This effective interaction between polydopamine and Fe³⁺ significantly changes the transverse relaxation time signal of Fe³⁺ supernatant solution, which can be used as a magnetic probe for highly sensitive detection of AFB₁. The sensor exhibited high specificity and sensitivity with a detection limit of 0.453 pg/mL owing to the Au NP-assisted triple self-assembly cascade signal amplification strategy. It has been successfully employed for AFB₁ detection in animal feed samples with consistent results of enzyme linked immune sorbent assay and high-performance liquid chromatography.

Nanozyme Applications: A Glimpse of Insight in Food Safety

Nanozymes own striking merits, including high enzyme-mimicking activity, good stability, and low cost. Due to the powerful and distinguished functions, nanozymes exhibit widespread applications in the field of biosensing and immunoassay, attracting researchers in various fields to design and engineer nanozymes. Recently, nanozymes have been innovatively used to bridge nanotechnology with analytical techniques to achieve the high sensitivity, specificity, and reproducibility. However, the applications of nanozymes in food applications are seldom reviewed. In this review, we summarize several typical nanozymes and provide a comprehensive description of the history, principles, designs, and applications of nanozyme-based analytical techniques in food contaminants detection. Based on engineering and modification of nanozymes, the food contaminants are classified and then discussed in detail via discriminating the roles of nanozymes in various analytical methods, including fluorescence, colorimetric and electrochemical assay, surface-enhanced Raman scattering, magnetic relaxing sensing, and electrochemiluminescence. Further, representative examples of nanozymes-based methods are highlighted for contaminants analysis and inhibition. Finally, the current challenges and prospects of nanozymes are discussed.

Recent Achievements in Electrochemical and Surface Plasmon Resonance Aptasensors for Mycotoxins Detection

Mycotoxins are secondary metabolites of fungi that contaminate agriculture products. Their release in the environment can cause severe damage to human health. Aptasensors are compact analytical devices that are intended for the fast and reliable detection of various species able to specifically interact with aptamers attached to the transducer surface. In this review, assembly of electrochemical and surface plasmon resonance (SPR) aptasensors are considered with emphasis on the mechanism of signal generation. Moreover, the properties of mycotoxins and the aptamers selected for their recognition are briefly considered. The analytical performance of biosensors developed within last three years makes it possible to determine mycotoxin residues in water and agriculture/food products on the levels below their maximal admissible concentrations. Requirements for the development of sample treatment and future trends in aptasensors are also discussed.