Emerging strategies to enhance the sensitivity of competitive ELISA for detection of chemical contaminants in food samples

Highly selective and sensitive immunoassays for flurogestone acetate analysis in goat milk: From rational hapten design and antibody production to assay development

The preparation of high specificity and affinity antibodies is challenging due to limited information on characteristic groups of haptens in traditional design strategy. In this study, we first predicted characteristic groups of flurogestone acetate (FGA) using quantitative analysis of molecular surface combined with atomic charge distribution. Subsequently, FGA haptens were rationally designed to expose these identified characteristic groups fully. As a result, seven monoclonal antibodies were obtained with satisfactory performance, exhibiting IC50 values from 0.17 to 0.45 μg/L and negligible cross-reactivities below 1% to other 18 hormones. The antibody recognition mechanism further confirmed hydrogen bonds and hydrophobic interactions involving predicted FGA characteristic groups and specific amino acids in the antibodies contributed to their high specificity and affinity. Finally, one selective and sensitive ic-ELISA was developed for FGA determination with a detection limit as low as 0.12 μg/L, providing an efficient tool for timely monitoring of FGA in goat milk samples.

Self-shedding MOF-nanocarriers modulated CdS/MoSe2 heterojunction activity through in-situ ion exchange: An enhanced split-type photoelectrochemical sensor for deoxynivalenol

Deoxynivalenol (DON), a mycotoxin produced by Fusarium, poses a significant risk to human health and the environment. Therefore, the development of a highly sensitive and accurate detection method is essential to monitor the pollution situation. In response to this imperative, we have devised an advanced split-type photoelectrochemical (PEC) sensor for DON analysis, which leverages self-shedding MOF-nanocarriers to modulate the photoelectric response ability of PEC substrate. The PEC sensing interface was constructed using CdS/MoSe2 heterostructures, while the self-shedding copper peroxide nanodots@ZIF-8 (CPNs@ZIF-8) served as the Cu2+ source for the in-situ ion exchange reaction, which generated a target-related signal reduction. The constructed PEC sensor exhibited a broad linear range of 0.1 pg mL-1 to 500 ng mL-1 with a low detection limit of 0.038 pg mL-1, demonstrating high stability, selectivity, and proactivity. This work not only introduces innovative ideas for the design of photosensitive materials, but also presents novel sensing strategies for detecting various environmental pollutants.

Development of a Phage-Displayed Nanobody-Based Competitive Immunoassay for the Sensitive Detection of Soybean Agglutinin

Soybean agglutinin (SBA) is a primary antinutritional factor in soybeans that can inhibit the growth of humans and mammals, disrupt the intestinal environment, and cause pathological changes. Therefore, detecting and monitoring SBA in foods is essential for safeguarding human health. In this paper, M13 phage-displayed nanobodies against SBA were isolated from a naive nanobody library. An M13 phage-displayed nanobody-based competitive enzyme-linked immunosorbent assay (P-cELISA) was then established for SBA analysis using biotinylated anti-M13 phage antibody (biotin-anti-M13) and streptavidin poly-HRP conjugate (SA-poly-HRP). The biotin-anti-M13@SA-poly-HRP probe can easily amplify the detection signal without the chemical modifications of phage-displayed nanobodies. The established P-cELISA presented a linear detection range of 0.56-250.23 ng/mL and a limit of detection (LOD) of 0.20 ng/mL, which was 12.6-fold more sensitive than the traditional phage-ELISA. Moreover, the developed method showed good specificity for SBA and acceptable recoveries (78.21-121.11%) in spiked wheat flour, albumen powder, and whole milk powder. This study proposes that P-cELISA based on biotin-anti-M13@SA-poly-HRP may provide a convenient and effective strategy for the sensitive detection of SBA.

A Straightforward, Sensitive, and Reliable Strategy for Ethyl Carbamate Detection in By-Products from Baijiu Production by Enzyme-Linked Immunosorbent Assay

Baijiu is a renowned Chinese distilled liquor, notable for its distinctive flavor profile and intricate production process, which prominently involves fermentation and distillation. Ethyl carbamate (EC), a probable human carcinogen, can be potentially formed during these procedures, thus prompting significant health concerns. Consequently, the contamination of EC during Baijiu production has become an increasingly pressing issue. In this study, we developed a rapid and easily operable immunoassay for determining EC in the fermented materials used in Baijiu production. The development of a high-quality antibody specific to EC facilitated a streamlined analytical procedure and heightened method sensitivity. Furthermore, we systematically evaluated other essential parameters. Following optimization, the method achieved an IC50 value of 11.83 μg/kg, with negligible cross-reactivity against EC analogs. The recovery study demonstrated the method's good accuracy and precision, with mean recovery rates ranging from 86.0% to 105.5% and coefficients of variation all below 10%. To validate the feasibility of the technique, we collected and analyzed 39 samples simultaneously using both the proposed immunoassay and confirmatory gas chromatography-mass spectrometry (GC-MS). A robust correlation was observed between the results obtained from the two methods (R2 > 0.99). The detected EC levels ranged from 2.36 μg/kg to 7.08 μg/kg, indicating an increase during the fermentation process.

Review of Detection Limits for Various Techniques for Bacterial Detection in Food Samples

Foodborne illnesses can be infectious and dangerous, and most of them are caused by bacteria. Some common food-related bacteria species exist widely in nature and pose a serious threat to both humans and animals; they can cause poisoning, diseases, disabilities and even death. Rapid, reliable and cost-effective methods for bacterial detection are of paramount importance in food safety and environmental monitoring. Polymerase chain reaction (PCR), lateral flow immunochromatographic assay (LFIA) and electrochemical methods have been widely used in food safety and environmental monitoring. In this paper, the recent developments (2013-2023) covering PCR, LFIA and electrochemical methods for various bacterial species (Salmonella, Listeria, Campylobacter, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)), considering different food sample types, analytical performances and the reported limit of detection (LOD), are discussed. It was found that the bacteria species and food sample type contributed significantly to the analytical performance and LOD. Detection via LFIA has a higher average LOD (24 CFU/mL) than detection via electrochemical methods (12 CFU/mL) and PCR (6 CFU/mL). Salmonella and E. coli in the Pseudomonadota domain usually have low LODs. LODs are usually lower for detection in fish and eggs. Gold and iron nanoparticles were the most studied in the reported articles for LFIA, and average LODs were 26 CFU/mL and 12 CFU/mL, respectively. The electrochemical method revealed that the average LOD was highest for cyclic voltammetry (CV) at 18 CFU/mL, followed by electrochemical impedance spectroscopy (EIS) at 12 CFU/mL and differential pulse voltammetry (DPV) at 8 CFU/mL. LOD usually decreases when the sample number increases until it remains unchanged. Exponential relations (R2 > 0.95) between LODs of Listeria in milk via LFIA and via the electrochemical method with sample numbers have been obtained. Finally, the review discusses challenges and future perspectives (including the role of nanomaterials/advanced materials) to improve analytical performance for bacterial detection.

A comprehensive review of mycotoxins: Toxicology, detection, and effective mitigation approaches

Mycotoxins, harmful compounds produced by fungal pathogens, pose a severe threat to food safety and consumer health. Some commonly produced mycotoxins such as aflatoxins, ochratoxin A, fumonisins, trichothecenes, zearalenone, and patulin have serious health implications in humans and animals. Mycotoxin contamination is particularly concerning in regions heavily reliant on staple foods like grains, cereals, and nuts. Preventing mycotoxin contamination is crucial for a sustainable food supply. Chromatographic methods like thin layer chromatography (TLC), gas chromatography (GC), high-performance liquid chromatography (HPLC), and liquid chromatography coupled with a mass spectrometer (LC/MS), are commonly used to detect mycotoxins; however, there is a need for on-site, rapid, and cost-effective detection methods. Currently, enzyme-linked immunosorbent assays (ELISA), lateral flow assays (LFAs), and biosensors are becoming popular analytical tools for rapid detection. Meanwhile, preventing mycotoxin contamination is crucial for food safety and a sustainable food supply. Physical, chemical, and biological approaches have been used to inhibit fungal growth and mycotoxin production. However, new strains resistant to conventional methods have led to the exploration of novel strategies like cold atmospheric plasma (CAP) technology, polyphenols and flavonoids, magnetic materials and nanoparticles, and natural essential oils (NEOs). This paper reviews recent scientific research on mycotoxin toxicity, explores advancements in detecting mycotoxins in various foods, and evaluates the effectiveness of innovative mitigation strategies for controlling and detoxifying mycotoxins.

Novel competitive electrochemical impedance biosensor for the ultrasensitive detection of umami substances based on Pd/Cu-TCPP(Fe)

The development of biosensors capable of assessing umami intensity has elicited significant attention. However, the detection range of these biosensors is constrained by the sensing components and strategies used. In this study, we introduce a novel competitive, ultra-high-sensitivity impedance biosensor by utilizing composite nanomaterials and T1R1 as a composite signal probe. Pd/Cu-TCPP(Fe) had a substantial surface area, effectively enhancing the loading capacity of the T1R1 and thus augmenting the biosensor's recognition precision. Furthermore, the Pd/Cu-TCPP(Fe) elevated peroxidase-like activity catalyzed the formation of insoluble precipitates of 4-chloro-1-naphthol (4-CN), resulting in cascaded amplification of the impedance signal. The remarkable catalytic activity of the composite signal probe endowed the biosensor with exceptional analytical performance, featuring a limit of detection (LOD) of 0.86 pg/mL and a linear detection range spanning from 10 to 10,000 pg/mL. Successful application of the biosensor for umami detection in fish was demonstrated, signifying its substantial potential in food-flavor evaluation.

A facile fluorescence microplate immunoassay based on an in situ fluorogenic reaction for the detection of two highly toxic anticoagulant rodenticides in food and biological matrix

Bromadiolone and brodifacoum, the most frequently used anticoagulant rodenticides, are highly toxic and pose a threat to public health by causing food poisoning incidents. Here, we developed a fluorescence microplate immunoassay for facile and sensitive detection of bromadiolone and brodifacoum by introducing three commercial chemicals (p-phenylenediamine, polyethyleneimine, H2O2) as a new substrate of horseradish peroxidase and then generating fluorescence signals based on an in situ fluorogenic reaction (detection time within 75 min). This assay exhibited higher efficiency in generating fluorescence signals, thereby exhibiting a 6-fold improvement in sensitivity compared with colorimetric ELISA. The limit of detection was 0.23-0.28 ng/mL (ng/g) for bromadiolone and 0.34-0.61 ng/mL (ng/g) for brodifacoum in corn and human serum, with recovery ratios higher than 82.3 %. These satisfactory results illustrated our proposed assay was a potential tool for food analysis and poisoning diagnosis caused by bromadiolone and brodifacoum.

Preparation and recognition mechanism study of an scFv targeting chloramphenicol for a hybridization chain reaction-CRISPR/Cas12a amplified fluoroimmunoassay

Recombinant antibody-based immunoassays have emerged as crucial techniques for detecting antibiotic residues in food samples. Developing a stable recombinant antibody production system and enhancing detection sensitivity are crucial for their biosensing applications. Here, we bioengineered a single-chain fragment variable (scFv) antibody to target chloramphenicol (CAP) using both Bacillus subtilis and HEK 293 systems, with the HEK 293-derived scFv demonstrating superior sensitivity. Computational chemistry analyses indicated that ASP-99 and ASN-102 residues in the scFv play key roles in antibody recognition, and the hydroxyl group near the benzene ring of the target molecule is critical for in antibody binding. Furthermore, we enhanced the scFv's biosensing sensitivity using an HCR-CRISPR/Cas12a amplification strategy in a streptavidin-based immunoassay. In the dual-step amplification process, detection limits for CAP in the HCR and HCR-CRISPR/Cas12a stages were significantly reduced to 55.23 pg/mL and 3.31 pg/mL, respectively. These findings introduce an effective method for developing CAP-specific scFv antibodies and also propose a multi-amplification strategy to increase immunoassay sensitivity. Additionally, theoretical studies also offer valuable guidance in CAP hapten design and genetic engineering for antibody modification.

Sensitive fluorescence ELISA for the detection of zearalenone based on self-assembly DNA nanocomposites and copper nanoclusters

Zearalenone (ZEN), produced by Fusarium species, is a potential risk to human health. Traditional enzyme-linked immunosorbent assay (ELISA) is restricted due to low sensitivity for the detection of ZEN. Herein, enzyme nanocomposites (ALP-SA-Bio-ssDNA, ASBD) were prepared with the self-assembly strategy based on streptavidin-labeled alkaline phosphatase (SA-ALP) and dual-biotinylated ssDNA (B2-ssDNA). The enzyme nanocomposites improved the loading amount of ALP and catalyzed more ascorbic acid 2-phosphate to generate ascorbic acid (AA). Subsequently, Cu2+ could be reduced to copper nanoclusters (CuNCs) having strong fluorescence signal by AA with poly T. Benefiting from the high enzyme load of nanocomposites and the strong signal of CuNCs, the fluorescence ELISA was successfully established for the detection of ZEN. The proposed method exhibited lower limit of detection (0.26 ng mL-1) than traditional ELISA (1.55 ng mL-1). The recovery rates ranged from 92.00% to 108.38% (coefficient of variation < 9.50%) for the detection of zearalenone in corn and wheat samples. In addition, the proposed method exhibited no cross reaction with four other mycotoxins. This proposed method could be used in trace detection for food safety.

Alkaline phosphatase triggered gold nanoclusters turn-on fluorescence immunoassay for detection of Ochratoxin A

Ochratoxin A (OTA) is a highly toxic mycotoxin which can cause a variety of diseases. Sensitive detection of OTA is significant for food safety. Herein, a feasible and sensitive immunoassay was established for OTA detection by alkaline phosphatase (ALP) triggered gold nanoclusters (AuNCs) turn-on fluorescence. The fluorescence of the AuNCs can be quenched by Cr6+ induced aggregation of AuNCs and the fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the catalytic action of ALP-labelled IgG (IgG-ALP), the ascorbic acid 2-phosphate (AA2P) was hydrolyzed to ascorbic acid (AA) for the reducing of Cr6+ to Cr3+. As a result, the degrees of AuNCs aggregation and FRET were weakened and the fluorescence of AuNCs was turned on. The amount of OTA in the sample was negatively correlated with the amount of IgG-ALP captured by anti-OTA monoclonal antibody (McAb) in the microplate. In optimal conditions, the turn-on fluorescence immunoassay had a good linear range of 6.25-100 ng/mL, and the detection limit was 0.693 ng/mL. The recoveries of OTA from corn were 95.89%-101.08% for the fluorescence immunoassay. This work provided a feasible, sensitive and good selectivity fluorescence method for OTA detection.

Detection mechanism and the outlook of metal-organic frameworks for the detection of hazardous substances in milk

Milk has a high nutritional value. However, milk is easily contaminated in the production, processing, and storage processes, which harms consumers' health. Therefore, the harmful substances' detection in milk is important. Metal-organic frameworks (MOFs) have proven high potential in food safety detection due to their unique porous structure, large effective surface area, large porosity, and structural tunability. This article systematically describes the detection mechanism of fluorescence, electrochemical, colorimetric, and enzyme-linked immunosorbent assay based on MOFs. The progress of the application of MOFs in the detection of antibiotics, harmful microorganisms and their toxins, harmful ions, and other harmful substances in milk in recent years is reviewed. The structural tunability of MOFs enables them to be functionalized, giving the ability to be applied to different detection methods or substances. Therefore, MOFs can be used as an advantageous sensing material for detecting harmful substances in the complex environment of milk.

A novel Recjf Exo signal amplification strategy based on bioinformatics-assisted truncated aptamer for efficient fluorescence detection of AFB1

Aflatoxin B1 (AFB1) is a typical mycotoxin that signifacntly endangers public health and economy. In this study, we systematically studied the interaction of aptamers with AFB1 using circular dichroism, molecular dynamics, molecular docking, and fluorescence analysis. The truncated sequence aptamers were screened using molecular docking. We successfully obtained the AFB1 aptamer with higher affinity and its truncated form was enhanced by 5.2-fold compared to the initial AFB1 aptamer. In addition, for rapid detection of AFB1, we designed a fluorescent nano-adaptor sensing platform using RecJf exonuclease signal amplification strategy based on the optimal aptamer. The aptasensor showed satisfactory sensitivity towards AFB1 with a linear detection range of 1-400 ng/mL and a detection limit of 0.57 ng/mL. The aptasensor was successfully applied to the determination of AFB1 in soybean oil and corn oil with recoveries of 91.02 %-106.59 % and 87.39 %-110.61 %, respectively. The successful application of the AFB1 aptasensor, developed through bioinformatics truncation of the aptamer, provides a novel approach to creating a cost-effective, eco-friendly, and rapid aptamer sensing platform.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Detection of Dibutyl Phthalate in Surface Water by Fluorescence Polarization Immunoassay

Dibutyl phthalate (DBP) is widely used as a plasticizer in the production of polymeric materials to give them flexibility, strength and extensibility. However, due to its negative impact on human health, in particular reproductive functions and fetal development, the content of DBP must be controlled in food and the environment. The present study aims to develop a sensitive, fast and simple fluorescence polarization immunoassay (FPIA) using monoclonal antibodies derived against DBP (MAb-DBP) for its detection in open waters. New conjugates of DBP with various fluorescein derivatives were obtained and characterized: 5-aminomethylfluorescein (AMF) and dichlorotriazinylaminofluorescein (DTAF). The advantages of using the DBP-AMF conjugate in the FPIA method are shown, the kinetics of binding of this chemical with antibodies are studied, the analysis is optimized, and the concentration of monoclonal antibodies is selected for sensitivity analysis-16 nM. The calibration dependence of the fluorescence polarization signal for the detection of DBP was obtained. The observed IC50 (DBP concentration at which a 50% decrease in the fluorescence polarization signal occurs, 40 ng/mL) and the limit of detection (LOD, 7.5 ng/mL) values were improved by a factor of 45 over the previously described FPIA using polyclonal antibodies. This technique was tested by the recovery method, and the high percentage of DBP discovery in water ranged from 85 to 110%. Using the developed method, real water samples from Lake Onega were tested, and a good correlation was shown between the results of the determination of DBP by the FPIA method and GC-MS. Thus, the FPIA method developed in this work can be used to determine DBP in open-water reservoirs.

Fluorescence Resonance Energy Transfer (FRET)-Based Sensor for Detection of Foodborne Pathogenic Bacteria: A Review

Sensitive and rapid determination of foodborne pathogenic bacteria is of practical importance for the control and prevention of foodborne illnesses. Nowadays, with the prosperous development of fluorescence assays, fluorescence resonance energy transfer (FRET)-derived diagnostic strategies are extensively employed in quantitative analysis of different pathogenic bacteria in food-related matrices, which displays a rapid, simple, stable, reliable, cost-effective, selective, sensitive, and real-time way. Considering the extensive efforts that have been made in this field so far, we here discuss the up-to-date developments of FRET-based diagnostic approaches for the determination of key foodborne pathogens like Staphylococcus aureus, Escherichia coli, Vibrio parahaemolyticus, Salmonella spp., Campylobacter spp., and Bacillus cereus in complex food-related matrices. Moreover, the principle of this technology, the choosing standards of acceptor-donor pairs, and the fluorescence properties are also profiled. Finally, the current prospects and challenges in this field are also put forward.

Oilomics: An important branch of foodomics dealing with oil science and technology

Oil is one of three nutritious elements. The application of omics techniques in the field of oil science and technology is attracted increasing attention. Oilomics, which emerged as an important branch of foodomics, has been widely used in various aspects of oil science and technology. However, there are currently no articles systematically reviewing the application of oilomics. This paper aims to provide a critical overview of the advantages and value of oilomics technology compared to traditional techniques in various aspects of oil science and technology, including oil nutrition, oil processing, oil quality, safety, and traceability. Moreover, this article intends to review major issues in oilomics and give a comprehensive, critical overview of the current state of the art, future challenges and trends in oilomics, with a view to promoting the optimal application and development of oilomics technology in oil science and technology.

CRISPR/Cas12a-Powered Competitive Immunosorbent Assay for Small Molecules

CRISPR/Cas systems are powerful tools for sensitive nucleic acid molecular diagnosis due to their specific nucleic acid recognition and high trans-cleavage activity and have also allowed for quantification of non-nucleic acid targets, relying on a strategy to convert the target detection to analysis of nucleic acids. Here, we describe a CRISPR/Cas12a-powered immunosorbent assay for sensitive small-molecule detection by using the antibody coated on the microplate to recognize the target and the small molecule-labeled active DNA (acDNA) to trigger the activity of CRISPR/Cas12a. In the absence of small-molecule targets, acDNA probes are captured by the antibody on the microplate and then activate Cas12a in catalytic trans-cleavage of fluorescent DNA reporters, generating strong fluorescence. The presence of small-molecule targets displaces the acDNA probes from the antibody, causing a decrease of acDNA probes on the microplate and reduction of activated Cas12a, so the fluorescence signal decreases, and small molecules can be detected by monitoring the fluorescence change. After systematically optimizing experimental conditions (e.g., Cas12a reaction), the proposed method achieved the detection of three model small molecules, biotin, digoxin, and folic acid, with low detection limits, and a flexible detection concentration range was obtained by simply changing the amount of acDNA probes and immobilized antibodies. The assay showed high selectivity and good applicability in complex media. The integration of the CRISPR/Cas12a system improves the analytical performance of immunoassay, broadening and facilitating its applications in rapid, simple, and sensitive small molecule analysis.

Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays

The drive to achieve ultrasensitive target detection with exceptional efficiency and accuracy requires the advancement of immunoassays. Optical immunoassays have demonstrated significant potential in clinical diagnosis, food safety, environmental protection, and other fields. Through the innovative and feasible combination of enzyme catalysis and optical immunoassays, notable progress has been made in enhancing analytical performances. Among the kinds of reporter enzymes, alkaline phosphatase (ALP) stands out due to its high catalytic activity, elevated turnover number, and broad substrate specificity, rendering it an excellent candidate for the development of various immunoassays. This review provides a systematic evaluation of the advancements in optical immunoassays by employing ALP as the signal label, encompassing fluorescence, colorimetry, chemiluminescence, and surface-enhanced Raman scattering. Particular emphasis is placed on the fundamental signal amplification strategies employed in ALP-linked immunoassays. Furthermore, this work briefly discusses the proposed solutions and challenges that need to be addressed to further enhance the performances of ALP-linked immunoassays.

Aptamer-modified metal organic frameworks for measurement of food contaminants: a review

The measurement of food contaminants faces a great challenge owing to the increasing demand for safe food, increasing consumption of fast food, and rapidly changing patterns of human consumption. As different types of contaminants in food products can pose different levels of threat to human health, it is desirable to develop specific and rapid methods for their identification and quantification. During the past few years, metal-organic framework (MOF)-based materials have been extensively explored in the development of food safety sensors. MOFs are porous crystalline materials with tunable composition, dynamic porosity, and facile surface functionalization. The construction of high-performance biosensors for a range of applications (e.g., food safety, environmental monitoring, and biochemical diagnostics) can thus be promoted through the synergistic combination of MOFs with aptamers. Accordingly, this review article delineates recent innovations achieved for the aptamer-functionalized MOFs toward the detection of food contaminants. First, we describe the basic concepts involved in the detection of food contaminants in terms of the advantages and disadvantages of the commonly used analytical methods (e.g., DNA-based methods (PCR/real-time PCR/multiplex PCR/digital PCR) and protein-based methods (enzyme-linked immunosorbent assay/immunochromatography assay/immunosensor/mass spectrometry). Afterward, the progress in aptamer-functionalized MOF biosensors is discussed with respect to the sensing mechanisms (e.g., the role of MOFs as signal probes and carriers for loading signal probes) along with their performance evaluation (e.g., in terms of sensitivity). We finally discuss challenges and opportunities associated with the development of aptamer-functionalized MOFs for the measurement of food contaminants.

Single-Walled Carbon Nanohorn-Based Fluorescence Energy Resonance Transfer Aptasensor Platform for the Detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is one of the most contaminated fungal toxins worldwide and is prone to cause serious economic losses, food insecurity, and health hazards to humans. The rapid, on-site, and economical method for AFB1 detection is need of the day. In this study, an AFB1 aptamer (AFB1-Apt) sensing platform was established for the detection of AFB1. Fluorescent moiety (FAM)-modified aptamers were used for fluorescence response and quenching, based on the adsorption quenching function of single-walled carbon nanohorns (SWCNHs). Basically, in our constructed sensing platform, the AFB1 specifically binds to AFB1-Apt, making a stable complex. This complex with fluorophore resists to be adsorbed by SWCNHs, thus prevent SWCNHs from quenching of fluorscence, resulting in a fluorescence response. This designed sensing strategy was highly selective with a good linear response in the range of 10-100 ng/mL and a low detection limit of 4.1 ng/mL. The practicality of this sensing strategy was verified by using successful spiking experiments on real samples of soybean oil and comparison with the enzyme-linked immunosorbent assay (ELISA) method.

Bi-functional antibody-CRISPR/Cas12a ribonucleoprotein conjugate for improved immunoassay performance

Protein conjugates are commonly used in biochemistry, including diagnostic platforms such as antibody-based immunoassays. Antibodies can be bound to a variety of molecules creating conjugates with desirable functions, particularly for imaging and signal amplification. Cas12a is a recently discovered programable nuclease with the remarkable capability to amplify assay signals due to its trans-cleavage property. In this study, we directly conjugated antibody with Cas12a/gRNA ribonucleoprotein without the loss of function in either constituent. The conjugated antibody was suitable for immunoassays and the conjugated Cas12a was capable of amplifying the signal produced in an immunosensor without the need to change the original assay protocol. We applied the bi-functional antibody-Cas12a/gRNA conjugate to successfully detect two different types of targets, a whole pathogenic microorganism, Cryptosporidium, and a small protein, cytokine IFN-γ, with sensitivity reaching one single microorganism per sample and 10 fg/mL for IFN-γ, respectively. With simple substitution of the antibody conjugated with the Cas12a/gRNA RNP, this approach can potentially be applied to increase sensitivity of a variety of immunoassays for a broad range of different analytes.

Amide-containing neoepitopes: the key factor in the preparation of hapten-specific antibodies and a strategy to overcome

For a long time, people have suffered from uncertainty, complexity, and a low success rate in generating and screening antibodies against small molecules, which have become the core bottlenecks of immunochemistry. Here, the influence of antigen preparation on antibody generation was investigated at both molecular and submolecular levels. Neoepitopes (amide-containing neoepitopes) formed in the preparation of complete antigens are one of the most important factors limiting the efficiency of generating hapten-specific antibodies, which was verified by different haptens, carrier proteins, and conjugation conditions. Amide-containing neoepitopes present electron-dense structural components on the surface of prepared complete antigens and, therefore, induce the generation of the corresponding antibody with much higher efficiency than target hapten. Crosslinkers should be carefully selected and not overdosed. According to these results, some misconceptions in the conventional anti-hapten antibody production were clarified and corrected. By controlling the content of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) during the synthesis of immunogen to limit the formation of amide-containing neoepitopes, the efficiency of hapten-specific antibody generation could be significantly improved, which verified the correctness of the conclusion and provided an efficient strategy for antibody preparation. The result of the work is of scientific significance in the preparation of high-quality antibodies against small molecules.

Ps-Pt nanozyme-based synergistic signal amplification biosensor for highly sensitive colorimetric detection of protein

Immunosorbent assay is one of the most popular immunological screening techniques which has been widely used for the clinical diagnosis of alpha-fetoprotein (AFP). While traditional immunosorbent assay (ELISA) suffers from low detection sensitivity due to its low intensity of colorimetric signal. To improve the sensitivity of AFP detection, we developed a new and sensitive immunocolorimetric biosensor by combining Ps-Pt nanozyme with terminal deoxynucleotidyl transferase (TdT)-mediated polymerization reaction. The determination of AFP was achieved by measuring the visual color intensity produced by the catalytic oxidation reaction of the 3,3',5,5'-tetramethylbenzidine (TMB) solution with Ps-Pt and horseradish peroxidase (HRP). Owing to the synergistic catalysis of Ps-Pt and horseradish peroxidase HRP enriched in polymerized amplification products, this biosensor exhibited a significant color change within 25 s in the presence of 10-500 pg/mL AFP. This proposed method allowed for the specific detection of AFP with a detection limit of 4.30 pg/mL and even 10 pg/mL target protein could be distinguished clearly by visual observation. Furthermore, this biosensor could be applied to analysis of AFP in the complex sample and could be easily extended to the detection of other proteins.

Ratiometric Fluorescence Immunoassay Based on MnO2 Nanoflakes for Sensitive and Accurate Detection of Tricaine

Tricaine is a common anesthetic used in the long-distance transport of live fish. Recently, its negative impact on human health has aroused extensive concern. Thus, rapid and reliable techniques for tricaine residue analysis are essential to ensuring the quality of aquatic products. Herein, a specific anti-tricaine monoclonal antibody (Mab) was prepared. Then, a sensitive and robust ratiometric fluorescence ELISA (RF-ELISA) was constructed for detecting tricaine based on two MnO₂ nanoflake-mediated (MnO₂ NFs) fluorogenic reactions. In the RF-ELISA protocol, MnO₂ NFs with oxidase-like activity can trigger the formation of fluorescent 2,3-diaminophenazine (oxOPD) with an emissive peak at 570 nm from non-fluorescent o-phenylenediamine (OPD), while ascorbic acid (AA) can decompose MnO₂ NFs to lose their oxidase-mimicking activity, which is accompanied by the oxidation of AA into dehydroascorbic acid (DHAA). The subsequent reaction between the generated DHAA and OPD will result in the production of 3-(1,2-dihydroxy ethyl)furo[3,4-b]quinoxalin-1(3H)-on (DFQ), which has a potent emission peak at 445 nm. By virtue of the alkaline phosphatase (ALP) labeled on the antibody, which can catalyze the production of AA from ascorbic acid 2-phosphate (AAP), the concentration of tricaine can be linked to the variation of the RF signal (F₄₄₅/F₅₇₀) via a competitive immunoreaction. After optimization, RF-ELISA displayed a detection limit (LOD) of 0.28 ng/mL toward tricaine (in buffer solution), which was 376-fold lower than that of the traditional colorimetric ELISA. For practical application, the LODs of RF-ELISA for tricaine detection in shrimp and tilapia samples were determined to be 2.8 and 5.6 ng/g, respectively. Recoveries for spiked shrimp and tilapia samples, as well as the validation data from LC-MS/MS, showed that RF-ELISA exhibited good accuracy, precision, and reliability. This RF-ELISA protocol opened up new ways for tricaine and other-target analyses in food safety detection.

CRISPR-based biosensors for pathogenic biosafety

Pathogenic biosafety is a worldwide concern. Tools for analyzing pathogenic biosafety, that are precise, rapid and field-deployable, are highly demanded. Recently developed biotechnological tools, especially those utilizing CRISPR/Cas systems which can couple with nanotechnologies, have enormous potential to achieve point-of-care (POC) testing for pathogen infection. In this review, we first introduce the working principle of class II CRISPR/Cas system for detecting nucleic acid and non-nucleic acid biomarkers, and highlight the molecular assays that leverage CRISPR technologies for POC detection. We summarize the application of CRISPR tools in detecting pathogens, including pathogenic bacteria, viruses, fungi and parasites and their variants, and highlight the profiling of pathogens' genotypes or phenotypes, such as the viability, and drug-resistance. In addition, we discuss the challenges and opportunities of CRISPR-based biosensors in pathogenic biosafety analysis.

Synthesizing Submicron Polyelectrolyte Capsules to Boost Enzyme Immobilization and Enhance Enzyme-Based Immunoassays

Polyelectrolyte capsules (PCs) exhibit attractive superiorities in enzyme immobilization, including providing a capacious microenvironment for enzyme conformational freedom, highly effective mass transfer, and protecting enzymes from the external environment. Herein, we provide the first systemic evaluation of submicron PCs (SPCs, 500 nm) for enzyme immobilization. The catalytic kinetics results show that SPC encapsulation affected the affinities of enzymes and substrates but significantly enhanced their catalytic activity. The stability test indicates that SPC-encapsulated horseradish peroxidase (HRP) exhibits ultrahigh resistance to external harsh conditions and has a longer storage life than that of soluble HRP. The proposed encapsulation strategy enables 7.73-, 2.22-, and 11.66-fold relative activities when working at a pH as low as 3, at a NaCl concentration as high as 500 mM, and at a trypsin concentration as high as 10 mg/mL. We find that SPC encapsulation accelerates the cascade reaction efficiency of HRP and glucose oxidase. Owing to SPCs enhancing the catalytic activity of the loaded enzymes, we established an amplified enzyme-linked immunosorbent assay (ELISA) for the detection of Escherichia coli O157:H7 using HRP-loaded SPCs. The detection sensitivity of SPC-improved ELISA was found to be 280 times greater than that of conventional HRP-based ELISA. Altogether, we provide an elaborate evaluation of 500 nm SPCs on enzyme immobilization and its application in the ultrasensitive detection of foodborne pathogens. This evaluation provides evidence to reveal the potential advantage of SPCs on enzyme immobilization for enzyme-based immunoassays. It has excellent biological activity and strong stability and broadens the application prospect in urine, soy sauce, sewage, and other special samples.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

CRISPR/Cas12a-Assisted Chemiluminescence Sensor for Aflatoxin B1 Detection in Cereal Based on Functional Nucleic Acid and In-Pipet Rolling Circle Amplification

Herein, we report a CRISPR/Cas12a-assisted chemiluminescence sensor for aflatoxin B₁ (AFB₁) detection based on functional nucleic-acid-mediated target recognition and in-pipet rolling circle amplification-mediated signal amplification. In this sensor, we performed rolling circle amplification on the inside of the pipet to enrich horseradish peroxidase (pipet-poly-HRP). When AFB₁ is present, it interacts with functional nucleic acids and results in the release of the activator. The activator is designed to activate the CRISPR/Cas12a system, which cleaves the pipet-poly-HRP to liberate HRP. The freed HRP can then be measured by chemiluminescence to quantify AFB₁. This CRISPR/Cas12a-assisted chemiluminescence sensor enables facile, highly sensitive, and specific detection of AFB₁, with a linear range from 50 pg/mL to 100 ng/mL and a detection limit of 5.2 pg/mL. Furthermore, it exhibits satisfactory recovery and has successfully challenged AFB₁ detection in cereal samples. The proposed sensor offers a novel rapid screening approach that holds great promise for food security monitoring.

The influence of hapten spacer arm length on antibody response and immunoassay development

Antibodies against small molecules with high titer and high affinity are always pursued in the field of vaccines for drugs of abuse, antidotes to toxins and immunoassays in medical, environmental, and food safety. The exposure degree of the target molecule to the immune system is critical to induce a strongly specific antibody response, thus, the spacer arm length between the target molecule and carrier protein plays an important role. However, the influence of spacer arm length on antibody titer, affinity, and assay performance is not yet clear and highly demanded to be addressed. In the present study, we proposed a model study to answer the question by using two typical small molecules, melamine and p-nitroaniline, which were introduced by varied spacer arms with increasing alkane linear length from 2 to 12 carbon atoms brick by brick. The spacer arm lengths of the haptens were obtained by computational chemistry. The titer and affinity of mouse antisera were analyzed and compared, showing that all haptens with spacer arms of 6-8 carbon atoms, i.e. 6.3-8.8 Å in length, induced strong antibodies represented by the highest titer and affinity without exception, while the haptens with spacer arms of 2-4 carbon atoms and 10-12 carbon atoms, i.e. 1.5-3.9 Å and 11.3-13.9 Å in length, failed to induce high-quality antibody response. Moreover, the titer and sensitivity of the subsequently developed immunoassays were significantly affected by using coating haptens with different spacer arm lengths, and coating haptens with a spacer arm of 6.3-8.8 Å in length delivered the optimum detection performance. The antibody recognition mechanism study further confirmed that the hapten spacer arm length had a critical effect on the recognition properties of the induced antibody, which should be interactive with the spacer arm each other. This study showed that the hapten with appropriate spacer arm length is important to antibody response and immunoassay development, providing a valuable and general clue for the rational design of hapten.

Improved Sensitivity and Wide Range Detection of Small Analytes Using a Two-Antigen-Combined Competitive Immunoassay

Competitive immunoassays have unique advantages in the detection of small molecules and are widely used in clinical practice. However, the concentrations of some analytes usually vary greatly among different populations, which makes it difficult to balance the sensitivity and detection range of competitive immunoassays. Studies have shown that using haptens with weaker affinity for specific antibodies as competitive antigens can help improve the sensitivity of the method. Here, we developed a competitive light initiated chemiluminescence assay based on the combination of antigens with different affinities, which has high sensitivity and wide detection range. As a proof of concept, estradiol was used as the analyte. After the mixing ratio was optimized, the two labeled haptens played different competitive roles due to the different concentrations of estradiol to be tested, which improved the sensitivity of estradiol detection, while ensuring a certain detection range. The limit of detection of this method was 5.30 pg/mL, which is lower than most current estradiol immunoassay kits. Good linearity (R ² = 0.9902) was obtained between estradiol concentrations of 17.07-2376.22 pg/mL. This study provides a new solution for the detection of small molecule biomarkers with a large concentration span, which also has considerable potential in other immunological detection methods.

Bifunctional M13 Phage as Enzyme Container for the Reinforced Colorimetric-Photothermal Dual-Modal Sensing of Ochratoxin A

"Point of care" (POC) methods without expensive instruments and special technicians are greatly needed for high-throughput analysis of mycotoxins. In comparison, the most widely used screening method of the conventional enzyme-linked immunosorbent assay (ELISA) confronts low sensitivity and harmful competing antigens. Herein, we develop a plasmonic-photothermal ELISA that allows precise readout by color-temperature dual-modal signals based on enzymatic reaction-induced AuNP aggregation for highly sensitive detection of ochratoxin A (OTA). The bifunctional M13 phage carrying OTA that mimics the mimotope on the end of p3 proteins and abundant biotin molecules on the major p8 proteins is adopted as an eco-friendly competing antigen and enzyme container for amplifying the signal intensity. Under optimal conditions, both colorimetric and photothermal signals enable good dynamic linearity for quantitative OTA detection with the limits of detection at 12.1 and 8.6 pg mL-1, respectively. Additionally, the proposed ELISA was adapted to visual determination with a cutoff limit of 78 pg mL-1 according to a vivid color change from deep blue to red. The recoveries of OTA-spiked corn samples indicate the high accuracy and robustness of the proposed method. In conclusion, our proposed strategy provides a promising method for eco-friendly and sensitive POC screening of OTA. Moreover, it can be easily applied to other analytes by changing the involved specific mimotope sequence.

Recent Progress in Spectroscopic Methods for the Detection of Foodborne Pathogenic Bacteria

Detection of foodborne pathogens at an early stage is very important to control food quality and improve medical response. Rapid detection of foodborne pathogens with high sensitivity and specificity is becoming an urgent requirement in health safety, medical diagnostics, environmental safety, and controlling food quality. Despite the existing bacterial detection methods being reliable and widely used, these methods are time-consuming, expensive, and cumbersome. Therefore, researchers are trying to find new methods by integrating spectroscopy techniques with artificial intelligence and advanced materials. Within this progress report, advances in the detection of foodborne pathogens using spectroscopy techniques are discussed. This paper presents an overview of the progress and application of spectroscopy techniques for the detection of foodborne pathogens, particularly new trends in the past few years, including surface-enhanced Raman spectroscopy, surface plasmon resonance, fluorescence spectroscopy, multiangle laser light scattering, and imaging analysis. In addition, the applications of artificial intelligence, microfluidics, smartphone-based techniques, and advanced materials related to spectroscopy for the detection of bacterial pathogens are discussed. Finally, we conclude and discuss possible research prospects in aspects of spectroscopy techniques for the identification and classification of pathogens.

Heterologous-coating antigen enhancing the sensitivity of enzyme-linked immunosorbent assay for detection of mebendazole residues

The heterologous strategy could improve the sensitivity of competitive enzyme-linked immunosorbent assay (ELISA) for detection of chemical contaminants in food samples. In this study, the heterologous coating antigen ELISA was developed to evaluate its sensitivity for mebendazole (MBZ). Results showed that the heterologous ELISA had a linear range of (IC₂₀-IC₈₀) 0.34-10.54 ng/mL, an IC₅₀ value of 1.83 ng/mL, and a limit of detection (LOD) of 0.13 ng/mL, in which the sensitivity of ELISA improved 1.7- and 2-fold (IC₅₀ value dropping from 7.41 and 3.65 ng/mL to 4.27 and 1.83 ng/mL) than that of rabbit IgG- and chicken IgY-based homologous ELISA for MBZ, respectively. The heterologous coating antigen ELISA showed negligible cross reactivity (<0.2%) with its structural analogues, including hydroxy-MBZ, albendazole, oxfendazole, fenbendazole, and flubendazole, except the value of 72.6% for amino-MBZ. The average recoveries of MBZ spiked in pork and chicken muscle samples by the assay ranged from 83.7% to 109.8% and agreed well with those of high-performance liquid chromatography. The results suggested that using heterologous coating antigen could distinctly improve the sensitivity of ELISA for routine screening of MBZ residues in food samples.

Liquid Crystal Droplet-Based Biosensors: Promising for Point-of-Care Testing

The development of biosensing platforms has been impressively accelerated by advancements in liquid crystal (LC) technology. High response rate, easy operation, and good stability of the LC droplet-based biosensors are all benefits of the long-range order of LC molecules. Bioprobes emerged when LC droplets were combined with biotechnology, and these bioprobes are used extensively for disease diagnosis, food safety, and environmental monitoring. The LC droplet biosensors have high sensitivity and excellent selectivity, making them an attractive tool for the label-free, economical, and real-time detection of different targets. Portable devices work well as the accessory kits for LC droplet-based biosensors to make them easier to use by anyone for on-site monitoring of targets. Herein, we offer a review of the latest developments in the design of LC droplet-based biosensors for qualitative target monitoring and quantitative target analysis.

Nanobody/NanoBiT system-mediated bioluminescence immunosensor for one-step homogeneous detection of trace ochratoxin A in food

Hazardous small molecules in food and environment seriously threatens human health, which requires sensitive and rapid tools for monitoring. Using a previously identified nanobody against ochratoxin A (OTA), we herein proposed a homogeneous sensing platform "nanobody/NanoLuc Binary Technology (NanoBiT) system" and developed a nanobody/NanoBiT system-mediated bioluminescence immunosensor (NBL-Immunosens) for OTA using LgBiT (Lg) and SmBiT (Sm), two subunits of the split nanoluciferase (NanoLuc). The core elements of NBL-Immunosens include Lg-nanobody fusion (NLg) and Sm-labeled OTA-bovine serum albumin conjugate (OSm). The antigen-antibody interaction between NLg and OSm triggers the reconstitution of NanoLuc for generating luminescence signals. Moreover, free OTA can compete with OSm for binding to NLg, resulting the decrease of dose-dependent signals. NBL-Immunosens can detect OTA in a one-step assay of 5 min without washing and exhibit a limit of detection of 0.01 ng/mL with a linear range of 0.04-2.23 ng/mL. It shows high selectivity for OTA and has good accuracy and precision in the spiking-and-recovery experiments. Furthermore, its effectiveness was evaluated with real cereal samples and confirmed by liquid chromatography tandem mass spectrometry and commercial ELISA kits. Hence, the NBL-Immunosens is a very promising tool for rapid, accurate, and selective detection of trace OTA in food.

Expanded detection range of lateral flow immunoassay endowed with a third-stage amplifier indirect probe

Here, a third-stage amplifier indirect probe (TsAIP) based lateral flow immunoassay (LFIA) was proposed to detect furazolidone (FZD) with Prussian blue nanoparticles (PBNPs) as carrier to label the goat anti-mouse antibody-horseradish peroxidase conjugation [GAMA(HRP)]. In this strategy, owing to the fact that one monoclonal antibody (mAb) can combine several GAMA molecules simultaneously, the indirect probe can generate primary signal amplification, then realize second-stage amplification attributing to PBNPs, and finally achieve third-stage amplification because of the conjugated HRP. The TsAIP-based LFIA shows improved performance for FZD metabolite derivative with a detection limit of 1 ng mL^-1. The detection range is expanded about 2-fold compared with the original outcome. Besides, the proposed sensor could be successfully applied in food samples. This method provides a platform for broadening the detection range and application of PBNPs based LFIAs.

Nanozyme enhanced paper-based biochip with a smartphone readout system for rapid detection of cyanotoxins in water

Cyanobacterial harmful algal blooms in freshwater systems can produce cyanotoxins, such as microcystins (MCs) and nodularins (NODs), presenting serious threats to human health and ecosystems. Required routine monitoring of cyanotoxins in water samples, as posed by U.S. EPA drinking water contaminant candidate list 5 (CCL5), demands for cost-effective, reliable and sensitive MCs/NODs detection methods. We report the development of a colorimetric paper-based immunochip assisted by nanozyme catalysis with a smartphone readout system for rapid detection of cyanotoxins in water. We show that the introduction of biorthogonal click reaction enables in situ facile self-assembly of multi-layers of peroxidase-like nanozyme onto the anti-MCs/NODs monoclonal antibody. We can detect 13 variants of MCs/NODs even in the sub-microgram per liter range with detection limit of below 0.7 μg/L and satisfactory recovery percentages between 88 and 120% in different water matrices. Our technology shows a good correlation with the well-developed ELISA technology, demonstrating its great potential applications in resource-limited or less-developed regions for on-site and large-scale screening of cyanotoxins in water environment.