A self-assembled electrochemical immunosensor for ultra-sensitive detection of ochratoxin A in medicinal and edible malt

Ratiometric absorbance and fluorescence dual model immunoassay for detecting ochratoxin a based on porphyrin metalation

In this work, a porphyrin metalation-based ratiometric absorbance and fluorescence dual model immunoassay was proposed to detect ochratoxin A (OTA). 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin (TMPyP) was pink and had a strong fluorescence, upon coordination with Hg(II), its fluorescence was quenched and the color became green. The alkaline phosphatase can catalyze the dephosphorylation of ascorbic acid 2-phosphate to produce ascorbic acid, which can reduce the coordinated Hg(II) to Hg(0) and then dissociated from TMPyP, its fluorescence was recovered. Meanwhile, the color changed from green to light pink, which can be identified by naked eye for semi-quantitative detection. The linear ranges of ratiometric absorbance and fluorescence model were 0-6.0 ng/mL and 0.1-6.0 ng/mL, respectively. The absorbance and fluorescence signals produced by porphyrin metalation can mutually verify to improve the accuracy of detection results. Besides, the ultra-sensitivity and high selectivity demonstrated this method was a powerful tool for trace OTA detection.

Rational design of molecularly imprinted electrochemical sensor based on Nb2C-MWCNTs heterostructures for highly sensitive and selective detection of Ochratoxin a

Developing an efficient method for screening Ochratoxin A (OTA) in agriculture products is vital to ensure food safety and human health. However, the complex food matrix seriously affects the sensitivity and accuracy. To address this issue, we designed a novel molecularly imprinted polymer (MIP) electrochemical sensor based on multiwalled carbon nanotube-modified niobium carbide (Nb2C-MWCNTs) with the aid of the density functional theory (DFT). In this design, a glassy carbon electrode (GCE) was first modified by Nb2C-MWCNTs heterostructure. Afterward, the MIP layer was prepared, with ortho-toluidine as a functional monomer selected via DFT and OTA acting as a template on the surface of Nb2C-MWCNTs/GCE using in-situ electropolymerization. Electrochemical tests and physical characterization revealed that Nb2C-MWCNTs improved the sensor's active surface area and electron transmission capacity. Nb2C-MWCNTs had a good synergistic effect on MIP, endowing the sensor with high sensitivity and specific recognition of OTA in complex food matrix systems. The MIP sensor showed a wide linear range from 0.04 to 10.0 μM with a limit of detection (LOD) of 3.6 nM. Moreover, it presented good repeatability and stability for its highly antifouling effect on OTA. In real sample analysis, the recoveries, ranging from 89.77% to 103.70%, agreed well with the results obtained by HPLC methods, suggesting the sensor has good accuracy and high potential in practical applications.

Recent advances in nucleic acid signal amplification-based aptasensors for sensing mycotoxins

Mycotoxin contamination in food products may cause serious health hazards and economic losses. The effective control and accurate detection of mycotoxins have become a global concern. Even though a variety of methods have been developed for mycotoxin detection, most conventional methods suffer from complicated operation procedures, low sensitivity, high cost, and long assay time. Therefore, the development of simple and sensitive methods for mycotoxin assay is highly needed. The introduction of nucleic acid signal amplification technology (NASAT) into aptasensors significantly improves the sensitivity and facilitates the detection of mycotoxins. Herein, we give a comprehensive review of the recent advances in NASAT-based aptasensors for assaying mycotoxins and summarize the principles, features, and applications of NASAT-based aptasensors. Moreover, we highlight the challenges and prospects in the field, including the simultaneous detection of multiple mycotoxins and the development of portable devices for field detection.

Electrochemical biosensors for pathogenic microorganisms detection based on recognition elements

The worldwide spread of pathogenic microorganisms poses a significant risk to human health. Electrochemical biosensors have emerged as dependable analytical tools for the point-of-care detection of pathogens and can effectively compensate for the limitations of conventional techniques. Real-time analysis, high throughput, portability, and rapidity make them pioneering tools for on-site detection of pathogens. Herein, this work comprehensively reviews the recent advances in electrochemical biosensors for pathogen detection, focusing on those based on the classification of recognition elements, and summarizes their principles, current challenges, and prospects. This review was conducted by a systematic search of PubMed and Web of Science databases to obtain relevant literature and construct a basic framework. A total of 171 publications were included after online screening and data extraction to obtain information of the research advances in electrochemical biosensors for pathogen detection. According to the findings, the research of electrochemical biosensors in pathogen detection has been increasing yearly in the past 3 years, which has a broad development prospect, but most of the biosensors have performance or economic limitations and are still in the primary stage. Therefore, significant research and funding are required to fuel the rapid development of electrochemical biosensors. The overview comprehensively evaluates the recent advances in different types of electrochemical biosensors utilized in pathogen detection, with a view to providing insights into future research directions in biosensors.

Overview-gold nanoparticles-based sensitive nanosensors in mycotoxins detection

Food-borne mycotoxins is one of the food safety concerns in the world. At present, nanosensors are widely used in the detection and analysis of mycotoxins due to their high specificity and sensitivity. In nanosensor-based mycotoxindetections, the sensitivity is mainly improved from two aspects. On the one hand, based on the principle of immune response, antigens and antibodies can be modified and developed. Such as single-domain heavy chain antibodies, aptamers, peptides, and antigen mimotopes. On the other hand, improvements and innovations have been made on signal amplification materials, including gold nanoparticles (AuNPs), quantum dots, and graphene, etc. Among them, gold nanoparticles can not only be used as a signal amplification material, but also can be used as carriers for identification elements, which can be used for signal amplification in detection. In this article, we systematically summarized the emerging strategies for enhancing the detection sensitivity of traditional gold nanoparticles-based nanosensors, in terms of recognition elements and signal amplification. Representative examples were selected to illustrate the potential mechanism of each strategy in enhancing the colorimetric signal intensity of AuNP and its potential application in biosensing. Finally, our review suggested the challenges and future prospects of gold particles in detection of mycotoxins.

Recent Advances in Electrochemical Biosensors for Food Control

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

Plasmon-enhanced electroreduction activity of Au-AgPd Janus nanoparticles for ochratoxin a detection

Ochratoxin A (OTA) was a dangerous biological toxin, and would easily contaminate food and induced food safety problems. The development of electrochemical aptasensors by designing strong and anti-interfere electroactive labels could improve the sensitivity and accuracy of OTA detection. In this contribution, novel electroactive Au-AgPd Janus NPs were firstly synthesized and exhibited electroreduction signal at -0.4 V, owing to the reduction process of Pd²⁺. The electroreduction signal was amplified 1.5 times under local surface plasmon resonance (LSPR) excitation, which could improve the sensitivity of OTA detection. Plasmon-enhanced electroreduction principle of Au-AgPd Janus NPs was verified, which endowed electrochemical aptasensor with high accuracy and anti-interference ability for OTA detection. Au-AgPd Janus NPs served as electrochemical beacon achieved sensitive and accurate OTA detection with the limit of detection (LOD) of 0.98 pM. This work opens up new directions for the construction of electroactive heterostructures for the sensitive and accurate biotoxins electroanalytical applications.

Ultrasensitive electrochemical aptasensor with Nafion-stabilized f-MWCNTs as signal enhancers for OTA detection

In this study, an ultrasensitive electrochemical (EC) aptasensor with Nafion-stabilized functionalized multi-walled carbon nanotubes (f-MWCNTs) as signal enhancers was established for ochratoxin A (OTA) determination. Herein, f-MWCNTs were prepared through functionalization with nitric acid. The incorporation of Nafion promoted a good dispersion of f-MWCNTs and prevented their leaching on the electrode, making a robust stability of the aptasensor. The Nafion-f-MWCNTs composites were used as the sensing substrates to largely enhance the electroactive surface area and the conductivity of the electrode, realizing a significant signal amplification. Carboxyl groups on the surface of f-MWCNTs readily exposed from Nafion membrane to couple with streptavidin, facilitating the immobilization of biotinylated aptamers to achieve selective recognition towards OTA. When OTA existed, aptamers preferentially combined with it, causing a noticeable decline in the current response. Under optimum conditions, a good linear relationship between the current changes and the logarithm of OTA concentration was observed from 0.005 ng/mL to 10 ng/mL, with a limit of detection low to 1 pg/mL for OTA. The specific, sensitive, and reproducible aptasensor succeeded in application in malt samples, confirming a great promise for more contaminants and providing a universal platform in complex matrices by simply replacing the corresponding aptamers.

Electrochemiluminescence Aptasensor Based on Gd(OH)3 Nanocrystalline for Ochratoxin A Detection in Food Samples

In the present study, the electrochemiluminescence (ECL) properties of Gd(OH)₃ nanocrystals with K₂S₂O₈ as the cathode coreactant were studied for the first time. Based on the prominent ECL behavior of this material and the excellent specificity of the aptamer technique, an ECL aptasensor for the detection of ochratoxin A (OTA) was formulated successfully. Over an OTA concentration range of 0.01 pg mL^-1 to 10 ng mL^-1, the change in the ECL signal was highly linear with the OTA concentration, and the limit of detection (LOD) was 0.0027 pg mL^-1. Finally, the ECL aptasensor was further used to detect OTA in real samples (grapes and corn) and satisfactory results were obtained, which indicated that the built method is expected to be applied in food detection.

Fluorescence and absorbance dual-mode immunoassay for detecting Ochratoxin A

In this work, a simple dual-mode immunoassay for detecting Ochratoxin A (OTA) was developed by mixing G-quadruplex/N-methylmesoporphyrin IX (G4/NMM) and 3,3',5,5'-tetramethylbenzidine (TMB). The fluorescence of G4/NMM can be quenched by oxidized TMB (oxTMB) because the absorbance of oxTMB overlapped with the fluorescence emission of G4/NMM. In the absence of OTA, large amounts of oxTMB were formed with blue color and the fluorescence of G4/NMM was quenched. In the presence of OTA, the concentration of oxTMB was decreased, therefore the fluorescence of G4/NMM increased. The linear range of fluorescence immunoassay was 0.195-25 ng/mL, and the linear range of the absorbance immunoassay was 0.049-1.563 ng/mL. Thus, the linear range of this dual-mode immunoassay can be expanded to 0.049-25 ng/mL. Meanwhile, the new method showed good selectivity for OTA. Besides, the satisfactory recovery rates implied the new method had a potential value for practical sample detection.

Antibody-receptor bioengineering and its implications in designing bioelectronic devices

Antibodies play a crucial role in the defense mechanism countering pathogens or foreign antigens in eukaryotes. Its potential as an analytical and diagnostic tool has been exploited for over a century. It forms immunocomplexes with a specific antigen, which is the basis of immunoassays and aids in developing potent biosensors. Antibody-based sensors allow for the quick and accurate detection of various analytes. Though classical antibodies have prolonged been used as bioreceptors in biosensors fabrication due to their increased fragility, they have been engineered into more stable fragments with increased exposure of their antigen-binding sites in the recent era. In biosensing, the formats constructed by antibody engineering can enhance the signal since the resistance offered by a conventional antibody is much more than these fragments. Hence, signal amplification can be observed when antibody fragments are utilized as bioreceptors instead of full-length antibodies. We present the first systematic review on engineered antibodies as bioreceptors with the description of their engineering methods. The detection of various target analytes, including small molecules, macromolecules, and cells using antibody-based biosensors, has been discussed. A comparison of the classical polyclonal, monoclonal, and engineered antibodies as bioreceptors to construct highly accurate, sensitive, and specific sensors is also discussed.

Chemical and biological assessments of environmental mixtures: A review of current trends, advances, and future perspectives

Considering the chemical complexity and toxicity data gaps of environmental mixtures, most studies evaluate the chemical risk individually. However, humans are usually exposed to a cocktail of chemicals in real life. Mixture health assessment remains to be a research area having significant knowledge gaps. Characterization of chemical composition and bioactivity/toxicity are the two critical aspects of mixture health assessments. This review seeks to introduce the recent progress and tools for the chemical and biological characterization of environmental mixtures. The state-of-the-art techniques include the sampling, extraction, rapid detection methods, and the in vitro, in vivo, and in silico approaches to generate the toxicity data of an environmental mixture. Application of these novel methods, or new approach methodologies (NAMs), has increased the throughput of generating chemical and toxicity data for mixtures and thus refined the mixture health assessment. Combined with computational methods, the chemical and biological information would shed light on identifying the bioactive/toxic components in an environmental mixture.

Simple and programmed three-dimensional DNA tweezer for simultaneous one-step detection of ochratoxin A and zearalenone

Three-dimensional (TD) deoxyribonucleic acid (DNA) tweezers were programmed for one-step identification and detection of ochratoxin A (OTA) and zearalenone (ZEN). The unfolding of the TD-DNA tweezers by aptamers specific to these two mycotoxins "turned" the fluorescent signals "on." The bonding of the aptamers to their corresponding targets in OTA and ZEN "turned" the fluorescent signals and the DNA tweezers "off." The detection limit of the TD-DNA tweezers for OTA and ZEN was 0.032 and 0.037 ng mL^-1, respectively. The feasibility of this method was tested using two samples. Detection via this method increased the recovery of OTA and ZEN from 95.8% to 110.2%. Spike recovery and certified food products were used to detect applicability in actual situations. Analyte detection in complex samples using TD-DNA tweezers is rapid, as the process involves a single operational step. This proposed design has considerable potential for application in mycotoxin detection.

A CdSe@CdS quantum dots based electrochemiluminescence aptasensor for sensitive detection of ochratoxin A

In this work, a CdSe@CdS quantum dots (QDs) based label-free electrochemiluminescence (ECL) aptasensor was developed for the specific and sensitive detection of ochratoxin A (OTA). Chitosan (CHI) could immobilize abundant QDs on the surface of an Au electrode as the luminescent nanomaterials. Glutaraldehyde was used as the crosslinking agent for coupling a large number of OTA aptamers. Thanks to the excellent stability, good biocompatibility, and strong ECL intensity of CdSe@CdS QDs, as well as the quick reactions of the generated SO₄•- in the electrolyte, strong ECL signals were measured. Because of the specific recognition of aptamer toward OTA, the reduced ECL signals caused by OTA in the samples were recorded for quantify the content of OTA. After optimizing a series of crucial conditions, the ECL aptasensor displayed superior sensitivity for OTA with a detection limit of 0.89 ng/mL and a wide linear concentration range of 1-100 ng/mL. The practicability and viability were verified through the rapid and facile analysis of OTA in real Lily and Rhubarb samples with recovery rates (n = 3) of 98.1-105.6% and 97.3-101.5%, respectively. The newly-developed QDs-based ECL aptasensor provided a new universal analytical tool for more mycotoxins in safety assessment of foods and feeds, environmental monitoring, and clinical diagnostics.

Bioactive Coatings on Titanium: A Review on Hydroxylation, Self-Assembled Monolayers (SAMs) and Surface Modification Strategies

Titanium (Ti) and its alloys have been demonstrated over the last decades to play an important role as inert materials in the field of orthopedic and dental implants. Nevertheless, with the widespread use of Ti, implant-associated rejection issues have arisen. To overcome these problems, antibacterial properties, fast and adequate osseointegration and long-term stability are essential features. Indeed, surface modification is currently presented as a versatile strategy for developing Ti coatings with all these challenging requirements and achieve a successful performance of the implant. Numerous approaches have been investigated to obtain stable and well-organized Ti coatings that promote the tailoring of surface chemical functionalization regardless of the geometry and shape of the implant. However, among all the approaches available in the literature to functionalize the Ti surface, a promising strategy is the combination of surface pre-activation treatments typically followed by the development of intermediate anchoring layers (self-assembled monolayers, SAMs) that serve as the supporting linkage of a final active layer. Therefore, this paper aims to review the latest approaches in the biomedical area to obtain bioactive coatings onto Ti surfaces with a special focus on (i) the most employed methods for Ti surface hydroxylation, (ii) SAMs-mediated active coatings development, and (iii) the latest advances in active agent immobilization and polymeric coatings for controlled release on Ti surfaces.

An Electrochemical Immunosensor Based on SPA and rGO-PEI-Ag-Nf for the Detection of Arsanilic Acid

A sensitive electrochemical immunosensor was prepared for rapid detection of ASA based on arsanilic acid (ASA) monoclonal antibody with high affinity. In the preparation of nanomaterials, polyethyleneimine (PEI) improved the stability of the solution and acted as a reducing agent to generate reduced graphene oxide (rGO) with relatively strong conductivity, thereby promoting the transfer of electrons. The dual conductivity of rGO and silver nanoparticles (AgNPs) improved the sensitivity of the sensor. The synthesis of nanomaterials were confirmed by UV-Vis spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. In the optimal experiment conditions, the sensor could achieve the detection range of 0.50–500 ng mL⁻¹ and the limit of detection (LOD) of 0.38 ng mL⁻¹ (S/N = 3). Moreover, the sensor exhibited excellent specificity and acceptable stability, suggesting that the proposed sensor possessed a good potential in ASA detection. Thus, the as-prepared biosensor may be a potential way for detecting other antibiotics in meat and animal-derived foods.

Electrochemiluminescence Immunosensor Based on Nanobody and Au/CaCO3 Synthesized Using Waste Eggshells for Ultrasensitive Detection of Ochratoxin A

A novel ultrasensitive electrochemiluminescence (ECL) immunoassay based on Au/CaCO₃ was proposed for detecting ochratoxin A (OTA) in coffee. Au/CaCO₃ nanocomposites synthesized using waste eggshells as the template with a large surface area and excellent electrochemical properties were applied for immobilizing a large amount of Ru(bpy)₃ ²⁺ and conjugating a high-affinity nanobody (prepared by the phage display technique). Coupling of the Au/CaCO₃ nanocomposites and nanobody technologies provided an ultrasensitive and highly selective ECL immunosensor for OTA detection in the range of 10 pg/mL-100 ng/mL with a low detection limit of 5.7 pg/mL. Moreover, the as-prepared ECL immunosensor showed excellent performance and high stability. Finally, the proposed ECL sensor was applied to analyze OTA in coffee samples, confirming the desirable accuracy and practical applicability potential. Overall, this work presents a new nanomaterial for fabricating the sensing interface of immunosensors by harnessing natural waste as the source and a method for detecting toxic OTA in foods.

Aptasensors for mycotoxins in foods: Recent advances and future trends

Mycotoxin contamination in foods has posed serious threat to public health and raised worldwide concern. The development of simple, rapid, facile, and cost-effective methods for mycotoxin detection is of urgent need. Aptamer-based sensors, abbreviated as aptasensors, with excellent recognition capacity to a wide variety of mycotoxins have attracted ever-increasing interest of researchers because of their simple fabrication, rapid response, high sensitivity, low cost, and easy adaptability for in situ measurement. The past few decades have witnessed the rapid advances of aptasensors for mycotoxin detection in foods. Therefore, this review first summarizes the reported aptamer sequences specific for mycotoxins. Then, the recent 5-year advancements in various newly developed aptasensors, which, according to the signal output mode, are divided into electrochemical, optical and photoelectrochemical categories, for mycotoxin detection are comprehensively discussed. A special attention is taken on their strengths and limitations in real-world application. Finally, the current challenges and future perspectives for developing novel highly reliable aptasensors for mycotoxin detection are highlighted, which is expected to provide powerful references for their thorough research and extended applications. Owing to their unique advantages, aptasensors display a fascinating prospect in food field for safety inspection and risk assessment.

Recent advances in immunoassays and biosensors for mycotoxins detection in feedstuffs and foods

Mycotoxins are secondary metabolites produced by fungus. Many mycotoxin species are highly toxic and are frequently found in cereals and feedstuffs. So, powerful detection methods are vital and effective ways to prevent feed contamination. Traditional detection methods can no longer meet the needs of massive, real-time, simple, and fast mycotoxin monitoring. Rapid detection methods based on advanced material and sensor technology are the future trend. In this review, we highlight recent progress of mycotoxin rapid detection strategies in feedstuffs and foods, especially for simultaneous multiplex mycotoxin determination. Immunoassays, biosensors, and the prominent roles of nanomaterials are introduced. The principles of different types of recognition and signal transduction are explained, and the merits and pitfalls of these methods are compared. Furthermore, limitations and challenges of existing rapid sensing strategies and perspectives of future research are discussed.

Multiwalled carbon nanotubes modified two dimensional MXene with high antifouling property for sensitive detection of ochratoxin A

Electrochemical sensor has great potential in the detection of small molecules by virtues of low cost, fast response, and easy to miniaturization. However, electrochemical sensing of ochratoxin A (OTA) was seriously hindered by the heavy electrode-fouling effect and poor electrochemical activity inherent from OTA molecular. Herein, two-dimensional titanium carbide (2D Ti₃C₂) MXene incorporated with carboxylic multiwalled carbon nanotubes (cMWCNTs) was developed as a glassy carbon electrode modifier for rapid and sensitive detection of OTA. Physical characterizations combined with electrochemical techniques revealed that cMWCNTs can not only prevent the restacking of 2D Ti₃C₂nanosheets but also facile its electron transfer, leading to a nanohybrid with a high specific surface and good electrocatalytic activity to OTA. Under optimal conditions, the electrochemical sensor showed a good linear response to OTA in a concentration range from 0.09 to 10μmol·l^-1and a low detection limit (LOD) of 0.028μmol·l^-1. The proposed sensor was impelled successive times to detect OTA, a good repeatability was obtained, indicating the constructed sensor possessed good anti-fouling property. Moreover, satisfactory recoveries between 91.8% and 103.2% were obtained in the real sample analysis of grape and beer, showing that the developed sensing technique is reliable for the screening of trace OTA in food resources.

Penicillin biosensor based on rhombus-shaped porous carbon/hematoxylin/penicillinase

In this experiment, we designed an electrochemical sensor using penicillinase (Pen X)-rhombus porous carbon (RPC) as the detection element and hematoxylin as the indicator to detect low concentrations of penicillin sodium (Pen G). A differential pulse voltammetry (DPV) method was used to detect Pen G in the concentration range of 10^-8 -10^-5 mg·mL^-1 under optimal experimental conditions. The results showed that the peak current value and the logarithm of Pen G concentration showed a good linear relationship (R² = 0.9915), and the LOD was 2.68 × 10^-7 mg·mL^-1 (S/N = 3). The actual milk samples were detected by the addition method and compared with the high-performance liquid phase method; no significant difference was found in the detection results. The working electrode prepared by cross-linking method not only extends the service life of the sensor, but also improves the sensitivity and reproducibility of the sensor. It can also be used to detect the Pen G residue in the actual milk samples repeatedly. PRACTICAL APPLICATION: In this study, an electrochemical sensor for the rapid detection of penicillin sodium in milk was prepared, which has good sensitivity and fast detection speed.

A novel electrochemical immunosensor for the sensitive detection of tiamulin based on staphylococcal protein A and silver nanoparticle-graphene oxide nanocomposites

Tiamulin (TML) is a pleuromutilin antibiotic and mainly used to treat pulmonary and gastrointestinal infections. However, excessive use of TML can bring health threats to consumers. In this work, a label-free electrochemical immunosensor was proposed for sensitive detection of TML in pork and pork liver. Silver nanoparticles (AgNPs) were synthesized in situ on graphene oxide (GO), in which GO acted as a carrier for loading more AgNPs and AgNPs exhibited both strong conductivity and good redox property. In addition, staphylococcal protein A (SPA) was applied to oriented immobilization of fragment crystallizable (Fc) region of the TML monoclonal antibody. Under the optimal condition, the developed electrochemical immunosensor exhibited a good linear response with a concentration of TML ranging from 0.05 ng mL^-1 to 100 ng mL^-1 and the limit of detection (LOD) was 0.04 ng mL^-1. Furthermore, the designed immunosensor was applied to detect TML in real samples with a good accuracy. Therefore, the label-free electrochemical immunosensor could be used as a potential method to detect TML and other antibiotic residues in animal derived foods.

Electrochemical Biosensors in Food Safety: Challenges and Perspectives

Safety and quality are key issues for the food industry. Consequently, there is growing demand to preserve the food chain and products against substances toxic, harmful to human health, such as contaminants, allergens, toxins, or pathogens. For this reason, it is mandatory to develop highly sensitive, reliable, rapid, and cost-effective sensing systems/devices, such as electrochemical sensors/biosensors. Generally, conventional techniques are limited by long analyses, expensive and complex procedures, and skilled personnel. Therefore, developing performant electrochemical biosensors can significantly support the screening of food chains and products. Here, we report some of the recent developments in this area and analyze the contributions produced by electrochemical biosensors in food screening and their challenges.

Developments in mycotoxin analysis: an update for 2019-2020

This review summarises developments on the analysis of various matrices for mycotoxins published in the period from mid-2019 to mid-2020. Notable developments in all aspects of mycotoxin analysis, from sampling and quality assurance/quality control of analytical results, to the various detection and quantitation technologies ranging from single mycotoxin biosensors to comprehensive instrumental methods are presented and discussed. Aside from sampling and quality control, discussion of this past year’s developments is organised by detection and quantitation technology and covers chromatography with targeted or non-targeted high resolution mass spectrometry, tandem mass spectrometry, detection other than mass spectrometry, biosensors, as well as assays that use alternatives to antibodies. This critical review aims to briefly present the most important recent developments and trends in mycotoxin determination as well as to address limitations of the presented methodologies.

Development and perspectives of rapid detection technology in food and environment

Food safety become a hot issue currently with globalization of food trade and food supply chains. Chemical pollution, microbial contamination and adulteration in food have attracted more attention worldwide. Contamination with antibiotics, estrogens and heavy metals in water environment and soil environment have also turn into an enormous threat to food safety. Traditional small-scale, long-term detection technologies have been unable to meet the current needs. In the monitoring process, rapid, convenient, accurate analysis and detection technologies have become the future development trend. We critically synthesizing the current knowledge of various rapid detection technology, and briefly touched upon the problem which still exist in research process. The review showed that the application of novel materials promotes the development of rapid detection technology, high-throughput and portability would be popular study directions in the future. Of course, the ultimate aim of the research is how to industrialization these technologies and apply to the market.

Horseradish Peroxidase Labelled-Sandwich Electrochemical Sensor Based on Ionic Liquid-Gold Nanoparticles for Lactobacillus brevis

Lactobacillus brevis is the most common bacteria that causes beer spoilage. In this work, a novel electrochemical immunosensor was fabricated for ultra-sensitive determination of L. brevis. Gold nanoparticles (AuNPs) were firstly electro-deposited on the electrode surface for enhancing the electro-conductivity and specific surface area. Ionic liquid was used for improving the immobilization performance of the immunosensor. After optimization, a linear regression equation can be observed between the ∆current and concentration of L. brevis from 104 CFU/mL to 109 CFU/mL. The limit of detection can be estimated to be 103 CFU/mL.

Broad-spectrum electrochemical immunosensor based on one-step electrodeposition of AuNP-Abs and Prussian blue nanocomposite for organophosphorus pesticide detection

Broad-spectrum antibodies can effectively recognize substances with similar structures and have broad application prospects in field rapid detection. In this study, broad-spectrum antibodies (Abs) against organophosphorus pesticides (OPs) were used as sensitive recognition elements, which could effectively recognize most OPs. Gold nanoparticles (AuNPs) have good biocompatibility. It combined with Abs to form a gold-labeled probe (AuNPs-Abs), which enhances the effective binding of antibodies to nanomaterials. Prussian blue (PB) was added to electrodeposition solution to enhance the conductivity, resulting in superior electrochemical performance. The AuNP-Abs-PB composite film was prepared by electrodeposition on the electrode surface to improve the anti-interference ability and stability of the immunosensor. Under the optimal experimental conditions, the immunosensor had a wide detection range (IC₂₀-IC₈₀: 1.82 × 10^-3-3.29 × 10⁴ ng/mL) and high sensitivity. Most importantly, it was simple to be prepared and could be used to detect multiple OPs.

A competitive fluorescence assay based on free-complementary DNA for ochratoxin A detection

An ultrasensitive, rapid, and specific method for Ochratoxin A (OTA) detection was designed using complementary sequence to aptamer as a target of molecular beacon (MB). The designed loop structure of the MB has the same sequence as the aptamer with a complementary DNA (cDNA) which translates the level of the target into a measurable response. The presence of the target holds aptamer at the corresponding amount and the additional cDNAs are consumed by unbound aptamers which avails free cDNAs that resulting in fluorescence rising due to unfolding of MBs. Under the optimized conditions, the fluorescence intensity increased linearly with OTA concentration over the range of 10 pg mL^-1-1 µg mL^-1 with the detection limit of 0.247 pg mL^-1. The application of this assay in wheat sample in comparison with HPLC-MS/MS method, demonstrated that the new assay could be a potential sensing platform for OTA detection.

Advances in immunosensor technology

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored.

Specific Coordination between Zr-MOF and Phosphate-Terminated DNA Coupled with Strand Displacement for the Construction of Reusable and Ultrasensitive Aptasensor

Electrochemical aptasensors involved in chemical labeling are often single-use and sensitivity-limited because the probes are commonly single-point labeled and irreversible. In this work, the specific coordination between Zr⁴⁺ and phosphate group (-PO₄^3-) was employed to construct a new aptasensor that is highly sensitive and reusable, using Ochratoxin A (OTA) as the test model. The OTA binding aptamer (OBA) was hybridized with the thiolated supporting sequence (TSS) immobilized on the surface of a gold electrode. The UiO-66 with a formula of [Zr₆O₄(OH)₄(BDC)₆], one of the class of Zr metal-organic frameworks (MOFs), was then particularly grafted on the terminal of OBA through the specific coordination between Zr⁴⁺ and 5'-PO₄^3-, i.e., the Zr-O-P coordination bond. Similarly, as much as the 5'-PO₄^3- and 3'-methylene blue dual-labeled sequences (DLS) were further assembled on UiO-66 due to the large surface area of MOF and rich active sites of Zr⁴⁺. Owing to the specific coordination for signal amplification, the developed aptasensor shows greatly enhanced sensitivity. A wide detection range from 0.1 fM to 2.0 μM and an ultralow detection limit of 0.079 fM (S/N = 3) for OTA were obtained. Additionally, the TSS can rehybridize with a new OBA to regenerate the aptasensor but without complicated pretreatments, enabling a aptasensor that is readily reusable for OTA detection. The aptasensor was successfully applied for OTA detection in the red wine samples, demonstrating a promising prospect for food safety monitoring.