Colorimetric aptasensor for ochratoxin A detection based on enzyme-induced gold nanoparticle aggregation

Fluorescence and colorimetric analysis of β-estradiol based on aptamer assembled spherical nucleic acids

Detecting β-estradiol (E2) in environmental monitoring is a complex task due to its status as a significant environmental contaminant. The detection methods require precision, sensitivity, and the ability to be conducted on-site without expensive instrumentation. Herein, we developed a novel approach using E2 aptamer assembled spherical nucleic acids (SNAs), which combines the sensitivity of fluorescence and the simplicity of colorimetry. Initially, a fluorescein (FAM)-labeled DNA aptamer is attached to the surface of gold nanoparticles (AuNPs) through hybridization with thiol-labeled DNA, resulting in fluorescence quenching. However, when E2 is present, the aptamer specifically binds to it, displacing from the thiol-DNA and releasing from the AuNP's surface. This leads to the recovery of fluorescence, allowing for quantitative detection of E2 by measuring the increase in fluorescence signal. Additionally, E2 detection can also be achieved visually using ultraviolet light. For colorimetric analysis, we introduce another set of AuNPs modified with thiol-DNA complementary to the DNA remaining on the surface of the previous AuNPs. When E2 triggers the release of the aptamer, the DNA on both AuNPs hybridized to each other, causing the aggregation of AuNPs and resulting in a distinct color change from red to purple. The detection limits for fluorescence and colorimetric analyses are 1 nM and 5 nM, respectively. We successfully applied this biosensing strategy to determine E2 concentrations in tap water and serum samples. Furthermore, our assay exhibits high selectivity towards E2 over other estrogens. Overall, this innovative approach provides an effective and versatile method for convenient on-site monitoring of E2.

Advances in Aptamer-Based Biosensors for the Detection of Foodborne Mycotoxins

Foodborne mycotoxins (FBMTs) are toxins produced by food itself or during processing and transportation that pose an enormous threat to public health security. However, traditional instrumental and chemical methods for detecting toxins have shortcomings, such as high operational difficulty, time consumption, and high cost, that limit their large-scale applications. In recent years, aptamer-based biosensors have become a new tool for food safety risk assessment and monitoring due to their high affinity, good specificity, and fast response. In this review, we focus on the progress of single-mode and dual-mode aptasensors in basic research and device applications over recent years. Furthermore, we also point out some problems in the current detection strategies, with the aim of stimulating future toxin detection systems for a transition toward ease of operation and rapid detection.

A CRISPR/Cas12a-based fluorescence method for the amplified detection of total antioxidant capacity

The CRISPR/Cas12a system is a powerful signal amplification tool that has been widely used in nucleic acid detection. It has also been applied to the assay of non-nucleic acid targets, mainly relying on strategies for converting target determination into nucleic acid detection. Herein, we describe a CRISPR/Cas12a-based fluorescence method for sensitive detection of the total antioxidant capacity (TAC) by utilizing a strategy of converting TAC determination into Mn2+ detection. Specifically, the reduction of MnO2 nanosheets by antioxidants produces plenty of Mn2+, which accelerates the trans-cleavage activity of CRISPR/Cas12a. Thus, a fluorescence enhanced detection method for TAC was established, with a detection limit as low as 0.04 mg L-1 for a typical antioxidant, ascorbic acid. More importantly, this method has been proven to successfully analyze TAC in beverages. The excellent analytical performance of this method demonstrates the great potential of the CRISPR/Cas12a system in simple and sensitive TAC analysis.

Recent advances towards point-of-care devices for fungal detection: Emphasizing the role of plasmonic nanomaterials in current and future technologies

Fungal infections are a significant global health problem, particularly affecting individuals with weakened immune systems. Moreover, as uncontrolled antibiotic and immunosuppressant use increases continuously, fungal infections have seen a dramatic increase, with some strains developing antibiotic resistance. Traditional approaches to identifying fungal strains often rely on morphological characteristics, thus owning limitations, such as struggles in identifying several strains or distinguishing between fungal strains with similar morphologies. This review explores the multifaceted impact of fungi infections on individuals, healthcare providers, and society, highlighting the often-underestimated economic burden and healthcare implications of these infections. In light of the serious constraints of traditional fungal identification methods, this review discusses the potential of plasmonic nanoparticle-based biosensors for fungal infection identification. These biosensors can enable rapid and precise fungal pathogen detection by exploiting several readout approaches, including various spectroscopic techniques, colorimetric and electrochemical assays, as well as lateral-flow immunoassay methods. Moreover, we report the remarkable impact of plasmonic Lab on a Chip technology and microfluidic devices, as they recently emerged as a class of advanced biosensors. Finally, we provide an overview of smartphone-based Point-of-Care devices and the associated technologies developed for detecting and identifying fungal pathogens.

A Portable Automated Microfluidic Platform for Point-of-Care Testing for Multiple Mycotoxins in Wine

Food safety requires point-of-care testing (POCT) for mycotoxins, since their presence in wine significantly impacts the wine industry and poses a severe threat to human life. Traditional detection methods are usually limited to detecting one mycotoxin and cannot achieve high-throughput, automated, and rapid quantitative analysis of multiple mycotoxins in real samples. Here, we propose a portable automated microfluidic platform (PAMP) integrating a chemiluminescence (CL) imaging system and a microfluidic chip to realize POCT for multiple mycotoxins in real samples, simplifying complex manual operations, shortening the detection time, and improving the detection sensitivity. Specially, silicone films were used as substrates on microfluidic chips to incubate mycotoxin conjugations, and the streptavidin-biotin (SA-B) system and an indirect immunoassay were implemented on silicone films to improve the sensitivity of reaction results. Interestingly, these methods significantly improved detection results, resulting in sensitive detection of mycotoxins, including zearalenone (ZEA) ranging from 1 to 32 ng/mL, aflatoxin B1 (AFB1) ranging from 0.2 to 6.4 ng/mL, and ochratoxin A (OTA) ranging from 2 to 64 ng/mL. The recovery of samples reached 91.39-109.14%, which verified the reliability and practicability of the PAMP. This PAMP enables sensitive and rapid detection of multiple mycotoxins in markets or wineries that lack advanced laboratory facilities. Therefore, it is essential to develop a portable microfluidic platform for POCT to detect mycotoxins in real samples.

A photothermal aptasensor based on rolling circle amplification-enriched DNAzyme for portable detection of ochratoxin A in grape juice

Aptasensors for detection of ochratoxin A (OTA) have been extensively studied, but the majority of them require costly and large-scale equipment as signal readers. Herein, a photothermal aptasensor capable of portable detection of OTA through a thermometer was developed on basis of aptamer structural switching and rolling circle amplification (RCA)-enriched DNAzyme. Oligonucleotides and alkaline phosphatase (ALP) modified magnetic beads were prepared. The binding of aptamers to OTA led to the release of ALP labeled complementary DNA. After magnetic separation, ALP catalyzed the padlock dephosphorylation, inhibiting the subsequent RCA reaction. This process converted the OTA concentration into the amount of the photothermal reagent oxTMB produced from the catalytic reaction induced by RCA-enriched DNAzyme. Under the optimal conditions, the detection limit (LOD) of this aptasensor was 2.28 nM in a clean buffer, while the LOD reached 2.43 nM in 2 % grape juice. The good performance of the photothermal aptasensor makes it possible to measure OTA pollution in low resource environments.

Diazo-functionalised immunoelectrochemical sensor for the detection of ochratoxin a in foods

Ochratoxin A (OTA) is a toxic fungal metabolite that is commonly found in cereals and animal feed. It is economically damaging and potentially hazardous to human health. Herein, we propose an electrochemical immunosensor for the rapid detection of OTA using anti-OTA antibodies and diazonium-functionalized, screen-printed electrodes. We attached 4-aminobenzoic acid to an electrode surface, activated the carboxyl groups on the surface with carbodiimide, and attached an antibody to the diazo layer. Subsequently, we used bovine serum protein as a blocker to prevent non-specific antigens from binding to the antibody. We evaluated the performance of the sensor by cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The sensor is highly specific and sensitive, has good linear responses in the range 20-200 ng/mL, a limit of detection of 0.5 ng/mL, and good recoveries of 90.5%-100.9% in spiked samples. It can be stored at 4 °C for approximately 2 weeks, and is highly stable, with a current response variation of no more than 4.6%.

A facile dual-mode immunosensor based on speckle Ag-doped nanohybrids for ultrasensitive detection of Ochratoxin A

Ochratoxin A (OTA) is a potent carcinogen, and is among the most dangerous mycotoxins in agricultural products. In this study, an ultrasensitive dual-mode immunosensor was developed for naked-eye and fluorescence detection of OTA based on Ag-doped core-shell nanohybrids (Ag@CSNH). Complete antigen-labeled Ag@CSNH (CA-Ag@CSNH) were used as a competitive bind and dual-mode probe. The diffused doping structure of CA-Ag@CSNH provided improved stability, color and fluorescence quencher performance. Antibodies modified magnetic beads were used as a capture probe. The competitive binding between OTA and CA-Ag@CSNH produced both color change and fluorescence quenching. Ultraviolet and fluorescence intensitie correlated linearly with OTA concentration ranges of 0.03-3 ng/mL and 10-10000 pg/mL, and limits of detection of 0.0235 ng/mL and 0.9921 pg/mL, respectively. The practical applicability of proposed strategy was demonstrated by analysis of OTA in spiked corn, soybean and flour samples. This study offers a new insight on multi-mode platforms for various applications.

Stimuli-triggered Self-Assembly of Gold Nanoparticles: Recent Advances in Fabrication and Biomedical Applications

Gold nanoparticles have been widely used in engineering, material chemistry, and biomedical applications owing to their ease of synthesis and functionalization, localized surface plasmon resonance (LSPR), great chemical stability, excellent biocompatibility, tunable optical and electronic property. In recent years, the decoration and modification of gold nanoparticles with small molecules, ligands, surfactants, peptides, DNA/RNA, and proteins have been systematically studied. In this review, we summarize the recent approaches on stimuli-triggered self-assembly of gold nanoparticles and introduce the breakthrough of gold nanoparticles in disease diagnosis and treatment. Finally, we discuss the current challenge and future prospective of stimuli-responsive gold nanoparticles for biomedical applications.

Double phage displayed peptides co-targeting-based biosensor with signal enhancement activity for colorimetric detection of Staphylococcus aureus

The development of simple, fast, sensitive, and specific strategies for the detection of foodborne pathogenic bacteria is crucial for ensuring food safety and promoting human health. Currently, detection methods for Staphylococcus aureus still suffer from issues such as low specificity and low sensitivity. To address this problem, we proposed a sensitivity enhancement strategy based on double phage-displayed peptides (PDPs) co-targeting. Firstly, we screened two PDPs and analyzed their binding mechanisms through fluorescent localization, pull-down assay, and molecular docking. The two PDPs target S. aureus by binding to specific proteins on its outer membrane. Based on this phenomenon, a convenient and sensitive double PDPs colorimetric biosensor was developed. Double thiol-modified phage-displayed peptides (PDP-SH) enhance the aggregation of gold nanoparticles (AuNPs), whereas the specific interaction between the double PDPs and bacteria inhibits the aggregation of AuNPs, resulting in an increased visible color change before and after the addition of bacteria. This one-step colorimetric approach displayed a high sensitivity of 2.35 CFU/mL and a wide detection range from 10-2 × 108 CFU/mL. The combination with smartphone-based image analysis improved the portability of this method. This strategy achieves the straightforward, highly sensitive and portable detection of pathogenic bacteria.

Ratiometric fluorescence immunoassay based on silver nanoclusters and calcein-Ce3+ for detecting ochratoxin A

Ochratoxin A (OTA), a dangerous mycotoxin, is found in many crops. It is essential to create sensitive OTA detection techniques to ensure food safety. Based on the principle of p-nitrophenol (PNP) quenched the fluorescence of bovine serum albumin silver nanocluster (BSA-AgNCs) through an internal filtering effect, and phosphate activated fluorescence of calcein-Ce3+ system, a ratiometric fluorescence immunoassay for OTA detection was developed. In this strategy, the value of F518/F640 was used as a signal for response of OTA concentration. The detection range of this strategy was 0.625-25 ng/mL, the limit of detection (LOD) was 0.04 ng/mL. This new immunoassay offered a brand-new platform for detecting OTA.

Colorimetric and photothermal dual readout biosensor for flap endonuclease 1 based on target-prevented gold nanoparticles aggregation

A colorimetric and photothermal dual readout biosensor for Flap endonuclease 1 (FEN1) quantification was developed on the basis of target-prevented gold nanoparticles (AuNPs) aggregation. The exposed 5'-flap of double-flap DNA substrate modified on SAMBs was firstly cleaved by FEN1. Large amount of cleaved 5'-flap remained in the supernatant after simple magnetic separation, which can adsorb on the surface of AuNPs and effectively prevent the dispersed AuNPs from aggregation under high ionic concentration, accompanied with the color changing of the system, which can be recognized by nake eyes easily. The absorption intensity at 528 nm shows a good linear relationship with the increasing FEN1 concentration from 5.0 × 10-3 to 3.1 × 10-2 U μL-1 with a LOD of 1.6 × 10-3 U μL-1 (S/N = 3). Given the aggregated AuNPs have higher photothermal effect than that of the dispersed AuNPs, the target-prevented AuNPs aggregation avoids a sharp increase of temperature for the system under the laser radiation. The temperature change is linearly correlated with the FEN1 concentration in the range of 3.1 × 10-3-6.1 × 10-2 U μL-1 with a LOD of 1.1 × 10-3 U μL-1. The whole detection process can be completed within 1 h. The proposed system had been applied to detect FEN1 concentration in serum samples with satisfied results, which can be applied in resource-limited area easily and quickly.

Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review

Food contaminants present a significant threat to public health. In response to escalating global concerns regarding food safety, there is a growing demand for straightforward, rapid, and sensitive detection technologies. Noble metal nanoclusters (NMNCs) have garnered considerable attention due to their superior attributes compared to other optical materials. These attributes include high catalytic activity, excellent biocompatibility, and outstanding photoluminescence properties. These features render NMNCs promising candidates for crafting nanosensors for food contaminant detection, offering the potential for the development of uncomplicated, swift, sensitive, user-friendly, and cost-effective detection approaches. This review investigates optical nanosensors based on NMNCs, including the synthesis methodologies of NMNCs, sensing strategies, and their applications in detecting food contaminants. Furthermore, it involves a comparative assessment of the applications of NMNCs in optical sensing and their performance. Ultimately, this paper imparts fresh perspectives on the forthcoming challenges. Hitherto, optical (particularly fluorescent) nanosensors founded on NMNCs have demonstrated exceptional sensing capabilities in the realm of food contaminant detection. To enhance sensing performance, future research should prioritize atomically precise NMNCs synthesis, augmentation of catalytic activity and optical properties, development of high-throughput and multimode sensing, integration of NMNCs with microfluidic devices, and the optimization of NMNCs storage, shelf life, and transportation conditions.

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

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

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.

Distinguishable Colorimetric Biosensor for Diagnosis of Prostate Cancer Bone Metastases

Castration-resistant prostate cancer (PCa) causes severe bone metastasis (BM), which significantly increases mortality in men with PCa. Imaging tests and radiometric scanning require long analysis times, expensive equipment, specialized personnel, and a slow turnaround. New visualization technologies are expected to solve the above problems. Nonetheless, existing visualization techniques barely meet the urgency for precise diagnosis because the human eyes cannot recognize and capture even slight variations in visual information. By using dye differentiated superposition enhancement colorimetric biosensors, an effective method to diagnose prostate cancer bone metastases (PCa-BM) with excellent accuracy for naked-eye quantitative detection of alkaline phosphatase (ALP) is developed. The biomarker ALP specific hydrolytic product ascorbic acid can be detected by rhodamine derivatives (Rd) as gold nanobipyramids (Au NBPs) are deposited and grown. Color-recombining enhancement effects between Rd and Au NBPs significantly improved abundance. The 150 U L-1 threshold between normal and abnormal can be identified by color. And with color enhancement effect and double signal response, the ALP index is visually measured to diagnose PCa-BM and provide handy treatment recommendations. Additionally, the proposed colorimetric sensing strategy can be used to diagnose other diseases.

Ratiometric fluorescent aptasensor for convenient detection of ochratoxin A in beer and orange juice

Based on the principle of fluorescence resonance energy transfer (FRET), a simple ratiometric fluorescent aptasensor for convenient detection of ochratoxin A (OTA), a Group IIB carcinogen secreted by some fungi, was established. Initially, the anti-OTA aptamer with a quadruplex structure was flanked with FAM and BHQ1, and its partially complementary DNA (cDNA) was tagged with Cy3. In the absence of OTA, this aptamer hybridized with the cDNA strand forming a DNA duplex structure, in which BHQ1 was adjacent to Cy3 and distant from FAM. Due to the FRET principle, the fluorescence intensity emitted by Cy3 (FCy3) was quenched by BHQ1, and the fluorescence intensity emitted by FAM (FFAM) recovered. In the presence of OTA, the prepared aptamer preferred to bind with OTA instead of cDNA, forming an aptamer-OTA complex structure in which BHQ1 was adjacent to FAM and distant from Cy3. As a result, FFAM was quenched and FCy3 was restored. OTA can be accurately detected via the determination of the FCy3/FFAM ratio value. Under optimal conditions, this ratiometric fluorescent aptasensor offers excellent OTA detection in the range of 0.6 nmol L-1-5 μmol L-1, with a limit of detection (LOD) of 0.3 nmol L-1. This ratiometric aptasensor showed the advantages of easy operation, accuracy and sensitive analysis. Good specificity of this aptasensor was demonstrated. This ratiometric aptasensor could be used for the detection of OTA in real samples, e.g. beer and orange juice, showing its promising application potential.

Micro- and nanosystems for the detection of hemorrhagic fever viruses

Hemorrhagic fever viruses (HFVs) are virulent pathogens that can cause severe and often fatal illnesses in humans. Timely and accurate detection of HFVs is critical for effective disease management and prevention. In recent years, micro- and nano-technologies have emerged as promising approaches for the detection of HFVs. This paper provides an overview of the current state-of-the-art systems for micro- and nano-scale approaches to detect HFVs. It covers various aspects of these technologies, including the principles behind their sensing assays, as well as the different types of diagnostic strategies that have been developed. This paper also explores future possibilities of employing micro- and nano-systems for the development of HFV diagnostic tools that meet the practical demands of clinical settings.

A G-triplex and G-quadruplex concatemer-enhanced fluorescence probe coupled with hybridization chain reaction for ultrasensitive aptasensing of ochratoxin A

Ochratoxin A (OTA), a typical mycotoxin contaminant found in various agricultural products and foods, poses a serious threat to human health. In this study, an aptasensor based on a novel fluorescence probe comprising a G-rich DNA sequence (G43) and thioflavin T (ThT) was designed via hybridization chain reaction (HCR) for the ultrasensitive detection of OTA. G43 is a concatemer of G-quadruplex and G-triplex (a G-quadruplex-like structure with one G-quartet removed), which can drastically enhance the fluorescence intensity of ThT. For this strategy to work, the OTA aptamer is pro-locked in a hairpin structure, denoted "hairpin-locked aptamer" (HL-Apt). OTA binds to HL-Apt, opens the hairpin structure, releases the trigger sequence, and initiates the HCR reaction to form a long DNA duplex and numerous side chains. The side chains combine entirely with the complementary DNA and liberate the pro-locked G43 DNA, dramatically enhancing the intensity of the ThT fluorescence signal. The fluorescence intensity correlates linearly with the OTA concentration between 0.02 and 2.00 ng mL^-1, and the method has a detection limit of 0.008 ng mL^-1. The developed aptasensor was used to detect OTA in foodstuffs with satisfactory results.

Novel Electrochemiluminescent Immunosensor Using Dual Amplified Signals from a CoFe Prussian Blue Analogue and Au Nanoparticle for the Detection of Lp-PLA2

Coronary heart disease (CHD) poses an important threat to human health, and its pathogenesis is the formation of atheromatous plaques in coronary ventricles. Compared to other biomarkers, lipoprotein-associated phospholipase A2 (Lp-PLA2), which is involved in multiple processes of atherosclerosis, is a noticeable inflammatory biomarker related to CHD. Herein, using a multifunctional nanocomposite containing a CoFe Prussian blue analogue (PBA) and Au nanoparticles (AuNPs) (AuNPs@CoFe PBA) as a sensing substrate, an electrochemiluminescent (ECL) immunosensor was developed for the highly sensitive detection of Lp-PLA2. Benefiting from the synergistic effect of the PBA and AuNPs, the nanocomposite exhibits excellent peroxidase-like activity and can catalyze the luminol-ECL reaction, amplifying the ECL signal by ∼29-fold. Meanwhile, the enlarged specific surface area of the nanocomposite and the presence of abundant AuNPs allow the immobilization of more antibody proteins, thereby improving the sensing response of the immunosensor. When the target Lp-PLA2 is captured by the antibody on the sensor surface, the sensor emits a reduced ECL signal because of the increased mass and electron transfer resistance due to the formation of the immune complex. Under optimized conditions, the constructed ECL immunosensor exhibits a broad linear range from 1 to 2200 ng/mL and a low detection limit of 0.21 ng/mL. Additionally, the ECL immunosensor exhibits high specificity, stability, and reproducibility. This work provides a new approach to diagnose CHD and broadened the application of the PBA in the field of ECL sensors.

Perspectives and trends in advanced optical and electrochemical biosensors based on engineered peptides

With the advancement of life medicine, in vitro diagnostics (IVD) technology has become an auxiliary tool for early diagnosis of diseases. However, biosensors for IVD now face some disadvantages such as poor targeting, significant antifouling properties, low density of recognized molecules, and poor stability. In recent years, peptides have been demonstrated to have various functions in unnatural biological systems, such as targeting properties, antifouling properties, and self-assembly properties, which indicates that peptides can be engineered. These properties of peptides, combined with their good biocompatibility, can be well applied to the design of biosensors to solve the problems mentioned above. This review provides an overview of the properties of engineered functional peptides and their applications in enhancing biosensor performance, mainly in the field of optics and electrochemistry.

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.

Advances in immunoassay-based strategies for mycotoxin detection in food: From single-mode immunosensors to dual-mode immunosensors

Mycotoxin contamination in foods and other goods has become a broad issue owing to serious toxicity, tremendous threat to public safety, and terrible loss of resources. Herein, it is necessary to develop simple, sensitive, inexpensive, and rapid platforms for the detection of mycotoxins. Currently, the limitation of instrumental and chemical methods cannot be massively applied in practice. Immunoassays are considered one of the best candidates for toxin detection due to their simplicity, rapidness, and cost-effectiveness. Especially, the field of dual-mode immunosensors and corresponding assays is rapidly developing as an advanced and intersected technology. So, this review summarized the types and detection principles of single-mode immunosensors including optical and electrical immunosensors in recent years, then focused on developing dual-mode immunosensors including integrated immunosensors and combined immunosensors to detect mycotoxins, as well as the combination of dual-mode immunosensors with a portable device for point-of-care test. The remaining challenges were discussed with the aim of stimulating future development of dual-mode immunosensors to accelerate the transformation of scientific laboratory technologies into easy-to-operate and rapid detection platforms.

Nile blue as reporter dye in salt aggregation based-colorimetric aptasensors for peptide, small molecule and metal ion detection

Herein, we report a novel approach for the design of a colorimetric aptasensor, relying on a Dye Salt Aggregation-based Colorimetric Oligonucleotide assay (DYSACO assay). This method is based on the use of an intercalating agent, Nile Blue (NB), whose aggregation capacities (and thus modification of its absorption spectrum) are drastically amplified by adding salts to the working solution. The presence of an aptamer could protect NB from such aggregation process due to its intercalation into double-stranded DNA and/or interaction with nucleobases. In response to the addition of the specific ligand, the competition between NB and the target for binding to the aptamer occurs, resulting in an increase in the dye salt aggregation and then in the blue-to-blank color change of the solution. The proof-of-principle was demonstrated by employing the anti-l-tyrosinamide aptamer and the assay was successfully applied to the trace enantiomer detection, allowing the detection of an enantiomeric impurity down to approximately 2% in a non-racemic sample. Through a reversed mechanism based on the increased capture of NB by DNA upon analyte binding, the sensing platform was further demonstrated for the Hg(II) detection. Water samples of different origin were spiked with Hg(II) analyte at final range concentrations comprised between (0.5-15 μM). An excellent overall recovery of 122 ± 14%; 105 ± 14%; 99 ± 9%; was respectively obtained from river, tap and mineral water, suggesting that the sensor can be used under real sample conditions. The assay was also shown to work for sensing the ochratoxin A and d-arginine vasopressin compounds, revealing its simplicity and generalizability potentialities.

Shape-specific MOF-derived Cu@Fe-NC with morphology-driven catalytic activity: Mimicking peroxidase for the fluorescent- colorimetric immunosignage of ochratoxin

Ochratoxin A (OTA), which has strong hepatotoxicity and nephrotoxicity, can accumulate in the human body through the food chain; thus, the selective and effective detection of OTA is urgently required for food security. Nanozymes with hyperfine size and shape control have attracted attention because of their controllable structure and intrinsic activity. Herein, CuFe-bimetal coordinated N-doped carbon (Cu@Fe-NC) with morphology-driven peroxidase-mimicking activity was synthesized using Cu₂O with specific polygonal cubes and fully exposed {111} crystalline facets as the template to produce a CuFe-bimetallic metal organic framework (MOF) and further treating CuFe-MOF with high-temperature pyrolysis. N-doping can confer electronegativity to exhibit high affinity, while the large surface area of the porous carbon support can facilitate rapid adsorption-desorption equilibrium. Using the peroxidase-mimicking Cu@Fe_0.5-NC as a carrier, a versatile immunoassay for the detection of OTA was implemented based on the ratiometric fluorescence and the localized surface plasmon resonance peak shift, achieving a detection limit of 0.52 ng/L in the range of 0.001-10 μg/L. Therefore, the strategy of enhancing enzyme-mimicking activity using specific shapes and crystalline facets may open new avenues for food and environmental analysis.

Bio-Tailored Sensing at the Nanoscale: Biochemical Aspects and Applications

The demonstration of the first enzyme-based electrode to detect glucose, published in 1967 by S. J. Updike and G. P. Hicks, kicked off huge efforts in building sensors where biomolecules are exploited as native or modified to achieve new or improved sensing performances. In this growing area, bionanotechnology has become prominent in demonstrating how nanomaterials can be tailored into responsive nanostructures using biomolecules and integrated into sensors to detect different analytes, e.g., biomarkers, antibiotics, toxins and organic compounds as well as whole cells and microorganisms with very high sensitivity. Accounting for the natural affinity between biomolecules and almost every type of nanomaterials and taking advantage of well-known crosslinking strategies to stabilize the resulting hybrid nanostructures, biosensors with broad applications and with unprecedented low detection limits have been realized. This review depicts a comprehensive collection of the most recent biochemical and biophysical strategies for building hybrid devices based on bioconjugated nanomaterials and their applications in label-free detection for diagnostics, food and environmental analysis.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

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.

Aptamer Molecular Beacon Sensor for Rapid and Sensitive Detection of Ochratoxin A

Ochratoxin A (OTA) is a carcinogenic fungal secondary metabolite which causes wide contamination in a variety of food stuffs and environments and has a high risk to human health. Developing a rapid and sensitive method for OTA detection is highly demanded in food safety, environment monitoring, and quality control. Here, we report a simple molecular aptamer beacon (MAB) sensor for rapid OTA detection. The anti-OTA aptamer has a fluorescein (FAM) labeled at the 5' end and a black hole quencher (BHQ1) labeled at the 3' end. The specific binding of OTA induced a conformational transition of the aptamer from a random coil to a duplex-quadruplex structure, which brought FAM and BHQ1 into spatial proximity causing fluorescence quenching. Under the optimized conditions, this aptamer sensor enabled OTA detection in a wide dynamic concentration range from 3.9 nM to 500 nM, and the detection limit was about 3.9 nM OTA. This method was selective for OTA detection and allowed to detect OTA spiked in diluted liquor and corn flour extraction samples, showing the capability for OTA analysis in practical applications.

Recent advances in simultaneous detection strategies for multi-mycotoxins in foods

Mycotoxin contamination has become a challenge in the field of food safety testing, given the increasing emphasis on food safety in recent years. Mycotoxins are widely distributed, in heavily polluted areas. Food contamination with these toxins is difficult to prevent and control. Mycotoxins, as are small-molecule toxic metabolites produced by several species belonging to the genera Aspergillus, Fusarium, and Penicillium growing in food. They are considered teratogenic, carcinogenic, and mutagenic to humans and animals. Food systems are often simultaneously contaminated with multiple mycotoxins. Due to the additive or synergistic toxicological effects caused by the co-existence of multiple mycotoxins, their individual detection requires reliable, accurate, and high-throughput techniques. Currently available, methods for the detection of multiple mycotoxins are mainly based on chromatography, spectroscopy (colorimetry, fluorescence, and surface-enhanced Raman scattering), and electrochemistry. This review provides a comprehensive overview of advances in the multiple detection methods of mycotoxins during the recent 5 years. The principles and features of these techniques are described. The practical applications and challenges associated with assays for multiple detection methods of mycotoxins are summarized. The potential for future development and application is discussed in an effort, to provide standards of references for further research.

Ochratoxin A in Dry-Cured Ham: OTA-Producing Fungi, Prevalence, Detection Methods, and Biocontrol Strategies-A Review

Traditional dry-cured hams are easily contaminated by toxigenic fungi during the fermentation and ripening stages. The detection and positive rates of ochratoxin A (OTA) are the highest among mycotoxins detected in traditional dry-cured hams, indicating that OTA in hams is a potential safety hazard to human health. This review addresses the mycotoxin-producing fungal species, the toxigenic conditions causing OTA contamination worldwide, the prevalence of OTA contamination in dry-cured hams, and the detection methods applied in OTA analysis. Additionally, this study introduces methods to prevent and control OTA in traditional dry-cured hams. The growth of common mycotoxin-producing fungi and the accumulation of mycotoxins in dry-cured ham can be controlled by a microbial starter. This review provides an important theoretical foundation for the research and control of OTA in traditional dry-cured hams.

Enhanced detection of ascorbic acid with cascaded fluorescence recovery of a dual-nanoquencher system

An innovative strategy with target-triggered cascade fluorescence recovery of a dual-nanoquencher system was developed to detect ascorbic acid (AA). Herein, manganese dioxide (MnO₂) nanosheets and gold nanoparticles (AuNPs) were used as nanoquenchers simultaneously. Owing to their synergistic effects, the fluorescence of 2,3-diaminophenazine (DAP) was decreased efficiently, thus minimizing the background fluorescence. The introduction of AA triggered the decomposition of MnO₂ into Mn²⁺, which induced the aggregation of AuNPs. Both the decomposed MnO₂ and aggregated AuNPs possess weak quenching abilities towards DAP. Such a cascade amplification strategy enhanced the detection sensitivity for AA with a LOD as low as 6.7 nM, which was two orders of magnitude lower than that of MnO₂-based fluorescence assay. Furthermore, this amplification strategy was successfully applied to detect AA in food samples.

A colorimetric aptasensor based on gold nanoparticles for detection of microbial toxins: an alternative approach to conventional methods

Frequent contamination of foods with microbial toxins produced by microorganisms such as bacteria, fungi, and algae represents an increasing public health problem that requires the development of quick and easy tools to detect them at trace levels. Recently, it has been found that colorimetric detection methods may replace traditional methods in the field because of their ease of use, quick response, ease of manufacture, low cost, and naked-eye visibility. Therefore, it is suitable for fieldwork, especially for work in remote areas of the world. However, the development of colorimetric detection methods with low detection limits is a challenge that limits their wide applicability in the detection of food contaminants. To address these challenges, nanomaterial-based transduction systems are used to construct colorimetric biosensors. For example, gold nanoparticles (AuNPs) provide an excellent platform for the development of colorimetric biosensors because they offer the advantages of easy synthesis, biocompatibility, advanced surface functionality, and adjustable physicochemical properties. The selectivity of the colorimetric biosensor can be achieved by the combination of aptamers and gold nanoparticles, which provides an unprecedented opportunity to detect microbial toxins. Compared to antibodies, aptamers have significant advantages in the analysis of microbial toxins due to their smaller size, higher binding affinity, reproducible chemical synthesis and modification, stability, and specificity. Two colorimetric mechanisms for the detection of microbial toxins based on AuNPs have been described. First, sensors that use the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles can exhibit very strong colors in the visible range because of changes caused by aggregation or disaggregation. Second, the detection mechanism of AuNPs is based on their enzyme mimetic properties and it is possible to construct a colorimetric biosensor based on the 3,3',5,5'-tetramethylbenzidine/Hydrogen peroxide, TMB/H₂O₂ reaction to detect microbial toxins. Therefore, this review summarizes the recent applications of AuNP-based colorimetric aptasensors for detecting microbial toxins, including bacterial toxins, fungal toxins, and algal toxins focusing on selectivity, sensitivity, and practicality. Finally, the most important current challenges in this field and future research opportunities are discussed.

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

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

Smartphone-based surface plasmon resonance sensing platform for rapid detection of bacteria

Bacterial infection poses severe threats to public health, and early rapid detection of the pathogen is critical for controlling bacterial infectious diseases. Current methods are commonly labor intensive, time consuming or dependent on lab-based equipment. In this study, we proposed a novel and practical method for bacterial detection based on smartphones using the surface plasmon resonance (SPR) phenomena of gold nanoparticles (AuNPs). The proposed smartphone-based SPR sensing method is achieved by utilizing color development that arises from the change in interparticle distance of AuNPs induced by bacterial lysate. The pictures of bacteria/AuNPs color development were captured, and their color signals were acquired through a commercial smartphone. The proposed method has a detection range between 2.44 × 10⁵ and 1.25 × 10⁸ cfu mL⁻¹ and a detection limit of 8.81 × 10⁴ cfu mL⁻¹. Furthermore, this method has acceptable recoveries (between 85.7% and 95.4%) when measuring spiked real waters. Combining smartphone-based signal reading with AuNP-dependent color development also offers the following advantages: easy-to-use, real-time detection, free of complex equipment and low cost. In view of these features, this sensing platform would have widespread applications in the fields of medical, food, and environmental sciences.

In this study, we propose a novel and practical method for bacterial detection based on smartphones using the surface plasmon resonance (SPR) phenomena of gold nanoparticles (AuNPs).

Contamination, Detection and Control of Mycotoxins in Fruits and Vegetables

Mycotoxins are secondary metabolites produced by pathogenic fungi that colonize fruits and vegetables either during harvesting or during storage. Mycotoxin contamination in fruits and vegetables has been a major problem worldwide, which poses a serious threat to human and animal health through the food chain. This review systematically describes the major mycotoxigenic fungi and the produced mycotoxins in fruits and vegetables, analyzes recent mycotoxin detection technologies including chromatography coupled with detector (i.e., mass, ultraviolet, fluorescence, etc.) technology, electrochemical biosensors technology and immunological techniques, as well as summarizes the degradation and detoxification technologies of mycotoxins in fruits and vegetables, including physical, chemical and biological methods. The future prospect is also proposed to provide an overview and suggestions for future mycotoxin research directions.

A simple and sensitive AuNPs-based colorimetric aptasensor for specific detection of azlocillin

A new colorimetric biosensor for specific detection of azlocillin was developed by using DNA aptamer as recognition element and unmodified gold nanoparticles (AuNPs) as colorimetric indicator. In the absence of azlocillin, the AuNPs were protected by the aptamer and stabilized at high NaCl concentrations, displaying a red solution. In the presence of azlocillin, the aptamer reacts specifically with azlocillin, resulting in the aggregation of AuNPs and an apparent red to blue color change. The characteristic change can be easily observed by the naked eye and quantitatively detected by an ultraviolet-visible (UV-Vis) spectrometer. Under the optimal conditions, the absorbance variation at 522 nm (ΔA₅₂₂) of AuNPs changed proportionally with increasing concentration of azlocillin, which exhibited a linear relationship in the concentration range of 50 nM to 500 nM, with a detection limit of 11.6 nM. Furthermore, the aptasensor was successfully used to detect azlocillin in milk and tap water samples, with recoveries ranging from 97.64% to 102.21% and a relative standard deviation (RSD) less than 3.81%.

CRISPR-Cas12a based fluorescence assay for organophosphorus pesticides in agricultural products

Herein, we propose a sensitive fluorescent assay for organophosphorus pesticides (OPs) detection based on a novel strategy of activating the CRISPR-Cas12a system. Specifically, acetylcholinesterase (AChE) hydrolyzes acetylthiocholine into thiocholine (TCh). Subsequently, TCh induces the degradation of MnO₂ nanosheets and generates sufficient Mn²⁺ ions to activate the Mn²⁺-dependent DNAzyme. Then, as the catalytic product of activated DNAzyme, the short DNA strand activates the CRISPR-Cas12a system to cleave the fluorophore-quencher-labeled DNA reporter (FQ) probe effectively; thus, increasing the fluorescence intensity (FI) in the solution. However, in the presence of OPs, the activity of AChE is suppressed, resulting in a decrease in FI. Under optimized conditions, the limits of detection for paraoxon, dichlorvos, and demeton were 270, 406, and 218 pg/mL, respectively. Benefiting from the outstanding MnO₂ nanosheets properties and three rounds of enzymatic signal amplification, the proposed fluorescence assay holds great potential for the detection of OPs in agricultural products.

Nanomaterial-based aptamer biosensors for ochratoxin A detection: a review

Ochratoxin A (OTA) is a widely distributed mycotoxin that often contaminates food, grains and animal feed. It poses a serious threat to human health because of its high toxicity and persistence. Therefore, the development of an inexpensive, highly sensitive, accurate and rapid method for OTA detection is imperative. In recent years, various nanomaterials used in the establishment of aptasensors have attracted great attention due to their large surface-to-volume ratio, good stability and facile preparation. This review summarizes the development of nanomaterial-based aptasensors for OTA determination and sample treatment over the past 5 years. The nanomaterials used in OTA aptasensors include metal, carbon, luminescent, magnetic and other nanomaterials. Finally, the limitations and future challenges in the development of nanomaterial-based OTA aptasensors are reviewed and discussed.

Engineering DNA G-quadruplex assembly for label-free detection of Ochratoxin A in colorimetric and fluorescent dual modes

Colorimetric and fluorescent methods for Ochratoxin A (OTA) detection are convenient and well received. However, the pigments and autofluorescence originated from food matrices often interfere with detection signals. We have developed a strategy with colorimetric and fluorescent dual modes to solve this challenge. In the colorimetric mode, OTA aptamer (AP9) was assembled into a DNA triple-helix switch with a specially designed signal-amplifying sequence. The OTA-induced G-quadruplex (G4) of AP9 would open the switch and release the signal-amplifying sequence for colorimetric signal amplification. The G4 structures of AP9 were further utilized to combine with the fluorogenic dye ThT for fluorescent mode. By skillfully engineering DNA G4 assembly for signal amplification, there was no need for any DNA amplification or nanomaterials labeling. Detections could be carried out in a wide temperature range (22-37 ℃) and finished rapidly (colorimetric mode, 60 min; fluorescent mode, 15 min). Broad linear ranges (colorimetric mode, 10-1.5 ×10³ μg/kg; fluorescent mode, 0.05-1.0 ×10³ μg/kg) were achieved. The limit of detection for colorimetric and fluorescent modes were 4 μg/kg and 0.01 μg/kg, respectively. The two modes have been successfully applied to detect OTA in samples with intrinsic pigments and autofluorescence, showing their applicability and reliability.

An ultra-sensitive dual-responsive aptasensor with combination of liquid crystal and intercalating dye molecules: A food toxin case study

Herein, a label-free aptasensor was designed through forming a double-stranded DNA skeleton on the glass substrate for ultrasensitive quantification of ochratoxin A (OTA) as a case study. The function fundament of the dual-responsive aptasensor was the perturbation of the vertical alignment of the liquid crystals (LCs) and intercalation of the SYBR Green I (SGI) dye molecules between the base pairs of the double-stranded DNA structure. The presence of OTA decomposed the double-stranded structure of DNA by releasing the OTA-specific aptamer from the sensing platform that induced an apparent alteration of the optical and fluorescent responses. The aptasensor specifically detected the ultra-low levels of OTA as 47.0E-9 pM (0.047 aM) and 34.0E-3 pM (34 fM) based on the polarized and fluorescent responses, respectively. The aptasensor monitored OTA in the coffee and grape drink samples. The aptasensor provides promising insight for manufacturing real-time, cost-effective, and portable sensing devices for food control usage.

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

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

Fluonanobody-based nanosensor via fluorescence resonance energy transfer for ultrasensitive detection of ochratoxin A

Ochratoxin A (OTA) contamination in food is a serious threat to public health. There is an urgent need for development of rapid and sensitive methods for OTA detection, to minimize consumer exposure to OTA. In this study, we constructed two OTA-specific fluonanobodies (FluoNbs), with a nanobody fused at the carboxyl-terminal (SGFP-Nb) or the amino-terminal (Nb-SGFP) of superfolder green fluorescence protein. SGFP-Nb, which displayed better fluorescence performance, was selected as the tracer for OTA, to develop a FluoNb-based nanosensor (FN-Nanosens) via the fluorescence resonance energy transfer, where the SGFP-Nb served as the donor and the chemical conjugates of OTA-quantum dots served as the acceptor. After optimization, FN-Nanosens showed a limit of detection of 5 pg/mL, with a linear detection range of 5-5000 pg/mL. FN-Nanosens was found to be highly selective for OTA and showed good accuracy and repeatability in recovery experiments using cereals with various complex matrix environments. Moreover, the contents of OTA in real samples measured using FN-Nanosens correlated well with those from the liquid chromatography with tandem mass spectrometry. Therefore, this work illustrated that the FluoNb is an ideal immunosensing tool and that FN-Nanosens is reliable for rapid detection of OTA in cereals with ultrahigh sensitivity.