Molecularly Imprinted Poly(thionine)-Based Electrochemical Sensing Platform for Fast and Selective Ultratrace Determination of Patulin

Smartphone-enabled flow injection amperometric glucose monitoring based on a screen-printed carbon electrode modified with PEDOT@PB and a GOx@PPtNPs@MWCNTs nanocomposite

This study presents a modified screen-printed carbon electrode (SPCE) to determine glucose in a custom-built flow injection system. The biosensor was constructed by immobilizing glucose oxidase on porous platinum nanoparticles decorated on multi-walled carbon nanotubes (GOx@PPtNPs@MWCTNs). The fabrication of the biosensor was completed by coating the GOx@PPtNPs@MWCTNs nanocomposite on an SPCE modified with a nanocomposite of poly(3,4-ethylenedioxythiophene) and Prussian blue (GOx@PPtNPs@MWCTNs/PEDOT@PB/SPCE). The fabricated electrode accurately measured hydrogen peroxide (H2O2), the byproduct of the GOx-catalyzed oxidation of glucose, and was then applied as a glucose biosensor. The glucose response was amperometrically determined from the PB-mediated reduction of H2O2 at an applied potential of -0.10 V in a flow injection system. Under optimal conditions, the developed biosensor produced a linear range from 2.50 μM to 1.250 mM, a limit of detection of 2.50 μM, operational stability over 500 sample injections, and good selectivity. The proposed biosensor determined glucose in human plasma samples, achieving recoveries and results that agreed with the hexokinase-spectrophotometric method (P > 0.05). Combining the proposed biosensor with the custom-built sample feed, a portable potentiostat and a smartphone, enabled on-site glucose monitoring.

An ionic liquid-modified PEDOT/Ti3C2TX based molecularly imprinted electrochemical sensor for pico-molar sensitive detection of L-Tryptophan in milk

L-Tryptophan (L-Trp) is essential for the human body and can only be obtained externally. It is important to develop a method to efficiently detect L-Trp in food. In this work, ionic liquid (IL) modified poly(3,4-ethylendioxythiophene)/ Titanium carbide (PEDOT/Ti3C2TX) was used as a substrate material to improve detection sensitivity. Molecular imprinted polymers (MIP) film for specific recognition of L-Trp was fabricated on the surface of modified electrodes using electrochemical polymerization. The monitoring results showed that the molecularly imprinted electrochemical sensors (MIECS) exhibited good linearity ranges (10-6 - 0.1 μM and 0.1-100 μM) with a low detection limit (LOD) of 2.09 × 10-7 μM. In addition, the MIECS exhibited remarkable stability, reproducibility, and immunity to interference. A good recovery (93.54-99.59%) was demonstrated in the detection of milk. The sensor was expected to be developed as a highly selective and sensitive portable assay, and applied to the detection of L-Trp in food.

Development of surface molecular-imprinted electrochemical sensor for palmitic acid with machine learning assistance

Palmitic acid (PA) is a kind of saturated high fatty acid, which is involved in physiological safety and food quality. A surface molecularly imprinted polymer (MIP) electrochemical sensor was prepared on MXene surface using dopamine (DA) as functional monomer. The electrode was modified with gold nanoparticles (AuNPs), ferrocene-graphene oxide-multiwalled carbon nanotubes (Fc-GO-MWCNT) composite to enhance the electroactive area and conductivity. The sensor was characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS) and Differential pulse voltammetry (DPV), respectively. The parameters concerning this assay and various regeneration conditions have been carefully studied. The sensor can detect PA in the range of 1 nM-1 mM (R2 = 0.995), the limit of detection (LOD) is 0.48 nM (S/N = 3), and the limit of quantification (LOQ) is 1.61 nM. The artificial neural network (ANN) model in machine learning is further used to analyze the data collected by the sensor. The results show that the back propagation (BP) neural network in ANN is more suitable for the intelligent analysis of PA. The practicality of the sensor was confirmed by detecting PA in pork samples. This is the first MIP-based electrochemical sensor for PA, and it has great potential in practical applications.

Advances in Aptamer-Based Conjugate Recognition Techniques for the Detection of Small Molecules in Food

Small molecules are significant risk factors for causing food safety issues, posing serious threats to human health. Sensitive screening for hazards is beneficial for enhancing public security. However, traditional detection methods are unable to meet the requirements for the field screening of small molecules. Therefore, it is necessary to develop applicable methods with high levels of sensitivity and specificity to identify the small molecules. Aptamers are short-chain nucleic acids that can specifically bind to small molecules. By utilizing aptamers to enhance the performance of recognition technology, it is possible to achieve high selectivity and sensitivity levels when detecting small molecules. There have been several varieties of aptamer target recognition techniques developed to improve the ability to detect small molecules in recent years. This review focuses on the principles of detection platforms, classifies the conjugating methods between small molecules and aptamers, summarizes advancements in aptamer-based conjugate recognition techniques for the detection of small molecules in food, and seeks to provide emerging powerful tools in the field of point-of-care diagnostics.

Progress on Electrochemical Biomimetic Nanosensors for the Detection and Monitoring of Mycotoxins and Pesticides

Monitoring agricultural toxins such as mycotoxins is crucial for a healthy society. High concentrations of these toxins lead to the cause of several chronic diseases; therefore, developing analytical systems for detecting/monitoring agricultural toxins is essential. These toxins are found in crops such as vegetables, fruits, food, and beverage products. Currently, screening of these toxins is mostly performed with sophisticated instrumentation such as chromatography and spectroscopy techniques. However, these techniques are very expensive and require extensive maintenance, and their availability is limited to metro cities only. Alternatively, electrochemical biomimetic sensing methodologies have progressed hugely during the last decade due to their unique advantages like point-of-care sensing, miniaturized instrumentations, and mobile/personalized monitoring systems. Specifically, affinity-based sensing strategies including immunosensors, aptasensors, and molecular imprinted polymers offer tremendous sensitivity, selectivity, and stability to the sensing system. The current review discusses the principal mechanisms and the recent developments in affinity-based sensing methodologies for the detection and continuous monitoring of mycotoxins and pesticides. The core discussion has mainly focused on the fabrication protocols, advantages, and disadvantages of affinity-based sensing systems and different exploited electrochemical transduction techniques.

A novel electrochemical sensor based on dual-functional MMIP-CuMOFs for both target recognition and signal reporting and its application for sensing bisphenol A in milk

In this work, novel magnetic molecularly imprinted CuMOFs (MMIP-CuMOFs) were synthesized and applied to construct an electrochemical bisphenol A sensor. The constructed sensor used an electrode modified with reduced graphene oxide (RGO/GCE) as the sensing platform to improve its stability and sensitivity. The Fe3O4 nanoparticles in magnetic MOFs simplified the preparation process. Moreover, the combination of CuMOFs and molecular imprinting methodology was beneficial for improving the detection specificity, and the electroactive copper hexacyanoferrate generated by the reaction of Cu2+ in CuMOFs with potassium ferricyanide was used as the signal probe. The sensor showed a good linear relationship in the range of 0.5 to 500 nmol/L, with a low detection limit of 0.18 nmol/L. In addition, the sensor had good selectivity, repeatability (RSD = 2.59 %), and a good recovery rate for actual milk sample detection (99.8-102.49 %). This technique holds great promise for the detection of detrimental substances in food.

A Redox Mediator-Free Highly Selective and Sensitive Electrochemical Aptasensor for Patulin Mycotoxin Detection in Apple Juice Using Ni-NiO Pseudocapacitive Nanomaterials

Pseudocapacitive nanomaterials have recently gained significant attention in electrochemical biosensors due to their rapid response, long cycle life, high surface area, biomolecule compatibility, and superior energy storage capabilities. In our study, we introduce the potential of using Ni-NiO nanofilm's pseudocapacitive traits as transducer signals in electrochemical aptasensors. Capitalizing on the innate affinity between histidine and nickel, we immobilized histidine-tagged streptavidin (HTS) onto Ni-NiO-modified electrodes. Additionally, we employed a biolayer interferometry-based SELEX to generate biotinylated patulin aptamers. These aptamers, when placed on Ni-NiO-HTS surfaces, make a suitable biosensing platform for rapid patulin mycotoxin detection in apple juice using electrochemical amperometry in microseconds. The novelty lies in optimizing pseudocapacitive nanomaterials structurally and electrochemically, offering the potential for redox mediator-free electrochemical aptasensors. Proof-of-concept is conducted by applying this surface for the ultrasensitive detection of a model analyte, patulin mycotoxin. The aptamer-functionalized bioelectrode showed an excellent linear response (10-106 fg/mL) and an impressive detection limit (1.65 fg/mL, +3σ of blank signal). Furthermore, reproducibility tests yielded a low relative standard deviation of 0.51%, indicating the good performance of the developed biosensor. Real sample analysis in freshly prepared apple juice revealed no significant difference (P < 0.05) in current intensity between spiked and real samples. The sensor interface maintained excellent stability for up to 2 weeks (signal retention 96.45%). The excellent selectivity, stability, and sensitivity of the electrochemical aptasensor exemplify the potential for using nickel-based pseudocapacitive nanomaterials for a wide variety of electrochemical sensing applications.

Ultrasensitive molecular imprinted electrochemical sensor for in vivo determination of glycine betaine in plants

Glycine betaine (GB) is a bioactive molecule protecting plants from abiotic stress. This study fabricated an ultrasensitive molecular imprinted polymer (MIP) electrochemical sensor to perform in vivo measurements of GB. Polydopamine (PDA) was formed on the carboxylated multi-walled carbon nanotubes (COOH-MWCNTs) by spontaneous polymerisation of dopamine (DA). Then MIP-coated MWCNTs were fabricated on a Au nanoparticles (NP) and thionine (Thi) modified screen-printed electrode (SPE). The MIP-COOH-MWCNTs/pThi/AuNPs/SPE exhibited an ultrasensitive GB detection response between 1 fmol/L and 10 mmol/L (R2 = 0.996) with a low detection limit (0.707 fmol/L, S/N = 3). In vivo measurement of GB in cucumber seedling leaves under different salinity stress conditions confirmed the practical applicability of the MIP sensor. Thus, this study proposed a novel and promising fabrication method for an electrochemical MIP sensor that has broad application prospects in precision agriculture.

MXene fibers-based molecularly imprinted disposable electrochemical sensor for sensitive and selective detection of hydrocortisone

A molecularly imprinted electrochemical sensor based on MXene fibers was proposed in this work. Firstly, the wet spinning technique prepared MXene fibers with a large aspect ratio, which can make the sheet-like MXene uniformly arranged, avoiding the agglomeration of MXene and improving the electrical conductivity. Afterwards, molecularly imprinted polymers (MIPs) with specific recognition sites were synthesized on the surface of MXene fibers using the electro-polymerization method. The electrochemical sensor utilized the advantages of MXene fibers and molecular imprinting techniques to gain superior selectivity and sensitivity of hydrocortisone (HC). Electrochemical tests with different concentrations of HC (0.5 nM-10.0 μM) under optimal measurement conditions exhibited excellent linearity and a limit of detection (LOD) of 0.17 nM. Furthermore, the electrochemical sensor displayed excellent selectivity, interference resistance, reproducibility, stability and outstanding application performance in serum. This work has promising applications in trace analysis in real sample.

Current Trends in Mycotoxin Detection with Various Types of Biosensors

One of the most important tasks in food safety is to properly manage the investigation of mycotoxin contamination in agricultural products and foods made from them, as well as to prevent its occurrence. Monitoring requires a wide range of analytical methods, from expensive analytical procedures with high-tech instrumentation to significantly cheaper biosensor developments or even single-use assays suitable for on-site monitoring. This review provides a summary of the development directions over approximately a decade and a half, grouped according to the biologically sensitive components used. We provide an overview of the use of antibodies, molecularly imprinted polymers, and aptamers, as well as the diversity of biosensors and their applications within the food industry. We also mention the possibility of determining multiple toxins side by side, which would significantly reduce the time required for the analyses.

Electroactive poly(thionine) as imprinted polymer and reference probe simultaneously for ratiometric ion imprinted electrochemical Pb2+sensor

In this work, an electrochemical sensor based on ion-imprinted polymer/Au nanoparticles/porous biochar (IIP/AuNPs/PBC) composite was proposed for the highly selective and sensitive detection of Pb2+. In this work, poly (thionine) (pTHI) served simultaneously as imprinted polymer and reference probe. It could not only realize the specific detection of Pb2+, but also provide an internal reference signal to eliminate the influence of human and environmental factors on the detection signal and further improve the stability of the sensor. In addition, the AuNPs/PBC composite with large specific surface area, excellent electron transport and electrocatalytic performance could effectively enhance the detection signal as a carrier material. At the same time, the AuNPs on the PBC surface would promote the formation of uniform and stable IIP through Au-S bonds. The synergistic effect between IIP, AuNPs/PBC and ratiometric signal mode gave the Pb2+sensor excellent performance, including a wide linear range (0.1-1000μg l-1), low detection limit (0.03μg l-1, S/N = 3), excellent selectivity and stability. All these results indicate that the proposed sensor could provide a meaningful reference for highly selective detection of heavy metal ions (HMIs).

In-depth interpretation of aptamer-based sensing on electrode: Dual-mode electrochemical-photoelectrochemical sensor for the ratiometric detection of patulin

Electrochemical aptasensors have been extensively used to quantify food contaminants (e.g., mycotoxin) by using high-affinity aptamer for target recognition. Yet, analytical performance of aptasensors using different aptamers can be varied for the same target. Here, four aptamers with different sequences (i.e., A22, A34, A42, and A45) of patulin (PAT) were selected to estimate sensing behaviors at electrodes with electrochemical (EC) and photoelectrochemical (PEC) assays. Synergistic effect of steric hindrance and electron transfer distance was found to significantly affect EC and PEC response for PAT at aptasensors fabricated with A22, A34, A42, or A45. Eventually, A22 emerged to be the optimal aptamer for aptasensing, despite the highest affinity of A42 to PAT. The A22-based EC-PEC dual-mode ratiometric aptasensor offered a linear range of 50 fg mL^-1 - 500 ng mL^-1 with a detection limit of 30 fg mL^-1 for PAT, and it was applied to apple product (i.e., juice, puree) analysis.

Patulin-imprinted origami 3D-ePAD based on graphene screen-printed electrode modified with Mn-ZnS quantum dot coated with a molecularly imprinted polymer

We developed a novel, compact, three-dimensional electrochemical paper-based analytical device (3D-ePAD) for patulin (PT) determination. The selective and sensitive PT-imprinted Origami 3D-ePAD was constructed based on a graphene screen-printed electrode modified with manganese-zinc sulfide quantum dots coated with patulin imprinted polymer (Mn-ZnS QDs@PT-MIP/GSPE). The Mn-ZnS QDs@PT-MIP was synthesized using 2-oxindole as the template, methacrylic acid (MAA) as a monomer, N,N'-(1,2-dihydroxyethylene) bis (acrylamide) (DHEBA) as cross-linker and 2,2'-azobis (2-methylpropionitrile) (AIBN) as initiator, respectively. The Origami 3D-ePAD was designed with hydrophobic barrier layers formed on filter paper to provide three-dimensional circular reservoirs and assembled electrodes. The synthesized Mn-ZnS QDs@PT-MIP was quickly loaded on the electrode surface by mixing with graphene ink and then screen-printing on the paper. The PT-imprinted sensor provides the greatest enhancement in redox response and electrocatalytic activity, which we attributed to synergetic effects. This arose from an excellent electrocatalytic activity and good electrical conductivity of Mn-ZnS QDs@PT-MIP, which improved electron transfer between PT and the electrode surface. Under the optimized DPV conditions, a well-defined PT oxidation peak appears at +0.15 V (vs Ag/AgCl) using 0.1 M of phosphate buffer (pH 6.5) containing 5 mM K₃Fe(CN)₆ as the supporting electrolyte. Our developed PT imprinted Origami 3D-ePAD revealed excellent linear dynamic ranges of 0.001-25 μM, with a detection limit of 0.2 nM. Detection performance indicated that our Origami 3D-ePAD possesses outstanding detection performance from fruits and CRM in terms of high accuracy (%Error for inter-day is 1.11%) and precision (%RSD less than 4.1%). Therefore, the proposed method is well-suited as an alternative platform for ready-to-use sensors in food safety. The imprinted Origami 3D-ePAD is an excellent disposable device with a simple, cost-effective, and fast analysis, and it is ready to use for determining patulin in actual samples.

An electrochemical chlorpromazine sensor based on a gold-copper bimetallic synergetic molecularly imprinted interface on an acupuncture needle electrode

Chlorpromazine (CPZ) is a medicine for nervous system disorders. Measuring CPZ in vivo can assist doctors in evaluating patients' blood drug concentration and monitoring drug metabolism. Therefore, an accurate in vivo detection of CPZ is crucial. In recent years, the acupuncture needle, traditionally used in Chinese medicine, has emerged as a potential electrode in the field of electrochemistry, with promising applications for in vivo detection. In this study, Au/Cu nanoparticles were electrodeposited onto an acupuncture needle electrode (ANE) to improve electrical conductivity and provide an electro-catalytic surface. Subsequently, 3-aminophenylboronic acid and CPZ were attracted to each other through intermolecular forces; at the same time, the interaction force of Au-S between CPZ and the AuNPs made the polymer layer grow around the CPZ molecules on the modified electrode surface. The imprinted nanocavities showed highly selective and sensitive detection performance for CPZ after elution. Inside the recognizable site and microenvironment of the cavities, the captured CPZ molecule provided a suitable configuration for the fluent electron transfer of the electroactive group within a short range from the Au/Cu bimetal. Under ideal conditions, the MIP/Au/Cu/ANE exhibited two good linear ranges of 0.1-100 μM and 100-1000 μM with a detection limit of 0.07 μM. Moreover, the sensors showed great selectivity, good stability and excellent repeatability, making them suitable for CPZ detection in human serum. This provides a novel idea for real-time and in vivo CPZ detection.

An Overview of Biosensors for the Detection of Patulin Focusing on Aptamer-Based Strategies

Patulin is a low molecular weight mycotoxin and poses a global problem, especially threatening food safety. It is also resistant to processing temperatures and is commonly found in fruits and vegetables. Studies have shown that it has toxic effects on animals and humans and the severity of patulin toxicity depends on the amount ingested. Therefore, the consumption of contaminated products, especially in infants and children, is important. The maximum daily intake of PAT that can be tolerated is found to be 0.4 µg/kg body weight to prevent chronic effects and the maximum residue limits in food samples were given as 50 ng/g (∼320 nM). Conventional methods for the detection of PAT have many disadvantages such as the use of expensive equipment, the need for trained personnel, and complicated sample preparation steps. To this extent, various numbers of research have been conducted on selective and sensitive detection of patulin using biosensor platforms in various media. This review presents an overview of the current literature dealing with the studies to develop patulin-specific aptamer-based biosensors and adapts various immobilization methods to increase the sensor response using different nanomaterials. Furthermore, a comparison of biosensors with conventional methods is presented using analytical performance parameters and their practicality for the detection of patulin.

Nanozyme-encoded luminescent detection for food safety analysis: An overview of mechanisms and recent applications

With the rapid growth in global food production, delivery, and consumption, reformative food analytical techniques are required to satisfy the monitoring requirements of speed and high sensitivity. Nanozyme-encoded luminescent detections (NLDs) integrating nanozyme-based rapid detections with luminescent output signals have emerged as powerful methods for food safety monitoring, not only because of their preeminent performance in analysis, such as rapid, facile, low background signal, and ultrasensitive, but also due to their strong attractiveness for future sensing research. However, the lack of a full understanding of the fundamentals of NLDs for food safety detection technologies limits their further application. In this review, a systematic overview of the mechanisms of NLDs and their applications in the food industry is summarized, which covers the nanozyme-mimicking types and their luminescent signal generation mechanisms, as well as their applications in monitoring common foodborne contaminants. As demonstrated by previous studies, NLDs are bridging the gap to practical-oriented food analytical technologies and various opportunities to improve their food analytical performance to be considered in the future are proposed.

Label-free fluorescence aptasensor for the detection of patulin using target-induced DNA gates and TCPP/BDC-NH2 mixed ligands functionalized Zr-MOF systems

Patulin (PAT) is an unsaturated lactone mycotoxin primarily produced by Penicillium expansum and Aspergillus clavatus. Given the potential health risks and economic losses associated with PAT, the rapid detection of PAT using fluorescent aptasensors is of significant importance in evaluating food safety. However, it easily increases the cost and complexity caused by signal labeling. We combined TCPP/BDC-NH₂ mixed ligands functionalized Zr metal-organic frameworks (Zr-MOF_mix) and terminated three-stranded DNA gates (ttsDNA gates) to fabricate a label-free fluorescent aptasensor for PAT detection. The Zr-MOF_mix system was synthesized via a one-pot strategy and could be used to address the problem of pore size limitation and increase the loading amounts of dyes. TtsDNA gate was integrated into the Zr-MOF_mix system to control the release of dyes, exhibiting a high signal-to-background ratio. The single-stranded aptamer region in ttsDNA gate situated away from the surface of the Zr-MOF_mix, resulting in a natural release of dyes in the absence of PAT. While binding to PAT resulted in target-induced conformational changes that helped form the hairpin structure of the aptamer. This structure hindered the release of dyes from the pores of Zr-MOF_mix, thus reducing the fluorescence signals intensity. The stimuli-responsive DNA-gated material provides a platform for PAT analysis under conditions of a low limit of detection (0.871 pg/mL). Furthermore, the excellent specificity and anti-interference of the fluorescent aptasensor make the system suitable for the analysis of apple juice samples. This label-free strategy is cheaper and simper compared with labeled detection, especially for the development of multi-target-detection.

Dual-template molecularly imprinted electrochemical biosensor for IgG-IgM combined assay based on a dual-signal strategy

Detection of immunoglobulins (Igs) is of clinical significance for early diagnosis and timely treatment of diseases. Herein, a dual-template molecularly imprinted (DTMI) electrochemical biosensor was developed for IgG-IgM combined assay. In this DTMI electrochemical biosensor, Prussian blue (PB) and thionine (TH) decorated on graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs), respectively, were utilized as the dual-signal probes, and Au nanoparticles (AuNPs) were used for Igs anchoring and signal amplification. Polypyrrole (PPy) was electrodeposited on the biosensor surface and acted as the molecularly imprinted polymers (MIPs). After the removal of the IgG and IgM templates, the resultant DTMI electrochemical biosensor was used for IgG-IgM combined assay, and the concentrations of IgG and IgM could be indicated by the changes in the peak currents of PB (ΔI_PB) and TH (ΔI_TH), respectively. The DTMI electrochemical biosensor displayed a wide linear range and a low limit of detection (LOD) for both IgG (28.80 pg mL^-1) and IgM (0.58 pg mL^-1). Finally, the developed DTMI biosensor was used for IgG-IgM combined assay in clinical serum samples, and the results were comparable to those obtained by conventional immunoturbidimetry, implying its great potential in clinical diagnosis.

Progress and challenges in sensing of mycotoxins using molecularly imprinted polymers

Mycotoxin is toxic secondary metabolite formed by certain filamentous fungi. This toxic compound can enter the food chain through contamination of food (e.g., by colonization of toxigenic fungi on food). In light of the growing concerns on the health hazards posed by mycotoxins, it is desirable to develop reliable analytical tools for their detection in food products in both sensitive and efficient manner. For this purpose, the potential utility of molecularly imprinted polymers (MIPs) has been explored due to their meritful properties (e.g., large number of tailor-made binding sites, sensitive template molecules, high recognition specificity, and structure predictability). This review addresses the recent advances in the application of MIPs toward the sensing of various mycotoxins (e.g., aflatoxins and patulin) along with their fabrication strategies. Then, performance evaluation is made for various types of MIP- and non-MIP-based sensing platforms built for the listed target mycotoxins in terms of quality assurance such as limit of detection (LOD). Further, the present challenges in the MIP-based sensing application of mycotoxins are discussed along with the future outlook in this research field.

Fullerenol Quantum Dots-Based Highly Sensitive Fluorescence Aptasensor for Patulin in Apple Juice

A highly selective and sensitive aptasensor for detecting patulin (PAT) was constructed based on the fluorescence quenching of fullerenol quantum dots (FOQDs) towards carboxytetramethylrhodamine (TAMRA) through PET mechanism. The π-π stacking interaction between PAT aptamer and FOQDs closed the distance between TAMRA and FOQDs and the fluorescence of TAMRA was quenched with maximum quenching efficiency reaching 85%. There was no non-specific fluorescence quenching caused by FOQDs. In the presence of PAT, the PAT aptamer was inclined to bind with PAT and its conformation was changed. Resulting in the weak π-π stacking interaction between PAT aptamer and FOQDs. Therefore, the fluorescence of TAMRA recovered and was linearly correlated to the concentration of PAT in the range of 0.02-1 ng/mL with a detection limit of 0.01 ng/mL. This PAT aptasensor also performed well in apple juice with linear dynamic range from 0.05-1 ng/mL. The homogeneous fluorescence aptasensor shows broad application prospect in the detection of various food pollutants.

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.

Mycotoxins detection: view in the lens of molecularly imprinted polymer and nanoparticles

Molecularly imprinted polymers (MIPs) are tailor-made functional composites which selectively recognize and bind the target molecule of interest. MIP composites are products of the massively cross-linked polymer matrices, generated via polymerization, with bio-inspired recognition cavities that are morphologically similar in size, shape and spatial patterns to the target conformation. These features have enabled researchers to expand the field of molecular recognition, more specifically for target with peculiar requirements. Nevertheless, MIPs alone are characterized with weak sensitivity. Besides, nanoparticles (NPs) are remarkably sensitive but also suffer from poor selectivity. Intriguingly, the combination of the two results in a highly sensitive and selective MIP composite. For instance, the conjugation of different functional NPs with MIPs can generate new flexible target capture tools, either a dynamic sensor or a novel drug delivery system. In this regard, although the technology is considered an established and feasible approach, it is still perceived as a burgeoning technology for various fields, which makes it unceasingly worthy reviewing. Therefore, in this review, we attempt to give an update on various custom-made biosensors based on MIPs in combination with various NPs for the detection of mycotoxins, the toxic secondary metabolites of fungi. We first summarize the classification, prevalence, and toxicological characteristics of common mycotoxins. Next, we provide an overview of MIP composites and their characterization, and then segment the role of NPs with respect to common types of MIP-based sensors. At last, conclusions and outlook are discussed.

A novel ratiometric electrochemical sensor based on dual-monomer molecularly imprinted polymer and Pt/Co3O4 for sensitive detection of chlorpromazine hydrochloride

In this work, a novel signal on/off ratiometric electrochemical sensor for the selective detection of chlorpromazine (CPZ) was developed. The sensor was constructed by electrodepositing dual-monomer molecularly imprinted polymer (DMMIP) film on the surface of Pt/Co₃O₄ nanoparticles modified glassy carbon electrode, using CPZ as template molecule, methylene blue and catechol as functional monomers. The copolymerization of two monomers increased the diversity of functional groups for binding template molecules, and enhanced stability. The quantitative detection of CPZ was performed by differential pulse voltammetry, using the peak current of poly (methylene blue) as reference signal and the peak current of CPZ as indicating signal. The results showed that the developed DMMIP sensor not only possessed high selectivity and sensitivity, but also exhibited satisfactory anti-interference ability. Under the optimum conditions, a linear detection range of 0.005-9 μmol L^-1 (R² = 0.9962) was obtained, and the limit of detection was 2.6 nmol L^-1. Moreover, the sensor showed good reproducibility and stability toward CPZ detection. It was applied to detect CPZ in serum and pharmaceutical samples, and satisfactory recoveries (ranging from 95.3% to 108.0%) were achieved.

Low-Cost and Convenient Microchannel Resistance Biosensing Platform by Directly Translating Biorecognition into a Current Signal

We report a low-cost and convenient microchannel resistance (MCR) biosensing platform that uses current signal to report biorecognition. The biorecognition behavior between targets and biometric molecules (antigens, antibodies, or oligonucleotides) immobilized on magnetic beads and polystyrene (PS) microspheres induces a quantitative change in the unreacted PS microspheres. After magnetic separation, the unreacted PS microsphere solution is passed through the microchannel, leading to an obvious blocking effect, resulting in an increase in resistance, which can in turn be measured by monitoring the electric current. Thus, the biorecognition is directly converted into a detectable current signal without any bulky instruments or additional chemical reactions. The MCR biosensing platform is cost-effective and user-friendly with high accuracy. It can be an appropriate analysis technique for point-of-care testing in resource-poor settings.

RuCu Cage/Alloy Nanoparticles with Controllable Electroactivity for Specific Electroanalysis Applications

Electrochemical nanotags with controllable and multiresponse electroactivity have a great capacity for overcoming the drawbacks of limited target monitoring and inaccurate detection results for electrochemical sensors. In this contribution, double electro-oxidative Ru and Cu metals were integrated into RuCu nanostructures for the generation of dual electro-oxidative signals. A facial approach was proposed for the controllable fabrication of RuCu cage nanoparticles (NPs) and RuCu alloy NPs by simply adjusting the pH value of the reaction system. RuCu cage NPs and RuCu alloy NPs demonstrated inherent different electro-oxidative responses owing to the remarkable distinction of structures with different metal valences. RuCu cage NPs showed a single electro-oxidization peak at 0.84 V, assigned to the exposure of more Ru⁰ electroactive sites on the hollow cage structures. RuCu alloy NPs illustrated dual electro-oxidization peak at 0.84 and -0.16 V, attributing to the presence of Ru⁰ and Cu⁺ electroactive sites on the alloy structures, respectively. RuCu cage NPs and RuCu alloy NPs served as specific electroactive tags, achieving the selective monitoring of Na₂S and ratiometric electrochemical detection of xanthine in monosodium glutamate, respectively. The limits of detection were as low as 27 pM for Na₂S and 70 nM for xanthine. The rational design of multimetal nanostructures holds enormous potential for the generation of multiresponse electroactivity with the impetus for exploring the capacity of specific electrochemical sensing.

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.

A novel ratiometric electrochemical sensor for the selective detection of citrinin based on molecularly imprinted poly(thionine) on ionic liquid decorated boron and nitrogen co-doped hierarchical porous carbon

Citrinin can cause serious human diseases, thus its detection in foods is necessary. Herein, a molecularly imprinted polymer-based ratiometric electrochemical sensor (MIP-RECS) was presented for citrinin detection. The sensor was fabricated by electropolymerization, using thionine as monomer and citrinin as template. The ionic liquid decorated boron and nitrogen co-doped hierarchical porous carbon (BN-HPC) as supporter, provided large surface for anchoring thionine and citrinin. Poly(thionine) not only acted as MIP, but also acted as reference probe. When [Fe(CN)₆] ^3-/4- was adopted as indicating probe, the resulting sensor demonstrated a wide linear detection range (i.e. 1 × 10^-3-10 ng mL^-1) and a low detection limit (i.e. 1 × 10^-4 ng mL^-1).The sensor was applied to the detection of spiked citrinin in real samples, and satisfactory recovery (i.e. 97% - 110%) was obtained. Hence, it was promising for citrinin detection.

Polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical sensors and biosensors: a review

In recent years, an increasing number of studies has demonstrated that redox polymers can be used in simple and effective electrochemical sensing platforms due to their fast electron transfer and electrocatalytic ability. To develop more sensitive and selective electrochemical (bio)sensors, the electrocatalytic properties of redox polymers and the electrical, mechanical, and catalytic properties of various nanomaterials are combined. This review aims to summarize and contribute to the development of (bio)sensors based on polyphenazine or polytriphenylmethane redox polymers combined with nanomaterials, including carbon-based nanomaterials, metal/metal oxide, and semiconductor nanoparticles. The synthesis, preparation, and modification of these nanocomposites is presented and the contribution of each material to the performance of (bio)sensor has been be examined. It is explained how the combined use of these redox polymers and nanomaterials as a sensing platform leads to improved analytical performance of the (bio)sensors. Finally, the analytical performance characteristics and practical applications of polyphenazine and polytriphenylmethane redox polymer/nanomaterial-based electrochemical (bio)sensors are compared and discussed.

Determination of patulin using dual-dummy templates imprinted electrochemical sensor with PtPd decorated N-doped porous carbon for amplification

A novel dual-dummy templates imprinted electrochemical sensor has been fabricated for the detection of patulin. Herein, 2-oxindole (2-oxin) and 6-hydroxynicotinic acid (6-HNA) as the dummy templates, 4-aminothiophenol as functional monomer, and ionic liquid (IL) as electropolymerization electrolyte are employed to prepare molecularly imprinted polymer (MIP) film. 2-Oxin and 6-HNA have multiple groups and the obtained MIP possesses different types of imprinted sites, thereby achieving a better recognition capacity than that of single-dummy imprinted film. ILs can regulate the density of molecularly imprinted film and facilitate effective molecular recognition. The composite of PtPd decorated N-doped porous carbon has good conductivity and large surface area, and can amplify the signal. With the aid of electrochemical probe [Fe(CN)₆]^3-/4- (0.16 V vs. SCE) patulin can be detected. Under the optimal conditions, this sensor shows a detection range from 0.01 to 10 μg L^-1, with a detection limit of 7.5 × 10^-3 μg L^-1 (S/N = 3). Two spiked juice samples were analyzed by this method, and the recovery ranges from 94 to 99.8% with RSD values of 2.4-4.6% (n = 3), indicating that this method can be applied for the detection of patulin in real samples. A novel dual-dummy templates imprinted electrochemical sensor is firstly fabricated for the detection of patulin. This sensor exhibits high recognition capacity and sensitivity.

A flexible assay strategy for non-glucose targets based on sulfhydryl-terminated liposomes combined with personal glucometer

The personal glucose meter (PGM) is one of the most successful point-of-care (POC) testing devices. It is simple, robust and inexpensive, but cannot be easily adapted to analytes other than glucose. We report a novel chemical conjugation-based assay strategy, using rational design of chemically-derivatized glucose-encapsulating liposomes, to repurpose a PGM, taking an important mycotoxin patulin as the model analyte. Sulfhydryl (-SH) was proposed for the first time as a specific functional group for efficient recognition of patulin. Multifunctional sulfhydryl-terminated glucose-encapsulating liposomes (G-LIP-SH) were synthesized in a simple, single step, which efficiently captured patulin by covalent bonding, and interacted strongly with NH₂-Au@Fe₃O₄ nanoparticles. Magnetic removal of nanoparticles efficiently and selectively separated patulin-derivatized from un-derivatized G-LIP-SH, permitting the latter to be lysed and the released glucose measured by PGM. The PGM signal was inversely proportional to the patulin concentration, over the range of 0.1-50 ng mL^-1 (R² = 0.995) with a detection limit of 0.05 ng mL^-1 (S/N = 3). This approach overcame interference from endogenous glucose, other mycotoxins and metal ions, allowing the analysis of a wide range of sample matrices and showed high specificity, acceptable reproducibility, good accuracy and optimal applicability. Other derivatization chemistries will enable this approach to be adapted to analytes with a wide range of chemical structures, to facilitate development of rapid, portable, user-friendly and cost-effective assays applicable to diverse analytes and sample matrices.

Patulin and Trichothecene: characteristics, occurrence, toxic effects and detection capabilities via clinical, analytical and nanostructured electrochemical sensing/biosensing assays in foodstuffs

Patulin and Trichothecene as the main groups of mycotoxins in significant quantities can cause health risks from allergic reactions to death on both humans and animals. Accordingly, rapid and highly sensitive determination of these toxics agents is of great importance. This review starts with a comprehensive outlook regarding the characteristics, occurrence and toxic effects of Patulin and Trichothecene. In the following, numerous clinical and analytical approaches have been extensively discussed. The main emphasis of this review is placed on the utilization of novel nanomaterial based electrochemical sensing/biosensing tools for highly sensitive determination of Patulin and Trichothecene. Furthermore, a detailed and comprehensive comparison has been performed between clinical, analytical and sensing methods. Subsequently, the nanomaterial based electrochemical sensing platforms have been approved as reliable tools for on-site analysis of Patulin and Trichothecene in food processing and manufacturing industries. Different nanomaterials in improving the performance of detecting assays were investigated and have various benefits toward clinical and analytical methods. This paper would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

Recent trends in detecting, controlling, and detoxifying of patulin mycotoxin using biotechnology methods

Patulin (PAT) is a mycotoxin that can contaminate many foods and especially fruits and fruit-based products. Therefore, accurate and effective testing is necessary to enable producers to comply with regulations and promote food safety. Traditional approaches involving the use of chemical compounds or physical treatments in food have provided practical methods that have been used to date. However, growing concerns about environmental and health problems associated with these approaches call for new alternatives. In contrast, recent advances in biotechnology have revolutionized the understanding of living organisms and brought more effective biological tools. This review, therefore, focuses on the study of biotechnology approaches for the detection, control, and mitigation of PAT in food. Future aspects of biotechnology development to overcome the food safety problem posed by PAT were also examined. We find that biotechnology advances offer novel, more effective, and environmental friendly approaches for the control and elimination of PAT in food compared to traditional methods. Biosensors represent the future of PAT detection and use biological tools such as aptamer, enzyme, and antibody. PAT prevention strategies include microbial biocontrol, the use of antifungal biomolecules, and the use of microorganisms in combination with antifungal molecules. PAT detoxification aims at the breakdown and removal of PAT in food by using enzymes, microorganisms, and various adsorbent biopolymers. Finally, biotechnology advances will be dependent on the understanding of fundamental biology of living organisms regarding PAT synthesis and resistance mechanisms.

Electrochemical assay of ampicillin using Fe3N-Co2N nanoarray coated with molecularly imprinted polymer

Self-supported Fe₃N-Co₂N nanoarray with high electric conductivity and large surface area was prepared for growth of MIPs and further constructing a sensitive and stable electrochemical sensor. For the evaluation of its performance, Fe₃N-Co₂N is used as sensing electrode material, and AMP is used as template molecule to construct the MIP electrochemical sensor. Under the optimized conditions, the developed MIPs electrochemical sensor detects AMP with a low detection limit of 3.65 × 10^-10 mol L^-1 and shows outstanding reproducibility and stability. When the MIPs electrochemical sensor was applied to detect AMP in milk samples via standard addition method, the recovery within 97.06-102.43% with RSD of 1.05-2.11% was obtained. The fabrication of MIPs electrochemical sensor is highly promising for sensitive and selective electrochemical measurement and food safety testing. This work can provide theoretical guidance for truly challenging problems. Graphical abstract Principle diagram of MIP-EC sensor for detecting AMP Molecular imprinted polymers (MIPs) are widely performed for construction of electrochemical (EC) sensors especially for detecting small molecules in complex environment. However, the large-scale and robust preparation of MIPs in situ on sensor platform limits their practical applications. We fabricated a MIPs EC sensor based on Fe₃N-Co₂N in situ grown on carbon cloth (CC) as the substrate platform (Fe₃N-Co₂N/CC) combining with MIPs as the target recognition element for the label-free detection of AMP. Under the optimal conditions, the developed MIPs EC sensor can detect AMP with a low detection limit of 3.65 × 10^-10 mol L^-1. When the AMP in milk is detected by the proposed EC sensor, it shows ideal results. Therefore, the use of self-supported Fe₃N-Co₂N nanoarray as the platform for the fabrication of MIPs EC sensors is highly promising for sensitive and selective EC measurement and point-of-care testing.

Ionic liquid assisted molecular self-assemble and molecular imprinting on gold nanoparticles decorated boron-doped ordered mesoporous carbon for the detection of zearalenone

Accurate and early diagnosis of zearalenone (ZEN) is particularly significant to the food safety. Herein, we propose an ionic liquid assisted self-assembly molecular imprinting strategy for ZEN based on ionic liquid functionalized boron-doped ordered mesoporous carbon -gold nanoparticles composite (BOMC-IL-Au NPs). During the composite synthesis, increased well-dispersed and uniform Au NPs are deposited on the surface of IL modified BOMC, due to the strong electrostatic interaction between AuCl₄^- and positively charged IL. For molecular imprinting, the BOMC-IL-Au NPs/GCE is immersed into p-aminothiophenol (p-ATP) solution and template solution in turn. Thus, the mercapto group contained p-ATP self-assembles on the Au NPs. Subsequently, the template molecules self-assemble onto the composite to form dense template layer, because of the hydrophobic interaction, π-π and hydrogen bond between template and IL/or p-ATP. After electropolymerization, the template layer is embedded into the p-ATP polymer membrane and produces lots of imprinting sites. Hence, the obtained sensor exhibits high sensitivity and selectivity. Under the optimal conditions, zearalenone can be quantified from 5 × 10^-4 to 1 ng mL^-1 with the low detection limit of 1 × 10^-4 ng mL^-1, by using [Fe(CN)₆]^3-/4- probe and square wave voltammetry. This strategy can also be employed to construct sensors for the detection of other substances.