High Affinity Aptamer for the Detection of the Biogenic Amine Histamine

Recognition and detection of histamine in foods using aptamer modified fluorescence polymer dots sensors

Histamine has been known as a momentous cause of biogenic amine poisoning. Therefore, the content of histamine in foods is strictly required to be controlled within a certain range. Here, an aptamer fluorescent sensor was developed for detection of histamine. Poly [(9, 9-di-n-octylfluorenyl-2, 7-diyl)-alt-(benzo [2,1,3] thiadia-zol-4, 8-diyl)] (PF8BT) and the styrene maleic anhydride copolymer (PSMA) were used for the preparation of PF8BT-Polymer dots (PF8BT-Pdots). PF8BT-Pdots and the cyanine3-phosphoramidite (Cy3) were linked through aptamer to achieve the ratiometric detection for histamine. PF8BT-Pdots were partly quenched by Cy3 due to the fluorescence resonance energy transfer (FRET), when the histamine molecule was recognized by aptamer on the surface of PF8BT-Pdots. A linear range (3-21 μmol/L) was obtained for histamine detection with a low limit of detection (LOD = 0.38 μmol/L). PF8BT aptamer Pdots (PF8BT-A) were used to detect histamine in simply treated aquaculture water and tuna. The cell imaging of HeLa cells presented a good biosecurity and outstanding fluorescent imaging capability of PF8BT-A. The aptamer fluorescent sensors provided a new platform for rapid and accurate detection of histamine in aquatic products and had great potential for the application in food safety and quality control.

Peptide-Based Recognition Agents of Histamine: A Biopanning Approach with Enhanced Specificity

Histamine is a biogenic amine that poses a potential threat to public health due to its toxicological effects. In this study, we identified histamine-binding peptides by screening a random 12-mer peptide library, employing a novel biopanning approach that excluded histidine-binding sequences in the final round. This additional step enhanced the selectivity of the peptides and prevented interference from histidine during detection. The binding affinities of synthesized peptides to histamine were assessed using isothermal titration calorimetry (ITC). Among the identified peptides, HBF10 (SGFRDGIEDFLW) and HBF26 (IPLENQHKIYST) showed significant affinity to histamine, with Ka values of 2.56×104 (M-1) and 8.94×104 (M-1), respectively. Notably, the identified peptides did not demonstrate binding affinity towards histidine, despite its structural similarity to histamine. Subsequently, the surface plasmon resonance (SPR) sensor surface was prepared by immobilizing the peptide HBF26 to investigate the potential of the peptide as a recognition agent for histamine detection. The findings suggest that the identified peptides have an affinity to histamine specifically, showcasing their potential applications as diagnostic agents with specific targeting capabilities.

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.

Structural Antagonism-Aided Conformational Regulation Enables an Aptamer-Loop G-Quadruplex Modular Sensor of β-Lactoglobulin

A simple, reliable method for identifying β-lactoglobulin (β-LG) in dairy products is needed to protect those with β-LG allergies. A common, practical strategy for target detection is designing simplified nucleic acid nanodevices by integrating functional components. This work presents a label-free modular β-LG aptasensor consisting of an aptamer-loop G-quadruplex (G4), the working conformation of which is regulated by conformational antagonism to ensure respective module functionality and the related signal transduction. The polymorphic conformations of the module-fused sequence are systematically characterized, and the cause is revealed as shifting antagonistic equilibrium. Combined with conformational folding dynamics, this helped regulate functional conformations by fine-tuning the sequences. Furthermore, the principle of specific β-LG detection by parallel G4 topology is examined as binding on the G4 aptamer loop by β-LG to reinforce the G4 topology and fluorescence. Finally, a label-free, assembly-free, succinct, and turn-on fluorescent aptasensor is established, achieving excellent sensitivity across five orders of magnitude, rapidly detecting β-LG within 22-min. This study provides a generalizable approach for the conformational regulation of module-fused G4 sequences and a reference model for creating simplified sensing devices for a variety of targets.

Highly selective and sensitive histamine and tryptamine analysis using SiO2@AuNPs@PDA molecularly imprinted polymer coupled with SALDI-TOF MS

A combination of SiO2@AuNPs@PDA molecularly imprinted and surface-assisted laser desorption/ionization-time-of-flight mass spectrometry (SALDI-TOF MS) was devised as a method for highly specific and ultrasensitive detection of two biogenic amines-histamine (HIS) and tryptamine (TRP)-in real samples. In this strategy, AuNPs modified amino-abundant silica nanospheres (SiO2@AuNPs). The prepared SiO2@AuNPs were used as a substrate to synthesize a molecularly imprinted polymer (MIP) through in situ dopamine self-polymerization with HIS and TRP as the template molecules (SiO2@AuNP@PDA-MIP). The as-prepared MIP structure, properties, and target-analyte identification conditions were characterized and optimized and it was used as the matrix for MS. Compared to the case of nonimprinted materials, the imprinting function endowed the matrix with a higher selectivity for capturing the target molecules. The enriched analytes were directly and rapidly identified using SALDI-TOF MS without elution. Meanwhile, the proposed method has low background interference, good reproducibility and stability, high salt tolerance, and satisfactory linearity (R2 > 0.99), and it enables ultrasensitive detection of HIS and TRP (limits of detection for HIS and TRP were 0.2 and 0.1 ng mL-1, respectively). Moreover, the proposed method was applied to analyze samples of real beer, sausage, and chicken, and the results agreed with those obtained via liquid chromatography-MS, suggesting that the method has excellent practical applications in the field of food safety.

Photoluminescence-Electrochemiluminescence Dual-Mode Sensor Arrays for Histidine and Its Metabolite Discrimination and Disease Identification

Histidine (His) and its metabolite analysis is significant due to their vital roles in the diagnosis of diseases. In practical applications, simple and effective detection and discrimination of these metabolic species are still a great challenge due to their highly similar structures. Herein, photoluminescence (PL)-electrochemiluminescence (ECL) dual-mode sensor arrays consisting of a series of sensing elements were proposed for simultaneous quantitation and accurate discrimination of His and its four key metabolites (including histamine, imidazole-4-acetic acid, N-acetylhistamine, and imidazole propionate). The sensing elements of these sensor arrays were constructed by employing two solvent iridium(III) complexes ([Ir(pbz)2(DMSO)Cl] and [Ir(ppy)2(DMSO)Cl], pbz = 3-(2-pyridyl)benzoic acid, ppy = 2-phenylpyridine) with excellent PL and ECL performances as cross-responsive sensing units. Based on diverse coordination abilities of the two complexes with the imidazole group of the five targets, PL and ECL responses of each sensing unit can be enhanced to various degrees, which generate unique fingerprint patterns for the corresponding targets. Through principal component analysis, the multifarious patterns (two-, three-, and four-element sensor arrays) can be transformed into simple visualization modes, from which His and its four key metabolites can be effectively discriminated against each other. Moreover, the quantitation of an individual metabolic species at different concentrations and the recognition of the mixtures with different ratios were also accurately achieved. Notably, His and its four key metabolites in urine can also be successfully discriminated by the as-fabricated sensor arrays, and the patients with kidney diseases can be identified clearly, providing a promising way for disease diagnosis.

Material Breakthroughs in Smart Food Monitoring: Intelligent Packaging and On-Site Testing Technologies for Spoilage and Contamination Detection

Despite extensive commercial and regulatory interventions, food spoilage and contamination continue to impose massive ramifications on human health and the global economy. Recognizing that such issues will be significantly eliminated by the accurate and timely monitoring of food quality markers, smart food sensors have garnered significant interest as platforms for both real-time, in-package food monitoring and on-site commercial testing. In both cases, the sensitivity, stability, and efficiency of the developed sensors are largely informed by underlying material design, driving focus toward the creation of advanced materials optimized for such applications. Herein, a comprehensive review of emerging intelligent materials and sensors developed in this space is provided, through the lens of three key food quality markers - biogenic amines, pH, and pathogenic microbes. Each sensing platform is presented with targeted consideration toward the contributions of the underlying metallic or polymeric substrate to the sensing mechanism and detection performance. Further, the real-world applicability of presented works is considered with respect to their capabilities, regulatory adherence, and commercial potential. Finally, a situational assessment of the current state of intelligent food monitoring technologies is provided, discussing material-centric strategies to address their existing limitations, regulatory concerns, and commercial considerations.

Silver metallization-triggered liposome-embedded AIE fluorophore for dual-mode detection of biogenic amines to fight food freshness fraud

To combat food freshness fraud, it is urgent to develop a method which could realize the detection of biogenic amines (BAs) present in food. In our study, we developed a colorimetric and ratiometric fluorescence dual-mode sensor which integrated with silver metallization-based response system of AIE liposome + OPD + RSM + Ag+ toward BAs in foods for fighting freshness fraud. With the hydrolysis from the alkaline of BAs to resorcinol monoacetate (RSM), the production resorcinol (RS) could metallize silver ion (Ag+) to silver atoms (Ag0) which could lead to a BAs concentration-dependent decrease of the oxidation product 2,3-diaminophenothiazine (DAP) of Ag+ to o-phenylenediamine (OPD). As a result, the dual-mode sensor has a low detection limit and wide linear range in the spiked detection of soy products, pork and milk samples for BAs. Thus, providing a reliable method for food safety and forestalling food freshness fraud.

Encoded Structural Color Microneedle Patches for Multiple Screening of Wound Small Molecules

Detection of biomarkers associated with wound conditions provides in-depth healthcare information and benefits wound healing treatment. The current aim of wound detection is to achieve in situ multiple detections. Novel encoded structural color microneedle patches (EMNs) combining photonic crystals (PhCs) and microneedle arrays (MNs) for multiple wound biomarker detection in situ are described here. Using a partitioned and layered casting strategy, the EMNs can be divided into different modules and each serves for the detection of small molecules , including pH, glucose, and histamine. pH sensing is based on the interaction between hydrogen ions and carboxyl groups from hydrolyzed polyacrylamide (PAM); glucose sensing is achieved with the help of glucose-responsive fluorophenylboronic acid (FPBA); while histamine sensing relies on specific recognition of aptamers and target molecules. Owing to the responsive volume change of these three modules in the presence of target molecules, the EMNs can create structural color change and characteristic peak shift of the PhCs, thus realizing the qualitative measurement of target molecules with a spectrum analyzer. It is further demonstrated that the EMNs behave well in the multivariate detection of rat wound molecules. These features indicate that the EMNs can be valuable smart detection systems for wound status screening.

Concentration-Guided Visual Detection of Multiphase Aliphatic Biogenic Amines through Amine-Phenol Recognition Using a Dual-State Emitter

Intermolecular amine-phenol interactions are largely recognized as unique models with diverse supramolecular interactions. However, fluorescence (FL) variations originating from such interactions are rare. Herein, FL changes are well realized from amine-phenol interactions to identify an important biomarker, biogenic amines (BAs). A simple, inexpensive, and thermally stable anthracenylphosphonate is linked with 2,2'-biphenol to design a functional dual-state emitter. Among the various amines tested, this emitter displays superior sensitivity with the lowest possible limit of detection as 5.8-9.7 ppb with aliphatic polyamines such as 1,3-, 1,4-, 1,5-, and 1,6- diamines and spermidine in the solution phase. Fast, on-spot detection of the BA vapors was visually conducted through a notable high-contrast change from blue to yellow emission in the solid state. FT-IR, ¹H/³¹P NMR, and mass spectroscopic studies identify the ground-state amine-phenol interactions. The failure in BA detection with the 2,2'-dimethoxy-biphenyl-linked analog verifies the role of amine-phenol interactions. Mechanistic studies determine amine-phenol interactions in the ground and excited states. The molecular structure and packing of the doubly twisted probe are documented with a substantial void space facilitating close contact of the BAs with the strong amine-phenol interactions desired for efficient detection. Finally, this probe governs the freshness of a piece of Catla catla fish and prawn. Further, a remarkable concentration-controlled diverse emission with a red shift difference of 141 nm is detected with 1,3-diaminopropane (1,3-DAP) vapor (from 29 to 319 mg/L) for the first time. Thus, a cost-effective device is developed to detect 1,3-DAP at a precise concentration, visible through the naked eye.

Selection of G-rich ssDNA aptamers for the detection of enterotoxins of the cholera toxin family

Cholera and milder diarrheal disease are caused by Vibrio cholerae and enterotoxigenic Escherichia coli and are still a prominent public health concern. Evaluation of suspicious isolates is essential for the rapid containment of acute diarrhea outbreaks or prevention of epidemic cholera. Existing detection techniques require expensive equipment, trained personnel and are time-consuming. Antibody-based methods are also available, but cost and stability issues can limit their applications for point-of-care testing. This study focused on the selection of single stranded DNA aptamers as simpler, more stable and more cost-effective alternatives to antibodies for the co-detection of AB₅ toxins secreted by enterobacteria causing acute diarrheal infections. Cholera toxin and Escherichia coli heat-labile enterotoxin, the key toxigenicity biomarkers of these bacteria, were immobilized on magnetic beads and were used in a SELEX-based selection strategy. This led to the enrichment of sequences with a high % GC content and a dominant G-rich motif as revealed by Next Generation Sequencing. Enriched sequences were confirmed to fold into G-quadruplex structures and the binding of one of the most abundant candidates to the two enterotoxins was confirmed. Ongoing work is focused on the development of monitoring tools for potential environmental surveillance of epidemic choleraand milder diarrheal disease.

Investigation of Charged Small Molecule-Aptamer Interactions with Surface Plasmon Resonance

Investigating the interactions between small, charged molecules and aptamers using surface plasmon resonance (SPR) is limited by the inherent low response of small molecules and difficulties with nonspecific electrostatic interactions between the aptamer, analyte, and sensor surface. However, aptamers are increasingly being used in sensors for small molecule detection in critical areas like healthcare and environmental safety. The ability to probe these interactions through simple, direct SPR assays would be greatly beneficial and allow for the development of improved sensors without the need for complicated signal enhancement. However, these assays are nearly nonexistent in the current literature and are instead surpassed by sandwich or competitive binding techniques, which require additional sample preparation and reagents. In this work, we develop a method to characterize the interaction between the charged small molecule serotonin (176 Da) and an aptamer with SPR using streptavidin-biotin capture and a high-ionic-strength buffer. Additionally, other methods, such as serotonin immobilization and thiol-coupling of the aptamer, were investigated for comparison. These techniques give insight into working with small molecules and allow for quickly adapting a binding affinity assay into a direct SPR sensor.

A Review on Bio- and Chemosensors for the Detection of Biogenic Amines in Food Safety Applications: The Status in 2022

This article provides an overview on the broad topic of biogenic amines (BAs) that are a persistent concern in the context of food quality and safety. They emerge mainly from the decomposition of amino acids in protein-rich food due to enzymes excreted by pathogenic bacteria that infect food under inappropriate storage conditions. While there are food authority regulations on the maximum allowed amounts of, e.g., histamine in fish, sensitive individuals can still suffer from medical conditions triggered by biogenic amines, and mass outbreaks of scombroid poisoning are reported regularly. We review first the classical techniques used for selective BA detection and quantification in analytical laboratories and focus then on sensor-based solutions aiming at on-site BA detection throughout the food chain. There are receptor-free chemosensors for BA detection and a vastly growing range of bio- and biomimetic sensors that employ receptors to enable selective molecular recognition. Regarding the receptors, we address enzymes, antibodies, molecularly imprinted polymers (MIPs), and aptamers as the most recent class of BA receptors. Furthermore, we address the underlying transducer technologies, including optical, electrochemical, mass-sensitive, and thermal-based sensing principles. The review concludes with an assessment on the persistent limitations of BA sensors, a technological forecast, and thoughts on short-term solutions.

Boronate Affinity-Amplified Electrochemical Aptasensing of Lipopolysaccharide

As lipopolysaccharide (LPS) is closely associated with sepsis and other life-threatening conditions, the point-of-care (POC) detection of LPS is of significant importance to human health. In this work, we illustrate an electrochemical aptasensor for the POC detection of low-abundance LPS by utilizing boronate affinity (BA) as a simple, efficient, and cost-effective amplification strategy. Briefly, the BA-amplified electrochemical aptasensing of LPS involves the tethering of the aptamer receptors and the BA-mediated direct decoration of LPS with redox signal tags. As the polysaccharide chain of LPS contains hundreds of cis-diol sites, the covalent crosslinking between the phenylboronic acid group and cis-diol sites can be harnessed for the site-specific decoration of each LPS with hundreds of redox signal tags, thereby enabling amplified detection. As it involves only a single-step operation (∼15 min), the BA-mediated signal amplification holds the significant advantages of unrivaled simplicity, rapidness, and cost-effectiveness over the conventional nanomaterial- and enzyme-based strategies. The BA-amplified electrochemical aptasensor has been successfully applied to specifically detect LPS within 45 min, with a detection limit of 0.34 pg/mL. Moreover, the clinical utility has been validated based on LPS detection in complex serum samples. As a proof of concept, a portable device has been developed to showcase the potential applicability of the BA-amplified electrochemical LPS aptasensor in the POC testing. In view of its simplicity, rapidness, and cost-effectiveness, the BA-amplified electrochemical LPS aptasensor holds broad application prospects in the POC testing.

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

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

Three-Dimensional Printed Microdevice to Enhance Headspace Microextraction for Enrichment of Histamine in Milk

In this work, a three-dimensional (3D) printed microdevice was designed to fix a drop of extractant that was applied to the enrichment of the most toxic biogenic amine, histamine, by headspace single-drop microextraction (HS-SDME). Concomitantly, based on the hybridization chain reaction of the histamine aptamer isothermal nucleic acid amplification strategy, a new fluorescence sensing method was developed to realize the highly sensitive detection of histamine. This is the first application of a 3D-printed microdevice to realize the HS-SDME process, which, among other advantages, effectively solves the problem of unstable and variable drop volumes that can plague traditional SDME and ensures the accuracy and repeatability of the extraction process. The calibration linear range of this SDME-fluorescence method was from 10 pM to 5 μM (R² > 0.98), and the limit of detection was as low as 3 pM. In addition, the method was successfully demonstrated to determine histamine spiked in milk, with recoveries of between 93% and 104%, and relative standard deviations of less than 5%. The method established in this study has important practical significance for food safety monitoring and human health and provides new ideas and solutions for the design and application of biosensors.

Colorimetric visualization of histamine secreted by basophils based on DSP-functionalized gold nanoparticles

Histamine released by activated basophils has become an important biomarker and therapeutic target in the development of allergic diseases. To date, several gold nanoparticle (AuNP)-based nanosensors have been reported for histamine detection in foods. However, rapid, highly sensitive and direct detection of histamine in allergic diseases is still lacking due to the complexity of the physical environment. Herein, we developed a novel nanosensor for colorimetric visualization of histamine in activated basophils by simply coupling dithiobis(succinimidylpropionate) (DSP) on the surface of AuNPs (DSP-AuNPs). The DSP moiety serves as a linker and can react with the aliphatic amino group of histamine, and the imidazole ring of histamine can selectively bind with Au by means of p-p conjugation, thus inducing the aggregation of AuNPs. In this study, we experimentally proved that DSP-AuNPs showed good sensitivity and selectivity to histamine among various amino acids, including histidine. Additionally, this nanosensor displayed a rapid response to histamine with a linear range of 0.8-2.5 μM, and the limit of detection (LOD) was 0.014 μM, which is a relatively low LOD in comparison with those of other AuNP-based nanosensors. Finally, DSP-AuNPs are used, for the first time, to successfully detect endogenous histamine changes in activated basophils. Therefore, our work may provide a promising strategy to monitor histamine levels in the basophil activation test.

Boronate-Affinity Cross-Linking-Based Ratiometric Electrochemical Detection of Glycoconjugates

Despite the widespread application of the boronate-affinity cross-linking (BAC) in the separation, enrichment, and sensing of glycoconjugates, it remains a huge challenge to integrate the BAC into the selective electrochemical detection of glycoconjugates due to the poor selectivity of the BAC. Herein, we demonstrate a BAC-based ratiometric electrochemical method for the simple, low-cost, and highly sensitive and selective detection of glycoconjugates. Briefly, the methylene blue (MB)-tagged nucleic acid aptamer is exploited as the recognition element to selectively capture target glycoconjugate, to which a large number of ferrocene (Fc) tags are subsequently labeled via the BAC between the phenylboronic acid (PBA) group and the cis-diol site of the oligosaccharide chains on the captured targets. Using the MB tag as the internal reference and the Fc tag as the reporter of the target capture, the dual-signal output enables the ratiometric detection. Due to the presence of a high density of the cis-diol sites on a glycoconjugate, sufficiently high sensitivity can be obtained even without using any amplification strategies. Using glycoprotein mucin 1 (MUC1) as the model target, the signal ratio (I_Fc/I_MB) exhibits good linearity over the range from 0.05 to 50 U/mL, with a detection limit of 0.021 U/mL. In addition to the high sensitivity and selectivity, the results of the analysis of MUC1 in serum samples are acceptable. By virtue of its simplicity, cost-effectiveness, and high robustness and reproducibility, this BAC-based ratiometric electrochemical method holds great promise in the highly sensitive and selective detection of glycoconjugates.

Rapid and Wash-Free Time-Gated FRET Histamine Assays Using Antibodies and Aptamers

Histamine (HA) is an indicator of food freshness and quality. However, high concentrations of HA can cause food poisoning. Simple, rapid, sensitive, and specific quantification can enable efficient screening of HA in food and beverages. However, conventional assays are complicated and time-consuming, as they require multiple incubation, washing, and separation steps. Here, we demonstrate that time-gated Förster resonance energy transfer (TG-FRET) between terbium (Tb) complexes and organic dyes can be implemented in both immunosensors and aptasensors for simple HA quantification using a rapid, single-step, mix-and-measure assay format. Both biosensors could quantify HA at concentrations relevant in food poisoning with limits of detection of 0.19 μg/mL and 0.03 μg/mL, respectively. Excellent specificity was documented against the structurally similar food components tryptamine and l-histidine. Direct applicability of the TG-FRET assays was demonstrated by quantifying HA in spiked fish and wine samples with both excellent concentration recovery and agreement with conventional multistep enzyme-linked immunosorbent assays (ELISAs). Our results show that the simplicity and rapidity of TG-FRET assays do not compromise sensitivity, specificity, and reliability, and both immunosensors and aptasensors have a strong potential for their implementation in advanced food safety screening.

Recent Progress of Fluorescence Sensors for Histamine in Foods

Biological amines are organic nitrogen compounds that can be produced by the decomposition of spoiled food. As an important biological amine, histamine has played an important role in food safety. Many methods have been used to detect histamine in foods. Compared with traditional analysis methods, fluorescence sensors as an adaptable detection tool for histamine in foods have the advantages of low cost, convenience, less operation, high sensitivity, and good visibility. In terms of food safety, fluorescence sensors have shown great utilization potential. In this review, we will introduce the applications and development of fluorescence sensors in food safety based on various types of materials. The performance and effectiveness of the fluorescence sensors are discussed in detail regarding their structure, luminescence mechanism, and recognition mechanism. This review may contribute to the exploration of the application of fluorescence sensors in food-related work.

Bacterial Vaginosis Monitoring with Carbon Nanotube Field-Effect Transistors

The ability to rapidly and reliably screen for bacterial vaginosis (BV) during pregnancy is of great significance for maternal health and pregnancy outcomes. In this proof-of-concept study, we demonstrated the potential of carbon nanotube field-effect transistors (NTFET) in the rapid diagnostics of BV with the sensing of BV-related factors such as pH and biogenic amines. The fabricated sensors showed good linearity to pH changes with a linear correlation coefficient of 0.99. The pH sensing performance was stable after more than one month of sensor storage. In addition, the sensor was able to classify BV-related biogenic amine-negative/positive samples with machine learning, utilizing different test strategies and algorithms, including linear discriminant analysis (LDA), support vector machine (SVM), and principal component analysis (PCA). The biogenic amine sample status could be well classified using a soft-margin SVM model with a validation accuracy of 87.5%. The accuracy could be further improved using a gold gate electrode for measurement, with accuracy higher than 90% in both LDA and SVM models. We also explored the sensing mechanisms and found that the change in NTFET off current was crucial for classification. The fabricated sensors successfully detect BV-related factors, demonstrating the competitive advantage of NTFET for point-of-care diagnostics of BV.

Aptamer-modified biosensors to visualize neurotransmitter flux

Chemical biosensors with the capacity to continuously monitor various neurotransmitter dynamics can be powerful tools to understand complex signaling pathways in the brain. However, in vivo detection of neurochemicals is challenging for many reasons such as the rapid release and clearance of neurotransmitters in the extracellular space, or the low target analyte concentrations in a sea of interfering biomolecules. Biosensing platforms with adequate spatiotemporal resolution coupled to specific and selective receptors termed aptamers, demonstrate high potential to tackle such challenges. Herein, we review existing literature in this field. We first discuss nanoparticle-based systems, which have a simple in vitro implementation and easily interpretable results. We then examine methods employing near-infrared detection for deeper tissue imaging, hence easier translation to in vivo implementation. We conclude by reviewing live cell imaging of neurotransmitter release via aptamer-modified platforms. For each of these sensors, we discuss the associated challenges for translation to real-time in vivo neurochemical imaging. Realization of in vivo biosensors for neurotransmitters will drive future development of early prevention strategies, treatments, and therapeutics for psychiatric and neurodegenerative diseases.

Effectively Selecting Aptamers for Targeting Aromatic Biogenic Amines and Their Application in Aptasensing Establishment

It is necessary to detect the biogenic amine (BA) content in food due to their toxicological effects and their role as an index of freshness for protein-rich foods. Aptamer-based techniques have the potential to provide alternative methods for sensitive and efficient monitoring of BAs. Herein, we described the selection and characterization of DNA aptamers for tyramine (TYR) and β-phenethylamine (PHE) using a one-pot coupled with separate selection strategy. During the selection process, melting curve analysis was developed to monitor the enrichment of the aptamer species, and a saturation of the selection was found at the 14th round. Based on the fluorescence assay, aptamers TYR-2 and PHE-2 showed high affinity to TYR and PHE with the dissociation constant values of 64.28 ± 10.4 and 71.64 ± 11.47 nM, respectively. The circular dichromatic and molecular docking technologies were employed for the preliminary binding mechanism analysis. The obtained aptamers TYR-2 and PHE-2 were used in a fluorescence method for the TYR and PHE determination with limits of detection of 0.34 and 0.39 ng/mL, respectively. In addition, the developed aptasensor was further applied to the TYR and PHE detection in pork and beer samples, and the recovery rate was between 95.6 and 104.2%. It was demonstrated that the selected aptamers had enormous potential as a molecular probe for the identification and determination of BAs.

Implantable aptamer-field-effect transistor neuroprobes for in vivo neurotransmitter monitoring

While tools for monitoring in vivo electrophysiology have been extensively developed, neurochemical recording technologies remain limited. Nevertheless, chemical communication via neurotransmitters plays central roles in brain information processing. We developed implantable aptamer–field-effect transistor (FET) neuroprobes for monitoring neurotransmitters. Neuroprobes were fabricated using high-throughput microelectromechanical system (MEMS) technologies, where 150 probes with shanks of either 150- or 50-μm widths and thicknesses were fabricated on 4-inch Si wafers. Nanoscale FETs with ultrathin (~3 to 4 nm) In₂O₃ semiconductor films were prepared using sol-gel processing. The In₂O₃ surfaces were coupled with synthetic oligonucleotide receptors (aptamers) to recognize and to detect the neurotransmitter serotonin. Aptamer-FET neuroprobes enabled femtomolar serotonin detection limits in brain tissue with minimal biofouling. Stimulated serotonin release was detected in vivo. This study opens opportunities for integrated neural activity recordings at high spatiotemporal resolution by combining these aptamer-FET sensors with other types of Si-based implantable probes to advance our understanding of brain function.

Hybrid Antibody-Aptamer Assay for Detection of Tetrodotoxin in Pufferfish

The marine toxin tetrodotoxin (TTX) poses a great risk to public health safety due to its severe paralytic effects after ingestion. Seafood poisoning caused by the consumption of contaminated marine species like pufferfish due to its expansion to nonendemic areas has increased the need for fast and reliable detection of the toxin to effectively implement prevention strategies. Liquid chromatography-mass spectrometry is considered the most accurate method, although competitive immunoassays have also been reported. In this work, we sought to develop an aptamer-based assay for the rapid, sensitive, and cost-effective detection of TTX in pufferfish. Using capture-SELEX combined with next-generation sequencing, aptamers were identified, and their binding properties were evaluated. Finally, a highly sensitive and user-friendly hybrid antibody–aptamer sandwich assay was developed with superior performance compared to several assays reported in the literature and commercial immunoassay kits. The assay was successfully applied to the quantification of TTX in pufferfish extracts, and the results obtained correlated very well with a competitive magnetic bead-based immunoassay performed in parallel for comparison. This is one of the very few works reported in the literature of such hybrid assays for small-molecule analytes whose compatibility with field samples is also demonstrated.

Identification of a New DNA Aptamer by Tissue-SELEX for Cancer Recognition and Imaging

Cancer has become one of the most common diseases with high mortality in humans. Early and accurate diagnosis of cancer is of great significance to enhance the survival rate of patients. Therefore, effective molecular ligands capable of selectively recognizing cancer are urgently needed. In this work, we identified a new DNA aptamer named SW1 by tissue-based systematic evolution of ligands by exponential enrichment (tissue-SELEX), in which cancerous liver tissue sections were used as the positive control and adjacent normal liver tissue sections were used as the negative control. Taking immobilized liver cancer SMMC-7721 cells as the research object, aptamer SW1 exhibited excellent affinity with a K_d value of 123.62 ± 17.53 nM, and its binding target was preliminarily determined as a non-nucleic acid substance in the nucleus. Moreover, tissue imaging results showed that SW1 explicitly recognized cancerous liver tissues with a high detection rate of 72.7% but displayed a low detection rate to adjacent normal tissues. In addition to liver cancer cells and tissues, aptamer SW1 has been demonstrated to recognize various other types of cancer cells and tissues. Furthermore, SW1-A, an optimized aptamer of SW1, maintained its excellent affinity toward liver cancer cells and tissues. Collectively, these results indicate that SW1 possesses great potential for use as an effective molecular probe for clinical diagnosis of cancer.

Biosensors for Biogenic Amines: A Review

Biogenic amines (BAs) are well-known biomolecules, mostly for their toxic and carcinogenic effects. Commonly, they are used as an indicator of quality preservation in food and beverages since their presence in higher concentrations is associated with poor quality. With respect to BA’s metabolic pathways, time plays a crucial factor in their formation. They are mainly formed by microbial decarboxylation of amino acids, which is closely related to food deterioration, therefore, making them unfit for human consumption. Pathogenic microorganisms grow in food without any noticeable change in odor, appearance, or taste, thus, they can reach toxic concentrations. The present review provides an overview of the most recent literature on BAs with special emphasis on food matrixes, including a description of the typical BA assay formats, along with its general structure, according to the biorecognition elements used (enzymes, nucleic acids, whole cells, and antibodies). The extensive and significant amount of research that has been done to the investigation of biorecognition elements, transducers, and their integration in biosensors, over the years has been reviewed.

Aptamers against the β-Conglutin Allergen: Insights into the Behavior of the Shortest Multimeric (Intra)Molecular DNA G-Quadruplex

In previous work, a 93-mer aptamer was selected against the anaphylactic allergen, β-conglutin and truncated to an 11-mer, improving the affinity by two orders of magnitude, whilst maintaining the specificity. This 11-mer was observed to fold in a G-quadruplex, and preliminary results indicated the existence of a combination of monomeric and higher-order structures. Building on this previous work, in the current study, we aimed to elucidate a deeper understanding of the structural forms of this 11-mer and the effect of the structure on its binding ability. A battery of techniques including polyacrylamide gel electrophoresis, high-performance liquid chromatography in combination with electrospray ionization time-of-flight mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight, thermal binding analysis, circular dichroism and nuclear magnetic resonance were used to probe the structure of both the 11-mer and the 11-mer flanked with TT- at either the 5′ or 3′ end or at both ends. The TT-tail at the 5′ end hinders stacking effects and effectively enforces the 11-mer to maintain a monomeric form. The 11-mer and the TT- derivatives of the 11-mer were also evaluated for their ability to bind its cognate target using microscale thermophoresis and surface plasmon resonance, and biolayer interferometry confirmed the nanomolar affinity of the 11-mer. All the techniques utilized confirmed that the 11-mer was found to exist in a combination of monomeric and higher-order structures, and that independent of the structural form present, nanomolar affinity was observed.

Electropolymerized Receptor Coatings for the Quantitative Detection of Histamine with a Catheter-Based, Diagnostic Sensor

In this article, we report on the development of a catheter-based, biomimetic sensor as a step toward a minimally invasive diagnostic instrument in the context of functional bowel disorders. Histamine is a key mediator in allergic and inflammatory processes in the small intestines; however, it is a challenge to determine histamine levels at the duodenal mucosa, and classical bioreceptors are unsuitable for use in the digestive medium of bowel fluid. Therefore, we have developed molecularly imprinted polypyrrole coatings for impedimetric sensing electrodes, which enable the quantification of histamine in nondiluted, human bowel fluid in a broad concentration range from 25 nM to 1 μM. The electrodes show negligible cross-sensitivity to histidine as a competitor molecule and, for comparison, we also evaluated the response of nonimprinted and taurine-imprinted polypyrrole to histamine. Furthermore, using equivalent-circuit modeling, we found that the molecular recognition of histamine by polypyrrole primarily increases the resistive component of the electrode-liquid interface while capacitive effects are negligible. The sensor, integrated into a catheter, measures differentially to correct for nonspecific adsorption effects in the complex matrix of bowel fluids, and a single triggering frequency is sufficient to determine histamine concentrations. Together, these features are beneficial for real-time diagnostic tests.

Novel aptasensor-based assay of sonic hedgehog ligand for detection of portal vein invasion of hepatocellular carcinoma

The high expression of sonic hedgehog ligand (SHh) is closely correlated to the metastasis, drug resistance and poor prognosis of hepatocellular carcinoma (HCC). Therefore, sensitive, specific and efficient detection methods for SHh are needed for the early diagnosis and assessment of prognosis. Herein, an aptamer, AP32 that specifically binds to SHh (K_D = 25.7 ± 4.1 nM) was obtained by SELEX technology with further optimization. In vivo experiments confirmed that AP32 has the potential to be an imaging probe for Huh-7 cell-derived xenograft. The interaction mode in 3-dimensional configuration between the aptamer and SHh was established by molecular simulation and confirmed by mutations at key sites of the aptamer. An aptasensor-based assay was successfully developed by conjugating Texas-Red-labeled AP32 to microbeads, and was used to analyze SHh content in hepatoma cell lysates, serum and HCC specimens. The method exhibited a broad detection range from 0.07 to 62.5 nM with a low detection limit of 69 pM, and a recovery rate of 104.6 ± 3.9% in serum. When the assay was used to measure SHh content in tissue lysates, the results demonstrated that it possessed 57.1% positivity, 100% specificity in distinguishing 28 HCC specimens from normal tissues, and was compensatory for detection of HCC in AFP-negative cases. Moreover, elevated SHh levels are indicative of portal vein invasion at 77.8% positive rate. This novel aptasensor-based SHh assay may offer a reliable means in predicting early metastasis and poor prognosis in hepatocellular carcinoma.

Gold nanoparticle aptamer assay for the determination of histamine in foodstuffs

The development of a gold nanoparticle aptamer assay is persued for rapid and sensitive determination of histamine in foodstuffs, which could be deployed for on-site use. The assay is based on a histamine-specific aptamer and gold nanoparticles and the salt-induced aggregation of the particles in the presence of histamine indicated by the color change from red to blue. Gold nanoparticle size, salt type, and concentration as well as aptamer concentration were optimized, and using optimum conditions, a limit of detection of 8 nM (~ 0.05 mg/kg) was obtained. Finally, the aptamer AuNP assay was applied to the determination of histamine in quality control fish samples. The histamine levels of these samples had previously been determined using HPLC and commercial ELISA kits by numerous independent laboratories and a good correlation was obtained. The developed AuNP assay is rapid, sensitive, and reproducible. Graphical abstract.

Synthesis of MOF-derived Ni@C materials for the electrochemical detection of histamine

Histamine (HA) plays an important role in food safety supervision and is also involved in various physiological functions. Accurate and rapid detection of HA in real sample is count for much as this is the significant prerequisite for its effective monitoring. In this study, we fabricated an electrochemical sensor to detect HA via the pyrolysis of the hydrothermal Ni-MOF (metal-organic frameworks), in which the obtained Ni@C material was deployed as the sensing agent. Ni@C was comprehensively characterized in terms of its morphology, constitution, as well as its electrochemical behavior. The as-prepared sensor (Ni@C/GCE) features excellent electrocatalytic activities. It was also observed that the electrochemical property of the sensor was substantially improved because Ni@C afforded an enlarged active surface and accelerated electron transport. This sensor affords amperometric analysis in the linear range of 10^-3-100 μM HA with a 3.2 × 10^-4 μM low detection limit (S/N = 3). Many important features, including decent anti-interference, reproducibility, stability, and reliability, were also observed. Importantly, the sensor enabled the measurement of HA in real samples obtained from fish, thus demonstrating its practical potential as a HA analytical detector.

Towards a catheter-based impedimetric sensor for the assessment of intestinal histamine levels in IBS patients

In this work, we report on the development of a catheter-based sensor designed for measuring the concentration of histamine in the human duodenum. Certain gut disorders, such as the irritable bowel syndrome (IBS), are associated with elevated levels of intestinal histamine due to chronic immune activation. As it is still impossible to determine histamine concentrations in vivo, a nasointestinal catheter with histamine-sensing capabilities has the potential to become a valuable diagnostic instrument. Regarding the sensing principle, we selected impedance spectroscopy using voltages that are compatible with intra-body applications with molecularly imprinted polymers (MIPs) as recognition elements. MIPs are synthetic receptors that offer the advantages of robustness, high specificity and selectivity for histamine as a target. In this specific case, the MIPs were synthesized from acryclic acid monomers, which guarantees a uniform binding capacity within the pH range of intestinal fluid. We have validated the catheter sensor on human intestinal liquids spiked with histamine in a testing setup that mimics the environment inside the duodenum. The dose-response curves show an analytical range between 5 and 200 nM of histamine, corresponding to physiologically normal conditions while higher concentrations correlate with disease. The key output signal of the sensor is the resistive component of the MIP-functionalized titanium electrodes as derived from the equivalent-circuit modelling of full-range impedance spectra. Future applications could be catheters tailored to cardiovascular, urological, gastrointestinal, and neurovascular applications. This, in combination with the versatility of the MIPs, will make this sensor platform a versatile diagnostic tool.

Perspective on the Future Role of Aptamers in Analytical Chemistry

It has been almost 30 years since the invention of Systematic Evolution of Ligands by Exponential Enrichment (SELEX) methodology and the description of the first aptamers. In retrospect over the past 30 years, advances in aptamer development and application have demonstrated that aptamers are potentially useful reagents that can be employed in diverse areas within analytical chemistry, biotechnology, biomedicine, and molecular biology. While often touted as artificial antibodies with an ability to be selected for any target, aptamer development, unfortunately, lags behind development of analytical methodologies that employ aptamers, hindering deeper integration into the application of analytical tool development. This perspective covers recent advances in SELEX methodology for improving efficiency of the SELEX procedure and enhancing affinity and specificity of the selected aptamers, what we view as a critical barrier in the future role of aptamers in analytical chemistry. We discuss postselection modifications that can be used for enhancing performance of the selected aptamers in an analytical device by including understanding intermolecular interaction forces in the binding domain. While highlighting promising properties of aptamers that enable several analytical advances, we provide discussion on the challenges of penetration of aptamers in the analytical field.

Development of a histamine aptasensor for food safety monitoring

Histamine produced by bacteria through decarboxylation of histidine in spoiled foods such as fish is known to cause food poisoning. Therefore, accurate and facile measurement of histamine is of practical importance. Using the recently discovered RNA aptamer that specifically recognizes histamine (A1-949 aptamer), we developed an aptasensor based on the structure-switching mechanism. Specifically, the aptamer A1-949 was fluorescently labeled at the 5′ end and hybridized with a short quencher DNA strand that is partially complementary to the aptamer. The quencher strand was modified with a fluorescence quencher at its 3′ terminus. Displacement of the quencher strand upon histamine binding results in an increased fluorescence. After optimizing the assay condition, the enantiomeric version of the aptasensor (L-RNA and L-DNA) was synthesized which could detect the achiral analyte with identical sensitivity and improved biochemical stability. The aptasensor performance was validated by measuring fish samples spiked with known concentrations of histamine. Finally, histamine content in spoiled fish samples was measured, and the results were compared with the measurements using a commercial enzymatic assay kit.

A Bottom-Up Approach for Developing Aptasensors for Abused Drugs: Biosensors in Forensics

Aptamer-based point-of-care (POC) diagnostics platforms may be of substantial benefit in forensic analysis as they provide rapid, sensitive, user-friendly, and selective analysis tools for detection. Aptasensors have not yet been adapted commercially. However, the significance of the applications of aptasensors in the literature exceeded their potential. Herein, in this review, a bottom-up approach is followed to describe the aptasensor development and application procedure, starting from the synthesis of the corresponding aptamer sequence for the selected analyte to creating a smart surface for the sensitive detection of the molecule of interest. Optical and electrochemical biosensing platforms, which are designed with aptamers as recognition molecules, detecting abused drugs are critically reviewed, and existing and possible applications of different designs are discussed. Several potential disciplines in which aptamer-based biosensing technology can be of greatest value, including forensic drug analysis and biological evidence, are then highlighted to encourage researchers to focus on developing aptasensors in these specific areas.

Identification and Application of an Aptamer Targeting Papillary Thyroid Carcinoma Using Tissue-SELEX

Aptamers, short DNA or RNA oligonucleotides, which evolved from systematic evolution of ligands by exponential enrichment (SELEX), can perform specific target recognition. Papillary thyroid carcinoma (PTC) is of high incidence worldwide, and the prognosis of advanced PTC is poor. Up to now, there is no specific biomarker that can identify PTC and defects still remain in existing diagnostic methods. Here we report an aptamer, termed TC-6, which is generated from tissue-SELEX by using sections of papillary thyroid carcinoma and a normal thyroid gland. TC-6 could specifically target intracellular components of papillary thyroid cells with high affinity ( K_d = 57.66 ± 5.93 nmol/L) and have performed excellent biocompatibility both in vivo and in vitro. Moreover, fluorescence imaging of PTC tumor-bearing mice revealed that TC-6 was able to accumulate in tumor sites and could distinguish thyroid carcinoma from other benign thyroid diseases efficiently. In addition, TC-6d, a truncated aptamer of TC-6, maintained its affinity toward PTC with K_d of 39.20 ± 8.20 nmol/L. Overall, these results indicate that TC-6 is a potential candidate for developing novel tools for diagnosis and targeted therapy of PTC.