Fluorescence detection of histamine based on specific binding bioreceptors and carbon quantum dots

Screening of specific binding peptide for β-lactoglobulin using phage display technology

β-lactoglobulin (β-Lg) is a major food allergen, there is an urgent need to develop a rapid method for detecting β-Lg in order to avoid contact or ingestion by allergic patients. Peptide aptamers have high affinity, specificity, and stability, and have broad prospects in the field of rapid detection. Using β-Lg as the target, this study screened 11 peptides (P1-11) from a phage display library. Using molecular docking technology to predict binding energy and binding mode of proteins and peptides. Select the peptides with the best binding ability to β-Lg (P5, P7, P8) through ELISA. Combining them with whey protein, casein, and bovine serum protein, it was found that P7 has the best specificity for β-Lg, with an inhibition rate of 87.99%. Verified by molecular dynamics that P7 binds well with β-Lg. Therefore, this peptide can be used for the recognition of β-Lg, becoming a new recognition element for detecting β-Lg.

Development of a smartphone-integrated microfluidic paper-based optosensing platform coupled with molecular imprinting technique for in-situ determination of histamine in canned tuna

We reported the development of a smartphone-integrated microfluidic paper-based optosensing platform for in-situ detection and quantification of histamine in canned tuna. Molecularly imprinted polymers were synthesized via precipitation polymerization and utilized as dispersive solid phase extraction sorbent to selectively extract histamine from canned tuna. Carbon quantum dots functioning as a fluorescent probe were synthesized and introduced onto the microzones of the microfluidic paper device. This facilitated a noticeable fluorescence color change from dark red to vivid blue upon the addition of histamine. The change in fluorescence on the paper device was converted into specific RGB values using a portable UV light box combined with a smartphone. This assay achieved the limit of detection of 14.04 mg/kg with the linear range from 20 to 100 mg/kg of histamine in canned tuna. The entire molecular imprinting-microfluidic optosensing test could be completed in 45 min including sample preparation.

Nanozyme-assisted molecularly imprinted polymer-based indirect competitive ELISA for the detection of marine biotoxin

Saxitoxin (STX), which is produced by certain dinoflagellate species, is a type of paralytic shellfish poisoning toxin that poses a serious threat to human health and the environment. Therefore, developing a technology for the convenient and cost-effective detection of STX is imperative. In this study, we developed an affinity peptide-imprinted polymer-based indirect competitive ELISA (ic-ELISA) without using enzyme-toxin conjugates. AuNP/Co3O4@Mg/Al cLDH was synthesized by calcining AuNP/ZIF-67@Mg/Al LDH, which was obtained by combining AuNPs, ZIF-67, and flower-like Mg/Al LDH. This synthesized nanozyme exhibited high catalytic activity (Km = 0.24 mM for TMB and 132.5 mM for H2O2). The affinity peptide-imprinted polymer (MIP) was imprinted with an STX-specific template peptide (STX MIP) on a multi-well microplate and then reacted with an STX-specific signal peptide (STX SP). The interaction between the STX SP and MIP was detected using a streptavidin-coated nanozyme (SA-AuNP/Co3O4@Mg/Al cLDH). The developed MIP-based ic-ELISA exhibited excellent selectivity and sensitivity, with a limit of detection of 3.17 ng/mL (equivalent: 0.317 μg/g). Furthermore, the system was validated using a commercial ELISA kit and mussel tissue samples, and it demonstrated a high STX recovery with a low coefficient of variation. These results imply that the developed ic-ELISA can be used to detect STX in real samples.

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.

Bridging biological and food monitoring: A colorimetric and fluorescent dual-mode sensor based on N-doped carbon dots for detection of pH and histamine

Rapid and sensitive monitoring of pH and histamine is crucial for bridging biological and food systems and identifying corresponding abnormal situations. Herein, N-doped carbon dots (CDs) are fabricated by a hydrothermal method employing dipicolinic acid and o-phenylenediamine as precursors. The CDs exhibit colorimetric and fluorescent dual-mode responses to track pH and histamine variations in living cells and food freshness, respectively. The aggregation-induced emission enhancement and intramolecular charge transfer result in a decrease in absorbance and an increase in fluorescence, which become readily apparent as the pH changes from acidic to neutral. This property enables precise differentiation between normal and cancerous cells. Furthermore, given the intrinsic basicity of histamine, pH-responsive CDs are advantageous for additional colorimetric and fluorescent monitoring of histamine in food freshness, achieving linearities of 25-1000 µM and 30-1000 µM, respectively, which are broader than those of alternative nanoprobes. Interestingly, the smartphone-integrated sensing platform can portably and visually evaluate pH and histamine changes due to sensitive color changes. Therefore, the sensor not only establishes a dynamic connection between pH and histamine for the purposes of biological and food monitoring, but also presents a novel approach for developing a multifunctional biosensor that can accomplish environmental monitoring and biosensing simultaneously.

A turn-on fluorescence probe for imaging tyrosinase at the wound site in broken tail of zebrafish

Tyrosinase (TYR) is a copper-containing oxidase that affects the synthesis of melanin in the human body, which is regulate to the pigmentation of the skin. Nevertheless, abnormal expression of TYR can lead to albinism, vitiligo and other skin diseases. Excessive accumulation of TYR is a marker of melanoma cancer and an important factor leading to pigmentation during wound healing, freckles and browning of fruits and vegetables. Efficient tracking of TYR is of significance for studying its pathophysiological mechanism. Herein, we synthesized a benzindole-based fluorescent probe Pro-OH to detect TYR in living cells and zebrafish. The probe displayed a high selectivity and sensitivity in distinguishing TYR from other analytes with the low detection limit of 1.024 U/mL. Importantly, Pro-OH was successfully used to imagine TYR at the wound site of broken tail of zebrafish.

Fluorescence turn-on mode of Eu3+ complex nanocomposite to detect histamine for seafood freshness

Biogenic amines (BAs), which naturally occur as chemicals in seafood, are indicators of food freshness and quality. High concentrations of BAs can cause an undesirable inflammatory response. However, traditional detection methods cannot meet the needs of rapid analysis nowadays. It is essential to explore a simple and valid method to monitor the food quality. Herein, we design and prepare a nanoclay-based turn on fluorescent material with BAs response, which could be used for the real-time and visual detection of raw fish freshness. As the concentration of BAs increase, the sensor of the fluorescence signal is significantly enhanced. The sensor demonstrated wonderful response and sensitivity which showed a detection limit of 0.935 mg/L for typical BAs histamine within a linear range of 2-14 mg/L in an aqueous solution. More importantly, we developed a responsive BAs device by doping the sensor into polyvinyl alcohol (PVA), which is well applied as a rapid-responsive fluorescent marker for visual monitoring the freshness of raw fish.

Recent advances in meat freshness "magnifier": fluorescence sensing

To address the serious waste of meat resources and food safety problems caused by the decrease in meat freshness due to the action of microorganisms and enzymes, a low-cost, time-saving and high-efficiency freshness monitoring method is urgently needed. Fluorescence sensing could act as a "magnifier" for meat freshness monitoring due to its ability to sense characteristic signal produced by meat spoilage. Here, the magnification mechanism of meat freshness via sensing the water activity, adenosine triphosphate, hydrogen ion, total volatile basic nitrogen, hydrogen sulfide, bioamines was comprehensively analyzed. The existing "magnifier" forms including paper chips, films, labels, arrays, probes, and hydrogels as well as the application in livestock, poultry and aquatic meat freshness monitoring were reviewed. Future research directions involving innovation of principles, visualization and quantification capabilities for various meats freshness were provided. By critically evaluating the potential and limitations, efficient and reliable meat freshness monitoring strategies wish to be developed for the post-epidemic era.

Spectro-Electrochemical Properties of A New Non-Enzymatic Modified Working Electrode Used for Histamine Assessment in the Diagnosis of Food Poisoning

We successfully prepared a non-enzymatic sensor based on a graphene-thiophene composite for histamine detection. The self-assembling properties of the thiophene onto Au support and the high electrical conductivity of graphene encouraged the choice of this type of composite. The composite was deposited via electrochemical polymerization onto the Au layer of a screen-printed microelectrode. The electropolymerization and electrochemical detection of histamine were both achieved by cyclic voltammetry. Two types of electrolytes were used for the electrochemical detection: (a) phosphate buffer solution (PBS), which showed low-intensity redox peaks for histamine; and (b) trichloroacetic acid (TCA) 0.01 M, which showed improved results over PBS and did not damage the microelectrode. For the concentration range of 100-200 mg/kg, the sensor shows a linear regression pattern for the oxidation peak fitted on the equation Ipa = 123.412 + 0.49933 ×x, with R2 = 0.94178. The lowest limit of detection was calculated to be 13.8 mg/kg and the limit of quantification was calculated at 46 mg/kg. These results are important since by monitoring the amount of histamine in a food product, early onset of spoilage can be easily detected, thus reducing foodborne poisoning and food waste (by recycling products that are still edible).

Antibody-free and selective detection of okadaic acid using an affinity peptide-based indirect assay

Okadaic acid (OA) is a type of marine biotoxin produced by some species of dinoflagellates in marine environments. Consumption of shellfish contaminated with OA can cause diarrhetic shellfish poisoning (DSP) in humans with symptoms that typically include abdominal pain, diarrhea and vomiting. In this study, we developed an affinity peptide-based direct competition enzyme-linked immunosorbent assay (dc-ELISA) for the detection of OA in real samples. The OA-specific peptide was successfully identified via M13 biopanning and a series of peptides were chemically synthesized and characterized their recognition activities. The dc-ELISA system showed good sensitivity and selectivity with a half-maximal inhibitory concentration (IC₅₀) of 148.7 ng/mL and a limit of detection (LOD) of 5.41 ng/mL (equivalent, 21.52 ng/g). Moreover, the effectiveness of the developed dc-ELISA was validated using OA-spiked shellfish samples, and the developed dc-ELISA showed a high recovery rate. These results suggest that the affinity peptide-based dc-ELISA can be a promising tool for detecting OA in shellfish samples.

Polyurethane Application to Transform Screen-Printed Electrode for Rapid Identification of Histamine Isolated from Fish

The toxicity of histamine has attracted numerous researchers to develop a method for histamine determination purposes. The Food and Drug Administration (FDA) unequivocally prohibits the consumption of histamine above 50 mg·kg^-1. Thus, an innovation in histamine detection in fish has been developed in this research. The investigation of the histamine level in fish has been conducted by using an electrochemical sensor approach and producing a polymer via molecularly imprinted polymer (MIP) on a screen-printed electrode. The technique was validated by assessing the shifts in electron shifting using the cyclic voltammetry (CV) approach and electrochemical impedance spectroscopy (EIS), whereas differential pulse voltammetry (DPV) was applied to validate the sensor method. The instruments showed a linear response ranging from 1-1000 nmol·L^-1, with a detection limit of MIP/SPE at 1.765 nmol·L^-1 and 709 nmol·L^-1 for the NIP/SPE, respectively. The sensing technique was employed to determine the histamine level in selected samples at room temperature (25°C). The outcomes of this study indicated that the validated chemical sensor allowed accurate and precise detection of fish samples and can be categorized as a simple approach. The instrument is inexpensive and suitable for on-site detection.

Zeolitic imidazolate framework-8 encapsulating gold nanoclusters and carbon dots for ratiometric fluorescent detection of adenosine triphosphate and cellular imaging

A novel nanoprobe was prepared by encapsulating carbon dots (CDs) and gold nanoclusters (AuNCs) into zeolitic imidazolate framework-8 (ZIF-8) for sensitive detecting adenosine triphosphate (ATP). Under excitation at 360 nm, the obtained CDs/AuNCs@ZIF-8 nanoprobe exhibits dual-emissions at 469 nm and 660 nm, respectively, corresponding to the fluorescence emission of CDs and the aggregation-induced emission enhancement (AIEE) of AuNCs. The framework of ZIF-8 in this probe can be degraded by ATP due to the coordination competition of ATP and 2-Methylimidazole towards zinc ion (Zn²⁺), resulting in the release of CDs and AuNCs. The following dispersion of CDs would improve efficiencies of the fluorescence excitation and the consequent emission of CDs. On the contrary, the AIEE of AuNCs would be decreased spontaneously after the AuNCs originally restricted in ZIF-8 were allowed to escape. The intensity ratio of fluorescence at 469 nm to that at 660 nm (I₄₆₉/I₆₆₀) was conveniently employed as the response signal for representing the amount of ATP. This nanoprobe exhibits excellent sensitivity and selectivity toward ATP, with a limit of detection (LOD) of 0.061 μM. Besides, low cytotoxicity of this nanoprobe facilitates its application as a fluorescent indicator in fluorescence imaging of living cells. Encapsulating two types of fluorescent nanomaterials by a degradable ZIF-8 structure makes the ratiometric fluorescence response of the nanocomposite probe towards the target analyte that destroys the ZIF-8 structure possible, and simplifies the application of the probe.

Humanoid shaped optical fiber plasmon biosensor functionalized with graphene oxide/multi-walled carbon nanotubes for histamine detection

Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

Phase transferred and non-coated, water soluble perovskite quantum dots for biocompatibility and sensing

Despite the excellent optoelectronic properties exhibited by CsPbBr₃ QDs (PQDs) for sensing applications, their poor resistance to water does not allow their utilization as probes to detect analytes in aqueous media. The present work provides water soluble PQDs (dispersed in water) prepared by an appropriate phase engineering of the ligand. The dicarboxylate functional ligands at a particular pH allow the protonated state to form solvated carboxyl dimers, which interconnects PQDs, thus avoiding Ostwald ripening and enhancing the photoluminescence quantum yield (PLQY). As a proof of concept, this probe was applied to detect bioamines in water, namely histamine, hexamethylenediamine, phenethylamine, dopamine and thiamine. The probe is highly selective to histamine at concentrations below 500 nM and this selectivity of histamine over dopamine is very interesting and rarely reported. More importantly, this work offers a standard protocol for transferring PQDs from the organic to aqueous phase, for the detection of such biomolecules in water.

Constructing hollow ZIF-8/CDs@MIPs fluorescent sensor from Osmanthus leaves to specifically recognize bovine hemoglobin

To develop non-toxic, highly efficient and selective fluorescence sensors was a significance research. In this work, a novel hollow fluorescence sensor was designed with biomass carbon dots (CDs), ZIF-8 and molecularly imprinted polymers (MIPs) via aqueous polymerization. The results demonstrated such unique structure fluorescence sensor exhibited fast response time, excellent stability and highly selectively towards bovine hemoglobin (BHb). Even in a complex environment, the hollow fluorescence sensor (H-ZIF-8/CDs@MIPs) still has a good recognition effect on BHb. Under an optimized condition, the hollow fluorescence sensor was quenched linearly with BHb concentration in the range of 0.058-4.5 μM with the detection limit of 15.6 nM. In addition, a possible quenching mechanism of hollow fluorescence towards BHb was confirmed resonance energy transfer (FRET). In the actual application process, the hollow fluorescence sensor showed a better detection performance towards BHb with the recoveries ranged of 98.6-101.1 %. This work provided a strategy to design green and unique hollow fluorescence sensor for practical application.

Progress in Fluorescence Biosensing and Food Safety towards Point-of-Detection (PoD) System

The detection of pathogens in food substances is of crucial concern for public health and for the safety of the natural environment. Nanomaterials, with their high sensitivity and selectivity have an edge over conventional organic dyes in fluorescent-based detection methods. Advances in microfluidic technology in biosensors have taken place to meet the user criteria of sensitive, inexpensive, user-friendly, and quick detection. In this review, we have summarized the use of fluorescence-based nanomaterials and the latest research approaches towards integrated biosensors, including microsystems containing fluorescence-based detection, various model systems with nano materials, DNA probes, and antibodies. Paper-based lateral-flow test strips and microchips as well as the most-used trapping components are also reviewed, and the possibility of their performance in portable devices evaluated. We also present a current market-available portable system which was developed for food screening and highlight the future direction for the development of fluorescence-based systems for on-site detection and stratification of common foodborne pathogens.

Neuromuscular blocking agent induced hypersensitivity reaction exploration: an update

Acute hypersensitivity reactions (AHRs) occurring in present-day anaesthesia can have severe, sometimes fatal, consequences and their incidence is increasing. The most frequent allergens responsible for AHR during anaesthesia are neuromuscular blocking agents (NMBAs) (70% of the cases) followed by antibiotics (18%), patent blue dye and methylene blue dye (5%), and latex (5%). Following an AHR, strategies for subsequent anaesthetic procedures (especially the choice of an NMBA) may be difficult to formulate due to inconclusive diagnostic analysis in up to 30% of AHRs. Current diagnosis of AHR relies on the detection of mast cell degranulation products and drug-specific type E immunoglobulins (IgE) in order to document an IgE-mediated anaphylaxis (IgE endotype). Nonetheless, other IgE-independent pathways can be involved in AHR, but their detection is not currently available in standard situations. The different mechanisms (endotypes) involved in peri-operative AHR may contribute to the inconclusive diagnostic work-up and this generates uncertainty concerning the culpable drug and strategy for subsequent anaesthetic procedures. This review provides details on the IgE endotype; an update on non-IgE related endotypes and the novel diagnostic tools that could characterise them. This detailed update is intended to provide explicit clinical reasoning tools to the anaesthesiologist faced with an incomplete AHR diagnostic work-up and to facilitate the decision-making process regarding anaesthetic procedures following an AHR to NMBAs.

Dipeptide nanostructures: Synthesis, interactions, advantages and biomedical applications

Short peptides are important in the design of self-assembled materials due to their versatility and flexibility. Self-assembled dipeptides, a group of peptide nanostructures, have highly attractive uses in the field of biomedicine. Recently these materials have proved to be important nanostructures because of their biocompatibility, low-cost and simplicity of synthesis, functionality/easy tunability and nano dimensions. Although there are different studies on peptide and protein-based nanostructures, more information about self-assembled nanostructures for dipeptides is still required to discover the advantages, challenges, importance, synthesis, interactions, and applications. This review describes and discusses the self-assembled dipeptide nanostructures especially for biomedical applications.

Development of an Immunoassay Method for the Sensitive Detection of Histamine and Tryptamine in Foods Based on a CuO@Au Nanoenzyme Label and Molecularly Imprinted Biomimetic Antibody

In this paper, a novel biomimetic enzyme-linked immunoassay method (BELISA) was successfully established for the detection of histamine and tryptamine, based on catalytically active cupric oxide@gold nanoparticles (CuO@Au NPs) as a marker and a molecularly imprinted polymer (MIP) as the biomimetic antibody. Under optimized conditions, the detection limitations of the BELISA method for histamine and tryptamine were 0.04 mg L^-1 and 0.14 mg L^-1, respectively. For liquor spiked with histamine and tryptamine, the BELISA method delivered satisfactory recoveries ranging from 89.90% to 115.00%. Furthermore, the levels of histamine and tryptamine in fish, soy sauce, and rice vinegar samples were detected by the BELISA method and a high performance liquid chromatography method, with no significant difference between the two methods being found. Although the catalytic activity of nanozymes is still lower than that of natural enzymes, the BELISA method could still sensitively determine the histamine and tryptamine levels in food samples.

Microwave-Assisted Synthesis of Sulfur Quantum Dots for Detection of Alkaline Phosphatase Activity

Sulfur quantum dots (SQDs) are a kind of pure elemental quantum dots, which are considered as potential green nanomaterials because they do not contain heavy metal elements and are friendly to biology and environment. In this paper, SQDs with size around 2 nm were synthesized by a microwave-assisted method using sulfur powder as precursor. The SQDs had the highest emission under the excitation of 380 nm and emit blue fluorescence at 470 nm. In addition, the SQDs had good water solubility and stability. Based on the synthesized SQDs, a fluorescence assay for detection of alkaline phosphatase (ALP) was reported. The fluorescence of the SQDs was initially quenched by Cr (VI). In the presence of ALP, ALP-catalyzed hydrolysis of 2-phospho-L-ascorbic acid to generate ascorbic acid. The generated ascorbic acid can reduce Cr (VI) to Cr (III), thus the fluorescence intensity of SQDs was restored. The assay has good sensitivity and selectivity and was applied to the detection of ALP in serum samples. The interesting properties of SQDs can find a wide range of applications in different sensing and imaging areas.

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.

Fluorescence-SERS dual-mode for sensing histamine on specific binding histamine-derivative and gold nanoparticles

Histamine (His) is used as an indicator of seafood quality, but it can be toxic at high intakes. A fluorescence (FL)-surface-enhanced Raman scattering (SERS) dual-mode assay system has been developed for His detection. The His detection method was established based on the specific binding capacity of gold nanoparticles (AuNPs) for the FL derivative of His and o-phthalaldehyde (OPA). In this strategy, His reacted with the OPA to form a Schiff base product (O-His) along with a change in FL and SERS activities. The usual nature of AuNPs could display a significant role both enhancement of SERS and quenching of FL signals. The current investigation displayed a good selectivity toward His over all other biogenic amines. Under the optimized analytical conditions, the SERS and FL intensity of the system were linearly proportional to the His concentration in the range of 0.05-4.5 mg/L and 1-20 mg/L with a detection limit of 0.04 mg/L and 0.32 mg/L, respectively. Moreover, the proposed method was successfully applied for His determination in seafood with promising results.

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.

A surface-imprinted surface-enhanced Raman scattering sensor for histamine detection based on dual semiconductors and Ag nanoparticles

A highly sensitive molecularly imprinted surface-enhanced Raman scattering (SERS) sensor was developed for selective detection of histamine. A combination of two semiconductors and Ag nanoparticles (NPs) was used as the SERS substrate. The SERS was induced by Ag NPs plasmon resonances as well as charge-transfer between the semiconductors and the Ag NPs. The Raman intensity and the logarithm of the histamine concentration were linear over the range 10^-8-10^-3 mol L^-1. The sensor exhibited good selectivity and had a sensitivity limit of 3.088 × 10^-9 mol L^-1. Histamine was detected in a spiked liquor sample, and its recoveries were in the range of 89.89%-109.18%.

Fluorescent Carbon Dots and their Applications in Sensing of Small Organic Molecules

Background:

Fluorescence-based sensing is considered highly sensitive and fluorescent probes with improved properties are always desired. Fluorescent carbon dots (CDs) are newly emerging quasi-spherical nanoparticles of less than 10 nm in size and belong to the carbon nano-material’s family. CDs have great potential as fluorescent probes and currently are under open deliberation by the researchers due to their striking properties such as low environmental hazard, high selectivity, greater sensitivity, good biocompatibility, tunable fluorescent properties and excitation dependent multicolor emission behavior.

Introduction:

This review demonstrates various available methods for fabrication of fluorescent CDs, capping of CDs and characterization with various techniques including UV-visible, FT-IR, and TEM. Analytical applications using CDs for the sensing of small organic molecules, specifically nitroaromatic compounds in the environmental samples are complied.

Methods:

The review covers literature related to synthesis and characterization of carbon dots. It includes around 171 research articles in this field.

Results:

Carbon dots can be synthesized using numerous routes. In all cases CDs possess spectral properties with little variation in wavelength maxima. Optical properties of CDs can be tuned by compositing these with metallic quantum dots or by modifying their surface with desired functionalities. HR-TEM is needed to see the morphology and size of particles whereas UV-Visible and FTIR are indispensable tools for this kind of research. These particles are successfully applied to sense small molecules in some matrices.

Conclusion:

Carbon dots are bright stars in fluorescent sensing of small molecules. However, more research is needed to determine small organic molecules in diversified areas of analysis.

Recyclable Magnetic Fluorescence Sensor Based on Fe3O4 and Carbon Dots for Detection and Purification of Methcathinone in Sewage

Sensitive, rapid, and low-cost detection of drug traces in sewage is very important for drug monitoring and control. In this study, a dual functional and recyclable magnetic fluorescent molecularly imprinted polymers (MFMIPs) sensor with high sensitivity for rapid detection and purification of methcathinone in sewage was developed. MFMIPs was prepared via molecular imprinting and conjugation with carbon dots as a fluorescent reporter on Fe₃O₄ (Fe₃O₄-MIPs@CDs). With strong recognition and adsorption toward methcathinone by the specific cavities on the surface of MFMIPs, the fluorescence of the sensor could dramatically be quenched once anchored with methcathinone. Under optimal conditions, the MFMIPs sensor presented high sensitivity with a linear range of 0.5-100 nM and a detection limit of 0.2 nM, which would be used to monitor drug prevalence and consumption within a certain region. This sensor was applied to the assay of methcathinone in sewage samples collected from Yuebeiyuan, Yanghu, and Xujiahu sewage pumping stations of Yuelu District. The calculated concentrations of methcathinone were 4.80, 15.33, and 8.59 nM in sewage samples, which were in good agreement with data tested by LC-MS/MS. For another function, MFMIPs exhibited purification toward methcathinone and the adsorption capacity was about 0.27 mg/g in a real sewage sample. Moreover, the sensor could be recycled and reused at least five times with the aid of an external magnetic field. Collectively, with good analytical performance and excellent recognition and selectivity to methcathinone, the proposed sensing system based on the magnetic core and molecularly imprinted polymers would open a door to establish highly sensitive and effective sensing systems for sewage analysis and purification.

Solid-Contact Ion-Selective Electrodes for Histamine Determination

Solid-contact ion-selective electrodes for histamine (HA) determination were fabricated and studied. Gold wire (0.5 mm diameter) was coated with poly(3,4-ethlenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) as a solid conductive layer. The polyvinyl chloride matrix embedded with 5,10,15,20-tetraphenyl(porphyrinato)iron(iii) chloride as an ionophore, 2-nitrophenyloctyl ether as a plasticizer and potassium tetrakis(p-chlorophenyl) borate as an ion exchanger was used to cover the PEDOT:PSS layer as a selective membrane. The characteristics of the HA electrodes were also investigated. The detection limit of 8.58 × 10-6 M, the fast response time of less than 5 s, the good reproducibility, the long-term stability and the selectivity in the presence of common interferences in biological fluids were satisfactory. The electrode also performed stably in the pH range of 7-8 and the temperature range of 35-41 °C. Additionally, the recovery rate of 99.7% in artificial cerebrospinal fluid showed the potential for the electrode to be used in biological applications.

An immunochromatographic sensor for ultrasensitive and direct detection of histamine in fish

To ensure food quality and prevent histamine (HA) toxicity, a rapid and direct method of detecting HA is required. In this work, we prepared a monoclonal antibody (mAb) against HA using a hapten produced by the introduction of a phenyl-containing linker. The novel mAb exhibited high sensitivity against HA as determined by ELISA, with a half-maximal inhibitory concentration of 21.51 ng/mL. A gold nanoparticle-based immunosensor was fabricated for rapid detection of HA in fish samples. After optimizing the immunosensor, a visual limit of detection (LOD) and a calculated LOD were 0.25 mg/kg and 10.48 μg/kg for HA, respectively. Recovery rates from the spiked fish samples ranged from 87.33% to 104.67% with the coefficient of variation below 10.82%. Concurrently, the whole process in testing real sample was completed within 15 min, and all results were well confirmed and comparable by liquid chromatography-mass spectrometry and the commercial test strip. These data revealed that the proposed immunosensor could be used as a monitoring tool for the rapid and direct detection of HA in fish samples.

A smartphone-integrated optosensing platform based on red-emission carbon dots for real-time detection of pyrethroids

This report described the development of an optosensing platform based on red-emission carbon dots (RCDs) integrated with a smartphone application that, together, can detect pyrethroids in real time. Based on the high stability and selectivity of molecular imprinting technology, RCDs-based optosensing imprinted polymers was obtained by using a one-pot inverse microemulsion surface imprinting method. Lambda-cyhalothrin (LC), which is a pyrethroid pesticide, can interact with the widely distributed -NH₂ groups on the surface of the RCD-based optosensing nanomaterials to achieve fixed-point adsorption. The quantitative detection of pyrethroids in a wide concentration range (1-120 μg/L) could be achieved, and the limit of detection (LOD) was 0.89 μg/L. Furthermore, a portable UV light box combined with a smartphone was used to convert the change in fluorescence of the RCDs-based optosensing nanomaterials into specific values upon adding pyrethroids, and the LOD by using smartphone was 6.66 μg/L. The developed platform has numerous advantages, including low cost, simple operation, high sensitivity, and good specificity, among others, and it achieves on-site visualization and rapid detection.

Portable molecularly imprinted polymer-based platform for detection of histamine in aqueous solutions

Histamine, which is a naturally occurring chemical in seafood, is known to cause undesirable inflammatory response when consumed in large amounts. Histamine is produced in unsafe amounts in colored seafood when improperly stored for just a few hours. Food and health regulatory bodies across the world have guidelines limiting the amount of histamine in fresh as well as processed seafood. Conventional histamine detection is performed in testing labs, which is a slow process and results in bottlenecks in the seafood supply-chain system. A system to rapidly detect the seafood histamine levels on site is very desirable for seafood suppliers. Herein, we describe an impedance-based histamine detection sensor built on a flexible substrate that can detect histamine in the range of 100-500 ppm. Moreover, our sensor discriminates histamine in the presence of DL-histidine and other biogenic amines, with the selectivity provided by molecular imprinting technology. As a proof of concept, a smartphone controlled, portable semi-quantitative histamine sensing device was fabricated that gave out reliable testing results for histamine in different test solutions as well as for real seafood. We believe this technology can be extended towards determination of other food contaminants in aqueous solutions.

Gold nanoparticles-mediated ratiometric fluorescence aptasensor for ultra-sensitive detection of Abscisic Acid

Herein, a novel ratiometric aptasensor based on carbon quantum dots@2-Methylimidazole zinc salt (CQDs@ZIF-8) and aptamer-functionalized gold nanoparticles (Apt-AuNPs) was developed for highly sensitive detection of ABA by fluorescence spectrometry. The CQDs@ZIF-8 nanomaterials displayed dual-emission properties at 490 nm and 657 nm with excitation at 420 nm were synthesized for the first time. ZIF-8 not only served as an anchor point for CQDs but also acted as a modulator to regulate fluorescence signals of CQDs. Interestingly, introduction of ZIF-8 changed the quenching properties of the AuNPs on CQDs. The AuNPs quenched the fluorescence of CQDs@ZIF-8 at 490 nm but not at the second peak of 657 nm. Few studies have been reported on the ineffectiveness of AuNPs in fluorescence quenching as far as we know. In this study, we found that incorporation of ABA triggered the aggregation of AuNPs due to the specific ABA-aptamer recognition and this changed the fluorescence intensity of the ratiometric probe (CQDs@ZIF-8@Apt-AuNPs). The proposed probe increased the sensitivity and selectivity of determining ABA levels in rice seeds in the range of 0.100-150 ng/mL with an LOD of 30.0 ng/L. Importantly, the method proposed here offers a new unique strategy for the construction of ratiometric probes and ultra-sensitive measurement of biomolecules.

A Fluorescent Metal-Organic Framework for Food Real-Time Visual Monitoring

Due to increasing food-safety issues, exploiting efficient approaches for food quality assessment and instrumentation has attracted concerns worldwide. Herein, a smart evaluation system based on a fluorescent metal-organic framework (MOF) is developed for real-time visual monitoring of food freshness. Via post-synthetic modification, a ratiometric fluorescent MOF probe is constructed by covalently coupling fluorescein 5-isothiocyanate (5-FITC) with NH₂ -rich lanthanide MOF. The probes exhibit a dual-emissive-responsive to biogenic amine, resulting in an increase in FITC emission along with a decrease in Eu³⁺ emission accompanied by a clear distinguishable color transition from orange red to green. After doping the probes on a flexible substrate, the obtained MOF composite film can be integrated with a smartphone-based portable platform easily. It is proved that this smart evaluation system can be used for on-site inspection of the freshness of raw fish samples. This work develops a fluorescent MOF-based smart evaluation system as a novel platform for application in food monitoring, which not only has enormous economic value but also holds great public health significance.