A Colorimetric Strip for Rapid Detection and Real-Time Monitoring of Histamine in Fish Based on Self-Assembled Polydiacetylene Vesicles

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.

A novel fluorescence platform for portable and visual monitoring of meat freshness

Biogenic amines (BAs) are crucial markers of meat spoilage. Developing practical and effective BAs detection methods is essential for monitoring meat freshness and ensuring daily consumption safety. This study prepared several naphthalene-based fluorescent compounds to visually monitor meat freshness in real-time. These probes show a colorimetric fluorescence response to putrescine and cadaverine (typical spoilage indicators) through nucleophilic addition/elimination reaction. The detectability of these probes can be optimized by altering the electronegativity and substitution position of the recognition group. Among these compounds, 2-((6-(4-(diphenylamino)phenyl)naphthalen-2-yl)methylene)malono nitrile (TNMA) demonstrated exceptional sensing performance toward putrescine and cadaverine, including high-contrast fluorescence color transition (red to blue), rapid response times (∼30 s), high selectivity and sensitivity (detection limit for putrescine: 2.69 ppm, cadaverine: 6.11 ppm). Furthermore, the B/R values of TNMA test strips output by RGB analysis presented a linear correlation with total volatile basic nitrogen (TVBN, an international standard for evaluating food spoilage) values in pork. Based on this correlation, we utilized smartphone applications to construct an intelligent evaluation system, enabling visual monitoring of pork, chicken, and shrimp freshness under various storage conditions. The TNMA-based system offers a reliable platform for real-time, portable and visual monitoring of meat freshness for consumers and suppliers in the food industry.

Light-Induced Self-Assembled Polydiacetylene/Carbon Dot Functional "Honeycomb"

The design of functional supramolecular assemblies from individual molecular building blocks is a fundamental challenge in chemistry and material science. We report on the fabrication of "honeycomb" films by light-induced coassembly of diacetylene derivatives and carbon dots. Specifically, modulating noncovalent interactions between the carbon dots, macrocyclic diacetylene, and anthraquinone diacetylene facilitates formation of thin films exhibiting a long-range, uniform pore structure. We show that light irradiation at distinct wavelengths plays a key role in the assembly process and generation of unique macro-porous morphology, by both initiating interactions between the carbon dots and the anthraquinone moieties and giving rise to the topotactic polymerization of the polydiacetylene network. We further demonstrate utilization of the macro-porous film as a photocatalytic platform for water pollutant degradation and as potential supercapacitor electrodes, both applications taking advantage of the high surface area, hydrophobicity, and pore structure of the film.

Stimuli-Responsive and Antibacterial Cellulose-Chitosan Hydrogels Containing Polydiacetylene Nanosheets

Herein, we report a stimuli-responsive hydrogel with inhibitory activity against Escherichia coli prepared by chemical crosslinking of carboxymethyl chitosan (CMCs) and hydroxyethyl cellulose (HEC). The hydrogels were prepared by esterification of chitosan (Cs) with monochloroacetic acid to produce CMCs which were then chemically crosslinked to HEC using citric acid as the crosslinking agent. To impart a stimuli responsiveness property to the hydrogels, polydiacetylene-zinc oxide (PDA-ZnO) nanosheets were synthesized in situ during the crosslinking reaction followed by photopolymerization of the resultant composite. To achieve this, ZnO was anchored on carboxylic groups in 10,12-pentacosadiynoic acid (PCDA) layers to restrict the movement of the alkyl portion of PCDA during crosslinking CMCs and HEC hydrogels. This was followed by irradiating the composite with UV radiation to photopolymerize the PCDA to PDA within the hydrogel matrix so as to impart thermal and pH responsiveness to the hydrogel. From the results obtained, the prepared hydrogel had a pH-dependent swelling capacity as it absorbed more water in acidic media as compared to basic media. The incorporation of PDA-ZnO resulted in a thermochromic composite responsive to pH evidenced by a visible colour transition from pale purple to pale pink. Upon swelling, PDA-ZnO-CMCs-HEC hydrogels had significant inhibitory activity against E. coli attributed to the slow release of the ZnO nanoparticles as compared to CMCs-HEC hydrogels. In conclusion, the developed hydrogel was found to have stimuli-responsive properties and inhibitory activity against E. coli attributed to zinc nanoparticles.

Sensitive colorimetric detection of antibiotic resistant Staphylococcus aureus on dairy farms using LAMP with pH-responsive polydiacetylene

Rapidly and accurately detecting antibiotic-resistant pathogens in agriculture and husbandry is important since these represent a major threat to public health. While much attention has been dedicated to detecting now-common resistant bacteria, such as methicillin-resistant Staphylococcus aureus, fewer methods have been developed to assess resistance against macrolides in Staphylococcus aureus (SA). Here, we report a visual on-site detection system for macrolide resistant SA in dairy products. First, metagenomic sequencing in raw milk, cow manure, water and aerosol deposit collected from dairy farms around Tianjin was used to identify the most abundant macrolide resistance gene, which was found to be the macB gene. In parallel, SA housekeeping genes were screened to allow selective identification of SA, which resulted in the selection of the SAOUHSC_01275 gene. Next, LAMP assays targeting the above-mentioned genes were developed and interpreted by agarose gel electrophoresis. For on-site application, different pH-sensitive colorimetric LAMP indicators were compared, which resulted in selection of polydiacetylene (PDA) as the most sensitive candidate. Additionally, a semi-quantitative detection could be realized by analyzing the RGB information via smartphone with a LOD of 1.344 × 10-7 ng/μL of genomic DNA from a milk sample. Finally, the proposed method was successfully carried out at a real farm within 1 h from sample to result by using freeze-dried reagents and portable devices. This is the first instance in which PDA is used to detect LAMP products, and this generic read-out system can be expanded to other antibiotic resistant genes and bacteria.

Wearable biosensors for human fatigue diagnosis: A review

Fatigue causes deleterious effects to physical and mental health of human being and may cause loss of lives. Therefore, the adverse effects of fatigue on individuals and the society are massive. With the ever-increasing frequency of overtraining among modern military and sports personnel, timely, portable and accurate fatigue diagnosis is essential to avoid fatigue-induced accidents. However, traditional detection methods require complex sample preparation and blood sampling processes, which cannot meet the timeliness and portability of fatigue diagnosis. With the development of flexible materials and biosensing technology, wearable biosensors have attracted increased attention to the researchers. Wearable biosensors collect biomarkers from noninvasive biofluids, such as sweat, saliva, and tears, followed by biosensing with the help of biosensing modules continuously and quantitatively. The detection signal can then be transmitted through wireless communication modules that constitute a method for real-time understanding of abnormality. Recent developments of wearable biosensors are focused on miniaturized wearable electrochemistry and optical biosensors for metabolites detection, of which, few have exhibited satisfactory results in medical diagnosis. However, detection performance limits the wide-range applicability of wearable fatigue diagnosis. In this article, the application of wearable biosensors in fatigue diagnosis has been discussed. In fact, exploration of the composition of different biofluids and their potential toward fatigue diagnosis have been discussed here for the very first time. Moreover, discussions regarding the current bottlenecks in wearable fatigue biosensors and the latest advancements in biochemical reaction and data communication modules have been incorporated herein. Finally, the main challenges and opportunities were discussed for wearable fatigue diagnosis in the future.

Determination Methods of the Risk Factors in Food Based on Nanozymes: A Review

Food safety issues caused by foodborne pathogens, chemical pollutants, and heavy metals have aroused widespread concern because they are closely related to human health. Nanozyme-based biosensors have excellent characteristics such as high sensitivity, selectivity, and cost-effectiveness and have been used to detect the risk factors in foods. In this work, the common detection methods for pathogenic microorganisms, toxins, heavy metals, pesticide residues, veterinary drugs, and illegal additives are firstly reviewed. Then, the principles and applications of immunosensors based on various nanozymes are reviewed and explained. Applying nanozymes to the detection of pathogenic bacteria holds great potential for real-time evaluation and detection protocols for food risk factors.

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.

Bifunctional ligand-mediated amplification of polydiacetylene response to biorecognition of diethylstilbestrol for on-site smartphone detection

Polydiacetylene (PDA) is very suited for sensitively detecting large biomolecules, and its unique chromatic properties enable visual read-out. However, application to the selective detection of small molecules remains challenging. Here, bifunctional ligands are studied to amplify the color change of PDA for biorecognition of small molecules for the smartphone-based detection of diethylstilbestrol (DES). PDA is decorated with streptavidin (PDA-SA, blue), and biotin-modified DES (bio-DES) is prepared as a bifunctional ligand to couple with PDA-SA and DES antibody. Since multiple bio-DES can bind to a single SA, then multiple SAs on PDA lead to an increased surface coverage of the vesicle. In samples without DES, PDA-SA-bio-DES-DES antibody complexes will form, leading to a color transition (blue to red); this color transition is greatly amplified by antibody-induced aggregation of the complexes. When DES is present, aggregation is inhibited due to competition for the antibody and PDA-SA-bio-DES retains its blue color. A linear relationship (0.4-1250 ng mL^-1) is found between the colorimetric response and the logarithmic DES concentration, with adequate selectivity, accuracy (82.24-118.64%), and precision (below 8.24%). Finally, a paper-based DES PDA biosensor is developed with visual and smartphone-based detection limits of 10 ng mL^-1 and 0.85 ng mL^-1 in water, respectively.

Quantitative Colorimetric Detection of Dissolved Ammonia Using Polydiacetylene Sensors Enabled by Machine Learning Classifiers

Easy-to-use and on-site detection of dissolved ammonia are essential for managing aquatic ecosystems and aquaculture products since low levels of ammonia can cause serious health risks and harm aquatic life. This work demonstrates quantitative naked eye detection of dissolved ammonia based on polydiacetylene (PDA) sensors with machine learning classifiers. PDA vesicles were assembled from diacetylene monomers through a facile green chemical synthesis which exhibited a blue-to-red color transition upon exposure to dissolved ammonia and was detectable by the naked eye. The quantitative color change was studied by UV-vis spectroscopy, and it was found that the absorption peak at 640 nm gradually decreased, and the absorption peak at 540 nm increased with increasing ammonia concentration. The fabricated PDA sensor exhibited a detection limit of ammonia below 10 ppm with a response time of 20 min. Also, the PDA sensor could be stably operated for up to 60 days by storing in a refrigerator. Furthermore, the quantitative on-site monitoring of dissolved ammonia was investigated using colorimetric images with machine learning classifiers. Using a support vector machine for the machine learning model, the classification of ammonia concentration was possible with a high accuracy of 100 and 95.1% using color RGB images captured by a scanner and a smartphone, respectively. These results indicate that using the developed PDA sensor, a simple naked eye detection for dissolved ammonia is possible with higher accuracy and on-site detection enabled by the smartphone and machine learning processes.

Prussian blue nanoparticles-enabled sensitive and accurate ratiometric fluorescence immunoassay for histamine

Herein, a nanozyme-mediated ratiometric fluorescence immunoassay for histamine (HA) has been developed. Prussian blue nanoparticles (PBNPs) with outstanding peroxidase-like activity were labelled with goat anti-mouse IgG via a facile electrostatic adsorption to yield the nanozyme-antibody conjugate which acted as a bridge to link the ratiometric fluorescence readout with HA concentration. As substrate, o-phenylenediamine (OPD) was oxidized into 2,3-diaminophenazine (oxOPD) by H2O2 under the catalysis of PBNPs, producing a novel emission at 570 nm and quenching the fluorescence of carbon dots (CDs) at 450 nm simultaneously. Under optimal conditions, the ratio of fluorescence intensity at 570 nm and 450 nm (I570/I450) linearly correlated with HA concentration ranging from 1.6 ng/mL to 125 μg/mL, with a detection limit (LOD) of 1.2 ng/mL. In addition, analytical performances including specificity, accuracy and applicability were evaluated, which revealed that this ratiometric fluorescence immunoassay affords an effective platform for sensitive and accurate detection of HA.

Histamine and Scombrotoxins

Histamine intoxications result when histamine-metabolizing enzymes are compromised or overwhelmed by dietary histamine in the human body. This can occur either due to metabolic enzyme deficiencies, such as in histamine intolerance to wines, aged cheese and other foods or from high concentrations of histamine following ingestion of decomposed fish. The presence of histamine in decomposed fish and fish products results from bacterial decarboxylation of free L-histidine following product mishandling. Consequently, histamine intoxications from mishandled fish, commonly referred to as scombrotoxin fish poisoning (SFP) or scombroid poisoning, require high levels of free L-histidine only found in certain species of pelagic fish. Differential diagnosis is required of clinicians since dietary histamine intoxications produce the same symptoms typical of release of endogenous histamine due to IgE -mediated seafood allergies or anisakiasis. Although high levels of dietary histamine are responsible for SFP, histamine has important physiological functions and tends to exert toxic effects only at doses beyond the physiological range. Endogenous histamine is essential to local immune responses, regulation of gastric acid secretion in the gut, and neurotransmission in the central nervous system. Scombrotoxins, postulated to explain histamine's augmented toxicity in scombrotoxic fish, are a milieu of histamine and other bioactives. Since time-and-temperature abuse is required to produce high levels of histamine in fish, management consists of ensuring proper handling by identifying hazards and critical control points (HACCP) and maintaining a "cold chain" from catch to consumption. Reference methods for detecting histamine have received increased attention and the European Commission has validated a popular precolumn dansylation-based HPLC method through inter-laboratory collaboration and studied method equivalence with the AOAC fluorescence method 977.13 recognized by Codex Alimentarius. Much progress has been made during the last decade in the development and validation of rapid screening methods for detecting histamine in food and especially in fish products. These include many innovative sensors and several validated commercial test kits, many of them based on a recombinant form of the enzyme histamine dehydrogenase (HD).

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.

Visual Simultaneous Detection and Real-Time Monitoring of Cadmium Ions Based on Conjugated Polydiacetylenes

We prepared the monomer PCDA-HP composed of 5-hydroxy-N ¹,N ³-bis(pyridin-2-ylmethyl)isophthalamide (HP) as a cadmium ion tweezer and then polymerized them to form a polydiacetylene (PDA)-based sensor (PDA-HP), which displayed selective and sensitive colorimetric and fluorometric change upon addition of a cadmium ion (Cd²⁺) at both pH 7.4 and 6.8. The PDA-HP polymer was highly selective for Cd²⁺ over other metal ions with colorimetric change. In addition, the PDA-HP chemosensor also showed a red fluorescence change in the presence of Cd²⁺ at both pH 7.4 and 6.8. Naked-eye detection of Cd²⁺ was accomplished in an aqueous solution through a PDA-based sensor system. Finally, the lowest energy structure of an HP chelator was obtained by the crystal structure and density functional theory (DFT) calculations.

Highly Sensitive Polydiacetylene Ensembles for Biosensing and Bioimaging

Polydiacetylenes are prepared from amphiphilic diacetylenes first through self-assembly and then polymerization. Different from common supramolecular assemblies, polydiacetylenes have stable structure and very special optical properties such as absorption, fluorescence, and Raman. The hydrophilic head of PDAs is easy to be chemically modified with functional groups for detection and imaging applications. PDAs will undergo a specific color change from blue to red, fluorescence enhancement and Raman spectrum changes in the presence of receptor ligands. These properties allow PDA-based sensors to have high sensitivity and specificity during analysis. Therefore, the PDAs have been widely used for detection of viruses, bacteria, proteins, antibiotics, hormones, sialic acid, metal ions and as probes for bioimaging in recent years. In this review, the preparation, polymerization, and detection mechanisms of PDAs are discussed, and some representative research advances in the field of bio-detection and bioimaging are highlighted.

On-spot quantitative analysis of dicamba in field waters using a lateral flow immunochromatographic strip with smartphone imaging

Dicamba herbicide is increasingly used in the world, in particular' with the widespread cultivation of genetically modified dicamba-resistant crops. However, the drift problem in the field has caused phytotoxicity against naive, sensitive crops, raising legal concerns. Thus, it is particularly timely to develop a method that can be used for on-the-spot rapid detection of dicamba in the field. In this paper, a lateral flow immunochromatographic strip (LFIC) was developed. The quantitative detection can be conducted by an app on a smartphone, named "Color Snap." The tool reported here provides results in 10 min and can detect dicamba in water with a LOD (detection limit) value of 0.1 mg/L. The developed LFIC shows excellent stability and sensitivity appropriate for field analysis. Our sensor is portable and excellent tool for on-site detection with smartphone imaging for better accuracy and precision of the results. Graphical abstract.

The rise of bio-inspired polymer compartments responding to pathology-related signals

Self-organized nano- and microscale polymer compartments such as polymersomes, giant unilamellar vesicles (GUVs), polyion complex vesicles (PICsomes) and layer-by-layer (LbL) capsules have increasing potential in many sensing applications. Besides modifying the physicochemical properties of the corresponding polymer building blocks, the versatility of these compartments can be markedly expanded by biomolecules that endow the nanomaterials with specific molecular and cellular functions. In this review, we focus on polymer-based compartments that preserve their structure, and highlight the key role they play in the field of medical diagnostics: first, the self-assembling abilities that result in preferred architectures are presented for a broad range of polymers. In the following, we describe different strategies for sensing disease-related signals (pH-change, reductive conditions, and presence of ions or biomolecules) by polymer compartments that exhibit stimuli-responsiveness. In particular, we distinguish between the stimulus-sensitivity contributed by the polymer itself or by additional compounds embedded in the compartments in different sensing systems. We then address necessary properties of sensing polymeric compartments, such as the enhancement of their stability and biocompatibility, or the targeting ability, that open up new perspectives for diagnostic applications.