Adaptive Evolution of the Greater Horseshoe Bat AANAT: Insights into the Link between AANAT and Hibernation Rhythms

Arylalkylamine N-acetyltransferase (AANAT) is a crucial rate-limiting enzyme in the synthesis of melatonin. AANAT has been confirmed to be independently duplicated and inactivated in different animal taxa in order to adapt to the environment. However, the evolutionary forces associated with having a single copy of AANAT remain unclear. The greater horseshoe bat has a single copy of AANAT but exhibits different hibernation rhythms in various populations. We analyzed the adaptive evolution at the gene and protein levels of AANAT from three distinct genetic lineages in China: northeast (NE), central east (CE), and southwest (SW). The results revealed greater genetic diversity in the AANAT loci of the NE and CE lineage populations that have longer hibernation times, and there were two positive selection loci. The catalytic capacity of AANAT in the Liaoning population that underwent positive selection was significantly higher than that of the Yunnan population (p < 0.05). This difference may be related to the lower proportion of α helix and the variation in two interface residues. The adaptive evolution of AANAT was significantly correlated with climate and environment (p < 0.05). After controlling for geographical factors (latitude and altitude), the evolution of AANAT by the negative temperature factor was represented by the monthly mean temperature (r = -0.6, p < 0.05). The results identified the gene level variation, functional adaptation, and evolutionary driving factors of AANAT, provide an important foundation for further understanding the adaptive evolution of the single copy of AANAT in pteropods, and may offer evidence for adaptive hibernation rhythms in bats.

Multiplex Detection of Biogenic Amines for Meat Freshness Monitoring Using Nanoplasmonic Colorimetric Sensor Array

Biogenic amines (BAs) were presented as significant markers for the evaluation of the spoilage of meat and meat products. In this work, a colorimetric sensor array was developed for the discrimination and detection of spermine (SP), spermidine (SD), histamine (HS), and tryptamine (TP) as important BAs in food assessment. For this aim, two important spherical plasmonic nanoparticles, namely gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), were utilized as the sensing elements of the probes. The cross-reactive interaction of the target biogenic amines and the plasmonic nanoparticles caused the aggregation-induced UV-Vis spectra changes, which were accompanied by visual color variation in the solution. The collected responses were analyzed by principal component analysis-linear discrimination analysis (PCA-LDA) to classify the four BAs. This colorimetric sensor array can also discriminate between the individual BAs and their mixture accurately. Partial least squares regression (PLS-R) was also utilized for quantitative analysis of the BAs. The wide linear concentration ranges of 0.1-10.0 µM for the four BAs and desirable figures of merits (FOMs) showed the potential of the developed sensor for quantitative detection of the BAs. Finally, the practical ability of the developed probe was studied by the determination of the BAs in the meat samples, which successfully proved the potential of the colorimetric sensor array in a food sample.

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.

A pyrylium salt-based fluorescent probe for the highly sensitive detection of methylamine vapour

The MTPY exhibits an obvious fluorescence response from yellow to cyan when reacted with CH3NH2 with a low detection limit (2.6 ppt, 8.4 × 10−8 M). The sensing mechanism was traced by mass spectrometry.

A hybrid upconversion nanoprobe for ratiometric detection of aliphatic biogenic amines in aqueous medium

We fabricated an inorganic-organic hybrid upconversion nanoprobe for the ratiometric detection of aliphatic biogenic amines in water. The hybrid nanoprobe comprises a thiophene-based acceptor-π-donor-π-acceptor organic fluorescent dye, TDPM, and near-infrared light-absorbing upconversion nanoparticles (UCNPs). The organic dye was loaded into a mesoporous silica-coated UCNP (UCNP@mSiO2) matrix to circumvent the issues of water insolubility and higher energy excitation. Yb3+ and Tm3+-doped UCNPs exhibited dual emission bands at 475 and 645 nm upon excitation with a 980 nm laser. The significant spectral overlap between the absorption and the emission bands of TDPM and UCNPs, respectively, at 475 nm led to resonance energy transfer (RET) from the UCNPs to TDPM resulting in the quenching of the UCNP emission. In contrast, 'turn-on' emission was noticeable with the addition of aliphatic biogenic amines due to an inhibition of the RET. The emission at 645 nm remained unaffected during the energy transfer process making the hybrid probe a versatile platform for the ratiometric detection of different aliphatic biogenic amines. Furthermore, we explored the sensing of aliphatic biogenic amines in adulterated milk and rotten fish. The unique material attributes demonstrated in the current study hold promise for further development of real-time sensors and switches based on hybrid upconversion nanoprobes.

Effect of amines on formation of gold/polyurethane foam nanocomposites and its sensing opportunities

Effect of amines on formation of gold nanoparticles (AuNPs)/polymer nanocomposites has been observed and studied. Nanocomposites based on polyurethane foam and AuNPs were synthesized by interaction between the polymer modified with sodium borohydride and aqueous solution of tetrachloroauric acid. It has been shown that some amines cause a remarkable decrease of the surface plasmon resonance band of AuNPs in the nanocomposite material. Both aliphatic and aromatic amines as well as amines containing several amino groups were studied. A possible mechanism of the effect is discussed. It is probably based on stabilization of AuNPs with an amine that entails a decrease in the degree of their adsorption on PUF and appearance of the stabilized AuNPs in solution. The decrease of the nanocomposite surface plasmon resonance band is proportional to the concentration of amine in the solution. Based on this effect, a method for the determination of cetylamine, β-naphthylamine and neomycin in water and medical formulations using a monitor calibrator as a portable household tool is proposed. Under the selected conditions, the detection limits for amines were in the range of 0.7-1.5 μM, the determination ranges were approximately an order of magnitude. The observed color change of the nanocomposite samples also provides a good basis for semiquantitative determinations.

A narrative review on biogenic amines in fermented fish and meat products

Biogenic amines (BAs) are organic nitrogenous compounds, formed mostly by decarboxylation of corresponding amino acids. BAs are responsible for several biological events. However, if the concentration of BAs reached the threshold level, it causes mild to serious health problems in human. The objective of this manuscript was to summarize the prevalence and prevention of Bas formation, detection methods and factors affecting the BAs formation in fermented fish and meat products. Meat sausages are the fermented meat product that contains high BAs. Fish sauces are reported to have high BAs compared to other fish products. Several chemosensors and chromatography methods are available to screen and detect BAs in foods. The prevention measures are vital to avoid toxic outbreaks. The use of starter culture, application of physical factors, control of environmental factors, and use of polyphenols could prevent or diminish the formation of BAs in fermented foods. The literature survey warrants that the development of potent starter with desirable characters, maintenance of hygienic food production and regular monitoring of commercial products are necessary to ensure the quality and safety of fermented fish and meat product.

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.

Intriguing pH-modulated Luminescence Chameleon System based on Postsynthetic Modified Dual-emitting Eu3+@Mn-MOF and Its Application for Histidine Chemosensor

Due to the disruption by other nonanalyte factors, single-emission probes have been limited in complicated detecting systems. In this work, a pH-modulated luminescence chameleon system based on lanthanide-based MOF (Eu³⁺@Mn-MOF), with stable structure and miraculous dual-emitting fluorescent properties, was synthesized by a postsynthetic modification (PSM) strategy of a simple hydrothermal and agitation method. Amazingly, not only can the Eu³⁺@Mn-MOF emit a broad emission at 500 nm attributed to the ligand-based fluorescence emission but it can also exhibit the characteristic emission of Eu³⁺ ions responding to the antenna effect. Moreover, the Eu³⁺@Mn-MOF displays an interesting luminescence color transition between acidic and basic solutions. Inspired by this phenomenon, a pH-modulated luminescence chameleon system was first constructed and employed to detect histidine, a kind of basic amino acid for a variety of biological matters, causing a unique fluorescence signal of the ratio-dependent color to change from yellow to light pink which differs from the color change of other water-soluble amino acids. Therefore, Eu³⁺@Mn-MOF can be as a practical pH-modulated luminescence chameleon system chemsensor for sensing histidine with low detection limit, high sensitivity, and rapid sensing time. In conclusion, the postsynthetic modified Eu³⁺@Mn-MOF has outstanding applications in the fields of chemical detection and human health.

A High-Throughput Method for Directed Evolution of NAD(P)+-Dependent Dehydrogenases for the Reduction of Biomimetic Nicotinamide Analogues

Engineering flavin-free NAD(P)⁺-dependent dehydrogenases to reduce biomimetic nicotinamide analogues (mNAD⁺s) is of importance for eliminating the need for costly NAD(P)⁺ in coenzyme regeneration systems. Current redox dye-based screening methods for engineering the mNAD⁺ specificity of dehydrogenases are frequently encumbered by a background signal from endogenous NAD(P) and intracellular reducing compounds, making the detection of low mNAD⁺-based activities a limiting factor for directed evolution. Here, we develop a high-throughput screening method, NAD(P)-eliminated solid-phase assay (NESPA), which can reliably identify mNAD⁺-active mutants of dehydrogenases with a minimal background signal. This method involves (1) heat lysis of colonies to permeabilize the cell membrane, (2) colony transfer onto filter paper, (3) washing to remove endogenous NAD(P) and reducing compounds, (4) enzyme-coupled assay for mNADH-dependent color production, and (5) digital imaging of colonies to identify mNAD⁺-active mutants. This method was used to improve the activity of 6-phosphogluconate dehydrogenase on nicotinamide mononucleotide (NMN⁺). The best mutant obtained after six rounds of directed evolution exhibits a 50-fold enhancement in catalytic efficiency (k _cat/K _M) and a specific activity of 17.7 U/mg on NMN⁺, which is comparable to the wild-type enzyme on its natural coenzyme, NADP⁺. The engineered dehydrogenase was then used to construct an NMNH regeneration system to drive an ene-reductase catalysis. A comparable level of turnover frequency and product yield was observed using the engineered system relative to NADPH regeneration by using the wild-type dehydrogenase. NESPA provides a simple and accurate readout of mNAD⁺-based activities and the screening at high-throughput levels (approximately tens of thousands per round), thus opening up an avenue for the evolution of dehydrogenases with specific activities on mNAD⁺s similar to the levels of natural enzyme/coenzyme pairs.

A highly selective "turn-on" electroanalysis strategy with reduced copper metal-organic frameworks for sensing histamine and histidine

A highly selective and sensitive electroanalysis strategy has been developed for sensing histamine (HTA) and histidine (His) with "turn-on" signal outputs using copper nanocomposites (Cu NCs) of reduced copper metal-organic frameworks (Cu MOFs). It was discovered that the Cu NC-modified electrodes could display the sharp and stable oxidation peaks of solid-state CuCl electrochemistry at a low potential (about -0.10 V). More interestingly, once HTA or His was introduced, the peaking currents of the electrodes would increase due to the specific interaction between Cu²⁺ and imidazole groups of HTA or His. A highly selective electroanalysis method was thereby developed for the detection of both HTA and His in the concentration range of 0.010-100 μM. Besides, the application feasibility of the developed electroanalysis strategy was demonstrated for the evaluation of HTA and His separately in red wine and urine samples. Such an electroanalysis candidate for HTA and His holds great potential for wide applications in the fields of food analysis and clinical disease diagnosis.

(Tetrahydrodibenzo[a,i]phenanthridin-5-yl)phenol as a Fluorescent Probe for the Detection of Aniline

Two (tetrahydrodibenzo[a,i]phenanthridin-5-yl)phenols that differ in their substituents at the para position (P1, R = H and P2, R = NEt₂) were designed and synthesized. The presence of a -NEt₂ group in probe P2 facilitates the twisted intramolecular charge transfer (TICT) process, making P2 emissive, which distinctly coordinated with boron trifluoride in the presence of different amines with different electronic properties. A substantial increase in emission intensity with increasing viscosity of the surrounding environment and smooth formation of a planar complex with boron and Zn²⁺ ions concluded the presence of a TICT process. The selective reactivity of P2 toward a tetracoordinated boron complex has been explored as a potential tool for colorimetric and fluorescent discrimination of aromatic primary amines, i.e., anilines. Selective detection of aniline with probe P2 can be viewed through the naked eye, and the corresponding fluorescence turn-on detection limit was found to be 12.65 nM. In addition, the detection of aniline on precoated aluminum-backed thin-layer chromatography plates and Whatman filter paper strips was found to be in good agreement with the color change of P2 in solution and in vapor phase.

Carbon Dots-Modified Nanoporous Membrane and Fe3O4@Au Magnet Nanocomposites-Based FRET Assay for Ultrasensitive Histamine Detection

Histamine can be formed by enzymatic decarbonylation of histidine, which is an important indicator of seafood quality. A rapid and sensitive assay method is necessary for histamine monitoring. A fluorescence resonance energy transfer (FRET) assay system based on a carbon dot (CD)-modified nanoporous alumina membrane and Fe₃O₄@Au magnet nanocomposites has been developed for histamine detection in mackerel fish. CDs immobilized on nanoporous alumina membranes were used as donors, which provided a fluorescence sensing substrate for histamine detection. Fe₃O₄@Au magnet nanocomposites can not only act as acceptors, but also concentrate histamine from fish samples to increase detection sensitivity. Histamine was detected by the fluorescence signal changes of CDs capturing histamine by an immune reaction. The fluorescence signals of CDs were quenched by Fe₃O₄@Au magnet nanocomposites via the FRET mechanism. With an increase of histamine, the fluorescence intensity decreased. By recording fluorescence spectra and calculating intensity change, histamine concentration can be determined with a limit of detection (LOD) of 70 pM. This assay system can be successfully applied for histamine determination in mackerel fish to monitor the fish spoilage process in different storage conditions. It shows the potential applications of CDs-modified nanoporous alumina membranes and Fe₃O₄@Au magnet nanocomposites-based biosensors in the food safety area.

Chemosensors for biogenic amines and biothiols

There is burgeoning interest among supramolecular chemists to develop novel molecular systems to detect biogenic amines and bio-thiols in aqueous and non-aqueous media due to their potential role in biological processes. Biogenic amines are biologically important targets because of their involvement in the energy metabolism of human biological systems and their requirement is met through food and nutrition. However, the increasing instances of serious health problems due to food toxicity have raised the quality of food nowadays. Biogenic amines have been frequently considered as the markers or primary quality parameters of foods like antioxidant properties, freshness and spoilage. For instance, these amines such as spermine, spermidine, cadavarine, etc. may originate during microbial decarboxylation of amino acids of fermented foods/beverages. These amines may also react with nitrite available in certain meat products and concomitantly produce carcinogenic nitrosamine compounds. On the other hand, it is also well established that biothiols, particularly, thiol amino acids, provide the basic characteristics to food including flavor, color and texture that determine its acceptability. For instance, the reduction of thiol groups produces hydrogen sulfide which reduces flavour as in rotten eggs and spoiled fish, and the presence of hydrogen sulfide in fish is indicative of spoilage. Thus, biogenic amines and bio-thiols have attracted the profound interest of researchers as analytical tools for their quantification. Much scientific and technological information is issued every year, where the establishment of precise interactions of biogenic amines and bio-thiols with other molecules is sought in aqueous and non-aqueous media. This review summarizes the optical chemosensors developed for the selective detection of biogenic amines and bio-thiols.

Design and Characterization of Dicyanovinyl Reactive Dyes for the Colorimetric Detection of Thiols and Biogenic Amines

The synthesis of two new azobenzene dyes, namely CR-528 and CR-555, and their spectral properties in ethanol solution are described. The recognition of sulfur-containing analytes (2-mercaptoethanol (2-ME), sodium hydrosulfide (NaHS)), and biogenic amines (spermine, spermidine, ethanolamine) bestowed significant spectral changes with color changes from pink/purple to pale yellow/orange-yellow. The nitro acceptor group in the dicyanovinyl reactive dye contributes to higher sensitivity and lower detected analyte concentrations. The absorption maxima of both the dyes are at wavelengths compatible with low-cost light sources and detectors, making them excellent candidates for optical probes that are economic, simple to use, and do not require well-trained personnel.

A facile molecularly imprinted polymer-based fluorometric assay for detection of histamine

Histamine is a biogenic amine naturally present in many body cells. It is also a contaminant that is mostly found in spoiled food. The consumption of foods containing high levels of histamine may lead to an allergy-like food poisoning. Analytical methods that can routinely screen histamine are thus urgently needed. In this paper, we developed a facile and cost-effective molecularly imprinted polymer (MIP)-based fluorometric assay to directly quantify histamine. Histamine-specific MIP nanoparticles (nanoMIPs) were synthesized using a modified solid-phase synthesis method. They were then immobilized in the wells of a microplate to bind the histamine in aqueous samples. After binding, o-phthaldialdehyde (OPA) was used to label the bound histamine, which converted the binding events into fluorescent signals. The obtained calibration curve of histamine showed a linear correlation ranging from 1.80 to 44.98 μM with the limit of detection of 1.80 μM. This method was successfully used to detect histamine in spiked diary milk with a recovery rate of more than 85%.

A Double-Stimuli-Responsive Fluorescent Center for Monitoring of Food Spoilage based on Dye Covalently Modified EuMOFs: From Sensory Hydrogels to Logic Devices

Unsafe food is a huge threat to human health and the economy, and detecting food spoilage early is an ongoing and imperative need. Herein, a simple and effective strategy combining a fluorescence sensor and one-to-two logic operation is designed for monitoring biogenic amines, indicators of food spoilage. Sensors (methyl red@lanthanide metal-organic frameworks (MR@EuMOFs)) are created by covalently modifying MR into NH₂ -rich EuMOFs, which have a high quantum yield (48%). A double-stimuli-responsive fluorescence center is produced via energy transfer from the ligands to Eu³⁺ and MR. Portable sensory hydrogels are obtained by dispersing and solidifying MR@EuMOFs in water-phase sodium salt of carboxy methyl cellulose (CMC-Na). The hydrogels exhibit a color transition upon "smelling" histamine (HI) vapor. This transition and shift in the MR-based emission peak are closely related to the HI concentration. Using the HI concentration as the input signal and the two fluorescence emissions as output signals, an advanced analytical device based on a one-to-two logic gate is constructed. The four output combinations, NOT (0, 1), YES (1, 0), PASS 1 (1, 1), and PASS 0 (0, 0), allow the direct analysis of HI levels, which can be used for real-time food-freshness evaluation. The novel strategy suggested here may be a new application for a molecular logic system in the sensing field.

Light-Activated Sensitive Probes for Amine Detection

Our new, simple, and accurate colorimetric method is based on diarylethenes (DAEs) for the rapid detection of a wide range of primary and secondary amines. The probes consist of aldehyde- or ketone-substituted diarylethenes, which undergo an amine-induced decoloration reaction, selectively to give the ring-closed isomer. Thus, these probes can be activated at the desired moment by light irradiation, with a sensitivity that allows the detection of amines at concentrations as low as 10^-6  m in solution. In addition, the practical immobilization of DAEs on paper makes it possible to detect biogenic amines, such as cadaverine, in the gas phase above a threshold of 12 ppbv within 30 seconds.

Visual Monitoring of Food Spoilage Based on Hydrolysis-Induced Silver Metallization of Au Nanorods

Colorimetric detection of biogenic amines, well-known indicators of food spoilage, plays an important role for monitoring of food safety. However, common colorimetric sensors for biogenic amines suffer from low color resolution or complicated design and intricate output for the end-users. Herein, we explored a simple but effective strategy for visual monitoring of biogenic amines with multiple color change based on hydrolysis-induced silver metallization reaction to tune the localized surface plasmon resonance (LSPR) adsorption of Au nanorods (NRs). The color change and blue shift of longitudinal LSPR peak of Au NRs were closely related to the concentration of biogenic amines. This strategy provided a simple, sensitive, robust, nondestructive, cost-effective, and user-friendly platform for in situ evaluating the freshness of foodstuffs.

A Nanoporous Alumina Membrane Based Electrochemical Biosensor for Histamine Determination with Biofunctionalized Magnetic Nanoparticles Concentration and Signal Amplification

Histamine is an indicator of food quality and indispensable in the efficient functioning of various physiological systems. Rapid and sensitive determination of histamine is urgently needed in food analysis and clinical diagnostics. Traditional histamine detection methods require qualified personnel, need complex operation processes, and are time-consuming. In this study, a biofunctionalized nanoporous alumina membrane based electrochemical biosensor with magnetic nanoparticles (MNPs) concentration and signal amplification was developed for histamine determination. Nanoporous alumina membranes were modified by anti-histamine antibody and integrated into polydimethylsiloxane (PDMS) chambers. The specific antibody modified MNPs were used to concentrate histamine from samples and transferred to the antibody modified nanoporous membrane. The MNPs conjugated to histamine were captured in the nanopores via specific reaction between histamine and anti-histamine antibody, resulting in a blocking effect that was amplified by MNPs in the nanopores. The blockage signals could be measured by electrochemical impedance spectroscopy across the nanoporous alumina membrane. The sensing platform had great sensitivity and the limit of detection (LOD) reached as low as 3 nM. This biosensor could be successfully applied for histamine determination in saury that was stored in frozen conditions for different hours, presenting a potentially novel, sensitive, and specific sensing system for food quality assessment and safety support.

Amperometric Biosensor Based on Diamine Oxidase/Platinum Nanoparticles/Graphene/Chitosan Modified Screen-Printed Carbon Electrode for Histamine Detection

This work describes the development and optimization studies of a novel biosensor employed in the detection and quantification of histamine in freshwater fish samples. The proposed biosensor is based on a modified carbon screen-printed electrode with diamineoxidase, graphene and platinum nanoparticles, which detects the hydrogen peroxide formed by the chemical process biocatalysed by the enzyme diamine oxidase and immobilized onto the nanostructurated surface of the receptor element. The amperometric measurements with the biosensor have been implemented in buffer solution of pH 7.4, applying an optimal low potential of +0.4 V. The novel biosensor shows high sensitivity (0.0631 μA·μM), low detection limit (2.54 × 10⁻⁸ M) and a broad linear domain from 0.1 to 300 μM. The applicability in natural complex samples and the analytical parameters of this enzyme sensor have been performed in the quantification of histamine in freshwater fish. An excellent correlation among results achieved with the developed biosensor and results found with the standard method for all freshwater fish samples has been achieved.

A Biginelli-based organic nanoprobe for simultaneous estimation of tyramine and 1,2-diaminopropane: application in real samples

An Ag(i) complex of organic nanoparticles has been developed for the detection of biogenic amines in milk and wine samples.