Colorimetric sensor array for versatile detection and discrimination of model analytes with environmental relevance

In the current work, a rapid, simple, low-cost, and sensitive smartphone-based colorimetric sensor array coupled with pattern-recognition methods was proposed for the determination and differentiation of some organic and inorganic bases (i.e., OH-, CO32-, PO43-, NH3, ClO-, diethanolamine, triethanolamine) as model compounds. The sensing system has been designed based on color-sensitive dyes (Fuchsine, Giemsa, Thionine, and CoCl2) which were used as sensor elements. The color changes of a sensor array were observed by the naked eye. The color patterns were recorded using digital imaging in a three-dimensional (red, green, and blue) space and quantitatively analyzed with color calibration techniques. Distinctive colorimetric patterns for target bases via linear discriminant analysis (LDA) and hierarchical clustering analysis (HCA) were observed. The results indicated that the analytes related to each class (at the different concentration levels in the range of 0.001-1.0 mol L-1) were clustered together in the canonical discriminant plot and HCA dendrogram with high sensitivity and an overall precision of 85%. Furthermore, the first function factor of LDA correlated with the concentration of each target analyte in a correlation coefficient (R2) range of 0.864-0.996. These described procedures based on the colorimetric sensor array technique could be a promising candidate for practical applications in package technology and facile detection of pollutants.

A paper-based ratiometric fluorescent sensor for NH3 detection in gaseous phase: Real-time monitoring of chilled chicken freshness

A ratiometric fluorescence sensor platform with easy-to-use and accurate is nanoengineered for NH3 quantitative detection and visual real-time monitoring of chicken freshness using smartphones. The ratiometric fluorescent probe formed by combining the zinc ion complex and carbon dots has a double-emitted fluorescence peak. The fluorescence intensity of the complex changed can be clearly observed with the increase of the concentration of ammonia solution under 365 nm wavelength excitation. In order to detect NH3 concentration in gaseous phase, a portable paper-based sensor was designed. The sensor had a good linear relationship with NH3 concentration ranging from 10.0 to 90.0 μmol/L and the LOD value was 288 nM. This fluorescent paper-based sensor was used to check the freshness of chicken breast refrigerated at 4 °C, revealed observable shifts from blue to green. The fluorescent paper-based sensor can detect NH3 concentration in real time and simplify the monitoring process of meat freshness while ensuring accuracy and stability.

Concentration-tuned diverse response to selective biogenic amines using a reusable fluorophore: monitoring protein-rich food spoilage

Maintaining the freshness of food is essential for a healthy and quality life. Nevertheless, it remains a global challenge. Hence, an easy detection and monitoring protocol would be highly desirable. A cyanoacrylic acid (CAA)-based fluorophore is manifested as a reusable platform that responds diversely against different concentrations of selective aliphatic biogenic amines (BAs) in both solution and vapor phases. Slow spoilage of the protein-rich food is progressively monitored through emission shifts visible to the naked eye. This fluorophore provides easy and naked-eye detection of the BA vapor through a change in emission, i.e., red → orange → orange-yellow → cyan → green and quantum yield enhancement, which occur in stepwise increments of vapor concentrations. The probe design includes π-conjugated functionalized fluorescent molecules linked to multiple twisting sites, resulting in both solid and solution-state emission. The attached carboxylic acid responds quickly with selective BAs, mainly putrescine (PUT), cadaverine (CAD), and spermidine (SPM), where the concentration-based emission variation has appeared to be distinct and prominent against PUT [sensitivity (μM): 2 (solution); 3.3 (vapour)]. The selectivity towards diamine can be clarified by the formation of carboxylic acid salts and the consequent proton exchanges between free and protonated amines. In addition, -CN···H interaction is likely to develop within this ammonium carboxylate system, providing extra stability. Such ammonium carboxylate salt formation and gradual change in the molecular arrangement, resulting in symmetry development, are validated by FT-IR and wide-angle X-ray diffraction studies. Besides, this fact is supported by DFT studies that validate intramolecular H-atom exchange between free amine and ammonium salt units. A fluorophore-coated coverslip, filter paper, or silica gel-coated Al-plate is fruitfully utilized to detect the freshness of fish and chicken, which reveals the potential of this probe to prevent food waste and control food safety.

Chromaticity sensor for discriminatory identification of aliphatic and aromatic primary amines based on conformational changes of polyacetylene

The design and construction of suitable sensors that can selectively recognize chemically similar substances such as aliphatic and aromatic amines remain challenging. In this work, we reported a poly(phenylacetylene) bearing two aldehyde pendants as the color indicator for discriminative identification of amines. Reversible Schiff-base reaction of the aldehyde group with the amine resulted in a conformational transition of the polyacetylene backbone from cis-cisoid to cis-transoid, which further achieved a colorimetric change. Thirteen aliphatic amines and aromatic amines had been studied. Compared with aromatic amines, aliphatic amines generally caused the polyene backbone to display perceivable colorimetric change. Steric and electronic effect played a significant role in the colorimetric response. In addition, external environment, including amine content, polymer concentration, and temperature, had influence on the sensitivity of this colorimetric indicator system. The amines-induced colorimetric variation was further demonstrated by the CIELAB color space. Moreover, the colorimetric sensor exhibited excellent reversibility and recyclability.

In Situ Optical Detection of Amines at a Parts-per-Quadrillion Level by Severing the Through-Space Conjugated Supramolecular Domino

Conventional fluorophores suffer from low sensitivity and selectivity in amine detection due to the inherent limitations in their "one-to-one" stoichiometric sensing mechanism. Herein, we propose a "one-to-many" chain reaction-like sensing mechanism by creating a domino chain consisting of one fluorescent molecule (e.g., PTF1) and up to 40 nonemissive polymer chains (pPFPA) comprising over thousand repeating units (PFPA). PTF1 (the domino trigger) interacts with adjacent PFPA units (the following blocks) through polar-π interactions and initiates the domino effect, creating effective through-space conjugation along pPFPA chains and generating amplified yellow fluorescent signals through charge transfer between PTF1 and pPFPA. Amine exposure causes rapid dismantling of the fluorophore-pPFPA-based domino chain and significantly reduces the amplified emissions, thus providing an ultrasensitive method for detecting amines. Relying on the above merits, we achieve a limit of detection of 177 ppq (or 1.67 × 10-12 M) for triethylamine, which is nearly 4 orders lower than that of previous methods. Additionally, the distinct reactivity of pPFPA toward different amines allows for the discrimination of primary, secondary, and tertiary amines. This study presents a "domino effect" sensing mechanism that has not yet been reported and provides a general approach for chemical detection that is beyond the reach of conventional methods.

A Chromo-fluorogenic Probe for Selective Detection of Picric Acid Alongside Its Recovery by Aliphatic Amines and Construction of Molecular Logic Gates

Nitroaromatic compounds are illicit explosive chemicals. For environmental security and homeland safety, selective and sensitive identification of these secondary-class explosives has been a reason for the exhaustive research arena of chemists for about a decade. We introduced a sensitive optical sensor with desalted neutral red (NR) dye. After ingressing picric acid (PA) in acetonitrile, the probe becomes non-fluorescent, displaying a colorimetric change from yellow to pink. The quenched phenomena and the changed color were re-established with aliphatic amine, trimethylamine (TEA). The reversibility is produced cyclically, both in fluorimetrically and spectrophotometrically. The detection limit for PA with our probe comes out as 0.639 µM; this value is significantly lower than many chemosensors available in the literature. Also, NR-stained filter paper strips-based test kit analysis has been deployed as a displayable photonic device for in-situ detection of PA. Furthermore, the whole system was conceptualized to produce single input, single output, and double input single output logic gates, which can be applied to digital devices. The chronological input manner as NTP (NR- TEA-PA) pushed us to configure a molecular keypad lock system, the basis of digital locking devices. The repeatable & reversible detection system exhibits "Write read- Erase-read Write-read' type memory devices.

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

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

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

Recent Advances in Chemodosimeters Designed for Amines

The analysis of amines has long been a very important task in science, industry, and healthcare. To date, this task has been accomplished by using expensive and time-consuming methods. Colorimetric and fluorescent chemodosimeters enable the fast, accurate, and sensitive analysis of various species with inexpensive instruments or the naked eye. Accordingly, the studies on these probes have gained great momentum in the last 20 years. In this review, amine chemodosimeters developed in the last 10 years were investigated. The investigated chemodosimeters are metal-free structures based on small organic compounds. The strategies for the detection, differentiation, and quantification of amines were discussed by considering the reaction types.

A combination of a graphene quantum dots-cationic red dye donor-acceptor pair and cucurbit[7]uril as a supramolecular sensor for ultrasensitive detection of cancer biomarkers spermine and spermidine

In a unique approach, the combination of a donor-acceptor pair of hydroxy graphene quantum dots (GQDs-OH) and a red-emissive donor-two-acceptor (D-2-A) type dye with pyridinium units (BPBP) and the well-known host cucurbit[7]uril (CB[7]) has been exploited as a supramolecular sensing assembly for the detection of cancer biomarkers spermine and spermidine in aqueous media at the sub-ppb level based on the affinity-driven exchange of guests from the CB[7] portal. In the binary conjugate, green fluorescent GQDs-OH transfers energy to trigger the emission of the dye BPBP and itself remains in the turn-off state. CB[7] withdraws the dye from the surface of GQDs-OH by strong host-guest interactions with its portal, making GQDs-OH fluoresce again to produce a ratiometric response. In the presence of spermine (SP) or spermidine (SPD), their strong affinity with CB[7] forces the ejection of the fluorophore to settle on the GQDs-OH surface, and the strong green emission of GQDs-OH turns off to device a supramolecular sensor for the detection of SP/SPD. The DFT studies revealed interesting excited-state charge-transfer conjugate formation between BPBP and GQDs leading to turn-on emission of the dye, and further supported the stronger binding modes of BPBP-CB[7], indicating the retrieval of the emission of GQDs. The assembly-disassembly based sensing mechanism was also established by Job's plot analysis, particle size analysis, zeta potential, time-resolved spectroscopy, ITC studies, microscopic studies, etc. The supramolecular sensing assembly is highly selective to SP and SPD, and showed nominal interference from other biogenic amines, amino acids, various metal ions, and anions. The limits of detection (LODs) were 0.1 ppb and 0.9 ppb for spermine and spermidine, respectively. The potential for the real-world application of this sensing assembly was demonstrated by spiking SP and SPD in human urine and blood serum with a high %recovery.

Water-soluble optical sensors: keys to detect aluminium in biological environment

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

Benzothiazole derivatives based colorimetric and fluorescent probes for detection of amine/ammonia and monitoring the decomposition of urea by urease

Amines play critical roles in chemical, agrochemical and pharmaceutical industries. However, volatile amine vapours cause widespread pollution and threaten human health. An efficient, highly sensitive and recyclable sensor for monitoring amine vapours is highly demanded. Typically, 2-(2-hydroxy-5-methyl) benzothiazole (HBT) derivates exhibit excellent aggregation-induced emission (AIE) phenomena in keto form originated from a unique excited-state intramolecular proton transfer (ESIPT) process. In this work, we have designed and synthesized two HBT-based fluorescent probes for ratiometric detection toward amine vapours and ammonia. In addition, the detection limits for ammonia were calculated as 226 ppm and 13 ppm respectively. Additionally, the test strips and electrospinning film dopped with fluorescent probes were utilized to recognize amine vapours and ammonia colorimetric with high sensitivity in solid states. According to the above characteristics, probes could monitor the biological activity of urease conveniently and rapidly.

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.

Aromatic fluorine atom-induced highly amine-sensitive trimethine cyanine dye showing colorimetric and ratiometric fluorescence change

The prepared ring-perfluorinated trimethine cyanine dye 2a has a significantly higher response to n-hexylamine than the non-fluorinated dye 2b, and exhibited a dual change in the solution and on filter paper and fluorescence color at widely shifted wavelengths, visible to the naked eye.

Development of a novel chromophore reaction-based fluorescent probe for biogenic amines detection

Biogenic amines (BAs) are important biomarkers to monitor meat spoilage. However, the design of efficient BA fluorescent probes with distinct colorimetric and ratiometric fluorescent dual-channels is still a critical challenge because of similar chemical properties and basicity between BAs and other amines. Herein, pyrrolopyrrole cyanine (PPCy-1) is reported to display distinctly high reactivity toward BAs through an ultrasensitive irreversible chromophore reaction for the first time. The reaction mechanism is ascribed to synergistic aza-Michael addition and B-N detachment, followed by hydrolysis to produce low-conjugated diketopyrrolopyrrole and heteroaromatic acetonitrile compounds. As a result, colorimetric and ratiometric fluorescent dual-channel (Δλ_ab = 188 nm and Δλ_em = 151 nm) signals and a limit of detection up to 62.1 nM level for BA solution are acquired. In addition, the colorimetric detection of volatile amine vapor using the PPCy-1-loaded filter paper, showing a color change from green to yellow, is feasible. A simple and cost-effective fluorescence "turn on" method using the filter paper or the CAD-40 resin loaded with PPCy-1 to detect TVB (total volatile bases) originating from shrimp spoilage is further demonstrated.

Synthesis of Catechol Derived Rosamine Dyes and Their Reactivity toward Biogenic Amines

Functional organic dyes play a key role in many fields, namely in biotechnology and medical diagnosis. Herein, we report two novel 2,3- and 3,4-dihydroxyphenyl substituted rosamines (3 and 4, respectively) that were successfully synthesized through a microwave-assisted protocol. The best reaction yields were obtained for rosamine 4, which also showed the most interesting photophysical properties, specially toward biogenic amines (BAs). Several amines including n- and t-butylamine, cadaverine, and putrescine cause spectral changes of 4, in UV–Vis and fluorescence spectra, which are indicative of their potential application as an effective tool to detect amines in acetonitrile solutions. In the gas phase, the probe response is more expressive for spermine and putrescine. Additionally, we found that methanolic solutions of rosamine 4 and n-butylamine undergo a pink to yellow color change over time, which has been attributed to the formation of a new compound. The latter was isolated and identified as 5 (9−aminopyronin), whose solutions exhibit a remarkable increase in fluorescence intensity together with a shift toward more energetic wavelengths. Other 9-aminopyronins 6a, 6b, 7a, and 7b were obtained from methanolic solutions of 4 with putrescine and cadaverine, demonstrating the potential of this new xanthene entity to react with primary amines.

Fluorescent chameleon labels for bioconjugation and imaging of proteins, nucleic acids, biogenic amines and surface amino groups. a review

Chameleon labels (ChLs) possess the unique property of changing (visible) color and fluorescence on binding to amino groups of biomolecules. MostChLs react with primary aliphatic amino groups such as those in lysine or with amino groups artificially introduced into polynucleic acids or saccharides, but someothers also react with secondary amino groups. Under controlled circumstances, the reactions are fairly specific. The review is subdivided into the following sections: (1) An introduction and classification of fluorescent labels; (2) pyrylium labels that undergo shortwave color changes upon labelling, typically from blue to red; (3) polymethine type of labels (that also undergo shortwave color changes, typically from green to blue; (4) various other (less common) chromogenic and fluorogenic systems; (5) hemicyanine labels that undergolongwavecolor changes, typically from yellow to purple; (6) the application of ChLs to labeling of proteins and oligonucleotides; (7) applications to fluorometric assays and sensing; (8) applications to fluorescence imaging of biomolecules; (9) applications in studies on affinity interactions (receptor-ligand binding); (10) applications in surface and interface chemistry; and (11) applications in chromatography, electrophoresis and isotachophoresis of biomolecules.

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

A new ESIPT-based fluorescent probe for the highly sensitive detection of amine vapors

A new ESIPT-based fluorescent probe has been developed as a rapid, highly sensitive, and selective sensor for amine vapors.

A review on chemical and electrochemical methodologies for the sensing of biogenic amines

Biogenic amines (BA) are biomolecules of low molecular weight with organic basic functionalities (amine group) that are formed by the microbial decarboxylation of amino acids of fermented food/beverages. Hence BAs are an important indicator in estimating the freshness and quality of meat, seafood, and industrial food products with high protein content. The reaction of BAs with nitrites available in certain meat products forms nitrosoamine, a carcinogenic compound. Hence BAs are in general considered to be a food hazard and monitoring the level of BAs in food samples becomes crucial as their high concentrations may lead to health problems. This review offers an overview of the available chemical and electrochemical methods that are typically used for the sensing of BAs in food samples. Certain compounds are known to selectively interact with BAs via chemical or non-covalent interactions and these interactions are often accompanied by fluorescence or visible color changes (sometimes visual detection) that could be monitored/assessed using a fluorescence spectrophotometer or UV-vis spectrophotometer (colorimetric methods). The colorimetric methods are limited by sensitivity and selectivity as they are based on straight-forward chemical reactions. In the case of electrochemical sensing of BAs, mediators are often used which undergo oxidation/reduction to produce intermediates that could interact with BAs accompanied by changes in their electrochemical potential. Overall, this review summarizes the available chemical and electrochemical strategies towards the sensing of BAs with a discussion on further prospects.

Aggregation Induced Emission Switching Based Ultrasensitive Ratiometric Detection of Biogenic Diamines Using a Perylenediimide-Based Smart Fluoroprobe

In recent years, the widely explored phenomenon "aggregation-induced emission (AIE)" has played a crucial role in the development of luminescent materials for light-emitting applications. In the same direction, the contribution of its sister concept "AIE switching" has been impressive. In comparison, the application of this concept in the field of biosensing or bioimaging is still in its infancy. Therefore, to shed light into the sensing of bioanalytes, we have developed a new perylenediimide (PDI)-based small fluorescent probe, benzoannulated PDI (Bp(Im)₂MA), that selectively detects diamines and biogenic amines (BAs) in solution via an "AIE-switching" phenomenon. The synthesized probe containing the bay-annulated anhydride moiety exhibits strong cyan emission in solution. In the mechanism, we have shown that the terminal free amine group of BAs readily reacts with a highly reactive anhydride moiety, which opens the cyclic anhydride moiety. In the open conformation, the free amine group along with a carboxylate group modulates the polarity of the system strikingly. Because of this induced polarity, the monomer of Bp(Im)₂MA-BAs conjugate aggregated in solution, thereby exhibiting a significant change in emission property in solution. This method may also be called a very simple and straightforward "naked eye" detection of BAs in solution, with a nanomolar detection limit. A detailed spectroscopic and microscopic investigation demonstrated the existence of the aggregated state. As the reporter dye also emits strongly in the solid state (yellowish orange), it therefore instantly made vapor-phase detection of BAs feasible. Finally, this vapor-phase detection of BAs by the probe was applied very effectively in the determination of spoilage of raw fish.

Perylene Bisimide Aggregates as Probes for Subnanomolar Discrimination of Aromatic Biogenic Amines

Perylene bisimide derivatives show peculiar physical chemical features, such as a highly conjugated system, high extinction coefficients and elevated fluorescence quantum yields, making them suitable for the development of optical sensors of compounds of interest. In particular, they are characterized by the tendency to aggregate into π-π stacked supramolecular structures. In this contribution, the behavior of the PBI derivative N, N'-bis(2-(trimethylammonium)ethylene)perylene bisimide dichloride was investigated both in aqueous solution and on solid support. The electronic communication between PBI aggregates and biogenic amines was exploited in order to discriminate aromatic amines down to subnanomolar concentrations by observing PBI fluorescence variations in the presence of various amines and at different concentrations. The experimental findings were corroborated by density functional theory calculations. In particular, phenylethylamine and tyramine were demonstrated to be selectively detected down to 10^-10 M concentration. Then, in order to develop a surface plasmon resonance (SPR) device, PBI was deposited onto a SPR support by means of the layer-by-layer method. PBI was deposited in the aggregated form and was demonstrated to preserve the capability to discriminate, selectively and with an outstanding analytical sensitivity, tyramine in the vapor phase and even if mixed with other aromatic amines.

A highly efficient, colorimetric and fluorescent probe for recognition of aliphatic primary amines based on a unique cascade chromophore reaction

Pyrrolopyrrole aza-BODIPY based nanoaggregates were reported as a highly selective and sensitive probe for recognition of aliphatic primary amines with a novel cascade chromophore reaction. Due to its distinct reaction characteristics, this probe loaded test strip can conveniently detect n-hexylamine vapor and monitor the freshness of shrimp.

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.

Study on the Binding Interaction of the α,α',δ,δ'-Tetramethylcucurbit[6]uril With Biogenic Amines in Solution and the Solid State

1H NMR spectroscopy and MALDI-TOF mass spectrometry were utilized to examine the binding interaction of α,α',δ,δ'-tetramethylcucurbit[6]uril (TMeQ[6]) and six biogenic amines (spermine, spermidine, 2-phenethylamine, tyramine, histamine, and tryptamine). Their 1H NMR spectra both at pD = 7 and pD = 3 revealed that four biogenic amines (spermine, spermidine, 2-phenethylamine, and histamine) can fit in the TMeQ[6] cavity, respectively, and other biogenic amines were located outside of the TMeQ[6] portal. In addition, a solid-state evaluation with single-crystal X-ray diffraction analysis showed the binding interaction of spermine, spermidine, 2-phenethylamine, and tyramine with TMeQ[6].

Naphthalimide-Based DNA-Coupled Hybrid Assembly for Sensing Dipicolinic Acid: A Biomarker for Bacillus anthracis Spores

We have designed and synthesized a novel, water-soluble naphthalimide-histidine receptor (1) with excellent fluorescent properties. Functioning of the synthesized receptor was performed through developing their DNA-receptor hybrid assembly (DRHA), which has shown significant changes in the emission profile upon interactions with dipicolinic acid (DPA), a biomarker for Bacillus anthracis spores. DRHA showed fluorescence enhancement upon binding with DPA with the characteristic of internal charge transfer. It is notable that this assembly exhibited a significant limit of detection (12 nM) toward DPA. The mechanism of sensing was fully defined using ethidium bromide (EtBr) interaction studies as well as Fourier transform infrared spectroscopic analysis, which describes the binding mode of DRHA with DPA. This assembly selectively interacts with DPA over other anions, common cellular cations, and aromatic acids in aqueous media.

A rapid, naked-eye detection of hypochlorite and bisulfite using a robust and highly-photostable indicator dye Quinaldine Red in aqueous medium

A "naked-eye" detection of health hazardous bisulfite (HSO₃^-) and hypochlorite (ClO^-) using an indicator dye (Quinaldine Red, QR) in a wide range of pH is demonstrated. The molecule contains a quinoline moiety linked to an N,N-dimethylaniline moiety with a conjugated double bond. Treatment of QR with HSO₃^- and ClO^-, in aqueous solution at near-neutral pH, resulted in a colorless product with high selectivity and sensitivity. The detection limit was 47.8μM and 0.2μM for HSO₃^- and ClO^- respectively. However, ClO^- was 50 times more sensitive and with 2 times faster response compared to HSO₃^-. The detail characterization and related analysis demonstrate the potential of QR for a rapid, robust and highly efficient colorimetric sensor for the practical applications to detect hypochlorite in water samples.

Spectroscopic investigation of bio-mimetic solvolysis of 6-(N,N-dimethylamino)-2,3-naphthalic anhydride in confined nanocavities

Enzymes are biological catalysts that can vastly accelerate the reaction rate of a substrate by accommodating it within the active site.