Star-Shaped Tripodal Chemosensors for the Detection of Aliphatic Amines

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.

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.

Freshness monitoring of raw fish by detecting biogenic amines using a gold nanoparticle-based colorimetric sensor array

We herein report the quantitative detection of biogenic amines using a gold nanoparticle-based colorimetric chemosensor array for food analysis. The gold nanoparticles are functionalized with carboxylate derivatives, which capture target amines through hydrogen bonds and electrostatic interactions. The simultaneous discrimination of 10 amine derivatives was achieved by a linear discriminant analysis with a 100% correct classification based on the multi-colorimetric response pattern of structural differences. Furthermore, a real sample analysis for raw fish (i.e., tuna) demonstrated highly accurate determination of histamine concentrations by a support vector machine, the result of which was matched with high-performance liquid chromatography. Most importantly, the chemosensor array succeeded in detecting the time-dependent concentration change of histamine in the raw fish, meaning that the decomposition of the fish could be monitored by the colorimetric changes. Hence, the proposed chemosensor array combined with pattern recognition techniques can be a user-friendly analytical method for food freshness monitoring.

A gold nanoparticle-based chemosensor array functionalized with carboxylate derivatives performed freshness monitoring of amines in a fish sample.

A competitive effect of acceptor substitutions on the opto-electronic features of triphenylamine cored di α-cyanostilbene derivatives

Acceptor strength regulates the ICT mechanism via AIE or ACQ processes.

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 reaction-based sensing scheme for volatile organic amine reagents with the chromophoric-fluorogenic dual mode

In this study, we present the classical Michael's addition reaction-based sensing scheme for volatile organic amine reagents such as ethylenediamine, N, N-dimethylethylenediamine and diethylenetriamine using a near-infrared fluorescent dye TCF1. Obvious spectral changes in the UV-vis absorption and fluorescence spectra of TCF1 were observed upon addition of these amine reagents with an effective catalyst DBU, resulting in significant and fast color changes detectable by the naked-eye. TCF1 showed an efficient response to these amine reagents with a low detection limit, especially for diethylenetriamine. NMR and MS spectral analysis proved that the mechanism of the detection was based on the classical Michael addition, which was also verified by the theoretical calculations. In addition, a portable test paper incorporated with TCF1 had also successfully realized the detection of a low concentration of these amine reagents.

Excitation/detection energy controlled anisotropy dynamics in asymmetrically cyano substituted tri-podal molecules

In the present work, the photophysical properties of two series of asymmetrical tri-podal molecules are studied, in order to determine the dependence of energy localization/delocalization phenomena on excitation and detection wavelength, by means of steady state, femtosecond time-resolved fluorescence and anisotropy spectroscopy. The molecules bear triphenylamine as an electron donating core and an acetylenic or olefinic π-conjugated bridge. At the periphery, they are substituted by no, one, two or three -CN groups used as electron acceptors. Thus, the compounds with only one or two -CN groups are asymmetrically substituted. As a comparison, the photophysics of their dipolar and quadrupolar analogues is also presented. The steady state absorption spectra of the asymmetrical tri-podal compounds exhibit a broadening and a low energy shoulder due to the splitting of the excited states. The fluorescence spectra are more red-shifted in the tri-podal molecules with a single -CN group, providing the first evidence of its mostly dipolar nature. Time-resolved anisotropy measurements by using different excitation and detection wavelengths provide clear evidence that the asymmetrical tri-podal molecules with one or two -CN groups behave like octupolar molecules upon high-energy excitation (the initial anisotropy is found 0.1-0.15), while upon low-energy excitation they reveal a behavior expected for linear dipolar or V-shaped quadrupolar molecules (the initial anisotropy is very close to 0.4 and 0.17, respectively). The symmetrical tri-podal compounds with no or three cyano groups, exhibit an anisotropy depolarization time of 2.5 ps attributed to energy hopping. The amplitude of this energy hopping component is wavelength dependent and increases as the excitation is shifted towards the long wavelength edge.

Detection of organic amines using a ratiometric chromophoric fluorescent probe with a significant emission shift

Taking advantages of both the well-known α,β-unsaturated structure and the special nucleophilicity of organic amines toward its acceptor moieties, intramolecular charge transfer as a signaling mechanism is used to design and synthesize a new ratiometric chromophoric fluorescent probe (BI-CA-ID) with large emission shifts toward organic amines. This probe is employed for the detection of organic amines with high selectivity and sensitivity and a “naked-eye” color change (from red to colorless). Ultraviolet–visible and fluorescence spectrometric measurements are used to determine detection limits as low as 0.024 and 0.43 μM. Furthermore, nucleophilic addition of the amine on the α,β-unsaturated of BI-CA-ID indicated that the sensing mechanism occurs via interruption of the π-conjugation.

Homochiral Supramolecular Thin Film from Self-Assembly of Achiral Triarylamine Molecules by Circularly Polarized Light

Here, we report the formation of homochiral supramolecular thin film from achiral molecules, by using circularly polarized light (CPL) only as a chiral source, on the condition that irradiation of CPL does not induce a photochemical change of the achiral molecules. Thin films of self-assembled structures consisting of chiral supramolecular fibrils was obtained from the triarylamine derivatives through evaporation of the self-assembled triarylamine solution. The homochiral supramolecular helices with the desired handedness was achieved by irradiation of circularly polarized visible light during the self-assembly process, and the chiral stability of supramolecular self-assembled product was achieved by photopolymerization of the diacetylene moieties at side chains of the building blocks, with irradiation of circularly polarized ultraviolet light. This work provides a novel methodology for the generation of homochiral supramolecular thin film from the corresponding achiral molecules.

Detecting and imaging of SO2 derivatives in living cells with zero cross-talk colorimetric mitochondria-targeted fluorescent probe

It is well known that excessive levels of sulfur dioxide and its derivatives are connected to diverse diseases. Therefore, developing highly sensitive probes to detect and monitor sulfite in living cells is important for the diagnosis of disease and the study of biochemical processes in vivo. In this report, two zero cross-talk ratiometric fluorescent probes were synthesized (CA-ID-MC and CA-BI-MC), which were derived from carbazole-indolenine π-conjugated system for effective detection of sulfite in living cells. Observably, CA-BI-MC exhibited the largest emission shift of 157 nm from 617 to 460 nm with the addition of various concentrations of sulfite, which is beneficial for high-resolution imaging of the sulfite. CA-BI-MC also exhibits high sensitivity and low cytotoxicity. More importantly, this probe successfully located mitochondria and sensed the sulfite in HeLa cells caused by exogenous stimulation.

Diphenylaminostyryl-substituted quinolizinium derivatives as fluorescent light-up probes for duplex and quadruplex DNA

(E)-2-[1'-((Diphenylamino)styryl)quinolizinium (3a) and 2,2'-{(phenylimino)-bis[(E)-1'',1'''-styryl]}-bis[quinolizinium] (3b) were synthesized, and their interactions with duplex DNA and quadruplex DNA were investigated with a particular focus on their ability to operate as DNA-sensitive fluorescent probes. Due to the significantly different size and steric demand of these quinolizinium derivatives they exhibit different binding modes. Thus, 3a intercalates into duplex DNA and binds through π stacking to quadruplex DNA, whereas 3b favours groove binding to both DNA forms. The emission intensity of these compounds is very low in aqueous solution, but it increases drastically upon association with duplex DNA by a factor of 11 (3a) and >100 (3b) and with quadruplex DNA by a factor of >100 (3a) and 10 (3b), with emission bands between 600 and 750 nm.

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.

Molecular Organization Induced Anisotropic Properties of Perylene - Silica Hybrid Nanoparticles

Optically active silica nanoparticles are interesting owing to high stability and easy accessibility. Unlike previous reports on dye loaded silica particles, here we address an important question on how optical properties are dependent on the aggregation-induced segregation of perylene molecules inside and outside the silica nanoparticles. Three differentially functionalized fluorescent perylene - silica hybrid nanoparticles are prepared from appropriate ratios of perylene derivatives and tetraethyl orthosilicate (TEOS) and investigated the structure property correlation (P-ST, P-NP and P-SF). The particles differ from each other on the distribution, organization and intermolecular interaction of perylene inside or outside the silica matrix. Structure and morphology of all hybrid nanoparticles were characterized using a range of techniques such as electron microscope, optical spectroscopic measurements and thermal analysis. The organizations of perylene in three different silica nanoparticles were explored using steady-state fluorescence, fluorescence anisotropy, lifetime measurements and solid state polarized spectroscopic studies. The interactions and changes in optical properties of the silica nanoparticles in presence of different amines were tested and quantified both in solution and in vapor phase using fluorescence quenching studies. The synthesized materials can be regenerated after washing with water and reused for sensing of amines.

Langmuir–Blodgett films of perylene bisimide derivatives and fluorescent recognition of diamines

A fluorescent film was constructed with the well-known Langmuir–Blodgett technique, and it showed exceptional sensing performances for some diamine vapors.

A novel low molecular weight supergelator showing an excellent gas adsorption, dye adsorption, self-sustaining and chemosensing properties in the gel state

The article describes the role of a novel amide based supergelator in gelating a wide range of copper salts. The metallogel was highly stable to heat, stress and mineral acids showing an unprecedented colorimetric gel-to gel sensing of amine vapours.

Europium metal–organic frameworks as recyclable and selective turn-off fluorescent sensors for aniline detection

Seven Eu(iii) compounds are ionothermally synthesized and well characterized, among which compounds 4 and 6 behave as highly selective turn-off fluorescent sensors for aniline detection with stable recycle repeatability.

A ratiometric fluorescent probe for detection of biogenic primary amines with nanomolar sensitivity

An ultrasensitive ratiometric fluorescent sensor made of an N,N-dimethylaminonaphthalene anhydride moiety for detection of aliphatic primary amines is reported.

Amine detection with distyrylbenzenedialdehyde-based Knoevenagel adducts

Eight acceptor-substituted distyrylbenzene (DSB) derivatives were obtained by postfunctionalization of dialdehyde precursor 1 using Knoevenagel condensation. Solubility in a water/THF 9:1 mixture was achieved through the addition of branched oligoethylene glycol side chains. The acceptor compounds discriminate primary and secondary amines in aqueous solution. The fluorescence responses were analyzed by the multivariate analysis of variance (MANOVA) protocol, a statistical tool. In contrast to 1, the adducts show reactivity toward secondary and aromatic amines. Nitroolefin 2f is the most active dosimeter molecule. Reaction with amines is completed after less than 3 min, and the limit of detection (LOD) is improved by a factor of 10. Propylenediamine can be detected at 75 μM. This is a 10-fold improvement for the detection limit when compared to the detection limit of the starting dialdehyde.

Selective chemosensing of spermidine based on fluorescent organic nanoparticles in aqueous media via a Fe3+ displacement assay

An organic–inorganic nanohybrid complex of a tripodal complex was used for the selective determination of spermidine and its use in real sample analysis.

A sensitive and efficient trifluoroacetyl-based aromatic fluorescent probe for organic amine vapour detection

Highly reversible, sensitive and efficient trifluoroacetyl-substituted fluorescent probes were designed for discriminating multiple trace organic amine vapours.

Reversible and “fingerprint” fluorescence differentiation of organic amine vapours using a single conjugated polymer probe

By embedding multiple reactive groups onto one polymer, an ultrasensitive and reversible fluorescent probe for different organic amines vapour has been reported.

Riboflavin-based fluorogenic sensor for chemo- and enantioselective detection of amine vapors

A novel turn-on fluorogenic chiral sensory system has been developed using a protonated riboflavin and riboflavin-derived cationic polymer as a fluorophore precursor and a specific amine receptor, respectively, which enables the solid-state chemo- and enantioselective fluorogenic visual detection of primary and secondary amine vapors.

Fast response and highly selective sensing of amine vapors using a luminescent coordination polymer

The first Eu-coordination polymer as a sensory material for the detection of amine vapors with high selectivity and rapid response.

A BODIPY dye as a reactive chromophoric/fluorogenic probe for selective and quick detection of vapors of secondary amines

A new reaction based fluorescence turn-off strategy for detection of secondary amines was developed. The probe shows fast response and high selectivity to secondary amines in solution/film at sub-ppm levels through chromogenic and fluorescent dual-mode signal changes.