Strong Fluorescent Smart Organogel as a Dual Sensing Material for Volatile Acid and Organic Amine Vapors

An L ‐phenylalanine derivative ( C12PhBPCP ) consisting of a strong emission fluorophore with benzoxazole and cyano groups is designed and synthesized to realize dual responses to volatile acid and organic amine vapors. The photophysical properties and self‐assembly of the said derivative in the gel phase are also studied. C12PhBPCP can gelate organic solvents and self‐assemble into 1 D nanofibers in the gels. UV/Vis absorption spectral results show H‐aggregate formation during gelation, which indicates strong exciton coupling between fluorophores. Both wet gel and xerogel emit strong green fluorescence because the cyano group suppresses fluorescence quenching in the self‐assemblies. Moreover, the xerogel film with strong green fluorescence can be used as a dual chemosensor for quantitative detection of volatile acid and organic amine vapors with fast response times and low detection limits owing to its large surface area and amplified fluorescence quenching. The detection limits are 796 ppt and 25 ppb for gaseous aniline and trifluoroacetic acid (TFA), respectively.     

Fluorescence Properties and Exciplex Formation of Emissive Naphthyridine Derivatives: Application as Sensors for Amines

Water-soluble donor–acceptor-type fluorophore 15Nap-Cl having two trifluoromethyl groups and a Cl group on a 1,5-aminonaphthyridine framework was prepared. Fluorophore 15Nap-Cl showed strong solvatochromic fluorescence, and, as the solvent polarity increased, a bathochromic shift was observed accompanied by an increase in the fluorescence quantum yield. In addition, in the presence of amines such as ethylamine, diethylamine, and aniline, further considerable bathochromic shifts in the fluorescence were observed. Density functional calculations identified the source of the fluorescence behavior as exciplex formation between 15-Nap-Cl and the corresponding amine. The fluorescence behavior was exploited to fabricate a sensor that can identify various primary, secondary, and tertiary amines.     

Luminescent Nanofibers Fabricated from Phenanthroimidazole Derivatives by Organogelation: Fluorescence Response towards Acid with High Performance

Nanofibers based on phenanthroimidazole derivatives PCC , PDC , and PSC were fabricated by organogelation processes, and their fluorescence sensory properties towards acid were investigated. It was found that the emission of PCC in the nanofiber‐based film could be quenched significantly upon exposure to gaseous TFA due to the formation of protonated PCC , in which ICT (intramolecular charge transfer) would occur. On the other hand, TFA vapor led to the emitting colors of PDC and PSC in the nanofiber‐based films to turn to yellow and green from sky blue and blue, respectively. Additionally, we found that the decay times of PCC were 0.1 s and 1.9 s in probing the saturated vapor of TFA in nanofiber‐based film and in spin‐coated film, respectively. The results suggested that the high surface‐to‐volume ratio and large interspace in the nanofiber‐based networks favored the enhanced adsorption, accumulation, and diffusion of gaseous molecules, resulting in such a high performance.     

Synthesis of Poly(anilineboronic acid) Nanofibers for Electrochemical Detection of Glucose

Poly(anilineboronic acid) (PABA) nanofibers with U‐shaped and ring‐shaped morphologies have been synthesized successfully by chemical polymerization of 3‐aminophenylboronic acid (APBA) in the presence of cetyltrimethylammonium bromide (CTAB) and NaF. The morphologies and sizes of PABA nanofibers can be controlled by adjusting the synthetic parameters, such as the concentrations of CTAB and APBA. The U‐shaped PABA nanofibers exhibit excellent electrochemical redox activity and high sensitive detection of D ‐glucose in phosphate‐buffered saline stock solution (pH 7.4) because of their high effective surface area as well as the high density of boronic acid groups.

     

Nanofibers as optical sensors for model VOCs dispersed in aqueous phase

Nanofibers mats, prepared from poly(vinyl chloride) (PVC) containing dispersed dye Nile red (NR) were applied in a proof of concept study as optical sensors for Volatile Organic Compounds (VOCs) dispersed in an aqueous phase. Benefiting from the solubility of the dye, and in some cases, also of the polymer in model solvents belonging to the group of VOCs, an increase of emission was observed for increasing solvent concentration in the sample. The optical signal formation was observed regardless if only the dye or both dye and PVC were soluble in the tested solvent. In both cases, high sensitivity emission increases for increasing VOCs present in the aqueous phase were observed within the range of concentration of model analytes: from 200 ppm of m-xylene or from 300 ppm of styrene, to up to ca 1500 ppm. The obtained higher detection limit was lower compared to films of PVC containing the dye due to the lower availability of the material to be dissolved by analyte – solvent. The large surface area of nanofibers was useful in the detection, leading to higher signal changes compared to films.     

The Formation of Organogels and Helical Nanofibers from Simple Organic Salts

Simple organic salts based on aniline‐derived cations and D ‐tartrate anions formed organogels and helical nanofibers. The organic salt (p‐fluoroanilinium)(D ‐tartrate) was found to generate an organogel despite the absence of a hydrophobic alkyl chain, whereas (p‐iodoanilinium)(D ‐tartrate) formed helical nanofibers in braided ropelike structures through a rolling‐up process. The helicity of these nanofibers could be reversed by changing the growth solvent. The driving forces responsible for the formation of the nanofibers were determined to be 1D O?H???O^? hydrogen‐bonding interactions between D ‐tartrate anions and π stacking of anilinium cations, as well as steric hindrance between the hydrogen‐bonded chains.     

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.     

Detection of Explosive Vapors: The Roles of Exciton and Molecular Diffusion in Real‐Time Sensing

Time‐resolved quartz crystal microbalance with in situ fluorescence measurements are used to monitor the sorption of the nitroaromatic (explosive) vapor, 2,4‐dinitrotoluene (DNT) into a porous pentiptycene‐containing poly(phenyleneethynylene) sensing film. Correlation of the nitroaromatic mass uptake with fluorescence quenching shows that the analyte diffusion follows the Case‐II transport model, a film‐swelling‐limited process, in which a sharp diffusional front propagates at a constant velocity through the film. At a low vapor pressure of DNT of ≈16 ppb, the analyte concentration in the front is sufficiently high to give an average fluorophore–analyte separation of ≈1.5 nm. Hence, a long exciton diffusion length is not required for real‐time sensing in the solid state. Rather the diffusion behavior of the analyte and the strength of the binding interaction between the analyte and the polymer play first‐order roles in the fluorescence quenching process.     

Synthesis of Carbon Nanofibers for Mediatorless Sensitive Detection of NADH

Highly sensitive amperometric detection of dihydronicotinamide adenine dinucleotide (NADH) by using novel synthesized carbon nanofibers (CNFs) without addition of any mediator has been proposed. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were applied without any oxidation pretreatment to construct the electrochemical sensor. In amperometric detection of NADH, a linear range up to 11.45 μM with a low detection limit of 20 nM was obtained with the CNF‐modified carbon paste electrode (CNF‐CPE). Good selectivity was exhibited for the simultaneous detection of NADH and its common interferent of ascorbic acid (AA) by differential pulse voltammogram. The attractive electrochemical performance and the versatile preparation process of the CNF‐CPE made it a promising candidate for designing effective NADH sensor.     

Coordination Polymer Nanobelts as an Effective Sensing Platform for Fluorescence‐enhanced Nucleic Acid Detection

In this communication, the application of coordination polymer nanobelts (CPNs) assembled from H₂PtCl₆ and 3,3′,5,5′‐tetramethylbenzidine (TMB) are explored as an effective fluorescent sensing platform for nucleic acid detection for the first time. The suggested method has a high selectivity down to single‐base mismatch. DNA detection is accomplished by the following two steps: (1) CPN binds fluorecent dye‐labeled single‐stranded DNA (ssDNA) probe via both electrostatic attraction and π‐π stacking interactions between unpaired DNA bases and CPN. As a result, the fluorescent dye is brought into close proximity to CPN and substantial fluorescence quenching occurs due to photoinduced electron transfer from the nitrogen atom in CPN to the excited fluorophore. (2) The hybridization of adsorbed ssDNA probe with its target generates a double stranded DNA (dsDNA). The duplex cannot be adsorbed by CPN due to its rigid conformation and the absence of unpaired DNA bases, leading to an obvious fluorescence enhancement.

     

Highly Sensitive Dual‐Mode Fluorescence Detection of Lead Ion in Water Using Aggregation‐Induced Emissive Polymers

A series of fluorene‐based conjugated polymers containing the aggregation‐induced emissive (AIE)‐active tetraphenylethene and dicarboxylate pseudocrown as a receptor exhibits a unique dual‐mode sensing ability for selective detection of lead ion in water. Fluorescence turn‐off and turn‐on detections are realized in 80%–90% and 20% water in tetrahydrofuran (THF), respectively, for lead ion with a concentration as low as 10⁻⁸ m .

     

Electrospun Nanofiber Membranes from 1,8-Naphthimide-Based Polymer/Poly(vinyl alcohol) for pH Fluorescence Sensing

Accurately and sensitively sensing and monitoring the pH in the environment is a key fundamental issue for human health. Nanomaterial and nanotechnology combined with fluorescent materials can be emerged as excellent possible methods to develop high-performance sensing membranes and help monitor pH. Herein, a series of fluorescent nanofiber membranes (NFMs) containing poly-1,8-naphthimide derivative-3-[dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate (PNI-SBMA) are fabricated by electrospinning the solution of PNI-SBMA blended with poly(vinyl alcohol) (PVA). The surfactant-like functionalities in side chains of PNI-SBMA endow the NFMs with outstanding hydrophilicity, and the naphthimide derivatives are sensitive to pH by photoinduced electron transfer effect, which contribute to highly efficient pH fluorescence sensing applications of NFMs. Specifically, the PNI-SBMA/PVA NFM with a ratio of 1:9 (NFM2) shows high sensitivity and good cyclability to pH. This work demonstrates an effective strategy to realize a fluorescent sensor NFM that has a fast and sensitive response to pH, which will benefit its application of pH sensor monitoring in the water treatment process.     

Direct In Situ Determination of Ascorbic Acid in Fruits by Screen‐Printed Carbon Electrodes Modified with Nylon‐6 Nanofibers

A simple sensing unit based on a disposable screen printed carbon electrode coated by an electrospun nylon‐6 nanofibrous membrane was developed for in situ selective determination of ascorbic acid (AA) in different types of fruits. The membrane, prepared by electrospinning, represents a selective barrier to possible interferents, such as phenolic compounds, allowing an improved selectivity towards AA. No sample preparation and/or dilution is necessary since the new device is applied directly “pricking” the fruit with the electrode. A good correlation was obtained between the amperometric in situ method and a reference chromatographic methodology (HPLC‐UV) when applied to various fruit samples.     

Carbonized Hemoglobin Nanofibers for Enhanced H2O2 Detection

Electrospun hemoglobin (Hb) microbelts were used as a novel precursor to produce a new class of carbon nanofibers (Hb‐CNFs) containing Fe species (Fe₂O₃ and/or Fe‐N₄ moiety). The Hb‐CNFs modified glassy carbon electrode (Hb‐CNFs/GCE) exhibits significant oxidation/reduction towards H₂O₂. The observed H₂O₂ oxidation/reduction starting at ca. +0.26 V and +0.15 V (vs. Ag/AgCl) are significantly lower than the values observed at other CNFs modified GCE. The Hb‐CNFs/GCE was also applied to the amperometric detection of H₂O₂ and the results showed fast response, high sensitivity, excellent reproducibility, good selectivity, and wide dynamic range with good limit of detection.     

Fluorescence Sensing of Amine Vapors Using a Cationic Conjugated Polymer Combined with Various Anions

A series of conjugated cationic polymers, differentiated only by their accompanying counter‐anions, was prepared and characterized. The choice of counter‐anion (CA) was found to drastically impact the solubility of the polymers and their optical properties in solution and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concentrations, and a mini‐array with CAs as variable elements was found to be able to differentiate amines with good fidelity.     

Hydrogels for the Detection and Management of Protease Levels

The design of hydrogels that simultaneously report protease activity and remove excess protease from solution is elucidated. The hydrogels, based on amino‐PEGA, combine enzyme‐specific peptides flanked with FRET complimented by charged amino acid residues that facilitate protease uptake via short range electrostatic interactions. Enzymatic response was analysed using a combination of fluorescence spectroscopy, two‐photon microscopy and UV/Vis spectroscopy. An optimised elastase‐responsive hydrogel resulted in lowering of elastase levels below those typical of chronic wounds. The versatility of the modular‐design approach was demonstrated by development of matrix metalloprotease and chymotrypsin sensitive systems.

     

Inverted Opal Fluorescent Film Chemosensor for the Detection of Explosive Nitroaromatic Vapors through Fluorescence Resonance Energy Transfer

This paper reports an inverted opal fluorescence chemosensor for the ultrasensitive detection of explosive nitroaromatic vapors through resonance‐energy‐transfer‐amplified fluorescence quenching. The inverted opal silica film with amino ligands was first fabricated by the acid–base interaction between 3‐aminopropyltriethoxysilane and surface sulfonic groups on polystyrene microsphere templates. The fluorescent dye was then chemically anchored onto the interconnected porous surface to form a hybrid monolayer of amino ligands and dye molecules. The amino ligands can efficiently capture vapor molecules of nitroaromatics such as 2,4,6‐trinitrotoluene (TNT) through the charge‐transfer complexing interaction between electron‐rich amino ligands and electron‐deficient aromatic rings. Meanwhile, the resultant TNT–amine complexes can strongly suppress the fluorescence emission of the chosen dye by the fluorescent resonance energy transfer (FRET) from the dye donor to the irradiative TNT–amino acceptor through intermolecular polar–polar resonance at spatial proximity. The quenching response of the highly ordered porous films with TNT is greatly amplified by at least 10‐fold that of the amorphous silica films, due to the interconnected porous structure and large surface‐to‐volume ratio. The inverted opal film with a stable fluorescence brightness and strong analyte affinity has lead to an ultrasensitive detection of several ppb of TNT vapor in air.     

Complex‐Formation‐Enhanced Fluorescence Quenching Effect for Efficient Detection of Picric Acid

Amine‐functionalized α‐cyanostilbene derivatives (Z)‐2‐(4‐aminophenyl)‐3‐(4‐butoxyphenyl)acrylonitrile (ABA) and (Z)‐3‐(4‐butoxyphenyl)‐2‐[4‐(butylamino)phenyl]acrylonitrile (BBA) were designed for specific recognition of picric acid (PA), an environmental and biological pollutant. The 1:1 host–guest complexes formed between the chemosensors and PA enhanced fluorescence quenching, thus leading to sensitive and selective detection in aqueous media and the solid phase.     

Semiconducting Fabrics by In Situ Topochemical Synthesis of Polydiacetylene: A New Dimension to the Use of Organogels

A diyne functionalized 4,6‐O‐benzylidene β‐d ‐galactopyranoside gelator, which can align its diyne motifs upon self‐assembly (gelation) have been synthesized. The organogel formed by this gelator undergoes topochemical polymerization to polydiacetylene (PDA) under photoirradiation. This strategically designed gelator has been used to make semi‐conducting fabrics. By developing the organogel on the fabrics, the gelator molecules were made not only to self‐assemble on the fibers, but also to adhere to fabrics through hydrogen bonding. UV irradiation of the gel‐coated fabric/fiber resulted in the formation of PDA on fibers. The benzylidene motif could be deprotected to get PDA with pendant free sugars that strongly bind to the cotton fibrils through multiple hydrogen bonds. Conductivity measurements revealed the semiconducting nature of these fabrics.