Total Protein Determination by Recovery Fluorescence of Trinitrotoluene-Quenched Protein-Functionalized Gold Nanoclusters

Determination of total protein content is very important for clinical, pharmaceutical and food chemistry, and the simplicity and rapidity of the existing total protein content assays should be improved. Here, a novel fluorescent sensor for total protein content measurement was described using near-infrared emitting fluorescent gold nanoclusters, which were prepared with egg whites. Trinitrotoluene served as highly efficient quencher to quench the fluorescence of gold nanoclusters. Interestingly, the trinitrotoluene-protein complex that formed by premixing of trinitrotoluene and protein-containing real samples maintained the fluorescence of gold nanoclusters. These new findings provided a novel mechanism to design a fluorescence sensor for determination of total protein levels in various real samples. With available and low-cost bovine serum albumin as reference, the obtained standard curve for total protein determination indicated a linear range of 0.1-3.5 g L- 1 with a detection limit of 0.06 g L- 1 (3σ rule) and a correlation efficiency (R2) of 0.9850. The applicability of the proposed sensor was validated by determination of total protein levels in real samples. Comparison with the existing spectrophotometric methods, the proposed sensor is advantageous of simplicity, rapidity, and cost-effectiveness.

A Novel Indolium-Based Fluorescent Probe for Fast Detection of Cyanide

A novel indolium-based fluorescent probe for the detection of CN- was developed based on the conjugation of 1, 2, 3, 3-Tetramethyl-3H-indolium iodide and 2-acetyl benzothiophene. The introduction of external CN- caused a nucleophilic attack to the quaternary amine salt structure in the probe and resulted in the departure of iodide ions and the steric rotation of the index salt group, which caused fluorescence quenching. The titration experiments showed that the probe had rapid qualitative and quantitative analysis capabilities for CN-. Moreover, the relevant biocompatibility experiments also demonstrated the potential application value of the probe.

A Gelation-Induced Enhanced Emission Active Stimuli Responsive and Superhydrophobic Organogelator: "Turn-On" Fluorogenic Detection of Cyanide and Dual-Channel Sensing of Nitroexplosives on Multiple Platforms

A pyrene-based highly emissive low-molecular-weight organogelator, [2-(4-fluorophenyl)-3-(pyren-1-yl)acrylonitrile] (F1), is presented, which divulges thixotropic and thermochromic fluorescence switching via reversible gel-to-sol transition and tremendous superhydrophobicity (mean contact angles: 149-160°), devoid of any gelling and/or hydrophobic units. The rationale for the design strategy reveals that the restricted intramolecular rotation (RIR) in J-type self-assembly promotes F1 for the prolific effects of aggregation- and gelation-induced enhanced emission (AIEE and GIEE). Meanwhile, hindrance in charge transfer via the nucleophilic reaction of cyanide (CN^-) on the C═C unit in F1 facilitates the selective fluorescence "turn-on" response in both solution [9:1 (v/v) DMSO/water] and solid state [paper kits] with significantly lower detection limits (DLs) of 37.23 nM and 13.4 pg/cm², respectively. Subsequently, F1 discloses CN^- modulated colorimetric and fluorescence "turn-off" dual-channel response for aqueous 2,4,6-trinitrophenol (PA) and 2,4-dinitrophenol (DNP) in both solution (DL = 49.98 and 44.1 nM) and solid state (DL = 114.5 and 92.05 fg/cm²). Furthermore, the fluorescent nanoaggregates of F1 in water and its xerogel films permit a rapid dual-channel "on-site" detection of PA and DNP, where the DLs ranged from nanomolar (nM) to sub-femtogram (fg) levels. Mechanistic insights reveal that the ground-state electron transfer from the fluorescent [F1-CN] ensemble to the analytes is responsible for anion driven sensory response, whereas the unusual inner filter effect (IFE) driven photoinduced electron transfer (PET) was responsible for self-assembled F1 response toward desired analytes. Additionally, the nanoaggregates and xerogel films also detect PA and DNP in their vapor phase with reasonable percentage of recovery from the soil and river water samples. Therefore, the elegant multifunctionality from a single luminogenic framework allows F1 to provide a smart pathway for achieving environmentally benign real-world applications on multiple platforms.

Highly Sensitive and Selective Detection of Melatonin in Biofluids by Antipyrine Based Fluorophore

A simple fluorescent based organic fluorophore was synthesized and it shows significant fluorescent intensity with melatonin (MLN). Hence, it was applicable to the detection of MLN by colorimetric and fluorimetric techniques at neutral pH. Under optimized experimental condition, the synthesized organic fluorophore detects MLN selectively in the presence of other interfering biomolecules through ICT mechanism. The melatonin sensing mechanism is supported by DFT and ¹H-NMR titration. Based on the findings, this method can be applied to design a simple clinical diagnostic tool for MLN.

Highly Selective and Sensitive Colorimetric and Fluorescent Chemosensors for Rapid Detection of Cyanide Anions in Aqueous Medium: Investigation on Supramolecular Recognition of Tweezer‑shaped Salophenes

Three tweezer‑shaped salophenes having catechols (1), phenols (2) and anisoles (3) units in conjunction to the dipodal Schiff bases have been applied for the optical sensing of cyanide (CN¯) ions in CH3CN-H2O (7:3) as solvent of choice. Among them, compounds 1 and 2 recognized CN¯, relying on distinct color and spectral changes. They are easy-to-use probes that exhibit extremely high sensitivity (limit of detection = 1-10 nM), rapid response (5 s) and excellent selectivity. Moreover, the visual detection and concentration determination of CN¯ by solution test kits of both sensors are the advantages for the practical applications. Based on the fluorescence and NMR spectroscopy, as well as the OH¯ and reversibility experiments, the explicit effect of hydroxyl groups on sensing and as well the different recognition of 1 and 2 toward CN¯ ions was proved. While probe 1 senses CN¯ via deprotonation, probe 2 recognizes it through an intramolecular aldimine condensation cyclization, leading to formation of anions of dihydroxyquinoxaline 4. This chemodosimetry is being reported for the first time in a Schiff's base. Furthermore, the similarity of fluorescence and NMR responses of 2 and 4 toward CN¯ supports the proposed process.

Hexaarylbenzene based high-performance p-channel molecules for electronic applications

Hexaarylbenzene-based molecules find potential applications in organic electronics due to wider energy gap, high HOMO level, higher photoconductivity, electron-rich nature, and high hole-transporting property. Due to the unique propeller structure, these molecules show low susceptibility towards self-aggregation. This property can be tailored by proper molecular engineering by the incorporation of appropriate groups. Therefore, hexaarylbenzene chromophores are widely used as the materials for high-efficiency light-emitting materials, charge transport materials, host materials, redox materials, photochemical switches, and molecular receptors. This review highlights the diverse structural modification techniques used for the synthesis of symmetrical and unsymmetrical structures. Also, the potential applications of these molecules in organic light-emitting diodes, organic field-effect transistors, organic photovoltaics, organic memory devices, and logic circuits are discussed.

'Light-Up' AIE-Active Materials: Self-Assembly, Molecular Recognition and Catalytic Applications

Aggregation induced emission enhancement (AIEE) is one of the most widely explored phenomena to develop 'light up' (fluorescent) materials having potential applications in the field of supramolecular chemistry, analytical chemistry and material chemistry. By applying the principles of host-guest chemistry, we have developed a variety of aggregation induced emission (AIE/AEE) active materials having specific affinity for metal ions, electron deficient/electron rich analytes. The interactions between AIE active assemblies and metal ions are further tuned to prepare nanohybrids having potential applications as catalytic/photocatalytic systems in various organic transformations under eco-friendly conditions. This account summarizes various design strategies developed in our labortary for the preparation of AIE/AEE active building blocks having sensing and catalytic applications.

Fast Detection of 2,4,6-Trinitrotoluene (TNT) at ppt Level by a Laser-Induced Immunofluorometric Biosensor

The illegal use of explosives by terrorists and other criminals is an increasing issue in public spaces, such as airports, railway stations, highways, sports venues, theaters, and other large buildings. Security in these environments can be achieved by different means, including the installation of scanners and other analytical devices to detect ultra-small traces of explosives in a very short time-frame to be able to take action as early as possible to prevent the detonation of such devices. Unfortunately, an ideal explosive detection system still does not exist, which means that a compromise is needed in practice. Most detection devices lack the extreme analytical sensitivity, which is nevertheless necessary due to the low vapor pressure of nearly all explosives. In addition, the rate of false positives needs to be virtually zero, which is also very difficult to achieve. Here we present an immunosensor system based on kinetic competition, which is known to be very fast and may even overcome affinity limitation, which impairs the performance of many traditional competitive assays. This immunosensor consists of a monolithic glass column with a vast excess of immobilized hapten, which traps the fluorescently labeled antibody as long as no explosive is present. In the case of the explosive 2,4,6-trinitrotoluene (TNT), some binding sites of the antibody will be blocked, which leads to an immediate breakthrough of the labeled protein, detectable by highly sensitive laser-induced fluorescence with the help of a Peltier-cooled complementary metal-oxide-semiconductor (CMOS) camera. Liquid handling is performed with high-precision syringe pumps and chip-based mixing-devices and flow-cells. The system achieved limits of detection of 1 pM (1 ppt) of the fluorescent label and around 100 pM (20 ppt) of TNT. The total assay time is less than 8 min. A cross-reactivity test with 5000 pM solutions showed no signal by pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). This immunosensor belongs to the most sensitive and fastest detectors for TNT with no significant cross-reactivity by non-related compounds. The consumption of the labeled antibody is surprisingly low: 1 mg of the reagent would be sufficient for more than one year of continuous biosensor operation.

β-Octaalkoxyporphyrins: Versatile fluorometric sensors towards nitrated explosives

Real time detection of explosive residues is important to mitigate increasing security threats. Therefore, systematic studies are essential to optimize the performance of sensors. In this work, we have explored β-octamethoxyporphyrin and β-octabutoxyporphyrin to evaluate the effect of alkoxy groups in solution and in vapor phase sensing of nitrated explosives. Our systematic studies revealed a marked difference in sensitivity of these free-base porphyrins in solution state and vapor phase sensing of nitrated explosives simply by modulation of alkyl chain lengths. Alkoxyporphyrins exhibit very good sensitivity towards not only nitro aromatics but also alkyl nitro explosive taggants compared to β-octaethylporphyrin. Therefore, alkoxyporphyrins may act as versatile fluorescence turn-off based chemical sensors for nitrated explosives.

Highly Sensitive Ratiometric Chemosensor and Biomarker for Cyanide Ions in the Aqueous Medium

A newly designed cyanide-selective chemosensor based on chromone containing benzothiazole groups [3-(2,3-dihydro-benzothiazol-2-yl)-chromen-4-one (DBTC)] was synthesized and structurally characterized by physico-chemical, spectroscopic, and single-crystal X-ray diffraction analyses. The compound DBTC can detect cyanide anions based on nucleophilic addition as low as 5.76 nM in dimethyl sulfoxide-N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer (20 mM, pH 7.4) (v/v = 1:3). The binding mode between receptor DBTC and cyanide nucleophile has also been demonstrated by experimental studies using various spectroscopic tools and theoretical studies, and the experimental work has also been verified by characterizing one supporting compound of similar probable structure of the final product formed between DBTC and cyanide ion (DBTC-CN compound) by single-crystal X-ray analysis for detailed structural analyses. In theoretical study, density functional theory procedures have been used to calculate the molecular structure and the calculation of the Fukui function for evaluation of the electrophilic properties of each individual acceptor atom. Furthermore, the efficacy of the probe (DBTC) to detect the distribution of CN^- ions in living cells has been checked by acquiring the fluorescence image using a confocal microscope. Notably, the paper strips with DBTC were prepared, and these could serve as efficient and suitable CN^- test kits successfully.

AIEE Active Donor-Acceptor-Donor-Based Hexaphenylbenzene Probe for Recognition of Aliphatic and Aromatic Amines

In the present investigation, an intramolecular charge transfer (ICT) and aggregation induced emission enhancement (AIEE) active donor-acceptor-donor (D-A-D) system 5 having fumaronitrile as the acceptor and hexaphenylbenzene (HPB) as the donor moieties joined through rotatable phenyl rings has been designed and synthesized that is highly emissive in the solid state and exhibits stimuli-responsive reversible piezochromic behavior upon grinding and heating. Because of its AIEE characteristics, HPB derivative 5 undergoes aggregation to form fluorescent aggregates in mixed aqueous media that exhibit ratiometric fluorescence response toward aliphatic amines (primary/secondary/tertiary) and turn-off response toward aromatic amines and hence differentiates between them. Further, the solution-coated portable paper strips of derivative 5 showed pronounced and sensitive response toward aromatic and aliphatic amines with a detection limit in the range of picogram and nanogram level, respectively.

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

“Not quenched” aggregates of a triphenylene derivative for the sensitive detection of trinitrotoluene in aqueous medium

“Not quenched” porous aggregates of triphenylene derivative 4 have been utilized for the detection of TNT in solution, solid and vapour phases with detection limits of 22.7 attograms cm⁻².

Hexaphenylbenzene-Stabilized Luminescent Silver Nanoclusters: A Potential Catalytic System for the Cycloaddition of Terminal Alkynes with Isocyanides

A hexaphenylbenzene (HPB)-based derivative bearing thiol groups has been designed and synthesized that undergoes aggregation-induced emission enhancement in mixed aqueous media to form rodlike fluorescent aggregates. These rodlike aggregates behave as a "not quenched" probe for the detection of silver ions and further act as reactors and stabilizers for reducing-agent-free preparation of blue luminescent silver nanoclusters at room temperature. The utilization of fluorescent supramolecular aggregates for the preparation of Ag NCs in mixed aqueous media is unprecedented in the literature. Moreover, the wet chemical method that we are reporting in the present paper for the preparation of luminescent silver nanoclusters is better than the other methods reported in the literature. Further, these in situ generated Ag NCs showed exceptional catalytic activity in the preparation of pyrroles involving cocyclization of isocyanides and terminal alkynes. Interestingly, the catalytic efficiency of in situ generated Ag NCs was found to be better than the other catalytic systems reported in the literature.

Advances in explosives analysis--part I: animal, chemical, ion, and mechanical methods

The number and capability of explosives detection and analysis methods have increased substantially since the publication of the Analytical and Bioanalytical Chemistry special issue devoted to Explosives Analysis (Moore and Goodpaster, Anal Bioanal Chem 395(2):245-246, 2009). Here we review and critically evaluate the latest (the past five years) important advances in explosives detection, with details of the improvements over previous methods, and suggest possible avenues towards further advances in, e.g., stand-off distance, detection limit, selectivity, and penetration through camouflage or packaging. The review consists of two parts. This part, Part I, reviews methods based on animals, chemicals (including colorimetry, molecularly imprinted polymers, electrochemistry, and immunochemistry), ions (both ion-mobility spectrometry and mass spectrometry), and mechanical devices. Part II will review methods based on photons, from very energetic photons including X-rays and gamma rays down to the terahertz range, and neutrons.

Coumarin benzothiazole derivatives as chemosensors for cyanide anions

Four coumarin benzothiazole derivatives, N-(benzo[d]thiazol-2-yl)-2-oxo-2H-chromene-3-carboxamide (1), (Z)-N-(3-methylbenzo[d]thiazol-2(3H)-ylidene)-2-oxo-2H-chromene-3-carboxamide (2), 7-(diethylamino)-N-(benzo[d]thiazol-2-yl)-2-oxo-2H-chromene-3-carboxamide (3) and (Z)-7-(diethylamino)-N-(3-methylbenzo[d]thiazol-2(3H)-ylidene)-2-oxo-2H-chromene-3-carboxamide) (4), have been synthesized. Their crystal structures, photophysical properties in acetonitrile and recognition properties for cyanide anions have been investigated. All the compounds are generally planar, especially compound 1 exhibits perfect planarity with dihedral angle between benzothiazolyl group and coumarin group being only 3.63°. Coumarin benzothiazole compounds 1 and 3 can recognize cyanide anions by Michael addition reaction and compound 3 exhibits color change from yellow to colorless and green fluorescence was quenched completely, which can be observed by naked eye. Coumarin benzothiazolyliden compound 4 can recognize cyanide anions with fluorescence turn-on response based on the copper complex ensemble displacement mechanism.

Monolayer molecular probes for detection of trace amounts of cyanide anions

A monolayer sensor M-P1 is developed for detection of cyanide ions in aqueous solution. The monolayer sensor has high sensitivity and selectivity, and is very efficient for detecting trace amounts of analytes in dilute solution.

Fluorescent aggregates of AIEE active triphenylene derivatives for the sensitive detection of picric acid

Fluorescent aggregates of triphenylene derivatives 3 and 5 having aggregation induced emission enhancement (AIEE) characteristics have been developed which selectively detect picric acid.

A small-molecule chemosensor for the selective detection of 2,4,6-trinitrophenol (TNP)

A pyridine-based receptor (L) was synthesised and characterized, which can serve as a small-molecule sensor for the specific recognition of TNP.

A hexaphenylbenzene based AIEE active two photon probe for the detection of hydrogen sulfide with tunable self-assembly in aqueous media and application in live cell imaging

AIEE active HPB based TPE probe exhibited modulation of self-assembled architecture in presence of H₂S and was utilized for TPM imaging for detection of H₂S in HeLa cells.

Silver nanoparticles: facile synthesis and their catalytic application for the degradation of dyes

The aggregates of pentacenequinone, HPB and PDI derivatives 3, 5 and 7 having aldehyde groups bind strongly with Ag⁺ and serve as reactors and stabilizers for the preparation of AgNPs at room temperature. In situ generated AgNPs show high catalytic efficiency for industrially important organic dye degradation.

Ultrasensitive detection of nitroexplosive – picric acid via a conjugated polyelectrolyte in aqueous media and solid support

Cationic polymer PMI detects picric acid at ppt levels via combination of ground state charge transfer, RET and electrostatic interactions. A paper strip test and a contact mode sensing platform using chitosan film confirm the method as simple, portable and cost-effective.

An imidazolyl-pyreno-imidazole conjugate as a cyanide sensor and a set–reset memorized sequential logic device

A pyrenyl-bisimidazole system can act as an efficient cyanide sensor and a ‘set–reset’ memory device.

Hexaphenylbenzene-based fluorescent aggregates for ratiometric detection of cyanide ions at nanomolar level: set-reset memorized sequential logic device

A hexaphenylbenzene-based receptor 3 has been synthesized that forms a fluorescent spherical aggregate in mixed aqueous media due to its aggregation-induced emission enhancement attributes. These fluorescent spherical aggregates show ratiometric response toward cyanide ions via nucleophilic addition and undergo deaggregation to form smaller nanoaggregates. In addition, the solution-coated paper strips of 3 can detect cyanide ions in the range of ∼2.6 ng/cm(2), thus, providing a simple, portable, and low-cost method for detection of cyanide ions in aqueous media. Receptor 3 also behaves as a set-reset memorized sequential logic circuit with chemical inputs of CN(-) ions and trifluoroacetic acid or H(+) (pH ≤ 3).

A hexaphenylbenzene based AIEE active probe for the preparation of ferromagnetic α-Fe2O3 nanoparticles: facile synthesis and catalytic applications

A hexaphenylbenzene based AIEE active probe has been synthesized which serves as reactor for the preparation of ferromagnetic α-Fe₂O₃ nanoparticles. These nanoparticles show excellent catalytic activity in Sonogashira coupling reactions.

A carbazole–fluorene molecular hybrid for quantitative detection of TNT using a combined fluorescence and quartz crystal microbalance method

Self-assembled fluorescent rods and nanoparticles prepared from a carbazole–fluorene molecular hybrid have been used for the sensing of TNT.

A new coumarin-based chromogenic chemosensor for the detection of dual analytes Al3+ and F−

A simple and easy-to-make colorimetric sensor for Al³⁺ and F⁻ was designed and synthesized.

A new thiacalix[4]arene-fluorescein based probe for detection of CN− and Cu2+ ions and construction of a sequential logic circuit

A thiacalix[4]arene-fluorescein based fluorescent probe for detection of CN⁻ and Cu²⁺ ions and its application in a sequential logic circuit.

Fluorescent supramolecular metal assemblies as ‘no quenching’ probes for detection of threonine in the nanomolar range

A highly sensitive detection of threonine is realized using a supramolecular ensemble of aggregates of hetero-oligophenylene derivative 3 and Zn²⁺ ions. On the basis of fluorogenic response of aggregates of 3 toward Zn²⁺ ions and threonine, we have constructed a 2-input, 3-output sequential logic circuit at the molecular level.

Fast detection of nitroaromatics using phosphonate pyrene motifs as dual chemosensors

A new class of dual fluorescent chemosensors for nitroaromatic compounds (NACs) based on phosphonated pyrene derivatives is reported, showing high selectivity towards trinitrotoluene (TNT).

A single chemosensor for multiple analytes: fluorogenic detection of Zn2+ and OAc− ions in aqueous solution, and an application to bioimaging

A single fluorescent chemosensor 1 for multiple analytes (Zn²⁺ and OAc⁻) has been developed and it can monitor Zn²⁺ ions in living cells.

Probing the dendritic architecture through AIE: challenges and successes

Since the aggregation-induced emission (AIE) phenomenon is very sensitive to steric hindrance, we set out to use it as a tool to probe the periphery of dendrimers.

Fluorescence and piezoresistive cantilever sensing of trinitrotoluene by an upper-rim tetrabenzimidazole conjugate of calix[4]arene and delineation of the features of the complex by molecular dynamics

A new benzimidazole-functionalized calix[4]arene receptor (R) was synthesized and characterized. The receptor R shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between R and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of R on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that R can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. R can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy.

Three hydroxy aurone compounds as chemosensors for cyanide anions

Three new 4-hydroxy aurone compounds 1-3 with dimethylamino (1), bromine (2) and cyano (3) as terminal group have been synthesized. Their photophysical properties as well as recognition properties for cyanide anions in acetonitrile and aqueous solution have also been examined. These compounds exhibit remarkable response to cyanide anions with obvious color and fluorescence change owing to hydrogen bonding reaction between cyanide anions and the O-H moiety of the sensors, which allows naked eye detection of cyanide anions.

Selective and efficient detection of nitro-aromatic explosives in multiple media including water, micelles, organogel, and solid support

Selective detection of nitro-aromatic compounds (NACs) at nanomolar concentration is achieved for the first time in multiple media including water, micelles or in organogels as well as using test strips. Mechanism of interaction of NACs with highly fluorescent p-phenylenevinylene-based molecules has been described as the electron transfer phenomenon from the electron-rich chromophoric probe to the electron deficient NACs. The selectivity in sensing is guided by the pKa of the probes as well as the NACs under consideration. TNP-induced selective gel-to-sol transition in THF medium is also observed through the reorganization of molecular self-assembly and the portable test trips are made successfully for rapid on-site detection purpose.