Turn-off Fluorescent Chemosensor Research Articles

Exploiting cyanide anion detection in food samples and for constructing logic gates by turn-off fluorescent chemosensor

A high-performance turn-off fluorescent chemosensor MSAP was developed for the selective sensing of cyanide anion without any interferences from other competing anions. MSAP's spectral responses to cyanide anion have been investigated by UV–vis and fluorescence spectroscopy. The limit of detection of cyanide anion was about 2.8 μM, which is much less than the WHO acceptable threshold level. The binding stoichiometry between the MSAP and cyanide anion was about 1:1, which was well augmented by Job`s plot. The quenching constant between MSAP and CN− ion calculated from the Stern-Volmer equation was about 8.7351×104M−1. The proposed detection mechanism of MSAP for the sensing of cyanide anion was further demonstrated by 1H NMR titration, ESI-MS and by density functional theory (DFT) studies. At last, probe MSAP was fruitfully exploited to analyse the presence of cyanide ion in diverse food samples and a XOR molecular logic gate was fabricated.

5-Oxo-7,7-Dimethyl-5,6,7,8-Tetrahydro-4-H-Chromene Bearing N, N-Dimethylaniline as Turn-Off Fluorescent Chemosensor for Picric Acid in Real Water Sample.

We have synthesized a one-pot, three-component pyran-based fluorescence chemosensor using onion extract as a green catalyst. The confirmed structure of the 1:2 binding of receptor SPR-2-picric acid adduct revealed that the pyran-based receptor accommodated two guest picric acid molecules through non-covalent interactions. UV-Vis and fluorescence spectroscopy show high selectivity and sensitivity towards picric acid. The 1D/2D NMR and Job's plot analysis show the complexation and stoichiometric binding of the receptor SPR-2 with picric acid are 1:2. The 1H NMR spectral studies confirm that the formation of receptor SPR-2-picric acid adduct via weak hydrogen bonding. The cooperativity of the receptor SPR-2-picric acid adduct shows negative cooperativity due to the weak hydrogen bonding of receptor SPR-2 and picric acid. Further, the density functional theory (DFT) confirmed the molecular level interaction of the SPR-2 and receptor SPR-2-Picric acid adduct. The receptor was effectively used to assess picric acid concentrations in real water samples.

A highly selective and sensitive quinoline-based fluorescent turn-off chemosensor for the detection of picric acid

A simple turn-off quinoline-based fluorescent chemosensor, 1-(6-amino-2-methyl-4-phenylquinolin-3-yl)ethan-1-one (QN) has been developed, synthesized, and characterized by various spectroscopic methods. This probe is selective for the sequential recognition of picric acid (PA), using a fluorescent turn-off method. QN exhibits a broad emission band at 504 nm, but fluorescence quenching occurs upon the addition of picric acid over other nitro compounds. The binding stoichiometric ratio between QN and picric acid was calculated to be 1:1 through Job's plot analysis, and the binding constant was determined. The limit of detection towards picric acid was found to be 9.33 µM. Further, the mechanistic approach for binding has been investigated by spectroscopic methods like 1H NMR titration, FT-IR studies, and density functional theory (DFT) studies.

Chromene Carbohydrazide- Schiff Base as a Highly Selective Turn-Off Fluorescence Chemosensor for In3+ Ion and its Application.

A new 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide design to synthesize a simple Schiff-base condition. The synthesized molecules' (probe L) photophysical properties were investigated in various solvent systems and solvent-poor-solvent assays. Probe L exhibits the absorbance band at 440nm and the emission band at 488nm in DMSO: H2O (7:3, v/v). Further, probe L shows selective turn-off emission recognition of In3+ ions in DMSO: H2O (7:3, pH = 7.4). By Job's plot and ESI mass analysis, probe L forms a 1:2 stoichiometry complex with an estimated association constant of 4.04 × 104 M- 2 with In3+ ions. Metal induces CHEQ (chelation-caused fluorescence quenching) to reduce the intensity of probe L's emission, and the estimated quenching constant was 4.52 × 104 M- 1. The limit of detection was found to be 5.93 nM; the time response of the sensor is instantaneous, and its reversible nature was confirmed using EDTA additions. Solid substrates (test strips) were designed and tested for fast, reliable, user-friendly, and real-time sensing of In3+ ions for on-site applications. The binding mechanism of probe L with In3+ ions was investigated using 1H NMR titration and DFT/TD-DFT studies.

A simple turn-off fluorescent chemosensor based on a Schiff base structure for ultrafast and highly selective trace detection of Cu2+ ions in aqueous solutions.

A simple turn-off fluorescent probe, 5-(diethylamino)-2-(hydrazonomethyl)phenol (DHP), is designed and synthesized for the sensitive and selective detection of Cu2+. The bright green fluorescence of DHP is quenched after the addition of Cu2+. The probe DHP exhibits good anti-interference performance against Cu2+ in the presence of multiple metal ions. The fluorescence intensity of DHP (10 μM) at 522 nm is well linearized with the Cu2+ concentration at 0-5 μM, and it has a detection limit of 0.29 nM (R2 = 0.9949). The complexation ratio of the probe DHP to Cu2+ is 2 : 1 and the complexation constant is 3.44 × 104 M-1 (R2 = 0.9974). In addition, the probe DHP can be recovered using EDTA and Cu2+ can be effectively monitored at pH 5-11, with good results in dipstick experiments and actual water samples. HepG-2 cells remained viable in excess of 90% after being exposed to DHP (50 μM) for 24 h, which demonstrates the extremely low toxicity of DHP, and it can be used for in vivo cell imaging.

A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu2+

A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu2+

The new coumarin derivative cyclotetraphosphazene fluorometric chemosensor with reversible, high selective and sensitive for Fe3+ ion detection

A new coumarin-based cyclotetraphosphazene molecule (OCCTP) that can show fluorescence and chemosensory properties has been designed and synthesized. For this purpose, the 7-hydroxy-3-(3,4,5-trimethoxyphenyl)coumarin (4) was synthesized.For the first time in this study, compound 4 which solid state structure and geometry were determined by using crystal X-ray structural analysis were crystallized in the orthorhombic Fdd2 space group. The purified compounds were structurally characterized by elemental analysis, NMR (1H, 13C and 31P) and FT-IR spectroscopy, and mass analysis. Photophysical and chemosensory properties of OCCTP against a range of analytes (various metal ions) were investigated by UV–vis and Fluorescent Spectrophotometer. As a result of fluorimetric studies, OCCTP was found to be a Turn-Off fluorescent chemosensor against Fe3+ ions. The limit of detection (LOD) of OCCTP for Fe3+ was calculated as 1.87 µM and its complex stoichiometry was determined as 1:2 (L/M) as a result of Job's plot. The reversibility study of the iron complex with EDTA showed that the free OCCTP chemosensor regenerated causing an increase in the fluorescence intensity of EDTA. The results showed that the newly synthesized coumarin-based cyclotetraphosphazene compound (OCCTP) can be used as a reversible, highly selective and sensitive fluorescent chemosensor (Turn- Off) which responds immediately against Fe3+ ions.

Novel phenylalanine derivative-based turn-off fluorescent chemosensor for selective Cu2+ detection in physiological pH

A novel and unnatural amino acid-based phenylalanine derivative bearing dansyl and benzoxazole moieties (DPB) as a side chain has fine-tuned fluorometric/colorimetric chemosensor was synthesized and characterized through various spectroscopic techniques. It was verified with 16 other competing alkali, alkali-earth, and transition metal ions but it was selectively quenched the Cu2+ ion in aqueous organic media with physiological pH (DMSO/H2O, 1:1, v/v, pH 7.4). The binding interaction was proved as 1:1 by Job’s plot method and the LOD value was found as 3.0 μM which is a much lower value than WHO and EPA guideline value. A naked eye color change was observed with Cu2+ ion, it induces a light yellow to light brown color with a large Red Shift value (307–539 nm) in emission spectra. The utilization of this sensor for water analysis also performing well with a high-level recovery rate of up to 99.92%. The encouraging photophysical results revealed that this probe DPB will act very well by selectively and sensibly as a “turn of” chemosensor towards Cu2+ ion.

A highly selective and sensitive thiophene substituted 1,3,4-oxadiazole based turn-off fluorescence chemosensor for Fe2+and turn on fluorescence chemosensor for Ni2+ and Cu2+ detection

In the present work, a newly synthesized thiophene substituted 1,3,4-oxadiazole derivative namely 2-(-4-(thiophene-3-yl)phenyl)-5-(5-(thiophene-3-yl)thiophene-2-yl)-1,3,4-oxadiazole [TTO] is characterized as chemosensor for detecting Fe2+, Ni2+ and Cu2+ metal ions through absorption and fluorescence studies. We found that, on changing media chemosensor shows different behavior with Fe2+, Ni2+ and Cu2+ metal ions. In ethanol-water (1/1,v/v, pH 7.2) medium on varying concentration of Fe2+, chemosensor shows turn off fluorescence, whereas Ni2+ and Cu2+ metal ions induced a strong turn on fluorescence respectively in methanol-water (1/1,v/v, pH 7.2) and acetonitrile-water (1/1,v/v, pH 7.2) media. The competitive metal ion experimental results revealed that chemosensor is highly selective for recognizing Fe2+, Ni2+ and Cu2+ ions without the interference of other metal ions (Pb2+, Ca2+, Mg2+, Co2+, Zn2+, Na+, and Mn2+). The detection limit of chemosensor for all targeted metal ions is in the range of 0.5–3 μM. The detection capacity for targeted metal ion studies shows less than 6.5 min indicating highly sensitive nature of the TTO. Job's plot indicates that, the binding stoichiometry between chemosensor TTO and targeted metal ions is 1:1 for Fe2+, Ni2+ and Cu2+ metal ions respectively. Further, linear variation in the fluorescence intensity of the chemosensor with different concentrations of the metal ions suggests the possibility of quantitative measurement of the targeted metal ions. Hence, our experimental findings very strongly suggest that, TTO can be used as chemosensor for detecting Fe2+, Ni2+ and Cu2+ metal ions in future.

Static interaction between colloidal carbon nano-dots and aniline: A novel platform for ultrasensitive detection of aniline in aqueous media

Aniline has been classified as a probable human carcinogen which can cause severe respiratory tract irritation and congestion to humans. Here, we propose using ultra-small (1.8 nm) colloidal nitrogen-doped carbon nano-dots (N-CDs), that is green synthesized at a low temperature of only 100 °C from ultrasonic-processed water-soluble folic acid, as a novel turn-off fluorescent chemo-sensor for ultrasensitive detection of aniline in aqueous medium. It was found that the Stern-Volmer relation describes very well the fluorescence quenching of N-CDs by aniline and confirms a static quenching mechanism between them. Compared to other techniques, our N-CDs based optical detection method, is the simplest and the most ultrasensitive method for aniline liquid detection, reaching an exceptional low detection limit of 3.57 nM (0.332 ppb). The proposed method was successfully applied for determination of aniline in a tap water sample without significant interferences from the matrix.

Novel fluorescent sensor for silver (I) based on the cinnamylidene derivatives of malononitrile trimer

The novel turn-off fluorescent chemosensor for silver ion based on cinnamylidene derivatives of malononitrile trimer with 1,1,3,3-tetracyanopropenide unit was developed. The quenching of fluorescent emission can be observed by naked eye, even in the presence of interference cations. The binding mode turned out to be a 1: 1 ratio as determined using Job plot. Good solubility in water can be applied for the detection of Ag+ in water samples.

A Facile Preparation of a New Water-Soluble Acridine Derivative and Application as a Turn-off Fluorescence Chemosensor for Selective Detection of Hg2.

A new acridine-based chemosensor was prepared, characterized and investigated for quantitative detection of Hg2+ ions in aqueous solutions. DFT and TD-DFT calculations showed that formation of a coordination bond between Hg2+ and the thiolate-sensor accounts for the fluorescence quenching, forming [HgLSCl2]2- as the most stable species. Limit of detection and limit of quantification were as low as 4.40 and 14.7μmolL-1, respectively (R2 = 0.9892, least squares method), and a linear concentration range of 14.7-100μmolL-1. Benesi-Hildebrand and Job formalisms are in accordance with the formation of a stable complex with a 1:1 (metal ion/sensor) ratio, and a determined binding constant of 5.14 × 103 L mol-1. Robustness was verified based on the variation of several analytical conditions. In addition, the method presented maximum relative standard deviation of 4.6%, and recovery results was (90.3± 4,6)% from distilled water, with no effect of interfering ions. Analytical figures of merit showed that the sensor can be an attractive low cost alternative for detection of Hg2+.

A turn-off fluorescent chemosensor for Cu(II) based on sensitive schiff base derived from 4-tert-Butyl-2,6-diformylphenol and p-toluic hydrazide

The novel Schiff base ligand (H3L), [Zn2(HL)(C2H3O2)2](C2H5OH) and [Cu2(H2L)(C2H5O)(NO3)]2(NO3)2 have been facilely and successfully synthesized, where H3L was fabricated using 4-tert-Butyl-2,6-diformylphenol and p-toluic hydrazide resulting in an N2O3 coordination environment. The as-made compounds were characterized by different spectroscopic techniques. The DFT calculations were performed at B3LYP/6–311 G(d) level for the determination of the optimized structure of the synthesized compounds. Further, the molecular structure of Zn-complex was confirmed by single-crystal X-ray diffraction. The interaction of H3L with different metal ions has been examined through the UV–Vis absorption and fluorescent spectra. The results indicated that H3L showed a highly sensitivity and selectivity for Cu2+ in the presence of many other metal cations in ethanolic solution.

Hydrogen bonding elements, π - hole functional moieties and C3v tripodal scaffold controlled turn-on cyanide and turn-off azide selective receptors.

Here in, we are reporting electron deficient amide and sulfonamide based tripodal receptors L, L1, L2 and L3. Systematic studies show a strong selectivity towards cyanide and azide anions. Detailed UV-Visible and fluorescent spectrometric investigation shows the amide based tripodal receptors L and L3 acts as a colorimetric and turn-on fluorescent chemo-sensor for cyanide, and the sulfonamide based tripodal receptors L1 and L2 acts as a colorimetric and turn-off fluorescent chemo-sensor for azide. At the end we have successfully prepared tripodal receptors for a particular anion with judicious choice of recognition elements such as hydrogen bonding amide/sulfonamide moiety, electron deficient pentafluorophenyl functionality for anion-π interaction and the well defined C3v symmetric tripodal backbone for perfect recognition.

A highly selective and reversible turn-off fluorescent chemosensor for Cu2+ based on electrospun nanofibrous membrane modified with pyrenecarboxaldehyde.

A fluorescent nanofibrous membrane (NFM) was successfully fabricated by functionalizing electrospun ethylene-vinyl alcohol copolymer (EVOH) NFM with 4‑aminobenzoic acid (PABA) and 1‑pyrenecarboxaldehyde (Py-CHO) for fast and selective determination of Cu2+ in aqueous solution. The effective grafting of PABA and Py-CHO on the surface of EVOH NFM was confirmed by FTIR and XPS spectra. Benefiting from the integrated merits of electrospun EVOH NFM, PABA and Py-CHO, the as-appeared EVOH-PABA-Py NFM exhibited high sensitivity and selectivity towards Cu2+ detection. The quenching efficiency was 91.7% when the concentration of Cu2+ reached 5 × 10-3 M, while the detectable fluorescence response of the NFM was still observed when the concentration of Cu2+ was 1 × 10-9 M. The fluorescence quenching caused by Cu2+ was hardly affected by other commonly co-existent metal ions. More importantly, the fluorescent NFM exhibited fast response and high reversibility towards Cu2+ detection. The "off-on" fluorescence switching process via alternating addition of Cu2+ and Na2EDTA occurred in 3 min, and the quenching efficiency of the NFM kept relatively stable values within 10 cycles. This work may provide a new insight into the development of rapid, portable, stable and reusable fluorescent sensor based on electrospun nanofibers that can satisfy the requirements of practical metal ions detection.

A coumarin based chemosensor for selective determination of Cu (II) ions based on fluorescence quenching

A potential fluorescent probe, N'-acetyl-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide (HMC1) was designed on the basis of photoinduced electron transfer (PET) and synthesized using cheap starting materials. HMC1 was found to be highly efficient as a Cu2+ ion quencher with a detection limit of 0.64 μM (~ 40 ppb). The binding mode of HMC1 towards Cu2+ was evaluated by 1H NMR, LC-MS and FT-IR techniques. In addition, cellular imaging studies further exhibited that HMC1 could be used an intracellular turn-off fluorescent chemosensor for Cu2+ in living cells.

Synthesis, photophysical studies, and application of novel 2,7-bis((1-butyl-1H-1,2,3-triazol-4-yl)methoxy)naphthalene as a highly selective, reversible fluorescence chemosensor for detection Fe3+ ions

The new reversible turn-off fluorescence chemosensor 2,7-bis((1-butyl-1H-1,2,3-triazol-4-yl)methoxy)naphthalene for selective detection of Fe3+ ions has been designed and synthesized using a multicomponent approach. The absorption and emission characteristics of this new chemosensor were studied in different solvents of varying polarities. The ground and excited state dipole moments were determined experimentally by solvatochromic methods and theoretically using DFT/TD-DFT calculations. The effect of common metal ions on emission spectra was investigated. The results showed that it can be used as reversible turn-off fluorescence chemosensor to determine Fe3+ ions with high selectivity among a series of other common cations. The binding stoichiometry of chemosensor with Fe3+ ions and association constant was investigated using global fit analyses as proposed by Thordarson. The mechanism of fluorescence quenching was studied by using a Stern-Volmer plot. The linear range of the chemosensor for detection of Fe3+ ions was found to be 8.0×10−7M to 1.0×10−5M with limit of detection (LOD) of 8.7×10−7M and limit of quantification (LOQ) of 2.6×10−6M. The Frontier molecular orbitals (FMO) analysis and chemical reactivity indices of this new chemosensor were also studied using DFT/TD-DFT calculations. The non-linear optical properties were also investigated. The values of total polarizability and first-order hyperpolarizability for the chemosensor were found to be higher than the standard urea molecule. Thus it can also be used as a potential NLO material. The thermodynamic parameters were also investigated.

Schiff base derived Fe3+-selective fluorescence turn-off chemsensors based on triphenylamine and indole: synthesis, properties and application in living cells

A Schiff base with an AIE effect could act as a turn-off fluorescent chemosensor for Fe3+in living cells.

Fluorescent oligomer as a chemosensor for the label-free detection of Fe3+ and dopamine with selectivity and sensitivity

In this article, a sensitive and selective turn-off fluorescence chemosensor, Tyloxapol (one kind of water soluble oligomer), was developed for the label-free detection of Fe3+ ions in aqueous solution. Fluorescence (FL) experiments demonstrated that Tyloxapol was a sensitive and selective fluorescence sensor for the detection of Fe3+ directly in water over a wide range of metal cations including Na+, K+, Ag+, Hg2+, Cd2+, Co2+, Cu2+, Cr3+, Mn2+, Ba2+, Zn2+, Ni2+, Mg2+, Ca2+, and Pb2+. Moreover, the fluorescence intensity of Tyloxapol has shown a linear response to Fe3+ in the concentration range of 0–100 μmol L−1 with a detection limit of 2.2 μmol L−1 in aqueous solution. Next, based on a competition mechanism, another turn-on sensing application of the Tyloxapol/Fe3+ platform to probe dopamine (DA) against various other biological molecules such as other neurotransmitters or amino acids (norepinephrine bitartrate, acetylcholine chloride, alanine, valine, phenylalanine, tyrosine, leucine, glycine, histidine) were also investigated. It is expected that our strategy may offer a new approach for developing simple, cost-effective, rapid and sensitive sensors in biological and environmental applications.

Spectroscopic and TD-DFT studies on the turn-off fluorescent chemosensor based on anthraldehyde N(4) cyclohexyl thiosemicarbazone for the selective recognition of fluoride and copper ions

The copper and fluoride ions sensing mechanism of a chemosensor based on anthraldehyde N(4) cyclohexyl thiosemicarbazone (AntCy) was investigated via colorimetric, fluorescence, electrochemical and NMR titration studies. Detailed investigations on their sensing mechanism was done using DFT and TD-DFT studies. 1H NMR titration shows deprotonation of NH protons by fluoride ion is a prominent step in naked eye recognition. The Gibbs free energy of overall sensing reaction has moderate transition barrier with 18.19kcalmol−1. Using the vibrational frequency analysis, all the local minima of ground state and excited state were confirmed. Due to the small size and strong electronegativity of fluoride, an intramolecular hydrogen bonding interaction with N(3)–H, which is closer to anthracene moiety was found to be preferentially formed. The excited state proton transfer mechanism was further confirmed with donor–acceptor interactions using Natural Bond Orbital (NBO) analysis and Potential Energy Surface (PES) analysis. The ICT mechanism for copper ion sensing was also confirmed with TD-DFT calculations.