On-off Sensor Research Articles

Coumarin based colorimetric and fluorescence on-off chemosensor for F−, CN− and Cu2 + ions

(E)-4-Chloro-3-[{2-(4-nitrophenyl)hydrazono}methyl]-2H-chromen-2-one (C), a coumarin derivative has been studied toward its ion sensing properties for F−, CN− and Cu2+. A proton-transfer mechanism for F− sensing has been deduced with the help of 1H NMR titration alongwith from the changes in the absorption and emission spectra of C in the presence of F−. C formed 1:1 stoichiometric complex with each of these analytes. Sensing of C toward Cu2+ is poor, but interestingly in the presence of F−or CN− the sensing ability of Cu2+ gets enhanced many folds, and C can act as F−or CN− mediated off-on sensor for Cu2+. Moreover, colorimetric strip (pre-coated with the coumarin derived compound) tests for F−and CN− from their DMSO solution at high temperature (~100°C) opens up the door for easiest naked eye recognition and distinction of these ions, and also for naked-eye detection of F− and CN− from its aqueous solution at high temperature (~100°C).

New Off-On Sensor for Captopril Sensing Based on Photoluminescent MoO x Quantum Dots.

Molybdenum oxide nanomaterials have recently attracted widespread attention for their unique optical properties and catalytic performance. However, until now, there is little literature on the application of photoluminescent molybdenum oxide nanomaterials in biological and pharmaceutical sensing. Herein, photoluminescent molybdenum oxide quantum dots (MoOx QDs) were synthesized via a facile method, and then, the synthesized MoOx QDs were further applied as a new type of photoluminescent probe to design a new off–on sensor for captopril (Cap) determination on the basis of the fact that the quenched photoluminescence of MoOx QDs by Cu2+ was restored with Cap through specific interaction between the thiol group of Cap and Cu2+. Under optimal conditions, the restored photoluminescence intensity showed a good linear relationship with the content of Cap, ranging from 1.0 to 150.0 μM, with a limit of detection of 0.51 μM (3σ/k). Additionally, the content of Cap in pharmaceutical samples was successfully detected with the newly developed off–on sensor, and the recoveries were 99.4–101.7%, which suggest that the present off–on sensor has a high accuracy.

Fluorescence-based logic gate for sensing of Ca2+ and F- ions using PVP crowned chrysene nanoparticles in aqueous medium.

Polyvinyl pyrrolidone (PVP) crowned chrysene nanoparticles (CHYNPs) were prepared by using a reprecipitation method. Dynamic light scattering (DLS) and scanning electron microscope (SEM) studies indicate that the monodispersed spherical nanoparticles bear a negative charge on their surfaces. The bathochromic spectral shift in the UV-visible and fluorescence spectrum of CHYNPs from chrysene (CHY) in acetone solution supports the J- type aggregation of nanoparticles. The aggregation-induced enhanced emission of CHYNPs at 486 and 522nm decreases by increasing the concentration of the Ca2+ ion solution. It can display an ON-OFF type fluorescence response with high selectivity towards Ca2+ ions aqueous medium. Furthermore, the in situ generated PVP-CHYNPs-Ca2+ ensemble could recover the quenched fluorescence upon the addition of fluoride anions resulting in an OFF-ON type sensor. The present method has a correlation coefficient R2 = 0.988 with a detection limit of 1.22μg/mL for Ca2+ in the aqueous medium. The fluorescence changes of PVP crowned CHYNPs upon the addition of Ca2+ and F- can be utilized as an INHIBIT logic gate at the molecular level, using Ca2+ and F- chemical inputs and the fluorescence intensity signal as output.

New Meso-ortho-hydroxy-decorating Fluorescent ON-OFF Bodipy sensor to Cu2 +

A new meso-ortho-hydroxy-modifying Bodipy compound (o-OH-Bodipy) has been designed and synthesized. Single crystal X-ray diffraction analysis reveals the slight lean of the meso-phenyl moiety to the o-OH side due to the effect of the o-OH substituent. Systematic optical studies indicate that introduction of the o-OH group onto the meso-phenyl moiety of this compound induces an increased binding affinity and in particular an obvious fluorescence quenching response to Cu2+ on the basis of the photo-induced electronic transition process, endowing o-OH-Bodipy a great potential as highly sensitive fluorescence ONOFF detector for Cu2+ even in the acidic condition.

Highly photoluminescent MoOx quantum dots: Facile synthesis and application in off-on Pi sensing in lake water samples

Molybdenum oxide (MoOx) is a well-studied transition-metal semiconductor material, and has a wider band gap than MoS2 which makes it become a promising versatile probe in a variety of fields, such as gas sensor, catalysis, energy storage ect. However, few MoOx nanomaterials possessing photoluminescence have been reported until now, not to mention the application as photoluminescent probes. Herein, a one-pot method is developed for facile synthesis of highly photoluminescent MoOx quantum dots (MoOx QDs) in which commercial molybdenum disulfide powder and hydrogen peroxide (H2O2) are involved as the precursor and oxidant, respectively. Compared with current synthesis methods, the proposed one has the advantages of rapid, one-pot, easily prepared, environment friendly as well as strong photoluminescence. The obtained MoOx QDs is further utilized as an efficient photoluminescent probe, and a new off-on sensor has been constructed for phosphate (Pi) determination in complicated lake water samples, attributed to the fact that the binding affinity of Eu3+ ions to the oxygen atoms from Pi is much higher than that from the surface of MoOx QDs. Under the optimal conditions, a good linear relationship was found between the enhanced photoluminescence intensity and Pi concentration in the range of 0.1–160.0 μM with the detection limit of 56 nM (3σ/k). The first application of the photoluminescent MoOx nanomaterials for ion photochemical sensing will open the gate of employing MoOx nanomaterials as versatile probes in a variety of fields, such as chemi-/bio-sensor, cell imaging, biomedical and so on.

A single thiourea-appended 1,8-naphthalimide chemosensor for three heavy metal ions: Fe3+, Pb2+, and Hg2+

A 1,8-naphthalimide-thiourea conjugate was developed for highly selective and sensitive colorimetric detection of Fe3+ and Pb2+ in MeCN/H2O (99/1, v/v) and fluorescent recognition of Hg2+ in MeCN/H2O (85/15, v/v). The linear concentration ranges for Fe3+, Pb2+, and Hg2+ were 0–150, 0–80, and 0–90μM with the detection limits of 6.86μM, 5.09μM, and 82.1nM, respectively. The sensor responded to Fe3+, Pb2+, and Hg2+ rapidly and a large number of coexisting ions such as Na+, K+, Ca2+, Mg2+, Fe2+, Cu2+, Zn2+, Cr3+, Ni2+, Mn2+, Co2+, Cd2+, and F− showed almost no obvious interference with the detection. Sensing mechanism of the sensor to Fe3+, Pb2+, and Hg2+ was investigated through job's plot experiment, reversible experiment, LC–MS and 1H NMR analysis. Moreover, the off-on sensor was successfully employed to monitor Hg2+ in pond and tap water as well as in living cells.

Cascade sensitive and selective fluorescence OFF–ON–OFF sensor for Cr3+ cation and F− anion

Cascade recognition of trivalent chromium cation (Cr3+) and fluoride anion (F−) via rhodamine-urea methacrylate-based fluorescent probe (RhBUA) and its subsequent cationic complex was reported. The non-fluorescent rhodamine derivatives can selectively detect Cr3+ cation over some other metal ions in CH3CN–H2O (90/10, v/v, pH 7.0) solutions with a 1:1 stoichiometry, leading to prominent fluorescence OFF–ON switching. The obtained RhBUA–Cr3+ complex can subsequently serve as a sensitive and selective chemosensor for F− ion. Complete signal quenching (fluorescence ON–OFF switching) can also be observed, ascribing to the extraction of Cr3+ cation and the resulting deformation of RhBUA–Cr3+ complex.

Modulating the sensor response to halide using NBD-based azamacrocycles.

Ligand L (2,6-bis{[7-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-3,10-dimethyl-1,4,7,10-tetraazacyclododeca-1-yl]methyl}phenol) is a fluorescent sensor that is useful for detecting Cu(II), Zn(II), and Cd(II). Some of the complexes formed are able to sense the presence of halides in solution. L passes through the cellular membrane, becoming fluorescent inside cells. The H(-1)L- species is able to form dinuclear complexes with [M(2)H(-1)L]3+ stoichiometry with Cu(II), Zn(II), and Cd(II) ions, experiencing a CHEF effect upon metal coordination in an acetonitrile/water 95:5 (v/v) solution. In all three of the complexes investigated, the metal cations are coordinatively unsaturated and can therefore bind secondary ligands as anionic species. The crystal structure of [Cd(2)(H(-1)L)Cl(2)](ClO(4))·4H(2)O is discussed. The Zn(II) complex behaves as an OFF-ON sensor for fluoride and chloride anions.

1-(2-Methyl-5H-chromeno[2,3-b]pyridin-5-ylidene) hydrazone as fluorescent probes for selective zinc sensing in DMSO

Two methyl-chromeno-pyridinylidene hydrazone derivatives L1, a cyclen derivative, and L2 were studied as potential fluorescent OFF–ON sensors towards Zn2+ in DMSO. Upon addition of one equivalent of Zn2+, L1 fluorescence was quenched, but addition of a second equivalent of Zn2+ restored partially the signal. Therefore ZnL1 behaved as a OFF–ON sensor for zinc. By comparison, L2 behaved as a very sensitive probe for zinc. ZnL1 and L2 sensor efficiencies were correlated to Zn2+ coordination via the hydrazone moiety of the fluorophore, which prevented a photoinduced electron transfer (PET), and allowed an efficient CHelation-Enhanced Fluorescence (CHEF) effect.

A Novel Quinazolinone Derivative as Fluorescence Quenching Off-On Sensor for High Selectivity of Fe3+

A novel quinazolinone compound containing quinazoline-fused moiety has been synthesized as fluorescence Off-On sensor QQ. The probe exhibited highly selective and sensitive recognition toward trivalent ferric ion (Fe(3+)) over other metal ions in HEPES buffer solution (10mM, pH = 7.0, DMF-H2O, 9:1, v/v). The significant quenching in the fluorescence spectral could be served as a selective fluorescence Off-On sensor. The titration study indicated the formation of 1:1 complex between QQ and Fe(3+).

A new highly selective fluorescent sensor for detection of Cd2+ and Hg2+ based on two different approaches in aqueous solution

A new fluorescence sensor (L) derived from 8-hydroxy-2-methylquinoline has been developed. This sensor can selectively detect Cd2+ in aqueous buffer solution based on chelation enhanced fluorescence (CHEF) and exhibit an almost 30-fold fluorescence increase. Besides, the complex (LCd) can also be considered as a good ON–OFF sensor for Hg2+ based on photoinduced electron transfer (PET). The sensor could be applied for fluorescence microscopic imaging.

N,N-di(2-pyridylmethyl)amino-modified porphyrinato zinc complexes. The “ON–OFF” fluorescence sensor for Fe3+

Two porphyrinato-zinc derivatives modified with two and four N,N-di(2-pyridylmethyl)amino groups, namely Zn-Porphyrin-2-DPA (1) and Zn-Porphyrin-4-DPA (2), have been designed, synthesized, and characterized. Systemic studies over a series of metal ions reveal that binding with Fe3+ for the former compound induces the decrease of fluorescence emission intensity by 37.2%, while for the latter one results in a more remarkable decrease in the fluorescence emission intensity by 90.3%, rendering compound 2 the first example of DPA-modified porphyrin fluorescence ON–OFF sensor for Fe3+.

A Ratiometric Fluorescent On–Off Zn2+ Chemosensor Based on a Tripropargylamine Pyrene Azide Click Adduct

A new, easy-to-prepare and highly selective pyrene-linked tris-triazole amine fluorescent chemosensor has been designed from tripropargylamine and pyrene azide using Cu(I)-catalyzed click chemistry. The fluorescence on-off sensor 1 is highly selective for Zn(2+) displaying a ratiometric change in emission. The relative intensity ratio of monomer to excimer fluorescence (M(376)/E(465)) of the sensor increases 80-fold upon the addition of 10 equiv of Zn(2+) ions (with a detection limit of 0.2 μM).

Multi‐Use NBD‐Based Tetra‐amino Macrocycle: Fluorescent Probe for Metals and Anions and Live Cell Marker

Ligand L (4-(7-nitrobenzo[1,2,5]oxadiazole-4-yl)-1,7-dimethyl-1,4,7,10-tetra-azacyclododecane) is a versatile fluorescent sensor useful for Cu(II), Zn(II) and Cd(II) metal detection, as a building block of fluorescent metallo-receptor for halide detection, and as an organelle marker inside live cells. Ligand L undergoes a chelation-enhanced fluorescence (CHEF) effect upon metal coordination in acetonitrile solution. In all three complexes investigated the metal cation is coordinatively unsaturated; thus, it can bind secondary ligands as anionic species. The crystal structure of [ZnLCl](ClO(4)) is discussed. Cu(II) and Zn(II) complexes are quenched upon halide interaction, whereas the [CdL](2+) species behaves as an OFF-ON sensor for halide anions in acetonitrile solution. The mechanism of the fluorescence response in the presence of the anion depends on the nature of the metal ion employed and has been studied by spectroscopic methods, such as NMR spectroscopy, UV/Vis and fluorescence techniques and by computational methods. Subcellular localization experiments performed on HeLa cells show that L mainly localizes in spot-like structures in a polarized portion of the cytosol that is occupied by the Golgi apparatus to give a green fluorescence signal.

Cyclam-methylbenzimidazole: a Selective OFF-ON Fluorescent Sensor for Zinc

The coordination properties and the photophysical response of a new cyclam fluorescent probe for Zn(II), [L1H: 1-(benzimidazol-2-ylmethyl]-1,4, 8,11-tetraazacyclotetradecane] toward Cu(II), Zn(II), and Cd(II) are reported. The stability constants of the corresponding complexes were determined by means of potentiometric measurements in aqueous solution. The fluorescence of L1H was quenched by the presence of Cu(II), and L1H behaves as an OFF-ON sensor for Zn(II) even in the presence of a wide range of biological divalent cations. Furthermore, on addition of successive amounts of Zn(II), the fluorescence emission of L1H increases linearly by a factor of 12. This can be correlated to the efficient Zn(II) binding of L1H and to the participation of all the amine functions in the metal coordination which prevents the photoinduced electron transfer (PET) effect and promotes a good chelation-enhanced fluorescence (CHEF) effect; this confers to the cyclam probe better sensing properties than the cyclen ionophore.

Fluorescent Sensors for Hg2+ in Micelles: A New Approach that Transforms an ON–OFF into an OFF–ON Response as a Function of the Lipophilicity of the Receptor

A new approach to the use of micelles in the fluorescent sensing of metal cations is proposed and applied to the case of Hg(2+). We demonstrate how it is possible to transform a system from an ON-OFF to an OFF-ON sensor by changing the length of the chain used to lipophilise a ligand that resides inside TritonX-100 micelles together with pyrene as the fluorophore. Three tetrathia-monoaza macrocyclic ligands have been synthesised with the same ring but functionalised on the nitrogen atom with a methyl (C1-NS4), an n-butyl (C4-NS4) or an n-dodecyl (C12-NS4) chain. The three ligands have been fully characterised in water containing TritonX-100 micelles by means of potentiometric titrations and their apparent protonation and complexation constants with Hg(2+) were determined. On the basis of the distribution diagrams obtained, the more lipophilic C12-NS4 has been developed as an ON-OFF fluorescent sensor for mercury: working at pH<4, in the absence of Hg(2+) the ligand is inside the micelles, protonated and non-quenching, while on addition of mercury the [C12-NS4Hg](2+) complex forms which remains inside the micelles and is quenching. On the other hand, the ligand of intermediate chain length, C4-NS4, can be used to obtain an OFF-ON sensor at 7.0<pH<9.5. In the absence of added metal at pH>7.0 the ligand is unprotonated, it stays inside the micelles and is quenching, while addition of Hg(2+) in the 7.0-9.5 pH range results in the formation of [C4-NS4Hg](2+), which is hydrophilic enough to leave the micelles and to be released into the bulk solution where it is no longer capable of quenching pyrene fluorescence. Additional studies on C1-NS4, C3-NS4 and C8-NS4 indicate that the optimal chain length to observe this OFF-ON behaviour is C(3)-C(4).

A [RuII(bipy)3]-[1,9-diamino-3,7-diazanonane-4,6-dione] two-component system, as an efficient ON–OFF luminescent chemosensor for Ni2+ and Cu2+ in water, based on an ET (energy transfer) mechanism

A dioxo-tetramine ligand (1,9-diamino-3,7-diazanonane-4,6-dione ≡ dioxo-2,3,2-tet) has been appended to a RuII(bipy)3 unit. This new system, 2, is water-soluble and capable of sensing Cu2+ and Ni2+ cations thanks to the strong quenching of the Ru(bipy)3 fluorescence, which takes place when a metal cation is coordinated by the dioxo-2,3,2-tet binding unit. Coordination requires the energetically expensive deprotonation of the amide nitrogens, so that only Cu2+ and Ni2+ are able to promote it among the series of divalent first-row transition metal cations. Moreover, the complexation reaction is pH-dependent and one can distinguish between the two metal cations on working at the proper pH. The quenching mechanism has been examined by measuring the lifetime of the excited state of the ruthenium luminophore both on the metal-free and metal-complexed system and by flash photolysis experiments carried out on the complexed systems. The results clearly indicate that an energy transfer mechanism holds both for the Cu2+ and Ni2+ complex. The characterization of 2 as a water soluble ON–OFF sensor for copper and nickel has also been checked for its lowest detection limit, finding that these two metals can be detected down to a 10–7 M concentration. Moreover, also system 3, containing a dioxo-2,3,2-tet ligand and the ReI(CO)3bipy(Cl) luminophore, has been examined as another possible water-soluble ON–OFF fluorescent sensor for the same transition metal cations. Again, only Cu2+ and Ni2+ are bound with a pH-dependent equilibrium, but incomplete luminescence quenching was observed, which prevented the determination of the quenching mechanism.