Relay Recognition Research Articles

A reactive primary fluorescence switch-on sensor for Hg 2+ and the generated fluorophore as secondary recognition receptor toward Cu 2+ in aqueous acetonitrile solution

Abstract A new N-methylbenzoimidazole-based fluorescence “turn-on” chemodosimeter (VPBA) was synthesized and characterized for cation to cation relay recognition (CCRR) with high sequence specificity (Hg2+ → Cu2+). The selectivity and sensitivity of VPBA have been explored in aqueous acetonitrile solution through a specific cyclization reaction triggered by the mercury-promoted hydrolysis of the vinylether group with a significant change of fluorescence color. The probe displayed a fast switch-on fluorescence response with 164 fold toward Hg2+in aquoues acetonitrile solution. Further, the in situ system generated from the sensing of Hg2+ showed good relay recognition ability for Cu2+ via fast fluorescence quenching by the formation of a 1:2 complex in aquoues acetonitrile. The complexation of Cu2+ by VPBA has been addressed by HR-MS, 1H NMR, and UV−vis spectra. The probe and their Cu-complex structures have been established by DFT calculations. TDDFT calculations were also performed in order to demonstrate the electronic properties of probe and their copper complex. By using the new strategy, the novel probe could be used for the detection of Hg2+ in real-life water samples with good recovery. The probe could be successfully used for the fluorescence image of Hg2+ in living cells. These results suggested that the probe has promising applications for Hg2+ sensing in biological and environmental sciences.

A fluorescent “on-off-on” assay for selective recognition of Cu(II) and glutathione based on modified carbon nanodots, and its application to cellular imaging

Carbon nanodots modified with triethylenetetramine (referred to as TCDs) are shown to be viable fluorescent probes for relay recognition of Cu(II) ion and glutathione (GSH). The assay is based on an “on-off-on” mechanism where the “on-off” effect, i.e. quenching by Cu(II) by up to 67%, is exploited to quantify it in concentrations as low as 3.4 nM. The unique quenching of fluorescence (measured at excitation/emission wavelengths of 380/470 nm; quantum yield 16%) is attributed to the fairly selective capture of Cu(II) by the amino and amide groups on the surface of the TCDs. On addition of GSH to the quenched TCD/Cu(II) complex, fluorescence is restored. This effect enables GSH to be quantified in the 0.2 to 175 μM concentration range, with a 0.11 μM detection limit. The turn-on response to GSH is highly selective over other natural amino acids and common anions. Furthermore, the TCDs were successfully applied to image Cu(II) and GSH in living yeast cells.

A fluorescein-based chemosensor for relay fluorescence recognition of Cu(ii) ions and biothiols in water and its applications to a molecular logic gate and living cell imaging.

Relay recognition of copper(ii) ions and biothiols via a fluorescence "on-off-on" cascade was designed and realized as a new sequential combination of cations and small molecules. Probe 1 bearing a fluorescein skeleton was thus synthesized, which performed well in 100% HEPES buffer (pH = 7.0) solution, as a highly sensitive, selective fluorescence sensor for Cu2+. The limit of detection (LOD, 0.017 ppm) was obtained, and this value is much lower than 1.3 ppm, allowed by US EPA. The 1 : 1 complex generated from fast sensing of Cu2+ when excited at 491 nm, showed good relay recognition for biothiols (i.e., Cys, Hcy and GSH with low detection limits of 0.12 μM, 0.036 μM and 0.024 μM, respectively) via remarkable fluorescence enhancement. The origin of this relay process was disclosed through ESI-MS and corresponding density functional theory (DFT) computations. Notably, probe 1 can be utilized for the construction of a molecular logic gate with the IMPLICATION function by using the above fluorescence changes. Moreover, this relay recognition was also applied to HepG2 cell imaging successfully.

Novel reversible fluorescent probe for relay recognition of Zn2+ and PPi in aqueous medium and living cells

Abstract A new fluorescent probe 4′-hydroxy-3′-((8-quinolineimino) methyl)-4-biphenylcarbonitrile (L) has been synthesized for the sequential detection of Zn 2+ and PPi in aqueous ethanolic (3/2 v/v) HEPES buffer (pH 7.1). Addition of Zn 2+ to the solution of L resulted in a red shift (Δλ = 18 nm) with a pronounced enhancement in the fluorescence intensity, while there was no enhancement in presence of other metal ions. The subsequent addition of PPi anion can switch off the fluorescence signal by bringing the Zn 2+ ion out of the coordination cavity of the chemosensor L. No interference was observed from other anions, making the L–Zn 2+ ensemble a highly sensitive and selective PPi probe. The detection limit is 5.31 × 10 −8 M and 9.41 × 10 −8 M for Zn 2+ and PPi, respectively. The sensing process is reversible and the probe may be recycled for further use. Cell imaging studies demonstrate that this sensor is capable of sensing Zn 2+ and PPi in living cells.

Imidazoloquinoline bearing thiol probe as fluorescent electrochemical sensing of Ag and relay recognition of Proline

Abstract A new highly selective fluorescent chemosensor for Ag + was developed based on an imidazole conjugated quinolone bearing a thiol group ( IQT ). The Chemosensor serves as fluorescence quencher for Ag + in solution in the presence of other competing metal ions. Further, the in situ formed IQT -Ag + complex is utilized as a reversible sensor for the amino acid, Proline with high selectivity over other amino acids by a fluorescence enhancement mechanism as relay recognition process. The practical applications for sensor IQT is also demonstrated by the complete removal of Ag + ions from the environmental water samples via electrochemical desalination techniques and its bioimaging in cellular micro-organisms.

“Cascade recognition” of Cu2+ and H2PO4− with high sensitivity and selectivity in aqueous media based on the effect of ESIPT

Organic molecular sensors have the advantage of being used through easy, fast, economical and reliable optical methods for detecting toxic metal ions in the environment. In the present work, a simple but specific organic ligand N,N-(3,3′-dimethyl biphenyl)-bis(4-diethylaminosalicyladimine) (Q2) was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). Q2 can be regarded as a colorimetric and fluorescent sensor for relay recognition of Cu2+ and H2PO4− in DMSO/H2O (8:2, v/v) HEPES buffer solutions. Moreover, sensor Q2 showed a highly sensitive and selective response towards Cu2+ and H2PO4− over other metal ions and anions. Particularly, the fluorescence “ON–OFF–ON” responding circle could be repeated over 4 times by the sequential addition of Cu2+ and H2PO4−. Notably, the actual usage of sensor Q2 was further demonstrated by test kits and silica gel plates. The fluorescence changes of Q2 upon the addition of Cu2+ and H2PO4− were utilized as an INHIBIT logic gate at the molecular level, using Cu2+ and H2PO4− as chemical inputs and the fluorescence intensity signal as the output.

A fluorescent sensor based on binaphthol-quinoline Schiff base for relay recognition of Zn2+ and oxalate in aqueous media

To develop an effective fluorescent chemosensor for relay recognition of Zn2+ and oxalate, a new fluorescent sensor based on binaphthol-quinoline Schiff base L 1 was designed and synthesized. In DMSO-H2O (1/1, v/v, HEPES 10 mM, pH = 7.4) solution, L 1 exhibits highly selective fluorescence turn on response to Zn2+ over other metal ions. The Zn2+ recognition event is barely interfered by other coexisting metal ions except Cu 2+, Co 2+ and Ni 2+. The in situ generated L 1 -Zn $^{\mathrm {2+}}_{\mathrm {}}$ complex was further used as a chemosensing ensemble for oxalate detection. The complex L 1 -Zn2+ displays high selectivity to oxalate with significant fluorescence quenching through Zn2+ ion displacement approach. In addition, application of L 1 for imaging of Zn2+ and oxalate in living HeLa cells was also examined.

A N‐(2‐hydroxyethyl)piperazine dangled 2,5‐diphenyl‐1,3,4‐oxadiazole‐based fluorescent sensor for selective relay recognition of Cu2+ and sulfide in water

A new 2,5-diphenyl-1,3,4-oxadiazole-based derivative (L) was synthesized and applied as a highly selective and sensitive fluorescent sensor for relay recognition of Cu2+ and S2- in water (Tris-HCl 10 mM, pH = 7.0) solution. L exhibits an excellent selectivity to Cu2+ over other examined metal ions with a prominent fluorescence 'turn-off' at 392 nm. L interacts with Cu2+ through a 1:2 binding stoichiometry with a detection limit of 4.8 × 10-7 M. The on-site formed L-2Cu2+ complex exhibits excellent selectivity to S2- with a fluorescence 'off-on' response via a Cu2+ displacement approach. Copyright © 2016 John Wiley & Sons, Ltd.

Modified 1H-phenanthro[9,10-d]imidazole derivative with the double acetohydrazide as fluorescent probe for sequential detection of Ni2+ and Al3+ with ‘on–off–on’ response

Ni2+ to Al3+ relay recognition in DMF/H2O (1:9, v/v, HEPES 20mM, pH=7.4) solution was designed and realized with sequential detection by use of novel modified 1H-phenanthro[9,10-d]imidazole with the double acetohydrazide as fluorescent probe (L) with ‘on–off–on’ response. The probe L exhibited a more than 40-fold fluorescence quenching in the presence of Ni2+ with a 1:1 binding stoichiometry between probe L and Ni2+. The resultant L–Ni2+ showed good relay recognition ability for Al3+ via fast fluorescent enhancement. Moreover, other ions failed to generate distinct inference, which meant that probe L had desirable selectivity for relay recognition of Ni2+ and Al3+. Furthermore, the different binding modes of probe L with Ni2+ and Al3+ were explained and confirmed by the 1H NMR spectra.

Relay recognition of F−and a nerve-agent mimic diethyl cyano-phosphonate in mixed aqueous media: discrimination of diethyl cyanophosphonate and diethyl chlorophosphate by cyclization induced fluorescence enhancement

F−to DCNP detection by relay recognition has been designed and realized for the first time with sequence specificity (F−→ DCNP)viaa fluorescence “off–on–on” mechanism.

A turn-on fluorescent sensor for relay recognition of two ions: from a F−-selective sensor to highly Zn2+-selective sensor by tuning electronic effects

A simple ion sensor bearing quinoline and an amide group was designed and synthesized, which showed both colorimetric detection for F− and a fluorescence turn-on response for Zn2+. Moreover, sensor L2 can distinguish F− and Zn2+via different sensing mechanisms.

A new fluorescent probe based on quinoline for detection of Al3+ and Fe3+ with “off–on–off” response in aqueous solution

A new quinoline-based fluorescent probe has been designed and synthesized. It showed highly selective relay recognition of Al3+ and Fe3+via a fluorescence “off–on–off” mechanism by central metal displacement.

A fluorescent probe for relay recognition of homocysteine and Group IIIA ions including Ga(iii)

Challenging relay recognition of Hcy and Ga(3+), has been realized for the first time. Chemodosimeter 1 bearing a 1,1'-binaphthyl skeleton is a fluorescence turn-on probe for Hcy over Cys. The system (2) generated from the recognition of Hcy exhibited further fluorescence enhancement for Ga(3+), which is the first example for specific fluorescent recognition of this metal ion.

A selective fluorescent probe for relay recognition of Al3+ and Cu2+ through fluorescence “off-on-off” functionality

A new 3-hydroxylflavone-based fluorescent probe N′-(3-(3-hydroxy-4-oxo-4H-chromen-2-yl)benzylidene)picolinohydrazide (1) with two different binding sites, 3-hydroxy-4-keto (site 1) and 2-picolinyl hydrazide (site 2), has been designed and synthesized. It shows highly selective relay recognition of Al3+ and Cu2+via a fluorescence “off-on-off” mechanism. In DMSO-H2O (1:9, v/v) solution, probe 1 displays highly selective response to Al3+ with remarkable emission enhancement through its binding of Al3+ to site 1. Moreover, the in situ system generated from the sensing of Al3+ demonstrates eminent relay recognition of Cu2+ via a fluorescence quenching through its binding of Cu2+ to site 2. These proposed binding modes are also proved by 1H NMR titration. The detection limits for Al3+ and Cu2+ are calculated to be 21.7μM and 0.95μM, respectively.

A fluorescent sensor based on bicarboxamidoquinoline for highly selective relay recognition of Zn2+ and citrate with ratiometric response

A novel bicarboxamidoquinoline-based fluorescent sensor 1 was designed and synthesized, which performed ratiometric recognition for Zn2+ without interference from Cd2+. The sensor 1 bound Zn2+ in 1:1 stoichiometry, with the binding constant of 2.07×103M−1. Moreover, the in situ generated 1–Zn2+ complex could serve as an excellent ratiometric citrate sensor via a Zn2+ displacement and discriminated citrate from a series of common carboxylates in neutral aqueous solution.

An Imidazole based probe for relay recognition of Cu2+ and OH− ions leading to AND logic gate

2-(2-methoxyphenyl)-4,5-diphenyl-1H-imidazole 1, an imidazole-based compound, was found to sense Cu2+ ions via fluorescence and absorption spectroscopy over a number of other metal ions. During Cu2+ sensing, the chemosensor 1 followed a “switch-off” mechanism. Job’s plot supported 1:1 stoichiometry of 1-Cu2+ complex. The 1-Cu2+ complex formed in situ underwent different absorption changes with OH− ions. These differential absorption changes observed with the addition of Cu2+ and OH− ions were used to mimic AND logic gate using A274nm as output. An imidazole based chemosensor 1 has been established as the molecular AND logic gate for relay recognition of Cu2+ and OH- ions. The differential absorption changes observed with addition of Cu2+ and OH- ions were used to mimic AND logic gate using A274 nm as output.

A novel flavone-based fluorescent probe for relay recognition of HSO3− and Al3+

In this work, a new flavone-based fluorescent probe 3-hydroxy-3′-formylflavone (3HFF) was designed to achieve highly selective relay recognition of HSO3− and Al3+ in DMSO–H2O (2:8, v/v) solution. 3HFF displayed a highly selective response to HSO3− with a green fluorescence appearing at 524nm. Moreover, the in situ generated 3HFF+HSO3− system demonstrated eminent relay recognition capability for Al3+ with a blue fluorescence appearing at 453nm by the formation of a 1:1 complex between 3HFF and Al3+ in DMSO–H2O (2:8, v/v) solution. However, only slight change was observed in emission intensity with addition of Al3+ to 3HFF, and indicated HSO3− was essential for the sensing of Al3+. This work achieves the detection of HSO3− and Al3+ by only one probe and provides another example for this rare combination (anion/metal).

Multi-analyte, ratiometric and relay recognition of a 2,5-diphenyl-1,3,4-oxadiazole-based fluorescent sensor through modulating ESIPT

A novel 2,5-diphenyl-1,3,4-oxadiazole-based fluorescent sensor for multi-analyte, ratiometric and relay recognition of a through modulating ESIPT has been developed.

Diketopyrrolopyrrole-derived Schiff base as colorimetric and fluoromertic probe for sequential detection of HSO4− and Fe3+ with “off-on-off” response

Anion to cation relay recognition was designed and realized for the first time with sequence specificity (HSO4−→Fe3+) by use of a novel diketopyrrolopyrrole-derived Schiff base (1) via a fluorescence “off-on-off” mechanism. 1 served as a chemodosimeter for HSO4−via hydrolysis process with 10.6 fold fluorescence enhancement as well as color changing from red to orange. The in situ system generated from 1+HSO4− showed good relay recognition ability for Fe3+via fast fluorescence quenching by the formation of a 1:1 complex with color change from orange to faint yellow. Moreover, other anions or metal ions failed to generate distinct response, which indicated that 1 had desirable selectivity for relay recognition of HSO4− and Fe3+. 1 also functioned when supported by silica, indicating that probe 1 had the potential for working as optical solid sensors.

Highly selective relay recognition of hydrogen sulfide and Hg(II) by a commercially available fluorescent chemosensor and its application in bioimaging

A simple fluorescent probe, perylene-3,4,9,10-tetracarboxylic dianhydride, which is a commercially available organic pigment intermediate was reported as a fluorescence chemosensor for Hg(II). This probe can high selectively recognize hydrogen sulfide in water:DMSO (1:1 (v/v), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, pH 7.4) solutions. Namely, with addition of various anions, only HS− can induce a turn on green fluorescence. The mechanism is that perylene-3,4,9,10-tetracarboxylic dianhydride was hydrolyzed and subsequently displaced when meeting with hydrogen sulfide. More interestingly, probe–hydrogen sulfide can successively detect Hg2+. The detection mechanism was based on Hg2+ snatching up sulfur group of probe–HS− adduct, which makes the probe regenerative. And their reaction products were proved by ESI-MS. Their potential application in bioimaging was also illustrated.