Selective Turn-on Fluorescent Probe Research Articles

Carbazole-alt-fluorene based π-conjugated Cu(II)-metallopolymer with pendent diketopyrrolopyrrole unit as highly selective and sensitive turn-on fluorescent probe for detection of amino acids

Highly emissive and soluble poly(carbazole-alt-fluorene) (P1) based π-conjugated alternative copolymers with thiophene-diketopyrrolopyrrole as pendent unit have been designed and synthesized via Pd(0)-catalyzed Suzuki coupling polymerization from the corresponding monomers 3,6-dibromo-9H-carbazol-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole and 2,7-bis-oxaborolan-9,9-dioctylfluorene. The well-defined copolymer P1 has been characterized by multinuclear NMR spectra as well as by tetradetector GPC showing molecular weight (Mn) of 15.6 kg/mol with the polydispersity indices of 1.38. The red emissive polymer has been explored for the detection of amino acids based on a secondary ‘‘turn-on’’ sensing approach. The thiophene-diketopyrrolopyrrole anchored carbazole-alt-fluorene copolymer shows high selectivity towards Cu2+ ions by changing the emission wavelength from red to blue due to the formation of the Cu(II)-metallopolymer (P1–Cu2+). The resulting metallopolymer P1–Cu2+ exhibits high sensitivity and selectivity towards amino acids over the other biologically relevant analytes. More importantly, the P1–Cu2+ metallopolymer exhibited higher sensitivity towards glycine, with the detection limit of 90 ppb (∼1.21 × 10−6 mol/L) along with relatively higher association constant of 2.55 × 108 M−1. To comprehend the sensing mechanism through photo-induced electron transfer (PET), the detailed photophysical studies have been carried out with P1 and its representative monomeric model compound M1. Furthermore, fluorescence anisotropy study has also been carried out to inspect the molecular interactions responsible for the sensing properties of P1–Cu2+ metallopolymer towards glycine.

Isatin-Schiff base functionalized graphene oxide as a highly selective turn-on fluorescent probe for the detection of Pd(II) via photoinduced electron transfer pathway

We investigated the use of isatin-Schiff base functionalized graphene oxide (ISBGO) as a selective fluorescent chemosensor for the detection of palladium ions. Selectivity tests indicated that over 23 metal ions tested, ISBGO (λex = 340 nm, λem = 504 nm) showed the highest affinity for Pd(II), displaying a 10.1-fold enhancement. Also, interference tests proved that in the presence of both Pd(II) and other metal ions, there was still high fluorescence intensity and no considerable quenching occurred. According to DFT and TD-DFT calculations, photo-induced electron transfer (PET) is responsible for the turn-on response produced by the chemosensor. Coordination of Pd(II) with ISBGO in fact blocks PET from imine nitrogen of 3-iminoindolin-2-one moiety to the benzene ring, which in turn leads to a turn-on response. In addition, Job’s plot analysis and Benesi-Hildebrand approach suggest that ISBGO preferably forms a 1:1 complex with Pd(II) with an association constant of 1.020 × 105 M−1. Moreover, FT-IR spectroscopy and DFT study showed that amide oxygen and imine nitrogen of 3-iminoindolin-2-one moiety acted as binding sites of ISBGO. High sensitivity, fast response, great degree of sensitivity, short life time, low detection limit of 32 nM combined with high association constant (Kf) of 1.020 × 105 M−1 and increased fluorescence quantum yield (Φf) of roughly 1.5-fold in the presence of Pd (II), highlight the role of ISBGO as an excellent probe for sensing Pd(II) in aqueous solution.

De Novo Construction of Fluorophores via CO Insertion-Initiated Lactamization: A Chemical Strategy toward Highly Sensitive and Highly Selective Turn-On Fluorescent Probes for Carbon Monoxide.

Extensive studies in the last few decades have led to the establishment of CO as an endogenous signaling molecule and subsequently to the exploration of CO's therapeutic roles. In the current state, there is a critical conundrum in CO-related research: the extensive knowledge of CO's biological effects and yet an insufficient understanding of the quantitative correlations between the CO concentration and biological responses of various natures. This conundrum is partially due to the difficulty in examining precise concentration-response relationships of a gaseous molecule. Another reason is the need for appropriate tools for the sensitive detection and concentration determination of CO in the biological system. We herein report a new chemical approach to the design of fluorescent CO probes through de novo construction of fluorophores by a CO insertion-initiated lactamization reaction, which allows for ultra-low background and exclusivity in CO detection. Two series of CO detection probes have been designed and synthesized using this strategy. Using these probes, we have extensively demonstrated their utility in quantifying CO in blood, tissue, and cell culture and in cellular imaging of CO from exogenous and endogenous sources. The probes described will enable many biology and chemistry labs to study CO's functions in a concentration-dependent fashion with very high sensitivity and selectivity. The chemical and design principles described will also be applicable in designing fluorescent probes for other small molecules.

Differential detection of strong acids in weak acids: a combination of a benzimidazole-carbazole backbone with AIE luminophores as highly sensitive and selective turn-on fluorescent probes

With the combination of a benzimidazole-carbazole backbone and AIE luminophores, highly sensitive and selective turn-on fluorescent probes are achieved and applicable for differential detection of strong acids in weak acids.

A novel water-soluble naphthalimide-based turn-on fluorescent probe for mercury ion detection in living cells and zebrafish

A highly selective and sensitive water-soluble naphthalimide-based turn-on fluorescent probe was synthesized to detect Hg2+ in living cells and zebrafish.

A Zn(II)-Based Sql Type 2D Coordination Polymer as a Highly Sensitive and Selective Turn-On Fluorescent Probe for Al3.

A luminescent coordination polymer with the overall formula {[Zn(tr2btd)(bpdc)]∙DMF}n (where tr2btd = 4,7-di(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole; bpdc = 4,4′-biphenyldicarboxylate) was synthesized and characterized by single-crystal and powder X-ray diffraction, thermogravimetric, infrared spectroscopy, and elemental analyses. Luminescent properties of the obtained compound were studied in detail both in the solid state and as a suspension in N,N-dimethylacetamide (DMA). It was found that {[Zn(tr2btd)(bpdc)]∙DMF}n exhibits bright turquoise luminescence with excellent quantum efficiency and demonstrates turn-on fluorescence enhancement effect upon soaking in DMA Al3+ solution. Fluorescence titration experiments were carried out and the detection limit for Al3+ ions was calculated to be 120 nM, which is among the lowest reported values for similar materials. Moreover, compound demonstrated excellent selectivity and reusability, and the mechanism of the response is discussed. These results indicate that {[Zn(tr2btd)(bpdc)]∙DMF}n is a promising probe for sensitive fluorescent Al3+ detection.

Simpler fluorescent probe for homocysteine selective detection

A simpler and selective turn-on fluorescent probe namely 4-(benzothiazol-2-yl) phenyl 2-chloroacetate ester 2 was synthesized by chloro‑acylation of 4-hydroxyphenyl benzothiazole (4-HBT). The probe 2 was investigated for the detection of biothiols among amino acids. The addition of Homocysteine (Hcy) selectively induced significant fluorescence enhancement and the detection limit was determined to be 7.7 × 10−6 M. The probe 2 conserves simple structure, and %atom economy. Paper strip tests were carried out to explore the potential application for naked-eye fluorescence detection of Hcy under UV lamp. We expect the presented probe 2 will offer a valuable approach to acquire selective detection and discrimination of Hcy over other biothiols especially cysteine (Cys).

A Highly Selective Turn-On Fluorescent Probe for the Detection of Zinc.

A novel turn-on fluorescence probe L has been designed that exhibits high selectivity and sensitivity with a detection limit of 9.53 × 10−8 mol/L for the quantification of Zn2+. 1H-NMR spectroscopy and single crystal X-ray diffraction analysis revealed the unsymmetrical nature of the structure of the Schiff base probe L. An emission titration experiment in the presence of different molar fractions of Zn2+ was used to perform a Job’s plot analysis. The results showed that the stoichiometric ratio of the complex formed by L and Zn2+ was 1:1. Moreover, the molecular structure of the mononuclear Cu complex reveals one ligand L coordinates with one Cu atom in the asymmetric unit. On adding CuCl2 to the ZnCl2/L system, a Cu-Zn complex was formed and a strong quenching behavior was observed, which inferred that the Cu2+ displaced Zn2+ to coordinate with the imine nitrogen atoms and hydroxyl oxygen atoms of probe L.

A novel carbazole-based highly sensitive and selective turn-on fluorescent probe for mercury (II) ions in aqueous THF

Based on the known deprotection reaction of thioacetal initiated by Hg2+, a new type of fluorescent probe 3-(4-(1,3-dithiolan-2-yl) phenyl)-9H-carbazole (DTCB) is designed and synthesized successfully. The probe shows a good fluorescence response to Hg2+ in THF-H2O (fw = 5%) mixed system. The addition of Hg2+ greatly enhances the fluorescence intensity of the probe and changed from dark blue to green fluorescence. Within a large Hg2+ concentration range (0–6×10−5 mol·L−1), the fluorescence intensity at 480nm presents good linear with the Hg2+ concentration (R2 = 0.993), and the detection limit of the probe to Hg2+ is below 2.05×10−7 mol·L−1. The DTCB probe shows good selectivity and anti-interference performance, and many metal ions and anions hardly effect on its detection performance. The sensing mechanism is confirmed by theory calculation based on DFT and TD-DFT theories, and the intramolecular charge transfer (ICT) is responsible for the significant fluorescence change of probe DTCB. Meanwhile, the probe is applied to the detection of Hg2+ in real water samples; and it is interesting that the DTCB-based test strip firstly reveals the strong fluorescence from solid-state 3-(4-formylphenyl)-9H-carbazole (FCB) with Hg2+ adding. The results show that the probe based on DTCB has potential application prospect in actual sample analysis.

A Highly Selective Turn-on Fluorescent and Naked-eye Colourimetric Dual-channel Probe for Cyanide Anions Detection in Water Samples.

A highly selective turn-on fluorescent and naked-eye colourimetric dual-channel probe for cyanide anions (CN-) has been designed and characterized. In the mixed solution (DMSO / H2O, 9:1, v / v), only CN- could cause an increase in the UV absorption intensity and the corresponding fluorescence intensity increased, and other anions had no significant effect on the probe. After treatment with cyanide in the probe solution, the solution showed a noticeable colour change, from light yellow to purple. Moreover, a fluorescence spectrophotometer can be used to observe that the fluorescence intensity of the solution is significantly enhanced. The response of the colourimetric and fluorescent dual-channel probe to CN- was attributed to nucleophilic addition, and the mechanism was determined by 1H NMR spectroscopy. In addition, this probe was used to detect CN- in actual water samples, including river water, drinking water, and tap water. The spiked CN- recovery rate is very high (97.2%-100.06%), and analytical precision is also very high (RSD < 2%), which shows its feasibility and reliability for detecting cyanide ions in actual water samples.

Highly selective turn-on fluorescent probe for hypochlorite and viscosity detection

Due to the important role of hypochlorous acid (HOCl) in immune prevention of bacteria towards living organisms and its variations may be related to the change of intracellular viscosity, it is significant to design fluorescent probe to accurately analyze changes for detecting HOCl and viscosity simultaneously. In this paper, water-soluble, very fast-responsive fluorescent probes PTZ-TPP and PTZ-MP based on phenothiazine moiety were developed. The sensing mechanism of the probe with HOCl was elucidated by emission spectra at long and short excited wavelength 480 and 380 nm, and the oxidation structure OPTZ-TPP, sulfur peroxide structure O3PTZ-TPP as well as carbon-carbon double bond cleavage structure OCy-TPP were confirmed by ESI-MS analysis. The detection limit (LOD) of probe PTZ-TPP and PTZ-MP was evaluated to be 14.7 and 19.4 nM respectively. Moreover, the probe PTZ-MP was further used for the detection of viscosity. Furthermore, cell imaging of PTZ-TPP towards HOCl was conducted. And it is expected to be used in simultaneous determination of HOCl and viscosity in intracellular.

Detecting Cysteine in Bioimaging with a Near-Infrared Probe Based on a Novel Fluorescence Quenching Mechanism.

Near-infrared (NIR) fluorescent probes are very significant for detecting cysteine in biological systems. Herein, we report a highly selective and sensitive NIR turn-on fluorescent probe (BDP-NIR) based on BODIPY with large Stokes shift (105 nm) for detecting Cys. We clarified the sensing mechanism based on the different thiol-induced SN Ar substitution/rearrangement reaction of the probe with cysteine and homocysteine/glutathione, which leads to the corresponding amino- and thiol-BODIPY dyes with distinct photophysical properties. Moreover, a novel mechanism of fluorescence quenching was demonstrated by density functional theory calculation. The reason for the fluorescence quenching of the probe might be intersystem crossing (from singlet to triplet excited state). Moreover, BDP-NIR had a high linear dynamic range of 0-500 μM, which was promising for detecting cysteine quantificationally. Significantly, BDP-NIR was capable of sensing endogenous cysteine in living cells and in vivo.

Simpler molecular structure as selective & sensitive ESIPT-based fluorescent probe for cysteine and Homocysteine detection with DFT studies

The undesired research results of triazole synthesis were successfully utilized as a simpler, sensitive and selective turn-on fluorescent probe 2 namely chloro-acetic acid 2-benzothiazol-2-yl-phenyl ester (HBT-AcCl) which was synthesized by simple chloroacylation of 2-hydroxyphenyl benzothiazole (HBT). Only one simple chloroacetate, a trigger unit as the reaction site of probe 2 makes it more simple, sensitive and selective for Cys and Hcy over other Amino Acids. The presented probe HBT-AcCl conserves simple structure, reduces the use of extra chloroacetate and improves %atom economy as compare to similar reported probes. Paper strip tests were carried out to explore the potential application for naked-eye detection of Cys under UV lamp. The selectivity of the HBT-AcCl probe for Cys and Hcy is supported by the results of absorbance and emission spectroscopy experiments and theoretical DFT calculations.

A selective turn-on fluorescent probe for Al3+ based-on a diacylhydrazone deritive in aqueous medium and its cell imaging

Al3+ has no spectroscopic characteristics and its coordination ability is very poor. Therefore, the detection of Al3+ is a challenging task. To address this issue, here we report a diacylhydrazone-based fluorescent chemosensor (L) for Al3+ structurally characterized by HRMS and NMR spectroscopy. The selective test revealed that L had a high selectivity towards Al3+ with a turn-on response in DMF/H2O (v/v, 8: 2) buffer solution. The combination ratio between L and Al3+ was determined to be 1: 2 as supported by Job’s plot analysis and NMR titration experiment. The recognition of Al3+ was without interference of other competing species. The detection limit was calculated to be as low as 2.41 μM. Moreover, the probe was proved to be of low cytotoxicity in physiological condition and it was applied to image Al3+ in living cells successfully.

Visualization of sulfur mustard in living cells and whole animals with a selective and sensitive turn-on fluorescent probe

Sulfur mustard is a potent blister agent and one of the most harmful chemical warfare agents. To explore the toxicokinetics and biodistribution of SM, a reliable detection method for monitoring sulfur mustard would be indispensable. We describe the design, synthesis and application of a selective and sensitive turn-on fluorescent probe for sulfur mustard detection. A good linear relationship between fluorescence emission intensity and SM concentration was observed. The probe, SM-Flu, was applied to the determination and imaging of sulfur mustard in living cells and Aurelia coerulea polyps. With SM-Flu, concentration and time profiles for SM in mouse brain after exposure to SM were first measured.

A Highly Selective Turn-on Fluorescent Probe for the Detection of Aluminum and Its Application to Bio-Imaging.

Aluminum is the most abundant metallic element in the Earth’s crust and acts as a non-essential element for biological species. The accumulation of excessive amounts of aluminum can be harmful to biological species. Thus, the development of convenient and selective tools for the aluminum detection is necessary. In this work, a highly selective aluminum ion fluorescent probe N’-(2,5-dihydroxybenzylidene)acetohydrazide (Al-II) has been successfully synthesized and systemically characterized. The fluorescence intensity of this probe shows a significant enhancement in the presence of Al3+, which is subject to the strong quench effects caused by Cu2+ and Fe3+. The binding ratio of probe-Al3+ was determined from the Job’s plot to be 1:1. Moreover, the probe was demonstrated to be effective for in vivo imaging of the intracellular aluminum ion in both living Drosophila S2 cells and Malpighian tubules.

Highly selective turn-on fluorescent probe for detection of cyanide in water and food materials

A naphthoquinone-imine based fluorescent probe (R) has been synthesized and characterized by NMR and mass spectral techniques. The receptor shows high selectivity towards cyanide in water in the presence of other competitive anions with an instantaneous colour change from non-emissive to green under UV light. The turn-on fluorescence is due to deprotonation of three hydroxyl groups by cyanide ions as evidenced from 1H NMR titration experiment. The LOD of cyanide by R in water is 0.6 μM, which is much lower than the permissible limit of cyanide in drinking water according to the WHO.

Polydopamine-coated carbon nanodots are a highly selective turn-on fluorescent probe for dopamine

Carbon nanodots (CDs) were prepared by the pyrolysis of lactose in hot alkali solution for 5 min. The resulting CDs possess spherical and monodisperse shape with an average diameter of ∼3 nm. The blue fluorescence of the CDs, with excitation/emission peaks at 414/470 nm, can be turned-on in the presence of very low concentrations of dopamine (DA) due to the formation of a poly-DA shell on the CDs. Fluorescence is only enhanced by DA, while other chemically related compounds do not interfere. Fluorescence increases linearly in the 1.0–10.0 μM DA concentration range, with a 0.22 μM lower detection limit. The nanoprobe was applied to the determination of DA in injections and in spiked urine samples, and the results compared well with those obtained by HPLC. The nanoprobe has a fast response, is inexpensive and highly selective.

Remarkably selective biocompatible turn-on fluorescent probe for detection of Fe3+ in human blood samples and cells.

The robust nature of a biocompatible fluorescent probe is demonstrated, by its detection of Fe3+ even after repeated rounds of quenching (reversibility) by acetate in real human blood samples and cells in vitro. Significantly trace levels of Fe3+ ions up to 8.2 nM could be detected, remaining unaffected by the existence of various other metal ions. The obtained results are validated by AAS and ICP-OES methods. A portable test strip is also fabricated for quick on field detection of Fe3+. As iron is a ubiquitous metal in cells and plays a prominent role in biological processes, the use of this probe to image Fe3+ in cells is a substantial development towards biosensing. Cytotoxicity studies also proved the nontoxic nature of this probe.

Highly selective and sensitive turn-on fluorescent probes for sensing Hg2+ ions in mixed aqueous solution

A highly selective and sensitive probe 1b was successfully developed for detecting Hg2+ ions in mixed aqueous medium with a “turn on” fluorescence mode, via a series of structural optimization of probes. These probes could be easily synthesized by one-step condensation reactions between o-phenylenediamine or 2, 3-diaminonaphthalene and o (salicylaldehyde), m, or p-hydroxybenzaldehyde. Introducing a certain amount of Hg2+ ions the fluorescence of probes bearing one or two salicylaldehyde moieties including probes 1a, 1b, and 4 could be turned on. The fluorescent response is likely due to the well matching between Hg2+ ions size and the geometric structure of probes, resulting in that probes bearing salicylaldehyde moiety are mostly favorable for binding with Hg2+ ions by way of 1:1 molar ratio. These bindings likely facilitate excited state internal proton transfer (ESIPT) or ESIPT coupled aggregation-induced enhancement of emission (AIEE) process. Considering the sensitivity and the potential of practical application, probe 1b was chosen to establish a fluorescent enhancement sensing system towards Hg2+ ions over other competing metal ions, with excellent limit of detection of 12.5 ppb.