Fluorescence Turn Research Articles

Fluorescence turn off-on probe (β-cyclodextrin-hydroxyquinoline) for monitoring of Cd2+ ions and tetracycline

In this paper, a photoluminescent turn off-on switch probe β-cyclodextrin-hydroxyquinoline (β-CD-HQ) was efficiently applied for detection and measurement of Cd2+ ions and detection of tetracycline. The proposed assay has shown an excellent selective fluorescence response toward Cd2+ ions over other ions like Al3+, Pb2+, Zn2+, Co2+, K+, Na+ and Sr2+. The fluorescence emission intensity of the probe is slightly affected by competing ions. In optimum pH value, 4, the limit of detection and linear concentration range were 0.05 nM and 0.1–1.5 nM, respectively. Additionally, the extraordinary output signal of β-CD-HQ was utilized to investigate the logic behavior of β-CD-HQ in the aqueous media. Accordingly, a solid support logic circuit was made by producing the fluorescence output signal under the stimulation of Cd2+ ions and tetracycline as inputs.

Pattern recognition of amino acids based on highly fluorescent SDS modified pyridyl thiazole derivative

• Pyridyl thiazole fluorophore for the selective optical sensing of aspartic and glutamic acid. • Modification of fluorophore with SDS assemblies for the discriminative sensing of acidic and basic amino acids. • A turn on fluorescence response for acidic amino acids and a turn off sensing for basic amino acids. • Principal component analysis for the classification and clustering of acidic, basic and neutral amino acids. Selective and sensitive detection of amino acids is extremely significant as they play a key role in many biological processes. Herein, a pyridyl-thiazole based fluorophore (PTCN), modified with sodium dodecyl sulphate (SDS) assemblies, has been employed for the sensing of AA in aqueous solution. PTCN molecule exhibited excellent pH response due to the protonation of pyridyl nitrogen followed by the intramolecular charge transfer. PTCN showed dual emission along with enhanced quantum yield in SDS micellar assemblies. This improved the sensitivity of the PTCN –SDS system (PS), not only by lowering the limit of detection but also by detecting basic AA along with acidic AA. A fluorescence turn on response of PS system with acidic AA i.e. Asp and Glu has been observed. However, the PS system exhibited a ratiometric sensing pattern for basic AA i.e. Arg, Lys and Hys. Protonation and deprotonation of the fluorophore in presence of different types of AA are responsible for the changes observed in fluorescence spectra. The detection limits for Asp and Glu were found to be 0.47 μM and 0.64 μM respectively. Arg, Lys and Hys showed a detection limit of 8.36 μM, 26.6 μM and 51.9 μM respectively. Principal component analysis (PCA) effectively demonstrated discrimination of acidic, basic and neutral AA clusters. This study demonstrates the efficiency of the PS ensemble for selective, sensitive and discriminative sensing of AA.

CQD@γ-Fe2O3 multifunctional nanoprobe for selective fluorescence sensing, detoxification and removal of Hg(II)

Abstract In this paper we have developed a simple integrated nanoprobe that combines fluorescent carbon quantum dots (CQD) and superparamagnetic magnetic iron oxide(SPION) equipped with –SH, -COOH functionalization for sensing and removal of mercury from aqueous medium. The probe has diminished fluorescence due to photoelectron transfer between CQD fluorophore and magnetic nanoparticle. A remarkable enhancement in fluorescence emission intensity is achieved in presence of Hg2+ which inhibits the PET mechanism. The limit of detection of this fluorescence turn on sensing is 0.376 nM which is the lowest among all reported protocol for Hg sensing. Due to presence of abundant functional groups such as –SH, -COOH in the magnetic component the probe shows excellent mercury removal efficiency of 70%. The utility of the probe has also been explored to monitor Hg in bacteria as well as in living fish sample.

A novel and sensitive ratiometric fluorescence assay for carbendazim based on N-doped carbon quantum dots and gold nanocluster nanohybrid

A novel fluorescence "turn on" ratiometric fluorescent sensor was employed to determine carbendazim. The sensing process was achieved through the strong fluorescence resonance energy transfer (FRET) between nitrogen doped carbon quantum dots (N-CQDs) and gold nanocluster (AuNCs). The photoluminescence intensity of N-CQDs can be deactivated by AuNCs through FRET effect and recovered by the addition of carbendazim. The ratiometric detection of carbendazim is achieved by recording the photoluminescence and second-order Rayleigh scattering (SRS) signal of N-CQDs/AuNCs system. With the introduction of carbendazim to the sensing platform resulted in the photoluminescence and SRS signal of N-CQDS/AuNCs enhancing. UV-vis absorption, Zeta potential and fluorescence lifetime analyses indicate that the fluorescence turn on process can be attributed to the aggregation of AuNCs breaks the FRET process and increases SRS intensity. N-CQDs/AuNCs probe present a good sensitivity and selectivity for carbendazim detection, with two linear response ranges (1-100 μM, 150-1000 μM), low detection limit of 0.83 μM and 37.25 μM. Furthermore, real sample analyses indicate that the as-presented sensor has potentials in carbendazim determination in real sample analyses.

A squaraine-based fluorescence turn on chemosensor with ICT character for highly selective and sensitive detection of Al3+ in aqueous media and its application in living cell imaging.

A novel and simple squaraine-based fluorescent chemosensor SQ-BH bearing the benzoylhydrazine moiety was developed for the highly sensitive and selective detection of Al3+ in methanol-water mixture. The chemosensing behaviors of SQ-BH and its binding interaction with Al3+ were explored by various spectroscopic analyses. The reversibility of Al3+ recognition process was investigated using EDTA. The results of experiments and DFT/TDDFT calculations revealed that the chemosensor SQ-BH obeyed a turn on mechanism which was associated with the inhibited photoinduced electron transfer (PET), the enhanced intramolecular charge transfer (ICT) and the activated chelation enhanced fluorescence (CHEF). Furthermore, the fluorescent chemosensor SQ-BH whose excellent biocompatibility was confirmed by a standard MTT assay could be used to detect Al3+ in living cells, indicating its potential application value in biological fields.

An antipyrine based fluorescence "turn-on" dual sensor for Zn2+ and Al3+ and its selective fluorescence "turn-off" sensing towards 2,4,6-trinitrophenol (TNP) in the aggregated state.

A 2,6-diformyl-p-cresol (DFC)-4-amino antipyrine (AP) based dual signaling fluorescent Schiff base ligand (DFCAP) is found to exhibit colorimetric and fluorescence turn on selective sensing towards metal ions, Zn2+ and Al3+. It also exhibits a significant aggregation induced emission (AIE) phenomenon by controlling the water-THF solvent ratio which provides robust green emissive fluorogenic aggregates with well-defined morphologies. Turn-on fluorescence enhancements as high as 195 fold and 168 fold in methanol for Al3+ and Zn2+ at 480 nm and 508 nm, respectively, were noticed. The binding constants and stoichiometry determined from the fluorescence titration data are K = 7.63 × 104 M-1 and 3.42 × 104 M-1 and 1 : 1 complexation for both Al3+ and Zn2+ respectively, supported by Job's method. DFCAP shows high sensitivity towards the detection of Zn2+ and Al3+ ions with very low detection limit values of ca. ∼21 nM and 30 nM respectively. Besides by applying its attractive AIE feature, the green emissive hydrosol functions as a good chemosensor with high sensitivity for a selected explosive TNP through ground state complexation with a LOD value of ca. ∼1.74 μM and especially a high Stern-Volmer quenching constant of ca. ∼4.14 × 105 M-1. For instant 'naked eye' response for the trace detection of TNP in the solution state, we fabricated a simple paper strip that could detect TNP on-site in a fast, inexpensive and simple way.

Antipyrine based Schiff's base as a reversible fluorescence turn "off-on-off" chemosensor for sequential recognition of Al3+ and F- ions: A theoretical and experimental perspective.

A Schiff's base probe (L) based on antipyrine has been intended, synthesized and assessed as a turn "off-on-off" probe for successive recognition of Al3+ and F-. The probe L act out as a turn "on" fluorescence probe towards Al3+ in methanol at pH 6 which turned "off" by F- at 433 nm. The 1:1 binding stoichiometry of L +Al3+ complex was revealed by Job's plot and approved by ESI-HRMS data. The binding constant and limit of detection of probe L for Al3+ were found to be 2.951 × 107 M-1 and 0.61 × 10-7 M respectively, which is lesser than the acceptable limit (0.74 × 10-7 M) in drinking water. The proposed binding sites and the mode of interaction of probe L was studied and validated by 1H NMR titration and 27Al NMR spectroscopic studies. To get detailed vision into binding mechanism and optimized structure of receptor L and L +Al3+, L +Al3++F- complex, theoretical calculations using DFT/DND and TDDFT method were performed. Furthermore, probe L can mimic INHIBIT logic function using Al3+ and F- being logic inputs and examining the fluorescence maxima at 433 nm as output.

A lysosome targeting probe based on fluorescent protein chromophore for selectively detecting GSH and Cys in living cells

The low-molecular weight biothiols like glutathione (GSH) and cysteine (Cys) play many important roles in various biological processes, the imbalance of biothiols level will lead to many diseases. However, methods that can selectively detect the GSH and Cys was rarely reported because of the similar reactivity and structure. Here, a fluorogenic method was presented to selectively detect the GSH and Cys in vitro using probe ML-FP based on fluorescent protein mimics. Probe ML-FP is a fluorescence turn on probe with lysosome targeting capacity. 2,4-dinitrobenzenesulfonyl serves as fluorescence quench and detection group in probe ML-FP. Differentiating the GSH and Cys was realized benefit from the different reaction time as well as fluorescence response between probe and target species. Low detection limit (4.98 nM for Cys and 4.39 nM for GSH) as well as fast response time was founded in this work. Probe ML-FP possess excellent biocompatibility due to fluorescent protein chromophore and was successfully used for bioimaging in living cells.

A new colorimetric and near-infrared fluorescent probe for biothiols and its application to image GSH in living cells and zebrafish

Abstract A new near-infrared (NIR) fluorescent probe based on 2-Methylchromone was exploited for relay recognition of Cu2+ and biothiols. The mechanism involved in complex between metal ion and probe, and subsequent displacement reaction, which make the probe can detect GSH by NIR fluorescence turn on emission. Probe showed a fluorescence band at 718 nm in PBS-EtOH (3:2, v/v, 10 mM PBS, pH 7.4) solution. Upon the addition of Cu2+, a large fluorescence quenching was observed due to the coordination between probe 1 and Cu2+. The 1-Cu2+ could be used to detect biothiols utilizing high affinity of biothiols with Cu2+. This “on-off-on” fluorescent probe was also successfully applied to image GSH in MCF-7 cells and zebrafish.

Negatively charged molybdate mediated nitrogen-doped graphene quantum dots as a fluorescence turn on probe for phosphate ion in aqueous media and living cells

Since inorganic phosphate ion (PO43-) plays very important roles in environment or living organisms, developing a selective and sensitive detection method for PO43- is highly desired. Owing to the superior optical properties, graphene quantum dots (GQDs) have been developed as a promising emitting material in fluorescence analysis. Herein, we reported the first example of negatively charged molybdate-mediated nitrogen doped graphene quantum dots (Mo7O246--mediated N-GQDs) as a fluorescence "off-on" probe for PO43-via "anion ion-mediated" strategy. The N-GQDs was firstly modified with Mo7O246- through a complex bonding system containing ionic and hydrogen bonds. The formation of N-GQDs/Mo7O246- complex leaded to photoluminescence (PL) quenching of N-GQDs. In the presence of PO43-, strong affinity between PO43- and Mo7O246- produced ammonium phosphomolybdate, which destroyed the pre-formed N-GQDs/Mo7O246- structure and detached Mo7O246- from N-GQDs surface. Thus, the PL of N-GQDS was in turn switched on. Under optimal conditions, this probe exhibited a good linear relationship between PL response and PO43- concentration in the range from 7.0 to 30.0 μM with a limit of detection of 50 nM. Also this probe with high selectivity and sensitivity has been successfully used to sense PO43- in natural water, biological fluid, and living cells.

2-Vinylfuran substituted BODIPY H2S fluorescent turn on probe based on hydrolysis of furfural and nucleophilic addition of double bond

In this work, a fluorescent H2S turn on probe BODIPY-vinylfuran has been synthesized by reaction of 8-methyl-BODIPY with functional group 5-methylfuranal. When H2S is present, the furan ring is hydrolyzed and ring-opened, and H2S further undergoes a nucleophilic addition reaction with carbon-carbon double bond (CC) of vinylfuran, resulting in enhanced fluorescence. Due to the addition reaction of carbon-carbon double bond with H2S, the π-π conjugated structure of furan and BODIPY is destroyed, resulting in the shifting of maximum emission peak from 535 nm to 496 nm. Sensor BODIPY-vinylfuran demonstrates remarkable performance with more than 150-folds increase in fluorescence intensity, low detection limit (99.4 nM) and selectivity to H2S specificity. Furthermore, BODIPY-vinylfuran possesses low cytotoxicity and good biocompatibility. Cellular fluorescence imaging further demonstrates that BODIPY-vinylfuran is highly responsive to both endogenous and exogenous H2S.

Hydrogen-Bond-Induced Emission of Carbon Dots for Wash-Free Nucleus Imaging.

Carbon dots (CDs) are emerging as powerful tools for biosensing and bioimaging because of their intrinsic properties such as abundant precursors, facile synthesis, high biocompatibility, low cost, and particularly robust tunability and stability. In this work, a new type of CDs was prepared from m-phenylenediamine and folic acid by hydrothermal method. Interestingly, the as-prepared CDs show blue emission in non-hydrogen-bonding solution, whereas robust green emission in hydrogen-bonding solution. Based on this phenomenon, a novel fluorescence sensing mechanism named as hydrogen-bonding-induced emission (HBIE) was proposed. The HBIE-CDs have large Stokes shift (141 nm) in water, good biocompatibility, and ultrasmall size, which facilitates their translocation into living cells. Very importantly, the as-prepared HBIE-CDs show strong affinity toward nucleic acid without interference from other biological species. After binding with DNA/RNA through hydrogen bond, as high as 6-fold green fluorescence enhancement of HBIE-CDs was observed. Since the nucleus is rich in DNA/RNA, these HBIE-CDs were successfully used for rapid and, especially, wash-free subcellular in situ imaging of the nucleus in living cells in a fluorescence turn on mode, which has a great practicability to be used for nucleus imaging in bioanalytical studies and clinical applications.

Carbon dots-based fluorescent turn off/on sensor for highly selective and sensitive detection of Hg2+ and biothiols.

In this work, sodium salicylate and ethylenediamine (EDA) are used as the precursors to synthesize green fluorescent carbon dots (CDs). The CDs have some attractive properties, including better oxidation resistance, good water solubility, and excellent stability in high ionic strength solutions in a pH range of 6.0-10.0. Compared to other metal ions, only Hg2+ can quench the fluorescence of CDs, and with the introduction of biothiols, the fluorescence of the CDs/Hg2+ system can be recovered. Therefore, a turn off/on fluorescent sensor is constructed using CDs as a fluorescent probe, and the sensor is applied to the detection of Hg2+ and biothiols (glutathione, homocysteine and cysteine). In addition, the fluorescent sensor exhibits excellent selectivity and sensitivity. The linear range of Hg2+ is 0.05-10 μM with the detection limit of 44 nM. Glutathione, homocysteine, and cysteine have a linear response in the range of 0.5-10 μM with the limit of detection of 80, 76, and 69 nM, respectively. Furthermore, the fluorescence method is successfully used to detect Hg2+ in actual water samples and biothiols in human plasma.

Betti base and its modified phthalonitrile derivative for the turn on fluorimetric detection of Hg2+ and Cr3+ ions

Abstract The Betti Base Phenyl-(2-pyridinylamino)-methyl-2-naphthalenol (BB) derived by the multicomponent Mannich aminoalkylations reaction from 2-naphthol, 2-aminopyridine and benzaldehyde. The modified phthalonitrile 4-((1-(phenyl(pyridin-2-ylamino)methyl)naphthalen-2-yl)oxy)phthalonitrile BBPN was obtained by aromatic nucleophilic coupling reaction of 4-nitrophthalonitrile with BB. The compounds were successfully characterized by common spectroscopic and single crystal XRD techniques. The compounds BB and BBPN was exhibited a selective and sensitive fluorescence detection tendency towards mercuric Hg2+ and chromium Cr3+ ions respectively by the fluorescence turn on processes. Job’s plot method is employed to obtain idea about the stoichiometric interaction of metal ions with fluorescent probes. Theoretical calculation was done by Density Functional Theory DFT-B3YLP in order to get atomistic insights into the coordination geometry of Hg2+ and Cr3+ with BB and BBPN respectively. The limit of detection (LOD) of Hg2+ with BB and Cr3+ with BBPN was estimated respectively as 9.7 × 10−7 mol/L and 7.03 × 10−6 mol/L. The fluorescence enhancement of both compounds were induced by the inhibition of Photoinduced Electron Transfer (PET) process in which electron transfer happens from amino group to the fluorophore naphthol unit. The PET process was blocked upon binding of the sensors BB and BBPN with Hg2+ and Cr3+ respectively.

From fluorescent proteins to fluorogenic RNAs: Tools for imaging cellular macromolecules.

The explosion in genome-wide sequencing has revealed that noncoding RNAs are ubiquitous and highly conserved in biology. New molecular tools are needed for their study in live cells. Fluorescent RNA-small molecule complexes have emerged as powerful counterparts to fluorescent proteins, which are well established, universal tools in the study of proteins in cell biology. No naturally fluorescent RNAs are known; all current fluorescent RNA tags are in vitro evolved or engineered molecules that bind a conditionally fluorescent small molecule and turn on its fluorescence by up to 5000-fold. Structural analyses of several such fluorescence turn-on aptamers show that these compact (30-100 nucleotides) RNAs have diverse molecular architectures that can restrain their photoexcited fluorophores in their maximally fluorescent states, typically by stacking between planar nucleotide arrangements, such as G-quadruplexes, base triples, or base pairs. The diversity of fluorogenic RNAs as well as fluorophores that are cell permeable and bind weakly to endogenous cellular macromolecules has already produced RNA-fluorophore complexes that span the visual spectrum and are useful for tagging and visualizing RNAs in cells. Because the ligand binding sites of fluorogenic RNAs are not constrained by the need to autocatalytically generate fluorophores as are fluorescent proteins, they may offer more flexibility in molecular engineering to generate photophysical properties that are tailored to experimental needs.

Zn(II) ion modulated red emitting copper nanocluster probe for the fluorescence turn on sensing of RDX

Abstract Field employed detection of hidden explosives has drawn intense attention as it poses significant threat to public safety and security. Among the explosives, the selective detection of heterocyclic nitramine compounds such as 1,3,5-trinitrotriazine (RDX) is still challenging since it lacks nitroaromatic rings, possess higher LUMO energies and even lower vapour pressure. In the present work, water soluble BSA stabilized copper nanocluster is synthesized by using sodium borohydride as reducing agent. The resultant nanocluster having size less than 3 nm showed intense red emission at 650 nm upon excitation at 440 nm. Fluorescence of the BSA stabilized copper nanocluster is effectively quenched by the addition of Zn(II) ion and the quenching is attributed to photoinduced electron transfer followed by aggregation. The limit of detection for Zn(II) ion is obtained as 15 nM and is much lower than that of the World Health organization permitted level of Zn(II) ion in drinking water which is 76 μM. The fast recovery of the fluorescence is observed after addition of RDX to the quenched system which is attributed to the high affinity of Zn(II) ion with RDX. The limit of detection for RDX sensing is obtained at 1.62 nM. Additionally, a straight forward fluorescent paper strip sensor is developed to detect both Zn(II) and RDX, providing an onsite detecting platform for both homeland and environmental security.

Near-infrared carbon dots-based fluorescence turn on aptasensor for determination of carcinoembryonic antigen in pleural effusion

Early detection of carcinoembryonic antigen (CEA) is of great significance for the screening, diagnosis, monitoring and prognosis analysis of lung cancer. Herein, a novel fluorescence aptasensor with high signal-noise ratio (SNR) was constructed to achieve highly-sensitive detection of CEA relied upon the fluorescence resonance energy transfer (FRET) between near-infrared carbon dots (NIR-CDs) and gold nanorods (AuNRs). Initially, AuNRs@SiO2-Aptamer and NIR-CDs-DNA probe were prepared via the covalent bonding reaction between their corresponding carboxyl and amino groups, respectively. After DNA hybridization, the aptasensor was formed, meanwhile, the fluorescence of NIR-CDs was quenched by AuNRs@SiO2. Once CEA encountered the aptasensor, it would selectively combine with CEA aptamer to unwind the preformed DNA double-strand architecture thereby resulting in the NIR-CDs-DNA detach from the surface of AuNRs@SiO2. The attendant fluorescence recovery of NIR-CDs was linearly correlated with the concentration of CEA. According to this relationship, the NIR-CDs based "turn on" sensing system was constructed and exhibited prominent responses toward CEA in the concentration range of 0.1-5000 pg/mL and a relatively low detection limit (0.02 pg/mL). Moreover, it displayed high specificity against other biomarkers or proteins, good reproducibility and acceptable accuracy regarding human pleural effusion samples.

Dual-emission ratio fluorescence detection of bleomycin based on nitrogen doped graphene quantum dots@gold nanoclusters assembly

Abstract Herein, a dual-emission ratio fluorescence probe for copper ions (Cu2+)-based bleomycin (BLM) detection was established for the first time. The ratio fluorescence probe, nitrogen doped graphene quantum dots@gold nanoclusters (NGQDs@AuNCs), showed two well-resolved emission peaks at 440 nm and 580 nm respectively. Fluorescence intensity of AuNCs at 580 nm can be quenched by Cu2+ but restored in the presence of BLM, while fluorescence intensity of NGQDs at 440 nm remained unchanged throughout the process. The Cu2+-triggered fluorescence quenching can be attributed to aggregation-induced quenching mechanism, and the strong affinity between Cu2+ and BLM can make the quenched fluorescence turn on. Under optimal conditions, the BLM can be detected in the range of 0.8–1800 nM and the limit of detection (LOD) was 0.27 nM. Furthermore, the established method in the application of human serum samples has been confirmed.

Red emission cysteine probe with high selectivity based on fluorescent protein chromophores and turn-on fluorescence in cell cultures

Abstract Cysteine (Cys) plays a vital role in many physiological processes, and also is closely related to various diseases, thus the development of novel high selectivity and sensitivity fluorescent probes for in situ monitoring of biothiol (Cys) is crucial. Herein, we present a fluorogenic method to detect Cys in vitro and live cells based on fluorescent protein chromophores, which have been modulated by chemical reaction. Probe (RFP) is a fluorescence turn on probe with red emission wavelength and large Stokes shift (127 nm). This Michael-addition reaction-based probe exhibits low detection limit (18.7 μM), fast response time, and low cytotoxicity. RFP can differentiate the Cys and Hcy, using the difference of reaction time between probe and Cys or Hcy. Together, this probe exhibited excellent cell permeability, and can be successfully applied to detect the endogenous Cys in living cells.

Photocaged probes for spatiotemporal imaging

Abstract Two compounds with nitrobenzene-derived caging groups were designed and synthesized for cells and tissues imaging. After 350 nm irradiation, the two reagents can realize highly efficient fluorescence turn on with large Stokes shift. As for the two probes can bare out a common functional group of aldehyde group under UV irradiation, it may be used for detection of cysteine, DNA methylation in a spatiotemporal method with selectivity. The idea of design and synthesis might be used in other modified reagents for controlling biological function with light.