A near-infrared fluorescence chemodosimeter for fluoride via specific Si–O cleavage

Near-infrared fluorescent indolizine-dicyanomethylene-4H-pyran hybrids for viscosity imaging in living cells

The development of near-infrared organic fluorescent dyes with tunable emission profiles is highly required in the field of biological sensing and imaging. In this paper, we designed and synthesized two organic fluorescent dyes, DCM-1 and DCM-2, through the hybridization of indolizine and dicyanomethylene-4H-pyran skeleton. These two compounds show near-infrared fluorescence with emission maximum approximately at 640 and 680 nm, respectively. Notably, both DCM-1 and DCM-2 have specific responses to viscosity without being interfered by biological relevant species. Cell experiments demonstrate that DCM-1 and DCM-2 can detect dynamic changes in viscosity within living cells, suggesting their potential applications in chemical biology research.

Ultrafast fluorescent probe with near-infrared analytical wavelength for fluoride ion detection in real samples

The first ultrafast fluorescence probe with response time in seconds (10 s) for fluoride ions (F^-) has been proposed by conjugating dimethylthiophosphoryl group as a recognition unit with the near-infrared fluorophore of hemicyanine. The response mechanism is the F^--induced cleavage of the dimethylthiophosphoryl group, along with the liberation of the fluorophore, which results in a distinctly enhanced fluorescence intensity at 730 nm (λ_ex = 680 nm). The fluorescence enhancement of the probe is directly proportional to the F^- concentration in the range of 10-300 µM with the detection limit of 4.28 µM. The probe has been successfully used to determine F^- concentration in real water and toothpaste samples as well as image F^- in living cells. The simplicity and quick response of this probe endow it with the ability of detecting F^- rapidly in real samples.

Red fluorescent pyrazoline-BODIPY nanoparticles for ultrafast and long-term bioimaging

Fluorescence bioimaging is very significant in studying biological processes. Fluorescent nanoparticles (NPs) manufactured from aggregation-induced emission (AIE) materials, as promising candidates, have attracted more attention. However, it is still a challenge to explore suitable AIE NPs for bioimaging. Herein, we synthesized pyrazoline-BODIPY (PZL-BDP) with a donor and acceptor (D-A) structure by a condensation reaction, cultured its single crystal, and studied its twisted intramolecular charge transfer (TICT) and AIE effects. PZL-BDP could self-assemble to form red fluorescent nanoparticles (PZL-BDP NPs) which showed a good fluorescence quantum yield of 15.8% in water. PZL-BDP NPs with excellent stability and biocompatibility exhibited a large Stokes shift (Δλ = 111 nm) which resulted in the reduction of external interference and enhancement of the fluorescence contrast. Furthermore, these nanoparticles could be readily internalized by HeLa cells and they stain the cells in just five seconds, indicating an ultrafast bioimaging protocol. Moreover, long-term tracking fluorescence signals in vivo for about 12 days were obtained. The bright red fluorescence, ultrafast cell staining ability, and long-term in vivo tracking competence outline the great potential of rational design nanomaterials with AIE characteristics for monitoring biological processes.

A novel fluorescent off–on probe for the sensitive and selective detection of fluoride ions

A highly sensitive and selective fluorescent probe for fluoride ions has been developed by incorporating the dimethylphosphinothionyl group as a recognition moiety into the fluorophore of coumarin. The detection mechanism is based on the fluoride ion-triggered cleavage of the dimethylphosphinothionyl group, followed by the release of coumarin, which leads to a large fluorescence enhancement at 455 nm (λ_ex = 385 nm). Under the optimized conditions, the fluorescence enhancement of the probe is directly proportional to the concentration of fluoride ions in the range of 0–30 μM with a detection limit of 0.29 μM, which is much lower than the maximum content of fluoride ions guided by WHO. Notably, satisfying results have been obtained by utilizing the probe to determine fluoride ions in real-water samples and commercially available toothpaste samples. The proposed probe is rather simple and may be useful in the detection of fluoride ions in more real samples.

A sensitive and selective fluorescent off–on probe is developed for fluoride ion detection, and its applicability has been demonstrated by determining fluoride ions in real-water samples and toothpaste samples.

Encumbrance in desilylation triggered fluorogenic detection of the fluoride ion - a kinetic approach

Highly selective fluorogenic detection of the fluoride ion becomes viable due to its propensity towards cleaving Si-O and Si-C bonds, the key reactive elements in fluoride selective chemodosimeters. Herein, acridinedione derived, two novel fluorescent probes bearing tertiarybutyldiphenylsilyloxy (TBDPS) and tertiarybutyldimethylsilyloxy (TBDMS) groups were synthesized and their fluoride selective dosimetric action in organic solvents and in mixed aqueous medium was established through steady state and time resolved fluorescence techniques. Unusually, these molecular probes maintain their sensitivity down to 10 ppb in both organic and mixed aqueous medium; hence they can be considered as highly selective and sensitive fluorescent probes for the fluoride anion. By following the kinetics of the desilylation process it is established that the reaction follows second order kinetics with respect to fluoride ion concentration in acetonitrile whereas it becomes first order in mixed aqueous medium owing to its high degree of hydration. Also, the hydrophobic and sterically crowded substitution on the silyl receptor hampers the reaction kinetics only in organic solvents whereas its influence in mixed aqueous medium is relatively very less. However, common inorganic cations (Na⁺) effectively hinder the reaction kinetics through strong ion pair interaction and prolong the response time. Therefore, the indigenous influences of three different factors which encumber the desilylation process were quantitatively enumerated and the prospective application of these fluorescent probes in detecting and validating fluoride ions in various environmental samples is demonstrated.

A naphthalene benzimidazole-based chemosensor for the colorimetric and on-off fluorescent detection of fluoride ion

A novel naphthalene benzimidazole (NBI)-based chemosensor (D2) was developed for fluoride ion (F^-) detection. The absorption spectrum of D2 changed dramatically from yellow to blue in the visible region accompanied with a 225nm red shift of its absorption maximum upon the addition of F^- in DMSO. D2 also exhibited a fluorescence turn-off response towards the fluoride ion. The emission intensity of D2 decreased drastically along the increasing F^- concentration and the detection limit for F^- was as low as 3.2×10^-9mol/L. ¹H NMR and HRMS-ESI results indicated that the formation of NBI-O^- through the desilylation reaction of F^- with NBI-OSi was responsible for the spectral changes. Overall, this kind of NBI-type molecules represent a new type chemosensor for the spectral detection of fluoride ion in solution.

Near-Infrared Dioxetane Luminophores with Direct Chemiluminescence Emission Mode

Chemiluminescent luminophores are considered as one of the most sensitive families of probes for detection and imaging applications. Due to their high signal-to-noise ratios, luminophores with near-infrared (NIR) emission are particularly important for in vivo use. In addition, light with such long wavelength has significantly greater capability for penetration through organic tissue. So far, only a few reports have described the use of chemiluminescence systems for in vivo imaging. Such systems are always based on an energy-transfer process from a chemiluminescent precursor to a nearby emissive fluorescent dye. Here, we describe the development of the first chemiluminescent luminophores with a direct mode of NIR light emission that are suitable for use under physiological conditions. Our strategy is based on incorporation of a substituent with an extended π-electron system on the excited species obtained during the chemiexcitation pathway of Schaap's adamantylidene-dioxetane probe. In this manner, we designed and synthesized two new luminophores with direct light emission wavelength in the NIR region. Masking of the luminophores with analyte-responsive groups has resulted in turn-ON probes for detection and imaging of β-galactosidase and hydrogen peroxide. The probes' ability to image their corresponding analyte/enzyme was effectively demonstrated in vitro for β-galactosidase activity and in vivo in a mouse model of inflammation. We anticipate that our strategy for obtaining NIR luminophores will open new doors for further exploration of complex biomolecular systems using non-invasive intravital chemiluminescence imaging techniques.

A novel silicon-oxygen aurone derivative assisted by graphene oxide as fluorescence chemosensor for fluoride anions

A novel silicon-oxygen aurone derivative TBDPSA was synthesized and used for the detection of fluoride anions in aqueous solution based on a specifically F^--triggered silicon-oxygen cleavage. Even though the compound has shown high selectivity, obvious absorption and fluorescence response for fluoride anions in aqueous solution, but it also is suffered from many limits, such as low detection sensitivity and long response time. Here the compound was successfully assembled on the graphene oxide (GO) surface by π-π stacking. GO improves recognition sensitivity and shortens response time of TBDPSA for fluoride anions by taking advantage of the nanocarrier GO. Compared with TBDPSA, the response time of GO/TBDPSA is shortened greatly from 1h to <5s and the detection limit is lowered about four times with fluorescence as detected signal. Generally speaking, GO is an excellent promoter for accelerate recognition.

A NIR fluorescent probe for the detection of fluoride ions and its application in in vivo bioimaging

A near-infrared fluorescent probe has been developed, which is available for visualizing exogenous fluoride ions in vitro and in vivo.

Selective turn-on near-infrared fluorescence probe for hypoxic tumor cell imaging

In this study, we designed a new selective turn on near-infrared fluorescence probe by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol to DCPO with ether linkage for hypoxic tumor cell imaging.

Red emission fluorescent probes for visualization of monoamine oxidase in living cells

Here we report two novel red emission fluorescent probes for the highly sensitive and selective detection of monoamine oxidase (MAO) with large Stokes shift (227 nm). Both of the probes possess solid state fluorescence and can accomplish the identification of MAO on test papers. The probe MAO-Red-1 exhibited a detection limit down to 1.2 μg mL⁻¹ towards MAO-B. Moreover, the cleavage product was unequivocally conformedby HPLC and LCMS and the result was in accordance with the proposed oxidative deamination mechanism. The excellent photostability of MAO-Red-1 was proved both in vitro and in vivo through fluorescent kinetic experiment and laser exposure experiment of confocal microscopy, respectively. Intracellular experiments also confirmed the low cytotoxity and exceptional cell imaging abilities of MAO-Red-1. It was validated both in HeLa and HepG2 cells that MAO-Red-1 was capable of reporting MAO activity through the variation of fluorescence intensity.

Fluoride-induced modulation of ionic transport in asymmetric nanopores functionalized with "caged" fluorescein moieties

We demonstrate experimentally and theoretically a nanofluidic fluoride sensing device based on a single conical pore functionalized with "caged" fluorescein moieties. The nanopore functionalization is based on an amine-terminated fluorescein whose phenolic hydroxyl groups are protected with tert-butyldiphenylsilyl (TBDPS) moieties. The protected fluorescein (Fcn-TBDPS-NH2) molecules are then immobilized on the nanopore surface via carbodiimide coupling chemistry. Exposure to fluoride ions removes the uncharged TBDPS moieties due to the fluoride-promoted cleavage of the silicon-oxygen bond, leading to the generation of negatively charged groups on the fluorescein moieties immobilized onto the pore surface. The asymmetrical distribution of these groups along the conical nanopore leads to the electrical rectification observed in the current-voltage (I-V) curve. On the contrary, other halides and anions are not able to induce any significant ionic rectification in the asymmetric pore. In each case, the success of the chemical functionalization and deprotection reactions is monitored through the changes observed in the I-V curves before and after the specified reaction step. The theoretical results based on the Nernst-Planck and Poisson equations further demonstrate the validity of an experimental approach to fluoride-induced modulation of nanopore current rectification behaviour.

NIR fluorescent DCPO glucose analogues and their application in cancer cell imaging

N3-DCPO and its glucose analogues were synthesized, and the linker's length impact on cellular uptake was studied.

A facile method to effectively combine plasmon enhanced fluorescence (PEF) and fluoride-Lewis acid based reactions to detect low concentrations of fluoride in solution

Synergizing the Purcell-effect of silver nanoparticles and fluoride-Lewis acid based reactions to enhance the sensitivity and detection limit of a fluoride ion chemodosimeter.

DCPO based nanoparticles as a near-infrared fluorescent probe for Cathepsin B

In this article we designed a Cathepsin B-sensitive near-infrared fluorescent probe which can self-assemble into nano-micelles.

Spectrometric and kinetics studies involving anionic chromogenic chemodosimeters based on silylated imines in acetonitrile or acetonitrile–water mixtures

The nucleophilic attack of F⁻ or CN⁻ on the silicon center of chemodosimeters, through an S_N2@Si mechanism, released colored phenolates as leaving groups. NMR, PGSE NMR, and UV-vis studies provided evidence on the mechanism of the reactions.

A novel pyrazoline-based fluorescent probe for detecting fluoride ion in water and its application on real samples

We have designed and synthesized a new fluorescent probe, pyrazoline-based probe 1, to detect fluoride ion with high selectivity and sensitivity in aqueous media.

Chromogenic and fluorescent 'turn-on' chemodosimeter for fluoride based on a F(-)-triggered cascade reaction

We developed a new chromogenic and fluorescent 'turn-on' chemodosimeter 1 based on a F(-)-triggered cascade reaction. This system displayed significant changes in UV/vis absorption and fluorescence emission intensities selectively for F(-) over other anions in a mixture of CH3CN/H2O(95 : 5, v/v) and in acetonitrile.

A near-infrared colorimetric fluorescent chemodosimeter for the detection of glutathione in living cells

A novel near-infrared (NIR) and colorimetric fluorescent molecular probe based on a dicyanomethylene-4H-pyran chromophore for the selective detection of glutathione in living cells has been developed. The fluorescence OFF-ON switch is triggered by cleavage of the 2,4-dinitrobenzensulfonyl (DNBS) unit by the interaction with GSH.

Near-infrared fluorescent probe for detection of thiophenols in water samples and living cells

The development of probes for rapid, selective, and sensitive detection of the highly toxic thiophenols is of great importance in both environmental and biological science. Despite the appealing advantages of near-infrared (NIR) fluorescent detection, no NIR fluorescent probes have been reported for thiophenols to date. Using the chemical properties of thiophenols that are able to cleave sulfonamide selectively and efficiently under mild conditions, we herein report a dicyanomethylene-benzopyran (DCMB)-based NIR fluorescent probe for thiophenols. This probe features remarkable large Stokes shift and shows a rapid, highly selective, and sensitive detection process for thiophenols with significant NIR fluorescent turn-on responses. The potential applications of this new NIR fluorescent probe were demonstrated by the quantitative detection of thiophenol in real water samples and by fluorescent imaging of thiophenol in living cells.

Highly selective colorimetric/fluorometric dual-channel fluoride ion probe, and its capability of differentiating cancer cells

A dual-channel naphthalimide-based chemosensor for rapid and sensitive detection of fluoride ion has been developed. Upon addition of F(-), it undergoes deprotonation reaction through H-bonding interactions, and its maximum absorption wavelength is red-shifted for 214 nm to the far-red region, together with drastically quenched fluorescence. In addition, it shows high selectivity toward F(-) anion, thus could be used for practical applications to detecting F(-) in both solution and solid state. Furthermore, the fluorescence of NIM could be enhanced in protein-containing acidic environments, hence NIM could act as lysosome marker to differentiate cancer cells from normal ones in cell imaging.

A colorimetric and near-infrared fluorescent probe for biothiols and its application in living cells

A new highly selective and sensitive colorimetric and NIR fluorescent probe for detection and bioimaging of biothiols was reported.

Dicyanomethylene-4H-pyran chromophores for OLED emitters, logic gates and optical chemosensors

Dicyanomethylene-4H-pyran (DCM) chromophores are typical donor-π-acceptor (D-π-A) type chromophores with a broad absorption band resulting from an ultra-fast internal charge-transfer (ICT) process. In 1989, Tang et al. firstly introduced a DCM derivative as a highly fluorescent dopant in organic electroluminescent diodes (OLEDs). Integration of ICT chromophore-receptor systems based on DCM chromophores with ion-induced shifts in absorption or emission is a convenient method to perform the logic expression for molecular logic gates. In recent years, various DCM-type derivatives have been explored due to their excellent optical-electronic properties and diverse structural modification. This feature article provides an insight into how the structural modification of DCM chromophores can be utilized for OLED emitters, logic gates and optical chemosensors. In addition, the aggregation-induced-emission (AIE) of DCM derivatives for further optical applications was also introduced.