A ratiometric fluorescence sensor for caffeine

The dye disodium 3,4:3',4'-bibenzo[b]thiophene-2,2'-disulfonate can be used as a molecular probe for the fluorimetric detection of caffeine in aqueous solution. The fluorescence response is attributed to non-covalent interactions of caffeine with the dye in the ground state and in the excited state. The bimodal interaction allows performing ratiometric measurements with very good selectivity over structurally related analytes. The dye was also used to develop a simple test strip for the visual differentiation of normal and decaffeinated coffee with a standard UV lamp.     

A sorbitol-selective fluorescence sensor

A new anthracene derivative bearing two phenylboronic acid groups at the 1,8-positions was prepared and its binding properties towards sorbitol, xylitol, fructose, glucose and galactose have been studied using fluorescence analysis.     

A near-infrared fluorescence turn-on sensor for sulfide anions

The first NIR fluorescent sensor for sulfide anions was constructed based on the displacement approach. The sensing ensemble is composed of a cyanine dye, a piperazine linker, an 8-aminoquinoline ligand, and copper. The favorable attributes of the sensor include a large NIR fluorescence turn-on signal in aqueous ethanol, high sensitivity, and high selectivity. The transition-metal-based displacement strategy may open an avenue for development of NIR fluorescent sensors for a wide variety of anion targets.     

A fluorescence enhancement-based sensor for hydrogen sulfate ion

Sugar-aza-crown ether-based cavitand 1 can act as a selective turn-on fluorescence sensor for hydrogen sulfate ion in methanol among a series of tested anions. Spectroscopic studies, particularly NMR spectroscopy, revealed that the C-H hydrogen bonding between 1,2,3-triazole ring of cavitand 1 and hydrogen sulfate ion is crucial for the high selectivity of the receptor for hydrogen sulfate.     

A fluorescent pyrophosphate sensor via excimer formation in water

A new fluorescent sensor based on a pyrene/Zn(II)-dpa (dpa = bis(2-pyridylmethyl)amine) conjugate displays excimer emission selective for pyrophosphate over other anions.     

A novel dansyl-appended glycoluril-based fluorescence sensor for silver ions

Tetra-dansylated diphenyl glycoluril has been synthesized and evaluated for ionic recognition. The synthesized molecular receptor shows selective response to silver ions as determined through the enhancement of fluorescence intensity.     

A turn-on Schiff base fluorescence sensor for zinc ion

A simple Schiff base type fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an ‘off-on-type’ mode with high selectivity in the presence of Zn²⁺ ion. The selectivity of 1 for Zn²⁺ is the consequence of combined effects of chelation-enhanced fluorescence (CHEF), CN isomerization, and inhibition of photoinduced electron transfer (PET).     

A turn-on and reversible fluorescence sensor for zinc ion

A simple Schiff base type fluorescent receptor was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor exhibits an "off-on-type" mode with high selectivity in the presence of Zn(2+) ion. The addition of EDTA quenches the fluorescence of receptor -Zn(2+) complex, making receptor a reversible chemosensor. The selectivity of for Zn(2+) is the consequence of combined effects of CHEF, C[double bond, length as m-dash]N isomerization and inhibition of ESIPT.     

FRET-derived ratiometric fluorescence sensor for Cu

New N-(pyrenylmethyl)naphtho-azacrown-5 (1) was synthesized as an ‘On-Off’ fluorescent chemosensor for Cu²⁺. Excited at 240 nm corresponding to the absorption of naphthalene unit (energy donor) of 1, emission at 380 nm from pyrene unit (energy acceptor) is observed, indicating that intramolecular fluorescence resonance energy transfer (FRET-On) occurs in 1. When Cu²⁺ is added to a solution of 1, however, the fluorescence of pyrene is strongly quenched (FRET-Off) whereas that of naphthalene group is revived. Such FRET ‘On-Off’ behavior of 1 is observed only in the case of Cu²⁺ binding, but not for other metal cations. The high selectivity of 1 toward Cu²⁺ can be potentially applied to a new kind of FRET-based chemosensor. The FRET On-Off behavior is supported by computational studies. The calculated molecular orbitals of HOMO and LUMOs suggest the excited-state interactions leading to FRET from naphthalene to pyrene in 1, but no electron density changes in 1·Cu²⁺ complex.     

A new fluorescent sensor for the detection of pyrophosphate based on a tetraphenylethylene moiety

We have developed a new fluorescent sensor 1-2Zn based on a tetraphenylethylene (TPE) moiety for the detection of PPi. This TPE-based chemosensor showed ‘turn-on’ fluorescence emission according to the concentration of PPi. The fluorescence enhancement upon binding of PPi to 1-2Zn resulted from the restriction of intramolecular rotation of phenyl rings in 1-2Zn.     

A carbon dioxide sensor based on fluorescence

The optical carbon dioxide sensor is prepared by covering a pH sensor based on fluorescence with a CO₂-permeable membrane and contacting the pH-sensitive membrane with a reservoir of hydrogen carbonate. As carbon dioxide diffuses across the membrane it causes a chnage in pH which is detected by measuring the change in fluorescence from the base form of the pH-sensitive fluorescentdye. The usable range of response depends on the concentration of hydrogen carbonate in contact with the membrane. The sensor also responds to sulfide and sulfite.     

A highly selective pyrophosphate sensor based on ESIPT turn-on in water

Pyrophosphate (PPi) is a biologically important target. A binuclear system 3?2Zn is found to selectively recognize PPi, leading to a ratiometric fluorescent sensor at pH 7.4 in water. The binding event triggered a large fluorescence response (～100 nm bathochromic shift) by turning on the excited state intramolecular proton transfer (ESIPT). Detection of PPi released from a PCR experiment indicated that this new probe could be a useful tool in bioanalytical applications.     

An azophenol-based chromogenic pyrophosphate sensor in water

A new azophenol-based colorimetric sensor shows a selective detection for pyrophosphate in aqueous solution.     

Glycosylated star-shaped conjugated oligomers for targeted two-photon fluorescence imaging

A glucopyranose functionalized star-shaped oligomer, N-tris{4,4',4'-[(1E)-2-(2-{(E)-2-[4-(benzo[d]thiazol-2-yl)phenyl]vinyl}-9,9-bis(6-2-amido-2-deoxy-1-thio-β-D-glucopyranose-hexyl)-9H-fluoren-7-yl)vinyl]phenyl}phenylamine (TVFVBN-S-NH(2)), is synthesized for two-photon fluorescence imaging. In water, TVFVBN-S-NH(2) self-assembles into nanoparticles with an average diameter of ～49?nm and shows a fluorescence quantum yield of 0.21. Two-photon fluorescence measurements reveal that TVFVBN-S-NH(2) has a two-photon absorption cross-section of ～1100 GM at 780?nm in water. The active amine group on the glucopyranose moiety allows further functionalization of TVFVBN-S-NH(2) with folic acid to yield TVFVBN-S-NH(2) FA with similar optical and physical properties as those for TVFVBN-S-NH(2). Cellular imaging studies reveal that TVFVBN-S-NH(2) FA has increased uptake by MCF-7 cells relative to that for TVFVBN-S-NH(2), due to specific interactions between folic acid and folate receptors on the MCF-7 cell membrane. This study demonstrates the effectiveness of glycosylation as a molecular engineering strategy to yield water-soluble materials with a large two-photon absorption (TPA) cross-section for targeted cancer-cell imaging.     

A nanoscale vesicular polydiacetylene sensor for organic amines by fluorescence recovery

We report a nanoscale lipid membrane-based sensor of conjugated polydiacetylene (PDA) vesicles for fluorescence detection of organic amines. The vesicle sensor was constructed by incorporation of a BODIPY fluorescent dye into the PDA vesicles. The fluorescent properties of the resulting vesicles can be manipulated by adjusting lipid components, and are controlled by environmental and solution conditions. The fluorescence of the BODIPY dye was significantly quenched in the polymerization of diacetylene lipid vesicles by a UV irradiation process. However, it was sufficiently recovered by external stimuli such as a hike of solution pH. The fluorescence recovery process was reversible, and a decrease in solution pH resulted in repeated quenching. The reported system transforms an external stimulus into a large fluorescence intensity change, demonstrating great potential in developing new signal reporting method for biosensor design. The quench-recovery phenomenon of the BODIPY-PDA is believed to be related to the energy transfer between the dye and the PDA conjugate backbone. The vesicle sensor was applied for detecting an organic amine, triethylamine (TEA) and a large linear relationship was obtained between the increase in fluorescence intensity and the concentrations of TEA. The detection limit of TEA by vesicle sensors using fluorescence recovery was found to be 10 μM.     

A new N-imidazolyl-1,8-naphthalimide based fluorescence sensor for fluoride detection

A chemosensor is reported with high sensitivity and selectivity for detection of fluoride anion. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bond between imidazole and naphthalimide moieties, resulting in a noncoplanar geometry with low fluorescence.     

A novel fluoride sensor based on fluorescence enhancement

A novel halide sensor, which yields greater fluorescence upon binding to fluoride, has been synthesized and characterized.     

A modular fluorescence intramolecular energy transfer saccharide sensor

[structure: see text] A modular fluorescence intramolecular energy transfer saccharide sensor 2 has been prepared with phenanthrene as the donor and pyrene as the acceptor.     

A colorimetric and fluorescent turn-on sensor for pyrophosphate anion based on a dicyanomethylene-4H-chromene framework

A new red fluorescent sensor DCCP-Cu2+ based on dicyanomethylene-4H-chromene shows turn-on fluorescence with high selectivity for pyrophosphate over other anions.