A ratiometric fluorescent probe for imaging hydroxyl radicals in living cells

A novel fluorescent probe, the detection mechanism of which is based on the 'on-off' switching of a FRET triggered by the *OH-induced cleavage of a DNA strand, has been developed for the ratiometric imaging of *OH.     

Investigation of the anthracene-nitroxide hybrid molecule as a probe for hydroxyl radicals.

A new method for the determination of hydroxyl radicals is proposed. The method is based on the use of a hybrid molecule consisting of a fluorescent chromophore, anthracene, and a nitroxide radical. In the hybrid molecule, the nitroxide quenches the fluorescence of anthracene strongly. The reaction of hydroxyl radicals with dimethyl sulfoxide generates quantitatively methyl radicals, which then combine with the nitroxide moiety of the hybrid molecules to result in an increase in the fluorescence intensity. The fluorescence increase is proportional to the concentration of hydroxyl radicals. The proposed method is capable of detecting hydroxyl radicals generated in the Fenton system. It is a simple and sensitive technique for the determination of hydroxyl radicals.     

Pyrene as a fluorescent probe for DNA base radicals

The steady-state emission spectra of 5-(1-pyrenyl)-modified pyrimidine and 8-(1-pyrenyl)-modified purine nucleosides in water at different pH values provide important information about the acidity or basicity of photochemically generated DNA base radicals which are key intermediates in DNA-mediated charge transport processes.     

Nitroolefin-based coumarin as a colorimetric and fluorescent dual probe for biothiols

A coumarin-based thiol probe featuring the 1,4-addition reaction of thiols to nitroolefin was reported. The molecular probe exhibited higher selectivity toward biothiols (Cys, Hcy and GSH) than other amino acids.     

Reactive sensing of gold (III) by coumarin tethered fluorescent probe through alkyne activation

A novel strategy, involving anchoring and un-anchoring of coumarin based fluorophore, has been established for the selective detection of Au³⁺ species. Selective sensing of Gold (Au³⁺) was triggered due to alkynophilicity of gold ions to create lateral fluorescence of a latent fluorophore. The 4-methyl-2-oxo-2H-chromen-7-yl 2-(2-phenylethynyl) benzoate (CEB) probe was synthesized by reacting 7-hydroxy-4-methylcoumarin with iodo-benzoic acid. CEB probe has an absorption at 300 nm and 335 nm which decreases gradually and new absorption appeared at 406 nm due to Au³⁺ promoted ester hydrolysis selectively over other metal ions with great sensitivity, which accompanies a turn on fluorescence change produced by 7-hydroxy coumarin. The principle behind this sensing strategy is activation of triple bond induced uniquely by Au⁺³ ions leading to cascade and delivers active fluorophore. The sensing mechanism was proposed and supported by ¹H NMR, MS and TD-DFT experiments. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) theoretical results of the CEB-probe and Au³⁺ reaction is in good agreement with the experimental results. Additionally, probe could be well incorporated onto the test strips for effective detection of Au^3+.     

Signaling of chloramine: a fluorescent probe for trichloroisocyanuric acid based on deoximation of a coumarin oxime

A new chloramine signaling probe, based on a coumarin oxime, was developed. The coumarin oxime 1 exhibited efficient off–on type fluorescent signaling behavior toward trichloroisocyanuric acid (TCCA) in an aqueous acetonitrile solution. The signaling is due to the TCCA-assisted transformation of the oxime function to its carbonyl analogue. The presence of common metal ions and anions did not interfere with the TCCA signaling of this probe. Probe 1 was found to be useful for the sensitive determination of the concentration of the practical oxidant TCCA in an aqueous environment, with a detection limit of 7.58 × 10⁻⁷ M.     

A coumarin derivative covalently immobilized on sensing membrane as a fluorescent carrier for nitrofurazone

A coumarin derivative 4-methyl-8-methylacrylamide-2H, 5H-pyrano [3, 2-C] benzpyran 2, 5-dione (MMPBD) has been synthesized as a fluorescent carrier for preparing an optical chemical sensor. The carrier is immobilized on a quartz glass plate surface treated with a silanizing agent to prevent the leakage of the dye. This MMPBD sensor can be utilized for a nitrofurazone (NF) assay based on fluorescence quenching. The sensor shows good repeatability, a long lifetime and a fast response of less then 50 s. NF can be determined in the range between 1.0x10(-6)-1.0x10(-3 )mol L(-1) with a detection limit of 8.0x10(-7) mol L(-1 )at pH 7.0.     

A near-infrared fluorescent probe for lipid hydroperoxides in living cells

An NIR (near-infrared) fluorescent probe TCP (tricarbocyanine diphenylphosphine) including a non-conjugated 'pre-tricarbocyanine' was designed and synthesized for visualizing lipid hydroperoxides (ROOH) in living cells. The excitation and emission spectra of tricarbocyanine in the NIR region can effectively avoid background fluorescence interference in biological systems. The probe exhibited a rapid fluorescence response to ROOH and high selectivity for ROOH over other ROS (reactive oxygen species) and some biological compounds, and the limit of detection was 38 pM. In addition, the probe was stable, and less cytotoxic, which indicated that it has potential application in detecting lipid hydroperoxides in living biological systems.     

Investigation on sensing mechanism of a fluorescent probe for TNP detection in aqueous solution

In this paper, the synthesis and spectral properties of a fluorescent probe Nph-An for TNP detection has been introduced and its sensing mechanism has been studied with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For TNP detection in aqueous solution the probe shows high sensitivity, selectivity and efficiency. The theoretical results demonstrate that the excited-state intermolecular hydrogen bonding (HB) plays an important role for the TNP detection. In the excited state, the intermolecular HB between Nph-An and TNP is strengthened, and thus strongly facilitates the nonirradiative PET process to induce the fluorescence quenching. Whereas, the probe Nph-An emits strong fluorescence because of the intramolecular charge transfer (ICT) properties, which is confirmed by the solvatochromism effect. The calculated absorption spectra of Nph-An and Nph-An + TNP agree well with the experimental values and theoretical analysis provides a detailed and clear explanation of the sensing mechanism.     

Naphthalimide-rhodamine based fluorescent probe for ratiometric sensing of cellular pH

The pH values of lysosomes in cancer cells is slightly lower than that in normal cells, which can be used to distinguish cancer cells from normal cells. According to this, a naphthalimide-rhodamine based fluorescent probe(hereafter referred to as RBN) with a pK_a of 4.20 was designed and synthesized for ratiometric sensing of cellular pH via fluorescence resonance energy transfer(FRET), which can respond to different pH precisely through ratiometric fluorescence intensity(Ⅰ_(577)/Ⅰ_(540)). RBN can be employed to distinguish cancer cells from normal cells on the basis of different fluorescent response, in particular, RBN showed excellent water solubility and low cell toxicity, all these are quite significant for potential application in cancer diagnose and therapy.     

Signal enhancement in ESR spin-trapping for hydroxyl radicals.

In an ESR spin-trapping measurement of hydroxyl radicals formed in a Fenton reaction, the trapping efficiency with DMPO increased by about 300 times in a sodium trifluoroacetate solution, whereas it was little changed in a phosphate buffer.     

An AIEE polyelectrolyte as a light-up fluorescent probe for heparin sensing in full detection range

Polyelectrolyte PTPEPyH, containing tetraphenylethene (TPE) and pyridinium, was synthesized. Its optical properties were investigated with spectroscopies and the results showed that there were two emission-enhanced stages in the interaction between positive-charged PTPEPyH and negative-charged biomacromolecule heparin. The mechanism was very different due to the reduced non-radiative energy loss and the change of surroundings. The polyelectrolyte PTPEPyH, compared with ChS and HA, also showed high selectivity for heparin in the buffer solution and could be used as a potential bio-probe for heparin quantification in the clinical full range.     

Scanning probe lithography on fluid lipid membranes

Scanning probe lithography (SPL) is applied to pattern fluid lipid membranes on a solid borosilicate substrate. Grids of metal lines, prepatterned onto the substrate by electron beam lithography, serve to partition the supported membrane into an array of isolated fluid pixels. By toggling the pH of the surrounding solution, the effect of the probe tip on the membrane can be regulated. Alkaline conditions favor membrane removal, while neutral pH favors membrane deposition. Arbitrary membrane patterns with spatial dimensions limited by the underlying grid size can be constructed by sequential SPL membrane removal followed by refill with a different membrane type. In the present study, bilayers of unique composition fill 1 x 1 mum corrals and were positioned 100 nm apart.     

A fluorescent hydrogen peroxide probe based on a ‘click’ modified coumarin fluorophore

Herein a water-soluble ‘click’ modified coumarin-based fluorescent probe for hydrogen peroxide is reported. This probe shows significant intensity increases (up to fivefold) in near-green fluorescence upon reaction with hydrogen peroxide, and good selectivity over other reactive oxygen species.     

An intramolecular charge transfer fluorescent probe: synthesis and selective fluorescent sensing of Ag+

An intramolecular charge transfer (ICT) fluorescent probe, in which the thiourea derivative moiety is linked to the fluorescent 4-(dimethylamino) benzamide, has been designed and synthesized. The ions-selective signaling behaviors of the probe were investigated. Upon the addition of Ag+, an overall emission enhancement of 14-fold was observed. Compound 1 displayed highly selective chelation enhanced fluorescence (CHEF) effect with Ag+ over alkali, alkali earth metal ions and some transition metal ions in aqueous methanol solutions. The prominent selective and efficient fluorescent enhancing behavior could be utilized as a new chemosensing probe for the analysis of Ag+ ion in aqueous environment.     

Evaluation of 1-naphthol as a convenient fluorescent probe for monitoring ethanol-induced interdigitation in lipid bilayer membrane.

In this work we have tried to evaluate the usefulness of 1-naphthol as an excited state proton transfer fluorescent probe for studying the ethanol-induced interdigitation in lipid bilayer membranes. When ethanol concentration in lipisome is progressively increased, the neutral form fluorescence of 1-naphthol is found to decrease with corresponding increase in the anionic form intensity. This behavior is in contrast to that observed in the absence of lipid where a reverse effect is noticed. Modification of lipid bilayer is known to occur in the presence of ethanol, which increases the packing density of the membrane. Due to this induction of interdigitated gel phase, redistribution of naphthol between the inner core and interfacial region of the lipid bilayer takes places, accounting for the reduction in neutral form fluorescence intensity. The partition coefficient values and the quenching studies also support the redistribution of 1-naphthol in the liposome membrane. The neutral form fluorescence of 1-naphthol successfully monitors the shift in phase transition temperature due to ethanol-induced interdigitation. It also explains the prevention of interdigitation in lipid bilayer at high cholesterol concentration.     

Two-photon fluorescent turn-on probe for lipid rafts in live cell and tissue

We report a new two-photon fluorescence turn-on probe 6-[(E)-3-oxo-1-dodecenyl]-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (CL2) that is designed specifically for visualizing lipid rafts in living cells and tissues. This probe emits much brighter two-photon excited fluorescence in lipid rafts than in non-raft domains and allows direct visualization of the lipid rafts in the live cells and pyramidal neuron layer of the CA1 region at a depth of 100-250 mum in live tissues using two-photon microscopy.     

HKGreen-3: a rhodol-based fluorescent probe for peroxynitrite

A novel fluorescent probe, HKGreen-3, for sensing peroxynitrite is designed on the basis of the rhodol scaffold and a peroxynitrite-specific oxidation reaction. The probe turns out to be highly sensitive and selective for detecting peroxynitrite in both chemical and biological systems.     

Red-emission fluorescent probe sensing cadmium and pyrophosphate selectively in aqueous solution

A fluorescent sensor for cadmium (CS) based on the BODIPY fluorophore exploiting the PET (Photoinduced Electron Transfer) mechanism was prepared. CS exhibited high selectivity and sensitivity for detecting cadmium in aqueous buffer solution. In addition, the complex of CS with cadmium could detect pyrophosphate (PPi) selectively and sensitively.