Novel fluorescent pH sensor based on coumarin with piperazine and imidazole substituents

A new coumarin derivative containing piperazine and imidazole moieties is reported as a fluorophore for hydrogen ions sensing. The fluorescence enhancement of the studied sensor with an increase in hydrogen ions concentration is based on the hindering of photoinduced electron transfer from the piperazinyl amine and the imidazolyl amine to the coumarin fluorophore by protonation. The presented sensor has a novel design of fluorophore-spacer-receptor(1)-receptor(2) format, which is proposed to sense two ranges of pH (from 2.5 to 5.5) and (from 10 to 12) instead of sensing one pH range. A model compound, in which the piperazinyl ring is absent, was synthesized as well to confirm the novel pH sensing of the proposed sensor.     

N-allyl-4-(N-2'-hydroxyethyl)amino-1,8-naphthalimide as a fluorophore for optical chemosensing of nitrofurantoin

N-Allyl-4-(N-2'-hydroxyethyl)amino-1,8-naphthalimide (AHEAN), a naphthalimide derivative, was synthesized as a new fluorophore for optical chemical sensor preparation. To prevent leakage of the fluorophore, AHEAN was photo-copolymerized with 2-hydroxypropyl methacrylate on a glass surface treated with a silanizing agent. An optical chemical sensor based on AHEAN can be utilized for nitrofurantoin assay based on fluorescence quenching. The sensor shows sufficient repeatability, selectivity and a fast response of less than 30 s. Nitrofurantoin can be determined in the range between 1.00 x 10(-6) and 1.00 x 10(-3) mol l(-1) with a detection limit of 4.8 x 10(-7) mol l(-1). Most commonly co-existing drug substances and ions do not interfere with the nitrofurantoin assay. The sensor was applied to the analysis of pharmaceutical and urine samples.     

Naphthalimide as Highly Selective Fluorescent Sensor for Ag^＋ Ions

The naphthalimide derivative. NA1 was synthesized, which consists of a bis（2-（ethylthio）ethyl）amine group binding cations and naphthalimide unit as chromogenic and fluorogenic signaling subunit. Absorption and emission spectra and the effect of polarity of solvents and pH values were studied. The photo-induced electron transfer （PET） occurred from the donor of bis（2-（ethylthio）ethyl）amine group to the naphthalimide fluorophore. The present study demonstrates that NA1 is a viable candidate as a fluorescent receptor for a new Ag^＋ ion sensor. This silver ion chemosensor can discriminate Ag^＋ ion well among heavy metal ions by an enhancement of the fluorescence intensity in ethanol-water （1 ： 9, V ： V）. And NA1 is also a pH-sensor because the fluorescence of the compound varies with the pH values.     

A ratiometric fluorescence sensor with broad dynamic range based on two pH-sensitive fluorophores

This paper describes a novel ratiometric fluorescence sensor for pH measurement. Two pH-sensitive fluorophores, N-allyl-4-(4'-methyl-piperazinyl)-1,8-naphthalimide (AMPN) and meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP), which served as referencing indicators for each other, were co-polymerized with acrylamide, hydroxyethyl methacrylate and triethylene glycol dimethacrylate on the silanized glass surface. The proposed sensor is based on the pH-dependent fluorescence intensities of the two fluorophores in different pH ranges. The sensor covers a broad dynamic range of pH 1.5-9.0. It exhibits satisfactory analytical performance in terms of selectivity, reproducibility and stability. The successful fabrication of the proposed sensor provides an alternative concept to utilizing two or more fluorophores for the development of ratiometric sensors covering a broad range of pH.     

A selective PVC membrane for di- or trinitrophenol based on N,N-dibenzyl-3,3',5,5'-tetramethylbenzidine

A new fluorophore, N,N-dibenzyl-3,3',5,5'-tetramethylbenzidine (NBTMB), was prepared and shown to exhibit significant and analytical usefulness for optical sensing toward 2,4-dinitrophenol or 2,4,6-trinitrophenol (picric acid) when it was immobilized in a plasticized poly(vinyl chloride) (PVC) membrane. When the membrane was applied to aqueous nitrophenol solution, NBTMB was able to extract selectively nitrophenol into the membrane phase. Since the extraction equilibrium was accompanied by fluorescence quenching of NBTMB, the chemical recognition process could be directly translated into an optical signal. The sensor showed reversible response in the concentration range from 2.0 x 10(-7) to 6.0 x 10(-5) mol L(-1) for the detection of 2,4-dinitrophenol in NaOAc-HOAc buffer at pH 4.0. It also showed a fast response time (t95% < 1.5 min) when the sensor was applied to 2,4-dinitrophenol solution at concentration levels of 5.26 x 10(-6) and 2.10 x 10(-5) mol L(-1) alternatively. A working principle is proposed and the responses of this sensor to various kinds of nitrophenol were studied. The sensor was applied to the direct determination of 2,4-dinitrophenol in prepared water samples and the indirect assay of the drug cinchonine and the results obtained were satisfactory.     

A selective optical chemical sensor for o-nitrophenol based on fluorescence quenching of curcumin

An optical chemical sensor has been prepared for the selective determination of o-nitrophenol in aqueous solutions based on the fluorescence quenching of curcumin in PVC membrane. The sensing mechanism of the proposed sensor for o-nitrophenol has been discussed in detail. The fluorescence changes of sensing membrane resulted from an associated complex formation between curcumin and o-nitrophenol. In pH 4.8 buffer solution, the sensor responds linearly in the measuring range from 1.0 x 10(-2) mol 1(-1) to 1.5 x 10(-4) mol 1(-1), and the experimental detection limit is evaluated to be 8.0 x 10(-5) mol 1(-1). A stable signal was obtained within less than 1.5 min. Under the optimum conditions, the sequence of selective response to the sensing membrane is o-nitrophenol > 2,4-dinitrophenol > m-nitrophenol > p-nitrophenol > 2,4,6-trinitrophenol. Phenol, aniline as well as other ions have less effect on the fluorescence of the sensor. The reproducibility for the determination of o-nitrophenol is better than 1%, and the response is reversible. The sensor can be used for the determination of o-nitrophenol in water samples.     

Novel mercury (II) ion-selective polymeric membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate

Mercury (II) ion-selective PVC membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate (EBPCA) as a novel nitrogen containing sensing material is successfully developed. The sensor exhibits good linear response of 30 mV per decade within the concentration range 10(-6)-10(-3) mol l(-1) Hg(II). The sensor shows good selectivity for mercury (II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The EBPCA-based sensor is suitable for use with aqueous solutions of pH 2.0-4.5 and exhibits minimal interference by Ag(I) and Fe(III), which are known to interfere with other previously suggested sensors. The nature and composition of the sensing material and its mercury complex are examined using Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques. The proposed sensor is applied as a sensor for the determination of Hg(II) content in some amalgam alloys. The results show good correlation with data obtained by atomic absorption spectrometric method.     

Fiber-optic sensor for iodine based on a covalently immobilized aminobenzanthrone Schiff base.

An aminobenzanthrone Schiff base has been synthesized as a new fluorescence carrier for the preparation of an optical chemical sensor for iodine. The response of the sensor is based on fluorescence quenching of the aminobenzanthrone Schiff base by iodine. The sensor shows a linear response toward iodine in the range of 1.0 x 10(-5) to 1.0 x 10(-3) mol l(-1), with a detection limit of 6.0 x 10(-6) mol l(-1) at pH 8.0. Leaching of the fluorophore from the membrane is effectively hindered by covalent immobilization, resulting in an enhanced sensor lifetime. In addition to satisfactory reproducibility and reversibility, the prepared sensor exhibits sufficient selectivity toward iodine with respect to other coexisting ions. The sensor has been applied to the determination of iodine in common salt samples.     

Ratiometric fluorescent detection of Cu(II) in semi-aqueous solution using a two-fluorophore approach

Schiff base sensor 1, containing naphthalene and naphthalimide fluorophores with separate and distinct emission wavelengths, showed good selectivity for Cu(II) over other tested physiological and environmentally important cations through changes in its fluorescence spectra in THF/H₂O (9:1) HEPES buffered solution. By taking the ratiometric change of the emissions at 435 nm (naphthalene-Schiff base) and 510 nm (naphthalimide) good linearity was observed in the 0-10 μM range. The enhancement of the 435 nm emission upon binding Cu²⁺ was attributed to a prevention of the rapid CN isomerisation that otherwise leads to non-radiative decay, while the quenching of the naphthalimide emission was attributed to electron transfer between the excited naphthalimide fluorophore and the redox active Cu²⁺.     

Fabrication of an optical sensor based on the immobilization of Qsal on the plasticized PVC membrane for the determination of copper(II)

A novel optical sensor has been proposed for sensitive determination of Cu(II) ion in aqueous solutions. The copper sensing membrane was prepared by incorporating Qsal (2-(2-hydroxyphenyl)-3H-anthra[2,1-d]imidazole-6,11-dione) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to Cu(II) ion by changing color reversibly from yellow to dark red in acetate buffer solution at pH 4.0. The proposed sensor displays a linear range of 6.3 × 10^?7?1.00 × 10^?4 M with a limit of detection of 3.3 × 10^?7 M. The response time of the optical sensor was about 3?C5 min, depending on the concentration of Cu(II) ions. The selectivity of the optical sensor to Cu(II) ions in acetate buffer is good. The sensor can readily be regenerated by hydrochloric acid (0.1 M). The optical sensor is fully reversible. The proposed optical sensor was applied to the determination of Cu(II) in environmental water samples.     

Manipulating FRET with polymeric vesicles: development of a "mix-and-detect" type fluorescence sensor for bacterial toxin

A simple "mix-and-detect" type of fluorescence sensor for cholera toxin (CT) is reported. The sensor consists of a BODIPY lipid dye and polydiacetylene (PDA) vesicles and utilizes the lipid insertion and FRET mechanism to offer a direct and fluorescence "turn-on" detection of the analyte. BODIPY conjugated GM1, dissolved in a Tris buffer through aggregate formation, demonstrated substantial fluorescence quenching with addition of PDA vesicle solution. The close proximity of the dye molecules to the conjugated chains as a result of lipid insertion enables energy transfer from dye to the polymer backbone, yielding the observed phenomenon. When CT is present, the binding of BO-GM1 to CT results in formation of a complex that prohibits it from membrane insertion, leading to the blocking of the quenching process. The fluorescence signal was found to be proportional to the CT concentration. The method is very simple and allows specific and sensitive detection of the protein toxin with just a few mixing steps. It can be further developed into a general sensing strategy for detection of other proteins with amplified FRET mechanism.     

An optode sensor for Cu2+ with high selectivity based on porphyrin derivative appended with bipyridine.

A porphyrin derivative (fluorophore) appended with bipyridine (ionophore) has been applied for preparation of a Cu2+-sensitive optical chemical sensor, which is based on fluorescence quenching of porphyrin derivative entrapped in a poly(vinyl chloride) membrane by the energy transfer process. The sensor exhibits a linear response toward Cu2+ in the concentration range 2.0 x 10(-8) - 1.0 x 10(-5) M, with a working pH range from 6.0 to 8.0 and a high selectivity. The detection limit is 5 x 10(-9) M. The response time for Cu2+ is less than 5 min with concentrations lower than 5 x 10(-6) M. The optode can be regenerated using 0.3 M EDTA (pH 9) and acetate buffer solution. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for direct determination of Cu2+ in water samples with satisfied results.     

A wide pH range optical sensing system based on a sol-gel encapsulated amino-functionalized corrole

The synthesis of a new compound, 10-(4-aminophenyl)-5,15-dimesitylcorrole, and its application for the preparation of optical chemical pH sensors is described. The dye materials were immobilized in a sol-gel glass matrix and characterised upon exposure to aqueous buffer solutions. The response of the sensor is based on the fluorescence intensity changing of corrole owing to multiple steps of protonation and deprotonation. Due to its containing several proton sensitive centers, the 10-(4-aminophenyl)-5,15-dimesitylcorrole based optode shows a wider response range toward pH than that of tetraphenylporphyrin (TPPH(2)) and 5,10,15-tris(pentafluorophenyl)corrole (H(3)(tpfc)). It shows a linear pH response in the range of 2.17-10.30. The effect of the composition of the sensor membrane has been studied and the experimental conditions were optimized. The optode showed good reproducibility and reversibility, and common co-existing inorganic ions did not show obvious interference to its pH measurement.     

A fluorescence aptasensor based on DNA charge transport for sensitive protein detection in serum

A novel fluorescence aptasensor based on DNA charge transport for sensitive protein detection has been developed. A 15nt DNA aptamer against thrombin was used as a model system. The aptamer was integrated into a double strand DNA (dsDNA) that was labeled with a hole injector, naphthalimide (NI), and a fluorophore, Alexa532, at its two ends. After irradiation by UV light, the fluorescence of Alexa532 was bleached due to the oxidization of Alexa532 by the positive charge transported from naphthalimide through the dsDNA. In the presence of thrombin, the binding of thrombin to the aptamer resulted in the unwinding of the dsDNA into ssDNA, which led to the blocking of charge transfer and the strong fluorescence emission of Alexa532. By monitoring the fluorescence signal change, we were able to detect thrombin in homogeneous solutions with high selectivity and high sensitivity down to 1.2 pM. Moreover, as DNA charge transfer is resistant to interferences from biological contexts, the aptasensor can be used directly in undiluted serum with similar sensitivity as that in buffer. This new sensing strategy is expected to promote the exploitation of aptamer-based biosensors for protein assays in complex biological matrixes.     

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.     

基于荧光内滤效应的锂离子荧光化学传感器研究

报道了一种基于荧光内滤效应的荧光增强型锂离子光化学传感器,将荧光试剂、亲脂性pH指示剂和锂离子中性载体结合在增塑的PVC膜中,Li⁺与H⁺在膜相中的竞争萃取效应引起受亲脂性pH指示剂调制的敏感膜荧光值的变化.推导了有关理论关系式,研究了该传感器的响应特性,并对人工合成样品进行测试,结果较为满意.     

A fluorescent water-soluble naphthalimide-based receptor for saccharides with highest sensitivity in the physiological pH range

A new water-soluble fluororeactand for the optical detection of saccharides is presented. We have combined the functional naphthalimide fluorophore with the well-known ability of boronic acids to bind to the diol moiety of saccharides. The fluororeactand exhibits sensitivity in the mM range, absorbance and emission in the visible spectral range, large Stokes' shift and fluorescence increase in the physiological pH range.     

Ratiometric and water-soluble fluorescent zinc sensor of carboxamidoquinoline with an alkoxyethylamino chain as receptor

A novel "naked-eye" and ratiometric fluorescent zinc sensor (AQZ) of carboxamidoquinoline with an alkoxyethylamino chain as receptor was designed and synthesized. AQZ shows good water solubility and high selectivity for sensing; about an 8-fold increase in fluorescence quantum yield and a 75 nm red-shift of fluorescence emission upon binding Zn2+ in buffer aqueous solution are observed. Moreover, AQZ can enter yeast cells and signal the presence of Zn2+.     

Covalent immobilization of a fluorescent pH-sensitive naphthalimide dye in sol–gel films

A pH indicator dye was covalently linked to inorganic?Corganic hybrid sol?Cgel layers via its carboxyl function by the formation of an amide bond. For this, the dye was activated by 2-succinimido-1,1,3,3-tetramethyluronium tetrafluoroborate and linked to N-(3-(trimethoxysilyl)propyl)-ethylendiamine. Different ratios of tetraethoxy-silane, diisobutyldimethoxysilane and 3-glycidoxypropyltrimethoxysilane were evaluated to tailor the performance of the sensing material. Fluorescence spectroscopy of the optimised sensor layers with a molar ratio of organically modified siloxane to tetraethoxysilane of 25.9 and of dye/amino groups of 1.16, showed a reversible fluorescence signal increase of 117?% upon protonation, and a pk _a 6.5. The signal changes were caused by photoinduced electron transfer between the methylpiperazine moiety and the naphthalimide fluorophore, its efficiency being modulated by protonation of the methylpiperazine nitrogen. The influence of parameters such as synthesis, dip-coating process and heat-treatment on the performance of the sensor layers was investigated. Optimum signal changes were obtained when heating the sol?Cgel structure up to 170?°C.     

Naphthalimide-based fluorescent Zn chemosensors showing PET effect according to their linker length in water

We have developed naphthalimide-based fluorescent chemosensors that exhibit fluorescence enhancement upon binding Zn²⁺ ion in 10 mM HEPES buffer (pH 7.4) at 25 °C. The fluorescence enhancement was induced by a PET inhibition process in which electron transfer from the nitrogen lone pair electrons of the Dpa unit to naphthalimide was blocked upon the binding of the sensor to Zn²⁺. The longer the linker length (n = 1-3) of the sensor, the less the PET efficiency becomes. Among the sensors (1, 2, and 3) examined, 1 shows the highest selectivity and sensitivity for Zn²⁺ over other transition metal ions and alkali metal ions in water.