A reversible chemosensor for nitrite based on the fluorescence quenching of a carbazole derivative

The carbazole derivative, with an amino group in 9-position (9-methylacryloylamino carbazole (MAC), has been utilized to prepare a fluorescent sensor and used for the determination of NO₂⁻ based on the reaction between nitrite (NO₂⁻) and excess I⁻ to form I₃⁻, which can quench the fluorescence of carbazole derivative. MAC, as a fluorescent carrier, has a terminal double bond and is covalently immobilized on a quartz glass plate surface by photo-polymerization to prevent the leakage of the dye. The sensor shows sufficient repeatability, selectivity, operational lifetime of 8 weeks, and a fast response of less then 30 s. NO₂⁻ can be determined in the range between 1.0×10⁻⁶ and 1.0×10⁻⁴ mol l⁻¹ with a detection limit of 8.0×10⁻⁷ mol l⁻¹ at pH of 2.0. The quenching mechanism is discussed. Most commonly coexisting ions do not interfer with the NO₂⁻ assay.     

A selective optical chemical sensor for 2,6-dinitrophenol based on fluorescence quenching of a novel functional polymer

A bifurcated optical fiber based chemical sensor for continuous monitoring of 2,6-dinitrophenol (2,6-DNP) has been proposed based on the reversible chemical reaction between a novel functional poly(vinyl chloride) (PVC) as the sensing material and the analytes. The functional PVC (FPVC), containing a fluorescent curcumin moiety, was synthesized by the nucleophilic substitution of a fraction of the chlorine atoms bound to the PVC backbone by curcumin. When plasticized in a membrane of 5 μm thickness, FPVC extracts 2,6-DNP from aqueous solution into the bulk membrane phase and reacts with the analyte to form a complex with low fluorescence efficiency through hydrogen bonding. Formation of the complex gave a significant fluorescence quenching which is suitable for signalling the occurrence of the host-guest interaction. At pH 3.50, the sensor exhibits a dynamic detection range from 2.5 × 10⁻⁶ to 7.0 × 10⁻³ mol L⁻¹ with a limit of detection of 1.0 × 10⁻⁶ mol L⁻¹. As 2,6-DNP can provide an optimal space geometry matches to the formation of hydrogen bonds, the sensor shows excellent selectivity for 2,6-DNP over other nitrophenols. The forward and reverse response time (t₉₅) of the sensor both was within 1 min. The repeatability, reproducibility, and lifetime of the sensor were also satisfied. The sensor was applied to determine 2,6-DNP in water samples successfully.     

An optical sensor for mercury ion based on the fluorescence quenching of tetra(p-dimethylaminophenyl)porphyrin

An optical sensor for mercury ion (Hg²⁺), based on quenching the fluorescence of the sensing reagent porphyrin immobilized in plasticized poly(vinyl chloride) (PVC) membrane, has been developed. The responses to mercury ion were compared for the sensors modified with three porphyrin compounds including 5,10,15,20-tetraphenylporphyrin (TPP), tetra(p-dimethylaminophenyl)porphyrin (TDMAPP) and tetra(N-phenylpyrazole) porphyrin (TPPP). Among them, TDMAPP showed the most remarkable response to Hg²⁺. The drastic decrease of the TDMAPP fluorescence intensity was attributed to the formation of a complex between TDMAPP and Hg²⁺, which has been utilized as the fabrication basis of a Hg²⁺-sensitive fluorescence sensor. The analytical performance characteristics of the TDMAPP modified sensor was investigated. The response mechanism, especially involving the response difference of three porphyrin compounds, was discussed in detail. The sensor can be applied to the quantification of Hg²⁺ with a linear range covering from 4.0 × 10⁻⁸ mol L⁻¹ to 4.0 × 10⁻⁶ mol L⁻¹. The limit of detection was 8.0 × 10⁻⁹ mol L⁻¹. The sensor exhibited excellent reproducibility, reversibility and selectivity. Also, the TDMAPP-based sensor was successfully used for the determination of Hg²⁺ in environmental water samples.     

A ratiometric fluorescence sensor for Be based on Beryllon II/layered double hydroxide ultrathin films

A ratiometric fluorescence sensor for Be²⁺ has been fabricated via alternate assembly of 2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate (Beryllon II) and MgAl-LDH nanosheets on quartz substrates using the layer-by-layer (LBL) deposition technique. UV–vis absorption and the fluorescence emission spectroscopy indicate a stepwise and regular growth of the Beryllon II/LDH UTFs upon increasing deposition cycle. The film of Beryllon II/LDH possesses a periodic layered structure perpendicular to the substrate revealed by X-ray diffraction and scanning electron microscopy. Atomic force microscopy images show that the film surface is continuous and uniform. The Beryllon II/LDH UTFs display ratiometric fluorescence response for Be²⁺ with a linear response range in 1.0 × 10⁻⁷–1.9 × 10⁻⁶ mol L⁻¹ and a detection limit of 4.2 × 10⁻⁹ mol L⁻¹. Furthermore, the ratiometric sensor exhibits good repeatability, high stability (thermal, storage and mechanical) as well as excellent selectivity toward Be²⁺. XPS and Raman measurements demonstrate that the specific response of the sensor is attributed to the coordination between Be²⁺ and Beryllon II in the UTF. The Beryllon II/LDH UTFs in this work can be potentially used as a chemosensor for the detection of Be²⁺ in the environmental and biomedical field.     

Electrochemical determination of L-phenylalanine at polyaniline modified carbon electrode based on β-cyclodextrin incorporated carbon nanotube composite material and imprinted sol-gel film

A sensitive and selective electrochemical sensor based on a polyaniline modified carbon electrode for the determination of l-phenylalanine has been proposed by utilizing β-cyclodextrin (β-CD) incorporated multi-walled carbon nanotube (MWNT) and imprinted sol-gel film. The electrochemical behavior of the sensor towards l-phenylalanine was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric i-t curve. The surface morphologies of layer-by-layer assembly electrodes were displayed by scanning electron microscope (SEM). The response mechanism of the imprinted sensor for l-phenylalanine was based on the inclusion interaction of β-CD and molecular recognition capacity of the imprinted film for l-phenylalanine. A linear calibration plot was obtained covering the concentration range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. With excellent sensitivity, selectivity, stability, reproducibility and recovery, the electrochemical imprinted sensor was used to detect l-phenylalanine in blood plasma samples successfully.     

Selective determination of bisphenol A (BPA) in water by a reversible fluorescence sensor using pyrene/dimethyl β-cyclodextrin complex

A bifurcated optical fiber chemical sensor for continuous monitoring of bisphenol A (BPA) has been proposed based on the fluorescence quenching (λ_ex/λ_em = 286/390 nm) of pyrene/dimethyl β-cyclodextrin (HDM-β-CD) supramolecular complex immobilized in a plasticized poly(vinyl chloride) (PVC) membrane, in which pyrene served as a sensitive fluorescence indicator probe. The decrease of the fluorescence intensity of pyrene/HDM-β-CD complex upon the addition of BPA was attributed to the displacement of pyrene by BPA, which has been utilized as the basis of the fabrication of a BPA-sensitive fluorescence sensor. The response mechanism of the sensor was discussed in detail. The sensor exhibited a dynamic detection range from 7.90 × 10⁻⁸ to 1.66 × 10⁻⁵ mol L⁻¹ with a detection limit of 7.00 × 10⁻⁸ mol L⁻¹, and showed excellent reproducibility, reversibility, selectivity, and lifetime. The proposed sensor was successfully used for the determination of BPA in water samples and landfill leachate.     

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10⁻⁹ mol L⁻¹ to 1.5 × 10⁻² mol L⁻¹ in atrazine) and low detection threshold (10⁻⁷ mol L⁻¹).     

Electrochemical bisphenol A sensor based on N-doped graphene sheets

Bisphenol A (BPA), which could disrupt endocrine system and cause cancer, has been considered as an endocrine disruptor. Therefore, it is very important and necessary to develop a sensitive and selective method for detection of BPA. Herein, nitrogen-doped graphene sheets (N-GS) and chitosan (CS) were used to prepare electrochemical BPA sensor. Compared with graphene, N-GS has favorable electron transfer ability and electrocatalytic property, which could enhance the response signal towards BPA. CS also exhibits excellent film forming ability and improves the electrochemical behavior of N-GS modified electrode. The sensor exhibits a sensitive response to BPA in the range of 1.0 × 10⁻⁸–1.3 × 10⁻⁶ mol L⁻¹ with a low detection limit of 5.0 × 10⁻⁹ mol L⁻¹ under the optimal conditions. Finally, this proposed sensor was successfully employed to determine BPA in water samples with satisfactory results.     

Highly selective and sensitive copper membrane electrode based on a new synthesized Schiff base

Bis(2-hydroxyacetophenone)butane-2,3-dihydrazone (BHAB) was used as new N-N Schiffs base which plays the role of an excellent ion carrier in the construction of a Cu(II) membrane sensor. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 55% o-nitrophenyloctyl ether (NPOE), 7% BHAB and 8% oleic acid (OA). This sensor shows very good selectivity and sensitivity towards copper ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of electrode were investigated. The electrode exhibits a Nernstian behavior (with slope of 29.6 mV per decade) over a very wide concentration range (5.0 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹) with a detection limit of 3.0 × 10⁻⁸ mol L⁻¹ (2.56 ng mL⁻¹). It shows relatively fast response time, in whole concentration range (<15 s), and can be used for at least 12 weeks in the pH range of 2.8-5.8. The proposed sensor was successfully used to determination of copper in different water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.     

Construction of a novel molecularly imprinted sensor for the determination of O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate

A novel voltammetric sensor for O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate (Phi-NO₂) based on molecularly imprinted polymer (MIP) film electrode is constructed by using sol-gel technology. The sensor responds linearly to Phi-NO₂ over the concentration range of 2.0 × 10⁻⁵ to 1.0 × 10⁻⁸ mol L⁻¹ and the detection limit is 1.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). This sensor provides an efficient way for eliminating interferences from coexisting substances in the solution. The high sensitivity, selectivity and stability of the sensor demonstrates its practical application for a simple and rapid determination of Phi-NO₂ in cabbage samples.     

A novel method for iodate determination using cadmium sulfide quantum dots as fluorescence probes

We have developed a novel method for the determination of iodate based on the carboxymethyl cellulose-capped CdS quantum dots (QDs). Factors affecting the iodate detection were investigated, and the optimum conditions were determined. Under the optimum conditions, the relative fluorescence intensity of CdS quantum dots was linearly proportional to IO₃⁻ over a concentration range from 1.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ with a correlation coefficient of 0.9987 and a detection limit of 6.0 nmol L⁻¹. Iodide, being oxidized by bromine to form iodate, was detected indirectly. The method was successfully applied to the determination of iodate and total amount of iodine in table salt samples. The related mechanism was also discussed.     

Biomimetic sensor based on MnMn complex as manganese peroxidase mimetic for determination of rutin

A novel biomimetic sensor for rutin determination based on a dinuclear complex [Mn^IIIMn^II(Ldtb)(μ-OAc)₂]BPh₄ containing an unsymmetrical dinucleating ligand, 2-[N,N-bis(2-pyridylmethyl)-aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidoben-zyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H₂Ldtb), as a manganese peroxidase mimetic was developed. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of the dinuclear complex in a carbon paste. The best performance was obtained in 75:15:10% (w/w/w) of the graphite powder:Nujol:Mn^IIIMn^II complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0) and 4.0 × 10⁻⁵ mol L⁻¹ hydrogen peroxide. The response of the sensor towards rutin concentration was linear using square wave voltammetry in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9998) with a detection limit of 1.75 × 10⁻⁷ mol L⁻¹. The recovery study performed with pharmaceuticals ranged from 96.6% to 103.2% and the relative standard deviation was 1.85% for a solution containing 1.0 × 10⁻³ mol L⁻¹ rutin (n = 6). The lifetime of this biomimetic sensor was 200 days (at least 750 determinations). The results obtained for rutin in pharmaceuticals using the biomimetic sensor and those obtained with the official method are in agreement at the 95% confidence level.     

A novel Mn PVC membrane electrode based on a recently synthesized Schiff base

A new PVC membrane electrode for manganese(II) ion based on a recently synthesized Schiff base of 5-[(4-nitrophenylazo)-N-hexylamine]salicylaldimine is reported. The electrode exhibits a Nernstian response for Mn²⁺ ions over a wide concentration range (4.0 × 10⁻⁷ to 1.8 × 10⁻² mol L⁻¹) with a slope of 30.1 (±1.0). The limit of detection is 1.0 × 10⁻⁷ mol L⁻¹. The electrode has a fast response time (∼10 s), a satisfactory reproducibility and relatively long life time. The proposed sensor revealed good selectivities over a wide variety of other cations include hard and soft metals. This electrode could be used in a pH range of 4.5-7.5. It was used as an indicator electrode in potentiometric titration of manganese(II) ions with EDTA solution.     

An electrochemiluminescent biosensor for glucose based on the electrochemiluminescence of luminol on the nafion/glucose oxidase/poly(nickel(II)tetrasulfophthalocyanine)/multi-walled carbon nanotubes modified electrode

A poly(nickel(II) tetrasulfophthalocyanine)/multi-walled carbon nanotubes composite modified electrode (polyNiTSPc/MWNTs) was fabricated by electropolymerization of NiTSPc on MWNTs-modified glassy carbon electrode (GCE). The modified electrode was found to be able to greatly improve the emission of luminol electrochemiluminescence (ECL) in a solution containing hydrogen peroxide. Glucose oxidase (GOD) was immobilized on the surface of polyNiTSPc/MWNTs modified GC electrode by Nafion to establish an ECL glucose sensor. Under the optimum conditions, the linear response range of glucose was 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol L⁻¹ (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The ECL sensor showed an outstanding well reproducibility and long-term stability. The established method has been applied to determine the glucose concentrations in real serum samples with satisfactory results.     

Flow injection chemiluminescence sensor based on core–shell magnetic molecularly imprinted nanoparticles for determination of sulfadiazine

A novel flow injection chemiluminescence (FI-CL) sensor for determination of sulfadiazine (SDZ) using core–shell magnetic molecularly imprinted polymers (MMIPs) as recognition element is developed. Briefly, a hydrophilic MMIPs layer was produced at the surface of Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. And it provided the MMIPs with excellent adsorption capacity and rapid adsorption rate due to the imprinted sites mostly situated on the surface of MMIPs. Then the prepared SDZ-MMIPs were packed into flow cell to establish a novel FI-CL sensor. The sensor provided a wide linear range for SDZ of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.54 × 10⁻⁷ mol L⁻¹. And the relative standard deviation (RSD) for the determination of 1.0 × 10⁻⁶ mol L⁻¹ SDZ was 2.56% (n = 11). The proposed method was applied to determine SDZ in urine samples and satisfactory results were obtained.     

Construction of a new Cu2+ coated wire ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylidene amino)phenyl)disufanyl)phenylimino)methyl)-4-methoxyphenol Schiff base

In this article a new coated platinum Cu²⁺ ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylideneamino)phenyl)disufanyl)phenylimino) methyl)-4-methoxyphenol Schiff base (L₁) as a new ionophore is described. This sensor has a wide linear range of concentration (1.2 × 10⁻⁷-1.0 × 10⁻¹ mol L⁻¹) and a low detection limit of 9.8 × 10⁻⁸ mol L⁻¹of Cu(NO₃)₂. It has a Nernstian response with slope of 29.54 ± 1.62 mV decade⁻¹ and it is applicable in the pH range of 4.0-6.0 without any divergence in potentioal. The coated electrode has a short response time of approximately 9 s and is stable at least for 3.5 months. The electrode shows a good selectivity for Cu²⁺ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of Cu²⁺ ion in different real and environmental samples and as indicator electrode for potentiometric titration of Cu²⁺ ion with EDTA.     

An optical redox chemical sensor for determination of iodide

A novel optical sensor based on a redox reaction for the determination of iodide has been developed. The optode membrane is constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of chloride as counter ion with iodate in the membrane changes the color to yellow, when it is placed in acidic solution of iodide. The sensor can readily be regenerated by 0.1 mol L⁻¹ NaOH in less than 15 s. The optode has a linear range of 3.94 × 10⁻⁶ to 5.51 × 10⁻⁵ mol L⁻¹ of iodide ions with a limit of detection 7.44 × 10⁻⁷ mol L⁻¹. The relative standard deviation for eight replicate measurements of 3.94 × 10⁻⁶ and 1.57 × 10⁻⁵ mol L⁻¹ of iodide was 2.83 and 1.38%, respectively. The sensor was successfully applied to the determination of iodide in tablet, powdered milk and urine samples.     

One-step synthesis and applications of fluorescent Cu nanoclusters stabilized by l-cysteine in aqueous solution

Herein, an innovative and simple strategy for synthesizing high fluorescent Cu nanoclusters was successfully established while l-cysteine played a role as the stabilizer. Meaningfully, the current Cu nanoclusters together with a quantum yield of 14.3% were prepared in aqueous solution, indicating their extensive applications. Subsequently, the possible fluorescence mechanism was elucidated by fluorescence, UV–vis, HR-TEM, FTIR, XPS, and MS. Additionally, the CuNCs were employed for assaying Hg²⁺ on the basis of the interactions between Hg²⁺ and l-cysteine; thus facilitating the quenching of their fluorescence. The proposed analytical strategy permitted detections of Hg²⁺ in a linear range of 1.0 × 10⁻⁷ mol L⁻¹ × 10⁻³ mol L⁻¹, with a detection limit of 2.4 × 10⁻⁸ mol L⁻¹ at a signal-to-noise ratio of 3. Significantly, this CuNCs described here were further applied for coding and fluorescent staining, suggesting may broaden avenues toward diverse applications.     

Ultrasensitive determination of silver ion based on synchronous fluorescence spectroscopy with nanoparticles

Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional cadmium sulphide (CdS) nanoparticles as a fluorescence probe. When Δλ (λ_em − λ_ex) = 215 nm, maximum synchronous fluorescence is produced at 304 nm. Under optimal conditions, functional cadmium sulphide displayed a calibration response for silver ion over a wide concentration range from 0.8 × 10⁻¹⁰ to 1.5 × 10⁻⁸ mol L⁻¹. The limit of detection was 0.4 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of seven replicate measurements for the lowest concentration (0.8 × 10⁻¹⁰ mol L⁻¹) was 2.8%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.     

Tris(2,2'-bipyridyl)ruthenium(II)-Zirconia-Nafion composite modified electrode applied as solid-state electrochemiluminescence detector on electrophoretic microchip for detection of pharmaceuticals of tramadol, lidocaine and ofloxacin

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-Zirconia-Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)-ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy)₃²⁺ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy)₃²⁺ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N = 3) were 2.5 × 10⁻⁵ mol L⁻¹ for tramadol, 5.0 × 10⁻⁶ mol L⁻¹ for lidocaine, 1.0 × 10⁻⁵ mol L⁻¹ for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for tramadol, 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹ for lidocaine, and 1.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for ofloxacin, respectively.