An optical sensor based on H-acid/layered double hydroxide composite film for the selective detection of mercury ion

A novel optical chemosensor was fabricated based on 1-amino-8-naphthol-3,6-disulfonic acid sodium (H-acid) intercalated layered double hydroxide (LDH) film via the electrophoretic deposition (EPD) method. The film of H-acid/LDH with the thickness of 1 μm possesses a well c-orientation of the LDH microcrystals confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fluorescence detection for Hg(II) in aqueous solution was performed by using the H-acid/LDH film sensor at pH 7.0, with a linear response range in 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹ and a detection limit of 6.3 × 10⁻⁸ mol L⁻¹. Furthermore, it exhibits excellent selectivity for Hg(II) over a large number of competitive cations including alkali, alkaline earth, heavy metal and transitional metals. The specific fluorescence response of the optical sensor is attributed to the coordination between Hg(II) and sulfonic group in the H-acid immobilized in the LDH matrix, which was verified by NMR spectroscopy and UV–vis spectra. In addition, density functional theory (DFT) calculation further confirms that the coordination occurs between one Hg²⁺ and two O atoms in the sulfonic group, which is responsible for the significant fluorescence quenching of the H-acid/LDH film. The results indicate that the H-acid/LDH composite film can be potentially used as a chemosensor for the detection of Hg²⁺ in the environmental and biomedical field.     

Novel amperometric sensor using metolcarb-imprinted film as the recognition element on a gold electrode and its application

A molecularly imprinted film is electrochemically synthesized on a gold electrode using cyclic voltammetry to electropolymerize o-aminothiophenol in the presence of metolcarb (MTMC). The mechanism of the imprinting process and a number of factors affecting the activity of the imprinted film are discussed and optimized. Scanning electron microscope observations and binding measurements have proved that an MTMC-imprinted film (with a thickness of nearly 100 nm) was formed on the surface of the gold electrode. The film exhibited high binding affinity and selectivity towards the template MTMC, as well as good penetrability, reproducibility and stability. A novel amperometry sensor using the imprinted film as recognition element was developed for MTMC determination in food samples. Under the experimental conditions, the MTMC standard is linear within the concentration range studied (r² = 0.9906). The limit of detection (S/N = 3) of the modified electrode was achieved to 1.34 × 10⁻⁸ mol L⁻¹. Recoveries of MTMC from spiked apple juice, cabbage and cucumber samples for the developed electrochemical assay ranged from 94.80% to 102.43%, which was with great correlation coefficient (0.9929) with results from high-performance liquid chromatography. In practical application, the prepared amperometric sensor also showed good reproducibility and long lifetime for storage. The research in this study has offered a rapid, accurate and sensitive electrochemical method for quantitative determination of MTMC in food products.     

Copper(II)-selective electrode based on dithioacetal

A PVC membrane electrode for copper ion based on 1,3-dithiane,2-(4-methoxy phenyl) as ionophore and o-nitrophenyl octyl ether as a plasticizer is demonstrated. The electrode exhibits a Nernstian slope of 29.5±1 mV per decade in a linear range of 3.0×10⁻⁶ to 5.0×10⁻² M for Cu²⁺ ion. The detection limit of this electrode is 1.0×10⁻⁶ mol/l. This sensor has a very short response time of about 5 s and could be used in a pH range of 4.0-7.0. High selectivity was obtained over a wide variety of metal ions. The proposed electrode was successfully applied as an indicator electrode for the potentiometric titration of copper ion with EDTA and for the direct determination of copper in river water.     

A sensitive nicotine sensor based on molecularly imprinted electropolymer of o-aminophenol

A sensitive nicotine sensor based on a molecularly imprinted electropolymer of o-aminophenol is proposed and its configuration and performance are studied in detail. On the condition of weak acidity, the sensitive layer was prepared by electropolymerization of o-aminophenol on a gold electrode in the presence of the template (nicotine). The sensor exhibits good selectivity and sensitivity to nicotine. The determination limit is 2.0×10⁻⁷ mol/L and a linear relationship between the current and concentration is found in the range of 4.0×10⁻⁷ ∼ 3.3 ×10⁻⁵ mol/L. The sensor has also been applied to the analysis of nicotine in tobacco samples with recovery rates ranging from 99.0% to 102%. __________ Translated from Journal of Hunan university (Nature Science), 2005, 32(3) (in Chinese)     

Construction of a novel electrochemical sensor based on molecularly imprinted polymers for the selective determination of chlorpyrifos in real samples

We present a novel electrochemical sensor based on an electrode modified with molecularly imprinted polymers for the detection of chlorpyrifos. The modified electrode was constructed by the synthesis of molecularly imprinted polymers by a precipitation method then coated on a glassy carbon electrode. The surface morphology of the modified electrode was characterized by using field‐emission scanning electron microscopy and transmission electron microscopy. The performance of the imprinted sensor was thoroughly investigated by using cyclic voltammetry and differential pulse voltammetry. The imprinted electrochemical sensor displayed high repeatability, stability, and selectivity towards the template molecules. Under the optimal experimental conditions, the peak current response of the imprinted electrochemical sensor was linearly related to the concentration of chlorpyrifos over the range 1 × 10⁻¹⁰–1 × 10⁻⁵ mol/L with a limit of detection of 4.08 × 10⁻⁹ mol/L (signal‐to‐noise ratio = 3). Furthermore, the proposed molecularly imprinted electrochemical sensor was applied to the determination of chlorpyrifos in the complicated matrixes of real samples with satisfactory results. Therefore, the molecularly imprinted polymers based electrochemical sensor might provide a highly selective, rapid, and cost‐effective method for chlorpyrifos determination and related analysis.     

Capacitive sensors using electropolymerized o-phenylenediamine film doped with ion-pair complex as selective elements for the determination of pentoxyverine

A capacitive sensing method based on electropolymerized o-phenylenediamine film doped with pentoxyverine ion-pair complex as selective element was successfully developed for the determination of pentoxyverine. Ion-pair complex, pentoxyverine-tetraphenylborate or pentoxyverine-picrolonate, was embedded in electropolymerized o-phenylenediamine film by electropolymerizing technique. The effects of working frequency and test solution pH on the detection of pentoxyverine were investigated in detail and optimized. For the sensor modified with pentoxyverine-tetraphenylborate, calibration curve was linear over the concentration range of 5.0×10⁻⁷ to 1.0×10⁻⁴ M with a detection limit of 1.0×10⁻⁷ M at pH 7. The proposed sensor exhibited high selectivity and sensitivity to pentoxyverine. The results in sample analysis confirmed the usefulness of the proposed ISC sensor for quantitative analysis, and also indicated that this method might find applications in the assay of other drugs.     

Microplate electrochemical DNA detection for phosphinothricin acetyltransferase gene sequence with cadmium sulfide nanoparticles

An electrochemical DNA detection method for the phosphinothricin acetyltransferase (PAT) gene sequence from the transgenetic plants was established by using a microplate hybridization assay with cadmium sulfide (CdS) nanoparticles as oligonucleotides label. The experiment included the following procedures. Firstly target PAT ssDNA sequences were immobilized on the polystyrene microplate by physical adsorption. Then CdS nanoparticle labeled oligonucleotide probes were added into the microplate and the hybridization reaction with target ssDNA sequences took place in the microplate. After washing the microplate for three times, certain amounts of HNO₃ were added into the microplate to dissolve the CdS nanoparticles anchored on the hybrids and a solution containing Cd²⁺ ion was obtained. At last differential pulse anodic stripping voltammetry (DPASV) was used for the sensitive detection of released Cd²⁺ ion. Based on this principle a sensitive electrochemical method for the PAT gene sequences detection was established. The voltammetric currents of Cd²⁺ were in linear range with the target ssDNA concentration from 5.0 × 10^− 13 to 1.0 × 10^− 10 mol/L and the detection limit was estimated to be 8.9 × 10^− 14 mol/L (3σ). The proposed method showed a good promise for the sensitive detection of specific gene sequences with good selectivity for the discrimination of the mismatched sequences.     

Development of a potentiometric sensor for the determination of saccharin in instant tea powders, diet soft drinks and strawberry dietetic jam

The construction and the analytical evaluation of a potentiometric sensor, namely, Pt∣Hg∣Hg₂(Sac)₂∣Graphite, where Sac stands for saccharinate ion, are described. This electrode has a wide linear dynamic range between 5.0 × 10^− 7 and 1.0 × 10^− 2 mol L^− 1 with a near-Nernstian slope of − 58.1 ± 1.1 mV decade^− 1 and a detection limit of 3.9 × 10^− 7 mol L^− 1. The potentiometric response is independent of the pH of the solution in the pH range 3.0-9.0. The electrode is easily constructed at a relatively low-cost with fast response time (within 10-30 s) and can be used for a period of 10 months without significant change in its performance characteristics. The proposed sensor displayed good selectivities over a variety of other anions (carboxylates and inorganic anions). The potentiometric sensor was successfully applied to the determination of saccharin in real food samples, that is, in instant tea powders, diet soft drinks and strawberry dietetic jam.     

A selective artemisinin-sensor using metalloporphyrin as a recognition element entrapped in the Au-nanoparticles-chitosan modified electrodes

An amperometric artemisinin (ARN) sensor based on the supramolecular recognition of glycosylated metalloporphyrin, which is included in the Au-nanoparticles-chitosan film coated on the glass carbon electrodes, was developed. For the improvement of the selectivity of artemisinin detection, 5,10,15,20-tetrakis[2-(2,3,4,6-tetraacetyl-β-d-glucopyranosyl)-1-O-phenyl]porphyrin (T(o-glu)PPH) metal complex [FeT(o-glu)PPCl] was synthesized and employed as a ARN-sensitive and -selective material in the amperometric sensors. The proposed [FeT(o-glu)PPCl]/Au-nanoparticles modified electrodes showed excellent selectivity and sensitivity toward ARN with respect to a number of interferents and exhibited stable current response, which can be attributed to the coordination of ARN with the [FeT(o-glu)PPCl] in the electrodes. The calibration graph obtained with the proposed sensor was linear over the range of 1.8 × 10⁻⁷-1.7 × 10⁻⁹ mol l⁻¹, with a detection limit of 1.7 × 10⁻⁹ mol l⁻¹ for ARN. Significant advantages of the proposed procedure over the conventional reductive electrochemical methods are the selective detection and the relatively low applied potential requirement of the ARN-sensor. The prepared sensor is applied for the determination of ARN in plant samples and the results agreed with the values obtained by the pharmacopoeia method.     

A cerium(III) selective polyvinyl chloride membrane sensor based on a Schiff base complex of N,N'-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine

A polyvinyl chloride (PVC) based membrane sensor for cerium ions was prepared by employing N,N′-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine as an ionophore, oleic acid (OA) as anion excluder and o-nitrophenyloctyl ether (o-NPOE) as plasticizer. The plasticized membrane sensor exhibits a Nernstian response for Ce(III) ions over a wide concentration range (1.41 × 10⁻⁷ to 1.0 × 10⁻² M) with a limit of detection as low as 8.91 × 10⁻⁸ M. It has a fast response time (<10 s) and can be used for 4 months. The sensor revealed a very good selectivity with respect to common alkali, alkaline earth and heavy metal ions. The response of the proposed sensor is independent of pH between 3.0 and 8.0. It was used as an indicator electrode in potentiometric titration of fluoride, carbonate and oxalate anions and determination of cerium in simulated mixtures.     

The double K+/Ca2+ sensor based on laser scanned silicon transducer (LSST) for multi-component analysis

In the present work a double ion sensor based on a laser scanned semiconductor transducer (LSST) for the simultaneous determination of K⁺- and Ca²⁺-ions in solutions has been developed. Specially elaborated ion-sensitive membrane compositions based on valinomycin and calcium ionophore calcium bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate (t-HDOPP-Ca) were deposited as separate layers on a silanized surface of the Si/SiO₂/Si₃N₄-transducer. The proposed multi-sensor exhibits theoretical sensitivities and the detection limits of the sensor were found to be 2×10⁻⁶ mol l⁻¹ for K⁺ and 5×10⁻⁶ mol l⁻¹ for Ca²⁺. The elaborated double sensor is proposed for the first time as a prototype of a new type of multi-sensor systems for chemical analysis.     

Fabrication of highly sensitive and selective nanocomposite film based on CuNPs/fullerene-C60/MWCNTs: An electrochemical nanosensor for trace recognition of paracetamol

Designing an electrochemical sensor for versatile clinical applications is a sophisticated task and how dedicatedly functionalized composite materials can perform on this stage is a challenge for today and tomorrow's Nanoscience and Nanotechnology. In the present work, we demonstrate a new strategy for the development of novel electrochemical sensor based on catalytic nanocomposite film. Fullerene-C₆₀ and multi-walled carbon nanotubes (MWCNTs) were dropped on the pre-treated carbon paste electrode (CPE) and copper nanoparticles (CuNPs) electrochemically deposited on the modified CPE to form nanocomposite film of CuNPs/C₆₀/MWCNTs/CPE. In this work, an electrochemical method based on square wave voltammetry (SWV) employing CuNPs/C₆₀/MWCNTs/CPE has been presented for the recognition and determination of paracetamol (PT). Developed electrochemical sensor was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. The composite film made the fabricated sensor to display high sensitivity and good selectivity for PT detection. The influence of the optimization parameters such as pH, accumulation time, deposition potential, scan rate and effect of loading of composite mixture of C₆₀-MWCNTs and CuNPs on the electrochemical performance of the sensor were evaluated. A linear range from 4.0 × 10⁻⁹ to 4.0 × 10⁻⁷ M for PT detection was obtained with a detection limit of 7.3 × 10⁻¹¹ M. The fabricated sensor was successfully applied to the detection of PT in biological samples with good recovery ranging from 99.21 to 103%.     

Sensitive and selective electrochemical determination of quinoxaline-2-carboxylic acid based on bilayer of novel poly(pyrrole) functional composite using one-step electro-polymerization and molecularly imprinted poly(o-phenylenediamine)

A facile and efficient molecularly imprinted polymer (MIP) recognition element of electrochemical sensor was fabricated by directly electro-polymerizing monomer o-phenylenediamine (oPD) in the presence of template quinoxaline-2-carboxylic acid (QCA), based on one-step controllable electrochemical modification of poly(pyrrole)-graphene oxide-binuclear phthalocyanine cobalt (II) sulphonate (PPY-GO-BiCoPc) functional composite on glassy carbon electrode (GCE). The MIP film coated on PPY-GO-BiCoPc functional composite decorated GCE (MIP/PPY-GO-BiCoPc/GCE) was presented for the first time. The synergistic effect and electro-catalytic activity toward QCA redox of PPY-GO-BiCoPc functional composite were discussed using various contrast tests. Also, the effect of experimental variables on the current response such as, electro-polymerization cycles, template/monomer ratio, elution condition for template removal, pH of the supporting electrolyte and accumulation time, were investigated in detail. Under the optimized conditions, the proposed MIP sensor possessed a fast rebinding dynamics and an excellent recognition capacity to QCA, while the anodic current response of square wave voltammetry (SWV) was well-proportional to the concentration of QCA in the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁴ and 1.0 × 10⁻⁴–5.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.1 nmol L⁻¹. The established sensor was applied successfully to determine QCA in commercial pork and chicken muscle samples with acceptable recoveries (91.6–98.2%) and satisfactory precision (1.9–3.5% of SD), demonstrating a promising feature for applying the MIP sensor to the measurement of QCA in real samples.     

Flow injection analysis of gallic acid with inhibited electrochemiluminescence detection

A flow injection (FI)–electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0×10^–9 mol/L and a dynamic concentration range of 2×10^–8–2×10^–5 mol/L. The relative standard deviation (RSD) was 1.0% for 1.0×10^–6 mol/L gallic acid (n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine—Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)₃²⁺/TPrA ECL system was the interaction of electrogenerated Ru(bpy)₃^2+* and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.     

基于静电自组装作用制备聚二烯丙基二甲基氯化铵巯基乙酸修饰金电极检测亚硝酸盐

利用常见易得的原材料聚二烯丙基二甲基氯化铵(PDDA)和巯基乙酸(MA),基于静电组装技术制备了PDDA-MA/Au传感器,用于亚硝酸盐的检测.试验表明,在0.2 mol/L磷酸缓冲盐溶液(PBS,pH 7.53,0.1 mol/L NaAc)中,NaNO_2的氧化峰电流与其浓度在6.9×10~(-7)~8.8×10~(-3)mol/L之间呈现良好的线性关系,试验测得检出限为6.9×10~(-7)mol/L,回收率在94.6%~101.8%之间.传感器制备简单、成本低,对NaNO_2具有较高的灵敏度、较低的检测限、良好的稳定性及重现性.     

Tripodal chelating ligand-based sensor for selective determination of Zn(II) in biological and environmental samples

Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate [KTt^t-Bu] and potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl)borate [KTp^t-Bu,i-Pr] have been synthesized and evaluated as ionophores for preparation of a poly(vinyl chloride) (PVC) membrane sensor for Zn(II) ions. The effect of different plasticizers, viz. benzyl acetate (BA), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tributyl phosphate (TBP), and o-nitrophenyl octyl ether (o-NPOE), and the anion excluders sodium tetraphenylborate (NaTPB), potassium tetrakis(p-chlorophenyl)borate (KTpClPB), and oleic acid (OA) were studied to improve the performance of the membrane sensor. The best performance was obtained from a sensor with a of [KTt^t-Bu] membrane of composition (mg): [KTt^t-Bu] (15), PVC (150), DBP (275), and NaTPB (4). This sensor had a Nernstian response (slope, 29.4 ± 0.2 mV decade of activity) for Zn²⁺ ions over a wide concentration range (1.4 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹) with a limit of detection of 9.5 × 10⁻⁸ mol L⁻¹. It had a relatively fast response time (12 s) and could be used for 3 months without substantial change of the potential. The membrane sensor had very good selectivity for Zn²⁺ ions over a wide variety of other cations and could be used in a working pH range of 3.5–7.8. The sensor was also found to work satisfactorily in partially non-aqueous media and could be successfully used for estimation of zinc at trace levels in biological and environmental samples. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

用聚(L-蛋氨酸)/纳米金修饰玻碳电极同时灵敏检测多巴胺和尿酸简

A novel electrochemical sensor was fabricated by electrodeposition of gold nanoparticles on a poly(L-methionine) (PMT)-modified glassy carbon electrode (GCE) to form a nano-Au/PMT composite-modified GCE (nano-Au/PMT/GCE). Scanning electron microscopy and electrochemical techniques were used to characterize the composite electrode. The modified electrode exhibited considerable electrocatalytic activity towards the oxidation of dopamine (DA) and uric acid (UA) in phosphate buffer solution (pH = 7.00). Differential pulse voltammetry revealed that the electrocatalytic oxidation currents of DA and UA were linearly related to concentration over the range of 5.0×10^-8 to 10^-6 mol/L for DA and 7.0×10^-8 to 10^-6 mol/L for UA. The detection limits were 3.7×10^-8 mol/L for DA and 4.5×10^-8 mol/L for UA at a signal-to-noise ratio of 3. According to our experimental results, nano-Au/PMT/GCE can be used as a sensitive and selective sensor for simultaneous determination of DA and UA.     

A new electrochemiluminescent sensing system for glucose based on the electrochemiluminescent reaction of bis-[3,4,6-trichloro-2-(pentyloxycarbonyl)-phenyl] oxalate

In this paper, the electrochemiluminescence (ECL) behavior of bis-[3,4,6-trichloro-2-(pentyloxycarbonyl)-phenyl] oxalate (BTPPO) at glassy carbon electrode (GCE) in phosphate buffer solution in the presence of hydrogen peroxide has been investigated when linear sweep voltammetry was applied. The optimum chemical conditions and electrochemical parameters for this ECL system have been investigated in detail. Under the optimum conditions, it was found that the concentration of BTPPO was linear with the ECL intensity in the range of 3.0 × l0⁻⁶ to 3.0 × 10⁻⁴ mol/L, and the detection limit (S/N = 3) for BTPPO was 1.0 × 10⁻⁷ mol/L. The possible mechanism for ECL of BTPPO at the GCE in the presence of hydrogen peroxide was also discussed. Furthermore, based on the fact that glucose oxidase can react with glucose to produce hydrogen peroxide, a new ECL sensing system of BTPPO has been developed for detection of glucose. The enhanced ECL intensity has a linear relationship with the concentration of glucose in the range of 1.0 × l0⁻⁴ to 1.0 × 10⁻³ mol/L, and the detection limit for glucose is found to be 5.0 × 10⁻⁵ mol/L (S/N = 3).     

Sensitive determination of verticine and verticinone in Bulbus Fritillariae by ionic liquid assisted capillary electrophoresis-electrochemiluminescence system

CE/Ru(bpy)₃²⁺ electrochemiluminescence (ECL) system with the assistance of ionic liquids (ILs) was successfully established for sensitive determination of verticine and verticinone in Bulbus Fritillariae for the first time. Migration behavior of alkaloid largely relies on the hydrogen bonding interactions between alkyl imidazolium cations in ILs and the alkaloids. Running buffer containing 40 mmol/L 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF₄) IL-8 mmol/L phosphate resulted in significant changes in separation selectivity for alkaloids with similar structures. The highest sensitivity of the detection was obtained by maintaining the detection potential at 1.2 V. Under the optimized conditions, relative standard derivations of the ECL intensity and the migration time were 3.27 and 2.84% for verticine and 4.42 and 1.69% for verticinone, respectively. The standard curves were linear between 1 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticine and between 5 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticinone, respectively. Detection limits of 1.25 × 10⁻¹⁰ mol/L for verticine and 1 × 10⁻¹⁰ mol/L for verticinone were obtained (S/N = 3). Developed method was successfully applied to determine the amounts of alkaloids in Bulbus Fritillariae.     

Graphene oxide amplified electrochemiluminescence of graphitic carbon nitride and its application in ultrasensitive sensing for Cu

Here for the first time, we present a novel electrochemiluminescence (ECL) sensor based on graphitic carbon nitride/graphene oxide (g-C₃N₄/GO) hybrid for the ultrasensitive detection of Cu²⁺, which is a common pollutant in environmental system. The g-C₃N₄/GO shows stable ECL signal in the presence of the self-produced coreactant from oxygen reduction, and the ECL signal could be effectively quenched by Cu²⁺, the possible ECL detection mechanism has been proposed in detail. GO can not only significantly enhance the cathodic ECL signal of g-C₃N₄ (∼3.8 times), but also serve as immobilization platform for g-C₃N₄. After optimization of experimental conditions, the proposed protocol can offer an ultrasensitive, highly selective and recyclable method for the detection of Cu²⁺ with a low detection limit of 1.0 × 10⁻¹¹ M and a wide linear range from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁷ M. Moreover, the practicability of the ECL sensor in real wastewater samples is also tested, showing that the proposed ECL sensor could be a promising alternative method for the emergency and routine monitoring of Cu²⁺ in real sample.