Fluorescence chemical sensor based on water‐soluble poly(p‐phenylene ethynylene)–graphene oxide composite for Cu2+

A chemical sensor for metal ions was fabricated based on a water‐soluble conjugated polymer–graphene oxide (GO) composite. Water‐soluble poly(p‐phenylene ethynylene) (PPE) with sulfonic acid side chain groups was used to prepare a very stable water‐soluble PPE–GO composite with strong π–π interactions in water. The relationship between the optical properties and metal ion sensing capability of the PPE–GO composite in aqueous solution was investigated. Addition of metal ions enhanced the fluorescence intensity of the composite, and, in particular, the composite enabled the fluorescence detection of Cu²⁺ in aqueous solutions with high selectivity and sensitivity. Therefore, this conjugated polymer–GO composite sensor system was found to be an effective turn‐on type chemical sensor for metal ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Simultaneous and Sensitive Detection of Cd(II) and Pb(II) Using a Novel Bismuth Film/Ordered Mesoporous Carbon‐molecular Wire Modified Graphite Carbon Paste Electrode

An electrochemical sensor for the simultaneous and sensitive detection of Cd(II) and Pb(II) is proposed on the basis of square‐wave anodic stripping voltammetry (SWASV) experiments using a novel bismuth film/ordered mesoporous carbon‐molecular wire modified graphite carbon paste electrode (Bi/OMC‐MW/GCPE). Ordered mesoporous carbon (OMC) and molecular wire (MW) (diphenylacetylene) were used as the modifier and binder, respectively. The Bi/OMC‐MW/GCPE was prepared with the addition of graphite powder, OMC and DPA at the ratio of 2 : 1 : 1. The electrochemical properties and morphology of the electrode were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), SWASV and scanning electron microscopy (SEM). The parameters affecting the stripping current response were investigated and optimized. The experimental results show that the prepared electrode exhibited excellent electrochemical performance, good electrical conductivity and a high stripping voltammetric response. Under optimized conditions, a linear range was achieved over a concentration range from 1.0 to 70.0 μg/L for both Cd(II) and Pb(II) metal ions, with detection limits of 0.07 μg/L for Cd(II) and 0.08 μg/L for Pb(II) (S/N=3) with the deposition time 150 s. Moreover, the sensor exhibited improved sensitivity and reproducibility compared to traditional CPEs. The fabricated electrode was then successfully used to satisfactorily detect Cd(II) and Pb(II) in real soil samples.     

Graphene Oxide‐Modified Electrode Coated with in‐situ Antimony Film for the Simultaneous Determination of Heavy Metals by Sequential Injection‐Anodic Stripping Voltammetry

The proposed chemically modified electrode was graphene oxide that was synthesized via Hummer's method followed by reduction of antimony film by in‐situ electrodeposition. The experimental process could be concluded in three main steps: preparation of antimony film, reduction of analyte ions on the electrode surface and stripping step under the conditions of square wave anodic stripping voltammetry (SWASV). A simple and rapid approach was developed for the determination of heavy metals simultaneously based on a sequential injection (SI), an automated flow‐based system, coupled with voltammetric method using antimony‐graphene oxide modified screen‐printed carbon electrode (SbF‐GO‐SPCE). The effects of main parameters involved with graphene oxide, antimony and measurement parameters were also investigated. Using SI‐SWASV under the optimal conditions, the proposed electrode platform has exhibited linear range from 0.1 to 1.5 M. Calculated limits of detection were 0.054, 0.026, 0.060, and 0.066 μM for Cd(II), Pb(II), Cu(II) and Hg(II), respectively. In addition, the optimized method has been successfully applied to determine heavy metals in real water samples with acceptable accuracy of 94.29 – 113.42 % recovery.     

Highly Sensitive Temperature‐responsive Sensor Based on PS‐PDEA‐PS/C60‐MWCNTs for Reversible Switch Detection of Catechol

A new type of temperature‐responsive electrochemical sensor was constructed based on a glass carbon electrode modified by the composite containing temperature‐responsive polymer polystyrene‐poly N, N‐diethyl acrylamide‐polystyrene (PS‐PDEA‐PS) and fullerenes‐carboxylate multi‐walled carbon nanotubes (C₆₀‐MWCNTs). The sensor was used for the electrochemical detection of catechol (CC). When the temperature is higher than the critical temperature (LCST) of PS‐PDEA‐PS, the electrochemical behavior of CC can be detected, which it is in the “on” state. When the temperature is lower than LCST, the composite modified film is in the “off” state and the electrochemical behavior of CC was not detected. Under the best experimental conditions, the sensor has a good detection range for catechol from 4.0 to 135.0 μM, with a LOD of 1.45 μM. In addition, the proposed sensor has good stability and reproducibility, and was successfully applied to the determination of catechol in real tap water.     

Highly Selective and Sensitive Copper(II) Membrane Sensors Based on 6‐Methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one as a New Neutral Ionophore

A new Cu(II) ion‐selective PVC membrane sensor based on 6‐methyl‐4‐(1‐phenylmethylidene)amino‐3‐thioxo‐1,2,4‐triazin‐5‐one (MATTO) as an excellent sensing material was developed. The electrode exhibits a Nernstian slope of 29.2±0.4 mV per decade over a very wide concentration range between 1.0×10^?1 and 1.0×10^?6 M, with a detection limit of 4.8×10^?7 M (30.5 ng/mL). The sensor possesses the advantages of short conditioning time, fast response time (<10 s), and especially, very good selectivity towards transition and heavy metal, and some mono, di and trivalent cations. The proposed electrode was successfully applied to the determination of copper in wastewater of copper electroplating samples and as an indicator electrode in potentiometric titration of Cu(II) ions with EDTA.     

A Highly Selective and Sensitive Barium(II)‐Selective PVC Membrane Based on Dimethyl 1‐Acetyl‐8‐oxo‐2,8‐dihydro‐ 1H‐pyra‐zolo[5,1‐a]isoindole‐2,3‐dicarboxylate

A poly(vinyl chloride)‐based membrane of dimethyl 1‐acetyl‐8‐oxo‐2,8‐dihydro‐1H‐pyra‐zolo[5,1‐a]isoindole‐2,3‐dicarboxylate as a neutral carrier with sodium tetraphenylborate (NaTPB) as an anion excluder and 2‐nitrophenyl octyl ether (NPOE) as plasticizer was prepared and investigated as a Ba(II)‐selective electrode. The electrode exhibits a Nernstian slope of 29.7±0.4 mV per decade over a wide concentration range (1.0×10^?6 to 1.0×10^?1 M) with a detection limit of 7.6×10^?7 M between pH 3.0 and 11.0. The response time of the sensor is about 10 s and it can be used over a period of 2 months without any divergence in potential. The proposed membrane sensor revealed good selectivity for Ba(II) over a wide variety of other metal ions. It was successfully used in direct determination of barium ions in industrial wastewater samples.     

Differential Pulse Voltammetry Determination of Ofloxacin in Human Serum and Urine Based on a Novel Tryptophan‐graphene Oxide‐carbon Nanotube Electrochemical Sensor

The highly sensitive determination of ofloxacin (OFL) in human serum and urine was achieved on a novel tryptophan‐graphene oxide‐carbon nanotube (Trp‐GO‐CNT) composite modified glassy carbon electrode (Trp‐GO‐CNT/GCE). The Trp‐GO‐CNT composite was fabricated, and its morphologies and surface functional groups were characterized by field emission scanning electron microscopy (FE‐SEM) and Fourier transform infrared (FT‐IR) spectroscopy. The electrochemical properties of Trp‐GO‐CNT/GCE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The superior electrochemical behaviors of Trp‐GO‐CNT/GCE toward OFL can be mainly assigned to the excellent electrocatalytic activity of Trp, the great conductivity and high surface area of GO and CNT, and the synergistic effect between Trp, GO and CNT. Under optimum conditions, a wide and valuable linear range (0.01–100 μM), a low detection limit (0.001 μM, S/N=3), a good linear relationship (R2>0.999), good stability and repeatability were obtained for the quantitative determination of OFL. Furthermore, the Trp‐GO‐CNT electrochemical sensor was successfully applied to the determination of OFL in human serum and urine samples, and satisfactory accuracy and recovery could be obtained.     

Simultaneous Determination of Cadmium,Lead, Copper and Mercury Ions Using Organofunctionalized SBA‐15 Nanostructured Silica Modified Graphite–Polyurethane Composite Electrode

A new sensor has been developed for the simultaneous detection of cadmium, lead, copper and mercury, using differential pulse and square wave anodic stripping voltammetry (DPASV and SWASV) at a graphite–polyurethane composite electrode with SBA‐15 silica organofunctionalized with 2‐benzothiazolethiol as bulk modifier. The heavy metal ions were preconcentrated on the surface of the modified electrode at ?1.1 V vs. SCE where they complex with 2‐benzothiazolethiol and are reduced to the metals, and are then reoxidized. Optimum SWASV conditions lead to nanomolar detection limits and simultaneous determination of Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ in natural waters was achieved.     

Square Wave‐Anodic Stripping Voltammetric Determination of Copper at a Bismuth Film/Glassy Carbon Electrode Using 3‐[(2‐Mercapto‐Vinyl)‐Hydrazono]‐ 1,3‐Dihydro‐Indol‐2‐One

This study reports a highly sensitive electrochemical sensor based on Bi film modified glassy carbon electrode (BiF/GCE) for total determination and speciation trace concentrations of copper(II) ions in environmental water samples. Square wave‐adsorptive anodic stripping voltammetric (SW‐ASV) experiment was performed for monitoring selective accumulation of copper(II) with reagent 3‐[(2‐mercapto‐vinyl)‐hydrazono]‐1,3‐dihydro‐indol‐2‐one (MHDI) at pH 9–10. The mechanism of the electrode reaction of Cu²⁺‐MHDI complex was safely assigned. The sensor exhibited a wide linear range (3.22×10⁻⁹–2.0×10⁻⁷ mol L⁻¹) with lower limits of detection (LOD) and quantitation (LOQ) of 9.6×1⁻¹⁰ and 3.22×10⁻⁹ mol L⁻¹, respectively (R²=0.9993). The proposed sensor exhibited interference from active metal ions e. g. Cd, Hg. The performance of the proposed method was compared successfully with most of the reported methods and comparable efficiencies were obtained. The analytical utility of the proposed SW‐ASV method has been successfully validated for trace analysis of copper(II) in environmental water samples. The method offers a precise, accurate approach with good reproducibility, robustness, ruggedness, and cost effectiveness.     

Construction of a Highly Selective and Sensitive La(III) Sensor Based on N‐(2‐Pyridyl)‐N′‐(4‐methoxyphenyl)‐thiourea for Nano Level Monitoring of La(III) Ions

N‐(2‐Pyridyl)‐N′‐(4‐methoxyphenyl)‐thiourea (PMPT) was found to be a suitable neutral ion carrier for the construction of a highly selective and sensitive La(III) membrane sensor. Poly(vinyl chloride) (PVC) based membranes of PMPT with potassium tetrakis (p‐chlorophenyl) borate (KTpClPB) as an anionic excluder and oleic acid (OA), dibutyl phthalate (DBP), benzyl acetate (BA) and o‐nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators were constructed and investigated as La(III) membrane sensors. A membrane composed of PMPT‐PVC‐KTpClPB‐BA with the ratio 8.0 : 35.0 : 3.0 : 54.0 works well over a very wide concentration range (4.0×10^?8 to 1.0×10^?1 M) with a Nernstian slope of 19.6±0.2 mV per decade of activity between pH values of 4.0 and 9.0. The detection limit of the sensor was calculated to be 2.0×10^?8 M (ca. 3.0 ppb). The sensor displays very good discrimination toward La(III) ions with regard to most common metal ions and lanthanide ions. The proposed sensor shows a short response time for whole concentration range (ca. 12 s). For evaluation of the analytical applicability of the La(III) sensor, it was successfully used as an indicator electrode for the titration of La(III) ions with EDTA. It was also applied to the determination of fluoride content of two mouth wash preparation samples and monitoring of La(III) ions in some binary and ternary mixtures.     

Graphite Electrode Coated with a 7,16‐Dibenzyl‐1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐Multiwalled Carbon Nanotube Composite as Sensor For Detection of Samarium

A composite multiwalled carbon nanotube polyvinyl chloride electrode based on 7,16‐dibenzyl‐1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane (DBDA18C6) as Sm³⁺ ionophore is reported. This potentiometric sensor showed a wide linear working range, 1×10^?2–1×10^?8 M, Nernstian slope, 20.2±0.48 mV per decade and a limit of detection, 6.3±0.36×10^?9 M. It works in the pH range 2.5–8.5 and shows a good selectivity over a number of metal ions. It has been found suitable for the analysis of ores and industrial effluents. The electrode surface is characterized by FRA and AFM.     

Determination of copper ion by square wave anodic stripping voltammetry at antimony trioxide-modified carbon nanotube paste electrode

In this work, an antimony trioxide-modified multi-walled carbon nanotube paste electrode (Sb₂O₃/CNTPE) was employed for determination of Cu²⁺ ions by using square wave anodic stripping voltammetry (SWASV) in the presence of 8-hydroxy-7-iodo-5-quinoline sulfonic acid (HIQSA) as a chelating agent. The field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS) methods were applied to estimate the morphology and properties of the modified electrode. Measurements related to SWASV were taken in 0.6 M HCl at ?1.0 V versus Ag|AgCl|KCl (3 M) for 90 s (deposition step). After equilibrium time of 15 s, an ASV appeared at 0.0 V versus Ag|AgCl|KCl (3 M) (stripping step). The sensor depicted a fairly linear response for Cu²⁺ in the concentration range of 2–100 ppb with appropriate detection limit about 0.39 ppb and limit of quantification about 1.3 ppb. The stability of the modified electrode during 7 weeks and its behavior in the presence of some metal ions was evaluated. The practical applicability of the Sb₂O₃/CNTPE was established on the voltammetric determination of Cu²⁺ in tap water as a sample.     

CC Bonding of Graphene Oxide on 4‐Aminophenyl Modified Gold Electrodes towards Simultaneous Detection of Heavy Metal Ions

This paper studied the electrochemical sensors based on C? C bonding of graphene oxide (GO) on π‐conjugated aromatic group modified gold electrodes for simultaneous detection of heavy metal ions. For comparison, another sensing interface Au‐Ph‐NH‐CO‐GO, in which GO was modified to Au‐Ph‐NH₂ interfaces by amide bonding. On the basis of the principle of heavy metal ions complexation with oxygenated species on GO, the fabricated sensing interfaces were used for the simultaneous determination of Pb²⁺, Cu²⁺ and Hg²⁺. The performance of two sensing interfaces for simultaneous detection of three metal ions was compared. Au‐Ph‐GO sensing interface demonstrated higher sensitivity and better repeatability than Au‐Ph‐NH‐CO‐GO sensing interface.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.     

Selective Hg2+ sensor performance based various carbon‐nanofillers into CuO‐PMMA nanocomposites

Ternary nanocomposites (NCs) containing copper oxide (CuO)/poly(methyl methacrylate)/various carbon‐based nanofillers have been successfully prepared as thin films by an ex situ method as a selective Hg⁺² sensor. The structural, morphological, and electrochemical properties of the NCs were identified by all common characterization tools. The FT‐IR curves of these NCs proved the efficiency of CuO mixed with single‐walled CNTs (CuO/SWCNTs), multi‐walled CNTs (CuO/MWCNTs), or graphene (CuO/G) nanoparticles in the PMMA polymer matrix. The mixed nanofillers significantly improved the properties of the PMMA film. The thermal characteristics of the pure PMMA polymer matrix were highly developed by adding nanofillers in the form of NCs. The maximum composite degradation temperature (CDT_max) values were comparable for all the NCs and were in the range of 345 to 406°C. For fabrication, the CuO‐PMMA‐SWCNT, CuO‐PMMA‐MWCNT, and CuO‐PMMA‐GNCs were coated onto a glassy carbon electrode (GCE) to form a tiny layer with orderly thickness using a conductive 5% Nafion chemical binder. During the electrochemical investigation, it was found that CuO‐PMMA‐SWCNT had the maximum response toward Hg²⁺ ions compared to the other nanofillers in a buffer medium (phosphate type). To calibrate the Hg²⁺ ionic sensor, the data were plotted against Hg²⁺ ion concentration and the proposed sensor showed linearity over a wide range of concentrations (0.1‐0.01 mM), which is called the linear dynamic range (LDR). The analytical parameters, such as sensitivity (1.70 × 102 μAμM^‐1 cm^?2), detection limit (55.76 ± 2.79 pM), and limit of quantification (185.87 pM) were calculated from the calibration curve. Moreover, it showed good reproducibility, fast response time, good linearity, large LDR, and good stability. The CuO‐PMMA‐SWCNT NC‐modified GCE offers a new route to fabricate novel heavy metal ionic sensors, which might be used in green environment and health development applications.     

Voltammetric Determination of Quercetin in Urine at Carbon Paste Electrode

Abstract

The electrochemical behavior of the quercetin (Q) at a carbon paste electrode (CPE) containing 15% paraffin oil is investigated. Square wave anodic stripping voltammetric (SWASV) was used to determine quercetin in the presence of 0.04 M phosphate buffer (pH ～4) containing 0.1 M KCl with 15 s accumulation time at 25±1°C. Under the optimal experimental conditions, the adsorbed form is oxidized irreversibly. The linear concentration ranged from 67.66 to 338.3 ppb quercetin. The detection limit of 6.77 ppb Q (r=0.9997), with 15 s accumulation time and the relative standard deviation of 0.45 (n=5) was calculated. The interferences of some metal ions and some amino acids were studied. The method was applied to the analysis of spiked urine, with recovery of 99.9±0.5, and the relative standard deviation of 3.2%. Results were compared with the reported methods.     

AgNP/Bi/Nafion‐modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square‐wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil‐printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray‐deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop‐casting. Using AgNP‐modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L⁻¹, 0.5–400.0 μg L⁻¹, and 0.1–500.0 μg L⁻¹ for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.     

A High Sensitivity Electrochemical Sensor Based on Fe3+‐Ion Molecularly Imprinted Film for the Detection of T‐2 Toxin

The excellent detection sensitivity in various matrices of T‐2 toxin (T‐2), which has cytotoxic and immunosuppressive effects in DNA and RNA synthesis, is a highly desirable characteristic. A sensitive molecularly imprinted electrochemical sensor was constructed for the selective detection of T‐2. In this study, iron ions (Fe³⁺) were introduced to increase the chelation of the metal ions and templates for preparing molecularly imprinted polymers (MIPs). With the increased chelation of the metal ions and templates, the selectivity and sensitivity of the MIPs were effectively improved. The imprinted sensor was successfully employed to detect T‐2 in cereals and human serum samples.     

Electrochemical Detection of As (III) on a Manganese Oxide‐Ceria (Mn2O3/CeO2) Nanocube Modified Au Electrode

Ceria cubes decorated with manganese oxide nanoparticles (Mn₂O₃/CeO₂ nanocubes) were synthesized and used to modify a Au electrode for analysis of As(III) in aqueous solution. This modified electrode displayed improved sensitivity than either oxide on their own, indicating a synergistic effect due to the effect of Mn₂O₃ on the properties of CeO₂. The improved sensitivity could be ascribed to the enhanced As (III) adsorption ability of Mn₂O₃/CeO₂ nanocube during electrochemical pre‐concentration, combined with the well known As(III) sensing qualities of the gold substrate. The Mn₂O₃/CeO₂ nanocube modified gold electrode behaved as a promising sensor with stable, repeatable square wave anodic stripping voltammetry (SWASV) peaks, separated from common interfering ions in natural water including Cu (II) under practical conditions. Repeatability and stability studies revealed the As (III) sensor to be robust and reliable, with a sensitivity of 0.0414 μA/ppb and a limit of detection (LoD) of 3.35 ppb under optimized conditions, indicating a possible general use of this class of heteronanostructures in electroanalytical chemistry for studies that rely upon adsorption of deposition of the analyte prior to stripping analysis.     

Organic‐inorganic‐hybrid‐enhancement Electrochemical Sensor for Determination of Cu (II) in River Water

A dual strategy that the L‐cysteine self‐assembling on three‐dimensional network of organic‐hybrid‐materials realized by successive interaction of Au−S bond is employed to construct as the amplified electrochemical sensor for determination Cu (II). Specifically, the sensor combined a rigid three‐dimension inorganic net which provides a higher interfacial area as well as faster adsorption of ions. Accordingly, surface and interfacial‐dominated electro‐catalysis reactivity is used as an ideal test‐bed to verify the reliability of electrochemical sensor that reveal enhancement sensitiveness and selectivity, low detection limit, and stability over a long period of time. Time‐dependent density functional theory (TD‐DFT) were used to calculating the all complexes energies at the B3LYP/LANL2DZ level associated with the polarized continuum model (PCM). The result of calculation indicates that the binding strength of Cu (II), Cd (II), As (III), Hg (II) with L‐cysteine are decrease successively, and this is in well agreement with experimental results. This work not only achieves an unprecedented understanding to L‐cysteine/Au/TiO₂/GCE sensor but also provides a new perspective for application in detection of Cu (II) in real river waters.