Cu chemosensing behaviour of self-organized micro-array structures of a donor-acceptor bichromophoric compound anchored onto Ag nanoisland films

This work reports on the Cu²⁺ chemosensing behaviour of self-organized micro-array structures of a novel donor-acceptor bichromophoric compound anchored onto Ag nanoisland films. The system exhibits quenching of the fluorescence in the presence of Cu²⁺ ions, with detection range extending from 2 × 10⁻⁸ M up to 3 × 10⁻⁶ M and limit of detection (LOD) of 8 × 10⁻⁹ M. The quenching of fluorescence is accompanied by a quenching of SERS signal from the metal-organic structure, which is consistent with an electron transfer between the copper cation and the organic moiety. The self-organization property of the sensing complexes into micrometric arrays offers great potential for miniaturization and future development of Cu²⁺ detection systems based on real-time observation of fluorescence or SERS quenching by fluorescence microscopy or microRaman spectroscopy.     

High sensitive optode for selective determination of Ni based on the covalently immobilized thionine in agarose membrane

A novel Ni²⁺ optode was prepared by covalent immobilization of thionine, 3,7-diamine-5-phenothiazoniom thionineacetate, in a transparent agarose membrane. Influences of various experimental parameters on Ni²⁺ sensing, including the reaction time, the solution pH and the concentration of reagents were investigated. Under the optimized conditions, a linear response was obtained for Ni²⁺ concentrations ranging from 1.00 × 10⁻¹⁰ to 1.00 × 10⁻⁷ mol l⁻¹ with an R² value of 0.9985. The detection limit (3σ) of the method for Ni²⁺ was 9.30 × 10⁻¹¹ mol l⁻¹. The influence of several potentially interfering ions such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Pb²⁺, Cu²⁺, Mn²⁺, Co³⁺, Cr³⁺, Al³⁺ and Fe³⁺ on the determination of Ni²⁺ was studied and no significant interference was observed. The membrane showed a good durability and short response time with no evidence of reagent leaching. The membrane was successfully applied for the determination of Ni²⁺ in environmental water samples.     

An All-solid-state Cd-selective electrode with a low detection limit

A new all-solid-state Cd²⁺-selective electrode with a low detection limit was prepared by using conjugated thiophene oligomer α-sexithiophene (α-6T) as solid contact deposited between an ionophore-doped poly(vinyl chloride) membrane and a gold disc substrate. The electrode exhibited a Nernstian response for Cd²⁺ ions over a wide concentration range of 10⁻³-10⁻⁷ M with a detection limit as low as 1.3 × 10⁻⁸ M. Results showed that the fabricated potentiometric sensor was suitable for use within the pH range of 2.0-9.0 and exhibited good reproducibility for long-term measurements.     

A dual functional near infrared fluorescent probe based on the bodipy fluorophores for selective detection of copper and aluminum ions

A new near infrared (NIR) fluorescent 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye with dual functionality was synthesized and characterized. The compound 1 responds to copper ion in NIR region with high selectivity through a photo-induced electron transfer process established between the substituted benzene group in the meso position and the BODIPY core when Cu²⁺ binds with the four oxygen atoms in the structure, and results in the quenching of the fluorescence. The response range to copper ions was from 10 to 50 μM, and other metal ions including Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Pb²⁺, Fe³⁺, Ag⁺, Hg²⁺, Co²⁺, Zn²⁺, Mn²⁺, Cd²⁺, Ni²⁺ and Al³⁺ had no interference. When excited at 520 nm, a new emission peak at 568 nm of compound 1 was used to detect Al³⁺ selectively from 30 μM to 110 μM without any interference from other metal ions including copper ions.     

A highly selective triphenylamine-based indolylmethane derivatives as colorimetric and turn-off fluorimetric sensor toward Cu detection by deprotonation of secondary amines

A new triphenylamine-based fluorogenic probe bearing an indolylmethane unit (R1) was developed as a fluorescent chemosensor with high selectivity toward Cu²⁺ over other cations tested. The new probe R1 only sensed Cu²⁺ among heavy and transition metal (HTM) ions in CH₃CN/H₂O (70/30, v/v) solution. The capture of Cu²⁺ by the receptor resulted in deprotonation of the secondary amine conjugated to the triphenylamine, so that the electron-donation ability of the “N” atom would be greatly enhanced; thus sensor showed a 250 nm change in the new absorption band (from 291 nm to 541 nm) and a large colorimetric response, it also exhibited the large decrease in fluorescence intensity at 378 nm and affinity to Cu²⁺ over other cations such as Hg²⁺, Fe³⁺, Pb²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Mn²⁺ make this compound a useful chemosensor for Cu²⁺ detection in CH₃CN/H₂O (70/30, v/v) mixture. The probe R1 (c = 1.0 × 10⁻⁶ M) displayed significant fluorescence change and colorimetric change upon addition of Cu²⁺ among the metal ions examined.     

Development of a new fluorescent sensor based on a triazolo-thiadiazin derivative immobilized in polyvinyl chloride membrane for sensitive detection of lead(II) ions

A new sensor membrane based on a novel triazolo-thiadiazin derivative immobilized in polyvinyl chloride has been developed for the determination of Pb(II) ions that displays excellent performance. The parameters involved in the preparation of the optode and determination of Pb(II) were optimized. Under the optimal conditions, the proposed sensor displays a calibration response for Pb(II) over a wide concentration range of 5.0 × 10⁻⁸ to 3.8 × 10⁻⁴ M with the detection limit of 2.2 × 10⁻⁸ M. In addition to high reproducibility and reversibility of the fluorescence signal, the sensor also exhibits good selectivity over common metal ions. The optode membrane developed is easily prepared, stable, rapid, and simple for the determination of Pb(II). The accuracy of the proposed sensor was confirmed by analyzing standard reference materials of natural water and surface water. The sensor was successfully used for the determination of Pb(II) ions in water samples with satisfactory results.     

Ultra trace mercury(II) detection by a highly selective new optical sensor

This paper presents the development and construction of a sensitive new optical sensor that is highly selective to Hg²⁺ ion in aqueous solution. The sensing element, the newly synthesized (1Z,2Z)-N′¹,N′²-dihydroxy-N¹,N²-dipyridin-2-ylethanediimidamide, incorporated into a plasticized poly(vinyl chloride) membrane, is capable of determining mercury(II) with a high selectivity over a wide dynamic range from 5.78 × 10⁻⁹ to 1.05 × 10⁻³ M at pH 4.0 with a lower detection limit of 1.71 × 10⁻⁹ M. The optode membrane's response to Hg²⁺ is fully reversible and reveals a very good selectivity towards Hg²⁺ ion over a wide variety of other metal ions in solution. Performance characteristics of the sensor evaluated as good reversibility, wide dynamic range, long life span, long-term response stability, and high reproducibility. The proposed optical sensor gives good results for applications in direct determination of mercury(II) in environmental real samples that are satisfactorily comparable with corresponding data from cold-vapor atomic absorption spectrometry.     

Optical fiber chemical sensing of Hg(II) ions in aqueous samples using a microfluidic device containing a selective tripodal chromoionophore-PVC film

A novel methodology for the determination of Hg(II) ions was developed based on optical fiber chemical sensing in a microfluidic device containing a selective tripodal chromoionophore (i.e. tris[2-(4-phenyldiazenyl)phenylamino)ethoxy]cyclotriveratrylene/TPPECTV)-PVC film. Absorbance detection was performed by incorporating a single optical fiber on the top and the bottom of the detection zone of the microfluidic device. In this micro-sensing system, the intensity of the absorption maximum at 495 nm of the TPPECTV-Hg(II) complex linearly increases as a function of the Hg(II) ion concentration in the range 1.0 × 10⁻⁶ to 2.5 × 10⁻⁴ M, with a detection limit of 0.5 μM. Interference from other heavy metal ions was not observed at significant levels. The absorbance results of the detection of Hg(II) ions in environmental water samples (river water) are in good agreement with those obtained by a macro-scale system (cold vapor atomic absorption spectrometry/CVAAS).     

Development of an optical sensor for determination of zinc by application of PC-ANN

A very sensitive and reversible optical chemical sensor based on dithizone as chromoionophore immobilized within a plasticized carboxylated PVC film for Zn²⁺ determination is described. At optimum conditions (i.e. pH 5.0), the proposed sensor displays a linear response to Zn²⁺ over 5.0 × 10⁻⁸-5.0 × 10⁻⁶ mol L⁻¹ range. This range was improved to 2.5 × 10⁻⁸-5.8 × 10⁻⁵ mol L⁻¹ range by applying principle component-feed forward artificial neural network with back-propagation training algorithm (PC-ANNB). Detection limit of 8.0 × 10⁻⁹ mol L⁻¹ was obtained. The sensor is fully reversible within the dynamic range and the response time (t_95%) is approximately 4 min under batch conditions. In addition to its high stability and reproducibility, the sensor shows good selectivity towards Zn²⁺ ion with respect to common metal cations. The sensor was successfully applied for determination of Zn²⁺ ion in hair sample.     

Tuning with pH: The selectivity of a new rhodamine B derivative chemosensor for Fe and Cu

A simple structure, a rhodamine fluorescent derivative, was synthesized easily by a one-step condensation reaction of rhodamine B ethylenediamine and acetylacetone. Its structure was characterized by X-ray crystallography, NMR, MS and IR spectroscopy. As a bi-functional and highly selective “OFF–ON” chemosensor for Fe³⁺ or Cu²⁺, the derivative displayed a selective fluorescence enhancement effect only with Fe³⁺ and an absorption enhancement effect only with Cu²⁺ by modulating the pH value. In an aqueous ethanol medium, Fe³⁺ formed a 1:1 complex with the derivative at pH 6, while Cu²⁺ formed a 1:1 complex at pH 8.5. The limits of detection of the ions were low: 3.9 × 10⁻⁹ and 4.8 × 10⁻⁸ mol L⁻¹. The derivative also functioned as a fluorescence sensor for CT-DNA, in which the Fe³⁺ ion that was used as a bridge between the derivative and DNA forming a ternary complex.     

A fluorescent chemosensor for cysteine based on naphthalimide derivative in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize cysteine (Cys) in aqueous solution. The fluorescence enhancement of 1 was attributed to the cyclization reaction of 1 with Cys by 1:1 binding stoichiometry, which has been utilized as the basis of fabrication of the Cys-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Cys indicated that the methods can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Cys-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Cys with a linear range covering from 3.9 × 10⁻⁸ to 1.4 × 10⁻⁵ M and a detection limit of 7.8 × 10⁻⁹ M. And the chemosensor shows excellent selectivity for Cys over other amino acids. Moreover, the response of the chemosensor toward Cys is fast (response time less than 3 min). In addition, the chemosensor has been used for determination of Cys in serum samples with satisfactory results.     

Synthesis of triazolo-thiadiazole fluorescent organic nanoparticles as primary sensor toward Ag and the complex of Ag as secondary sensor toward cysteine

Fluorescent organic nanoparticles (FONs) have received considerable attention in the past few years, since the material holds great flexibility in materials synthesis and optical properties. In this study, we report a novel Ag⁺-selective turn-on fluorescent chemosensor based on the triazolo-thiadiazole (TTD) FONs, which show a significant fluorescence enhancement to silver ions among fourteen metal ions due to the formation of Ag–FONs cation complex, and also exhibit a lowest detectable concentration of 2.87 × 10⁻⁹ M. Upon the addition of Cysteine (Cys), a thiol-containing amino acid, the fluorescence intensity of the colloidal solution decreases significantly with a limit detection concentration of 2.58 × 10⁻⁷ M, indicating that Cys can form the Ag–Cys complex. Thus FONs are a potential primary sensor toward Ag⁺ and a secondary sensor toward Cys. The method is a basis for further two-component recognition study of TTD FONs. The possible mechanism is also discussed.     

Lead (II) carbon paste electrode based on derivatized multi-walled carbon nanotubes: Application to lead content determination in environmental samples

For the first time a novel derivatized multi-walled carbon nanotubes-based Pb²⁺ carbon paste electrode is reported. The electrode with optimum composition, exhibits an excellent Nernstian response to Pb²⁺ ion ranging from 5.9 × 10⁻¹⁰ to 1.0 × 10⁻² M with a detection limit of 3.2 × 10⁻¹⁰ M and a slope of 29.5 ± 0.3 mV dec⁻¹ over a wide pH range (2.5-6.5) with a fast response time (25 s) at 25 °C. Moreover, it also shows a high selectivity and a long life time (more than 3 months). Importantly, the response mechanism of the proposed electrode was investigated using AC impedance technique. Finally, the electrode was successfully applied for the determination of Pb²⁺ ion concentration in environmental samples, e.g. soils, waste waters, lead accumulator waste and black tea, and for potentiometric titration of sulfate anion.     

Electrochemical behaviors and determination of isoniazid at ordered mesoporous carbon modified electrode

In this work, an electrochemical sensor based on ordered mesoporous carbon (OMC) for the amperometric detection of isoniazid was developed. OMC was dispersed in a solution of Nafion, and the suspension was modified onto the surface of glassy carbon (GC) electrode. Cyclic voltammetry and amperometry were used to investigate the electrochemical behaviors of isoniazid on Nafion-OMC modified electrode (Nafion-OMC/GC). The results indicate that OMC can facilitate the electrochemical oxidation of isoniazid with a great decrease of overpotential in pH 7.0 phosphate buffer solution. The proposed biosensor provides excellent performance towards the determination of isoniazid with a high sensitivity of 0.031 μA/μM, a low detection limit of 8.4 × 10⁻⁸ M and wide linear range from 1.0 × 10⁻⁷ M to 3.7 × 10⁻⁴ M at +0.20 V vs. Ag/AgCl. The method was successfully applied to the determination of isoniazid tablets with satisfying results. All the results suggest that Nafion-OMC/GC electrode is a potential candidate for a stable and efficient electrochemical sensor to detect isoniazid.     

Two-dimensional molecular imprinting approach for the electrochemical detection of trinitrotoluene

In this work, we demonstrated a sensitive and selective electrochemical sensing protocol for the detection of TNT prepared from alkanethiols self-assembled on AuNPs modified glassy carbon (GC) electrode with preadsorbed templates of TNT. It demonstrated that the 2D molecular imprinting monolayers (MIMs) can provide a better site accessibility and lower mass-transfer resistance, while the AuNPs can enhance electrode conductivity, facilitate the electron transfer and increase the amount of TNT-imprinted sites. The prepared sensor showed not only high selectivity toward TNT in comparison to other similar nitroaromatic compounds (NACs), but also a wide linear range over TNT concentration from 4.0 × 10⁻⁸ to 3.2 × 10⁻⁶ M with a detection limit of 1.3 × 10⁻⁸ M (S/N = 3). Moreover, the imprinted sensor has been applied to the determination of TNT in spiked environmental water samples and shows promise for fast and sensitive measurement of trace levels of TNT in real samples.     

Hybridization biosensor based on the covalent immobilization of probe DNA on chitosan-mutiwalled carbon nanotubes nanocomposite by using glutaraldehyde as an arm linker

A label-free DNA biosensor for hybridization detection of short DNA species related to the transgenic plants gene fragment of cauliflower mosaic virus (CaMV) 35S promoter was developed in this paper. The nanocomposite containing chitosan (CS) and mutiwalled carbon nanotubes (MWNTs) was first coated on a glassy carbon electrode. Then a highly reactive dialdehyde reagent of glutaraldehyde (GTD) was applied as an arm linker to covalently graft the 5′-amino modified probe DNA to the CS-MWNTs surface via the facile aldehyde-ammonia condensation reaction. The hybridization capacity of the developed biosensor was monitored with electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3−/4− as an indicating probe, and the experimental results showed that the biosensor had fast hybridization rate and low background interference. A wide dynamic detection range (1.0 × 10⁻¹³-5 × 10⁻¹⁰ M) and a low detection limit (8.5 × 10⁻¹⁴ M) were achieved for the complementary sequence. In addition, the hybridization specificity experiments showed that the sensing system can accurately discriminate complementary sequence from mismatch and noncomplementary sequences.     

High sensitive simultaneous determination of hydroquinone and catechol based on graphene/BMIMPF6 nanocomposite modified electrode

A novel nanocomposite, comprising of graphene sheet (GS) and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), was developed on the glassy carbon electrode (GCE) for the simultaneous determination of hydroquinone and catechol in 0.10 M acetate buffer solution (pH 5.0). At the GS/BMIMPF₆/GCE, both hydroquinone and catechol can cause a pair of quasi-reversible and well-defined redox peaks. In comparison with bare GCE and GS modified electrode, GS/BMIMPF₆/GCE showed larger peak currents, which was related to the higher specific surface area of graphene and high ionic conductivity of BMIMPF₆. Under the optimized condition, the cathodic peak current were linear over ranges from 5.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M for hydroquinone and from 5.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M for catechol, with the detection limits of 1.0 × 10⁻⁸ M and 2.0 × 10⁻⁸ M, respectively. The proposed method was successfully applied to the simultaneous determination of hydroquinone and catechol in artificial sample, and the results are satisfactory.     

Novel pyrazoline-based selective fluorescent sensor for Zn in aqueous media

This work describes the preparation of a novel pyrazoline compound and the properties of its UV-vis absorption and fluorescence emission. Moreover, this compound can be used to determine Zn²⁺ ion with high selectivity and a low detection limit in the HEPES (20 mM HEPES, pH = 7.2, 50% (v/v) CH₃CN) buffer solution. This sensor forms a 1:1 complex with Zn²⁺ and shows a fluorescent enhancement by chelation enhanced fluorescence effect with good tolerance of other metal ions. In addition, this sensor is very sensitive with fluorometric detection limit of 0.12 μM.     

Electrocatalytic determination of hydrazine by a glassy carbon electrode modified with PEDOP/MWCNTs-Pd nanoparticles

The electrocatalysis of hydrazine oxidation by poly-ethylenedioxy pyrrole (PEDOP)-coated MWCNTs-palladium nanoparticles [PEDOP/MWCNTs-Pd] was investigated as an electrochemical sensor on the surface of glassy carbon electrode (GCE) in aqueous medium. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7.4) was performed using cyclic voltammetry (CV) and chronoamperometry (CA) methods. Using the proposed electrode, the catalytic oxidation peak current of hydrazine was high and the overpotential of its oxidation decreased. Based on the obtained results, a mechanism for electrooxidation of hydrazine at [PEDOP/MWCNTs-Pd/GCE] demonstrated an irreversible diffusion-controlled electrode process and a four-electron transfer involved in the overall reaction. The experimental results showed that the mediated oxidation peak currents of the hydrazine were linearly dependent on the concentration of hydrazine in the range of 1.0 × 10⁻⁷ to 5.0 × 10⁻³ M. The detection limit (S/N = 3) was found to be 4 × 10⁻⁸ M with a fast response time of 10 s.     

Electrochemical performances of B doped and undoped diamond-like carbon (DLC) films deposited by femtosecond pulsed laser ablation for heavy metal detection using square wave anodic stripping voltammetric (SWASV) technique

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets.In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd²⁺, Pb²⁺, Ni²⁺ and Hg²⁺, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at −1.3 V deposition potential, and 90 s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si₃N₄ electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 μg/L or 2 μg/L and a dynamic range from 1 or 2 to 25 μg/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 μA/ppb or μA μg⁻¹ L for Cd²⁺, Pb²⁺, Ni²⁺ and Hg²⁺, respectively.