A sensitive signal-on electrochemiluminescence sensor based on a nanocomposite of polypyrrole-Gd2O3 for the determination of L-cysteine in biological fluids.

A sensitive solid-state electrochemiluminescence (ECL) electrode for L-cysteine was developed based on depositing layers of a hybrid nanocomposite of polypyrrole-dodecyl benzene sulfate-sodium perchlorate-sodium carbonate-gadolinium (PPy-Gd2O3) on a platinum substrate. The presence of the Gd2O3 nanoparticle layer improved the ECL signal, and under optimum conditions, a linear relationship was observed between the signal and the logarithm of L-cysteine concentration from 1.0 × 10-13 to 1.0 × 10-6 M (R2 = 0.9937). At the emission wavelength around 425 nm , at which the analytical signal was measured, the electrode showed an RSD of less than 4% and a low detection limit of 4.2 × 10-14 M. The results proved to be reproducible and stable, and the electrode was applicable in the determination of L-cysteine in biological fluids with recoveries from 94.0-107%. Graphical abstract The results of this research indicated that the weak ECL of luminol is greatly improved by traces of L-cysteine on a solid-state platinum electrode coated with polypyrrole and gadolinium oxide nanoparticles (NPs) and have hence been effectively used in the analysis of L-cysteine in plasma and saliva.

Comparative Study of Various Types of Metal-Free N and S Co-Doped Porous Graphene for High Performance Oxygen Reduction Reaction in Alkaline Solution.

Heteroatom doping into carbon structures is an effective approach to enhance the electrochemical performance of carbon materials. In the work presented here, the electrocatalysts including: nitrogen and co-doped nitrogen and sulfur on porous graphene (PG) were synthesized by different precursors. The physico-chemical properties of the prepared samples were determined using X-ray Diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), N2 sorption-desorption, Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The prepared samples were further applied for oxygen reduction reaction (ORR) and the effects of pyrolysis temperature, precursor type and dose, on the prepared samples structure and their electrochemical performances were investigated. The results revealed that synergistic effect of nitrogen and sulfur co-doped on the graphene structure leads to improvement in catalytic activity and current. Furthermore, S and N co-doped graphene prepared using sulfur trioxide pyridine complex exhibited excellent methanol tolerance and long-term stability.

3D-QSAR and docking studies on adenosine A2A receptor antagonists by the CoMFA method.

Parkinson's disease affects millions of people around the world. Recently, adenosine A2A receptor antagonists have been identified as a drug target for the treatment of Parkinson's disease. Consequently, there is an immediate need to develop new classes of A2A receptor antagonists. In the present analysis, three-dimensional quantitative structure-activity relationship (3D-QSAR) studies were performed on a series of pyrimidines, using comparative molecular field analysis (CoMFA). The best prediction was obtained with a CoMFA standard model (q(2) = 0.475, r(2) = 0.977) and a CoMFA region focusing model (q(2) = 0.637, r(2) = 0.976) combined with steric and electrostatic fields. The structural insights derived from the contour maps helped to better interpret the structure-activity relationships. Also, to understand the structure-activity correlation of A2A receptor antagonists, we have carried out molecular docking analysis. Based on the results obtained from the present 3D-QSAR and docking studies, we have identified some key features for increasing the activity of compounds, which have been used to design new A2A receptor antagonists. The newly designed molecules showed high activity with the obtained models.

Selective recognition of Ni2+ ion based on fluorescence enhancement chemosensor.

A new enhancing fluorescent chemosensor was introduced for selective and sensitive determination of nickel ions based on 2-(1-H-benzo[d]imidazol-2yl)-N-phenyl hydrazine carbothioamide (L). L has an intrinsic fluorescent emission which enhances in presence of nickel ions in CH3CN/H2O (70:30, v/v) solution. The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and Ni2+ ion which has been used for selective detection of Ni2+ ion. At the optimum conditions, the fluorescence intensity of L at 352 nm enhances linearly by the concentration of nickel ion from 1.6×10(-5) to 1.6×10(-7) M and detection limit of 7.9×10(-8) M. The new fluorescent probe exhibited high selectivity to Ni2+ ion over the other common mono, di-and trivalent cations.

Turn-on fluorescent chemosensor for determination of lutetium ion.

A turn-on fluorescent chemosensor is introduced for the detection of Lu(3+) ion using N-[3-methyl]-2-[pyridine-2-amido] phenyl] pyridine-2-carboxamide (L) molecule. Fluorescent emission intensity of L enhances after binding to Lu(3+) ions in ethanol-water solution (1:9, v/v). The observed enhancement is the result of a strong covalent binding between Lu(3+) ion and L (the binding constant value is 2.0×10(6) mol(-1) L). The proposed optical chemosensor can be applied for the analysis of Lu(3+) ion in a linear range of 3.3×10(-7) to 1.0×10(-5) mol L(-1). The limit of detection was obtained 8.6×10(-7) mol L(-1). The probe exhibits high selectivity toward Lu(3+) ion in comparison with common metal ions. The proposed fluorescent chemosensor was successfully used in the determination of Lu(3+) ion in some water samples.

DNA methylation detection by a novel fluorimetric nanobiosensor for early cancer diagnosis.

A very sensitive and convenient fluorescence nanobiosensor for rapid detection of DNA methylation based on Fe3O4/Au core/shell nanoparticles has been developed. Specific site of CpG islands of adenomatous polyposis coli (APC), a well studied tumor suppressor gene, was used as the detection target DNA sequence. The characteristics of nanoparticles were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), UV-visible spectroscopy and X-ray diffraction (XRD) spectroscopy. Fe@Au nanoparticles functionalized by bounding of single stranded DNA (ssDNA) probe through sulfhydryl group at the 5' phosphate end. Then unmethylated and methylated complementary target ssDNA were hybridized with the immobilized ssDNA probe. Dipyridamole, a pharmaceutical agent used for the first time as a fluorescence probe which significantly interacted with hybridized unmethylated and methylated DNA. Upon the addition of the target unmethylated and methylated ssDNA, the fluorescence intensity increased in linear range by concentration of unmethylated ssDNA from 1.6 × 10(-15) to 6.6 × 10(-13)M with detection limit of 1.2 × 10(-16)M and on the other hand, fluorescence intensity declined linearly with concentration of 3.2 × 10(-15)-8.0 × 10(-13)M methylated DNA and detection limit was 3.1 × 10(-16)M. We have also shown that nanobiosensor could distinguish ratio of methylation in series of partially methylated DNA targets with identical sequences. A density functional theory (DFT) calculation was also performed to investigate the interaction between Dipyridamole with unmethylated and methylated cytosine. Finally real sample analysis suggested that nanobiosensor could have practical application for methylation detection in human plasma sample.

Selective recognition of Pr3+ based on fluorescence enhancement sensor.

(E)-2-(1-(4-hydroxy-2-oxo-2H-chromen-3-yl)ethylidene)hydrazinecarbothioamide (L) has been used to detect trace amounts of praseodymium ion in acetonitrile-water solution (MeCN/H2O) by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to Pr(3+) ions in MeCN/H2O (9/1:v/v) solution. The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and Pr(3+), which has been utilized as the basis for selective detection of Pr(3+). The sensor can be applied to the quantification of praseodymium ion with a linear range of 1.6×10(-7) to 1.0×10(-5) M. The limit of detection was 8.3×10(-8) M. The sensor exhibits high selectivity toward praseodymium ions in comparison with common metal ions. The proposed fluorescent sensor was successfully used for determination of Pr(3+) in water samples.

A novel fluoride-selective electrode based on metalloporphyrin grafted-grapheneoxide.

In this work, the unique properties of graphene oxide were combined with the anion selectivity of metalloporphyrin to fabricate a novel fluoride-selective sensor. The electrode made of 27% PVC, 54% NPOE, 4% NaTPB and 15% NbTPP-GO was found to show the most favorable behavior. The sensor shows a Nernstian response (58.3 mV decade(-1)) in the concentration window of 5.0×10(-1)-5.0×10(-7) mol L(-1)with detection limit of 8.0×10(-87) mol L(-1). The response of the sensor was found to be stable in the pH range of 3.0-7.0 and the metalloporphyrin grafted-GO based F(-) sensors displayed very good selectivity with respect to a number of anions. The proposed sensor displays a long life time (more than 12 weeks) with a short response time of about 20 s.

A highly selective fluorescent probe for pyrophosphate detection in aqueous solutions.

A novel and simple fluorescence enhancement method is introduced for selective pyrophosphate (PPi) sensing in an aqueous solution. The method is based on a 1:1 metal complex formation between tris(8-hydroxyquinoline-5-sulphonate) thulium(III) [Tm(QS)(3)] and PPi ion. The linear response covers a concentration range of 1.6 × 10(-7) -1.0 × 10(-5) mol/L PPi and the detection limit is 2.3 × 10(-8) mol/L. The association constant of Tm(QS)(3) -PPi complex was calculated as 2.6 × 10(5) mol/L. Tm(QS)(3) shows a selective and sensitive fluorescence enhancement toward PPi ion in comparison with I(3)(-), NO(3)(-), CN(-), CO(3)(2-), Br(-), Cl(-), F(-), H(2) PO(4) (-) and SO(4)(2-), which is attributed to higher stability of the inorganic complex between pyrophosphate ion and Tm(QS)(3).

Modified ionic liquid cold-induced aggregation dispersive liquid-liquid microextraction combined with spectrofluorimetry for trace determination of ofloxacin in pharmaceutical and biological samples.

BACKGROUND AND THE PURPOSE OF THE STUDY: Ofloxacin is a quinolone synthetic antibiotic, which acts against resistant mutants of bacteria by inhibiting DNA gyrase. This antibacterial agent is widely used in the treatment of respiratory tract, urinary tract and tissue-based infections, which are caused by Gram-positive and Gram-negative bacteria. In this work, an efficient modified ionic liquid cold-induced aggregation dispersive liquid-liquid microextraction (M-IL-CIA-DLLME) was combined with spectrofluorimetry for trace determination of ofloxacin in real samples. METHODS: In this microextraction method, hydrophobic 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim] [PF(6)]) ionic liquid (IL) as a microextraction solvent was dispersed into a heated sample solution containing sodium hexafluorophosphate (NaPF(6)) (as a common ion) and the analyte of interest. Afterwards, the resultant solution was cooled in an ice-water bath and a cloudy condition was formed due to a considerable decrease of IL solubility. After centrifuging, the enriched phase was introduced to the spectrofluorimeter for the determination of ofloxacin. RESULTS AND MAJOR CONCLUSION: In this technique, the performance of the microextraction method was not influenced by variations in the ionic strength of the sample solution (up to 30% w/v). Furthermore, [Hmim][PF(6)] IL was chosen as a green microextraction phase and an alternative to traditional toxic organic solvents. Different parameters affecting the analytical performance were studied and optimized. At optimum conditions, a relatively broad linear dynamic range of 0.15-125 µg l(-1) and a limit of detection (LOD) of 0.029 µg l(-1) were obtained. The relative standard deviation (R.S.D.) obtained for the determination of five replicates of the 10 ml solution containing 50 µg l(-1) ofloxacin was 2.7%. Finally, the combined methodology was successfully applied to ofloxacin determination in actual pharmaceutical formulations and biological samples.

Electrochemical Analysis of Some Toxic Metals by Ion-Selective Electrodes.

An overview of potentiometric sensors that are capable of detecting toxic heavy metal ions in environmental samples is presented and discussed. Notwithstanding the tremendous work performed so far, it is obvious that still several limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. A survey on important advances in potentiometric sensors with regard to high selectivity, lower detection limit, fast response time, and on-line environmental analysis is presented in this review article. [Supplemental materials are available for this article. Go to the publisher's online edition of Critical Reviews in Analytical Chemistry to view the free supplemental file.].

A new Tb3+-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide.

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 x 10(-7) to 1.0 x 10(-5) M and the detection limit is 1.4 x 10(-7) M. The association constant of the 1:1 complex formation for L-Tb(+3) was calculated to be 6.01 x 10(6) M(-1), and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations.

Optimization of solid-phase extraction using developed modern sorbent for trace determination of ametryn in environmental matrices.

In recent years, there has been a significant increase in molecularly imprinted solid-phase extraction (MISPE) technique for the purification and clean-up of environmental samples. In this study, solid-phase extraction using the imprinted polymer has been optimized with the experimental design approach for a triazine herbicide, named ametryn with regard to the critical factors such as sample pH, sample concentration, sample flow-rate, sample volume, elution solvent, washing solvent and sorbent mass. These factors were evaluated statistically and also validated with spiked drinking water samples and showed a good reproducibility over six consecutive days as well as six within-day experiments. Also, in order to the evaluate efficiency of the optimized MISPE protocols, enrichment capacity, reusability and cross-reactivity of cartridges have been studied. Finally, a selective MISPE was successfully demonstrated for ametryn with a recovery of above 90% for spiked drinking water samples. It was concluded that the central composite design could prove beneficial for aiding the MIP and MISPE development.

Design of a novel optical sensor for determination of trace gadolinium.

In this work, a highly selective and sensitive gadolinium (Gd) optical sensor based on immobilization of bis(thiophenal) pyridine-2,6-diamine (BPD), on a triacetylcellulose membrane has been reported. This optode exhibits a linear range of the Gd(III) ion concentration of 2.5 x 10(-6)M with a detection limit of 0.93 x 10(-8) M. Response time of the newly designed optode was within 1-2 min, depending on the Gd(III) ion concentration. Response of the sensor is independent of solution pH in the range of 2.0-9.0. It manifests advantages of: low detection limit, fast response time, and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, Tm, Ho, and Eu ions). The sensor was successfully regenerated with thiourea solutions and its response was reversible and reproducible (R.S.D. less than 1.4%). This optode was applied to determine Gd(III) in synthetic and water samples, and validated with certified reference materials (CRMs).

Sub-second adsorption for the pico-molar monitoring of diltiazem in pharmaceutical preparations by fast Fourier transformation with the use of continuous cyclic voltammetry at an Au microelectrode in a flowing system.

Diltiazem was determined at the sub-nanomolar level for the first time by a new technique, involving fast Fourier continuous cyclic voltammetry in a flow-injection system. The best performance was achieved with the basic parameters being set at pH value of 2.0, scan rate value of 35 V/s, accumulation potential of 300 mV and accumulation time of 0.8 s. This paper additionally introduces a special computer based numerical method for the calculation of the analyte signal and the noise reduction. Concerning the electrode response calculations were carried out according to the partial and total charge exchanges on the electrode surface after subtraction of background current from that of noise. Furthermore, to obtain a sensitive determination, the currents integration range included all potential scan ranges, even oxidation and reduction of the Au surface electrode, during the measurements. In general, the potential waveform includes the potential steps for cleaning, accumulation and the step of the potential ramp of the analyte. This potential waveform was applied to an Au disk microelectrode in a continuous way. Finally, the method was found to be linear for the concentration range of 1-41450 pg/ml (r = 0.9986), while showing a limit of detection and quantitation of 0.29 and 1 pg/ml, respectively.

Application of multivariate analysis to the screening of molecularly imprinted polymers (MIPs) for ametryn.

Among the solid-phase extraction (SPE) techniques, a novel system for a triazine herbicide named ametryn, has been developed based on a molecular imprinted polymer (MIP) phase. Through this method, the synthesis of the complementary to ametryn MIP was accomplished and the factors influencing its efficiency have been optimized. Through the optimization process, the type and the amounts of functional monomer and solvents, template amount, cross-linker, initiator as well as the polymerization temperature were considered to be evaluated. Based on the obtained results, the optimum conditions for the efficient polymerized sorbent, considering the recovery efficiency were solvent: acetonitrile, 6.41 mL; monomer: methacrylic acid, 5.41 mmol; template: 1.204 mmol; cross-linker: 27.070 mmol; initiator: 2.03 mmol; temperature: 40.86 degrees C. The optimum molar ratio among the template, monomer and cross-linker for ametryn was 1:4.49:22.48. The reversed-phase HPLC-UV was used for the ametryn determination, using an isocratic solvent delivery system (acetonitrile: H(2)O, 60:40), flow-rate of 0.8 mL min(-1) and a UV wavelength of 220 nm. In line with the obtained results, using central composite design (CCD) can increase the precision and accuracy of synthesis and optimization of MIP to ametryn and possibly other similar analogues.

Electrochemical investigation of the effect of some organic phosphates on haemoglobin.

The effects of DPG,IHP,GTP,GDP and GMP on the structure and stability of haemoglobin were electrochemically investigated with an iodide-modified silver electrode in 0.01 M KNO 3 at pH 7.0.Anodic and cathodic peaks of haemoglobin were observed at 250 mV and 12 mV with a formal potential value of 133 mV vs.Ag/AgCl.The effects of different concentrations of DPG,IHP,GTP,GDP and GMP on the anaerobic redox reaction were determined. The results showed that DPG and IHP can lead to a positive shift in the reduction peak of haemoglobin,indicating that the oxidation peak shift of haemoglobin was small as a result of stabilization of the reduced state and destabilization of the R-like state of haemoglobin.GTP elicited a more positive shift in the cathodic and anodic peaks of haemoglobin at a higher concentration,signifying that it has a low-affinity binding site on haemoglobin.The positive shift of the cathodic and anodic peaks revealed a slight variation in the structure and indicated the unfolding of haemoglobin in the presence of high concentrations of GTP.Our study also showed that GDP and GMP did not cause significant shift the cathodic and anodic peaks of haemoglobin even at high concentrations,refuting the existence of specific GDP-and GMP-binding sites on the protein.Moreover,the iodide-modified silver electrode method proved to be easy and useful in investigating the effects of ligands or other effectors on haemoglobin in solution.

Development of fast Fourier transform continuous cyclic voltammetry at Au microelectrode in flowing solutions as a novel method for sub-nanomolar monitoring of lidocaine in injection and biological fluids.

In this work a novel method for the fast monitoring of lidocaine in flow-injection systems has been developed. The fast Fourier transform continuous cyclic voltammetry (FFTCV) at gold microelectrode in flowing solution system was used for determination of lidocaine in its pharmaceutical formulation. The presented technique was very simple, precise, accurate, time saving and economical, compared with all of the previously reported methods. The recommended technique demonstrated some advantages over other reported methods. Firstly, there was no need for the oxygen removal from the test solution. Secondly, a picomolar detection limit was achieved, and additionally, the method was fast enough for the determination of any such compound, in a wide variety of chromatographic methods. The method was linear across the concentration range of 240-1.1 x 10(5) pg mL(-1) (r=0.996) with a limit of detection and quantitation 117.3 and 240 pg mL(-1), respectively. As a conclusion this system offers the requisite accuracy, sensitivity, precision and selectivity to assay lidocaine in injections.

Parasites as heavy metal bioindicators in the shark Carcharhinus dussumieri from the Persian Gulf.

In this study the lead and cadmium concentrations in the liver, intestine, muscle and gonad of the shark Carcharhinus dussumieri and its parasites, Anthobothrium sp. and Paraorigmatobothrium sp. (Cestoda), were measured and compared. Tissue samples were collected from Iranian coastal waters of the Persian Gulf. After tissue preparation, the cadmium and lead concentrations were analysed using the Inductively Coupled Plasma technique. The results revealed that lead and cadmium concentrations in both parasite species were many times higher than in the host tissues. The results strongly support the view that helminth parasites are extremely sensitive early warning bioindicators, particularly in sensitive environments under threat but where pollution levels are presently low. They may also have a beneficial effect on the health of their hosts by acting as heavy metal filters.

Nano-level detection of naltrexone hydrochloride in its pharmaceutical preparation at Au microelectrode in flowing solutions by fast fourier transforms continuous cyclic voltammetry as a novel detector.

An easy and fast Fourier transform continuous cyclic voltammetric technique for monitoring of ultra trace amounts of naltrexone in a flow-injection system has been introduced in this work. The potential waveform, consisting of the potential steps for cleaning, stripping and potential ramp, was continuously applied on an Au disk microelectrode (with a 12.5 microm in radius). The proposed detection method has some of advantages, the greatest of which are as follows: first, it is no more necessary to remove oxygen from the analyte solution and second, this is a very fast and appropriate technique for determination of the drug compound in a wide variety of chromatographic analysis methods. The method was linear over the concentration range of 0.34-34000 pg/mL (r = 0.9985) with a limit of detection 8.0 x 10(-4) nM. The method has the requisite accuracy, sensitivity, precision, and selectivity to assay naltrexone in tablets. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the naltrexone were considered.