A new tripodal rhodamine B derivative as a highly selective and sensitive fluorescence chemosensor for copper(II)

A new tripodal rhodamine B derivative 2 was designed and synthesized by tripodal trialdehyde and rhodamine B hydrazide for the first time. This derivative could be used as a fluorescent chemosensor for the selective and sensitive determination of copper(II) in Tris-HCl buffer and ethanol aqueous mixed media. Under the optimum conditions described herein, fluorescence enhancement at 557/577 nm was linearly related to the concentration of copper(II) in the range of 0.10 to 10.00×10⁻⁵ mol·L⁻¹, with a correlation coefficient of R ²=0.9964 (n=15) and a detection limit of 1.129×10⁻⁷ mol·L⁻¹ (the relative standard deviation for five repeated measurements at 4.00×10⁻⁵ mol·L⁻¹ Cu(II) was 2.2%). The absorbance measurements at 557 nm were linearly related to the concentration of Cu(II) in the range of 0.50 to 25.00×10⁻⁵ mol·L⁻¹, with a correlation coefficient of R ²=0.9948 (n=13) and a detection limit of 3.338×10⁻⁷mol·L⁻¹. Supported by the Foundation of the Governor of Guizhou Province, China (Grant No. 200617) and the Talented Person Foundation of Guizhou University (Grant No. 2007039)     

Development of an amperometric glucose biosensor based on the immobilization of glucose oxidase in an ormosil-PVA matrix onto a Prussian Blue modified electrode

An amperometric glucose biosensor was developed based on the immobilization of glucose oxidase in the organically modified silicate (ormosil)-polyvinyl acetate (PVA) matrix onto a Prussian Blue (PB)-modified glassy carbon electrode. A higher stability PB-modified electrode was prepared by the electrochemical deposition of FeCl₃, K₃[Fe(CN)₆] and ethylenediamine tetraacetic acid (EDTA) under cyclic voltammetric (CV) conditions. The effects of the potential range of CV conditions, electrolyte cations, applied potential, pH, temperature and co-existing substances were investigated. The detection limit of the glucose biosensor was 8.1 μmol·L⁻¹ (S/N = 3) with a linear range from 20 μmol·L⁻¹ to 2 mmol·L⁻¹ (R = 0.9965). The biosensor presented a fast response and good selectivity. Additionally, excellent reproducibility and stability of the biosensor were observed. Supported by the National High Technical Development Project (863 project) Foundation (Grant No. 2006AA09Z160) and the National Natural Science Foundation of China (Grant No. 20775064)     

Determination of rutin using a CeO2 nanoparticle-modified electrode

CeO₂ nanoparticles approximately 12 nm in size were synthesized and subsequently characterized by XRD, TEM and UV-vis spectroscopy. Then, a gold electrode modified with CeO₂ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified electrode demonstrated strong catalytic effects with high stability towards electrochemical oxidation of rutin. The anodic peak currents (measured by differential pulse voltammetry) increased linearly with the concentration of rutin in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁴ mol · L⁻¹. The detection limit (S/N = 3) was 2.0 × 10⁻⁷ mol · L⁻¹. The relative standard deviation (RSD) of 8 successive scans was 3.7% for 5.0 × 10⁻⁶ mol · L⁻¹ rutin. The method showed excellent sensitivity and stability, and the determination of rutin in tablets was satisfactory.     

Determination of hemoglobin at a novel NH2/ITO ion implantation modified electrode

A novel electrode was prepared by implanting NH₂ ⁺ into an ITO film (NH₂/ITO). Gold nanoparticles were deposited on the surface of NH₂/ITO electrode. The NH₂/ITO and Au/NH₂/ITO electrodes were used to determine hemoglobin (Hb) immobilized on the electrodes surfaces. The relationship of the reductive peak current value of Hb among different electrodes was: Hb/ITO:Hb/Au/ITO:Hb/NH₂/ITO:Hb/Au/NH₂/ITO=1:1.5:2:4. The linkage between the –NH₂ implanted into ITO film and the –COOH of Hb was recognized to be the reason for the increase of active Hb coverage on NH₂/ITO electrode compared with the ITO electrode. Increase of active Hb coverage on Au/NH₂/ITO compared with Au/ITO was attributed to the different amount of gold nanoparticles deposited. The determination of Hb at an Au/NH₂/ITO electrode was optimized. Calibration curve was obtained over the range of 1.0 × 10⁻⁸ – 1.0 × 10⁻⁶ mol · L⁻¹ with a detection limit of 1.0 × 10⁻⁸ mol · L⁻¹. Results showed that the novel NH₂/ITO and Au/NH₂/ITO electrodes exhibited good stability, reproducibility besides better electrochemical performance. Correspondence: Jing Bo Hu, Department of Chemistry, Beijing Normal University, Beijing 100875, China     

Immobilization and hybridization of DNA based on magnesium ion modified 2,6-pyridinedicarboxylic acid polymer and its application for label-free PAT gene fragment detection by electrochemical impedance spectroscopy

A new approach for a simple electrochemical detection of PAT gene fragment is described. Poly(2,6-pyridinedicarboxylic acid) (PDC) modified glassy carbon electrode (GCE) was prepared by potential scan electropolymerization in an aqueous solution. Mg2 ions were incorporated by immer-sion of the modified electrode in 0.5 mol/L aqueous solution of MgCl2 to complete the preparation of a generic "activated" electrode ready for binding the probe DNA. The ssDNA was linked to the conduct-ing polymer by forming a bidentate complex between the carboxyl groups on the polymer and the phosphate groups of DNA via Mg2 . DNA immobilization and hybridization were characterized with dif-ferential pulse voltammetry (DPV) by using methylene blue (MB) as indicator and electrochemical im-pedance spectroscopy (EIS). The EIS was of higher sensitivity for DNA detection as compared with voltammetric methods in our strategy. The electron transfer resistance (Ret) of the electrode surface in EIS in [Fe(CN)6]3-/4- solution increased after the immobilization of the DNA probe on the Mg/PDC/GCE electrode. The hybridization of the DNA probe with complementary DNA (cDNA) made Ret increase further. The difference between the Ret at ssDNA/Mg/PDC/GCE and that at hybridization DNA modified electrode (dsDNA/Mg/PDC/GCE) was applied to determine the specific sequence related to the target PAT gene with the dynamic range comprised between 1.0 × 10-9 and 1.0 × 10_5 mol/L. A detection limit of 3.4 × 10-10 mol/L of oligonucleotides can be estimated.     

A capacitive sensor based on molecularly imprinted polymers and poly( p -aminobenzene sulfonic acid) film for detection of pazufloxacin mesilate

A novel capacitive sensor for pazufloxacin mesilate (pazufloxacin) determination was developed by electropolymerizing p-aminobenzene sulfonic (p-ABSA) and molecularly imprinted polymers (MPs), which was synthesized through thermal radical copolymerization of metharylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) in the presence of pazufloxacin template molecules, on the gold electrode surface. Furthermore, 1-dedecanethiol was used to insulate the modified electrode. Alternating current (ac) impedance experiments were carried out with a Model IM6e to obtain the capacitance responses. Under the optimum conditions, the sensor showed linear capacitance response to pazufloxacin in the range of 5 ng·mL⁻¹ to 5 μg·mL⁻¹ with a relative standard deviation (RSD) 5.3% (n=7) and a detection limit of 1.8 ng·mL⁻¹. The recoveries for different concentration levels of pazufloxacin samples varied from 94.0% to 102.0%. Electrochemical experiments indicated the capacitive sensor exhibited good sensitivity and selectivity and showed excellent parameters of regeneration and stability. Supported by the National Natural Science Foundation of China (Grant No. 20675064), the Natural Science Foundation of Chongqing City (Grant No. CSTC-2004BB4149 and 2005BB4100) and High Technology Project Foundation of Southwest University (Grant No. XSGX02).     

Ensemble of carbon fiber ultra-microelectrodes modified with nanotubes, and its application to the determination of dopamine

An ensemble of carbon fibers ultra-microelectrode modified with carbon nanotubes (EUME-CNTS) has been constructed based on a thin carbon nanotubes film which was coated onto surfaces of carbon fibers of ultra-microelectrode. SEM micrographs illustrated the image of carbon nanotubes on the carbon fiber surface. The electrochemical characteristics of the EUME-CNTS has been investigated by cyclic voltammetry. The electrochemical properties of dopamine on this electrode were also studied, and the detection limit was found to be 2.0 × 10⁻⁹ mol·L⁻¹. Linear calibration plots were obtained for the oxidation peak current in a range 1.0 × 10⁻⁷–8.0 × 10⁻⁵ mol·L⁻¹. Correspondence: Xiuhua Liu, Kuaizhi Liu, Department of Chemistry and Chemical Engineering, Henan University, Henan Kaifeng 475001, P.R. China     

Determination of Tannic Acid by Flow Injection Analysis with Inhibited Chemiluminescence Detection

A novel flow injection procedure has been developed for the determination of tannic acid based on the inhibition of the chemiluminescences in luminol-H₂O₂-Manganese tetrasulfonatophthalocyanine (MnTSPc) system by tannic acid. The method is simple, rapid and sensitive with a detection limit of 8 × 10⁻¹⁰ mol·L⁻¹ and a linear range of 7 × 10⁻⁹–5 × 10⁻⁶ mol·L⁻¹. The relative standard deviation is 1.9% for eleven measurements of 5 × 10⁻⁷ mol·L⁻¹ tannic acid. The method has been successfully applied to the determination of tannic acid in real Chinese gall and hop pellets samples.     

Effect of inorganic positive ions on the adsorption of surfactant Triton X-100 at quartz/solution interface

The electrode-separated piezoelectric sensor (ESPS), an improved setup of quartz crystal microbalance (QCM), has been employed to investigate the adsorption behavior of nonionic surfactant Triton X-100 at the hydrophilic quartz-solution interface in mineralized water medium in situ, which contained CaCl2 0.01 mol·L?1, MgCl2 0.01 mol·L?1, NaCl 0.35 mol·L?1. In a large scale of surfactant concentration, the effects of Ca2 , Mg2 and Na on the adsorption isotherm and kinetics are obviously different. In aque-ous solution containing NaCl only, adsorption of Triton X-100 on quartz-solution interface is promoted, both adsorption rate and adsorption amount increase. While in mineralized water medium, multivalent positive ions Ca2 and Mg2 are firmly adsorbed on quartz-solution interface, result in the increasing of adsorption rate and adsorption amount at low concentration of surfactant and the peculiar desorption of surfactant at high concentration of Triton X-100. The results got by solution depletion method are in good agreement with which obtained by ESPS. The "bridge" and "separate" effect of inorganic positive ions on the adsorption and desorption mechanism of Triton X-100 at the quartz- solution interface is discussed with molecular dynamics simulations (MD), flame atomic absorption spectrometry (FAAS) and atomic force microscopy (AFM) methods.     

Effects of La<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> on outward potassium channels in Vicia guard cells

Effects of La³⁺ and Eu³⁺ on outward potassium channels (K_out⁺) in Vicia guard cells have been studied by patch clamping technique. Extracellular La³⁺ inhibited K_out⁺ currents with a half-inhibition concentration (IC₅₀) of 81 μmol·L⁻¹. Interestingly, intracellular La³⁺ activated K_out⁺ currents at a free concentration of 1.13 × 10⁻¹⁴ mol·L⁻¹, and inhibited K_out⁺ currents at a free concentration of 5.86 × 10⁻¹⁴ mol·L⁻¹. Extracellular Eu³⁺ also activated K_out⁺ currents at concentrations of 10 μmol·L⁻¹ and 50 μmol·L⁻¹, and inhibited K_out⁺ currents at concentrations of more than 1 mmol·L⁻¹. The effects of La³⁺ and Eu³⁺ on K_out⁺ currents may contribute to regulation of the plant water status, which may be one of the mechanisms of the biological effect of rare earth elements.     

Chemometrics to evaluate the quality of water sources for human consumption

Multilayer films of multiwalled carbon nanotubes (MWNTs) were homogeneously and stably assembled on a glassy carbon (GC) electrode using the layer-by-layer (LBL) method based on electrostatic interaction between MWNTs (negatively charged) and a biopolymer chitosan (CHIT) (positively charged). Scanning electron microscopy (SEM) image of the resulting {CHIT/MWNTs}₉ film indicated that the substrate was mostly covered with MWNTs in the form of small bundles or single nanotubes. The multilayer film was used to study the electrocatalytic oxidation of NADH. The assembled {CHIT/MWNTs}₉/GC electrode could decrease the oxidation overpotential of NADH by more than 350 mV. The {CHIT/MWNTs}₉/GC electrode exhibited a wide linear response range of 8 × 10⁻⁷ to 1.6 × 10⁻³ mol · L⁻¹ with a correlation coefficient of 0.997 for the detection of NADH. The response time and detection limit (S/N = 3) were determined to be 3 s and 0.3 × 10⁻⁶ mol · L⁻¹, respectively. Another attractive characteristic was that the method was simple and the assembled {CHIT/MWNTs}₉/GC electrode was highly stable.     

Investigations on the amalgamation of gold nanorods by iodine and the detection of tetracycline

The morphological transformation process of gold nanorods (Au-NRs) resulting from the reaction between tetracycline and iodine was monitored by the plasmon resonance absorption (PRA) spectra and the scanning electron microscope (SEM) images. It was found that iodine could fuse Au-NRs into sphericity with the lower aspect ratio and blue shift of the longitudinal PRA band. It was found, however, that the presence of tetracycline, since it can react with I₂, decreases the effective concentration of I₂ and its fusion effect on Au-NRs. As a result, the longitudinal PRA of Au-NRs shifts to longer wavelength linearly with increasing the concentration of tetracycline. With that, tetracycline can be detected in the range of 5.0×10^∮5- 5.0×10⁻⁴ mol·L⁻¹, with a limit of determination (LOD) of 2.4×10⁻⁶ mol·L⁻¹ (3σ). Most foreign substances in the samples did not interfere in the detection, and tetracycline in the synthetic samples could be detected with the recovery in the range of 92.8%–107.2%, and RSD lower than 4.3%. The concentration of tetracycline in milk detected with standard addition method was so low that it accorded with the safety regulation. Supported by the National Natural Science Foundation of China (Grant Nos. 30570465 and 20425517)     

Methane and nitrous oxide concentration and emission flux of Yangtze Delta plain river net

Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tio...     

Study of third-order nonlinear susceptibility of polySchiff base containing triphenylamine

PolySchiff base containing triphenylamine has been synthesized by polycondensation and character-ized by FT-IR,NMR,UV-visible spectrometer. Measurements of the third-order optical nonlinear sus-ceptibility χ(3) by Z-scan technique have shown that the large nonlinearity is dominated by the two-photon absorption in PSB. The sign and size of real part Reχ(3) ,nonlinear refractive index n2 have been measured with the condition of 532 nm,8 ns-duration pulses to be -1.23×10-10 esu,-3.06×10-12 esu;nonlinear absorption index β and size of image part Imχ(3) to be 3.63×10-10 m/W,1.15×10-11 esu,respec-tively,so the third-order nonlinear susceptibility χ(3) is 1.19×10-11 esu. The value is larger than other polymers reported. PSB is self-focusing material and has potential application in nonlinear optic field.     

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10⁻⁶ cm² s⁻¹. In 0.1 mol L⁻¹ phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10⁻⁵–2.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁷–1.0 × 10⁻⁶ mol L⁻¹. The detection limit is 5 × 10⁻⁸ mol L⁻¹. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.     

Simultaneous Detection of Dopamine and Uric Acid under Coexistence of Ascorbic Acid with DNA/Pt Nanocluster Modified Electrode

A novel biosensor by electrochemically codeposited Pt nanoclusters and DNA film was constructed and applied to detection of dopamine (DA) and uric acid (UA) in the presence of high concentration ascorbic acid (AA). Scanning electron microscopy and X‐ray photoelectron spectroscopy were used for characterization. This electrode was successfully used to resolve the overlapping voltammetric response of DA, UA and AA into three well‐defined peaks with a large anodic peak difference (ΔE_pa) of about 184 mV for DA and 324 mV for UA. The catalytic peak current obtained from differential pulse voltammetry was linearly dependent on the DA concentration from 1.1× 10^?7 to 3.8×10^?5 mol·L^?1 with a detection limit of 3.6×10^?8 mol·L^?1 (S/N=3) and on the UA concentration from 3.0×10^?7 to 5.7×10^?5 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 with coexistence of 1.0×10^?3 mol·L^?1 AA. The modified electrode shows good sensitivity and selectivity.     

Voltammetric study of the interaction of the ofloxacin–copper complex with DNA, and its analytical application

The electrochemical behavior of the ofloxacin–copper complex, Cu(II)L₂, at a mercury electrode, and the interaction of DNA with the complex have been investigated. The experiments indicate that the electrode reaction of Cu(II)L₂ is an irreversible surface electrochemical reaction and that the reactant is of adsorbed character. In the presence of DNA, the formation of the electrochemically non-active complexes Cu(II)L₂-DNA, results in the decrease of the peak current of Cu(II)L₂. Based on the electrochemical behavior of the Cu(II)L₂ with DNA, binding by electrostatic interaction is suggested and a new method for determining nucleic acid is proposed. Under the optimum conditions, the decrease of the peak current is in proportional to the concentration of nucleic acids in the range from 3 × 10⁻⁸ to 3 × 10⁻⁶ g · mL⁻¹ for calf thymus DNA, from 1.6 × 10⁻⁸ to 9.0 × 10⁻⁷ g · mL⁻¹ for fish sperm DNA, and from 3.3 × 10⁻⁸ to 5.5 × 10⁻⁷ g · mL⁻¹ for yeast RNA. The detection limits are 3.3 × 10⁻⁹, 6.7 × 10⁻⁹ and 8.0 × 10⁻⁹ g · mL⁻¹, respectively. The method exhibits good recovery and high sensitivity in synthetic samples and in real samples.     

Electrochemical synthesis of ammonia using a cell with a Nafion membrane and SmFe0.7Cu0.3?xNixO3 (x = 0?0.3) cathode at atmospheric pressure and lower temperature

Samaria-doped ceria Ce_0.8Sm_0.2O_2−δ (SDC) and SmFe_0.7Cu_0.3−x Ni _x O₃ have been synthesized by the sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The electrochemical synthesis of ammonia was investigated at atmospheric pressure and low temperature, using the SFCN materials as the cathode, a Nafion membrane as the electrolyte, nickel-doped SDC (Ni-SDC) as the anode and silver-platinum paste as the current collector. Ammonia was synthesized from 25 to 100°C when the SFCN materials were used as cathode, with SmFe_0.7Cu_0.1Ni_0.2O₃ giving the highest rates of ammonia formation. The maximum rate of evolution of ammonia was 1.13 × 10⁻⁸ mol·cm⁻²·s⁻¹ at 80°C, and the current efficiency reached as high as 90.4%. Supported by the National Natural Science Foundation of China (Grant No. 20863007)     

A Sensitive Hydrogen Peroxide Sensor Based on Hemoglobin Immobilized on Gold Nanoparticles and 1,6-hexanedithiol Modified Gold Electrode

Hemoglobin (Hb) was successfully immobilized on a gold electrode modified with gold nanoparticles (AuNPs) via a molecule bridge 1,6-hexanedithiol (HDT). The AFM images suggested that the HDT/gold electrode could adsorb more AuNPs. UV-vis spectra indicated that Hb on AuNPs/HDT film retained its near-native secondary structures. The electrochemical behaviors of the sensor were characterized with cyclic voltammetric techniques. The resultant electrode displayed an excellent electrocatalytical response to the reduction of hydrogen peroxide (H₂O₂). The linear relationship existed between the catalytic current and the H₂O₂ concentration ranging from 5.0 × 10^?8 to 1.0 × 10^?6 mol · L^?1. The detection limit (S/N = 3) was 1.0 × 10^?8 mol · L^?1.     

Application of cadmium sulfide nanoparticles as oligonucleotide labels for the electrochemical detection of NOS terminator gene sequences

A mercaptoacetic acid (MAA)-modified cadmium sulfide (CdS) nanoparticle was synthesized in aqueous solution and used as an oligonucleotide label for the electrochemical detection of nopaline synthase (NOS) terminator gene sequence. The carboxyl groups on the surface of the CdS nanoparticle can be easily covalently linked with NH₂-modified NOS oligonucleotide probe sequences. The target ssDNA sequence was fixed onto the electrode surface by covalently linking to a mercaptoethanol self-assembled gold electrode, and the DNA hybridization of target ssDNA with probe ssDNA was accomplished on the electrode surface. The CdS nanoparticles anchored on the hybrids were dissolved in the solution by the oxidation with HNO₃ and further detected by a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used for monitoring the hybridization, and the NOS target sequence was satisfactorily detected in the approximate range from 8.0 × 10⁻¹² to 4.0 × 10⁻⁹ mol L⁻¹ with a detection limit of 2.75 × 10⁻¹² mol L⁻¹ (3σ). The established method extended the nanoparticle-labeled electrochemical DNA analysis to genetically modified organisms (GMOs) specific sequence samples with higher sensitivity and selectivity.