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.     

Nano Au/TiO2 hollow microsphere membranes for the improved sensitivity of detecting specific DNA sequences related to transgenes in transgenic plants

Gold nanoparticles (nano Au)/titanium dioxide (TiO₂) hollow microsphere membranes were prepared on the carbon paste electrode (CPE) for enhancing the sensitivity of DNA hybridization detection. The immobilization of nano Au and TiO₂ microsphere was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The hybridization events were monitored with EIS using [Fe(CN)₆]^3?/4? as indicator. The sequence-specific DNA of the 35S promoter from cauliflower mosaic virus (CaMV35S) gene was detected with this DNA electrochemical sensor. The dynamic detection range was from 1.0×10^?12 to 1.0×10^?8 mol/L DNA and a detection limit of 2.3×10^?13 mol/L could be obtained. The polymerase chain reaction (PCR) amplification of the terminator of nopaline synthase (NOS) gene from the real sample of a kind of transgenic soybean was also satisfactorily detected.     

Direct electrochemistry and enzymatic activity of hemoglobin in positively charged colloid Au nanoparticles and hemoglobin layer-by-layer self-assembly films

Alternate adsorption of positively charged colloid-Au nanoparticles (nano-Au⊕) and negatively charged hemoglobin (Hb) on L-cysteine (L-cys) modified gold electrode resulted in the assembly of {Hb/nano-Au⊕}n layer-by-layer films/L-cys modified gold electrode. The nano-Au⊕ was characterized by transmission electron micrograph (TEM) and microelectrophoresis. The modified electrode interface morphology was characterized by electrochemical impedance spectroscopy (EIS), atomic force mi- croscopy (AFM), cyclic voltammograms (CV) and chronoamperometry. Direct electron transfer between hemoglobin and gold electrodes was studied, and the apparent Michaelis-Menten constant ( km app) of the modified electrode was evaluated to be 0.10 mmol·L?1. Moreover, the higher activity of proteins in the nano-Au⊕ films could be retained compared with the electropolymerization membrane, since the pro- teins in nano-Au⊕ films retained their near-native structure. Direct electron transfer between hemoglo- bin and electrode and electrochemically catalyzed reduction of hydrogen peroxide on a modified elec- trode was studied, and the linear range was from 2.1×10-8 to 1.2 ×10?3 mol·L-1 (r = 0.994) with a detection limit of 1.1×10-8 mol·L-1 H2O2.     

Influence of MnO<Subscript>2</Subscript> on the photocatalytic activity of P-25 TiO<Subscript>2</Subscript> in the degradation of methyl orange

Influences of α-MnO₂, β-MnO₂, and δ-MnO₂ on the photocatalytic activity of Degussa P-25 TiO₂ have been investigated through the photocatalytic degradation of methyl orange. The TiO₂ photocatalyst, before and after being contaminated by MnO₂, was characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The results showed that photocatalytic activity of TiO₂ could be inhibited significantly or completely deactivated due to the presence of even a small amount of MnO₂ particles. It was found that the poisoning effect varied with the crystal phases of MnO₂ and the effect was in the order δ-MnO₂ >α-MnO₂ >β-MnO₂. The poisoning effect was attributed to the formation of heterojunctions between MnO₂ and TiO₂ particles. The heterojunctions changed the chemical state of Ti⁴⁺ and O²⁻ sites in the crystalline phase of TiO₂. MnO₂ in contact with TiO₂ particles also broadens the band-gap of TiO₂, which decreases UV absorption of TiO₂. It can also create some deep impurity energy levels serving as photoelectron-photohole recombination center, which accelerates the electron-hole recombination. Supported by the National Natural Science Foundation of China (Grant No. 20477009) and the Natural Science Foundation of Hebei Province (Grant No. E2005000183)     

Preparation of TiO<Subscript>2</Subscript>/activated carbon with Fe ions doping photocatalyst and its application to photocatalytic degradation of reactive brilliant red K2G

Titanium dioxide coated on activated carbon (AC) with Fe ions doping (Fe-TiO₂/AC) composite was prepared by an improved sol-gel method. The photocatalytic activities were tested by photocatalytic degradation of reactive brilliant red K2G in solution. The results show that in comparison with the agglomeration of pure TiO₂, the TiO₂ nanoparticles are well dispersed in the AC matrix, of which sizes are decreased with Fe ions doping. Additionally, the iron species on TiO₂ of composite are Fe₂O₃ and FeO, which do not affect the crystalline structures of TiO₂ nanoparticles. The AC matrix and iron doping content influence the fluorescence intensity of composite due to their effects on recombination probability of hole-electron pairs. Compared with TiO₂, 0.3% Fe-TiO₂, TiO₂/AC, 0.5% Fe-TiO₂/AC and 0.1% Fe-TiO₂/AC, the 0.3% Fe-TiO₂/AC shows the highest photoactivity with the complete mineralization of K2G for finite time due to the optimum Fe ions content and AC matrix. Furthermore, the kinetic constant (k = 0.0229 min⁻¹) of 0.3% Fe-TiO₂/AC composite is more than the sum of both TiO₂/AC (0.0154 min⁻¹) and 0.3% Fe-TiO₂ (0.0057 min⁻¹) because coexistence of the AC and Fe ions has an enlarging effect on improving the photoactivity of TiO₂. Supported by the Education Department Foundation of Hunan Province (Grant No. 08B063) and Science and Natural Science Foundation of Hunan Province (Grant No. 09JJ6101)     

Application of peptide nucleic acids containing azobenzene self-assembled electrochemical biosensors in detecting DNA sequences

Hybridization of peptide nucleic acids probe containing azobenzene (NH₂-TNT₄, N-PNAs) with DNA was performed by covalently immobilizing of NH₂-TNT₄ in sequence on the 3-mercaptopropionic acid self-assembled monolayer modified gold electrode with the helps of N-(3-dimethylaminopropy1)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), and the hybrid was coded as N-PNAs/DNA. Using [Fe(CN)₆]^4−/3− (1:1) as the electrochemical indicator, the electrochemical properties of the N-PNAs self-assembled monolayer (N-PNAs-SAMs) and N-PNAs/DNA hybridization system under the conditions of before and after UV light irradiation were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectra (EIS). Results showed that the redox currents decreased with the increase of irradiation time, suggesting that the ability of the charge transfer on the electrode surface was weakened and the conformation of hybrid system had been changed, and the control of PNAs/DNA hybridization could be realized by UV light irradiation. Supported by the National Natural Science Foundation of China (Grant No. 50572107) and “Top Hundred Talents Program” of Chinese Academy of Science     

The protection effect of β-CD on DNA damage induced by ultrafine TiO2

Under the photocatalysis of 365 nm ultraviolet radiation, ultrafine TiO2 caused the oxidative damage of Teasy plasmid DNA. The damage was determined by gel-electrophoresis. Then, a different dose of β-CD was added to the reaction, and the damage was restrained. The rate of damage restraining reached 97% when the mass of β-CD was 4 times as that of TiO2. Through UV scan and IR spectroscopy, it was found that the Ti-O of ultrafine TiO2 was bound with -OH of β-CD cavum and the -OH on the surface of ultrafine TiO2 disappeared, so the formation of · OH was controlled. The ultrafine TiO2 has been widely used, but it was determined to be carcinogenic by some research. The protection effect of β-CD to DNA in the molecular level takes a new look on the surface modification of nano particles to decrease the toxic effect.     

Potential energy curves for the X1∑ g, B1△g and B''''1∑ g states of C2 using MRCI and approximate CI methods

The potential energy curves for the X1∑ g, B1△g and B′1∑ g states of C2 have been studied by using MRCI and approximate CI methods, and are benchmarked against the calculations of full configuration interaction (FCI). The results obtained by MRCI method agree with the FCI very well, and even are accurate enough to compare other approximate methods as benchmark, when the calculations of FCI are not feasible. The approximate CI methods mentioned in this paper are reliable for treating chemical problems.     

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.     

Planar or quasi-planar octa- and ennea-coordinate aluminum and gallium in boron rings

An ab initio theoretical investigation has been performed on planar or quasi-planar octa-and ennea-coordinate Al and Ga centered in X@B8- and X@B9 (X=Al, Ga). These high symmetry molecular wheels all turned out to be true minima of the systems and σ+π double aromatic in nature, similar to the previously characterized D8h B@B8- both electronically and geometrically. Adiabatic and vertical detachment energies of the anions and the ionization potentials of the neutrals have been calculated to aid their eventua...     

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.     

Adsorption of TTF,TCNQ and TTF-TCNQ on Au(111): An <Emphasis Type="Italic">in situ</Emphasis> ECSTM study

The adsorption and adlayer structures of tetrathiofulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ on Au(111) have been systematically investigated by in situ electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry in 0.1 mol L⁻¹ HClO₄. All the three molecules were found to form well-ordered adlayers in the double-layer potential region of Au(111). For TTF and TCNQ adlayers, (6×3) and (4×7) structures have been observed, respectively. A structural transition was observed on TCNQ adlayer at potential negative of 0.08 V vs. the reversible hydrogen electrode (RHE), and induced a new phase with (3 × 12) structure. On the other hand, the charge transfer complex, TTF-TCNQ, self-organized into ordered domains with a lamellar structure different from those of the pure TTF and TCNQ adlayers on Au(111). Its packing arrangement was comparable to surface structures of either single crystal or thin film of TTF-TCNQ. Supported by the National Natural Science Foundation of China (Grant Nos. 20673121, 20733004 & 20821003), the National Key Project for Basic Research (Grant Nos. 2006CB806101 & 2006CB932100) and Chinese Academy of Sciences     

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)     

A DNA electrochemical sensor prepared by electrodepositing zirconia on composite films of single-walled carbon nanotubes and poly(2,6-pyridinedicarboxylic acid), and its application to detection of the PAT gene fragment

Carboxyl group-functionalized single-walled carbon nanotubes (SWNTs) and 2,6-pyridinedicarboxylic acid (PDC) were electropolymerized by cyclic voltammetry on a glassy-carbon electrode (GCE) surface to form composite films (SWNTs/PDC). Zirconia was then electrodeposited on the SWNTs/PDC/GCE from an aqueous electrolyte containing ZrOCl₂ and KCl by cycling the potential between −1.1 V and +0.7 V at a scan rate of 20 mV s⁻¹. DNA probes with a phosphate group at the 5′ end were easily immobilized on the zirconia thin films, because of the strong affinity between zirconia and phosphate groups. The sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was used for label-free detection of the target DNA by measuring the increase of the electron transfer resistance (R _et) of the electrode surface after the hybridization of the probe DNA with the target DNA. The PAT gene fragment and polymerase chain reaction (PCR) amplification of the NOS gene from transgenically modified beans were satisfactorily detected by use of this DNA electrochemical sensor. The dynamic range of detection of the sensor for the PAT gene fragment was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol L⁻¹ and the detection limit was 1.38 × 10⁻¹² mol L⁻¹.     

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).     

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...     

A fluorescent sensing membrane for iodine based on intramolecular excitation energy transfer of anthryl appended porphyrin

A single anthryl appended meso-tetraphenylporphyrin (TPP) dyad has been synthesized and applied in fluorescence sensing of iodine based on the intramolecular excitation energy transfer. The molecular recognition of the sensor is based on the interaction of iodine with inner anthracene moiety of the dyad, while the signal reporter for the recognition process is the TPP fluorescence quenching. Because the emission spectrum of anthracene is largely overlapped with the Soret band absorption of TPP, intramolecular excitation energy transfer interaction occurs between the donor, anthracene and acceptor, TPP. This energy transfer leads to TPP fluorescence emission by excitation of anthracene. The sensor was constructed by immobilizing the dyad in a plasticized poly(vinyl chloride) (PVC) membrane. The sensing membrane shows higher sensitivity compared to the sensors by using anthracene, TPP, or a mixture of anthracene and TPP as sensing materials. Under the optimum conditions, iodine in a sample solution can be determined from 2.04 to 23.6 mmol·L⁻¹ with a detection limit of 33 nmol·L⁻¹. The sensing membrane shows satisfactory response characteristics including good reproducibility, reversibility and stability, as well as the short response time of less than 60 s. Except for Cr₂O₇²⁻ and MnO₄⁻, other common metal ions and anions in foodstuff do not interfere with iodine determination. The proposed method was applied in the determination of iodine in table salt samples. The results agree well with those obtained by other methods. Supported by the National Outstanding Youth Science Foundation of China (Grant No. 20525518), the National Natural Science Foundation of China (Grant No. 20775005), and the National Natural Science Foundation of Hunan province (Grant No. JJ076021)     

Impact and mechanism of TiO2 nanoparticles on DNA synthesis in vitro

The impact of TiO₂ nanoparticles on DNA synthesis in vitro in the dark and the molecular mechanism of such impact were studied. The impact of TiO₂ nanoparticles on DNA synthesis was investigated by adding TiO₂ nanoparticles in different sizes and at various concentrations into the polymerase chain reaction (PCR) system. TiO₂ nanoparticles were premixed with the DNA polymerase, the primer or the template, respectively and then the supernatant and the precipitation of each mixture were added into the PCR system separately to observe the impact on DNA synthesis. Sequentially the interaction between TiO₂ nanoparticles and the DNA polymerase, the primer or the template was further analyzed by using UV-visible spectroscopy and polyacrylamide gel electrophoresis (PAGE). The results suggest that TiO₂ nanoparticles inhibit DNA synthesis in the PCR system in the dark more severely than microscale TiO₂ particles at the equivalent concentration and the inhibition effect of TiO₂ nanoparticles is concentration dependent. The molecular mechanism of such inhibition is that in the dark, TiO₂ nanoparticles interact with the DNA polymerase through physical adsorption while TiO₂ nanoparticles do with the primer or the template in a chemical adsorption manner. The disfunction levels of the bio-molecules under the impact of TiO₂ nanoparticles are in the following order: the primer > the template > the DNA polymerase. Supported by the National Natural Science Foundation of China (Grant Nos. 50572074 & 50673078), the Shanghai Key Fundamental Project (Grant No. 06JC14068) and the Innovation Program of Shanghai Municipal Education Commission (Grant No. 08ZZ21)     

Preparation and characterization of CoFe2O4/TiO2 magnetic composite films

CoFe₂O₄/TiO₂ magnetic composite films were prepared using the sol-gel method with tetrabutyltitanate and metallic chlorates as starting materials. The effects of heat treatment temperatures on microstructures and on magnetic properties were studied. The microstructure and properties of the samples at different heat treatment temperatures were characterized by X-ray diffraction, Raman spectrum, scanning electron microscopy, polarized microscopy and vibrating sample magnetometry. The results show that crystals of different substances grow up independently. Cobalt ferrite is evenly embedded into the titanium dioxide matrix in the prepared composite films. The magnetism of the composite films is enhanced with an increase of the heat temperature. Supported by the National Natural Science Foundation of China (Grant Nos. 50632030 and 10474077), and the Natural Science Foundation of Shaanxi Province (Grant No. 2006E135)     

Effect of strontium substitution on the activity of La2?xSrxNiO4 (x = 0.0–1.2) in NO decomposition

The aim of this work is to study the effect of Sr substitution on the redox properties and catalytic activity of La_2−x Sr _x NiO₄ (x = 0.0–1.2) for NO decomposition. Results suggest that the x = 0.6 sample shows the highest activity. The characterization (TPD, TPR, etc.) of samples indicates that the x = 0.6 sample possesses suitable abilities in both oxidation and reduction, which facilitates the proceeding of oxygen desorption and NO adsorption. At temperature below 700°C, the oxygen desorption is difficult, and is the rate-determining step of NO decomposition. With the increase of reaction temperature (T > 700°C), the oxygen desorption is favorable and, the active adsorption of NO on the active site (NO + V _o + Ni²⁺ → NO⁻-Ni³⁺) turns out to be the rate-determining step. The existence of oxygen vacancy is the prerequisite condition for NO decomposition, but its quantity does not relate much to the activity. Supported by the National Hi-Tech Research and Development Program of China (863 Program)(Grant No. 2004CB 719502) and the National Natural Science Foundation of China (Grant No. 20177022)