摘要:

AbstractTailoring of electrically contacted enzyme electrodes provides the grounds for bioelectronic and biosensor systems. Redox‐enzymes organized onto electrodes as monolayer assemblies, and chemically functionalized by redox‐relay groups, yield electrically contacted enzyme electrodes exhibiting bioelectrocatalytic features. The sensitivity of the enzyme electrode can be enhanced, or tuned, by the organization of multilayer enzyme electrodes and the application of rough metal supports. Enzyme electrodes of extremely efficient electrical communication with the electrode are generated by the reconstitution of apo‐flavoenzymes onto relay‐FAD monolayers associated with electrodes. The reconstitution process results in an aligned enzyme on the surface, and its effective electrical contact with the electrode yields selective enzyme electrodes of unprecedented high current responses. Integrated electrodes consisting of relay‐NAD(P)+‐cofactor and enzyme units are generated by the reconstitution of NAD(P)+‐dependent enzymes onto a relay‐NAD(P)+monolayer assembly followed by lateral crosslinking of the

ISSN:1040-0397    

DOI:10.1002/elan.1140091302

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe modification of carbon paste electrodes by incorporation of the enzyme glucose oxidase (GOx) and a conducting redox osmium bis‐bipyridyl poly(4‐vinylpyridine) polymer (Os‐polymer) is described. The resulting enzyme electrodes were operated as amperometric glucose sensors in the presence or absence of a stabilizer, polyethyleneimine (PEI), mixed into the paste. Cyclic voltammetric studies showed that Os‐polymer containing Os2+/3+redox couple mediated the electron transfer from reduced GOx to the carbon paste electrode material. Steady‐state amperometric responses of the sensors to 2–120 mM glucose at an operating potential of 350 mV (vs. Ag/AgCl) were determined in 0.1 M phosphate buffer (pH 7.0) medium. The study showed that PEI enhances both, the sensitivity and stability of the carbon paste enzyme electrode and that a diffusion‐limited step precedes electrocatalytic reactions of the biosensor. Cyclic voltammetric data and the Arrhenius analysis of the apparent turnover rate constant,k′catshowed that PEI decreases the diffusion limitations of CPE, thereby increasing the frequency of collision of reacting species in this b

ISSN:1040-0397    

DOI:10.1002/elan.1140091303

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn adsorptive linear sweep stripping voltammetric method has been developed for the determination of nitrosamines at polymer modified gold electrodes.N‐nitroso‐N‐butyl‐N‐propylamine has been quantified over a 10−10M to 10−6M concentration range at Nafion modified electrodes. CA coatings inhibited the determination ofN‐nitroso‐N‐butyl‐N‐propylamine, while small enhancements were observed at CAB modified electrodes. This improvement may be due to the anionic butyrate groups within the CAB polymer facilitating nitrosamine sorption. It is postulated, that the insulating effect of the polymer and the incorporation of anionic moieties compete to give either a net enhancement or depreciation of

ISSN:1040-0397    

DOI:10.1002/elan.1140091304

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractDenatured (single‐stranded, ss) and native (double‐stranded, ds) DNAs were studied by constant current chronopotentiometric stripping analysis (CPSA) at a hanging mercury drop electrode (HMDE). In agreement with the previous voltammetric studies at neutral pH values ssDNA produced CPS cathodic peak CA (due to reduction of cytosine and adenine) and anodic peak G (due to oxidation of the guanine reduction product) at dt/dEagainstEcurves. The same peaks produced by dsDNA were substantially smaller. Differences in heights (areas) of peaks G and CA produced by ss and dsDNAs at partial and full electrode coverage are compared and discussed. Using CPSA a well‐developed and symmetrical peak CA was obtained at low DNA concentrations compared to a poorly measurable inflection produced by differential pulse or linear sweep voltammetries under the same conditions. The CPS peak CA can be used also in adsorptive transfer stripping (AdTS, medium exchange) experiments. In the previous AdTS voltammetric measurements only peak G was exploited while the voltammetric peak CA was poorly defined to be of any use in combination with DNA‐modified electrodes. CPS peaks were measured in the presence and in absence of air. It was shown that in the presence of air peak CA is enhanced while peak G decreased. We compared the CPSA of ssDNA at the mercury and carbon paste electrodes (CPE). The CPS peak G (obtained with HMDE) seems to be the best choice for the electrochemical determination of DNA in highly diluted solution. With 10 min adsorptive preconcentration a detection limit below 20 ng of ssDNA per mL was obtained at HMDE. At CPE the limit of detection (of the same ssDNA) was at least two‐fo

ISSN:1040-0397    

DOI:10.1002/elan.1140091305

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractMonoenzyme (HRP) and bilyer/monolayer bienzyme (HRP‐GOX) bioelectrodes were realized by the oxidative electropolymerization of amphiphilic pyrrole monomer 1 enzyme(s) mixtures, previously adsorbed on the surface of a glassy carbon electrode. Cyclic voltammetry measurements, carried out on poly 1‐HRP modified electrodes showed that the electrocatalytical reduction of H2O2, in the presence of K4Fe(CN)6as mediator, occurs at applied potentials well placed in the optimal potential range for amperometric detection. An optimization study concerning the mediator concentration, the amount of the immobilized enzyme(s), the electrode material and the matrix structure (mono‐ or bilayer) was performed in order to obtain the glucose biosensor. At an applied potential of −0.1 V (vs. SCE), batch amperometric response to H2O2for the HRP modified electrodes gave a sensitivity of ca. 280 mA M−1cm−2(up to 0.65 mM). For monolayer biosensor the sensitivity to glucose was ca. 170 mA M−1cm−2(up to 1.9 mM). The interference of ascorbate, urate and acetaminophen was found al

ISSN:1040-0397    

DOI:10.1002/elan.1140091306

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA quadridentate dihydrogen perchlorate macrocyclic membrane is found to exhibit quite promising selectivity for Zn2+. It can be used to estimate zinc in the range 2.5 × 10−6to 1.0 × 10−1mol dm−3(0.16 to 6.50 × 103mg dm−3) with a near‐Nernstian slope of ≈︁ 28 mV per decade of concentration. The working pH range of the sensor is 3.0 to 7.0. The polystyrene based membrane electrode is found to possess adequate stability and specific selectivity with a response time of 10 s. Most of the ions that interfere with Zn2+electrode do not cause any significant disturbance with this assembly and the sensor can be used for more than three months in aqueous as well as in partially nonaqueous media. The utility of the membrane sensor has also been observed in solutions contaminated with detergent matter. The membrane sensor has also been used successfully to analyse some baby food products and soft drinks for the determina

ISSN:1040-0397    

DOI:10.1002/elan.1140091307

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA poly(4‐vinylpyridine)‐coated carbon paste electrode (PVP/CPE) was developed for the selective determination of uric acid (UA) in the presence of ascorbic acid (AA) by square wave voltammetry. The oxidation of UA at carbon‐based electrodes in acidic solutions suffers from interference from AA which can be oxidized at a potential close to that of UA. Due to the very distinct ability of AA and UA to form hydrogen bonds with PVP, the overlapped oxidation potentials of AA and UA can be separated. Linear calibration plots are obtained over the 0–9 μM and 10–30 μM in pH 1.1 buffer solution with slopes (μA/μM) and correlation coefficients of 3.6, 0.9992 and 7.5, 0.9989, respectively. The detection limit (3σ) is 0.2 μM. The acceptable tolerance of concentration of AA for the determination of 20 μM UA is at least as high as 0.1 mM. The practical analytical utility is illustrated by selective measurements of UA in human urine without any preli

ISSN:1040-0397    

DOI:10.1002/elan.1140091308

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractDifferential pulse anodic and cathodic stripping voltammetry have been employed for the simultaneous determination of AsIII, SeIVCuII, PbIIand CdIIin environmental matrices. The voltammetric measurements were carried out using a conventional three‐electrode cell and the ammonia‐ammonium chloride buffer (pH 9.2) as supporting electrolyte. The analytical procedure was verified by the analysis of the standard reference materials: Mussel Tissue BCR‐CRM 278 and Ulva Lactuca BCR‐CRM 279. The precision and the accuracy, expressed as relative standard deviation (sr) and relative error (e), respectively, were of the order of 3 to 5%, while the detection limit for each element, under the experimental conditions employed, was aroun

ISSN:1040-0397    

DOI:10.1002/elan.1140091309

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractRotating disk electrode voltammetry (RDEV) in conjunction with anodic stripping voltammetry (ASV) with a thin mercury film electrode (TMFE) or with a Nafion‐coated thin mercury film electrode (NCTMFE) has been evaluated for the direct determination (i.e., without preconcentration) of lead and cadmium speciation in aqueous solutions containing dissolved organic matter. The RDEV technique has been used to estimate dissociation rate constants and diffusion coefficients; pseudopolarograms have indicated the identity of the metal complexes undergoing electrode reductions at the corresponding plateaus of the pseudopolarograms in a number of model solutions containing Cd or Pb and known amounts of fulvic acid. It has been found that the effect of dissolved organic material is measurable when the concentrations of fulvic acid are equal to or less than 20 μg/mL (which is below the concentration of naturally occurring dissolved organic carbon in most freshwaters). The effective electrode surface area has been found to be considerably less than the geometric surface area, and if this fact is not explicitly taken into consideration, the result would be an erroneous estimation of dissociation rate constants and diffusion coefficients. Pseudopolarograms of aqueous samples containing Cd or Pb and fulvic acid and samples of Rideau river surface water clearly show that NCTMFEs effectively block the transport of large inert metal‐FA complexes to the electrode surface, resulting in interference‐free determination, and giving well‐defined pseudopolarograms, and yet do not hinder the transport of small metal‐FA complexes to the electrode surface. It is concluded that RDEV/ASV offers promise of being a valuable technique for determining chemical speciation of lead and cadmium in river surf

ISSN:1040-0397    

DOI:10.1002/elan.1140091310

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA silver electrode coated with captopril, 1‐[(2S)‐3‐mercapto‐2‐methyl‐1‐oxopropyl]‐L‐proline, was prepared by covalent bonding method. The modified electrode was long‐lived and stable. Experimental results revealed that myoglobin (Myb) could exhibit good voltammetric response at the modified electrode. Square wave voltammetric measurements of Myb with the modified electrode gave a linear relationship between the anodic peak current and the protein concentration in the range of 4 × 10−6−5 × 10−5mol/L. The relative standard deviation is 5 % for 6 successive determin

ISSN:1040-0397    

DOI:10.1002/elan.1140091311

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY