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Indirectly heated electrodes operating in a non-isothermal mode have been used as transducers for reagentless glucose biosensors. Pyrroloquinoline quinone-dependent soluble glucose dehydrogenase (PQQ-sGDH) was entrapped on the electrode surface within a redox hydrogel layer. Localized polymer film precipitation was invoked by electrochemically modulating the pH-value in the diffusion zone in front of the electrode. The resulting decrease in solubility of an anodic electrodeposition paint (EDP) functionalized with Osmium complexes leads to precipitation of the redox hydrogel concomitantly entrapping the enzyme. The resulting sensor architecture enables a fast electron transfer between enzyme and electrode surface. The glucose sensor was operated at pre-defined temperatures using a multiple current-pulse mode allowing reproducible indirect heating of the sensor. The sensor characteristics such as the apparent Michaelis constants K(M)(app) and maximum currents I(max)(app) were determined at different temperatures for the main substrate glucose as well as a potential interfering co-substrate maltose. The limit of detection increased with higher temperatures for both substrates (0.020 mM for glucose, and 0.023 mM for maltose at 48 degrees C). The substrate specificity of PQQ-sGDH is highly temperature dependent. Therefore, a mathematical model based on a multiple linear regression approach could be applied to discriminate between the current response for glucose and maltose. This allowed accurate determination of glucose in a concentration range of 0-0.1mM in the presence of unknown maltose concentrations ranging from 0 to 0.04 mM.

This communication reports about preliminary studies of self-assembled monolayers (SAMs) on bismuth bulk electrodes (BiBEs) using daunomycin and picric acid as electrochemical indicators. The cyclic voltammetric signals of these indicators decreased after the modification of the bismuth electrode with alkanethiols, indicating the formation of SAMs on bismuth. Signal decrease as well as the stability of the SAMs depends strongly upon the length of the alkanethiol. The bismuth-based SAMs were significantly more stable at negative potentials than SAMs on a gold substrate, yielding an useful potential range from −0.3 V to −1.3 V. Such highly stable SAMs could be beneficial for trace metal detection and biosensors. Keywords: Bismuth bulk electrode, Self-assembled monolayer, SAM, Voltammetry, Daunomycin, Picric acid

This paper describes how the surface of an oil–graphite based carbon paste electrode (CPE) can be studied by means of atomic force microscopy (AFM). By choosing the scanning parameters very carefully, it is possible to scan even such a soft and delicate surface. Both intermittent contact and phase shift scan modes provide useful information about nano-distribution of topographical details as well as hard and soft areas on the surface. The electrochemical bismuth film deposition from a 0.05 M sulphuric acid +1 ppm Bi(III) containing electrolyte can be investigated by both scan modes. Intermittent scan mode yields very thin (2 nm) layer-shaped structures sizing from 20 nm to some microns. Phase shift scans of the same sections depict extensive areas of high and uniform phase shift, which cannot be found on the bare CPE, and thus have to be attributed to the newly formed bismuth film. AFM holds great promise for the investigation of all kinds of carbon paste electrodes. Keywords: Carbon paste electrode, CPE, Bismuth film electrode, BiFE, Atomic force microscopy, AFM

DNA hybridization plays an important role in medical diagnostics, drug development and biological threat discovery. Despite the wide use of optical hybridization detection, electrochemical methods, and especially covalently attached redox markers, attain an increasing interest. However, one problem is that the number of suppliers of electrochemically labelled oligonucleotides is very limited. This paper reports about the use of the commercially available fluorescence quenching label dabcyl (p-methyl red) as a redox active DNA-marker. We investigated the polarographic, voltammetric and adsorptive stripping voltammetric behaviour of this compound in a TRIS buffer at pH 7.5 and found that two polarographic waves (at −0.48 and −1.28 V vs. Ag/AgCl) can be easily distinguished compared to only one clear signal between −0.4 and −0.7 V in most voltammetric techniques.The alternating-current voltammetric (ACV) signal of a dabcyl-labelled target at a thiollinker-probe-SAM modified gold disk electrode was very clear but small due to a fast and irreversible decay of the reduction product. Despite of this, non-complementary DNA-strands could be discriminated and at 15 min hybridization time, trace amounts down to 50 nM target concentration could be detected. Such electrochemical use of optically active labels could open new possibilities for spectroelectrochemical studies of DNA hybridization. Keywords: DNA hybridization, Gold electrode, Voltammetry, Dabcyl, Methyl red, Self-assembled monolayer

Heated electrodes were applied for the non-isothermal operation of amperometric glucose biosensors based on glucose oxidase immobilised on the electrode surface by entrapment within a polymer layer. The localised deposition of the polymer film under simultaneous entrapment of the enzyme was achieved by an electrochemically induced pH-modulation in the diffusion zone in front of the electrode, thus altering the solubility of the polymer chains. This non-manual sensor preparation protocol could be successfully used for the modification of a novel indirectly heated electrode. The non-isothermal operating mode allows working at the optimum temperature of the enzyme sensors without any thermal distortion of the bulk solution. Increased surface temperature of the sensor thus accelerates transport as well as kinetic processes, resulting in an enhanced amperometric signal. In the presence of interfering compounds such as ascorbic acid, the proposed technique allows use of the diverging thermal impact on the sensing process, for different electrochemically active compounds, for a deconvolution of the amperometric signal at different electrode temperatures. A calculation method for determination of glucose in the presence of one interfering compound is presented as a basis for a calculative interference elimination.

Highly conductive boron-doped diamond (BDD) electrodes are well suited for performing electrochemical measurements of nucleic acids in aqueous solution under diffusion-only control. The advantageous properties of this electrodic material in this context include reproducibility and the small background currents observed at very positive potentials, along with its robustness under extreme conditions so offering promising capabilities in future applications involving thermal heating or ultrasonic treatment. tRNA, single and double stranded DNA and 2'-deoxyguanosine 5'-monophosphate (dGMP) have been studied and well defined peaks were observed in all cases, directly assignable to the electro-oxidation of deoxyguanosine monophosphate.

An improved electrode design to perform electroanalytical measurements in organic solutions at elevated temperatures was constructed. In this method, a thin platinum wire is directly heated by ac current and an electrochemical signal at this wire is measured simultaneously. The electrode temperature in THF was determined by investigating the open circuit potential of the redox couple ferrocene|ferrocenium. The heating effects are demonstrated by cyclovoltammetric measurements of ferrocene at different scan rates and temperatures. The observed mass transport limiting current values strongly depend on the temperature. The quality of the measurements was examined using an Arrhenius plot. Keywords: Hot wire electrochemistry, Ac heating, Cyclic voltammetry, Cylindrical microelectrodes, Ferrocene, Tetrahydrofuran

A simple galvanic cell without any external voltage for the trace determination of hydrogen sulphide is described. The signal corresponds to the concentration of the dissolved molecular H2S. For the calculation of total sulphide, the pH has to be taken into consideration. The sensor was tested in the range of concentration from 3·10−6 mol/l H2S to 9·10−5 mol/l H2S for pH

A directly heated mercury film electrode (MFE) extends the operational capabilities of the hot layer technique to a wide range of electroanalytical systems. Wires or layers of gold and platinum have been used as sensors so far, but they were suitable only for the analysis of a small number of metals. The development of a heated MFE is described, including electrode construction and mercury deposition procedures. The thermal properties of the sensor were investigated. As a first application, cadmium was determined by anodic stripping voltammetry (ASV) with the result of an improved signal-to-background ratio. Keywords: Mercury film electrodes, Heated electrodes, Iridium, Anodic stripping voltammetry, Cadmium

Voltammetry with continuously heated microelectrodes yields well-defined sigmoidal current-voltage curves. Unlike hydrodynamic electrodes, the surface temperature of a heated electrode can be adjusted arbitrarily within a certain range. Inside a thermal layer, a virtually stagnant diffusion layer of constant thickness δ diff exists. δ diff is independent of temperature within a certain range. On the basis of this theory, equations are derived which play a similar role to, for instance, the Levich equation for the rotating disk electrode. Reasonable agreement of the derived relationship with the results from voltammetric experiments is obtained.

The electrodeposition of lead on boron-doped diamond has been studied with a view to identifying the fundamental parameters controlling the sensitivity and lower detection limit in anodic stripping voltammetry. Chronoamperometric transients are used to explore the deposition, indicating a progressive growth mechanism confirmed by ex situ AFM images. Linear sweep ASV experiments show a threshold concentration of ca 10−6 M below which no lead is detected; this is attributed to the need for nucleation of the solid phase on the electrode. Experiments with variable temperature show that this threshold can be usefully lowered at elevated temperatures.

Microelectrode wires heated directly in situ by an electric current generate mass as well as heat energy transport phenomena. With continuous heating, a stationary surface temperature is established as a result of thermally promoted convection. The geometry of concentration and temperature profiles under these conditions are investigated by cyclic voltammetry, potential step experiments, and finite element simulation of convection and diffusion processes. It is shown that the Nernst diffusion layer approaches a constant, temperature-independent thickness if the temperature difference between bulk and electrode surface exceeds ca. 30 K in aqueous solution. At continuously heated wire electrodes, diffusion coefficient values as well as kinetic data can be determined under well-defined temperature conditions, and in a very convenient way.

A new electrochemical technique is presented that allows peak-shaped voltammograms to be recorded at local temperature values from room temperature to above boiling point. This new method, temperature pulse voltammetry (TPV), is analogous to differential pulse voltammetry (DPV), but makes use of temperature jumps instead of potential pulses. Fundamentals are presented and potentialities demonstrated. As an example, ferrocyanide is investigated using a new kind of heated electrode on the basis of screen-printed gold layer structures on low-temperature cofired ceramics (LTCC) substrates. Keywords: Hot-layer electrochemistry, Temperature pulse voltammetry, Differential pulse voltammetry, Low-temperature cofired ceramics, Heated electrodes, Redox entropy