Table of Contents

Abstract: This review focuses on the stability of voltammetric signals recorded overperiods of months with carbon paste electrodes (CPEs) implanted in the brain. The keyinteraction underlying this stability is between the pasting oil and brain lipids that arecapable of inhibiting the fouling caused by proteins. In brain regions receiving a significantdopaminergic input, a peak due to the methylated metabolites of dopamine, principallyhomovanillic acid (HVA), is clearly resolved using slow sweep voltammetry. Although anumber of factors limit the time resolution for monitoring brain HVA concentrationdynamics, the stability of CPEs allows investigations of long-term effects of drugs, as wellas behavioral studies, not possible using other in-vivo monitoring techniques.

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Abstract: An electrochemical DNA biosensor based on recognition of double or singlestranded DNA (ds-DNA/ss-DNA) immobilised on a self-assembled modified gold electrodeis presented for denaturalisation and hybridisation detection. DNA is covalently bond on aself assembled 3-mercaptopropionic acid monolayer by using water soluble N-3-(dimethylaminopropyl)-N´ethylcarbodiimide hydrochloride (EDC) and Nhydroxisulfosuccinimide(NHSS) as linkers. The interaction between the immobilised DNAand methylene blue (MB) is investigated using square wave voltammetry (SWV). Theincrease or diminution of peak currents of the MB upon the hybridisation or denaturalisationevent at the modified electrode surface is studied.

Abstract: Novel DNA-sensor with enzymatic amplification of the signal has beendeveloped on the base of glassy carbon electrode modified with ds-DNA and horseradishperoxidase (HRP). Phenothiazine dyes Methylene Blue and Methylene Green were used aselectrochemical markers for the detection of sulfonamide and anthracycline preparationsable to interact with DNA. The biosensor signal related to HRP oxidation of the markersdepends on the relation between their bonded and readily oxidized forms which depends onthe nature and concentration of pharmaceuticals. Sulfonamides diminish surfaceconcentration of MB accessible for HRP reaction whereas anthracyclines releaseintercalated marker and increase the signal. The DNA-HRP sensor developed makes itpossible to detect down to 0.002 nmol L^-1 of sulfamethoxazole, 0.1 nmol L^-1 of sulfadiazine,0.01 nmol L^-1 of sulfamethazine, 0.1 nmol L^-1 of sulfaguanine, 0.05 μmol L^-1 of rubomycinand 0.08 μmol L^-1 of doxorubicin.

Abstract: Electrochemical devices have received particular attention due to their rapiddetection and great sensitivity for the evaluation of DNA-hazard compounds interactionmechanisms. Several types of bioanalytical method use nucleic acids probes to detect DNAdamage. This article reviews current directions and strategies in the development andapplications of electrochemical DNA sensors for the detection of DNA damage.

Abstract: An electrochemical DNA-based biosensor is proposed as a fast and easyscreening method for the detection of genotoxic compounds in soil samples. The biosensorwas assembled by immobilising double stranded Calf thymus DNA on screen-printedelectrodes. The interactions between DNA and environmental pollutants can causevariations of the electrochemical proprieties of DNA when they cause a DNA damage.Preliminary studies were performed using benzene, naphthalene and anthracene derivativesas model compounds. The effect of these compounds on the surface-confined DNA wasfound to be linearly related to their concentration in solution. On the other hand, theobjective was to optimise the ultrasonic extraction conditions of these compounds fromartificially spiked soil samples. Then, the applicability of such a biosensor was evaluated byanalysing soil samples from an Italian region with ecological risk (ACNA of Cengio, SV).DNA biosensor for qualitative analysis of soil presented a good correlation with a semiquantitativemethod for aromatic ring systems determination as fixed wavelengthfluorescence and interestingly, according results were found also with other bioassays.This kind of biosensors represent a new, easy and fast way of analysis of polluted sites, therefore they can be used as early warnings devices in areas with ecological risk as in situ measurement.

Abstract: DNA biosensor can serve as a powerfull tool for simple in vitro tests of chemicaltoxicity. In this paper, damage to DNA attached to the surface of screen-printed carbonelectrode by arsenic compounds in solution is described. Using the Co(III) complex with1,10-phenanthroline, [Co(phen)₃]³⁺ , as an electrochemical DNA marker and the Ru(II)complex with bipyridyne, [Ru(bipy)₃]²⁺ , as a DNA oxidation catalyst, the portion of originaldsDNA which survives an incubation of the biosensor in the cleavage medium was evaluated.The model cleavage mixture was composed of an arsenic compound at 10-3 mol/Lconcentration corresponding to real contaminated water, 2x10^-4 mol/L Fe(II) or Cu(II) ions asthe redox catalyst, and 1.5x10^-2 mol/L hydrogen peroxide. DNA damage by arsenite,dimethylarsinic acid as the metabolic product of inorganic arsenic and widely used herbicide,as well as phenylarsonic acid and p-arsanilic acid as the representatives of feed additives wasfound in difference to arsenate.

Abstract: In this work we present a critical study of the nucleic acid layer immobilized atglassy carbon electrodes. Different studies were performed in order to assess the nature of theinteraction between DNA and the electrode surface. The adsorption and electrooxidation of DNAdemonstrated to be highly dependent on the surface and nature of the glassy carbon electrode. TheDNA layer immobilized at a freshly polished glassy carbon electrode was very stable even afterapplying highly negative potentials. The electron transfer of potassium ferricyanide, catechol anddopamine at glassy carbon surfaces modified with thin (obtained by adsorption under controlledpotential conditions) and thick (obtained by casting the glassy carbon surface with highly concentratedDNA solutions) DNA layers was slower than that at the bare glassy carbon electrode, although thiseffect was dependent on the thickness of the layer and was not charge selective. Raman experimentsshowed an important decrease of the vibrational modes assigned to the nucleobases residues,suggesting a strong interaction of these residues with the electrode surface. The hybridization ofoligo(dG)₂₁ and oligo(dC)₂₁ was evaluated from the guanine oxidation signal and the reduction of theredox indicator Co(phen)₃³⁺ . In both cases the chronopotentiometric response indicated that thecompromise of the bases in the interaction of DNA with the electrode surface is too strong, preventingfurther hybridization. In summary, glassy carbon is a useful electrode material to detect DNA in adirect and very sensitive way, but not to be used for the preparation of biorecognition layers by directadsorption of the probe sequence on the electrode surface for detecting the hybridization event.

Abstract: The paper describes successful coupling of adsorptive transfer stripping (AdTS) andelimination voltammetry with linear scan (EVLS) for the resolution of reduction signals of cytosine (C)and adenine (A) residues in hetero-oligodeoxynucleotides (ODNs). Short ODNs (9-mers and 20-mers)were adsorbed from a small volume on a hanging mercury drop electrode (HMDE). After washing ofthe ODN-modified electrode by water and its transferring to an electrochemical cell, voltammetric curves were measured. The AdTS EVLS was able to determine of C/A ratio of ODNs through theelimination function conserving the diffusion current component and eliminating kinetic and chargingcurrent components. This function, which provides the elimination signal in a peak-counterpeak form,increased the current sensitivity for A and C resolution, and for the recognition of bases sequences inODN chains. Optimal conditions of elimination experiments such as pH, time of adsorption, and scanrate were found. The combination of EVLS with AdTS procedure can be considered as a newdetection method in a DNA sensor.