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The emergence of the coronavirus 2019 (COVID-19) arose the need for rapid, accurate and massive virus detection methods to control the spread of infectious diseases. In this work, a device, deployable in non-medical environments, has been developed for the detection of non-amplified SARS-CoV-2 RNA. A SARS-CoV-2 specific probe was designed and covalently immobilized at the surface of glass slides to fabricate a DNA biosensor. The resulting system was integrated in a microfluidic platform, in which viral RNA was extracted from non-treated human saliva, before hybridizing at the surface of the sensor. The formed DNA/RNA duplex was detected in presence of SYBR Green I using an opto-electronic system, based on a high-power LED and a photo multiplier tube, which convert the emitted fluorescence into an electrical signal that can be processed in less than 10 min. The limit of detection of the resulting microfluidic platform reached six copies of viral RNA per microliter of sample (equal to 10 aM) and satisfied the safety margin. The absence of non-specific adsorption and the selectivity for SARS-CoV-2 RNA were established. In addition, the designed device could be applicable for the detection of a variety of viruses by simple modification of the immobilized probe.

For anticancer therapy and disease prognosis in breast cancer, three PIK3CA point-mutations (H1047R, E545K, and E542K) play a significant role. To allow for specific and sensitive detection of these point-mutations with a hybridization-based detection concept, the assay conditions were optimized on a microarray technology platform. The resulting fluorescence-based microarray assay enables simultaneous and specific detection of three PIK3CA point-mutations. The optimized protocol was then adapted for use on a screen-printed and gold-plated silver sensor array with twelve working electrodes, one common counter electrode, and one common reference electrode. Chronoamperometric measurements employing an enzyme-amplified electrochemical assay allow for detecting PIK3CA point-mutations with a detection limit of 10 pM for short 24-mer target DNA. The mutant and the wild-type target DNA sequences gave significantly different signals in a broad concentration range of 1 nM – 100 nM, with the best separation found at 10 nM – 20 nM. Comparing the hybridization of short 24-mer and long 80-mer target DNA sequences reveals that the hybridization efficiency is reduced for long target DNA sequences. However, both the 24-mer and the 80-mer target DNA lead to successful detection of point-mutations. Finally, the electrochemical sensor allows for multiplexed detection of the three PIK3CA point-mutations.

Abstract Nucleic acids, the hereditary material of living beings, perform a vital role in major life activities including growth, heredity, and variation. The genetic information is coded in specific nitrogenous bases, which are the key players in genetic transformation and identification of hereditary diseases. Telomeres are specialized DNA structures present at the end of eukaryotic chromosomes, consisting of repetitive non-transcribed sequences (TTAGGG) and some binding proteins. They protect the chromosomal ends from sticking to each other, and play a key role in the maintenance of genomic integrity. Currently, a number of methods are reported for nucleic acids and telomeres detection but they are not easy going. Therefore, development of sensitive and fast DNA-biosensors to measure the nucleic acids and telomeres sequences is of great importance. This paper describes a systematic study on the preparation of simple ultrathin films (UTFs) composite of fluorescent dye 4′,6-diamidino-2-phenylindole (DAPI), having binding properties in the minor groove of AT-rich DNA segments, blending with single-stranded DNA (ssDNA) and incorporation into layered double hydroxides (LDH) nanosheets using layer-by-layer self-assembly method. The resulting UTFs exhibits excellent sensitivity, selectivity and reversibility for long complementary ssDNA sequence on the basis of DNA hybridization and fluorescence enhancement strategy. The dynamic range was 3–20 μg/mL with a detection limit of 20 μg/mL. This new (ssDNA @DAPI/LDHs) n UTFs, could be an efficient hybrid composite with potential applications in the field of bioluminescent sensoring materials. Graphical abstract Image 1 Highlights • DAPI@ssDNA was assembled into LDH nanosheets by the LbL method making UTFs. • The UTFs showed uniform and long-range-ordered periodic layered structure. • It can be used to detect the telomere sequence with various lengths. • The UTFs has potential applications in the field of bioluminescent sensoring materials. [ABSTRACT FROM AUTHOR]

As part of the ongoing evolution towards personalized anticancer therapy, mutation screening is becoming increasingly important and, therefore, also alternative detection strategies that allow for fast genetic diagnostics at the point of care. In the case of breast cancer, detecting cancer-associated point mutations in the PIK3CA gene is of particular importance for treatment decisions. We developed a recombinase polymerase amplification assay combined with an enzyme-linked electrochemical assay on multi-channel screen-printed gold sensors for specific and highly sensitive detection of three PIK3CA point mutations (H1047R, E545K, and E542K). Recombinase polymerase amplification (RPA) of the target sequences was optimized and characterized with a real-time RPA assay. Comparison with real-time PCR reveals that RPA is slightly inferior in terms of efficiency and sensitivity. However, the desired target DNA is successfully amplified at initial concentrations down to 100 copies μL−1. For electrochemical readout, biotinylated dCTP is used to label the target DNA during RPA. Single-stranded target DNA is produced with either asymmetric RPA or symmetric RPA followed by lambda exonuclease digestion. Characterization of the two different approaches in terms of sensitivity results in comparable detection limits (229 copies μL−1 and 224 copies μL−1, respectively), though RPA followed by lambda exonuclease digestion yields significantly higher currents. Finally, this method, together with a designed wild-type blocking oligo that inhibits binding of the wild-type target DNA during probe-target hybridization, allows for detecting the PIK3CA point mutations H1047R, E545K, and E542K in the presence of wild-type target DNA when the proportion of mutant target DNA is >20%. [Display omitted] • Recombinase polymerase amplification combined with electrochemical detection. • SsDNA generation via asymmetric RPA or lambda exonuclease digestion. • Enzyme-linked electrochemical assay on multi-channel screen-printed sensors. • Multiplex electrochemical detection of three different PIK3CA point mutations. • Improved mutation-specificity by using wt-blocking oligos during hybridization. [ABSTRACT FROM AUTHOR]

Herein, a facile and highly sensitive electroanalytical tool for monitoring and quantifying the antineoplastic drug gemcitabine in real sample was provided. In this regard, a novel DNA-biosensor based on Pt-doped ZnO decorated single walled carbon nanotubes (Pt–ZnO/SWCNTs) hybrid nanomaterial modification of glassy carbon electrode (GCE) was fabricated. Ds-DNA (Calf Thymus), as a biological recognition element, was decorated onto nanomaterial-modified GCE via layer-by-layer fabrication strategy to attain ultimate biosensor ds-DNA/Pt–ZnO/SWCNTs/GCE. The characterizations confirmed the successful fabrication of hybrid nanomaterial, as well as the modification of electrode surface by fabricated nanomaterial. The electrochemical impedance spectroscopy (EIS) analysis revealed that the nanomaterial modification of GCE surface enhanced the electrical conductivity thanks to the synergistic effects of Pt–ZnO and SWCNTs structures, thereby boosted the electrocatalytic activity of the resultant biosensor. The electrochemical characterization results showed that the suggested biosensor is capable of detecting gemcitabine in a wide concentration range of 0.01–30.0 μM, with a detection limit of 5.0 nM. The intercalation binding mode of Gemcitabine inside guanine and cytosine rich region of DNA receptor was approved by molecular docking study. The results of the experimental data were well congruent with the molecular docking analysis, which showed that the binding mode of gemcitabine drug with ds-DNA was intercalation. [Display omitted] • Gemcitabine drug intercalation with ds-DNA. • A DNA-biosensor for Gemcitabine monitoring confirmed by molecular docking study. • Pt–ZnO/SWCNTs as new catalyst to fabrication of electrochemical biosensor. [ABSTRACT FROM AUTHOR]

Abstract: We report the effect of electrochemical anodization on the properties of monolayer graphene as the main aim of this research and consequently using the resulting label‐free impedimetric biosensor for DNA sequences detection. Monolayer graphene was grown by chemical vapor deposition (CVD) with methane as precursor on copper foil, transferred onto a glassy carbon electrode and electrochemically anodized. Raman spectroscopy and X‐Ray photo electron spectroscopy revealed enhancement of defect density, roughness and formation of C−O−C, C−O−H and C=O functional groups after anodization. Amine‐terminated poly T probe was linked covalently to the carboxylic groups of anodized graphene by the zero‐length linker to fabricate the impedance‐based DNA biosensor. The anodized graphene electrode demonstrated a superior performance for electrochemical impedance detection of DNA. The DNA biosensor showed a large linear dynamic range from 2.0×10−18 to 1.0×10−12 M with a limit of detection of 1.0×10−18 M using electrochemical impedance spectroscopy (EIS) method. Equivalent circuit modeling shows that DNA hybridization is detected through a change in charge transfer resistance. [ABSTRACT FROM AUTHOR]

• Comparing noble metal screen-printed sensors for EC detection of point-mutations. • Investigation of surface topography, sensitivity, and immobilization efficiency. • Study of hybridization specificity for detecting three different point-mutations. • Improved mutation specificity achieved by AuNP modification of the sensors. Screen-printed electrochemical sensors are of particular interest for point-of-care diagnostic applications due to their high sensitivity, short analysis times, and cost-efficient large-scale fabrication. Especially noble metal-based sensors offer the possibility of easy surface modification via self-assembly of thiol-labelled compounds. We examined silver, gold, and palladium as electrode materials regarding their suitability for highly specific and sensitive DNA detection with a chronoamperometric enzyme-amplified electrochemical assay. Modification with either gold nanoparticles or silver-coated microbeads was tested as a possibility to improve the performance of the electrochemical sensors. The sensors were characterized regarding surface topography, sensitivity towards the redox-active substrate TMB, efficiency of capture probe immobilization, as well as mutation specificity. The highest sensitivity for oxidized TMB was observed for gold sensors that yielded a limit of detection of 2.1 µM, while no improvement in sensitivity was observed for sensors modified with gold nanoparticles or silver-coated microbeads. DNA probe immobilization and multiplexed target DNA detection was successful with all tested electrode materials. However, modification with silver-coated microbeads led to both reduced probe immobilization efficiency and hybridization specificity. Gold nanoparticle modification of both silver and of gold sensors induced a highly porous sensor surface after sintering, which increases the surface area of the electrodes. The gold nanoparticle modified sensors showed particularly appreciable results in terms of improved hybridization specificity, as demonstrated by successful multiplexed detection of three PIK3CA point-mutations (H1047R, E545K, and E542K). Average discrimination factors D of 2.7 and 2.1 were obtained for gold and silver sensors modified with one layer of gold nanoparticles, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

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The emergence of the coronavirus 2019 (COVID-19) arose the need for rapid, accurate and massive virus detection methods to control the spread of infectious diseases. In this work, a device, deployable in non-medical environments, has been developed for the detection of non-amplified SARS-CoV-2 RNA. A SARS-CoV-2 specific probe was designed and covalently immobilized at the surface of glass slides to fabricate a DNA biosensor. The resulting system was integrated in a microfluidic platform, in which viral RNA was extracted from non-treated human saliva, before hybridizing at the surface of the sensor. The formed DNA/RNA duplex was detected in presence of SYBR Green I using an opto-electronic system, based on a high-power LED and a photo multiplier tube, which convert the emitted fluorescence into an electrical signal that can be processed in less than 10 min. The limit of detection of the resulting microfluidic platform reached six copies of viral RNA per microliter of sample (equal to 10 aM) and satisfied the safety margin. The absence of non-specific adsorption and the selectivity for SARS-CoV-2 RNA were established. In addition, the designed device could be applicable for the detection of a variety of viruses by simple modification of the immobilized probe., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Authors.)

We report on the design of electrochemical DNA-biosensors made from 15, 25 and 50 μm diameter gold ultramicroelectrodes (UMEs) in a two-electrode setup. The biosensors were prepared by chemical adsorption of 22-base thiol-labeled DNA-probes in a self-assembled monolayer configuration onto the surface of the gold UME. Hybridization events were transduced by Fe III /Fe II redox process electro-mediated by DNA-redox intercalated mediators. The optimization of the DNA-biosensors was achieved by using different Fe III /Fe II ligands (cyanide, cefadroxil, deferoxamine) and intercalators (methylene blue, proflavine). Optimized biosensors allowed direct and selective amperometric detection in the femtomolar range and of single mismatch within a 35 minutes protocol. [ABSTRACT FROM AUTHOR]

In this research, we have developed lable free DNA biosensors based on modified glassy carbon electrodes (GCE) with reduced graphene oxide (RGO) and carbon nanotubes (MWCNTs) for detection of DNA sequences. This paper compares the detection of BRCA1 5382insC mutation using independent glassy carbon electrodes (GCE) modified with RGO and MWCNTs. A probe ( BRCA1 5382insC mutation detection (ssDNA)) was then immobilized on the modified electrodes for a specific time. The immobilization of the probe and its hybridization with the target DNA (Complementary DNA) were performed under optimum conditions using different electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed biosensors were used for determination of complementary DNA sequences. The non-modified DNA biosensor (1-pyrenebutyric acid-N- hydroxysuccinimide ester (PANHS)/GCE), revealed a linear relationship between ∆ R ct and logarithm of the complementary target DNA concentration ranging from 1.0×10 −16 mol L −1 to 1.0×10 −10 mol L −1 with a correlation coefficient of 0.992, for DNA biosensors modified with multi-wall carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) wider linear range and lower detection limit were obtained. For ssDNA/PANHS/MWCNTs/GCE a linear range 1.0×10 −17 mol L −1 –1.0×10 −10 mol L −1 with a correlation coefficient of 0.993 and for ssDNA/PANHS/RGO/GCE a linear range from 1.0×10 −18 mol L −1 to 1.0×10 −10 mol L −1 with a correlation coefficient of 0.985 were obtained. In addition, the mentioned biosensors were satisfactorily applied for discriminating of complementary sequences from noncomplementary sequences, so the mentioned biosensors can be used for the detection of BRCA1 -associated breast cancer. [ABSTRACT FROM AUTHOR]

In this study, a new methodology was used to develop a novel and sensitive electrochemical DNA biosensor for determination of furazolidone. This biosensor was fabricated from TiO 2 -reduced graphene oxide (rGO) modified-carbon paste electrode (CPE) decorated with ds-DNA. The oxidation signals of guanine and adenine were used as probes to study the interactions, using differential pulse voltammetry. By interaction of furazolidone with the ds-DNA, the oxidation peaks current of guanine and adenine were decreased at the modified-CPE. A linear dependence of the guanine and adenine oxidation signals with furazolidone concentration were observed in the range of 1.0–150.0 pmol L −1 with a detection limit of 0.55 and 0.43 pmol L −1 based on guanine and adenine signals, respectively. The relative standard deviation for five replicate measurements of 10.0 pmol L −1 furazolidone was 4.3%. The influence of potential interfering compounds on the selectivity was studied. This biosensor was successfully applied for determination of trace amounts of furazolidone in real samples. [ABSTRACT FROM AUTHOR]

A simple and inexpensive methodology was used to develop a new method in order to inspect the DNA damage due to dopamine and some ionic metals. In addition, the inhibitory and repair effects of some antioxidant such as glutathione and ascorbic acid were studied and compared with each other using electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). In this work a pencil graphite electrode (PGE) was modified with multiwall carbon nanotubes (MWCNTs) and chitosan (CHIT), then it was decorated with a ds-DNA (ds-DNA/CHIT–MWCNTs/PGE). Due to interaction of ds-DNA and the damaging agents (dopamine + metallic ions), electrochemical and spectroscopy properties of ds-DNA at the surface of the modified electrode was changed, and these changes are followed with EIS and DPV methods. Our study showed that dopamine, Cu(II) and Fe(III) alone could not destroy DNA, but dopamine + Cu(II) and dopamine + Fe(III) can damage DNA. In addition, the ability of dopamine–Cu(II) was greater than dopamine–Fe(III). Moreover, some antioxidant such as glutathione and ascorbic acid can overcome and/or minimize the influence of these damaging interactions. [ABSTRACT FROM AUTHOR]

A novel, selective, rapid and simple electrochemical method is developed for the determination of atropine sulfate. UV–Vis and differential pulse voltammetry are used to study the interaction of atropine sulfate with salmon sperm ds-DNA on the surface of salmon sperm ds-DNA modified-pencil graphite electrode (PGE). For this purpose, a pencil graphite electrode (PGE) modified with multiwall carbon nanotubes (MWCNTs), titanium dioxide nanoparticles (TiO 2 NPs), and poly-dialyldimethylammonium chloride (PDDA) decorated with ds-DNA is tested for the determination of atropine sulfate. The electrochemical oxidation peak current of adenine and guanine bonded on the surface of ds-DNA/PDDA–TiO 2 NPs–MWCNTs/PGE is used to obtain the analytical signal. Decreases in the intensities of guanine and adenine oxidation signals after their interaction with atropine sulfate are used as indicator signals for the sensitive determination of atropine sulfate. Using ds-DNA/PDDA–TiO 2 NPs–MWCNTs/PGE and based on the guanine signal, linear calibration curves were obtained in the range of 0.6 to 30.0 μmol L −1 and 30.0 to 600.0 μmol L −1 atropine sulfate with low detection limits of 30.0 nmol L −1 . The biosensor shows a good selectivity for the determination of atropine sulfate. Finally, the applicability of the biosensor is evaluated by measuring atropine sulfate in real samples with good accuracy. [ABSTRACT FROM AUTHOR]

Abstract: The proof of concept of a DNA-biosensor based on a two-electrode electrochemical setup and using a microelectrode as working electrode, well adapted for detection in microliter samples and miniaturization, is presented herein. A 23-base DNA-probe self-assembled monolayer was first formed onto a 50μm-diameter gold surface. The microelectrode extremity was then immersed in a 50μL DNA-target solution drop itself deposited onto a 2mm-diameter gold counter electrode. Transduction occurs via long-range electron transfer, which is enhanced subsequently to hybridization, due to DNA-base π-stacking. Single mismatch detection of this first prototype was matched at room temperature in the nanomolar range without any optimization. [Copyright &y& Elsevier]

Abstract: DNA testing requires the development of sensitive and fast devices to measure the presence of nucleic acid sequences by DNA hybridization. In this paper, a simple and label-free DNA-biosensor has been investigated based on the detection of DNA hybridization on layered double hydroxide (LDH) nanomaterials with special emphasis on targeting long single stranded DNA sequences. First, the immobilization of a 20 bases long DNA probe on a thin layer of Mg2AlCO3 and Mg3AlCO3 LDH was studied. Then, DNA hybridization reaction was detected by means of Electrochemical Impedance Spectroscopy. The resulting biosensor showed a high sensitivity for the detection of 80 bases long DNA complementary sequences. The dynamic range was 18–270ng/ml with a detection limit lower than 1.8ng/ml. [Copyright &y& Elsevier]

Abstract: A simple and inexpensive methodology was used to develop a novel electrochemical sensor for the determination of Sudan II. The interaction of Sudan II with salmon sperm ds-DNA on the surface of salmon sperm ds-DNA-modified pencil graphite electrode (PGE) and in solution phase was studied, using differential pulse voltammetry. The difference between adenine and guanine signals of the ds-DNA after and before interaction with Sudan II was directly proportional to Sudan II concentration, which used for quantitative inspections. Using PGE, a linear calibration curve (R 2 =0.9958) was observed with 0.5–6.0μgmL−1 Sudan II. Furthermore, the LOD of 0.4μgmL−1 and linear range between 0.5 and 4.0μgmL−1 were achieved in solution phase. In the second part, Sudan II was determined on a pretreated pencil graphite electrode by means of adsorptive stripping differential pulse voltammetry. The peak current was linearly dependent on Sudan II concentration over the range of 0.0015–0.30μgmL−1, with a detection limit of 0.00007μgmL−1 Sudan II. Both ds-DNA-modified PGE and PPGE were applied to analyze Sudan II in real samples. [Copyright &y& Elsevier]

Abstract: We report on the binding of cisplatin, carboplatin and oxaliplatin to double-stranded DNA in two different (phosphate and carbonate) buffers, using an electrochemical DNA-biosensor. The propensity of the electrophilic agent produced by hydrolysis to interact with DNA was measured as a function of the decrease of guanine oxidation signal of the metal–DNA adduct immobilized on a screen-printed electrode, by using square wave voltammetry. The results obtained confirm that carbonate reacts with platinum drugs to form activated carbonato complexes, which are able to react readily with DNA. [Copyright &y& Elsevier]

Abstract: In order to better understand the adsorption mechanism of nucleic acids at electrode surface, MAC Mode atomic force microscopy (MAC Mode AFM) was used to investigate the adsorption of a 10-base synthetic oligodeoxynucleotide (ODN) with the sequence 5′-CTTTTTCTTT-3′ containing only pyrimidinic bases, onto a highly oriented pyrolytic graphite (HOPG) electrode. Free adsorption and adsorption at applied potentials of +0.30 and +0.65V versus AgQRE, were carried out. AFM images in air demonstrated that the molecules adsorb spontaneously on the electrode surface. The ODNs have the tendency to self-assemble from solution onto the solid support in a tight and well-spread two-dimensional lattice covering the entire surface, showing the existence of different molecular conformations and exposing parts of the HOPG surface. The degree of surface coverage and the adsorption pattern were directly dependent on ODN concentration and immobilization procedure. During free adsorption, the hydrophobic interactions of the ODNs with the HOPG represent the main adsorption mechanism. When a positive potential is applied to the HOPG, electrostatic interactions between the positively charged electrode surface and the negatively charged sugar-phosphate backbones of ODNs are predominant. [Copyright &y& Elsevier]

Abstract: DNA adsorption on electrode surfaces is of fundamental interest for the development of DNA-based biosensors. The free adsorption of 10-mer synthetic oligodeoxynucleotides (ODNs) onto highly oriented pyrolytic graphite (HOPG) surfaces was studied using Magnetic AC mode atomic force microscopy (MAC Mode AFM). The mechanism of interaction of nucleic acids with carbon electrode surfaces was elucidated, using 10-mer synthetic homo- and hetero-ODNs sequences of known base sequences, because they allow clear interpretation of the experimental data. AFM images in air revealed different adsorption patterns and degree of HOPG surface coverage for the ODNs, and correlation with the individual structure and base sequence of each ODN molecule will be presented. The results demonstrated that the hydrophobic interactions with the HOPG hydrophobic surface explain the main adsorption mechanism, although other effects such as electrostatic and Van der Waals interactions may contribute to the free adsorption process. The ODNs interacted differently with the HOPG surface, according to the ODN sequence hydrophobic characteristics, being directly depending on the molecular mass, the hydrophobic character of the individual bases and on the secondary structure of the molecule. The importance of the type of base existent at the ODN chain extremities on the adsorption process was investigated and different adsorption patterns were obtained with ODN sequences composed by the same group of bases aligned in a different order. [Copyright &y& Elsevier]

The steady rise of observations of harmful or toxic algal blooms throughout the world in the past decades constitute a menace for coastal ecosystems and human interests. As a consequence, a number of programs have been launched to monitor the occurrence of harmful and toxic algae. However, the identification is currently done by microscopic examination, which requires a broad taxonomic knowledge, expensive equipment and is very time consuming. In order to facilitate the identification of toxic algae, an inexpensive and easy-to-handle DNA-biosensor has been adapted for the electrochemical detection of the toxic dinoflagellate Alexandrium ostenfeldii. The detection of the toxic algae is based on a sandwich hybridisation, which is carried out on a disposable sensor chip. A set of two probes for the species-specific identification of A. ostenfeldii was developed. The specificity of the probes could be shown in dot-blot hybridisations and with the DNA-biosensor. The sensitivity of the DNA-biosensor was optimised with respect to hybridisation temperature and NaCl-concentration and a significant increase of the sensitivity of the DNA-biosensor could be obtained by a fragmentation of the rRNA prior to the hybridisation and by adding a helper oligonucleotide, which binds in close proximity to the probes to the hybridisation. [Copyright &y& Elsevier]

The first and most important step in the development and manufacture of a sensitive DNA-biosensor for hybridization detection is the immobilization procedure of the nucleic acid probe on the transducer surface, maintaining its mobility and conformational flexibility. MAC Mode AFM images were used to demonstrate that oligonucleotide (ODN) molecules adsorb spontaneously at the electrode surface. After adsorption, the ODN layers were formed by molecules with restricted mobility, as well as by superposed molecules, which can lead to reduced hybridization efficiency. The images also showed the existence of pores in the adsorbed ODN film that revealed large parts of the electrode surface, and enabled non-specific adsorption of other ODNs on the uncovered areas. Electrostatic immobilization onto a clean glassy carbon electrode surface was followed by hybridization with complementary sequences and by control experiments with non-complementary sequences, studied using differential pulse voltammetry. The data obtained showed that non-specific adsorption strongly influenced the results, which depended on the sequence of the ODNs. In order to reduce the contribution of non-specific adsorbed ODNs during hybridization experiments, the carbon electrode surface was modified. After modification, the AFM images showed an electrode completely covered by the ODN probe film, which prevented the undesirable binding of target ODN molecules to the electrode surface. The changes of interfacial capacitance that took place after hybridization or control experiments showed the formation of a mixed multilayer that strongly depended on the local environment of the immobilized ODN. [Copyright &y& Elsevier]

Electrode surface characteristics represent an important aspect on the construction of sensitive DNA electrochemical biosensors for rapid detection of DNA interaction and damage. Two different immobilization procedures of double-stranded DNA (dsDNA) at the surface of a HOPG electrode were evaluated by MAC mode AFM performed in air. A thin dsDNA adsorbed film forming a network structure with holes exposing the electrode surface and a thick dsDNA film completely covering the electrode surface, presenting a much rougher structure, were investigated. The DNA surface characteristics and structure are discussed with respect to the degree of surface coverage. [Copyright &y& Elsevier]

The electrochemistry of 3,4-dibenzyl-2,5-dimethylthiophene-S-oxide was investigated as well as its interaction with dsDNA. The electrochemical study of the thiophene-S-oxide was performed at different pH values, in a mixed solvent and by solid state voltammetry, and showed that the molecule is reduced at a very negative potential, and the reduction is pH dependent. A glassy carbon electrode modified with a thick thiophene-S-oxide+dsDNA mixture was used to study the interaction of thiophene-S-oxide in situ with dsDNA at a charged interface. The experimental results give strong evidence that the reduced thiophene-S-oxide interacts with dsDNA causing damage with possible strand break and that the thiophene-S-oxide adduct formed with dsDNA can still undergo reduction. [Copyright &y& Elsevier]

The oxidation mechanism and adsorption of inosine 5′-monophosphate and hypoxanthine were investigated in solutions of different pH using voltammetric and impedance methods at glassy carbon electrodes. For both compounds, the pH dependence from differential pulse voltammetry showed that the same number of electrons and protons are involved in the rate-determining step of the electrochemical reaction. In the case of hypoxanthine, it was also possible to study the effect of different concentrations. At high concentrations of hypoxanthine, two oxidation peaks were observed, the first due to hypoxanthine oxidation with formation of oligomers and the second due to hypoxanthine oligomer oxidation, both compounds adsorbing strongly. Impedance measurements corroborated the voltammetric results and enabled the study of the adsorption of hypoxanthine on glassy carbon. [Copyright &y& Elsevier]

Adriamycin adsorbs strongly and irreversibly onto surfaces and this enabled electrochemical detection of in situ adriamycin oxidative damage to DNA. The adsorption of adriamycin onto glassy carbon and highly oriented pyrolytic graphite (HOPG) electrodes was studied by voltammetry and mode atomic force microscopy (MAC). At a glassy carbon electrode (GCE), the adsorbate has similar voltammetric behaviour to adriamycin in solution, which enabled the cyclic, differential pulse and square wave voltammetric study of the electron transfer reaction. The total surface concentration of adriamycin adsorbed onto GCE, from a 50 nM adriamycin solution during 3 min, was calculated to be 2.57×10−12 mol cm−2. The oxidation of adsorbed adriamycin is pH-dependent and corresponds to a two electron/two proton mechanism, and the detection limit for adriamycin adsorbed onto the GCE was 3.33×10−10 M. In situ AFM images show quick and spontaneous adsorption of the adriamycin onto a HOPG surface. Adriamycin forms a stable monolayer when adsorbed from different concentrations of adriamycin solutions and for short adsorption times. The strong and irreversible chemisorption of adriamycin onto carbon electrodes enables detection limits of the order of picomolar, which is much lower than the detection limits attainable by voltammetric methods for most organic compounds. [Copyright &y& Elsevier]

Benznidazole is a drug used commonly as a therapeutic agent against Chagas’ disease in Brazil. To clarify the cytotoxic action of benznidazole the electrochemical reduction of benznidazole has been investigated using a DNA-electrochemical biosensor, prepared by modification of a glassy carbon electrode with DNA, and the results compared with reduction at a bare glassy carbon electrode. The dependence of peak potential with pH follows slopes of 59 and 52 mV per pH unit in acid media, respectively, which corresponds to a mechanism involving the same number of electrons and protons. In neutral and alkaline solution no significant dependence of peak potential with pH was found. During the electrochemical reduction of benznidazole the formation of the hydroxylamine derivative occurs, involving a total of four electrons. The potentials for reduction were less negative when using the DNA-modified glassy carbon electrode than at the bare glassy carbon electrode although the mechanism was the same, and at pH 7.51 the peak current was four times higher than that obtained with the bare electrode. The DNA-biosensor enabled pre-concentration of the drug onto the electrode surface and the in situ damage caused to the DNA on the electrode surface by the product of benznidazole reduction could be detected electrochemically. The results are in agreement with the hypothesis that the hydroxylamine derivative is the reactive species responsible for the cytotoxic action of benznidazole. [Copyright &y& Elsevier]

Adriamycin intercalation and in situ interaction with double helix DNA was investigated using a voltammetric DNA-biosensor. Oxidation and reduction of adriamycin molecules intercalated in double helix DNA were investigated in order to understand the in vivo mechanism of action with this anti-neoplasic drug. The results showed that the interaction of adriamycin with DNA is potential-dependent causing contact between DNA guanine and adenine bases and the electrode surface such that their oxidation is easily detected. A mechanism for adriamycin reduction and oxidation in situ when intercalated in double helix DNA immobilised onto the glassy carbon electrode surface is presented and the formation of the mutagenic 8-oxoguanine explained. [Copyright &y& Elsevier]

Adriamycin, a cancerostatic anthracycline antibiotic, causes considerable death of tumour cells, together with the induction of breaks in DNA single and double strands. The interaction of this compound with DNA was investigated using an electrochemical DNA-biosensor. Adriamycin intercalation in DNA disrupts the double helix and the detection of guanine and 8-oxoguanine could mimic one possible mechanism for the in vivo adriamycin drug action. [Copyright &y& Elsevier]

We present new approaches to improve the efficiency of DNA by scanning probe microscopy using a highly specific hybridization on affine surfaces and nanostructures of gold as a labels. Scanning probe microscopy allows to register of individual acts of hybridization by the detection of gold labels on the surface affinity followed by automatic calculation of the total.