Methylene Blue Interactions with Chromosomal and Plasmid DNA on Screen‐Printed Carbon Electrodes

Abstract

Methylene blue (MB) is a typical photosensitizing agent and a DNA hybridization indicator, but its modes of interaction with the DNA molecules are not clearly described, particularly in relation to its electrochemical oxidation signals. To probe the DNA-MB interactions we have used chromosomal salmon testes and supercoiled plasmid sc pUC19 DNA immobilized on home-made screen-printed electrodes (SPEs) and a wide range of MB concentrations, from nano-to micromolar. The applicability of the home-made screen-printed electrodes used for the DNA-MB studies were tested using standard calf thymus DNA. Two MB oxidation peak signals: MB(I) at ca. À 0.18 V and MB(II) at 0 V vs. Ag/AgCl were detected within AE 10 -15% standard deviation, signals different from adsorbed MB signal (À 0.25 V, pH 4.7). The MB(I) signal, seen when both DNAs were used, showed two plateaus, one at nano-and another at micromolar MB concentrations; these were accompanied by the changes in the oxidation signal at 0.98 V, usually attributed to guanine oxidation. In contrast, the MB(II) signal was only seen for salmon testes DNA, indicating various modes of MB interactions with chromosomal and plasmid DNA. In the presence of MB, the guanine related signal (G) at 0.98 V has been amplified significantly (10 Â ), allowing for the identification of the DNAs at low DNA concentrations, the feature particularly useful in the plasmid sc pUC19 detection. The use of another DNA intercalator, riboflavin (RF), aided in the identification of the relation between MB(I), MB(II) and G oxidation signals.

The coupled photocycle of phenyl-p-benzoquinone and Light-Harvesting Complex II (LHCII) within the biohybrid system

“…All electrochemical experiments were carried out using a disposable planar screen-printed three-electrode system composed of a round graphite working electrode (geometric area of 0.07 cm 2 ), an Ag/AgCl pseudo-reference electrode (Ag/AgCl RE), and a graphite counter electrode. The properties of this graphite electrode (GE), as well as the procedure of cleaning and activation of the carbon surface, were described in details previously 12 , 44 . The potential of a pseudo-reference electrode in HEPES buffer (20 mM HEPES, 15 mM NaCl, 4 mM MgCl 2 , pH 7.5) was controlled against the saturated calomel electrode (SCE) and was equal to 0.080 ± 0.005 V. This gives a potential equal to 0.324 ± 0.005 V against a normal hydrogen electrode (NHE).…”

Voltammetric and Spectrophotometric Studies on DNA Interacting with Daunorubicin and its Amidino Derivatives

“…All electrochemical experiments were carried out using disposable planar screen‐printed three electrode system, which consisted of a round graphite working electrode (3 mm in diameter, geometric area 0.07 cm 2 ), an Ag/AgCl reference electrode, and a graphite counter electrode (geometric area 0.47 cm 2 ) .…”

“…The electrodes were cured after each screen‐printing step: silver paste and graphite paste for 15 min at 120 °C, and isolating paste for 30 s under UV light (2000 W Philips HOK 20/100). The testing of the applicability of the SPEs to the DNA studies were done in our previous experiments .…”