Binary and Ternary Deep Eutectic Solvents for Methylene Green Electropolymerization on Multiwalled Carbon Nanotubes: Optimization, Characterization and Application.

Choline chloride (ChCl) based binary and ternary deep eutectic solvents (DES) were evaluated for methylene green electropolymerization with oxalic acid (OA) and ethylene glycol (EG) as hydrogen bond donors. Binary DES ChCl : OA in molar ratios 1 : 1 and 2 : 1 and ChCl : EG 1 : 2 and ternary DES (tDES) in different molar ratios and percentages of water were evaluated. The highest polymer growth was in ChCl : OA : EG-tDES with 13% added water, that had a lower viscosity and higher ionic conductivity when associated with HCl as dopant. This enhanced the formation of more cation radicals and, consequently, more polymer formation. The PMG/MWCNT/GCE-tDES sensor was successfully applied to the simultaneous determination of 5-aminosalicylic acid (5-ASA) and acetaminophen (APAP) by differential pulse voltammetry in the concentration range 1 µM-200 µM, with detection limits of 0.37 µM and 0.49 µM for 5-ASA and APAP, respectively. The sensor demonstrated good repeatability, reproducibility and stability, and was successfully applied in pharmaceutical formulations.

In situ evaluation of gemcitabine-DNA interaction using a DNA-electrochemical biosensor.

The electrochemical behaviour of the cytosine nucleoside analogue and anti-cancer drug gemcitabine (GEM) was investigated at glassy carbon electrode, using cyclic, differential pulse and square wave voltammetry, in different pH supporting electrolytes, and no electrochemical redox process was observed. The evaluation of the interaction between GEM and DNA in incubated solutions and using the DNA-electrochemical biosensor was studied. The DNA structural modifications and damage were electrochemically detected following the changes in the oxidation peaks of guanosine and adenosine residues and the occurrence of the free guanine residues electrochemical signal. The DNA-GEM interaction mechanism occurred in two sequential steps. The initial process was independent of the DNA sequence and led to the condensation/aggregation of the DNA strands, producing rigid structures, which favoured a second step, in which the guanine hydrogen atoms, participating in the C-G base pair, interacted with the GEM ribose moiety fluorine atoms.