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Voltammetric sensors have been developed on the bases of polyaniline and polymeric forms of methylene blue, methylene green, and neutral red obtained by multiple cycling of the potential. The integrity of the layers and expansion of the pH range of redox activity have been achieved by intermediate adsorption of native DNA that stabilized the oxidized polyaniline form. The formation of the coating layer was confirmed by electrochemical impedance spectroscopy and scanning electron microscopy. Model oxidants (ascorbic acid, hydroquinone, and quercetin) in the concentration range from 1 × 10−6 to 1 × 10−3 mol L−1 influenced the measured redox peaks of polymeric dyes with standard deviations from 2.4 to 5.5%. The peak currents were used for classification of tea brands using principal component analysis and linear discrimination analysis. The average discrimination of the tea brands purchased on local market was approximately 100%. The assessment of antioxidant properties of tea infusions was in agreement with results obtained using a coulometric bromine titration. [ABSTRACT FROM AUTHOR]

Mycotoxins are highly toxic metabolites of some fungi that frequently contaminate water, food and feed and hence cause several human and animal diseases. In this work, a new approach to the fast and reliable determination of aflatoxin M1 (AFM1) in water and milk has been proposed with reagent free protocol of signal measurement. For this purpose, DNA aptamer selective to AFM1 was entrapped between two thin layers of polyaniline (PANI) electrodeposited on glassy carbon electrode. The incubation of the aptasensor in the AFM1 solution results in remarkable decrease of the PANI intrinsic activity monitored by direct current voltammetry or electrochemical impedance spectroscopy. Appropriate calibration curves were linear in the range from 3 to 90 ng/L with limit of detection (LOD) 1–5 ng/L depending on the measurement mode. Mechanism of signal generation involves shielding electrostatic interactions between the PANI and aptamer in the surface layer and variation of its redox activity attributed to the emeraldine form of PANI. Selectivity of the response was proved by similar experiments with aflatoxin B1 and ochratoxin A and by comparison of the results with those obtained with non‐specific aptamer in the sensing layer. Simple protocol for milk pretreatment has been proposed for reliable detection of AFM1 on the level of its threshold limited values (20 ng/L). [ABSTRACT FROM AUTHOR]

New voltammetric DNA sensor has been developed on the base of glassy carbon electrode covered with electropolymerized polyaniline with entrapped native DNA saturated with Methylene blue. The thickness and redox properties of the coating are easily regulated by the number of potential cycles and pH of the solution. Doxorubicin competes with Methylene blue for DNA binding sites and suppresses the electron transfer within the layer. The measurement of the decay of the cathodic peak current made it possible to determine down to 0.01 nM doxorubicin. After that, DNA can be replaced by consecutive treatment of the biosensor with concentrated HCl and fresh DNA solution. Second involvement of DNA was confirmed by electrochemical impedance spectroscopy. The DNA sensor developed was tested on artificial samples mimicking ionic content of human serum and on commercial drug formulation containing doxorubicin. [ABSTRACT FROM AUTHOR]