A DNA sensor has been proposed on the platform of glassy carbon electrode modified with native DNA implemented between two electropolymerized layers of polyaniline. The surface layer was assembled by consecutive stages of potentiodynamic electrolysis, DNA drop casting, and second electrolysis, which was required for capsulation of the DNA molecules and prevented their leaching into the solution. Surface layer assembling was controlled by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force, and scanning electron microscopy. For doxorubicin measurement, the DNA sensor was first incubated in the Methylene blue solution that amplified signal due to DNA intercalation and competition with the doxorubicin molecules for the DNA binding sites. The charge transfer resistance of the inner layer interface decreased with the doxorubicin concentration in the range from 1.0 pM to 0.1 μM (LOD 0.6 pM). The DNA sensor was tested for the analysis of spiked artificial urine samples and showed satisfactory recovery in concentration range of 0.05–10 μM. The DNA sensor developed can find application in testing of antitumor drugs and some other DNA damaging factors.
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.
Mycotoxins are secondary metabolites of fungi that contaminate agriculture products. Their release in the environment can cause severe damage to human health. Aptasensors are compact analytical devices that are intended for the fast and reliable detection of various species able to specifically interact with aptamers attached to the transducer surface. In this review, assembly of electrochemical and surface plasmon resonance (SPR) aptasensors are considered with emphasis on the mechanism of signal generation. Moreover, the properties of mycotoxins and the aptamers selected for their recognition are briefly considered. The analytical performance of biosensors developed within last three years makes it possible to determine mycotoxin residues in water and agriculture/food products on the levels below their maximal admissible concentrations. Requirements for the development of sample treatment and future trends in aptasensors are also discussed.
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).
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