ИСТИНА

In this work polyaniline (PANI) was considered as a typical polyelectrolyte. A protonation function of PANI on pH, ionic strength, and the nature of the counterions was studied using potentiometric titration. It was found that the ionic strength of the model buffer affects the pH sensitivity of PANI by hindering its deprotonation in a wide pH range. Hence, it also affects the potentiometric response of the PANI electrodes to changes in pH and its double layer capacitance [1]. The obtained results can be well explained by polyelectrolyte counterions condensation that depends on the ionic strength of the chemical environment. Based on acquired knowledge, a potentiometric detection of the DNA hybridization with the use of PANI composite materials has been optimized and studied using PANI-Nylon films as indicator electrodes. We report that covalent and non-covalent immobilization of single stranded oligonucleotides (probe) can be carried out efficiently by at a narrow range of pH and the ionic strength. The decrease of the indicator electrode potential was observed during the immobilization due to electrostatic interactions between positively charged PANI and negatively charged phosphate groups of the oligonucleotide strands. The addition of the complementary stranded oligonucleotide (target) to the solution containing the functionalized indicator electrode (with the immobilized probe) leads to the increase of the indicator electrode potential due to the hybridization event occurring on the surface of PANI [2]. The formation of the double helix and its release form PANI surface was proved with fluorescent spectroscopy. The experiments with synthetic polyanions have shown that the addition of the negatively charged polymer (such as poly-(4-styrenesulfonic acid)) to the solution containing PANI as an indicator electrode causes only a minor response compared to that observed with the immobilized probe. This fact indicates that the interactions of single stranded oligonucleotides with PANI have rather a specific than electrostatic nature. The obtained results are important for fundamental understanding of the physicochemical processes occurring on the surface of conducting polymers and are of importance for development of electrochemical biosensors. References: 1. Wang, J. & Bard, A. J. On the Absence of a Diffuse Double Layer at Electronically Conductive Polymer Film Electrodes. Direct Evidence by Atomic Force Microscopy of Complete Charge Compensation. J. Am. Chem. Soc. 123, 498–499 (2001). 2. Zhou, Y., Yu, B., Guiseppi-Elie, A., Sergeyev, V. & Levon, K. Potentiometric monitoring DNA hybridization. Biosens. Bioelectron. 24, 3275–80 (2009).