ИСТИНА

Detection of microorganisms can be achieved by recognition of carbohydrate and hydroxy acids (mainly, sialic acid) commponents of their cells walls. Undoubtedly the most receptor for this purpose is the phenylboronic acid [1] able to bind polyols even being incorporated in a polymer chain [2]. We investigated conductivity of boronic acid substituted polyaniline by means of impedance spectroscopy. With the samples obtained after thorough optimization of 3-aminophenylboronic acid electropolymerization process we succeeded to observe an increase in the polymer conductivity as a result of injection of polyols in the working electrode medium. We note that in all previous reports the only conductivity decrease of boronic acid substituted polymers was registered under similar conditions. However, regular conductive and electroactive polymers (including unsubstituted polyaniline) also display a decrease in conductivity after injection of saccharides. This makes hardly possible to distinguish a specific signal versus an unspecific one. The great advantage of the proposed system is, that the specific signal resulting in conductivity increase, is generated in the opposite direction to the unspecific one. We confirmed that the impedimetric response resulted in conductivity increase is indeed due to complexation with polyols, by calculating from this effect binding constants with saccharides (glucose, fructose, galactose) and hydroxy acids (lactic and sialic acids), with characteristic trend in their relative values and characteristic shape of pH-profiles indicating a decreased pKa for polymeric phenylboronic acid. A tentative mechanism for the conductivity increase involves phenylboronic acid complexation with polyols converting neutral acid groups into negatively charged esters. As known, polyaniline conductivity is decreased as solution pH is increased. However, negatively charged substituents in polymer chain are known to prolong polyaniline electroactivity to neutral solutions, the corresponding polymers are referred to as ‘self-doped’ ones [3,4]. Accordingly, complexation of boronic acid substituents with polyols can be considered as polyaniline self-doping obviously resulting in increase of polymer conductivity. An impedimetric response of boronic acid substituted polyaniline towards microorga-nisms allowed up to achieve of the lowest detection limits reported for such analytes. References. 1. G. Springsteen, B. Wang Tetrahedron 58 (2002) 5291-5300. 2. E. Shoji, M. S. Freund J. Am. Chem. Soc. 124 (2002) 12486. 3. J. Yue, A.J. Epstein, A.G. MacDiarmid Mol. Cryst .Liq. Cryst. 189 (1990) 255-61. 4. A.A. Karyakin, A.K. Strakhova, A.K. Yatsimirsky J. Electroanal. Chem. 371 (1994) 259-65.