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The majority of reagentless affinity sensors suffer from poor selectivity because specific binding and non-specific interactions generate responses in the same direction, commonly causing resistance increase. We report on the advanced transducer, synthesized in course of molecular imprinting, which generates conductivity increase as a result of specific binding. Electropolymerization of 3-aminophenylboronic acid (3-APBA) known to yield conductive polyaniline only in the presence of F−, has been carried substituted the latter for hydroxy acids. The achieved synthesis of conductive polymer in course of fluoride-free 3-APBA electropolymerization indicates successful imprinting of hydroxy acids. Imprinting poly(3-APBA) provides as 10–15 times increased, as even decreased binding constants towards target analytes as compared to the non-imprinted polymer. This allows one to achieve the desired selectivity among polyols. Tuning binding properties of boronate functionalized polyaniline we’ve demonstrated the enzyme-free selective detection of saccharides and hydroxy acids via conductivity increase of the conductive polymer.

Electropolymerization of aminophenylboronic acids proceeds by the mechanism typical of conducting polyaniline, if the substituent in the ring is the electron donor and its position favors the electrophilic substitution into the para position with respect to the amino group in the ring. For the same reason, the polymerization of meta-aminophenylboronic acid requires the presence of fluoride ions to transform the weak electron acceptor, boronic acid group into the electron-donating trifluoroborate anion. It is shown that electropolymerization of ortho-aminophenylboronic acid can be carried out in strongly acidic media in the absence of fluoride ions, in analogy to unsubstituted polyaniline. The conductivity of the resulting polyanilineboronic acids synthesized under optimal conditions increases upon their binding with sugars and oxyacids, which allows detecting the specific interactions only, while the nonspecific interactions lower down the polymer conductivity.

The reduction of activated 5-(indol-3-yl)pyrrolidin-2-ones leading to a mixture of the respective indolyl pyrrolidines and their borane complexes, as well as several other transformations indicate that the electrophilicity of carbonyl group in 5-indolylpyrrolidin-2-ones is significantly decreased.

We report on the novel reagentless and label-free detection principle allowing discrimination of specific binding over non-specific interactions. Unlike majority of impedimetric and conductometric (bio)sensors, which specific and unspecific signals are directed in the same way (resistance increase), making doubtful their real applications, the response of the reported system results in resistance decrease, which is directed oppositely to the background. The mechanism of the resistance decrease is the polyaniline self-doping, i.e. as an alternative to proton doping, an appearance of the negatively charged aromatic ring substituents in polymer chain. Negative charge at boronic ring substituent appears as a result of complex formation with di- and triols, i.e. specific binding. Thermodynamic data on interaction of the electropolymerized aminophenylboronic acids with saccharides and hydroxy acids indicate that the observed resistance decrease is due to polymer interaction with polyols. A possibility to detect microorganisms (Penicillum chrysogenum) on the basis of interdigitated electrodes modified with boronate substituted polyaniline is also shown. The first reported conductivity increase as a specific signal opens new horizons for reagentless affinity sensors.

Boronate-substituted polyanilines are able to serve as advanced affinity transducers if synthesized at their highest conductivity and remind properties (particularly, cyclic voltammograms in acidic media) of common conductive polyaniline. This presumes growing conditions, when the substituent promotes electrophilic substitution in para-position relatively amino-group. Thus electropolymerization of 3-aminophenylboronic acid (3-APBA) requires free fluoride ions to convert boronic acid residue to trifluoroborate serving as electron donor. On the contrary, when in ortho-position to amino-group, boronic acid does not hamper the polyaniline-type growth, but its conversion to trifluoroborate inhibits the polymerization. Accordingly, optimal media for electropolymerization of 2-aminobenzeneboronic acid (2-APBA) are strong acidic solutions similar to unsubstituted aniline. Conducting polyaniline-type polymers synthesized from both isomers generate an increase in their conductivity as a response to polyols (saccharides and hydroxy acids) according to the mechanism of self-doping by freezing negative charges in ring substituents upon complexation. This comprises the novel detection principle for reagentless affinity sensors, allowing to discriminate the specific affinity interactions from non-specific bindings. Keywords: Sensor, Polyaniline self-doping, Electropolymerization, Polyols, Conductivity

We report on the novel reagentless and label-free detection principle based on electroactive (conducting) polymers considering sensors for polyols, particularly, saccharides and hydroxy acids. Unlike the majority of impedimetric and conductometric (bio)sensors, which specific and unspecific signals are directed in the same way (resistance increase), making doubtful their real applications, the response of the reported system results in resistance decrease, which is directed oppositely to the background. The mechanism of the resistance decrease is the polyaniline self-doping, i.e., as an alternative to proton doping, an appearance of the negatively charged aromatic ring substituents in polymer chain. Negative charge "freezing" at the boron atom is indeed a result of complex formation with di- and polyols, specific binding. Changes in Raman spectra of boronate-substituted polyaniline after addition of glucose are similar to those caused by proton doping of the polymer. Thermodynamic data on interaction of the electropolymerized 3-aminophenylboronic acid with saccharides and hydroxy acids also confirm that the observed resistance decrease is due to polymer interaction with polyols. The first reported conductivity increase as a specific signal opens new horizons for reagentless affinity sensors, allowing the discrimination of specific affinity bindings from nonspecific interactions.