Novel Reagentless Label-Free Detection Principle for Affinity Interactions Resulted in Conductivity Increase of Conducting Polymer

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.