Organic electrochemical transistors based on PEDOT:PSS: biocompatible devices to sense the pore formation in bilayer lipid membranes attacked by bacterial pore forming toxins

The interest towards organic materials for the realization of devices for its flexibility, low cost and chemical engineering have attracted a great deal of attention.1 Between the different possible applications sensing could play a crucial role in use of these materials and of particular interest is the possibility to use these materials as sensors in water solution. For these reasons since the 1980's organic electrochemical transistors (OECTs) have attracted a great deal of interest for biosensor applications.2 The basic structure of OECTs consists of two stripes of conducting polymeric film in contact with the electrolyte solution.3 The working principle is practically the same of two electrochemical electrodes but with the great advantage due to that the current that flows in one electrode could be modulated by the potential applied to the other electrode.4 This is the gate electrode and controls the doping level of the conducting polymer inside the other electrode. OECTs can be operated in aqueous electrolytes, providing an interface between the worlds of biology and electronic materials. The inherent signal amplification of OECTs has the potential to yield sensors with low detection limits and high sensitivity. The vision is to build a disposable "lab on a chip", a diagnostic device consisting of multiple sensors, where one can input a drop of analyte and receive an analysis of as many indicators of health as possible. The present research was aimed at development the basic methods for a novel generation of electrochemical transistor (OECT) based on biocompatible molecules. The method and prototype devices have been specifically developed aiming at functioning in biological environment and tailored for possibly sensing cellular damage under different controlled conditions and in particular when attacked by bacterial pore forming toxins. To this end we have implemented bilayer lipid membranes (BLM) into the OECT developed aiming at studying their performance in assessing dynamics of pore formation. In fact when the lipid bilayer integrity was lost, due to the pore-forming toxin action, characteristic current increases could be observed. In figure 1, an example of current measurement through perforated membrane is reported. The current increase is proportional to the number of pores open into the membrane. As reported in the inset, the aperture of each pore induced a step like increase in ionic current. The amplitude of each step is characteristic for the low-conductance state (hexameric structure) of pore forming toxin used. The single channel conductance measured with this system is about 40-45 pS at 0.1 M salt concentration, which is consistent with the published data. The slightly smaller conductance measured in our system could be related to its geometrical design which could decrease the ionic mobility in bulk solution.