The function of the nervous system is dictated by the communication mechanism through the release of neurotransmitters and rapid propagation of membrane depolarization by the flux of ions. As understanding the nervous system physiology holds the key for the diagnosis and therapy of neurological disorders, monitoring or controlling this communication mechanism is of great interest. For this aim, an increasing number of studies over the last years concentrated on the development of electronic devices based on organic materials, developing the field of bioelectronics. One of the most technologically important conducting material employed for the state-of-the-art devices of bioelectronics is poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This polymer offers great advantages in enabling communication between electronic and the biological systems due to the low impedance and ion permeability of its films along with its compatibility with biological molecules. For instance, PEDOT:PSS coated microelectrode arrays allow in vitro recordings of action potentials from rat hippocampus slices.[1] On the other hand, devices that can electronically control the lateral transport and delivery of charged molecules were developed, relying on the electrochemical switching of PEDOT:PSS.[2] Known as organic electronic ion pumps, these devices allow for the electrophoretic delivery of neurotransmitters through an ionic conductor film in a controlled and precise manner.
One interest in this field is the development of multifunctional probes which can combine the above mentioned approaches. Such a device, capable of releasing of drugs of interest as well as sensing the triggered neural activity, is a breakthrough in therapeutic strategies aiming to treat brain dysfunctions. Here, we report a multifunctional probe which involves recording electrodes that are located in the exact position of electrically-controllable ion release channels. We use the same polymer-based electronic device as a chemical stimulator/inhibitor and a sensor. While neurotransmitters such as gamma-aminobutyric acid (GABA) or ions such as K+ are electrophoretically delivered through an ion conductor, the low impedance of PEDOT:PSS electrodes allows for high signal-to-noise ratio recordings of broadband physiological activity at the delivery site. The function of these probes was evaluated in rat hippocampal slices through an in vitro design. We used epileptiform activity evoked by pharmacological treatments as a model system of a pathological state. Delivery of GABA, the main inhibitory neurotransmitter in the brain, abolished epileptiform activity within a minute in close proximity to the pump outlets, without affecting the activity at distant sites. This control over neuronal signaling with precise spatiotemporal delivery of ions paves the way for implantable drug release devices with feedback regulation function and represents a major advancement in therapeutic technology. [1] M. Sessolo et al. Advanced Materials 2013, 25, 2135. [2] K. C. Larsson et al. Biochimica et Biophysica Acta-General Subjects 2013, 1830, 4334.