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- Bioelectrical signal detection using conducting polymer electrodes and the displacement current methodPublication . Inácio, Pedro; Mestre, Ana L G; Medeiros, C.R.; Asgarifar, Sanaz; ELAMINE, Youssef; Canudo, Joana; Santos, João; Bragança, José; Morgado, Jorge; Biscarini, Fabio; Gomes, Henrique L.Conducting polymer electrodes based on poly (3, 4 ethylenedioxythiophene): polystyrene sulfonate were used to record electrophysiological signals from autonomous cardiac contractile cells present in embryoid bodies. Signal detection was carried out by measuring the displacement current across the polymer/electrolyte double-layer capacitance, and compared with voltage detection. While for relatively low capacitance electrodes, the voltage amplification provides higher signal quality, and for high capacitive electrodes, the displacement current method exhibits a higher signal-to-noise ratio. It is proposed that the displacement current method combined with high capacitive polymer-based electrodes is adequate to measure clusters of cells and whole organs. Our approach has a great potential in fundamental studies of drug discovery and safety pharmacology.
- Ultrasensitive gold micro-structured electrodes enabling the detection of extra-cellular long-lasting potentials in astrocytes populationsPublication . Mestre, Ana L. G.; Cerquido, Monica; INÁCIO, PEDRO; Asgarifar, Sanaz; Lourenco, Ana S.; Lurdes S. Cristiano, M.; Aguiar, Paulo; Medeiros, Maria C. R.; Araújo, Inês; Ventura, Joao; Gomes, Henrique L.Ultra-sensitive electrodes for extracellular recordings were fabricated and electrically characterized. A signal detection limit defined by a noise level of 0.3-0.4 mu V for a bandwidth of 12.5 Hz was achieved. To obtain this high sensitivity, large area (4 mm(2)) electrodes were used. The electrode surface is also micro-structured with an array of gold mushroom-like shapes to further enhance the active area. In comparison with a flat gold surface, the micro-structured surface increases the capacitance of the electrode/electrolyte interface by 54%. The electrode low impedance and low noise enable the detection of weak and low frequency quasi-periodic signals produced by astrocytes populations that thus far had remained inaccessible using conventional extracellular electrodes. Signals with 5 mu V in amplitude and lasting for 5-10 s were measured, with a peak-to-peak signal-to-noise ratio of 16. The electrodes and the methodology developed here can be used as an ultrasensitive electrophysiological tool to reveal the synchronization dynamics of ultra-slow ionic signalling between non-electrogenic cells.
- Performance assessment of polymer based electrodes for in vitro electrophysiological sensing: the role of the electrode impedancePublication . Medeiros, Maria C. R.; Mestre, Ana L. G.; INÁCIO, PEDRO; Santos, João M. L.; Araújo, Inês; Bragança, José; Biscarini, Fabio; Gomes, Henrique L.Conducting polymer electrodes based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are used to record extracellular signals from autonomous cardiac contractile cells and glioma cell cultures. The performance of these conducting polymer electrodes is compared with Au electrodes. A small-signal impedance analysis shows that in the presence of an electrolyte, both Au and polymer electrodes establish high capacitive double-layers. However, the polymer/electrolyte interfacial resistance is 3 orders of magnitude lower than the resistance of the metal/electrolyte interface. The polymer low interfacial resistance minimizes the intrinsic thermal noise and increases the system sensitivity. However, when measurements are carried out in current mode a low interfacial resistance partially acts as a short circuit of the interfacial capacitance, this affects the signal shape.
- Extracellular electrophysiological measurements of cooperative signals in astrocytes populationsPublication . Mestre, Ana L. G.; INÁCIO, PEDRO; ELAMINE, Youssef; Asgarifar, Sanaz; Lourenco, Ana S.; Cristiano, Maria L. S.; Aguiar, Paulo; Medeiros, Maria C. R.; Araújo, Inês; Ventura, Joao; Gomes, Henrique L.Astrocytes are neuroglial cells that exhibit functional electrical properties sensitive to neuronal activity and capable of modulating neurotransmission. Thus, electrophysiological recordings of astroglial activity are very attractive to study the dynamics of glial signaling. This contribution reports on the use of ultra-sensitive planar electrodes combined with low noise and low frequency amplifiers that enable the detection of extracellular signals produced by primary cultures of astrocytes isolated from mouse cerebral cortex. Recorded activity is characterized by spontaneous bursts comprised of discrete signals with pronounced changes on the signal rate and amplitude. Weak and sporadic signals become synchronized and evolve with time to higher amplitude signals with a quasi-periodic behavior, revealing a cooperative signaling process. The methodology presented herewith enables the study of ionic fluctuations of population of cells, complementing the single cells observation by calcium imaging as well as by patch-clamp techniques.