Electrochemical and nanostructural characterization of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films as coatings for neural electrodes
Abstract:
Poly(3,4-ethylenedioxythiophene) (PEDOT), a well-characterized conducting polymer, has been applied for coating metal neural electrodes to improve their stimulating or recording performance. The coated electrodes possess advantages in better neuron attachment, lower impedance, and larger capacitance compared to the bare metal substrate due to the biocompatibility and porous surface of the polymer. However, the PEDOT-coated electrodes have frequently reported issues associated with mechanical instability, such as cracking and delamination. Solving this problem is crucial for stimulating electrodes, whereas a massive film is unnecessary for recording purposes. Moreover, the thickness control for the latter has rarely been investigated. In this work, we systematically studied and characterized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with cyclic voltammetry and atomic force microscopy (AFM) to evaluate the electropolymerization of PEDOT:PSS from the basis and analyze the surface morphology for a range of deposition times. The polymerization potential was obtained, and the deposition charge density was optimized for recording neural electrodes. In addition, high-resolution AFM height and phase images reveal the heterogeneity of the polymer surface. The modified electrode was also tested for its electrochemical performance in a small potential window with both a standard electrochemical cell setup and stainless steel microscrews. The results showed that despite a shift of potential (0.42 V) due to the change of setup, the electrode functions well in the capacitive region without triggering redox reactions.Cell-wall fucosylation in Arabidopsis influences control of leaf water loss and alters stomatal development and mechanical properties
Abstract:
The Arabidopsis sensitive-to-freezing8 (sfr8) mutant exhibits reduced cell wall (CW) fucose levels and compromised freezing tolerance. To examine whether CW fucosylation also affects the response to desiccation, we tested the effect of leaf excision in sfr8 and the allelic mutant mur1-1. Leaf water loss was strikingly higher than in the wild type in these, but not other, fucosylation mutants. We hypothesized that reduced fucosylation in guard cell (GC) walls might limit stomatal closure through altering mechanical properties. Multifrequency atomic force microscopy (AFM) measurements revealed a reduced elastic modulus (E使), representing reduced stiffness, in sfr8 GC walls. Interestingly, however, we discovered a compensatory mechanism whereby a concomitant reduction in the storage modulus (E使使) maintained a wild-type viscoelastic time response (tau) in sfr8. Stomata in intact leaf discs of sfr8 responded normally to a closure stimulus, abscisic acid, suggesting that the time response may relate more to closure properties than stiffness does. sfr8 stomatal pore complexes were larger than those of the wild type, and GCs lacked a fully developed cuticular ledge, both potential contributors to the greater leaf water loss in sfr8. We present data that indicate that fucosylation-dependent dimerization of the CW pectic domain rhamnogalacturonan-II may be essential for normal cuticular ledge development and leaf water retention.