Impedance spectroscopy of protein polymer modified silicon micromachined probes

The electrical properties of thin films of a biologically active protein polymer (SLPF) deposited onto micromachined neural prosthetic devices were examined by impedance spectroscopy (IS) over a broad range of temporal frequencies (10 Hz to 1 MHz). The properties of the protein polymer films were examined as a function of morphology as characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the differences between continuous and discontinuous films were determined and compared. There was an increase in the capacitive component of the impedance as the coverage increased. The total increase in impedance of a coated probe at the biologically-relevant frequency of I kHz was less than the decrease in impedance seen during probe activation. For a given thickness, solution cast continuous films were of higher impedance than discontinuous electrospun films. The magnitude of the impedance of the coated probes as a function of temporal frequency showed a power law dependence which was correlated with the roughness of the surface, By combining information from IS and quantitative measurements of surface roughness from AFM, it was possible to estimate the dynamics of carrier transport at the interface between the electronically conductive device and the ionically conductive solution. (C) 1999 Elsevier Science S.A. All rights reserved.