PEDOT Site Coating

PEDOT is polymerized from solution directly onto the metal site, usually with a counter-ion such as poly(styrene sulfonate) (PSS). The film is typically open and porous, which gives ions access to a larger effective surface than the flat metal beneath it. On the gold sites of neural probes, PEDOT/PSS lowered the impedance at 1 kHz by almost two orders of magnitude and was electrochemically more stable than polypyrrole, an earlier conducting polymer (Cui & Martin (2003)). The reduction depends on the underlying metal and the deposition conditions. On the iridium sites of silicon probes, for example, it was about tenfold in vitro (Ludwig et al. (2006)).

A coating that increases the effective surface area generally lowers a site's thermal noise (Siegle & Steinmetz (2026)). The benefit in tissue can be smaller than bench measurements suggest. In a six-week study in rat motor cortex, 58% of PEDOT sites and 41% of uncoated iridium sites on the same silicon probes recorded at least one quality unit on average. The PEDOT sites also showed less low-frequency artifact in local field potential recordings. Over that period, tissue encapsulation added impedance to every site, and the impedance ratio between uncoated and coated sites fell from about ten to one to about two to one (Ludwig et al., 2006).

Charge storage capacity increases with the amount of PEDOT deposited, which is relevant to stimulation (Kozai et al. (2012)). Stability is the main practical consideration. Thicker films can partially detach during insertion (Ludwig et al., 2006), and some degradation under prolonged electrical stimulation has been reported (Kozai et al., 2012).

Z-Coat is the proprietary NeuroNexus form of PEDOT site coating. NeuroNexus optimized it not to delaminate, not to drift in performance, and to have excellent electrical properties. It is specified at order as a site option on catalog silicon probe designs, alongside iridium and SIROF sites.