Dbsa surfactant

The OECT channel was made of PEDOT:PSS, a p-type semiconductive polymer widely used in bioelectronics because of its demonstrated properties of stability and biocompatibility.^{29 ,30 (link)} Before patterning, the solution was doped with diethylene glycol 20% (Sigma) with 0.05% by vol. of dodecyl benzene sulfonic acid (DBSA) surfactant (Sigma Aldrich), in order to enhance its electrical conductivity and film-forming properties, respectively.^{31 ,32} The OECT channel, with a final width of 2 mm, was patterned on a square glass slide of 2 × 2 cm and the PEDOT:PSS was spun onto the substrate using a first ramp of 6 s (at 450 rpm) followed by a 30 s plateau at 1500 rpm. The final film thickness was d ∼ 100 nm, as measured using a profilometer. Devices were finally baked on a hotplate at 120 °C for 120 min. A PDMS well of about 500 μL in volume was used to confine the mould onto the channel, defined by the overlapping area of the mould with the PEDOT:PSS stripe.

A solution of poly(3,4-ethylenedioxythiophene) doped with poly (styrene sulfonate), PEDOT:PSS (H.C. StarckClevios PH500), was spun onto the silicon substrate with pillars substrate so that an estimated film thickness d ∼ 80 nm was achieved. The PEDOT:PSS solution was previously doped with ethylene glycol (Sigma Aldrich) to enhance its electrical conductivity and dodecyl benzene sulfonic acid (DBSA) surfactant (Sigma Aldrich) to improve film forming. After the spinning the device was baked on a hotplate at 140 °C for 60 min. The substrates were then covered with a thin (few nm) film of a teflon-like (C4F8) polymer to ensure hydrophobicity; to do this, a modified Bosch/RIE process was utilized (SI 500 Sentech Instruments Gmbh, Berlin, Germany), where solely the passivation mode was activated. In this phase, all gas flows, including SF6, argon, and oxygen, are set to zero, with the exception of the chemical inert passivation layer C4F8.