Probes were fabricated following standard photolithography practices using plastic photomasks (Selba), a SUSS MJB4 contact aligner, and an SCS Labcoater 2. Glass sides with dimensions of 50 × 76 mm were cleaned and coated with 2-μm-thick parylene-C. The base layer was subsequently formed by selective ultraviolet (UV) exposure (201 mJ/cm2) and development of a 10-μm-thick spin-coated SU8 film (SU-8 2000 series, MicroChem). A photoresist liftoff process using Oscar 5001 (Orthogonal) was used to pattern gold interconnects (2-nm Cr, 150-nm Au) deposited by thermal evaporation. Following Au liftoff, substrates were activated with 100-W O2 plasma (Oxford RIE 80 plus) for 1 min and spin-coated with a 40-μm-thick SU8 layer. Selective UV exposure and development of the SU8 layer formed the walls of the microfluidic channel. Substrates were rinsed with acetone and deionized (DI) water and then activated for 15 s with a 30-W O2 plasma before filling the fluidic channel with 2 μl of 1-butyl-3-methylimidazolium chloride (Alfa Aesar) dissolved in DI water (680 mg/ml). Approximately 4 μm of parylene-C was deposited on the substrates, thereby encapsulating the ionic liquid within the fluidic channel. AZ9260 was subsequently spin-coated, exposed, and developed using MF-26A, followed by reactive ion etching to open the probe outline, electrode openings, fluidic connections ports, and ion pump outlets. Residual photoresist was rinsed away with acetone and isopropyl alcohol, and then rubber adhesive fluidic connectors were applied to the fluidic inlet/outlets before removing probes from the parylene-coated glass substrates using a razor blade. The upper part of the free-standing probes was glued to Kapton substrates (500HN, 127 μm thick) for added structural support (not including the implantable shank). Following 1 min of 100-W O2 plasma activation, the first 0.5 mm of the probe tips was dip-coated into an aqueous dispersion of PEDOT:PSS (PH 1000 from H.C. Stark) containing 5 volume percent (volume %) of ethylene glycol, 0.1 volume % of dodecyl benzene sulfonic acid, and 1 weight % of 3-glycidoxypropyltrimethoxysilane. The devices were then placed in an oven at 120°C for 1 hour. After cooling to room temperature, the microfluidic channels were flushed with DI water at a rate of 5 μl/min for 30 min. The PEDOT:PSS covering the ion pump outlets was then selectively exposed to a 10% solution of sodium hypochlorite (Sigma-Aldrich) by flushing the fluidic channel with the solution at a rate of 2 μl/min for 30 s, followed by 45 min of flowing DI water.

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