Multi-microelectrode probe for neurophysiological experiments

Four-site, passive microprobes for use in acute neurophysiological experiments are described. These microprobes allow simultaneous recordings of action potential activity to be made from multiple neurons at different locations in the neural tissue. The microprobe is a planar structure, fabricated using integrated-circuit techniques. It consists of gold electrode structures sandwiched between two polyimide dielectric layers and bonded to a 15-μm-thick molybdenum substrate. The top dielectric layer has windows to expose the bonding pads and electrode sites. The bonding pads and interconnect wires at the probe head are entirely encapsulated in a polycarbonate resin tube filled with silicone sealant to protect the interconnections from contact with body fluids. The four recording sites are approximately 25-μm square and arranged colinearly, 500 μm apart, on a dagger-shaped structure 2.7 mm long by 0.15 mm wide at the lowest electrode site. The site impedances, measured in saline solution at 1 kHz, were between 3 and 4 MΩ. Probe lifetime was characterized; the more recent design has three sites that survived over 750 hours