An apparatus includes an end effector having loop members with electrodes thereon and is usable with catheter-based systems to measure or provide electrical signals. The end effector can include three loop members that are non-coplanar when expanded unconstrained that become contiguous to a planar surface when the loop members are deflected against the surface, a mechanical linkage that joins the loop members at a distal vertex of the end effector, electrodes having surface treatment to enhance surface roughness of the electrodes, twisted pair electrode wires, a bonded spine cover, and/or any combination thereof.