A system may include a conductive substrate, a plurality of conductive nanostructures disposed on a first side of the conductive substrate, an insulating substrate, and a plurality of electrodes disposed on a first side of the insulating substrate. The first side of the conductive substrate faces the first side of the insulating substrate, and each of the plurality of electrodes is electrically connected to the conductive substrate. In other aspects, a system may include a first insulating substrate and a second insulating substrate, where a first side of the first insulating substrate faces a first side of the second insulating substrate, and each of a first plurality of electrodes is electrically connected to a respective one of a second plurality of electrodes.