Sensor platforms and methods of making them are described, and include platforms having horizontally oriented sensor elements comprising nanotubes or other nanostructures, such as nanowires. Under certain embodiments, a sensor element has an affinity for an analyte. Under certain embodiments, such a sensor element comprises one or more pristine nanotubes, and, under certain embodiments, it comprises derivatized or functionalized nanotubes. Under certain embodiments, a sensor is made by providing a support structure; providing a collection of nanotubes on the structure; defining a pattern within the nanotube collection; removing part of the collection so that a patterned collection remains to form a sensor element; and providing circuitry to electrically sense the sensor's electrical characterization. Under certain embodiments, the sensor element comprises pre-derivatized or pre-functionalized nanotubes. Under certain embodiments, sensor material is derivatized or functionalized after provision on the structure or after patterning. Under certain embodiments, a large-scale array includes multiple sensors.