The present invention generally relates to nanotechnology, including field effect transistors and other devices used as sensors (for example, for electrophysiological studies), nanotube structures, and applications. Certain aspects of the present invention are generally directed to transistors such as field effect transistors, and other similar devices. In one set of embodiments, a field effect transistor is used where a nanoscale wire, for example, a silicon nanowire, acts as a transistor channel connecting a source electrode to a drain electrode. In some cases, a portion of the transistor channel is exposed to an environment that is to be determined, for example, the interior or cytosol of a cell. A nanotube or other suitable fluidic channel may be extended from the transistor channel into a suitable environment, such as a contained environment within a cell, so that the environment is in electrical communication with the transistor channel via the fluidic channel. In some embodiments, the rest of the transistor channel may be coated, e.g., so that the electrical properties of the transistor channel reflect the electrical behavior of the environment that the fluidic channel is in communication with. Other aspects of the invention are generally directed to methods of making such sensors, methods of using such sensors, kits involving such sensors, or the like.