An apparatus comprising: a channel (4) configured to conduct charge carriers; and a charge carrier generator (22) configured to generate charge carriers for populating the channel, wherein the charge carrier generator is configured for resonance energy transfer (FRET). The charge carrier generator may be a nanoparticle or quantum dot (22), functionalised with at least one moiety (28A, 28B) to enable detection of an analyte. The charge carrier generator may also be a nanoparticle or quantum dot (22) configured to photo-generate charge carriers. The channel (4) may be made of a material having a very high carrier mobility like graphene or carbon nanotubes.