Controlling the location and physical orientation of nanobuilding blocks in assemblies of nanodevices become challenging tasks when it comes to the use of “bottom-up” chemical approaches for nanodevice fabrication. Here, a strategy is reported for in situ fabrication of horizontal nanochannels, which allows control over their orientation and average pore size to an unprecedented range of ∼5−20 nm. Using this approach, we selectively fabricated nanochannels with controlled average pore sizes at known positions on a sapphire surface. Equally important, nanochannels, either single or group, are addressable photolithographically and integrable to microchannels without the use of any high resolution lithography. This technique uses horizontal ZnO nanowires (NWs) as a sacrificial template and could provide the capability of fabrication of complex micro- and nanofluidic platforms. Cross-sections of nanowires and nanochannels are prepared via a focused-ion beam and examined by electron microscopy and energy-dispe...