Photonic device structures such as photonic crystals, photonic wires and optical metamaterials - all with submicron features can be described as `nanophotonic'. Many of these devices and structures can be used as sensors. The usual approach is to photonic sensing is to change the refractive index of a surrounding medium. Here we consider several nanophotonic sensing systems, including asymmetric split ring resonators, photonic wire cavities and polymer Bragg gratings. We compare the relative merits of high Q structures with a small shift in wavelength from the analyte versus low Q structures with a large shift in wavelength.