Confinement of electromagnetic waves in nanogaps offers vast possibilities for optical sensing and signal modulation because the overall electromagnetic response of the whole metasurface becomes highly responsive to the dielectric environment of the nanogaps. Here, some methods controlling the environment will be presented. 1) Mechanical control of the gap width: conductivity across the nanogap changes, and accordingly, the impedance changes. 2) Optical tweezing to position nanoparticles in nanogaps: conductivity changes depending on the nanoparticle’s characteristics. 3) Application of phase change materials: the dielectric contrast between the gap and the sidewalls is controlled by external stimuli such as heat. Some other applications of nanogaps also will be discussed.