Figure 1.

Quantitative analysis of single-molecule measurements based on photons, force, and electrons. Photonic measurements (left) are usually based on one or more fluorescent labels (either small molecules or fluorescent proteins) or a larger nanoparticle label. Force-based measurements (center) typically use a macroscopic cantilever or a micrometer-scale bead to apply forces from piconewtons to nanonewtons. Electron-based methods (right) can involve electron conductance, tunneling, or scattering.