Physicists are using nanoscopic techniques with photo-switchable fluorescent probes to see biological structures beyond the resolution limits of conventional microscopes. These probes can be switched on and off reversibly for many cycles and can be used for non-linear nanoscopic imaging techniques. In this thesis I characterized a photo-switchable probe called rsEGFP2 (reversibly photo-switchable Enhanced Green Fluorescent Protein 2) to know its suitability for the nanoscopic imaging technique, Nonlinear Structured Illumination Microscopy (NLSIM). The switching behavior of rsEGFP2 were measured in U2OS cells in which rsEGFP2-actin was expressed. The switch fatigue, decay time constants and background were measured. A switch fatigue greater than 1100 cycles, a decay time constant of 4.5 ms and a ratio of background to peak intensity of 0. 189 at high laser powers (25 mW) were obtained. The high number of switching cycles, fast time constant, and low background confirm the suitability of rsEGFP2 for NLSIM.