Two-photon excitation STED-CW microscopy

Here, we report sub-diffraction resolution in two-photon excitation (TPE) fluorescence microscopy achieved by merging this technique with continuous-wave (CW) stimulated-emission depletion (STED). We show an easy-to- implement and promising laser combination based on Ti:Sapphire ultrafast laser source for two-photon excitation and a commercial Leica TCS STED-CW microscope for resolution enhancement. Images of fluorescent nanoparticles produce comparative similar resolution to the one photon excitation. Two-photon excitation STED microscopy achieves approximately 3-4 fold improvement in resolution in the radial direction over conventional 2PELSM. Further improvements in resolution are theoretically achievable, suggesting that 2PE STED microscopy will permit nanoscale imaging, for instance, of neuronal structures located in relatively intact brain tissue. © 2011 SPIE.