Fig. 2.

A demonstration of the streaking observed by two-photon scanning microscopy when contrast agents with long luminescence lifetimes are used. The image is of 665 nm emission from lipid coated ${\mathrm{NaYF}}_4:{\mathrm{Yb}}^{3+}$, ${\mathrm{Er}}^{3+}$ nanoparticles following 980 nm excitation. The fast-scan axis represents the direction of a single line acquisition, with lines added sequentially in the direction of the slow scan axis. Long-lasting luminescence collected in nondescanning mode obscures the actual distribution of luminescent nanoparticles. In this example, the pixel dwell time was 4.6 μs per pixel and the luminescence lifetime is approximately 358 μs.