Imaging characterization of the high-resolution, large-FOV endomicroscope based on a composite cantilever. (A) Large FOV imaging of stained bovine pulmonary artery endothelial cells with the cytoskeletal filamentous actins labeled by Alexa Flour 488 Phalloidin and the intracellular mitochondrial network labeled with MitoTracker Red CMXRos. The excitation power was ~10 mW at 750 nm. (B) Representative images of 500-nm fluorescent beads at progressively increasing field heights (i.e., off-axis distances, annotated at the upper-left corner). The full-width-at-half-maximum (FWHM) of point-spread function (PSF) grows with off-axis distance. The mean and standard deviation of FWHM PSF size are (from on-axis to peripheral regions; 4 beads measured for each location): 0.66 ± 0.019 μm, 0.81 ± 0.029 μm, 0.88 ± 0.058 μm, and 1.12 ± 0.075 μm, respectively, before deconvolution, and 0.61 ± 0.024 μm, 0.77 ± 0.033 μm, 0.84 ± 0.057 μm and 1.10 ± 0.073 μm, respectively, after deconvolution. Scale bars: 0.5 μm. (C) Endomicroscopic label-free two-photon NADH imaging of mouse kidney in vivo. The dark round-to-elliptical signal void regions scattered along the renal tubule walls (square boxes) are nuclei of epithelial cells, while the predominant concentration of NADH fluorescence appeared along the basolateral side of renal tubules (arrows). Scale bars: 30 μm. For both (A) and (C), the dimmer signal outside the yellow dash circle results mainly from vignetting of the current micro objective. (D) Three label-free two-photon NADH images of mouse kidney in vivo acquired with the traditional DCF-only cantilever-based endomicroscope with the same scale bar as in (C). The increased FOV (shown in (C)) afforded by the new endomicroscope based on the composite cantilever is very pronounced (by almost 3 fold in length or 9 fold in area). Nuclei of epithelial cells and the predominant concentration of NADH along the basolateral side of renal tubules are also indicated by square boxes and arrows, respectively.