Figure 3. Stained MSC depth detection dependence.

When the depth dependence of detection for MSCs dyed with each stain is analyzed, no discernable difference in the depth histogram or in the average MSC depth is observable (a). However, a modest increase in the number of MSCs detectable below the depth of 100 µm appears with longer wavelength dyes. Normalized intensity of cells analyzed over depth indicates a close match between experimental results and theoretical predictions, with an improvement in the intensity retention of the near-IR emitting DiR labeled cells (b). Average signal intensity revealed a lower intensity for DiO- likely due to high background near the skin surface and signal degradation at greater depth- and for DiR. However, DiR intensity was mostly recovered when corrected for detector quantum efficiency, suggesting the importance of detector characteristics in cell detection.