Since FocusClear™ treated samples will become completely transparent, it is expected to see more fluorescence from focus as well as out-of-focus planes. This becomes a problem when using a conventional fluorescence microscope because it often becomes too bright. The increased background fluorescence is coming mostly from out-of-focus planes. In fact, in some cases, fluorescence signals become so strong that we cannot even look at the samples under a conventional fluorescence microscope directly without using a ND filter. Thus, for the observation of thick samples under conventional fluorescence microscope, FocusClear™ is only useful for increasing detection sensitivity from samples with weak signals, which is often the case for many samples. On the other hand, strong fluorescence signals become a great advantage when using a confocal microscope that allows the use of a smaller pinhole size to filter out all the out-of-focus signals. Under this situation, in fact, many of our users found that the background fluorescence of the focus plane of samples mounted in FocusClear™ is much lower than the samples mounted in glycerol.