As with probe 2, the APP/PS1 mice displayed much brighter brain fluorescence than that of WT mice at 10 min post injection of each probe (Figure 6, More imaging details are shown in Figure S36, S37 and S38), with average brain fluorescence intensity considerably higher than that from the age-matched WT mice, suggesting that these three probes could also cross the BBB and efficiently differentiate the APP/PS1 AD mice from WT mice (Figure 6). Here, APP is linked to Alzheimer disease.