The first ratiometric fluorescent probe for aminopeptidase N

The current work describes the design and synthesis of the first ratiometric fluorescent probe, Ala-PABA-7HC, for the detection of aminopeptidase N (APN) at both the enzymatic and the cellular level. Upon addition of APN to the solution of Ala-PABA-7HC in PBS or culture medium, the maximum emission peak experienced a red shift from 390 nm to 450 nm, and the ratio of fluorescence intensity (I450/I390) (λex = 330 nm) significantly increased from 0.26 to 3.05 (R = 11.7-fold) in 15 min.