5‐Formyluracil as a Multifunctional Building Block in Biosensor Designs

: In organisms 5-formyluracil (5fU), which is known as a vital natural nucleobase, is widely present. Despite the recent development of sensor designs for organic fluorescent molecules for selective targeting applications, biocompatible and easily operated probe designs that are based on natural nucleobase modifications have rarely been reported. Here, we introduce the idea of 5fU as a multifunctional building block to facilitate the design and synthetic development of biosensors. The azide group was derived from the sugar of a nucleoside, which can be further used in the selective binding of cells or organelles through click chemistry with alkynyl-modified targeting groups. The aldehyde group of 5fU can react with different chemicals to generate environmentally sensitive nucleobases that have obvious characteristics, which precious reactants cannot achieve for selective fluorogenic switch-on detection of a specific target. We first synthesized 5fU analogues that had aggregation-induced emission properties, and then we used triphenylphosphonium as a mitochondria-targeting group to selectively image mitochondria in cancer cells and mouse embryonic stem cells. Additionally, the reagents exhibit a high selectivity for reaction with 5fU, which means that the method can also be used for the detection of 5fU. Combining the two characteristics, the idea of 5fU as a multifunctional building block in biosensor designs may potentially be applicable in 5fU site-specific microenvironment detection in future research.