18F‐Labeling Chemistry in Aqueous Media

18 F-Labeled molecular tracers and subsequent positron emission tomography are indispensable molecular imaging tools in medical diagnosis and research. The preparation of 18 F-labeled molecular tracers involves critical steps such as the 18 F-labeling reaction, work-up, and 18 F-product purification, which are governed by 18 F-labeling chemistry. Since direct incorporation of 18 F in aqueous media exhibits many advantages in practice, this Review summarizes the existing 18 F-labeling methods in aqueous media, which are sorted by atoms forming chemical covalent bonds with F. The Review is focused on the respective reaction mechanism, the water effect and the applications of these methods for the development of 18 F-radiopharmaceuticals. The research progress on aqueous nucleophilic labeling methods using [18 F]F- as the 18 F source has been mainly discussed.