Fluorescent β‐Sheet‐Based Peptide Hydrogels with Aggregation‐Enhanced Emission Properties

Novel fluorescent peptide hydrogels are reported by combining 1,8‐naphthalimide‐derived amino acids with a previously developed peptide‐based controlled drug release matrix. Aggregation‐enhanced emission is achieved by inserting the fluorescent naphthalimide moieties in a peptide sequence with self‐assembling properties. The formation of β‐sheets directs the orientation of the luminescent side chains, leading to the avoidance of aggregation‐caused quenching. The relation between the β‐sheet‐underpinned fiber formation and the emission characteristics is further elucidated by spectroscopic and microscopic techniques, including correlative fluorescence and atomic force microscopy imaging. Owing to the incorporation of the naphthalimide moiety, the gelation concentration is lowered and the gel strength improved. The resulting hydrogels does not contain any organic solvent (in contrast to ample literature examples), present thixotropic behavior, and the fluorescent properties are sensitive to environmental conditions such as temperature and medium. These features make the soft biomaterials interesting for applications such as biosensing, real‐time bioimaging, and 3D printing. The high tunability of the peptide sequence composition and configuration, as well as the chemical structure of the 1,8‐naphthalimide moiety, allows for modulating the material toward desired properties.